New Holley 750 loads up at idle
09-11-2018 | 10:52 AM
#11
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From: On A Dirt Floor
09-11-2018 | 12:32 PM
#14
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From: Lake Winnebago
This likely does not apply to your issue but.......
One of my good friends purchased a new 650 double pumper for his street car. I instructed him how to initially set it up over the phone and idle mixture setting. No matter what he did the rear plugs were lean and front plugs would foul. I told him to clean out the carb as there may be left over metal from machining/manufacturing/etc. He did this a few times...no difference...
I finally got off my butt and went over to help him out (I had my own project going at the time). I tore apart the carb and checked every orifice....the secondary idle discharge holes were never drilled in the throttle body (2 corner idle mixture screws)......I drilled them out and set the idle...surprise...no more fouling plugs and of course idle quality improved.
09-11-2018 | 01:03 PM
#15
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From: Lake Winnebago
This likely does not apply to your issue but.......
One of my good friends purchased a new 650 double pumper for his street car. I instructed him how to initially set it up over the phone and idle mixture setting. No matter what he did the rear plugs were lean and front plugs would foul. I told him to clean out the carb as there may be left over metal from machining/manufacturing/etc. He did this a few times...no difference...
I finally got off my butt and went over to help him out (I had my own project going at the time). I tore apart the carb and checked every orifice....the secondary idle discharge holes were never drilled in the throttle body (2 corner idle mixture screws)......I drilled them out and set the idle...surprise...no more fouling plugs and of course idle quality improved.
09-11-2018 | 01:05 PM
#16
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From: Lake Winnebago
This is assuming your timing is set right....Have you verified what it is?
Those do seem like an unusual carb choice (4160) for that cam/engine (from the few specs posted)
1. FLOAT LEVELS!
2. Check for vacuum leaks
3. Check for idle mixture screw authority. Make sure you can "snub" the engine out by turning the screws in all the way. If you cant make the engine stall with the idle mixture screws all the way in....you likely have too much of the transfer slot showing. Try opening the secondary blades a little bit (but dont show too much of the transfer slot) and readjusting the idle. If you cant get it to "snub" out...where is the fuel coming from ?......plugged air bleeds...too high of floats...torn PV diaphram....missed gasket under PV....cross talk in metering circuits....loose secondary metering plate...or it could be running off the metering plate idle orifices (doubtful..they are generally tiny).
4. Set idle speed/mixture. I do mine in gear tied off to the dock.....engines warm....lean out until manifold vacuum (or RPM) just hints on dropping from its highest reading (although I use an idle reserve spark timing strategy, so you may need to be slightly richer to prevent stalling going into gear)
Those do seem like an unusual carb choice (4160) for that cam/engine (from the few specs posted)
1. FLOAT LEVELS!
2. Check for vacuum leaks
3. Check for idle mixture screw authority. Make sure you can "snub" the engine out by turning the screws in all the way. If you cant make the engine stall with the idle mixture screws all the way in....you likely have too much of the transfer slot showing. Try opening the secondary blades a little bit (but dont show too much of the transfer slot) and readjusting the idle. If you cant get it to "snub" out...where is the fuel coming from ?......plugged air bleeds...too high of floats...torn PV diaphram....missed gasket under PV....cross talk in metering circuits....loose secondary metering plate...or it could be running off the metering plate idle orifices (doubtful..they are generally tiny).
4. Set idle speed/mixture. I do mine in gear tied off to the dock.....engines warm....lean out until manifold vacuum (or RPM) just hints on dropping from its highest reading (although I use an idle reserve spark timing strategy, so you may need to be slightly richer to prevent stalling going into gear)
Last edited by SS496; 09-11-2018 at 01:15 PM.
09-12-2018 | 01:52 PM
#17
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From: NW Michigan
I realize your getting a lot of idle mixture adjustment feedback however while runnning and adjusting can you get to stall out or get any changes while turning in. If I'm not mistaking those carbs only have the two front mixture screws. MT had a very good point with base gasdket and wouldn't be the first time something like that could be overlooked and even right from holley.
Is it possible with the overlap in the cam is sucking fuel into the ports. Single plane intakes.. Just throwing it out there. What's strange is you initially had same problem with both and got one to work properly. I never did like those carbs. Make the guy an offer on the two 750 dp's in the swap shop and list yours on eBay as new other. Description - would not work for your applicattion with idle issues. Just saying. Can you post a cam card just for chits and grins. Seems like a lot of overlap.
Is it possible with the overlap in the cam is sucking fuel into the ports. Single plane intakes.. Just throwing it out there. What's strange is you initially had same problem with both and got one to work properly. I never did like those carbs. Make the guy an offer on the two 750 dp's in the swap shop and list yours on eBay as new other. Description - would not work for your applicattion with idle issues. Just saying. Can you post a cam card just for chits and grins. Seems like a lot of overlap.
Last edited by getrdunn; 09-12-2018 at 02:15 PM.
09-15-2018 | 09:24 AM
#19
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Joined: Nov 2005
Posts: 4,554
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From: Fredericksburg, Va
couple of things, again where is the base timing ? may need 15 or more to clean idle up, I run dist locked on some..your vac is low, as long as you have a good starter and normal compression setting 32-34 locked still should start fine hot. If it does not work on advance to only give you 10-15deg to get more initial. Your carb also is not really ideal for a single plane intake, those are more suited for dual plane so ?? good luck..Rob
