CarburetorsCarb discussion and questions. Upgrading a Third Gen carburetor, swapping TBI to carburetor, or TPI to carburetor? Need LG4 or H.O. info? Post it here.
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I have three issues keeping my car off the street as a reliable driver.
1. Overheating
2. No start after the car is hot
3. Starter click occasionally
I need some help with all three but the main one I'm concerned about is the no hot start. I am getting some sort of spark but I have this coming out of my carb when I shut it off...
Is this a for sure sign of my fuel overheating?
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__________________ 1991 Pearl White Z28
Previous: 383 HSR
Now: 383 Demon
9.17@81 with the 305
RIP: 1992 RS 305 TBI 5-Speed
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I have seen mine do this sometimes after shutting it down. I think it's from some exhaust gasses exiting which ever cylinders have exhaust valves stopping in the open position once the engine has stopped. When you go to start it hot- what does it do? Just dead crank or fire and die, or what? What the time frame when it won't start after sitting? Are the outside of the carb bowls extremely hot? Do you have a carb spacer?
I would worry about the over heating first. What kind of radiator and fan setup are you running. Also sounds like your stater is getting heat soak, you might want to buy a heat sheild for it. Once you get the car running cooler your vapor lock issue might go away.
I would worry about the over heating first. What kind of radiator and fan setup are you running. Also sounds like your stater is getting heat soak, you might want to buy a heat sheild for it. Once you get the car running cooler your vapor lock issue might go away.
Am in the process of sorting out the overheating, I know it is a huge factor in the vapor lock. Trying to do multiple things at once sucks!
Fan, WP and airdam in place and functional. Need to fabricate a shroud badly!
Also running the Air-Gap RPM, will purchase phenolic spacer with next summit purchase.
Timing is conservative until all bugs are worked out and carb is tuned.
I know this is not a one trick fix but many little issues adding up....its tough sorting all of these out, however, when they affect one another!
So that "fog" is normal? This was the first indication to me that I was getting vapor lock or boiling fuel and not some electronic issue with the coil or HEI module.
From the cooling upgrades you have posted you should be running cool.Is your fan pushing or pulling ? And whats your carb setup ? What jets are you running ? You might be running way to lean and thats where the excess heat is coming from. Also, where is your timing at currently ?
Timing is conservative until all bugs are worked out and carb is tuned.[/b]
The tune, or lack of proper tune, will cause the engine to run hot. If the motor is not getting the proper mixture of fuel and air it'll be running less efficiently, meaning more throttle opening for the same amount of power. If the spark is late less of the charge goes towards engine power and more of it is burning in the exhaust. If it's too early the ignited charge is pushing the piston down before it has reached top.
An out of tune motor burns more fuel than it needs for the required level of power. The extra fuel that is burned is dissipated as heat energy. Get it tuned up and some of these other problems will likely take care of themselves.
Vapor lock is when fuel in the lines from the tank off gasses and the mechanical pump can not pump liquid fuel to the carb because of the vapor. My guess is you're either flooding it or your spark is weak.
From the cooling upgrades you have posted you should be running cool.Is your fan pushing or pulling ? And whats your carb setup ? What jets are you running ? You might be running way to lean and thats where the excess heat is coming from. Also, where is your timing at currently ?
Fan is a puller, spinning in the right direction. Carb is a Speed Demon 750 mech secondaries. Jets are 'stock' Demon jets 76 primary and 83 secondary; the car runs rich. Stinging eyes, black plugs, smells rich... Timing is approx 14 initial and 28 total for the moment.
Quote:
Originally Posted by naf
The tune, or lack of proper tune, will cause the engine to run hot. If the motor is not getting the proper mixture of fuel and air it'll be running less efficiently, meaning more throttle opening for the same amount of power. If the spark is late less of the charge goes towards engine power and more of it is burning in the exhaust. If it's too early the ignited charge is pushing the piston down before it has reached top.
An out of tune motor burns more fuel than it needs for the required level of power. The extra fuel that is burned is dissipated as heat energy. Get it tuned up and some of these other problems will likely take care of themselves.
Vapor lock is when fuel in the lines from the tank off gasses and the mechanical pump can not pump liquid fuel to the carb because of the vapor. My guess is you're either flooding it or your spark is weak.
You are certainly correct. The motor is FAR from efficient but its hard to tune when the engine overheats and doesn't restart after it gets up to temp. While timing and A/F ratio play a role in engine temp I don't think they would solve my overheating in traffic.
Its not being flooded but weak spark may play a role. I plan to change the coil and module once again after I get it all put back together from this shroud ordeal. Don't know how much the shroud I'm capable of building will help but I have to give it a shot.
