Holley Carb BOG Issue
Safety Car
Joined: Jan 2009
Posts: 4,000
Likes: 299
From: New York
Good question, I read a lot of good things about annular boosters and tried to find a carb that had them. This carb popped up on ebay. Although, aside from this stumble issue, which oddly wasn't always present, is the best carb I have tried yet. When I dynoed the car, it had an amazingly consistent A/F ratio from idle through 6500 rpm. I think part of the issue is 830 cfm is too big from my 427. I bet a 750-800 would be better. I am at a loss as to what to try next. I thought it was due to a rich condition, I dropped my PV down to 3.5 from 6.5, reduced my jet sizes from 78 to 75 and also reduced the squirter size from 48 to 28. I am running a bit lean and when I punch it she lean spikes as I would suspect it would, however, I would also suspect the stumble would at least be minimized if it were due to a rich condition. No change... apparently it is not. Maybe it is something completely different. I read that if the carb is too big, upon low vacuum low speed (off idle) situations the velocity is not high enough in the carb to properly atomize the fuel so it just drips into the intake. At a minimum, I am going to change the plug wires and if that doesn't work, I am going to pull the distributor and send to DUI for a tune up and check out. I also checked my vacuum and it appears there are no leaks.
Your actually at a good starting point.
I run a 800 DP on a 350 ZZ430 clone.. Runs perfect even when everyone says it is to big . . .
Set the idle transition slot correctly. If your idling off that slot you will get a big stumble when you attempt to accelerate. I am suggesting this because of the 48 squirter you said you had. I am guessing that helped push massive fuel and covered up a lot of the off idle stumble or even a steady cruse stumble when you went to accelerate.
Once you set transition slot correctly and set the idle mixtures take her for a ride .. At full stop nail it and if you have any bog and the A/F says it is leaning out jump the primary squirt to a 35 from the 28 your using now.
When you set the carb correctly , your gonna idle 12. to 13.5 ,, when you nail her you will see 11.5 to 12.5 under full throttle,,and cruse should be 14.2 to about 13.5 .. A CARB will be hard pressed to offer and maintain fuel injection a/f ratios and typically will run a bit richer . You can also use the air bleeds to dial her in to very specific ranges if you want to take the time to do so..
Team Owner
Joined: Apr 1999
Posts: 21,953
Likes: 1,445
From: Reno Nevada
2024 C3 of the Year Finalist- Modified
This is the place that did my carb. I tried for a couple of years to perfect my Demon carb. Squirters, jets, power valves, titanium needle and seats I even drilled all four throttle blades and polished the boosters.
What person can't do is air bleeds and emulsifiers.
http://www.competitioncarburetion.com/
What person can't do is air bleeds and emulsifiers.
http://www.competitioncarburetion.com/
Thread Starter
Melting Slicks
Joined: Nov 2000
Posts: 2,738
Likes: 53
From: Bogart GA
Today I realized that the spring on the throttle return had relaxed a bit often times not allowing the the throttle blades to return to the throttle stop completely. I would have to stab the throttle to get her to return to normal idle. This is where this issue is most problematic when I am coming off coasting and applying the throttle, in this situation she was probably not sitting on the throttle stop. I tightened the spring and plan on taking her for a test drive drive shortly.
Thread Starter
Melting Slicks
Joined: Nov 2000
Posts: 2,738
Likes: 53
From: Bogart GA
Ran better today, but did not dive a lot of stop and go stuff. I also noticed that there is not spring on my accelerator pump plunger. I have the 50cc accel pump and the plunger is bottomed out. It is correctly adjusted however. There in no play at idle and there is still some travel left at the WOT. The spring buffers out the flow however.
Team Owner
Joined: Apr 1999
Posts: 21,953
Likes: 1,445
From: Reno Nevada
2024 C3 of the Year Finalist- Modified
Whenever i have my bowls off i just go ahead and change the little rubber squirter diaphrams. years ago I had one tear and the squiter on the secondary quit
Team Owner
Joined: Apr 1999
Posts: 21,953
Likes: 1,445
From: Reno Nevada
2024 C3 of the Year Finalist- Modified
Mine is drilled on the primary like the first picture. It give a bigger range of adjustment on the four corner idle screws.
You must set all four throttle blades the same. So set them to .030then reinstall your carb and then adjust your idle hot speed exactly the same number of turns on both primary and secondary
You must set all four throttle blades the same. So set them to .030then reinstall your carb and then adjust your idle hot speed exactly the same number of turns on both primary and secondary
