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CarburetorsCarb discussion and questions. Upgrading your Third Gen's carburetor, swapping TBI to carburetor, or TPI to carburetor? Need LG4 or H.O. info? Post it here.
ive had an 87 TA for years and rebuilt the entire TPI motor so this sounds a bit stupid but ive never owned a car with a carburetor before !
Anyway, i brought home an 84 Trans Am a few weeks ago, the car itself has had a lot of work done to it and the engine looks as if its had a rebuild at some point as has lots of new parts fitted. However the carb doesnt appear to be putting fuel in properly.
If i operate the accelerator cable and look through the flap fuel squirts in on the passenger side of the carb but only seems to trickle a tiny bit on the drivers side ? im assuming fuel should squirt into both sides when pumping the accelerator. also the choke doesnt work, not sure whats wrong with it but it just clicks when you switch the ignition on for a little while then stops.
A friend of mine came and had a look who has an 83 TA so he knows his carbs and he thinks it is just a fuel delivery issue preventing it from starting, it tries but just wont quite fire up.
He has very kindly given me a fully rebuilt rochester quad carb which he has spare, its set up for a manual car so i need to swap over the bracket that holds the accelerator and kick down cables and it should be good to go.
Managed to get the bracket off the spare carb, im just slightly dubious about pulling a pretty much new carb apart to fit it
I know it might be a bit difficult because you're in England, but I would try to find an entire throttle plate that has the auto trans linkage hook ups and just swap it with the manual plate.
Might be able to negotiate a straight trade with someone that has the correct plate?
Ive got a whole spare carb, ive got the part i need in my hand in the picture, i just need to take apart the new carb to swap them over which is what im a but dubious about incase a ruin it
I Agree, Would have been easier to swap the entire carb base with shaft in place, those screws should be staked at the bottom of the air plates on the shaft, and/or thread locker used on the rebuilt. sometimes they can be a pain, but you can always tap the hole the next size up if need be.. Last thing anyone wants is a small screw vibrating loose, and, well you know the rest..
Next Time,, Starting fluid would have confirmed a fuel delivery problem, before pulling the carb...
Got some starter fluid in the post as i cant find any locally.
the entire bottom plate swap sounds a lot easier your right i feel a bit stupid now. I can always do that with the current carb that is still on the car as they are all rochester quadrajets
Pulled the carb off the engine, stripped it to get the base plate off and noticed something odd, it looks like someone has hacked into the base plate to expose.....whatever these two things are ?? comparison with another base plate i have
Is this base plate still ok to use ? i want to swap this onto the new carb so it has hookup for the auto transmission. the other base plate thats pictured is the one i took all the linkages off before realising it would of been easier to swap the entire thing. aaaaargh !
Pulled the carb off the engine, stripped it to get the base plate off and noticed something odd, it looks like someone has hacked into the base plate to expose.....whatever these two things are ?? comparison with another base plate i have
Is this base plate still ok to use ? i want to swap this onto the new carb so it has hookup for the auto transmission. the other base plate thats pictured is the one i took all the linkages off before realising it would of been easier to swap the entire thing. aaaaargh !
What you're looking at is the result of removing the anti-tamper caps/covers that are installed at the factory to keep people from tampering with the idle mixture screws that lie beneath them.
ah right ok. is the ECU supposed to take care of that ? i noticed the car has an o2 sensor in the exhaust manifold. Would manually adjusting them screw up the ECU's efforts ?
Manually adjusting the idle mixture puts it into the middle of a range where the ECM can move it around to wherever it needs it to go.
In point of fact, the idle mixture screws in this type of carb have very very very very little "authority". They aren't the main control element at all, like they were in older carbs. I usually put them at about 6 turns out and just leave them alone after that, and tune with the part that DOES have the "authority", which is, the idle air bleed.
before swapping that base plate, ensure that the primary throttle bushings are not worn and allowing slop in the throttle shaft. with the throttle slightly open, check for play fore and aft.
that being good, I'd clean that thing up good to include removing the idle mixture screws and spraying some cleaner through those passages.
as said above, where they're set isn't terribly important. just be sure they're both set to the same number of turns out (no less than 3 and no more than 7 turns out).