Thanks for the help guys, keep the discussion going.
I had the same issues once with my 406. I think you need more inital timing. Your rich idle comes from the throttle blades exposing too much of the transfer slot (which means more fuel). With not enough inital timing, the motor will need a higher idle setting. Which is why you have a rich idle, and vapor when shut off. What are your engine and cam specs?
You are certainly correct. The motor is FAR from efficient but its hard to tune when the engine overheats and doesn't restart after it gets up to temp. While timing and A/F ratio play a role in engine temp I don't think they would solve my overheating in traffic.
You're concerned about it overheating in traffic but can't let it idle in the driveway long enough to set timing correctly and do a basic tune?
And a tune MAY solve your overheating problem AND save you tons in gas. If anyone doubts this try driving around town for a day with your ESC connector unplugged and timing at base. Note how hot it runs and how crappy your mileage is.
Your tune certainly isn't necessarily your only problem but it is the problem you should tackle first. You're surely not treating that new motor with respect.
This definetly seems like it is running VERY rich and you have residual fuel burning off upon engine shutdown. You really should try adjusting the timing around and maybe even swap out some jets.
I had the same issues once with my 406. I think you need more inital timing. Your rich idle comes from the throttle blades exposing too much of the transfer slot (which means more fuel). With not enough inital timing, the motor will need a higher idle setting. Which is why you have a rich idle, and vapor when shut off. What are your engine and cam specs?
Sounds like a great lead! Thanks for the post! I didn't think that running 14 degrees base would lead to vapor at shut off but I am going to delve into that. I honestly haven't even gone through the 4 corner idle with my vac gauge yet
Motor is 383 approx 10.5:1 C/R, Standard 23* Trickflows, RPM Air-Gap with the mech 750 Speed Demon. Cam is .540/.562 242/248 @ .050 on a 110 LSA.
Quote:
Originally Posted by naf
You're concerned about it overheating in traffic but can't let it idle in the driveway long enough to set timing correctly and do a basic tune?
And a tune MAY solve your overheating problem AND save you tons in gas. If anyone doubts this try driving around town for a day with your ESC connector unplugged and timing at base. Note how hot it runs and how crappy your mileage is.
Your tune certainly isn't necessarily your only problem but it is the problem you should tackle first. You're surely not treating that new motor with respect.
Duly noted, sir. Very true, I'm pretty sure it will idle long enough to do a basic tune. The jets, PV, and acc pump need serious work for sure. Also still have to dive into the dizzy advance springs but I was just having a hard time prioritizing all these damn issues. Thanks for the correct, honest response.
Quote:
Originally Posted by Blaize
This definetly seems like it is running VERY rich and you have residual fuel burning off upon engine shutdown. You really should try adjusting the timing around and maybe even swap out some jets.
I'll look at the timing a little better. still need to play with the weights and springs to dial it in. Jets will come, was trying to wait until the other bugs were worked out but I'm starting to believe they are ALL tied in together
A extensive JEGS order in oncoming; I will purchase a shroud for the overheating, thermo sleeves for the fuel lines, some jets and misc stuff to tune the carb, also needing a coil and HEI module since there is a chance this is contributing to the no hot start. Have a second 16" SPAL fan coming from eBay for good measure.
Can anyone recommend, besides jets and a power valve, what things I need to purchase to get the carb in tune?? Gaskets I will need etc?
Can you see fuel vapors coming out of the carb bowl vent tubes when it does this? I had an issue where the fuel in my fuel bowls was boiling, the floats would sink, and the bowls would overflow sometimes because of it. So next time it does it, look and see if you can see fuel boiling off through the vent tubes.
This doesnt really sound your like your problem though. But I had a problem where it wouldn't fire when hot because the boiling fuel would sink the floats as soon as I switched on my fuel pump, and then it would flood the motor and it wouldnt fire for a while after that unless I held the throttle absolutely WIDE open during cranking and eventually it would catch and spit a bunch of black smoke out.
I changed my fuel line routing and changed brands of fuel and never had that problem again. Fuel boils anywhere between 100 and 400F depending on what it is. So try a different brand.
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Last edited by InfernalVortex; 10-06-2009 at 01:11 AM.
Can you see fuel vapors coming out of the carb bowl vent tubes when it does this? I had an issue where the fuel in my fuel bowls was boiling, the floats would sink, and the bowls would overflow sometimes because of it. So next time it does it, look and see if you can see fuel boiling off through the vent tubes.
I changed my fuel line routing and changed brands of fuel and never had that problem again. Fuel burns anywhere between 100 and 400F depending on what it is. So try a different brand.
I originally thought the carb was scorching but I felt the bowls after a cruise yesterday. Temp got to approx 240 and wouldn't restart after I shut the car off in the garage.
