relagp1

I have a 87 iroc, initially was TPI fuel injected. I swapped to a carbed 355 and am having trouble starting the engine when it is warm. It turns over for maybe 20 secs before it catches. After this, it will start immediately after I shut it off, but if I let it sit for maybe 15 mins after being warm, it will start hard again. I have a 750 double pumper Holley

What Have I tried?
Temp Control Carb Spacer
Replaced 60 psi fuel pump with 14 psi pump with pressure regulator (with return line)
Set fuel pressure to 3-5 psi
Wrapped Fuel Lines
Adjusted Floats to decrease fuel in bowls
Replaced starter with racing started (wrapped also to reduce temp)

Someone help me PLEASE!!!! Have had this issue since the engine swap two years ago, and have taken it to several shops and no one knows what to do.

Jorlain

iTrader: (4)

Can you see any fuel in the bowls (if you have a sight glass) prior to trying to do a hot start? Kind of sounds like your bowls are empty.

relagp1

Right now the bowls are 1/4 full but i have tried it with them totally full, 3/4, 1/2 to almost empty. In either case the problem still exists. The only other piece of information I have is when its trying to start while hot, the fumes smell is very noticeable which is expected I guess since its trying to start. It almost seems like its flooded but fuel pressure is low, and regulated below what holly requires. I am supposed to be running 8psi. I definetely think its in the delivery somewhere between the electric fuel pump and the carb. I have also switched the diameter of the return line ...up and down and no luck. I am trying to figure this out before i go through the hassle of using a mechanical fuel pump amd changing all my lines.

pancherj

Run the car to warm it up. Turn it off. Let it sit for 15-20 minutes. Pull the carb and look down in the manifold. It sounds like gas is leaking from the carb into the engine while it is sitting and not running. (I think that is what Jorlain was saying in his post above)

relagp1

Been down this road before to. Thanks for suggesting. Sad thing is i have put 3 brand new carbs on to check this issue before. Same issue with a edelbrock 750 and 2 different holley 750 carbs

Jorlain

iTrader: (4)

That or the fuel is evaporating.

With it hot, if you leave the key on for say 6-10 seconds prior to cranking (allowing the fuel pump to build pressure and\or fill the bowls) does it still take an additional 10 seconds before it fires?

Another thing to try would be to try pumping the throttle while looking down the carb during a time it normally wouldn't start right away. Do you get a full pump shot? If you give it a couple of pumps does it start normally or faster?

relagp1

i have looked down the carb before and it does give a full shot. Now as far as pumping priming the pump (for lack of better words) with the key, that doesnt change the hard start. Giving it gas doesnt alter the issue either.

So far we have tried all of these suggestions over a two year span. The only other thing I can think of is there is some over pressure when the engine is shut off? I took my carb off and put it on my friends 86 which has a mechanical pump and he has zero issues. I swapped him for his carb, and i get the same hard start. We swapped back and his runs fine with either carb. I think its related to either the plumbing set up or soemething in the fuel delivery. The electric pump is currently set to turn on when the ignition is activated, then shuts off when the ignition is turned off.

i did some research on another thread and there are a few other people with the same issue with a variety of different carbs.

relagp1

Just adjust the floats to 1/4 and ran it for an hour and let it sit for 35 mins and now there is nothing in the bowls. Is this a sign of evaporation? If so besides the thermal gasket and wrapping the fuel line, what can be done?

Jorlain

iTrader: (4)

That much fuel disappearing in 30 minutes makes it sound like a leak rather than a fuel boil\evaporation issue. But you've changed carbs, so that seems unlikely. But, you might want to take a peek down into the intake anyways to see.

What type of fuel line are you using? And what are you using to insulate it? What are your engine temps like? How are the lines routed? Obviously, the hotter the fuel is the faster it'll evaporate. I think modern fuels might even evaporate more quickly due to the ethanol in them.

NoEmissions84TA

iTrader: (1)

It is 1 of 3 things: boiling/evaporating, leaking, or draining back towards the tank through the fuel lines.
That might mean that there is a vacuum created in your tank while running and the fuel is getting sucked out of the carb when you stop the engine. Is your tank vented properly?
How hot is it under your friends hood compared to yours?

