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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.
hello im kinda new to carbs (my last carb car was a 77 Mustang II like 7 yrs ago) i just picked up this 1987 Trans Am that had the carb replaced. anyone have any info on this carb? what is it? is this a stock unit? does anything look out of place?
reason i ask is the transmission shifts harsh. its not late or anything just hard even harsh shifting into D. i though maybe a TV cable adjustment but the cable looks ok
thanks for the reply, it looks like the part numbers match with the one in your link so im glad at least the previous owner got the right part. its been a while so could you give me a refresh on adjusting the cable please?
does this carb have an electric choke? meaning im not supposed to depress the accelerator to engage? she will not start on her own i usually have to give her some gas. maybe choke is not working right?
Harsh shifting is a classic symptom of a failed or disconnected vacuum modulator. The modulator "lives" on the transmission, and has a vacuum hose coming up to the engine. I'm betting since you have open vacuum ports, it's probably not even connected. Get under the car, find the modulator, then follow the vacuum line, and confirm it's connected.
update: so doing more research i see that since my car has the TV cable i do not have the vacuum modulator valve, am i correct in the statement? anybody have a diagram of there these to open ports on carb connect to?
Last edited by 87tunedport; 04-06-2017 at 08:00 AM.
does this carb have an electric choke? meaning im not supposed to depress the accelerator to engage? she will not start on her own i usually have to give her some gas. maybe choke is not working right?
It does have electric choke.
The procedure I was taught to start a cold engine, you should turn on the key, wait couple seconds, depress the accelerator pedal to the floor once and let off. This will set the choke flap and put the proper amount of fuel in. Then turn the car over. If car does not start right away (less than 10 seconds) on colder days, I will repeat and try again. The only time I had to do it more than twice was trying to start it at 10 below without it being plugged in.
In the 75 owners manual I looked at last night, it said on extremely cold days to depress the pedal two or three times at the start. When I mentioned that in my drivers ed class waaaay back, the instructor said no you would flood the car. I just learned this week, you only need to depress 1/3 of the way unless it is cold out.
Regardless, you need to depress pedal to set the choke flap even with an electric choke.
i just got back from doing the TV cable adjustment, i dont have the vehicle legal yet as i just got her 2 days ago but i did start her let her run for couple seconds and shifted to reverse. it was a smooth shift to reverse and didnt have to floor the brake to keep the car stopped. i shifted to drive and got same results so hopefully that solved the problem. once i get my insurance ill take her for a test drive and see how the gears shift. keeping fingers crossed lol
Originally Posted by dlinger
It does have electric choke.
The procedure I was taught to start a cold engine, you should turn on the key, wait couple seconds, depress the accelerator pedal to the floor once and let off. This will set the choke flap and put the proper amount of fuel in. Then turn the car over. If car does not start right away (less than 10 seconds) on colder days, I will repeat and try again. The only time I had to do it more than twice was trying to start it at 10 below without it being plugged in.
In the 75 owners manual I looked at last night, it said on extremely cold days to depress the pedal two or three times at the start. When I mentioned that in my drivers ed class waaaay back, the instructor said no you would flood the car. I just learned this week, you only need to depress 1/3 of the way unless it is cold out.
Regardless, you need to depress pedal to set the choke flap even with an electric choke.
thanks for the info ill keep doing what im doing then
Last edited by 87tunedport; 04-06-2017 at 09:28 AM.
The one open port that is high on the carb is for the air cleaner vacuum tube. The open port on the bottom is for the CCV which is missing. It looks like the tube that would normally go to the valve has been replaced with one going directly to the charcoal canister. Just a note here for the OP, 1987 was the last year for carbureted engines in F-body cars. And your engine should be a roller rocker type if it is the original 305. You are correct about the vacuum modulator; there isn't one. If your TV cable is adjust properly, then it should shift into overdrive around 35mph. The overdrive function does not work until the engine has warmed to operating temperature. The same is true of the newer vehicles with the 4L60E transmission (found in 90s trucks). This temp signal comes from the temp sensor in the driver side cylinder head, so make sure that works.
