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ofm7432 · 03-20-2005, 03:17 PM

Question from a newbie? I'm getting the car ready for the track for the first time and trying to get the tune-up as close as possible. It's a 850 race Holley and I started out with 80's on 4 corners, ran great at idle to partial and full throttle but thought it was running a little too rich so I went to 78's in the front and 86's in the back.... now it still run's good at idle and partial throttle but at full throttle from idle it stumbles very bad unless I launch at around 3000rpm. Is this to be expected or did I make too big of a change. Being a weekend warrior I was leaning out the front's to make it more streetable. Also I have a 2.5 PV front and rear, from reading another post I'm planning on plugging the rear PV. I know it's not an easy question to answer, but maybe one of you guy's can point me in the right direction.

ofm7432 · 03-20-2005, 03:17 PM

Question from a newbie? I'm getting the car ready for the track for the first time and trying to get the tune-up as close as possible. It's a 850 race Holley and I started out with 80's on 4 corners, ran great at idle to partial and full throttle but thought it was running a little too rich so I went to 78's in the front and 86's in the back.... now it still run's good at idle and partial throttle but at full throttle from idle it stumbles very bad unless I launch at around 3000rpm. Is this to be expected or did I make too big of a change. Being a weekend warrior I was leaning out the front's to make it more streetable. Also I have a 2.5 PV front and rear, from reading another post I'm planning on plugging the rear PV. I know it's not an easy question to answer, but maybe one of you guy's can point me in the right direction.

Nine Ninety · 03-20-2005, 05:35 PM

From your description, it sounds like the car stumbles when floored from under 3000 rpm. Sounds like you need more accelerator pump shot (e.g. bigger squirters or different pump cams). Main jetting doesn't normally control how well the carb transistions off of the idle circuit.

Nine Ninety · 03-20-2005, 05:40 PM

What size accelerator pump squirters are you running and what cam color (front & rear if you have a DP) are you currently running?

The other thing that can cause the carb to stumble is having the primary blades open too far (typical with a large cam). The trick is to open the secondaries slightly (you have to remove the carb and adjust the screw on the bottom of the base plate. The objective is to open the secondaries enough to allow you to close the primary back down where it covers some of the transition slot.

ofm7432 · 03-20-2005, 06:22 PM

Thanks Nine Ninety, I'll post the squirter and cam specs tomorrow.... the cars parked at work right now. Also I understand what your saying about the throttle plates, I'll give it a try.

ofm7432 · 03-21-2005, 02:34 PM

Well I checked out the carb today and I've got #35 squirters and the red pump cams front and rear. I also have 50cc accel. pumps.

fasteddy · 03-21-2005, 03:24 PM

MB1966, I think you have too much of a pump charge with 2 50CC pumps and 35 squirters. Put in 32 squirters and see if it stumbles or stumbles less. If less--play with the lesser is better idea.

Nine Ninety · 03-21-2005, 05:55 PM

MB1966 I agree that 2 50cc pump and .035 squirters may be too much. If smaller squirters help but don't eliminate the stumble, you may want to consider going back to the 30cc pumps.

Have someone watch the car (or better yet video tape it) when you launch. Other than using an A/F monitor, one sure tell tale sign that you have too much pump shot is a black puff out the exhaust indicating a "way too rich" condition when you mash the throttle.

ofm7432 · 03-22-2005, 03:18 PM

Thanks for the info guy's. I'll try that, if not, I'll go back to the 80's on all four corners and wait till I get it to the track and tune it from there. On the squirters, should you change them in pairs or can you stagger the sizes front and rear?

Nine Ninety · 03-22-2005, 06:32 PM

MB1966

Although most initial setups are the same, there is no reason you can't use different squirter sizes on the primary & secondary. Keep in mind that the rate of opening the secondaries is different (faster) than the primaries since they start later.

Bottom line, go by what the car tells you it likes regardless of the number on the squirter.

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