Have you checked the fuel level in the bowl?
How about the seal on the accelerator pump?
Whats wrong with the shaft, you feel the need to swap them?
HAve you tried adjusting the idle air bleed screw?
That clicking is the MC solenoid (blue piece), not the choke.Its suppose to cycle for 10sec w/ the ing on/eng off, then stops.Perfectly normal.
So for the idle screws, i have no idea where they are currently set too so is it a case of turning them both clockwise until they stop and then turning them 6 times in the opposite direction ?
The carb was suspect as me and a friend went round the car checking for spark, inside the dizzy cap etc then when he looked inside the carb while i pressed the accelerator, fuel was squirting into the passenger side of the bowl but on the drivers side it was barely even trickling in, he had a fully rebuilt carb in the box he just gave me so it was getting swapped regardless.
I swapped it all over last night and connected it back up, had to pump the throttle a bit until the fuel started coming back into the carb and there was two nice even jets of fuel being squirted in. also when i switch the ignition on the choke light on the dash came on which i dont think it did previously. Although i dont know if the choke is supposed to spray fuel in when you switch the ignition on itself ?? not sure how it works to be honest.
I tried starting the car and it still wouldnt fire. it tried a few times but that was about it. I removed all 8 plugs which were all wet and black so its definitley getting fuel, i also checked for spark again at no. 1 which its getting.
Try holding the choke plate open with a short screwdriver inserted into carb top if you haven't already tried that.After seating idle screws,yes,you back them out the 6 turns(opposite direction).
Also.if it doesn't fire....you can try advancing initial timing by loosening hold down bolt and turning distributor ccw a bit while cranking engine and see if that helps it fire.You can mark base of distributor to engine block for rough reference of initial timing before turning distributor. Good Luck..
Thanks guys, got a few things to try then. So the choke keeps the plate closed and gradually opens it as the engine warms up, is that how it works ?
i was thinking i could take the cap off the dizzy and check the rotor is pointing to number 1 on the compression stroke. Im inclined to say its right as the guy i bought it off had it running and idiling in a vid he sent. But the timing could be way out as you say
I took the dizzy cap off as i was going to make sure the rotor arm was pointing at #1 at TDC, however i noticed this piece is broken, immediatley i thought great thats my problem, but i dont think it is, its just a plastic cover part and nothing else, or am i wrong ?
Anyway i gave up trying to turn the engine by hand for now, the fan gets right in the way and i cant get my arm in there, nothing like my 87 with its twin electric fans, theres a ton of room.
It did run, the previous owner who is a friend sent me vids of him starting it up for me. It was troublesome to start he had to pump the pedal a lot and it would eventually fire and run rough until it warmed up.
the carb looked like the suspect as the drivers side bowel was only trickling in a bit of fuel whereas the passenger side was squirting in nicely. Ive put a new rochester carb on the car, checked for spark, had the plugs out and cleaned them and it still wont fire
check for fuel going into the primary bores from the booster pump when the throttle is pumped. if it's flooding hold the throttle completely down (open) while trying to crank it.
the original owner has finally got in touch with me. The engine has been rebuilt and he said he could never get the ecu to talk to the dizzy and carb. He said it needs a holly carb and a vacuum advance dizzy fitting to solve that. He also said he could get it running one minute and it would.ve great then the next time he went to start it it wouldnt or it would struggle because the timing would go out of whack.
hmmmm.... do these early 3rd gens have a plug to disconnect before you set the timing like my 87 ? Or possibly is the ECU faulty ?
if this carb and dizzy etc is what the car originally had then i want it to work, my dizzy has no vacuum advance on is that how it should be ?
your carb and dist look to be the correct original parts.
timing is set by disconnecting the four wire connector to the dist for base timing at 0-4 degrees advanced.
now we know we have no good base line setting for the timing and everything else is suspect
Pull out every plug and if any are suspect, replace them.
check that the plug wires are routed correctly and the firing order is correct. then check again.
if the plug wires, cap and rotor are suspect, replace them.
after checking for fuel through the booster shot:
with everything connected, mark where the dist is now for reference. try starting it after turning it a few degrees each way until you can get it to run. try counter-clockwise first and go up to about an eighth of a turn, a few increments at a time. doesn't work, go the other way. when you get it to idle adjust it until the timing mark is around 20something degrees advanced (you'll have to estimate this as the marks don't go that high). once there you should be able to disconnect the four-wire connector and set base timing properly.
