Carb Help please!
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Laughing Gas
Joined: Dec 2010
Posts: 924
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Carb Help please!
So today i notice my truck today when i was driving back home from work i noticed my RPM would go a little bit higher then idle when i would press the clutch in when i would be at a stop or coming to a stop, they would shoot up to 1000 rpm and i would have literally press the gas pedal so it could calm down... its weird because it use to do that when my truck was bone stock. It just started doing it tonight... i wouldn't think this is normal?
Does anyone know what it might be?
Does anyone know what it might be?
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Joined: Dec 2007
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From: Boise, Idaho
You have a 600cfm Holley, right?
I dealt with this problem for a little bit. It was a combination of a few things.
First, is the return spring on the throttle strong? If it isn't, it may not be pulling the throttle fully closed.
Next, is the distributor on ported or full manifold vacuum?
When I had mine on full manifold vac with the 600cfm, it had a problem closing the throttle all the way at idle. Not sure why. I had the exact issue you did. It'd usually close and idle at 700 or so RPMs, but randomly would sit at 1000 - 1500 and I'd have to tap the throttle a few times to get it down. Very annoying.
Last, is your linkage simply binding, kinking in any way?
I dealt with this problem for a little bit. It was a combination of a few things.
First, is the return spring on the throttle strong? If it isn't, it may not be pulling the throttle fully closed.
Next, is the distributor on ported or full manifold vacuum?
When I had mine on full manifold vac with the 600cfm, it had a problem closing the throttle all the way at idle. Not sure why. I had the exact issue you did. It'd usually close and idle at 700 or so RPMs, but randomly would sit at 1000 - 1500 and I'd have to tap the throttle a few times to get it down. Very annoying.
Last, is your linkage simply binding, kinking in any way?
Thread Starter
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Laughing Gas
Joined: Dec 2010
Posts: 924
Likes: 1
Well return spring are pretty stuff.I haven't checked but when we first put them on they were stiff.
I know the distributor vacuum is hooked up to the carb. I don't want to deal with this again.
I don't feel like it is my mechanic adjusted the pedal
I know the distributor vacuum is hooked up to the carb. I don't want to deal with this again.
I don't feel like it is my mechanic adjusted the pedal
Moderator
Joined: Dec 2007
Posts: 7,986
Likes: 104
From: Boise, Idaho
One thing to keep in mind is that your idle is completely physical. It's held open by a screw, the linkage operates the throttle, the cable pulls on it, the spring returns it to its closed position. If your idle is fluctuating like that, something mechanical is going on.
My point about ported vs. full manifold vacuum is that on mechanical, the throttle plates generally have to close even further to get your base RPM.
Also, there are both a mechanical and ported vacuum port on your carb, so saying your distributor's hooked to the carb doesn't say much.
Your base idle's very important to the overall performance of the carb, as well as even cruising on the interstate and gas mileage, so you want to get it right.
Not to be picky, but can you reword your symptoms explanation? The lack of punctuation makes it difficult to discern exactly what's happening, when the idle increases, symptoms, etc. It'd be helpful in figuring out what's going on.
My point about ported vs. full manifold vacuum is that on mechanical, the throttle plates generally have to close even further to get your base RPM.
Also, there are both a mechanical and ported vacuum port on your carb, so saying your distributor's hooked to the carb doesn't say much.
Your base idle's very important to the overall performance of the carb, as well as even cruising on the interstate and gas mileage, so you want to get it right.
Not to be picky, but can you reword your symptoms explanation? The lack of punctuation makes it difficult to discern exactly what's happening, when the idle increases, symptoms, etc. It'd be helpful in figuring out what's going on.
Thread Starter
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Laughing Gas
Joined: Dec 2010
Posts: 924
Likes: 1
One thing to keep in mind is that your idle is completely physical. It's held open by a screw, the linkage operates the throttle, the cable pulls on it, the spring returns it to its closed position. If your idle is fluctuating like that, something mechanical is going on.
My point about ported vs. full manifold vacuum is that on mechanical, the throttle plates generally have to close even further to get your base RPM.
Also, there are both a mechanical and ported vacuum port on your carb, so saying your distributor's hooked to the carb doesn't say much.
Your base idle's very important to the overall performance of the carb, as well as even cruising on the interstate and gas mileage, so you want to get it right.
