Stumbling, hesitation rich after sitting
10-18-2018, 01:07 PM
#1
Melting Slicks
Thread Starter
Stumbling, hesitation rich after sitting
All,
Tech question for ya.
After sitting for a few weeks, when I start my 63 up, it has difficulty running smooth and idles really low. I turned the idle up, let it warm up, assuming it was the choke, but it is not.
Runs rich and stumbles for the first several miles until it fully warms up. Acts like its running real rich.
Any idea where to start? Gummy carb? Vacuum leak when cold? Don't let it sit?
D
Tech question for ya.
After sitting for a few weeks, when I start my 63 up, it has difficulty running smooth and idles really low. I turned the idle up, let it warm up, assuming it was the choke, but it is not.
Runs rich and stumbles for the first several miles until it fully warms up. Acts like its running real rich.
Any idea where to start? Gummy carb? Vacuum leak when cold? Don't let it sit?
D
10-18-2018, 01:19 PM
#2
Race Director
Sounds like the choke is set too rich if it runs OK when fully warmed up. It also could be the choke break is not adjusted correctly. What carb are you running?
10-18-2018, 01:44 PM
#3
Team Owner
While holding the throttle linkage wide open on a cold engine work the choke linkage on the other side back and forth. If it’s sticky, even a little bit, the piston in the choke housing may be carbozined. When things heat up and expand it may move again.
HOWEVER - this condition would cause the car to run on the fast idle cam which doesn’t quite fit the symptom of low idle. Maybe sticking float. Next time rap on the fuel bowls sharply a few times with the plastic handle of a screwdriver and see what happens.
HOWEVER - this condition would cause the car to run on the fast idle cam which doesn’t quite fit the symptom of low idle. Maybe sticking float. Next time rap on the fuel bowls sharply a few times with the plastic handle of a screwdriver and see what happens.
Last edited by Frankie the Fink; 10-18-2018 at 01:47 PM.
10-18-2018, 02:54 PM
#4
Melting Slicks
Thread Starter
Holley 3310
No choke, It has been disconnected.
No choke, It has been disconnected.
Last edited by DucatiDon; 10-18-2018 at 02:55 PM.
10-18-2018, 02:56 PM
#5
Team Owner
Maybe that's your problem, it's trying to run too lean and since you don't have the choke you don't have a fast idle.
The following users liked this post:
DucatiDon (10-18-2018)
10-18-2018, 04:03 PM
#7
Team Owner
10-18-2018, 06:55 PM
#8
Race Director
Well - that would have been good to know at the start. It's disconnected - I assume the choke plate secured in the open position so it can't close? It might be worthwhile to pull the carb and use a can of spray carb cleaner to blow out all the air bleeds, idle passages behind the idle mixture screws, accelerator pump shooters, etc. But be sure to wear eye protection as it sometime comes right back at you. A 3310 wasn't used back then - is this a 340 HP motor? It may be that considering the cam and compression, without choke and fast idle, it may just have to be babied on a cold start (feathering the accelerator) until it builds some heat in the motor. But it sounds from your post that this is something different from how it used to behave.
10-18-2018, 08:03 PM
#9
Melting Slicks
Thread Starter
Its a 383. The problem has been pretty common after sitting, but clears up and runs fine as long as its freshly driven.
I resconnected the choke just to eliminate that as problem.
This is on my 383. Aluminum heads, no crossover, no heat riser. No exactly cold, +/- 60 degress this morning. But it has done this on hot days too in the morning.
It may just require getting some heat into it to run correctly i guess. Drove it to work, and it stumbled all the way (12 miles) cleared up fine for lunch run and drive home.
I resconnected the choke just to eliminate that as problem.
This is on my 383. Aluminum heads, no crossover, no heat riser. No exactly cold, +/- 60 degress this morning. But it has done this on hot days too in the morning.
It may just require getting some heat into it to run correctly i guess. Drove it to work, and it stumbled all the way (12 miles) cleared up fine for lunch run and drive home.
Well - that would have been good to know at the start. It's disconnected - I assume the choke plate secured in the open position so it can't close? It might be worthwhile to pull the carb and use a can of spray carb cleaner to blow out all the air bleeds, idle passages behind the idle mixture screws, accelerator pump shooters, etc. But be sure to wear eye protection as it sometime comes right back at you. A 3310 wasn't used back then - is this a 340 HP motor? It may be that considering the cam and compression, without choke and fast idle, it may just have to be babied on a cold start (feathering the accelerator) until it builds some heat in the motor. But it sounds from your post that this is something different from how it used to behave.