If temperatures are moderate you may want to hold the choke open for this. will reduce the tendency to flood the motor.
as inexpensive as distributors are, I'd replace that one. I'd first try to get it running with the original installed though.
timing is set by disconnecting the four wire connector to the dist for base timing at 0-4 degrees advanced.
So there is a 4 wire connector going into the dizzy i need to unplug to set the timing ??? I am really REALLY hoping this is the problem. From what the original owner said in his message it kind of sounds like it.
He said he would set the timing and it would be great, then after he switched off and went to restart the car, it either wouldnt start or it would run like utter crap. So to me that sounds like he hadnt unplugged the connector so the ECU and dizzy are way out of whack
As for replacing parts, way ahead of you, a big box from rock auto arrived today. plugs, leads, dizzy cap, rotor arm and a few other non ignition related bits too
doesn't sound like improperly set timing. maybe a loose hold down clamp allowing the distributor to turn on it's own or a bad distributor. But that's just guessing here.
a bad dist (or dist parts) will generally work OK until it get's hot or will fail on a hot restart.
don't worry about properly setting the timing or even using a timing light. just try to turn the dist in increments until you can get it to run.
a spark tester would be handy to ensure you have good spark. in a pinch you can visually check the spark with a plug out, hooked up and grounded while cranking.
I did take number 1 plug out last week to check for spark which it did have.
I spent last night fitting new plugs, leads and the dizzy cap etc but i havnt tried to start it yet as i dont think it will fire anyway. i need a helper to turn the key while i move the dizzy
I was also looking at the carb because the butterfly is totally closed and a few have said it should be open a little bit, at least until i get it running then it stay closed until the choke opens it up ?
I moved the silver part the arrow is pointing too which seems to manually adjust the butterfly, is that ok ? ive left it open a little to see if it helps when trying to start the car
when you get it to idle adjust it until the timing mark is around 20something degrees advanced (you'll have to estimate this as the marks don't go that high). once there you should be able to disconnect the four-wire connector and set base timing properly.
Also Naf i forgot to ask about this, so if i do get it to run and idle, i can set the timing while its running ? is the 4 wire connector you speak of the one that plugs into the coil cover on the top of the distributor ? then set the timing, which is 0-4 degrees on this engine ? then once its there plug it back in and thats it ?
on my TPI engine i have to unplug the connector above the heater box before starting the car, then adjust it, switch car off, plug it back in and then its perfect.
In your first pic of the dist, it is the one at the rear of the dist, up against the firewall. That pigtail is around 8 - 10" long and the connector in question is at the end of it. It's a large flat 4-pin inline Weatherpak.
The white wire that's hanging out in space is the tach connection. I'd suggest leaving that off while troubleshooting. Once the engine is running, try hooking it back up and see if it still runs. It's possible that something is wrong with that, in which case it could very easily prevent spark from being generated.
The choke should close fully at any engine temp below 70°F or so. The colder it is, the tighter it should close, and the longer it should stay closed after the engine is running.
Correct starting procedure is, press the gas pedal fully ONCE, take your foot off the gas, turn the key. If the temp is below 50°F or so, press it TWICE. If the temp is below freezing, 3 times. And so on, as it gets colder. The engine should start right up IMMEDIATELY if there's fuel in the carb (another matter entirely...) and run a bit rough for a few seconds but smooth out quickly.
I'd suggest not messing around with numbers, marks, specs, lights, etc. for the timing. The factory setting is NOT the point at which the engine runs best; it's a compromise between emissions, CAFE, emissions, wide temp range, emissions, altitude variations, emissions, and a few other things. Oh I forgot to mention - emissions are a significant input to the factory's "spec", in fact the DOMINANT factor as far as they're concerned. It is NOT the setting at which the car runs the best, therefore IS NOT what you want.