Not to be picky, but can you reword your symptoms explanation? The lack of punctuation makes it difficult to discern exactly what's happening, when the idle increases, symptoms, etc. It'd be helpful in figuring out what's going on.
My point about ported vs. full manifold vacuum is that on mechanical, the throttle plates generally have to close even further to get your base RPM.
Also, there are both a mechanical and ported vacuum port on your carb, so saying your distributor's hooked to the carb doesn't say much.
Your base idle's very important to the overall performance of the carb, as well as even cruising on the interstate and gas mileage, so you want to get it right.
Not to be picky, but can you reword your symptoms explanation? The lack of punctuation makes it difficult to discern exactly what's happening, when the idle increases, symptoms, etc. It'd be helpful in figuring out what's going on.
Sorry about my punctuation i was on my phone. I'm on the computer now, and i forget about my periods, commas, and what not. Sorry bud!
To tell you the truth when it come to this carburetor i know nothing about it. I didn't adjust nothing on it I'm really afraid to touch anything on it. I wish in school they would teach us on carburetors. When i had my little electrical problem the Mechanic said i should've went with Edelbrock Carburetor because they have a better drivability, and you rarely have to tune them but i kind of like Holley better because they could out perform Edelbrock. He did adjust the carb and this was like 3 weeks ago. Since then i haven't had a problem till last night. Now i haven't driven the truck yet so I'm not sure if it'll do it again.
Moderator
Joined: Dec 2007
Posts: 7,986
Likes: 104
From: Boise, Idaho
No prob. Wasn't trying to be rude or anything, I just couldn't honestly figure out exactly what symptoms you were experiencing.
That's the tough spot about owning an older vehicle, especially one that's modified. You're best bet is to learn and understand how they works, even more so with a Holley. They're super tuneable, which means there's a lot that can be out of tune.
Sure are fun when they're dialed in right though.
That's the tough spot about owning an older vehicle, especially one that's modified. You're best bet is to learn and understand how they works, even more so with a Holley. They're super tuneable, which means there's a lot that can be out of tune.
Sure are fun when they're dialed in right though.
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Laughing Gas
Joined: Dec 2010
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Yeah I know believe it or not I'm here at work and my pickup acted completely fine nothing out of the ordinary. Dunno what it could've been I was rather cold and rainy.
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Senior User
Joined: Aug 2010
Posts: 330
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From: Sacramento
Did you replace the entire clutch when you rebuilt the engine? My sc did the same thing when I installed a new clutch on it. To be 100% honest I have no idea if it was for sure the HD clutch kit but once I put some miles on the setup it stopped. My truck may have? I can't be 100% sure being as I had no tach at the time I installed my centerforce and it was running a straight pipe which dumped right behind the cab so if it only jumped a little I would've never known.
Senior User
Joined: Aug 2010
Posts: 330
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From: Sacramento
Depends on the clutch used, with the stiffer pressure plates I've run in other cars sometimes the idle bumps up rpm a little when you disengage it and from what I have been told its not uncommon. It is a tad confusing with the way you posted it but if your saying the idle jumps when you press the clutch pedal to the floor then depending on which pressure plate you went with it may or may not be related. I typically run centerforces and usually a stageII or better being as I am not easy on clutches and have had it happen.
If it is idling higher then you have it set to and it drops back down when nudging the peddle then its something else.
If it is idling higher then you have it set to and it drops back down when nudging the peddle then its something else.
Postmaster
Joined: Mar 2005
Posts: 2,949
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From: Earth
Make sure your choke is opening all the way and not hitting the air cleaner. Check all the linkages for looseness or binding. Any wiggle in the throttle cable mount? Is the cable adjusted so the throttle plates shut all the way?
Senior User
Joined: Aug 2010
Posts: 330
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From: Sacramento
Its very possible the choke wasn't all the way open, not all carbs are set up with fast idle linkage/cam but I'm pretty sure holleys are. The stock carbs are setup like that so if it was doing it before and goes away when warm I would leave it be. Carbs are cold blooded and until the engine if completely up to running temp don't expect it to run perfectly, my carb doesn't have a fast idle cam and in the morning my trucks idle is so choppy and rough it has a habit of shaking things loose.
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