# Engine Surging at First Start



## dvarghes92 (Aug 9, 2018)

Hey guys, 

I have a 68 GTO, 400 engine with turbo 400 transmission.
Holley double pumper carburetor.

Lately, during my first start of the car, I let the car warm up and when I go for a spin, the car seems to surge when driving, i.e. if I consistently mash the gas after 10 mph, the rpm are surging up and down (between 1800rpm - 2500rpm). After a few minutes of driving, it seems to fix itself. This only happens during the first start of the day. Any ideas on what it could be?


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## BearGFR (Aug 25, 2008)

My first guess would be that what you're getting is a lean surge. Has it started getting cooler outside lately? Do you have a functioning choke on the carb and is it properly adjusted? Are you running with the intake manifold heat riser passages blocked, or with aftermarket heads that don't have the passages?
If any/all of the above are true, then the most likely explanation is a lean surge. The air coming into the engine, and the fuel, is cool enough that it's allowing the fuel to 'drop out' of the air stream and is probably starting to pool inside the intake, resulting in a lean mixture. Once the engine gets warm, including the metal in the intake manifold, this stops happening and the problem goes away.

Just a guess on my part...

Bear


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## dvarghes92 (Aug 9, 2018)

Bear - Thanks for the quick response. Here are the answers to your questions
1. It has gotten cooler out but I did notice this issue slightly before it started getting cooler
2. See picture attached, its got a manual choke, but its wide open at all times. Maybe this affects it? Don’t have too much of a hard time getting it started. I live in GA.
3. See picture attached, is the arrow I am pointing to the heat riser passages? Should I unblock this? If so, what do I do/connect it to? I do not think I have aftermarket heads, previous owner said #13 heads.

Thanks again.


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## BearGFR (Aug 25, 2008)

Since you've got that manual choke, something that would be very easy for you to try would be to take the car out, cold, get it to where you can tell the surge is occuring, and then slowly engage the choke a little at a time each time you repeat the "test" to see if you can make the surge go away. That would be pretty hard to ignore proof.

Bear


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## dvarghes92 (Aug 9, 2018)

Thanks Bear, adjusting the choke little by little did not work. It was surging again, however, the car did run without a problem on my last try when I had the choke wide open and not the air filter on. It might have been just a coincidence, but i will try and get a new filter on and see if that fixes it although I am not convinced air filter would just cause an issue on cold starts.


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## dvarghes92 (Aug 9, 2018)

dvarghes92 said:


> Thanks Bear, adjusting the choke little by little did not work. It was surging again, however, the car did run without a problem on my last try when I had the choke wide open and not the air filter on. It might have been just a coincidence, but i will try and get a new filter on and see if that fixes it although I am not convinced air filter would just cause an issue on cold starts.


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## dvarghes92 (Aug 9, 2018)

So replacing the air filter did not help, any other ideas?

couple of other notes:
1. I noticed the car idles very very low during cold start, to where it wants to cut off. After keeping on the pedal for about a minute, it keeps rising to the desired idle speed.
2. The surging seems to stop once I turn my car on and off.


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## Sixty7GTO (May 4, 2017)

I believe you have a few things going on. You have to learn how to use the manual choke when it starts to get cold. When the motor starts you can't simply open up the butterfly on the carburetor all the way. You have to feather it as the motor warms up. Number 2, you have to set the high idle on the manual choke cam and screw settings. You could also convert the manual choke to an electric choke but I don't think the problem would be any better. The third option is to convert the carburetor to a hot air choke system but you would have to open up the hot air port on the manifold. Then the question comes up if the crossover ports in the heads have been blocked off at any time in the past.


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## Lemans guy (Oct 14, 2014)

Sixty is right here. Your problem is the choke and like Bear said it is causing a lean surge. Chokes make the mixture richer when cold. Your mixture is too lean cold…that is why it is surging and you are feathering the pedal which adds more fuel, making it richer….and run

but the choke is designed to do this. I would highly recommend an electric choke to mostly fix this. But since you have a manual choke you have to operate it correctly…you said it was wide open “all the time” a wide open choke is no choke, so it won’t enriched when it is wide open.

A choke closes a butterfly to “choke” off air thereby making the mixture much richer for cold starts and the first few minutes of cold operation. Your choke should be almost closed when starting, with just a slit of an opening and the car should run like that for a minute, and then be opened a little more for the next couple of minutes. It opens gradually as the engine warms.

You can do this by hand but you have to understand choke operation. An electric choke does it a mostly for you. You just initially set it by putting the pedal to the floor.

So try this on a cold start. Three fast pumps of the gas pedal, to fuel into the intake. Now pull the choke closed. Wait exactly one minute before starting, get you sunglasses and coffee and set your music but don’t start the car. Now without pumping the gas start the car and leave it in park or neutral for a minute as it warms. Leave the choke closed. Then put it in drive foot on the brake and begin to drive, if it feels good pull the choke open just a bit. And continue with small pulls on the choke as you reach operating temp. Then drive to the store and buy an electric choke.


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## dvarghes92 (Aug 9, 2018)

Thanks guys, I am going to stick with a manual choke for the time being. But sounds like all of you guys are right, appreciate all the help thus far.


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