Once you get it running we can talk about how to set it for "best" operation.
All of the connectors in that thing are severely deteriorated. I'd recommend replacing all of them. Not sure if you can get them that way; might be easier, cheaper, and more effective, to just replace the entire distributor. Best one you could get would probably be this one. https://www.summitracing.com/parts/d...00bk/overview/
the choke plate should stay fully closed UNTIL the engine starts running. the choke pull off (front of carb) will receive a vacuum signal when the engine starts and will slightly open the choke once the engine starts.
what you moved is the counterweight that engages the high idle cam. when the choke is closed, the cam is engaged and the primary throttle is opened slightly more than the curb idle adjustment allows.
hard to explain without pictures, but if you tinker around with all of it, the operation becomes pretty self evident. the intent it to raise the idle slightly when the choke is on, keep the choke plate closed when cold to aid starting and crack the choke open slightly once started to keep the engine running. then as it runs the choke coil receives 12v power which slowly warms the bi-metal coil inside and the choke slowly opens.
Thanks for the replies guys its really helping. As a result......IT RUNS !!!!!!!!!! There are still problems though so dont go anywhere... lol Here's a vid
turns out the distributor was in wrong, i turned the engine to TDC to check and the rotor arm was facing the radiator, instead of plug 1. so i got that put right, put it back together and after 2 tries it started up quite easily and ran perfectly for 5 minutes before i switched it off. i turned the dizzy counter clockwise first i think and still no good, turned it back the other way it it roared into life finally.
I let it sit for a few minutes and tried again and it wouldnt start, well it did briefly and sounded like it was running on 3 cylinders then it cut out. This is pretty much what the original owner described too. So im wondering if this is because the timing hasnt been set yet by removing the connector from the back of the dizzy ? when i have come to restart it the ECU thinks the dizzy is somewhere else and it wont run again ?
Theres also lots of tuning to do on the carb no doubt which i think my friend can take care of as he is a carb guy
Originally Posted by sofakingdom
The white wire that's hanging out in space is the tach connection. I'd suggest leaving that off while troubleshooting. Once the engine is running, try hooking it back up and see if it still runs. It's possible that something is wrong with that, in which case it could very easily prevent spark from being generated.
The tach was going crazy when i got the car running, it starts off at the bottom so its not even on the rev band and while cranking it keeps going up and up all the way around, when the engine started it was around about 9 thousand rpm, ha ha, but doesnt actually move, likes its totally maxed out, so im not sure what is going on with that, faulty gauge in the cluster perhaps ? you can see it doing its thing in the video. volt meter appears to be working and the oil pressure goes upto full too when it started up, temp gauge im not so sure about
Last edited by gta_knight; 01-15-2017 at 02:28 PM.
your symptoms are consistent with a failed, or failing, distributor or pickup coil. when they are bad, they will run 'ok' when cold then fail on a hot re-start. based on the condition of your existing dist, a replacement will be a worthwhile investment. a new one should come with a new ignition control module.
do not worry about timing now. the ecm just adds to the base timing. just get it running consistently then you can tinker with the timing to get it where it's best.
I've not had problems with the stock-style replacement distributors for these. used Dorman distributors a time or two if $ is an issue.
I just had to replace the distributor on my 87 two weeks ago, it would crank constantly then start up and be totally fine one day, then the next time it happened it wouldnt fire at all, new dizzy in and its been fine since.
So the 84 needs a dizzy then... well ordering a new cap and rotor arm was a waste of time then lol. the car was only running for 5 minutes though so it wasnt hot, barely even warm, or would that still cause the dizzy to fail upon restart
The distributor hadnt moved from starting it the first time.
ive just tried it again today and it started up quite easily and ran fine for a bit. I reved it and it stumbled a bit and the rpm dropped. I noticed the choke flap had closed itself. It seems to run better with that flap open slightly and cuts out if it closes.
Is power getting to choke? check for 12 volts on wire to choke assembly.After car starts and runs for a minute...open choke plate manually and see if it will stay running.Choke should eventually open fully if it is getting power and functioning properly with correct adjustments/tension on internal choke assembly.You still probably have an issue with ignition system as previously explained in addition to carb issues.