Another thing I noticed was that the temp switch for the EFE valve is broken off in the thermostat housing. If you live in a warm climate, then that isn't really an issue. But if you do live somewhere that gets cold in the winter, the EFE system comes in handy. The valve is located at the end of the passenger side exhaust manifold. If it is still there, it may have been locked in the open position. If you have headers, then it is gone, as it will only mount to stock manifolds.
Last edited by gearhead141; 04-06-2017 at 12:53 PM.
Harsh shifting is a classic symptom of a failed or disconnected vacuum modulator. The modulator "lives" on the transmission, and has a vacuum hose coming up to the engine. I'm betting since you have open vacuum ports, it's probably not even connected. Get under the car, find the modulator, then follow the vacuum line, and confirm it's connected.
TH700R-4 doesn't have a vacuum modulator. That's why TV cable adjustment is critical.
And the TV cable is not a "detent" cable. Don't call it that, because that's not what it is (even if the linked tech article calls it that). This explains it all very well: http://www.tvmadeez.com/article/index.php
The open vacuum nipple on the front of the carb with the "T" goes to the air cleaner. If you don't have a factory air cleaner, cap off that open nipple.
The vacuum nipple on the front of the carb under the large vapor hose goes to the vapor control valve, which appears to be missing on your car. I'd suggest capping it off as well.
There is also supposed to be a nipple just in front of the accelerator pump rod, which appears to have some sort of goober over it. Hopefully it is sealing well.
This is a computer controlled carb (factory called it "computer command carburetor"). It needs a signal from the O2 sensor to operate correctly. That wire was routed by the factory in front of the carb. With all the clipped wires in there, I hope that isn't one they cut.
The EGR vacuum hook-up isn't correct, either. It's supposed to go to a solenoid, which doesn't appear to be there. The vacuum hose for that is supposed to go to the EGR solenoid appears to go down to the EFE valve on the exhaust manifold, and the EGR valve is tee'd to the PCV valve.
That "goober" that five7kid is referring to is covering a screw on the carburetor cover. I just looked at mine and there is no port in that area.
The O2 sensor input is important and hopefully you still have that. Otherwise the carb will stay in "open loop" and your engine will run rich all the time. In other words, bad gas mileage.
I would take a guess that the previous owner of your car removed all the emissions equipment. And it would appear it wasn't done in a methodical or intelligent manner. We are here to help you get it back to a reliable and safe condition. Ask questions and we will provide guidance and photos to help.
yes the PO had all the emissions removed. he told me that when i asked him about the check engine light thats illuminated on the dash. he said the light was for o2 sensors but all the wiring was removed so i may be screwed on that one, ill have to check to make sure. there is no emissions testing here in MI so thats probably why its all gone. what should i do? i want the light off in the dash and i want the car to get into of closed loop and get good mileage.
shes a summer car for me and will only be taken on cruises and car shows (im a member of USMA) so cold temps dont matter to me
yes the PO had all the emissions removed. he told me that when i asked him about the check engine light thats illuminated on the dash. he said the light was for o2 sensors but all the wiring was removed so i may be screwed on that one, ill have to check to make sure. there is no emissions testing here in MI so thats probably why its all gone. what should i do? i want the light off in the dash and i want the car to get into of closed loop and get good mileage.
shes a summer car for me and will only be taken on cruises and car shows (im a member of USMA) so cold temps dont matter to me
It's been awhile, but I believe the light blue wire that is clipped off on the passenger side harness is the O2 sensor. Whichever it is, you should be able to get a repair pigtail to get the O2 sensor back working. Can't see what your exhaust is from your pics, but from the factory it's in the driver side exhaust manifold.
That "goober" that five7kid is referring to is covering a screw on the carburetor cover.
I believe you are right about that being on a screw.
Originally Posted by gearhead141
I just looked at mine and there is no port in that area.
Different years had different vacuum ports. '87 should have it, but no guarantee this carb is an '87 (I can't read the carb # from the pics posted). Regardless, the carb will work when all the inputs are there (I bought an all-stock '82 from California in which they had replaced the carb with an '87 model - I was able to get all of the vacuum stuff working, and when all adjustments were to factory specs, it ran great and passed emissions with flying colors).
Harsh engagement into reverse or OD/drive is kind of normal for this vintage 700R4. The TV cable and its adjustment will have no effect on this.
