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Holley tuning Question
I have this problem with my 770 Street Avenger carb, that when the engine gets warmed up, after an hour or so of driving, the idle seems to work its way up. When some what cold, or after reaching operating temperature and running for a half hour or so, the idle is perfect at 800rpm. I come to a stop and it settles right down to 800. I can stab the throttle and do anything with the right foot and it settles down to 800rpm. Then after about an hour, if I come to a light, it will be up around 1300rpm. If I stab the throttle, it will return to 1300rpm or so. Then after idling for several minutes, it will sneak its way back to 800rpm. What could be causing this? It’s not bad to drive, its just real annoying. It seems to happen more often with warmer temperatures outside. I also seem to have an issue with the car wanting to “diesel” when I shut it down after a long trip. This does not always happen, but sometime the engine wants to keep running for a revolution or two after I turn the key off. Most of the time it just shuts down but its really embarrassing when I do go to shut the engine off and it trys to keep running. There is no spark when I shut it down so it sounds terrible when this happens.
Any ideas would be greatly appreciated. |
When this problem occurs, check to make sure that the throttle is returning all the way and resting on the idle adjustment screw. If not, check to make sure that the choke is fully open. Sounds like the advance weights in the dist. might be hanging up. That would cause exactly what you are experiencing.
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The after run is because it is idling at 1300 RPM. Until you cure that problem to shut down cleanly apply the brake firmly and let the clutch out as you turn off the key. Time it so you shut her off and then load the engine with the clutch to stop from dieseling.
As far as the reason why she is creeping up on idle only after an hour or so has me beat. I would look for a vac leak that was leaning her out and increasing RPM but after an hour is strange. Please post the fix when you or others find it. |
My experience with Street Avengers has been all good, unless there is a vacume leak somewhere.
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I had the same idle problem as you describe. It was the mechanical advance in the distributor hanging up. Try pulling the distributor cap and manually move the advance. It should snap right back to where it started. If not then pull the distibutor and spray some cleaner down the shaft and you will probably find some nasty stuff coming out. Get it good and clean and re-lube then reinstall.
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I have to say I have been experiencing this too. While the engine is at a good operating temp, (long run on the fwy for example) then when I stop at a light it idles higher than it should. Usually a quick stab of the throttle will settle it back down. It has become habbit to stab the throttle while braking to a stop. I will look into the advance mech. in the dist. to see if that makes a difference. I think it's great to be able to solve these little anoyances by sharing information. Thanks.
John |
I think I am going to look into the distributor first. Now that I think about it, it started having these issues after my first dyno tune, when they "recurved" the distributor. Maybe it is hanging up and needs to be cleaned out.
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Make sure they didn't use too light of a spring when they recurved your dist.
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All things heat up on a long run...including return springs due to the heat making them not as elastic as they were when cool. Make sure you have two on the carb. Solved my problem of the escalating idle.
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Back in the days when doing a few street engines I would adapt the 'emission' type electric solenoid idle unit on to the holley equipped cars. This allowed me to set the 'running idle' speed slightly higher than would normally be acceptable to prevent stalling etc by means of the adjustment on the solenoid and adjust the original holley idle speed down to an absolute minimum to avoid any possibility of 'run on' after shutdown. In doing so the throttle plates will be below any discharge holes and fuel wont be drawn into the engine.It was also important to ensure that the secondaries were pushed completely shut at this position as well- this could also be the cause of your current problem.
Jac Mac |
JWD is so right.
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In addition, I would check other simple stuff too such as the parts on your throttle linkage or cable, and return spring, to make sure something is not hanging up anywhere on anything once it gets hot. Things can expand and bind once hot. Sometimes just making sure things are not binding anywhere, are lubricated and free, can help if other things don't check out.
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Pulled off cap and rotor last night. There is one silver spring and one blue spring installed. According to the MSD Manual tables, this allows for a lighter spring tension.
When I turn the rotor and let go of it, there is hardly enough spring to pull the weights back in. I do not beleive that the weights are even being pulled in all the way. I bet this is my problem. Going to try to find a MSD distributor timing kit that has new springs and clean out the distributor tonight. Another thing I noticed, is on the wiring of the choke on the carb. According to the Holley manual, the wire lanyard that goes from the carb to the choke should be connected to the positive terminal on the choke. The negative choke terminal goes to 12V. This sounds completely backwards to me. Right now the lanyard goes to the negative terminal and 12V to the positive terminal of choke. I looked at several pictures of other Holley 770's in Cobra's and they are hooked up like mine. Not sure if the choke would see a difference with how this is hooked up or not. |
Mark,
The question of proper timing/advance function is best determined by checking your timing. Record readings from a cold idle, record cold engine reading at 1300 RPM and the final reading taken when engine is sticking at 1300 RPM and hot. If the engine does not have a significant amount of advance above the cold reading at the same RPM you need to keep looking. (Significant = 10 degrees or more above cold reading RPM). The timing curve was set up or adjusted on a dyno as stated in earlier post so gotta believe you are set up optimally. A vacuum reading at idle and 1300 RPM cold and another reading when hot may shed some light on this. The fact it takes an hour to give you grief is what makes no sense to me. |
The springs you have should be able to pull it back. There should be little to no resistance in the weights moving back and forth. I bet if you clean up the pivots and the shaft it will return just fine.
Jimi, The problem I had with this was the same way with it taking a full heat soak to cause the issue. Once cleaned out it worked as expected. |
If I clean the pivot points out with carb cleaner, is there a grease or something that needs to be applied as a lubricant for the pivot points?
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Mark, I don't use any lube as that could cause it to gum up. I just wipe everything with a little WD40 on a rag to keep it from corroding.
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Was doing a search on more holley tuning and found one of my older posts (this one). The creaping idle was fixed by putting in heavier springs in the distributor. The springs that had been installed during dyno tuning did not have the strenth to pull the timing advance weights back in. It was an easy fix. No more problems with the creaping idle!
I still have an issue with car stalling when braking. Going to keep lowering the secondary float bowl a little at a time to try'n fix that. Thanks! |
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