Last edited by hockeyman48; 01-16-2017 at 03:11 PM.
Still got that to check once i find my volt meter ! I started the car today, it fired first time just on the key, no pressing the gas pedal or anything which was great, the dizzy is advanced a **** load though lol, hopefully i can get a good garage day at the weekend and check the timing with my gun etc.
just trying to get to that 4 wire connector on the back of the dizzy seems like a pain in itself.
Do i disconnect that while the engine is running then set the timing, and plug it back in all while the engine is running ? on my 87 i have to unplug the connector with the engine off then start it and down the adjustments, then switch off and plug it back in.
just trying to get to that 4 wire connector on the back of the dizzy seems like a pain in itself.
So you reach around the base of the dist, find the harness coming out the back, pull it up where you can see it, .... ??? it's not rocket surgery, really.
To set "timing" to "spec" according to "book" using "light" and "mark", you disconnect it with the engine off, start the engine which will run like hammered elephant crap, screw up the "timing" that way during which process the SES light will come on within a few seconds, turn the engine off, reconnect the connector, and disconnect the battery to clear the SES light.
Or you could just do what sensible people do, and set the "timing" to where the engine runs the best. Which is ABSOLUTELY POSTIVELY 100% CERTAINLY TAKE IT TO THE BANK FOR SURE NOT going to be where "book" says to put it. As someone described above,
The factory setting is NOT the point at which the engine runs best; it's a compromise between emissions, CAFE, emissions, wide temp range, emissions, altitude variations, emissions, and a few other things. Oh I forgot to mention - emissions are a significant input to the factory's "spec", in fact the DOMINANT factor as far as they're concerned. It is NOT the setting at which the car runs the best, therefore IS NOT what you want.
The ecm will advance the timing significantly from base timing, even at idle. Should be around + 20ish degrees advanced.
when the ESC plug is disconnected the ecm should engage the throttle kicker relay which raises the throttle off of the curb idle stop so that the engine has a chance to run with the now significantly reduced timing.
I set timing on these at around 0 degrees base and then increase a few degrees at a time until the motor begins to ping under throttle tip in at cruise. may wind up in the 4-6 range. the final optimum setting will be dependent on a lot of factors, as said above.
Usually when I've done this, it's on a start up after some type of work (H/C change maybe) that allowed me to verify the timing marks lined up with TDC. No reason the optimum timing setting can not be determined WITHOUT a timing light.
Ive adjusted the timing loads backwards and forwards. Thats not an issue with or without the timing light.
Problem is it doesnt seem to want to stay there, if i shut the car off after its been running for a few minutes and go to restart it, sometimes it will either start up again rough as if ive turned the dizzy back the other way making it run crap, or it wont start period.
Ive been going backwards and forwards with a friend who has an 84 too and he has a factory service manual so has been quite helpful with vacuum diagrams etc, looks like ive got lines to check over and theres a few vacuum lines that have been plugged for whatever reason.
I also adjusted the idle screw, but as it began to touch the throttle and push it backwards, idle started going up as you would expect but then the choke plate closed and the engine died. this engine will not run unless the choke plate is open slightly ??
the choke pulloff should open the choke slightly once it receives a vacuum signal (from the running engine)
check it by pushing in the plunger then hold your finger over the vacuum nipple. the plunger should stay in until you release your finger. steps for adjusting it, and the choke, are in the carb sticky in this forum.
your big problem appears to still be the old, wore-out dist.
Ive noticed my choke body has rivets on so i cant adjust it, presumably because its new, when compared to my friends 84 his has 7 visible notches too so im guessing its set correctly.
The car will not run unless i manually open the choke flap slightly, if its running and i press the flap closed the engine dies as its getting no air, makes sense. So i assume it should always be slightly open ? if not how does the engine run if it gets no air.
While it was running i tested the wire and the voltage was jumping all over the place between 1 and 4 volts. Im guessing that aint right ! Any ideas where to start with that one wire ?
The only way to get it running is to back off the idle screw which slackens the silver part near the choke which you can see in the pic below, and i can push it with my finger to open the choke flap slightly, and its fine.