IIRC, GM addressed this sometime in early 1987.
It could also be that the engine might be running at fast idle (when cold) when you put it in gear and this will also make engagement feel harsh (which is also normal).
It's been awhile, but I believe the light blue wire that is clipped off on the passenger side harness is the O2 sensor. Whichever it is, you should be able to get a repair pigtail to get the O2 sensor back working. Can't see what your exhaust is from your pics, but from the factory it's in the driver side exhaust manifold.
can you tell me where the wire is supposed to go? your talking about the cut wire right next to the carb electric choke right?
Originally Posted by five7kid
I believe you are right about that being on a screw.
Different years had different vacuum ports. '87 should have it, but no guarantee this carb is an '87 (I can't read the carb # from the pics posted). Regardless, the carb will work when all the inputs are there (I bought an all-stock '82 from California in which they had replaced the carb with an '87 model - I was able to get all of the vacuum stuff working, and when all adjustments were to factory specs, it ran great and passed emissions with flying colors).
the PO told me the carb was replaced last year and the only numbers are that ND-4477. im going back to the car today to work on the hatch pull down motor so ill try to get a better pic of that label but according to amazon.com its the right carb for my car
Originally Posted by paulo57509
Harsh engagement into reverse or OD/drive is kind of normal for this vintage 700R4. The TV cable and its adjustment will have no effect on this.
IIRC, GM addressed this sometime in early 1987.
It could also be that the engine might be running at fast idle (when cold) when you put it in gear and this will also make engagement feel harsh (which is also normal).
it was harsher that usual as harsh as shift to R, ohh S*** floor the brake cause the car starts moving after re-adjusting the TV cable i dont have to stomp the brake and i dont feel like "brace yourself" so i believe it helped but not sure yet as i have yet to drive and go through gears
the engine runs at about 900 rpm even when cold so i doubt the choke is even working if it is it just starts the car, doesn't raise prm to keep running
The O2 sensor wire should be in that taped up bundle sitting right in front of the carb. It is a dark blue wire I believe. It would be running across the driver side valve cover to the oxygen sensor located in the driver exhaust manifold. Normally there is a harness plug for the sensor to connect to. In the photo I've attached you can see the harness connector and the wire going down to the sensor.
The transmission going into gear with a "thunk", I found to be caused by a loose cross member trans mount bolt. So every time I'm under the car for an oil change, I simply tighten it up. But this is a common thing with the thirdgen F-body.
Your carb identification number is stamped in the body near that sticker. If you look at the flat portion directly in front of the sticker, you should see a number beginning with "1708". The entire number can be deciphered to tell what year the carb was made and if it is for a manual trans or automatic.
Last edited by gearhead141; 04-07-2017 at 01:11 PM.
This diagram from the FSM shows the harness routing which should help you. It also calls out the wire color as purple (PPL), but if so, it is a dark purple. The item listed as "B" is the O2 sensor.
That sensor that you show has a "weatherpak" connector. That came along in '86 or '87 and you would need the female part of the plug to make it work. Our cars use single wire sensors, so it isn't critical to use a factory connector. When I replaced my sensor, I just bought a generic single wire. There are a few different manufacturers.
Last edited by gearhead141; 04-08-2017 at 12:40 PM.
So I just pulled the codes (should have done that earlier instead of listening to previous owner and wasting all your and mines time) I got a code 15 and code 23
The o2 sensor is present as is the wiring. I saw the EGR piping has been chopped going to the back of the head
So I just pulled the codes (should have done that earlier instead of listening to previous owner and wasting all your and mines time) I got a code 15 and code 23
The o2 sensor is present as is the wiring. I saw the EGR piping has been chopped going to the back of the head
Code 15 is for coolant sensor open circuit.
Code 23 is M/C solenoid voltage low to ECM.
The mixture control solenoid is that blue plastic item on top of the carb. Check wiring, if that is good, check the ECM fuse as it may be blown. When you turn the ignition key to the ON position, the M/C solenoid should be heard making a clicking sound.
Last edited by gearhead141; 04-08-2017 at 06:39 PM.
The transmission going into gear with a "thunk", I found to be caused by a loose cross member trans mount bolt. So every time I'm under the car for an oil change, I simply tighten it up. But this is a common thing with the thirdgen F-body.
