Hi all. I have a 67 275 horse malibu that has stumped me and I'm hoping someone has experienced the same problem so they could help me. Here it goes. I go out to start the car in the morning and it fires up without hesitation. After I drive it and the engine is at operating temp. I park it and let it set for about 10-15 minutes to let the heat build up. After the 15 minutes when the engine is at its hottest point, I have to crank it for more than 8 revolutions before it will fire up. It does the same thing day in and out. When it does fire up I have to rev it a little then it rums like a champ once again. Before you start thinking it's anything simple like fuel probs or iginition listen to what I have done to try and eliminate the problem.
1. I checked the compression and every cylinder reads 150-160.
2. I replaced the stock intake with a performer rpm.
3. I took off the quadrabog and replaced it with a new edelbrock 600cfm.
4. I replaced the points dist. with a new hei electronic ignition.
5. The timing is set at 10 deg. as always
It's worth mentioning that It started hard before I replaced all the parts, and it still does the same thing. It has clean fuel squirting out of the carb If you were thing vapor lock. It has good spark to! It does crank over just as easily when it's hot or cold.
Any ideas now! All I can think of is maybe fuel pump. but it has fuel in the bowl obviously because I can see the fuel squirting out the jets when I engage the throttle by hand. I also checked the electric choke and it is open when the engine is hot so that isn't it. The car runs like a champ and idles great other than the strange mentioned problem. Could it be an internal engine or head problem?? I have checked all I know to. PLEASE HELP.....

When you got the Edelbrock carb, did you by chance check the float level?

AFB carbs are very picky about float level. That may be part of it.

They're also picky about heat. A thermal spacer would probably fix you right up.

The fact that you have good fuel coming out of the pump squirter is no indication that it's staying cool on the way down the throttle body.

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My Web Site (http://www.landry-family.com) (updated 01-04-03)

"Long Live Freedom!"

Chad Landry
TC Member #643
ACES Member #4556
'68 El Camino

Yes, the float level is set correctly and I do have a spacer between the carb and intake. Like I siad earlier though, it did the same thing with the old carb. Thanks for your input though. Jos R....

Do you have to hold the throttle all the way open when you are trying to start it when warm?Does the engine act as if it's flooded when it does start?If so it sounds like the fuel is percolating in the float bowl.The carb spacer should have cured that problem though.This might sound weird but you could try to put a bag of ice just around the carb when you shut the engine off.If the problem is cured at least you know where to look.Also maybe try some different fuel,I think gasahol fuels are more suseptible to percolation if that is what yopu are using

I ran into a problem simular and it ended up being the Mech fuel pump draining back. Don't ask me how, but after changing it out, she fired the same hot or cold.

I guess if you're thowing parts at it, pick up a fuel pump. If you run a mech. http://www.chevelles.com/forum/wink.gif

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Tommy B.
71-72 Malibu (http://www.geocities.com/beldarr/Chevelle.htm)
"I'm high all right, but on the real stuff
High octane gasoline
A clean windshield
And a shoe shine"

Thanks, the fuel pump will be my next item to check. It just seems strange that I get a clean squirt of gas into the carb and the engine not fire up as quickly when hot and sitting after 15 minutes or so. The fuel is definitely not boiling out of the carb. the engine does not hit over 200 deg. after sitting for approx. 15 minutes. I'll change the mech. fuel pump. It might be the original. thanks, Jos R...

