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Old 09-22-2008, 07:09 PM
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Ongoing Cold Start Issues

I apologize for posting another thread about the same subject, but I'm beside myself over the cold start issue I continue to have with my car. As previously posted. I have a 350 Chevy crate engine with an Edelbrock Performer 600 cfm. carburetor and a GM HEI ignition. About 10 minutes after a cold start the car stutters and sputters like it's running out of gas. I've changed the plugs, replaced the carburetor, fuel pump, fuel filter and had the timing checked. In addition, I've worked with Edelbrock technical support who have had me adjust the choke and swap out the metering rods and step up springs. All to no avail. Once started and warmed up, it will start and run all day without a hiccup. It's only after a completely cold start. Everybody I've spoken to and have had look at it has ruled out the gas tank citing that if it were a problem it wouldn't be unique to a cold start. About the only thing left to attribute it to is a sticking (when cold) advance mechanism in the distributor. I even had a guy tell me to replace the temperature sending unit as he claimed it was linked to the HEI ignition and was causing it to malfunction when the car was cold and in the process of warming up. While I don't think this is the case, I wish it were so I could overcome this very annoying issue. What else could possibly cause these problems only after a cold start?
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Old 09-22-2008, 07:36 PM
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could it be a vacuum leak. The gasket might expand when hot. Just a thought and an easy check. Hook up a vacuum gage and see what that does when cold and then hot. Just a thought. You might be on the right track with the timing thing.

Last edited by tomthecomic; 09-22-2008 at 07:37 PM. Reason: spelling
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Old 09-22-2008, 07:40 PM
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and this crate engine is in what year and make of car?
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Old 09-22-2008, 08:23 PM
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sounds like carb icing , is the heat riser installed are the heat tubes on the air cleaner installed are the air doors working .

hope this helps ,
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Old 09-22-2008, 09:41 PM
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Thanks for the responses. The engine is in a 37 Ford street rod. The carburetor is now sitting on a 1" aluminum 4 hole spacer over a GM dual plane aluminum intake manifold. There was previously a 1/2" laminated spacer with a large square hole. It has a B&M dual element air cleaner (this is the predecessor of the Holley Hi-Tech dual element air cleaner). There is no provision for heating the fuel charge from what I can tell. Can carb. icing take place in warm weather? If so, what can be done to prevent it? Is there a possibility that the air flow from this air cleaner could be causing this?
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Old 09-23-2008, 07:21 PM
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Yes it will ice in warm weather when conditions are right ,lean mixture and high humidity . You should be able to see if it is icing , when the motor stalls or starts to run rough look at the base of the carburetor for signs of ice or condensation also look in the carburetor .
The only way I know of to stop ice is heat and or open throttles
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Old 09-28-2008, 09:32 AM
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New Observations

Since my last post regarding this dilemma, I've been doing some experimenting. I've learned that if I make a point of avoiding any hard acceleration I can completely avoid my cold start issues. I'm fairly sure this problem isn't caused by the choke or fuel mixture. What I'm beginning to suspect is the mechanical advance in my GM HEI distributor. It's my understanding that mechanical advance is determined by RPM. What I'm wondering is if the mechanical advance is advances the timing under moderate acceleration when cold, but is not retarding it properly until the distributor and its internals become warm. As indicated previously, once the engine and all of its components become warm, this problem doesn't occur. I've replaced all of the fuel system so I can pretty much rule that out. Has anyone ever experienced problems with a sticking mechanical advance? What are the symptoms? Does anyone have any experience with the GM Performance Parts HEI distributors? Are they a viable alternative to their MSD counterparts?
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Old 09-28-2008, 10:08 AM
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Justold is correct.
BUT I have also seen that by the time the engine quits and you run around there and open the hood and look at the carb, the evidence is not visible after those few seconds.

Various temperature and humidity conditions CAN cause venturi icing, as the pressure drops. Factory cars had heated intake manifolds, sometimes heated intake air (like airplanes), etc.

Also various temperature and humidity conditions can cause varying atomization and vaporization patterns in the fuel mixture that can even cause fuel suspension drop out... fuel puddling in the manifold, and gas rivulets running raw liquid into the cylinders.... to the extent that the engine will not run because the available burnable mixture is too lean.

Even a multi-strike MSD ignition might help light the bad mixture.

I also saw one case where a tiny hole was drilled into each throttle valve so the butterfly could be closed farther, which altered the flow pattern, which in turn seemed to change the atomization rate and the problem was cured.

You could also borrow a Holley (usually too rich) and install it and see if the problem goes away. It might.... though causing another fuel delivery problem in its stead. The richer mixture might alter the atomization in the manifold enough to make the engine keep running. Which almost seems like what Edel tech was trying to do.
The venturi temp drop on a Holley might be enough different to alter your problem.

In the old days we ran MANUAL chokes so that we could add fuel when conditions warranted to keep it running. You know, keep enough burnable mixture so the engine wouldn't quit.

This could be a situation where a stepped or annular booster might help.
You could even use a heated manifold (but most people don't need them)

Or you could just blame the HEI and Edelbrock for making crappy products .

Last edited by ScoTFrenzel; 09-28-2008 at 10:28 AM.
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Old 09-28-2008, 01:52 PM
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Sounds like your choke is opening a little to fast. If it is adjustable, tighten it up a little and see if the issue goes away.

Chet
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Old 09-28-2008, 03:24 PM
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I suspect this is the reason the 'manufactures' decided to use the 'ported vacuum switches', to cut the vacuum advance 'out' untill the engine got up to temperature.

As stated above, Tighten up the choke a little, it should take care of your problem.
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