T.L.

Carbs don't like ethanol. Major contributor to hard starts while hot...

midias

Something ez to try is leave the gas cap loose so no pressure can build See if the problem persists. You may get some odors but you can deal with that for now.

relagp1

i am going to try this. If this renders the problem, whats tje permanent fix?

relagp1

Tank may not be vented properly. How should this be done? Also my engine runs at 165 degrees. Using the IR gun the carb gets to 90 degrees max on a hot day, no feul bowling. My regulator has a return line. I also have another fuel line that is not being used and it has a rubber cap on it.

relagp1

also i may add my friends engine runs slightly hotter around 190 degrees.

relagp1

I do notice that after sitting, the fuel pressure drops on my fuel line pressure gauge but maybe this is expected?

NoEmissions84TA

iTrader: (1)

That unused line most likely went to your charcoal canister, which I'm betting is not there either. There is also supposed to be a "UFO" valve under the car by the driver's rear wheel. Together, these take care of your tank venting. Cap them off and you now have problems.

relagp1

If you dont mind can you post pics of both the ufo valve and canister? The gas line that is not used is under the hood on the drivers side. I see something by the tire but i want to make sure I am looking at both right parts. So are you saying both parts need to be there in order to eliminate this issue? Also I have a vented gas cap as well. Not sure if this will cause an issue.

relagp1

also i do notice after sitting there is no gas in the bowls. Could this possible vacuum be the cause?

relagp1

my canister is gone. They removed it when i did the tpi swap. Do i just get a canister and run that line to it? Do i plug the red plug back into it?

NoEmissions84TA

iTrader: (1)

If a vacuum is being created in the tank as the fuel is consumed, then it is entirely possible. But if your cap is vented, a vacuum should not be created. Do what midias said above - Something ez to try is leave the gas cap loose so no pressure can build. See if the problem persists. You may get some odors but you can deal with that for now.
Leaving the cap loose would also prevent a vacuum from being created.

NoEmissions84TA

iTrader: (1)

UFO Valve - no longer available
You have to take yours apart and clean, or get really lucky finding one used.

Below - charcoal canister.

NoEmissions84TA

iTrader: (1)

That red plug is the solenoid that was controlled by your ECM.
The ECM is gone also, I assume.

NoEmissions84TA

iTrader: (1)

Yes, you are feeding a carb now, not fuel rails and injectors.

relagp1

Took the gas cap off and drove it, still has the same issue. I still have the UFO valve in place and in line. The canister is gone. UFO valve. Car has 70,000 miles on it.

NoEmissions84TA

iTrader: (1)

Took the gas cap off and drove it, still has the same issue. I still have the UFO valve in place and in line.
This is very strange. It has to be a problem with your car, because you said that it does not happen when you swap your carb to your buddies car, and it still happens if you put his carb on your engine.
I'm starting to run out of ideas.


OK, describe your fuel supply system (type of pump, regulator, pressures, etc).

Boxtruck

Not sure if this has anything to do with it, everyone is looking at fuel, but How advanced is your Timing? When my Bird was *HOT* from climbing up hills or on a hot day, the timing was so advanced that you could barely start the car over 210 degrees. Spin the distributor back a bit and off I went, I lived in a High Elevation Area as well.

relagp1

My timing has been adjusted several times but we left it alone thinking it was a heating issue. Maybe we will revisit this because it occurs when the car is not hot at all.

relagp1

Just realized we left out a major component..my friend has a mechanical fuel pump so we are not in the same playing field. I am trying not to go that route due to plumbing of has lines and such.

i started with the stock 60 psi fuel pump but now have a 14 psi tbi pump. I have tried mallory and holley regulators. My current is a mallory with return line. Holley recommends 8 psi for carb but i run 4-6 psi.

Floats are down to where you can barely see fuel in sight plug.

NoEmissions84TA

iTrader: (1)

Float level should be just at the bottom of the plug's threads, so you're good.
6 psi would work. Where is your regulator installed, before or after the carb? I'm guessing before, as in FP, Regulator, Carb.
Here is the better way, if you can set it up like this. In this way the regulator cannot act as a restriction to the carb.

