my 84 trans am has a 305 rebuilt with a edelbrock 1406 carb and clear inline filter. sometimes the car has a hard time starting after it is warmed up. I have a heat shield around the starter. the engine is at normal temps. when I shut it off after 15 minutes it takes a while to start back. It just keeps cranking and finally starts but takes a long time. I noticed that when this happens and I shut the car off, I hear a bubbling sound and notice the gas leaves the filter within 10 seconds and the filter is dry. no fuel sitting in it. is this normal? I noticed for a while the fuel stayed in it and didn't run out. that was on short trips. could this be why it's hard to start when warmed up?

 

What fuel pump are you using?

 

I don't remember what brand, I just know it was the stock replacement one. it wasn't the cheapest, I remember that. I just don't remember what brand name.

 

When did you replace it?

 

it was replaced when we had the engine rebuilt at the end of May. It had been running fine but we ran it with no filter for 500 miles. the guy told us he put a filter into the carb but we later realized the carb doesn't have an inside filter and nothing was in it. I cleaned out some junk from the carb and we put a clear inline filter.

 

mechanical fuel pump or electric or both?

 

it's mechanical. it's fine until the car has been driven more than 15 minutes and it doesn't always do this but most of the time now but again only when it's been driven for more than 15 minutes. I hear the bubbling sound and it drains out of the filter.

 

any clues???? the engine can be at normal temps and run for 5-10 mintutes and it starts fine. at normal temp about 15- 30 minutes and it has trouble. bubbling noise from gas and it drains out. is the gas getting too hot for some reason? can I do something to cool it down?

 

Is this a return style pump, ie just like stock?
Or is it only an old style deadhead pump?

Headers on the car? Close to the pump?
Carb gasket style? Perhaps carb is getting too hot and boiling fuel in the bowl? Try a spacer or double gaskets?

Does the filter have an anti-drainback system? It should have a one way valve in there somehow....

 

This guy said he put one in and yet the carb has no fuel filter. May want to ask the guy where the filter went.

How is the fuel line routed from the fuel tank to the mechanical fuel pump? Is the in line fuel filter installed correctly?

 

I'm not sure what the difference is between return style or deadhead pump. I know it is whatever was stock for the 305 H.O. engine for 84. I know when the engine isn't run more than 15 minutes the duel stays in the filter and doesn't drain. It only drains when it runs more than 15 minutes and I hear the bubbling sound. I have stock exhaust manifolds on ,no headers. I have an edelbrock 1406 carb that has an adapter plate under the carb to fit the intake. I don't think the filter is suppose to drain back. I think I remember reading that. I know the carb gets extremely hot when this happens and I can't even touch the air cleaner due to this. the fuel line is routed the same as it was stock and we checked the filter direction. I read someone's post from before that had the same problem but it never got answered. the guy had said the card had heat soak. I'd never heard of that but if that's true how would you stop that. the guy also had the same carb as me.

 

Could it be vapor lock. Sounds like the fuel is getting WAY to hot.

 

sorry if I seem a little clueless. I'm not sure what vapor lock is? not sure if it matters but I do not have any smog equipment on the car anymore. it was all bad so it was just taken off. no egr either. it has a block off plate now. I'm thinking maybe I need another adapter. I got the one that was suppose to be used for the 1406 carb but maybe I need another one to help with heat. I don't know if I can add another one or if I just need to replace the one I have.

 

I would reccomend buying another fuel filter with an anti-drainback valve (Check valve) and make sure it's installed in the correct direction.

 

I may try that. I turned the timing down, turned up the idle a little and readjusted the choke since the heat has been bad. I took it out and ran it pretty hard. It seems to be fine right now. I could actually touch the carb and I didn't hear a bubbling sound although the fuel did drain back out again. no problems starting so far. Thanks

 

Vapor lock is when a hot engine is turned off and the heat from the engine boils the gas in the carb. The vapors fill the space in the air cleaner. If the engine is hot enough, it heats the carb so much that when the engine is cranked, the gas coming into the carb boils immediately and the vapors flood the engine and keep it from starting. This usually happens on engines that are overheated.
In your case, even if the fuel in the line drained back, the carb would still hold enough gas to run the engine for 15 seconds, more than enough time for the pump to supply more.
The problem is probably two-fold. The "gasket" between the intake and the carb acts as a heat insulator. Some carbs have quite a thick gasket (1/4").
The other part is probably the gasoline* that is being sold nowdays. They think everyone is using fuel-injection so there is alchohol in most gasolines today. Alchohol boils at 88 degrees C, much lower than gas.
The biggest problem with "gasohol" is mentioned above. (they don't call it that any more because it was a big flop in the early '80s)
Try a heat barrier/insulator under the carb, verify the actual engine temp, and join the hunt like me for "real" gas...

 

thanks, I didn't know that. that's some good information. what exactly is the heat barrier? is it like a spacer?

 

It looks like a really thick gasket with plastic grommets where the bolts go thru to keep from distorting the bottom of the carb when the bolts pull down.
Can't remember where to find them. They were just always in a Q-jet kit. Maybe they offer a 1/2" plastic spacer for the square bore carb. That would work.
EDIT: Here's ONE.
And ANOTHER.