The bowls of the carb weren't hot to the touch but the manifold was scorching. I'm thinking a phenolic carb spacer maybe no benefit to the situation. I am still going to shround the fuel lines with some thermo sleeve where they are close to the headers.
Will try the fuel brand suggestion. Never heard different brands would burn at that much of a difference in temp.
Quote:
Originally Posted by bluegrassz
You need closer to 32*-36* total timing all in by 3k. Get the timing set and carb tuned before you start throwing parts at it.
I am going to fool around with the basic tune and timing a little this weekend to see if I can get it a bit closer. I wanted to keep it conservative for possible detonation issues since I'm experimenting with the plug heat range.
Will try the fuel brand suggestion. Never heard different brands would burn at that much of a difference in temp.
Whoops. Not burn. I meant boil. They boil at different temps. I fixed my original post for the sake of anyone doing searches.
But my problem was the fuel in the feed lines was boiling as the car sat after a drive, and that was what was making my carb hot and causing my issues. As the fuel sat and depressurized over hte water neck for a few minutes it would get hotter and hotter until it began to boil. As soon as I cranked the car it would run fine. Then I'd hit my fuel pump switch and the car would do all sorts of crazy things as the floats sank and the carb overflowed and spewed boiling fuel everywhere.
I almost bought a phenolic spacer myself, but it wouldn't have done any good so Im glad I didn't. If you feel the lines you may be able to tell whether they're getting too hot. My fuel line was too hot to touch near their heat sources, and that was the waterneck and valvecover. They MIGHT have gotten to 200F or so which isnt that hot, but it was enough to boil the fuel I was using. Someone on TGO was having a similar issue to mine and I suggested they changed brands of fuel and it fixed the problem for them. So it might have fixed the problem for me too, but I changed the fuel line routing anyway.
Last edited by InfernalVortex; 10-06-2009 at 01:16 AM.
Bumped the timing up to 20* initial and 34* total right at 3000 RPM. Worked out well with the springs that came in the dizzy. Haven't messed with any additional vac advance yet. If I want to run any less initial I'll need to start experimenting with my springs and weights. This is good until I can get other bugs worked out.
Did some slight tuning with the carb. Got the throttle blades set correctly but I have to idle around 900-1000 with this cam and couldn't get the idle mixture screws right....might have vac leak or the vac gauge needle just loves bouncing around. Obviously the jets, PV and acc pump need serious work.
Still seems rich.
I can't tell until I drive it (tomorrow), but I'm hoping the timing adjustment might help the overheating :crosses fingers:
I've been searching tonight and can't find the threads that addressed this specifically...
When messing with the idle mixture screws I killed the car once. I immediately fired it back up and it started no problem.
When I was done for the night I shut it off and let it sit for 5 minutes. After this 5 minutes it wouldn't start again. UNTIL I held the carb at WOT and let it crank for a couple revolutions. Started fine and ran decent again.
Any ideas why it won't re-start when hot unless you hold it at WOT??? I noticed the "vapors" coming from the carb (seen in the pics above) weren't as dense as before.
Your timing should be good enough to tune the carb now. The vapors, seen coming from the carb, is the reason that your car isn't starting when hot. I had this problem also. Vapor comes from fuel entering the intake after the engine stops. If your transfer slots (primary and secondary) are set to a square (about .020") then you need to look at the power valve for fuel leakage. Maybe BG double stacked gaskets on the pv, or maybe a bad pv. Or maybe the pv could be opening to soon. Try a 4.5 pv.
I was told by Demon tech. that when you set the transfer slots you leave them set. Demon carbs are very touchy here. Any adjustments here should be minimal if any.
You just dont through in different power valves. You go by the engine vacum and thats it. And that whole transfer slot thing is BS. Some cars need more then the the .020 transfer slot exposed because of more aggressive cams etc.
Bumped the timing up to 20* initial and 34* total right at 3000 RPM. Worked out well with the springs that came in the dizzy. Haven't messed with any additional vac advance yet. If I want to run any less initial I'll need to start experimenting with my springs and weights. This is good until I can get other bugs worked out.
Did some slight tuning with the carb. Got the throttle blades set correctly but I have to idle around 900-1000 with this cam and couldn't get the idle mixture screws right....might have vac leak or the vac gauge needle just loves bouncing around. Obviously the jets, PV and acc pump need serious work.
Still seems rich.
I can't tell until I drive it (tomorrow), but I'm hoping the timing adjustment might help the overheating :crosses fingers:
I've been searching tonight and can't find the threads that addressed this specifically...
When messing with the idle mixture screws I killed the car once. I immediately fired it back up and it started no problem.