If you had to add a mechanical FP, the TBI pump could give the fuel a push from the tank to the block mounted mechanical.
GM also did that to try to solve the "vapor lock" problem. L69 cars came set up this way from the factory.

relagp1

Yes mine setup is currently similar to this with the exception of my electrical fuel pump is inside the tank. Everything else is the same. I still think the issue is somewhere with the fuel delivery after the engine is shut off. I think we are getting close.

relagp1

Here is my current setup

NoEmissions84TA

iTrader: (1)

1) You MUST be using a bypass regulator.
2) Change the line routing to this. The only thing you need to change to this is a log type of fuel line at the carb.
But for a test, you can get away with a tee.

relagp1

NoEmissions84TA

iTrader: (1)

OK great, you're onto something.
3 things come to my mind.
1) your needles & seats in the carb are not completely sealing. So the pressure left in the line after you shut the engine off is forced past - "flooding" your engine. A not-so-soon-after restart takes a lot of cranking to get that fuel out of there.
2) if it only takes 6 seconds for the line pressure to drop, then the return line is working fine.
3) or is it? What is the part number of your Mallory regulator? If it is anything like the Holley 12-803, then that regulator is a non-return style and will not work properly in this situation. https://www.summitracing.com/parts/h...SABEgLByPD_BwE

relagp1

I will take a pic of the regulator tonight. I am leaning towards the regulator either not being right for my setup or faulty. I say this because I do get a jumpy fuel pressure gauge when I adjust the pressure on the regulator. Jumpy gauge is sometimes linked to flow or volume. In my case I have a good size return line, and I didn't get the jumpy gauge until I switched regulators. The fact that I have put 3 carbs on the engine, voids out the seats being bad on all 3 carbs. The carb I have on now has maybe 600 miles on it fresh out of the box. The last 2 were the same, just different size and or name.

I think we are getting very close and the good thing is there are at least 8 people with the same or similar problem with the tpi swap on another thread.

midias

Even good seats can be over powered by too much pressure and it does not take much.

sootie007

I can only relay what happened in my case with my TBI to CARB swap...car ran absolutely great BUT I had the hot hard start problem...I tried the foamy thermal type carb gasket / spacer that came with my carb and it didnt fix it..I tried shielding my fuel lines from exhaust heat sources yada yada still didnt fix it. We dont have emissions in Florida so I drilled a pinhole in my gas cap to vent it if it were a pressurization issue ....I then went full circle and tried a better hard plastic 1/2 inch carb spacer and it 100% fixed it here in Florida (hot) ....ethanol gas was apparently boiling during the ignition off heat soak......fyi if you are running your bowls LOW on purpose think about it you are lessening the volume of the fuel in the bowls which means you are heating the reduced volume in those bowls quicker / worse and the carb as a whole will run hotter as it has reduced fuel volume in the bowls which provide a tiny bit of cooling to the carb body ....not saying this is exactly whats wrong in your setup but sometimes it is the simplest thing.... FWIW

relagp1

Thanks for your tips!. Yea I played around with the floats for a while now. My issue is slightly different because I initially thought my issue was temperature driven, but as of last week its not. My issue would occur just from running the engine for 3-5 mins as well. I keep my floats 1/4 full to where you can see fuel in the bowl near the bottom of the sight hole. Halfway or more burns way too much gas for my setup and it runs a little rich. I will keep you updated once I switch out this regulator. Hopefully that will render this issue.

NoEmissions84TA

iTrader: (1)

sootie007, what you are describing here is EXACTLY the reason for using a fuel log connection at the carb, with the regulator plumbed in AFTERWARDS. This keeps the fuel constantly circulating back to the tank, keeping the carb cool(er). But a bypass style of regulator MUST be used.
I believe the original TPI fuel system is plumbed this way also.

relagp1

I do currently have a fuel log but my regulator is right off the fuel line before it hits the carb. If I switch the plumbing to match this, will the regulator truly regulate the fuel before it enters the carb, or just after it leaves the carb?

sootie007

Yes mine is plumbed differently...I go from tank pump to regulator / return , to carb .....it works fine now but may have been fixed too just configuring it as you say .....