 

thanks, I'll look for one

 

Is your fuel tank building up too much vacuum? i dunno if you would have the charcoal canister, but if it's a vented tank, maybe the venting is blocked?

Maybe try experimenting by removing the bas cap when you park to see if it has a lot of vacuum.. see what happens. just a guess.

 

our canister is gone, as well. the guy that rebuilt our engine just left the tube there and it is unplugged.

 

I think I'm back to this again. fuel still bubbling in gas tank and hard to start when it's run for 30 minutes or so. it cranks slowly. I have a new adapter for carb that keeps heat down and the carb is cooler, have heat shield on starter and wrapped the fuel line the best I could. just not sure what's the problem. maybe my line is too close to the block

 

I'm thinking tank vacuum myself. Sucking the fuel back down.
Try this just to see if a difference is seen in fuel being sucked...
open your gas cap before you shut off the motor.If you hear alot of sucking I'm thinking it's not good. This would relieve the vacuum. Then see if the fuel is still being sucked back down.
I think someone said to do this already sorta.
If this is a success then it's more than likely a tank pressure issue.

 

I will try this tomorrow. do you think it's o.k. about the tube that went to the canister bubbling? I can see a little fuel sitting in it and hear it bubbling. it doesn't come out all over the place just sits in that tube close to the washer fluid tank.

 

Have you tried hooking up a pressure gauge at the carb to see what the pressure is during the hard-start condition?

 

no. the auto mechanic teacher at my husband school told me try the timing so I turned it down and it starts now. just fuel is leaving still no bubbling sounds though

 

I'm not familiar with the edelbrock carb design. But if it were a holley: IF the carb was leaking fuel into the engine, it would allow the float to open, which would allow air to flow in from the venting of the carb and allow the fuel in the line to siphon back down. Normally if the fuel bowl were full, the needle/seat should be closed and would be sealed, shich would not allow the fuel to drain downward as there would be no air to displace it.

Even if there were a strong vacuum in the tank, the air that fills the filter and such would have to be getting into the line from past the filter. Fuel leaking through the carb into the engine would also cause a more difficult start if enough went down, until it dries out. Of course, then you have to wait for the lines to prime, so that would also make it a hard start.

BTW, I know that with a Holley, the Seat for the needle should probably be the Alcohol compatible one, not the standard one.. As modern fuels use Ethanol.. Which also may have caused other parts in your carb to deteriorate?

 

I've heard of that problem with L69s-they run hot
under the hood because underhood ventilation is
reduced with the electric radiator fan-looked at an '84
L69 Z28 and it had a small blower mounted in the RH
fender,behind the battery,with a hose to blow cool
air on the carb. The blower's motor had a late '85 date
code on it,so i think it was added as a retro fit(same
blower as used to cool the coil and alternator on a v6
fiero BTW). Also a lot of '80s q-jets had crimped in
plugs on the bottom that often seep gas into the
intake manifold when car is shut off,draining the
float bowl and flooding the engine a bit-these can
be sealed with epoxy if that problem is present
(i did read you don't have q-jet anymore)
If car was mine i would insulate all the fuel line
underhood,remove the mechanical fuel pump and
replace with a low pressure electric turned on by
an oil pressure switch and also a relay activated by
the crank wire on the starter, so the pump will run
when cranking starts. Might add that carb blower too
if your car does not have it.

 

I'm pretty much having this same problem, as soon as i shut the car off the gas starts bubbling and within 30 seconds its gone. I have both the mechanical pump and the in tank pump and I'm not sure how the last guy set it up. I know when I turn the key the filter fills back up but its still hard to start so im suspecting maybe the gas is spilling into the motor. Also there is no return line on the mechanical pump yet. Anyone have any ideas?

 

If the TPI pump isn't hooked up to a bypass regulator, it will put way too much pressure on the carb regardless of whether the mechanical pump is in line or not.
Check your fuel pressure at the carb, it shouldn't be over 6-8 psi.
Also read the above thread about insulating the carb from the intake.

 

Ok how many psi does a tbi pump put out cause thats whats in the tank. I don't know if it and carb pumps are similar but for some reason there are 2 fuel lines on my car, one of them I thought was the mechanical pump and one was the one for the TBI pump, one is blocked off with a bolt cause when I turn the key on gas will start coming out of it but it also fills up my fuel filter that comes off my mechanical pump...i dunno why. plus theres no return hooked up from either line. This guy really knew what he was doing

 

The fuel pressure (13psi) in a TBI setup is set by the pressure regulator (part of the TBI "carb"). The regulator closes off the return to the tank until the pressure builds to it's opening pressure and the excess fuel flows back to the tank in a circle. This is what the return line does. If you dead-head the pump (connecting it to a full carb) you will get more psi as the pump will run until the pump motor stalls because the fuel that it is pumping has nowhere to go.
It's just not as simple as: "gas comes out this hose , lets hook it to the mechanical fuel pump". Do a search on "TBI to carb swap". There are hundreds of posts on how to do it right.