Hey gearhead141.....you wouldn't happen to have a pic of that cross member trans bolt that keeps loosening up on you?
Last edited by stahrman0612; 04-12-2017 at 04:14 AM.
This is a photo I captured off the internet. You can see the crossmember directly behind the trans pan. I don't recall now if it is a nut or a bolt, but you can clearly see it.
This is a photo I captured off the internet. You can see the crossmember directly behind the trans pan. I don't recall now if it is a nut or a bolt, but you can clearly see it.
Awesome!!! Thanks for the pic. Going to check mine out on my next day off.
I read 17087130. This carburetor came Factory on 87-88 Camaro, Monte Carlo LS, Caprice & Caprice Classic. Although this carburetor will also fit other makes/models listed on the fitment chart based on the Tomco carb replacement chart.
so to bring this thread back up, i just ordered a CCV and purge valve to get everything back to normal again
i just finished re installing the AC in my car and i must say the engine bay looks very respectful. now im working on the vacuum lines and im gonna remove the TVS and put a brass plug in its place to help clean up the engine bay some more since this car will be going to car shows.
not really what i had in mind for this car, every time i finish something i find more that has to be done, but the car has to be right in order to give me a few years of service and enjoyment. ohh well its a labor of love
Once you get it all sorted out, take a few pics so we can all see your hard work. You must have found a donor car at the salvage yard. That could be the only explanation for such a cruddy CCV. A lot of people on here are always asking about removing the emissions equipment. There aren't as many that ask about putting it back on.
Once you get it all sorted out, take a few pics so we can all see your hard work. You must have found a donor car at the salvage yard. That could be the only explanation for such a cruddy CCV. A lot of people on here are always asking about removing the emissions equipment. There aren't as many that ask about putting it back on.
so doing more research i dont think i need the valve in pic 1 since i thought that was the purge valve seen in this diagram but its the TVS switch mounted on the intake. the one thats by the charcoal canister i believe is still present on my car. so looks like i just need to hook up the CCV and connect the purge TVS from second pic. should clean up engine bay a little and make use of the open vacuum ports
So I have had a change of heart and decided to go in a different direction. In instead of putting it all back I decided to scale it down and cap off the rest. I only have the canister and the EGR connected. For the canister I just have the fuel bowl vent and I replaced the lines. Everything has been capped off.
Further more I removed both TVS switches and got 1/2 and 3/8 brass plugs. The last hurdle I have to go through is the stupid EFE heat riser valve still on the exhaust. And a small diameter tube that looks ugly as hell cause it's chopped off going into the engine. I believe it was for the EFE system or smog pump. It was the metal line that went to 4 ports on exhaust manifolds either way I want it gone along with HRV
Right now I'm gonna take the air cleaner and AC dryer home clean them up and paint black to help clean it up
For the exhaust manifold heat control valve, take it out, remove the plate and tap the hole where the shaft was for a 1/8" pipe plug.
You need to have your gas tank vented. If you don't, it will either build up pressure, or a vacuum will be created as the fuel gets used, making your pump unable to do its job. You can prove this by removing the gas cap after driving around - there will be a whoosh sound. That is air entering the tank from a vacuum situation, or gas fumes will blow out from escaping. You should keep the charcoal canister and CCV canister control valve, at least. The green top TVS is the control for this system. See these posts: https://www.thirdgen.org/forums/carb...e-routing.html https://www.thirdgen.org/forums/tech...grams-i-5.html
see post #221
Last edited by NoEmissions84TA; 05-27-2017 at 06:06 PM.
i still have the canister in the car and its attached to the carburetor by means of the fuel bowl vent. the tank pressure control valve is also still attached and going to a vacuum source on the carburetor i just dont have the CCV, the purge TVS, or the EFE system. i have the pressure valve hooked to "H" on the YCX hose routing pic seen in post 36
i have all the stuff but after i discovered the purge TVS was broken i decided against installing all it. the tank can still vent this way right? if its a problem ill hook the CCV up but the purge TVS is broken and i am having a hard time finding a replacement
Last edited by 87tunedport; 05-27-2017 at 07:41 PM.