NoEmissions84TA

iTrader: (1)

Using a bypass style of regulator AFTER the carb allows full unrestricted flow to the carb. And the carb only takes what fuel it needs.
The pressure is controlled by the regulator allowing the excess fuel pressure to be relieved back to the tank. This is what allows the fuel to constantly recirculate, and at the correct pressure.

A dead head regulator (old school Holley 12-803 type) is plumbed before the carb and works just like you putting your thumb over a garden hose, trying to restrict the water down to a dribble. This puts quite a load on your fuel pump and also ends up heating the fuel.

relagp1

i have a Mallory 3 port bypass regulator. I have attached my setup so you can check it out. I am not sure how to change my setup to put the regulator after the carb. Do you have any pics of how to do that or can you look at my setup and tell me what I need? Regulator
Fuel Log
Gas line entering regulator

relagp1

I am slightly confused with the fuel diagram you posted and wanted to know if you can help me get mine setup this way. Currently, my main fuel line goes into the regulator (IN)) the goes out the regulator (out) and then goes into the fuel log which feeds that carb. From the diagram you posted, I need to take the main fuel line and go directly to the fuel log then out to the (IN) of the regulator, but if I do that there is no connection for the gas to exit and go to the regulator. My fuel log connects on one side of the carb, and two spots and there is no other connection open, which means my regulator wont be in the loop at all. How and where do I add the regulator after the carb? Take a look at my pics that I posted so you can maybe draw right on them if need be. Thanks!

relagp1

I am slightly confused with the fuel diagram you posted and wanted to know if you can help me get mine setup this way. Currently, my main fuel line goes into the regulator (IN)) the goes out the regulator (out) and then goes into the fuel log which feeds that carb. From the diagram you posted, I need to take the main fuel line and go directly to the fuel log then out to the (IN) of the regulator, but if I do that there is no connection for the gas to exit and go to the regulator. My fuel log connects on one side of the carb, and two spots and there is no other connection open, which means my regulator wont be in the loop at all. Lastly, from the diagram is just the (IN) on the regulator used and the (return) is used, and the (out) is plugged off? How and where do I add the regulator after the carb? Take a look at my pics that I posted so you can maybe draw right on them if need be. Thanks!

NoEmissions84TA

iTrader: (1)

This is easy. You want to achieve the same as this.
https://www.jegs.com/i/Aeromotive/027/17249/10002/-1
But you don't need to purchase a $561. fuel log. You already have everything you need, except for a tee fitting. Or here are some much cheaper logs.
https://www.jegs.com/i/Speedmaster/7....1006/10002/-1
https://www.jegs.com/i/RPC/707/R2157/10002/-1
https://www.jegs.com/i/JEGS/555/100825/10002/-1
https://www.jegs.com/i/JEGS/555/15190/10002/-1

You will want to connect the tee at the input of your current dual feed fuel line.
So now you have created an additional connection. Connect your fuel pump directly to one port of the tee (FP directly feeding carb).
The other (new) port will connect to the input of your bypass regulator. Block the OUT on the regulator.

It works like this - your regulator will now control how much fuel is sent back to the tank, instead of controlling how much is sent to the carb.
Yes I know, not volume - pressure. Regulator controls pressure. But you get the idea. See it now?

camarito

I had the same problem for some time, it starts fine when cold but when hot it's hard to start, goes very lean and stumbles until i drive it a few miles, i tried everything even swapped carburetors but if i tried to keep the same AFR i ended up with the same results, it was just lean idle, my engine has to idle at 12.4:1 for this not to happen, now i don't even have to hit the gas before starting it when hot.

relagp1

What type of fuel pump are you running? Was your Camaro initially TPI?
Also what carb are you running? I am a novice to carbs. To lean my Holley I just dial the screws in but I only have a guage that reads vacuum. What do you use to measure you AFR?

Jorlain

iTrader: (4)

Get yourself one of these or similar: https://www.summitracing.com/parts/a...0aAnS-EALw_wcB

Best investment I ever made for tuning.