What did I do? (Carb adjustment) Long..
09-10-2003, 03:56 PM
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What did I do? (Carb adjustment) Long..
I have a 358SBC pushing about [email protected] have been chasing alot of minor problems since I installed the new motor last spring...I have gotten all of them pretty well cleared up. A few have hung around
One I have had a bear of a time with is a very noticeable bog/hesitation/stumble off idle under hard acceleration from idle...I purchased a used Holley 750vaccum secondary carb(Model 4010) early this summer and have been pretty happy with it. Now everything I have read by Holley and Dennis Moore states that a 750 is too big and a 600-650 is what I need. But that the 750 will work with adjustments..I worked every accelerator pump cam Holley makes and still had the symptoms...I went with the 50cc pump and cams and still nothing..I installed 6.5 power valve(s) in the carb based on testing and vaccum readings. Well I read a article in Powerboat this month and someone wrote in about running a Holley 1050 dominator on his engine. (If my 750 is too big the 1050 sure as hell is too) Teague recommended running 2.5 powervalves to help with throttle response with a N/A motor and 10.5 for a blower motor. Well I tried a 2.5 on my primary side and WOW!!! Instant throttle response
All this time messing with every setting possible and to finally have it run great is fantastic...My question is this why did this happen. I have read zilch about changing powervalves to help a stumble/bog. I mean I have 3 Holley books and have posted several posts here a while back about my problems and no one suggested this as a possible fix? My guess is that it has to do with my camshaft and the size of carb being to big. The setup I have gone with now is the 2.5 powervalve in the front with the 50cc pump and biggest pump cam. The secondary powervalve is a 6.5. Someone please explain why going to a 2.5 powervalve has done the trick
Thanks
Randy
a.k.a. Bad-Habit
One I have had a bear of a time with is a very noticeable bog/hesitation/stumble off idle under hard acceleration from idle...I purchased a used Holley 750vaccum secondary carb(Model 4010) early this summer and have been pretty happy with it. Now everything I have read by Holley and Dennis Moore states that a 750 is too big and a 600-650 is what I need. But that the 750 will work with adjustments..I worked every accelerator pump cam Holley makes and still had the symptoms...I went with the 50cc pump and cams and still nothing..I installed 6.5 power valve(s) in the carb based on testing and vaccum readings. Well I read a article in Powerboat this month and someone wrote in about running a Holley 1050 dominator on his engine. (If my 750 is too big the 1050 sure as hell is too) Teague recommended running 2.5 powervalves to help with throttle response with a N/A motor and 10.5 for a blower motor. Well I tried a 2.5 on my primary side and WOW!!! Instant throttle response All this time messing with every setting possible and to finally have it run great is fantastic...My question is this why did this happen. I have read zilch about changing powervalves to help a stumble/bog. I mean I have 3 Holley books and have posted several posts here a while back about my problems and no one suggested this as a possible fix? My guess is that it has to do with my camshaft and the size of carb being to big. The setup I have gone with now is the 2.5 powervalve in the front with the 50cc pump and biggest pump cam. The secondary powervalve is a 6.5. Someone please explain why going to a 2.5 powervalve has done the trick Thanks
Randy
a.k.a. Bad-Habit
Last edited by BAD-HABIT; 09-10-2003 at 03:59 PM.
09-10-2003, 04:43 PM
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Alot of people will actually plug the power valve on the primary side and fuel through the jets. It works on a marine app. because you are almost always into the secondaries. Just don't run just below the opening of the secondaries as there is a lean spot in the curve.
09-10-2003, 04:52 PM
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Originally posted by Cord
Alot of people will actually plug the power valve on the primary side and fuel through the jets. It works on a marine app. because you are almost always into the secondaries. Just don't run just below the opening of the secondaries as there is a lean spot in the curve.
Alot of people will actually plug the power valve on the primary side and fuel through the jets. It works on a marine app. because you are almost always into the secondaries. Just don't run just below the opening of the secondaries as there is a lean spot in the curve.
BH
09-10-2003, 04:55 PM
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Originally posted by cuda
I don't know why, but I just saved this thread for the sbc I'm rebuilding. What cam did you use?
I don't know why, but I just saved this thread for the sbc I'm rebuilding. What cam did you use?
Http://www.compcams.com/catalog/080_081.html
BH
09-10-2003, 05:43 PM
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I solved my hesitation problem by installing a very small accelerator pump squirter with the 50 cc pump and the biggest ramp cam so it reduced the amount of fuel but lenghtened the time of the squirt. Never tried smaller power valve but I monitor vacuum pretty good and never get below 6.5 until 4000 or so. 780 cfm on 461 cu/in.
09-10-2003, 09:14 PM
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By changing to a 2.5 power valve, you have actually leaned out the carb by delaying the opening of the power valve until it sees 2.5 inches manifold pressure. There are a couple of possibilities; the old power valve may have been bad and not opening, in which case this one is a little better. Or it was working correctly but it was opening too soon and flooding the engine. This is common on modified engines that don't generate much vacuum
Your carb is used and may have gone through a lot of changes. Holley has a web site that lists all of their carbs and what jetting and power valve etc. comes stock.www.Holley.com. You shouldn't have to deviate much.
Your carb is used and may have gone through a lot of changes. Holley has a web site that lists all of their carbs and what jetting and power valve etc. comes stock.www.Holley.com. You shouldn't have to deviate much.
09-11-2003, 02:55 AM
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Originally posted by PatriYacht
By changing to a 2.5 power valve, you have actually leaned out the carb by delaying the opening of the power valve until it sees 2.5 inches manifold pressure. There are a couple of possibilities; the old power valve may have been bad and not opening, in which case this one is a little better. Or it was working correctly but it was opening too soon and flooding the engine. This is common on modified engines that don't generate much vacuum
Your carb is used and may have gone through a lot of changes. Holley has a web site that lists all of their carbs and what jetting and power valve etc. comes stock.www.Holley.com. You shouldn't have to deviate much.
By changing to a 2.5 power valve, you have actually leaned out the carb by delaying the opening of the power valve until it sees 2.5 inches manifold pressure. There are a couple of possibilities; the old power valve may have been bad and not opening, in which case this one is a little better. Or it was working correctly but it was opening too soon and flooding the engine. This is common on modified engines that don't generate much vacuum
Your carb is used and may have gone through a lot of changes. Holley has a web site that lists all of their carbs and what jetting and power valve etc. comes stock.www.Holley.com. You shouldn't have to deviate much.
Remember everyone my carb does have a secondary powervalve not just a primary. Im running a 6.5 valve in the secondary side now..HELP!!BH
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