For the exhaust manifold heat control valve, take it out, remove the plate and tap the hole where the shaft was for a 1/8" pipe plug.
You need to have your gas tank vented. If you don't, it will either build up pressure, or a vacuum will be created as the fuel gets used, making your pump unable to do its job. You can prove this by removing the gas cap after driving around - there will be a whoosh sound. That is air entering the tank from a vacuum situation, or gas fumes will blow out from escaping. You should keep the charcoal canister and CCV canister control valve, at least. The green top TVS is the control for this system. See these posts: https://www.thirdgen.org/forums/carb...e-routing.html https://www.thirdgen.org/forums/tech...grams-i-5.html
see post #221
to remove the valve is it just 2 bolts? i know ill be in for a ride getting the bolts loose but what else will i be in for?
You have to at least partially drop the y-pipe to get the heat control valve out. Get new gaskets. Depending upon how much rust and corrosion you have, that will determine how hard this job will be. Use RED loctite on the 1/8 pipe plug. Spray the bolts and studs for a couple of days with your favorite penetrant before you tackle the job.
Last edited by NoEmissions84TA; 05-28-2017 at 05:48 PM.
You have to at least partially drop the y-pipe to get the heat control valve out. Get new gaskets. Depending upon how much rust and corrosion you have, that will determine how hard this job will be. Use RED loctite on the 1/8 pipe plug. Spray the bolts and studs for a couple of days with your favorite penetrant before you tackle the job.
thanks for the info, ill give it a shot this week. not looking forward to it at all though lol
figured i would get some pics of my progress. im still waiting on the high pressure line for the AC and gotta deal with the heat valve
no they have bolts in there that protrude out (from PO) i was just gonna get the same plugs i used for the TVS switches. do they make actual plugs for those ports?
side note, i still have the tank pressure control valve on the canister. do i need that valve? will the system still vent without it? or is fuel gonna be getting into the canister? i also read im supposed to put a fuel filter in the fuel bowl vent line to keep charcoal bits from entering the engine is this true?
Last edited by 87tunedport; 05-29-2017 at 07:18 AM.
5/16" inverted flare. You'll see the the mating surface for the flare when you remove the existing.
your tank has an over pressure relief valve but will still try to vent through the line that runs to the canister unless an alternate vent method is installed.
this is the setup i have. im asking if i can remove the tank pressure valve and just connect the lines together or do i need the valve to vent the tank properly? just trying to remove some more vacuum lines and clean things up a little more
ill get some of those inverted flare nuts thanks for the info
you'll need to keep the over pressure valve at the tank. it will allow the tank/system to develop some pressure to force fumes towards the charcoal canister, but vent higher pressures that may otherwise damage that system or the tank.
the valve is also two-way, allowing air into the tank to prevent negative pressures, which can also be bad.
while you're thinking about it, a bit of maintenance/checks on this valve may be in order. there's a thread somewhere on dismantling it and repairing. you can check that it releases pressure by running compressed air into the system at either the feed or return fuel lines. should hear it phart off the excess pressure.
wait, is the over pressure valve the same as the tank pressure control valve? meaning the vacuum operated valve located at the charcoal canister thats connected to the fuel tank?
no they have bolts in there that protrude out (from PO) i was just gonna get the same plugs i used for the TVS switches. do they make actual plugs for those ports?
side note, i still have the tank pressure control valve on the canister. do i need that valve? will the system still vent without it? or is fuel gonna be getting into the canister? i also read im supposed to put a fuel filter in the fuel bowl vent line to keep charcoal bits from entering the engine is this true?
The plugs for the exhaust manifold are essentially blocked off tube nuts. NAPA should have them.
The tank will vent without the TPCV, but since you are keeping the charcoal canister, then why not keep it? It is just 1 extra vacuum line. With it, the fuel vapors will be sucked into the carb to be burnt.
The fuel filter in the fuel bowl vent line to keep charcoal bits from entering the engine is my idea because I read about this happening to someone else. I figure that it's a cheap and easy way to prevent this from happening. You could even use a plastic, see-thru filter.
You don't really need it because you already removed the TVS valves and CCV.
Last edited by NoEmissions84TA; 05-29-2017 at 11:09 PM.
04-05-2017, 02:44 PM