10-18-2018, 10:55 PM
#10
Team Owner
I don't know your level of experience with a choke/fast idle setup, but I would take the breather off and see where the choke plate is when it's cold, then start it up and see if the choke opens fully. If the choke works freely and correctly, then I'd be checking into the carb. It's kind of hard to draw info out of you, what kind of choke, electric, divorced, etc? Just connecting it up doesn't really say it's working.
10-18-2018, 11:04 PM
#11
Le Mans Master
Member Since: Jul 2018
Location: San Antonio, TX/Mahopac, NY
Posts: 8,380
Received 5,554 Likes
on
2,797 Posts
2024 Corvette of the Year Finalist - Modified
2024 Corvette of the Year Finalist - Unmodified
2023 C7 of the Year Winner - Modified
The 3310 is a 750cfm, vacuum secondary carb that comes stock with a manual choke. You can buy an electric choke conversion kit, but we need to know what you have. It sounds like it is the stock, manual choke with the plate wired open. A picture would be really helpful.
10-19-2018, 07:39 AM
#12
Team Owner
10-19-2018, 09:13 AM
#13
Race Director
This is on my 383. Aluminum heads, no crossover, no heat riser. No exactly cold, +/- 60 degress this morning. But it has done this on hot days too in the morning. It may just require getting some heat into it to run correctly i guess. Drove it to work, and it stumbled all the way (12 miles) cleared up fine for lunch run and drive home.
The following users liked this post:
DucatiDon (10-19-2018)
10-19-2018, 11:02 AM
#14
Melting Slicks
Thread Starter
Yes, sorry all...been real busy.
Drove it last night and again today and no issues at all, It just creeps up after sitting for a while.
3310 vac sec 750 electric choke (now functioning correctly) was previously just wired open. Fast idle now working correctly +/- 1400 rpm.
No heat riser, crossover plugged.
Maybe gas is gumming something up after sitting? Pretty sure its nothing to do with the choke system.
Also noted the vacuum was real low when acting up, as the brakes had little power assist.
Drove it last night and again today and no issues at all, It just creeps up after sitting for a while.
3310 vac sec 750 electric choke (now functioning correctly) was previously just wired open. Fast idle now working correctly +/- 1400 rpm.
No heat riser, crossover plugged.
Maybe gas is gumming something up after sitting? Pretty sure its nothing to do with the choke system.
Also noted the vacuum was real low when acting up, as the brakes had little power assist.
10-19-2018, 11:22 AM
#15
Team Owner
Maybe you have a vacuum leak until things warm up and expand....you can check that with an unlit propane torch passed around likely leak spots (e.g. carb to intake fitting) - if the engine speeds up you've found your leak..
10-19-2018, 12:57 PM
#16
Safety Car
Member Since: Jan 2000
Location: Poway CA
Posts: 4,845
Received 1,295 Likes
on
560 Posts
2023 C1 of the Year Finalist - Unmodified
2022 C1 of the Year Finalist - Unmodified
2021 C1 of the Year Finalist - Unmodified
2019 C1 of Year Finalist (stock)
2016 C1 of Year Finalist
We're all kinda guessing here with little facts.. so here is my guess! Fouled spark plug, not firing when cold.
I would pull the plugs and see how they look. Pretty easy to do, and you'll probably get more info.
I would pull the plugs and see how they look. Pretty easy to do, and you'll probably get more info.
01-20-2021, 12:16 PM
#17
Melting Slicks
Thread Starter
Solved. Accelerator pump was leaking, AND the Choke was way too rich.
Runs like a champ now.
D
Runs like a champ now.
D
01-20-2021, 01:50 PM
#18
Race Director
Member Since: Apr 2015
Location: Fresno California
Posts: 17,505
Received 3,443 Likes
on
2,113 Posts
If you blocked your crossover passages that could be the issue. I would NEVER do that on a street driven car, personally. Not even where I live. Car will run poorly cold due to poor atomization of fuel, and lead to pre-mature cylinder wear, etc. A functional cross-over and a functioning choke are good things if you drive the car as a car.