When I was done for the night I shut it off and let it sit for 5 minutes. After this 5 minutes it wouldn't start again. UNTIL I held the carb at WOT and let it crank for a couple revolutions. Started fine and ran decent again.
Any ideas why it won't re-start when hot unless you hold it at WOT??? I noticed the "vapors" coming from the carb (seen in the pics above) weren't as dense as before.
Sounds like your running to lean at idle and the car wont run unless you give it WOT. You need to put everything back to the original settings and go from there. Does your carb have the idle eze ? leave your transfer slots at .020 to start. Put your floats so you have the fuel level at the half way mark on the sight glass and put your idle screws at 1.5 turns out.
Your timing should be good enough to tune the carb now. The vapors, seen coming from the carb, is the reason that your car isn't starting when hot. I had this problem also. Vapor comes from fuel entering the intake after the engine stops. If your transfer slots (primary and secondary) are set to a square (about .020") then you need to look at the power valve for fuel leakage. Maybe BG double stacked gaskets on the pv, or maybe a bad pv. Or maybe the pv could be opening to soon. Try a 4.5 pv.
I was told by Demon tech. that when you set the transfer slots you leave them set. Demon carbs are very touchy here. Any adjustments here should be minimal if any.
Thanks red!! After some tinkering today I found out I am, in fact, getting fuel into the carb at shutoff. It is seeping in and pooling on the throttle blades (more so in the secondaries) as well as the intake.
I set the transfer slots to .020" and made very small adjustments.
I need to look into the PV but can't get a repeatable, somewhat close idle to get a vacuum reading. It will fluctuate anywhere from almost 10" to 6" at idle, depending on how I adjust the idle circuits. However, the highest vacuum reading is probably when the car is running on its richer side.
It has backfired previously but I was under the impression the PV check valve stops most blown valves anymore.
Quote:
Originally Posted by 84 z28
Sounds like your running to lean at idle and the car wont run unless you give it WOT. You need to put everything back to the original settings and go from there. Does your carb have the idle eze ? leave your transfer slots at .020 to start. Put your floats so you have the fuel level at the half way mark on the sight glass and put your idle screws at 1.5 turns out.
Car is rich everywhere. Burns your eyes almost and stinks up the exhaust. Carb was started with the transfer slots set up correctly and the idle mixture screws 1.5 out. It does have the idle eeze as well.
I know the carb needs jetting and probably a PV to idle and cruise correctly I just don't know where to start. I wanted to get this setup somewhat close before I started tweaking things.
The motor is being flooded so I have to find out why its seeping fuel and causing these vapors. I'm sure that has to be the issue of my no hot start and will probably make the car idle much better! What are some other things I should look into for this flooding issue at shutdown??
what demon carb do you have ? Are you running a mech or electric fuel pump ? If you have a leak it might be a good time to go through the whole carb and replace gaskets,needle and seat etc. I would get a master rebuild kit from jegs.
Looking like I want to rebuild it anyway. Try a different PV, needle and seat and clean everything out. Maybe some grit got into the idle passages. Turning the idle mixtures screws gave a very erratic response, nothing that was consistent (from what I could tell).
I just wish I knew what was causing a flooding situation when the car is turned off??
BTW...(for the moment) I think the timing adjustment may have solved my overheating. Can ran upwards of 220* tonight, then I switched on the fan and it dropped back down to about 190* idling in the garage. I'll have to see what it does when I can take it for a spin.
__________________ 1991 Pearl White Z28
Previous: 383 HSR
Now: 383 Demon
9.17@81 with the 305
RIP: 1992 RS 305 TBI 5-Speed
Last edited by CamarosRUS; 10-08-2009 at 10:00 PM.
Yeah the reason it will start when you hold the throttle wide open is because it's flooded. A flooded engine will start eventually if you do that. You know you've got fuel getting in the motor when it shouldn't be, figure out why - that is your problem. It can be caused by fuel boiling (As in my case), fuel pressure being too high (I think you ruled that out) or perhaps something internal in the carb like the power valve leaking.
The fuel draining into the motor is the problem, find out why. Im not knowledgable enough to give you anything beyond what I already have.
I've decided I need to for sure. I want to hope a bad needle and seat or power valve is causing the flooding at shutdown but I can't seem to find out how those being bad would only cause a problem when hot.
Fuel bowls are not warm, fuel is cool, even the spacer is not that hot. I don't understand this....
Im not positive, but I'm pretty sure most of the fuel in my carb drains back down while it sits. So when I go to crank it cold there's not much if any fuel in the carb.
So it may just be that it happens only when the bowls are full.
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Last edited by InfernalVortex; 10-11-2009 at 04:43 PM.