So the problem im having trying to set the timing and get it idiling is proving a nightmare as im advancing the distributor a lot when i need to set the idle screw instead as its not even touching the throttle at the moment, but once i start turning the screw the choke flap snaps shut and the engine cuts out lol
Ive noticed my choke body has rivets on so i cant adjust it, presumably because its new, when compared to my friends 84 his has 7 visible notches too so im guessing its set correctly.
The car will not run unless i manually open the choke flap slightly, if its running and i press the flap closed the engine dies as its getting no air, makes sense. So i assume it should always be slightly open ? if not how does the engine run if it gets no air.
While it was running i tested the wire and the voltage was jumping all over the place between 1 and 4 volts. Im guessing that aint right ! Any ideas where to start with that one wire ?
The only way to get it running is to back off the idle screw which slackens the silver part near the choke which you can see in the pic below, and i can push it with my finger to open the choke flap slightly, and its fine.
So the problem im having trying to set the timing and get it idiling is proving a nightmare as im advancing the distributor a lot when i need to set the idle screw instead as its not even touching the throttle at the moment, but once i start turning the screw the choke flap snaps shut and the engine cuts out lol
You're correct regarding the rivets. This is GM's response to the US EPA regulation that emission controls and adjustments shall not be tampered with as set from the factory. It doesn't prevent anyone from drilling out the rivets, re-adjusting the choke stove and re-securing it with replacement rivets or screws. For now, leave the choke stove alone.
When describing choke issues, you always need to include information regarding engine temperature at which the problem is occurring.
I'm going to assume that your choke closure problem is happening when the engine is cold (not at operating temperature).
When the engine is cold, such as when it's been sitting overnight, the choke is supposed to be fully closed prior to starting the engine. When the engine starts, the choke is supposed to open slightly. You report that this isn't happening.
The first thing to check before you start messing with adjustments is to confirm that the choke pull-off diaphragm isn't punctured. The diaphragm is supposed to open the choke slightly immediately after start-up.
Disconnect the vacuum hose from the pull-off and apply vacuum to it. You should see the arm pull in and it should hold vacuum. You should also see the choke open slightly (if the engine is cold during your vacuum test).
Last edited by paulo57509; 02-12-2017 at 02:27 PM.
Reason: Spelling
Thanks man i will try that tomorrow when i get in from work. Yeah the choke just doesnt seem to work at all, possibly because of the crazy fluctuating voltage going to it ?
The longest i have had this engine running is about 15 minutes and i cant recall the choke flap opening up anymore at all, where i set it by moving the silver part is where it stays
Disconnect the vacuum hose from the pull-off and apply vacuum to it. You should see the arm pull in and it should hold vacuum. You should also see the choke open slightly (if the engine is cold during your vacuum test).
Hooked my vacuum brake bleeder up (handy thing) and it works fine, i thought it would saying as the carburetor is brand new. Should it work exactly like this when starting the engine ? because i dont think it does, hard to see when im in the car starting it, i will have to get my wife to check. So if its not working like that when starting im guessing i have bad vacuum lines or they are connected wrong ?
Hooked my vacuum brake bleeder up (handy thing) and it works fine, i thought it would saying as the carburetor is brand new. Should it work exactly like this when starting the engine ? because i dont think it does, hard to see when im in the car starting it, i will have to get my wife to check. So if its not working like that when starting im guessing i have bad vacuum lines or they are connected wrong ?
Thanks man, i will take a look through them. Ive just had the car running again tonight just for the sake of it, it started immediatley on the key ! idled great, but thats because i had opened the choke plate manually again before i did. let it run for 5 mins or so then shut it off, tried to restart it a few minutes later but the choke flap closed itself as i was watching through the windshield, i opened it again manually and it struggled to start but did, then started running rough because the flap closed itself again, by time i gave it some gas it just stalled out as it wouldnt open.
So i am wondering if the choke pull off is getting decent vacuum when the engine is starting, i couldnt check that on my own tonight. Im also wondering what the power wire controls exactly, my voltage is jumping all over the place from 1 to 4 volts with the engine running
01-01-2017, 04:25 PM
