Carburetor hesitation - Team Camaro Tech
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post #1 of 14 (permalink) Old Apr 24th, 09, 07:19 PM Thread Starter
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Carburetor hesitation

In need of some help here fellas. I have a 69 camaro with a sbc, electric fuel pump (aeromotive ss series) with -10AN feed line to the regualtor (aeromotive A1000 set at 7psi) and -8AN return line. -6AN lines feed the carb from the regulator. The carb is an AED holley 750 cfm. I reconfigured my fuel system this winter and up to today I've driven it about 300 miles with no issues. Today was a hot day at about 84* and after driving the car for about an hour I noticed that the car had a hesitation. I was sitting at a light and when I disengaged the clutch the car started out fine. As I was shifting into second gear, when I let the clutch out and applied the gas the car hesitated and then caught gear and continued to roll. 3rd and 4th gear were fine and I made it home.

I pulled in the garaged for about 2 minutes and decided to go back out. When I was backing down the driveway I put it in first gear and went to let the clutch out and the car stalled. I started it back up and was pulling up the driveway and the car stalled again (This time it sputtered). I started the car again and made it into the garage. I let the car run and got out pulled the air cleaner off and tried reving the engine with the linkage at the carb. When I went to rev the engine as soon as I began opening the throttle the engine hesitated (almost like it was going to shut off). I released the throttle and tried it again and it reved up. I did this a couple of times with the same results. I did check for a vacum leak by placing my hands over the carb and appeared to be fine. I let the car idle in the garage and after 4-5 minutes at idle the car would stall. But when it stalled it didn't just shut off, it slowly declined in rpm and eventually shut off. The car would start right back up again with no problem.

The only difference between the last few times I took the car out (anywhere between 50-60*) and today is that today was warmer at 84*. I have no idea what it could be. Any ideas?
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post #2 of 14 (permalink) Old Apr 25th, 09, 03:31 AM
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Re: Carburetor hesitation

sounds like a fuel delivery issue
clogging filter or some crap in the carb


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post #3 of 14 (permalink) Old Apr 25th, 09, 07:05 AM Thread Starter
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Re: Carburetor hesitation

I'm hoping that's all it is. I'm going to look at the filters and pull the bowl off today and have a look. Any other ideas what it could be if it's not any dirt or debris?
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post #4 of 14 (permalink) Old Apr 25th, 09, 12:49 PM
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Re: Carburetor hesitation

I t can also be heat soak
might need an insulating spacer under the carb


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post #5 of 14 (permalink) Old Apr 25th, 09, 03:23 PM
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Re: Carburetor hesitation

It is not uncommon on a new engine/rebuild, over the 1st 1000miles to have such issues
I doubt the hot day is a factor, rather picked up crap out of the tank, partly blocked filter, crap in the carb bowel, or valve.

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post #6 of 14 (permalink) Old Apr 25th, 09, 05:51 PM Thread Starter
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Re: Carburetor hesitation

Quote:
Originally Posted by dawg View Post
I t can also be heat soak
might need an insulating spacer under the carb
With heat soak, will the gas percolate in the bowl?
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post #7 of 14 (permalink) Old Apr 25th, 09, 06:11 PM
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Re: Carburetor hesitation

Quote:
Originally Posted by Carbo View Post
With heat soak, will the gas percolate in the bowl?
All carbs experiance heat soak.The hotter the soak..the more likely to perculate.Fuel lines and logs also experiance this.
Phenolic carbs spacers do a good job of isolating the carb from manifold transfered heat.
Fwiw..my buddy had a black t-stat housing that created havoc with his primary float bowl.he stripped it and painted it white and the issue went away.

George
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post #8 of 14 (permalink) Old Apr 25th, 09, 07:58 PM
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Re: Carburetor hesitation

i had a similar issue with stalling after running for no appearant reason. it turned out to be a worn HEI rotor. The tip of the rotor was so worn, a large gap was created between the tip and distributor contacts, resulting in a weaker than normal spark to the plugs. funny thing was it had to get hot to fail.

replaced the rotor and hasn't happed again. worth a look if it has some miles of use on it.

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post #9 of 14 (permalink) Old Apr 25th, 09, 08:24 PM Thread Starter
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Re: Carburetor hesitation

Quote:
Originally Posted by fatblock View Post
All carbs experiance heat soak.The hotter the soak..the more likely to perculate.Fuel lines and logs also experiance this.
Phenolic carbs spacers do a good job of isolating the carb from manifold transfered heat.
Fwiw..my buddy had a black t-stat housing that created havoc with his primary float bowl.he stripped it and painted it white and the issue went away.
My carb does have a 1" carb spacer already but I might have to consider this option as well.

Quote:
Originally Posted by joe clance View Post
i had a similar issue with stalling after running for no appearant reason. it turned out to be a worn HEI rotor. The tip of the rotor was so worn, a large gap was created between the tip and distributor contacts, resulting in a weaker than normal spark to the plugs. funny thing was it had to get hot to fail.

replaced the rotor and hasn't happed again. worth a look if it has some miles of use on it.
The motor is completely new with only 1200 miles on it. I just had the distributor off this winter and it looked good. Good thought though.
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post #10 of 14 (permalink) Old Apr 26th, 09, 12:10 PM
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Re: Carburetor hesitation

Quote:
Originally Posted by Carbo View Post
My carb does have a 1" carb spacer already but I might have to consider this option as well...
Most 1" spacers I've seen are made of aluminum which is an excellent heat conductor. Phenolic spacers are made of a type of plastic or are made of paper with phenolic washers at the mounting point. They insullate well. That's the type of spacer that'll affect a heat soak problem - not an aluminum one.

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post #11 of 14 (permalink) Old Apr 26th, 09, 01:56 PM Thread Starter
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Re: Carburetor hesitation

Quote:
Originally Posted by dnult View Post
Most 1" spacers I've seen are made of aluminum which is an excellent heat conductor. Phenolic spacers are made of a type of plastic or are made of paper with phenolic washers at the mounting point. They insullate well. That's the type of spacer that'll affect a heat soak problem - not an aluminum one.
That's a good point. I'm going to summit racing tomorrow to buy a phenolic spacer as I need new fuel filters anyway. I hope this cures the problem. I'm also going to call AED tomorrow to see if they have any input on the carb. When I purchased my engine the carb that was used was from AED. I believe they are located in Virginia. I'll let you know what they have to say as well.
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post #12 of 14 (permalink) Old Apr 26th, 09, 02:06 PM
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Re: Carburetor hesitation

A soft AL sheet plate about 1" overlap betwen the carb and manifold, painted with a thin layer of black makes an execent gasket, very effective heat sink, and doesnt mess with the phlem configuration.
Or a fiber impregnated resin block the thickness of the required block, can be easy made..again no requirement for gaskets.

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post #13 of 14 (permalink) Old Apr 27th, 09, 02:28 PM Thread Starter
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Re: Carburetor hesitation

Well, I spoke with AED today as well as T&L engine (where I purchased the engine from) and they both said it sounds like dirt in the carb. T&L also said the carb might be gummed up. I told him this engine only has 1200 miles, but anything is possible. I pulled the 100 micron filter off last night and the filter itself came apart and there was a ton of crap (large and small) inside the filter canister. That could very well be the problem.

I'm still not ruling out heat soak. One thing at a time. I will update when I get an answer.
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post #14 of 14 (permalink) Old Apr 27th, 09, 04:52 PM
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Re: Carburetor hesitation

I hear ya - one thing at a time. Good find on the filter, I've heard of that happening to others.

Dave
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