I think that changing your fuel pump will disappoint you. If your engine runs down the road just fine then the fuel pump is capable of supplying a sufficient amount of fuel to fill the float bowl and keep it filled until you shut off the engine. The very nature of the design of a Carter (uh, I mean,) Edelbrock AFB (oops, I mean,) Performer carburetor is such that the needle and seat opening is above the fuel level in the float bowl and THAT means that the fuel cannot be siphoned back down into the fuel pump if the check valves in your mechanical fuel pump were old and just not good at stopping the reversal of fuel flow while not running.
You may, however, have given away just enough clues to possibly explain the problem.
Since you didn't mention the age of your engine but stated that the fuel pump is probably stock and that the problem continued unaffected by the numerous and various component changes, I will venture my opinion as such:
Your car obviously starts fine when cold AND your have a properly operating electric choke. Your car does NOT start easily after the engine and (thus) the choke have warmed up to a normal operating temperature. It apparently (as you stated) requires a little longer cranking period and some amount of accelerator pumping to start reliably when hot and allowed to sit for even a short period of time.
Your engine requires an abnormally rich mixture while cranking to predictably start. It is easily provided by the closed choke when cold but not when the engine is warm and the choke is now open.
Either or both of two things will cause and/or complicate this condition. A generous build-up of carbon deposits on the back side (intake port side) of the intake valves and/or a lean idle fuel pick-up tube restriction orifice. The pick-up tube orifice is easy to fix. The good people at Edelbrock can explain how to enlarge the restriction by .002" and richen up the idle fuel circuit. The other fix is to try to clean off the carbon deposits with a can of GM Top Engine Cleaner but beware, this is not for the faint of heart. Follow the directions TO THE LETTER!
Getting rid of the carbon may eliminate the need to richen the carburetor's idle fuel calibration. The reason being that the carbon deposits 'dry out' during a hot soak condition and then 'absorb' the incoming idle and accel pump fuel trying to get into the cylinders which effectively delays the ability of that fuel to enter the cylinder and begin combustion immediately.

Just my humble opinion,
good luck,

Louie

"I ran into a problem simular and it ended up being the Mech fuel pump draining back." Same thing here, plus their cheap.

Very good points Louie, and if the fuel pump (cheap & easy fix) didn't do the job I would start looking in the same direction. Both carbs could have the same setup, and deliver the same problem for that engine.

On a side note, about that GM Top Engine Cleaner, can you elaborate a little on how it works. I have 30K worth of build-up and it seems to be quite a lot, for that milage. And what causes so much build up - Not cleaning'er out every once in a while???


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Tommy B.
71-72 Malibu (http://www.geocities.com/beldarr/Chevelle.htm)
"I'm high all right, but on the real stuff
High octane gasoline
A clean windshield
And a shoe shine"

Thanks everyone for your advice. Louie, it sounds like you are on to something with your post. When I bought the car a few months ago I was told the engine had been rebuilt 6k ago, but we all know that a new can of chevy orange can disguise many things. I pulled a plug again and do see oil around the threads and a pretty oily/crusty residue on the perimeter at the end of the threads. I will start thinking about a rebuild myself so i know what I have. Thanks again, Jos R......

"I pulled a plug again and do see oil around the threads and a pretty oily/crusty residue on the perimeter at the end of the threads."
That much oil is ussually the intake gasket, deffinetly look into that. Mine leaked like a sieve, the Fel-pro blue's don't like aluminum intakes and that "was" my problem. I don't think however that would cuase the hot start problem, I'm sticking with the fuel pump.

The logic I am following to eliminate the fuel pump is the difference in the design of the QuadraJet® and AFB (Edelbrock Performer). The needle and seats are in different places. In a QuadraJet® the needle and seat fill the fuel bowl at the BOTTOM of the fuel bowl. Because of this a fuel pump that is not keeping the fuel from flowing back toward the gas tank due to worn check valves WILL allow the fuel bowl to drain down and possibly cause a long-crank, hard-start condition.
The AFB, however, is different because the needle and seat in an AFB fills the fuel bowl from ABOVE the fuel level in the bowl and IF the fuel pump were to drain back due to worn/leaky check valves, it would only allow AIR to go towards the fuel pump and the fuel in the fuel bowl would remain there until it evaporated, was used by the engine, was boiled away, or physically removed by someone.
Jos stated that the problem did not change throughout the QuadraJet® (can ya' tell I respect the ol' Q-jet?) to AFB swap and that particular detail eliminated the drain-back issue. If anyone has a fuel pump that is suspect or has a high mileage life then just spend the thirty bucks and put on a new one; no big deal.
Here in this forum we all try to help each other by sharing learned information and experience. Nothing saves money more than the correct information BEFORE you buy anything. I have saved a lot myself from the advice I have read here and I hope that I can help others do the same.
So, yes, change that fuel pump, it's old and a new one is cheap insurance. My personal guess is still that it won't solve the problem.

