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Carb Tuning problem

Odmark91

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Hello.

The Holley 850 DP on my stroker motor was leaky and old so I decided to swap it out for a new Quick Fuel 850 Brawler race carb (pretty mutch identical to the Holley.

Since the holley was adjusted to the engine on a dyno I figured I would just swap everything in between the carbs, so I did. (Jets, power valve, accelerator pump diaphragms and cam etc).

Installed the carb, set the accelerator pumps so they squirt immediately when the butterflies open.

Started the car and it fired immediately when the float bowls filled up.
Set float levels (middle of sight glass, is this correct?) And set air mixture screws with a vacuum gauge (this was hard though because the cam makes very low vacuum)

And it runs good, but when I floor it from idle it bogs and sometimes backfires through the carb. If I keep my foot down it dies.

If I floor it from just a bit higher rpm, it works perfectly.

What could I be doing wrong? Backfire through carb means lean condition right?
Could I need bigger/to drill the squirter nozzles?
 
Where you went wrong is you shouldn't have done a back alley power tune.
The carbs are set up nearly perfect from factory. I would put it all back to brand new . And start from there.
 
Where you went wrong is you shouldn't have done a back alley power tune.
The carbs are set up nearly perfect from factory. I would put it all back to brand new . And start from there.
Just run it out the box first, then see if it performs.
 
Where you went wrong is you shouldn't have done a back alley power tune.
The carbs are set up nearly perfect from factory. I would put it all back to brand new . And start from there.

I had to adjust the accelerator pumps since I replaced both the diaphragms and the cams. So the only thing I could reset to factory is the floats and the air mixture screws.

I did run it with stock cams at first because i forgot to swap them out but then the bog was even worse.
 
Right. So if it was new why did it need diaphragms ?
 
Right. So if it was new why did it need diaphragms ?

Because they are higher cc then the stock ones. I don't know if you missed the part of stroker engine in my first post, this is not a stock engine.

It is built by a engine shop that builds high performance street and drag racing engines and tuned by them on a dyno.
 
I did read your post carefully.
My suggestion was, you should put it back to exactly stock and start from there. It should need very little, if any, "modifications".
Your original carb, and the new one are not the same. They may share one thing, the number 850.
 
Ive always set float level at bottom of the hole. 440 6pack and 750 DP
 
Its sounds like not enough pump shot. Do both carbs have the same color pump cams? Same squirter diameter? Bigger squirter will give more fuel earlier over a shorter period of time. Cams are available to increase the total amount of fuel discharged. Pump cams and squiters changed my car in 3 passes. From a stumbling flat leave 9.25. To the picture below 9.05.
Doug

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Aaaaaaaaaaaah the joys of Holley ownership. I put all that behind by switching to Carter/Edel.
First thought is the low idle vacuum. That often requires bypass air [ t/blades drilled or some means of adding extra idle air ] to reset the transition slot relationship. You want 0.020 -0.060" slot showing below the blades at idle, less is better.
 
I have a brawler 950 on a 499, I had to change the jetting pretty significantly from stock as it was lean everywhere so I dont agree with running out of the box. The fuel should only come up to the bottom of the sight glass, so I would adjust the floats. High levels in the bowl can cause problems.
 
On the clear sight glass bowls, you set the float halfway in the glass. For the older carbs you would pull out the plug and wiggle the car until fuel seeps out.
 
On the clear sight glass bowls, you set the float halfway in the glass. For the older carbs you would pull out the plug and wiggle the car until fuel seeps out.
correct ,if the fuel level was at the bottom of the sight glass, it would be lean -leading to erroneously jetting up to cover for the mis adjusted float levels.
 
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