GM Top Engine Cleaner (TEC): Honestly, I can't even tell you if they still sell it. It's been a long time since I've worked on anything so worn out or clogged up that I would consider it an option. It is a liquid that gets poured down the carburetor while the engine is held at part throttle. As the engine starts dying you give it more throttle and more TEC and then finally pour the last half of the can in as fast as you can while then engine drowns and dies. You then let it sit for a specific amount of time to let the cleaner soften the carbon deposits. Then you start the engine and rev the crap out of it to blow out the carbon residue. It's really hard to do to a car you like because it's pretty harsh. I would personally resort to rebuilding the engine if it was mine but this was a procedure that GM used for heavy carbon deposits on cars still under warranty. I was a GM Diagnostic and Repair technician years ago and that's what GM said to do so I did it; it wasn't my call.
Someone asked about the cause of the carbon deposits; what causes this. Carbon tends to find cool surfaces where it can combine with various components of unburnt gasoline and then cling to minute pores in the metal. Once started, the process just continues to layer upon itself.

Man, you guys always get me to write too much. Does Betty Ford have a clinic for Automotive Rehab?
I'm gonna' go eat some rice crispies, keep me up to date.

Louie

You want no more carbon, pour a tiny bit of water down the throats at 3000rpm or so. He's thrown alot of money at it all ready, a $30 pump isn't gonna kill him plus it's nice to have a spare.

A squirt bottle with water like Cammin1 said will steam off the carbon buildup.
Wait until the motor is at normal opperating
temp and then begin squirting water into the
carb while keeping the motor runnning. Works
pretty good and it's cheap.

Water works inside the combustion chamber just fine. This carbon is on the back of the intake valves. The water doesn't become steam until the combustion process heats it up. Go figure.

Louie

"Carbon tends to find cool surfaces where it can combine with various components of unburnt gasoline and then cling to minute pores in the metal."

If the carbon can find it's way to the back of the valve couldn't the steam?

I have had some success using just water to clean carbon off both sides of the exhaust valves but the intake valves seem to experience a much lower average temperature on the intake port side of the valve and don't seem to get 'steam-cleaned' by the water. It may just be that the short overlap period contributes a portion of unburnt fuel and some exhaust byproducts that lead to the carbon build-up but does not allow enough time or velocity of the combustion-induced steam to effectively remove the carbon from the back of the intake valves.
I will also mention that the single worst contributor to the carbon build-up in high mileage engines is oil leaking past the valve guides and cooking itself onto the back of the valves; exhaust more than intake.
As some of you have stated, I too would like to see the results of a fuel pump only change.
Please change the fuel pump and let us know if the situation changes or is improved.

Louie

[This message has been edited by LouieHammel (edited 02-19-2003).]

"I pulled a plug again and do see oil around the threads and a pretty oily/crusty residue on the perimeter at the end of the threads."

Where they not oily when u first had them out to comp check?

"When I bought the car a few months ago I was told the engine had been rebuilt 6k ago,"

I really think u have two problems, fuel pump and one that started with the new intake and that is a leaking/weeping intake gasket.

[This message has been edited by Cammin1 (edited 02-19-2003).]

I have had the same problem with my 67 327 with a perfomer carb and on my mopar with a holley.Its the crap fuel we get on the west coast.Try some good race fuel like 108 cam2 or sunnoco.It worked for me.It seems the reg unleaded with oxegenates dosent like to heat soak.Yes the fuel will boil in the carb causing a rich mixture and hard start.in the summer it gets worse like stumbling and stalling till the carb cools off. 5$ a gallon though,is a reasonable test and the car will love it!!!

Hey louie. You were right. The fuel pump add was not the problem. I guess I will try to squirt some water down the throat at around 3000prm after I heat it up. I really can't see carbon being the problem though since I have ran some octane boost in the last week and really pushed it on the highway with the same consistent problem. I was at the SanDiego swapmeet this weekend and picked up a really nice 4bolt 350 block for $75. I think its time for some big cubes and fun! Thanks for all of your help. Jos R...

Don't use a squirter in the carb. Waste of time. Get a gallon milk jug and slowly pour it down the carb at about 3000RPM pr whatever it takes to keep it running. Don't let it die on you. Change the oil afterwards because you could very well get water in the oil from all the steam you create. An old GM machanic told me it use to be a procedure GM had in their tech reference manual to do for cars with suspected carbon build up. I thought it was for engine with deadination after run. It use to stop mine from doing that. I had bad valve seals and would have to do that every 10k or so to stop that afterrun.