Help, Holley 850 has light throttle stumble

[340doc]

Trying this 850 DP on my car. Idles and drives good, mash the pedal and it responds good. Problem I'm having is when your cruising and you give it easy pedal it stumbles. Accelerator pump is adjusted and responsive. I've tried different squirters and no change, but I don't really believe its a pump issue. Here's where I'm at. Transfer slots are just above square, mixture screws are responsive. Timing is at 36, all in at idle. Vacuum is at 10. Power valve is 6.5. Thanks

 

[brian6pac]

Check your pump cam if its on #2 move it to #1 and see if it makes a difference, the best thing to do is take a vacuum gauge and a long hose and tape it to your windshield in front of you so when you have the stumble you know what the vacuum is at that time.

 

[340doc]

Thanks Brian, it had a red cam on it and I tried a white cam with no difference. I'll do the vacuum gauge thing and see what I learn

 

[brian6pac]

FYI the squirter nozzle will squirt the same amount of fuel no matter what size, the smaller the hole the longer the squirt duration, the bigger the hole the shorter the duration.

 

[340doc]

I see what your saying. I didn't think the squirter would be that critical in a light throttle application once I'm moving. I'll play with the cams and cross my fingers.

 

[MOPAROFFICIAL]

I see what your saying. I didn't think the squirter would be that critical in a light throttle application once I'm moving. I'll play with the cams and cross my fingers.

What transmission are you running and if automatic...what convertor stall?
If you run a manual trans I'd say you'd need a 8.5 power valve to start and if this is a 340/360 I'd say you need a mid high 30's numbered squirter/nozzle. The red or orange cam might fit, but need a the info above.

 

[brian6pac]

You have to know what the vacuum is before you can tune

 

[340doc]

What transmission are you running and if automatic...what convertor stall?
If you run a manual trans I'd say you'd need a 8.5 power valve to start and if this is a 340/360 I'd say you need a mid high 30's numbered squirter/nozzle. The red or orange cam might fit, but need a the info above.

I'm running a 904 with a 3800 convertor. It's a 372 motor. Stock squirter #35 is in place. I put the red cam back in and tweaked the float level to just seeping out. Throttle response is good but couldent test drive it tonight. I still have to drive it with the vacuum gauge hooked up.

 

[MOPAROFFICIAL]

You have to know what the vacuum is before you can tune

Maybe I read wrong but I think he said he had 10" of vacuum.

 

[MOPAROFFICIAL]

Trying this 850 DP Transfer slots are just above square, mixture screws are responsive. Timing is at 36, all in at idle. Vacuum is at 10. Power valve is 6.5. Thanks

There it is in short form.

 

[MOPAROFFICIAL]

I'm running a 904 with a 3800 convertor. It's a 372 motor. Stock squirter #35 is in place. I put the red cam back in and tweaked the float level to just seeping out. Throttle response is good but couldent test drive it tonight. I still have to drive it with the vacuum gauge hooked up.

Big convertor tends to like 35+ squirter, I'd even say a 37 squirter in this case, but test what you've done and see where you're at, good luck.

 

[brian6pac]

He said he has 10" at Idle that means nothing when cruising down the road then tipping in the throttle. If you are cruising down the road and open the throttle how far does the vacuum drop? You wont know unless you have a gauge on it. if it drops to 7" than a 6.5 pv wont do you any good.

 

[MOPAROFFICIAL]

He said he has 10" at Idle that means nothing when cruising down the road then tipping in the throttle. If you are cruising down the road and open the throttle how far does the vacuum drop? You wont know unless you have a gauge on it. if it drops to 7" than a 6.5 pv wont do you any good.

A more factual statement would be 10" of vacuum means nothing to you.
Like I said already , with that convertor I would expect a 8.5 pv and possibly a 37 squirter. I see a trend,tune how you like..but if he ends up with a 8.5 PV and bigger shooter like I'm saying...are you going to tell me I'm wrong In how I figure it?

 

[brian6pac]

Well how does a pv work?

 

[MOPAROFFICIAL]

You should know if you're giving advice on how to select one.
With 3800 stall the power valve should be opening sooner than 6.5, pump shot is part of it, but imo thats part of his stumble, lean stumble!

 

[brian6pac]

Yes It's lean, The power valve is held closed by vacuum, a 6.5 pv opens a 6.5" of vacuum. the amount of intake vacuum depends on engine load. If it revs up fast, say high stall going down hill the vacuum may never get to 6.5" and the engine probably wont have a lean bog. Same set up going up a large grade will be lean and bog if the power valve does not open. You don't even know what his gear ratio is 3.23 or 4.88, makes a big difference on engine load, and on manifold vacuum. Just because it works on your set up doesn't mean it will work on every body else's.

 

[brian6pac]

Also the main jets might not be big enough. if the throttle plates are open far enough you are off the intermediate circuit and on the main jets, they all work together.

 

[MOPAROFFICIAL]

Also the main jets might not be big enough. if the throttle plates are open far enough you are off the intermediate circuit and on the main jets, they all work together.

He said the blades were in correct postion to the transfer slot, square...idle screws responsive... he also said his timing is locked out at 35 degrees. He does not say anything about a lean surge at cruise, he says stumble off idle.
I'm giving him advice on his problem with his motor and you are over here critiquing my advice because I'm not using your method to get possibly the same conclusion. What's up with some of you people? Can no one else have the answer? I know how a PV works, and I tune , build and port heads and I'm really good at what I do..... I'm also good about letting others think what they want....so please continue with that and stop pestering me.

 

[brian6pac]

Sorry if I'm pestering you that's not my intent. If you read it the problem is at cruise speed and ease into the pedal, not off idle. I think you misunderstood the problem.

 

[340doc]

Guts I appreciate both of you trying to help me. I do believe its a lean tip in. Off idle is fine. I need to check my cruise vacuum and go from there. The stock primary main jet is #80. I'm at 77. I'll probably put the 80 in and start from there also. When I'm trying a different carb I like to put them back to stock specs and eliminate any changes someone else may have made. I left the 77 jet this time though but I don't see that as the problem. I will go to the 80 just to start from stock. I'll post my results.

 

[MOPAROFFICIAL]

Guts I appreciate both of you trying to help me. I do believe its a lean tip in. Off idle is fine. I need to check my cruise vacuum and go from there. The stock primary main jet is #80. I'm at 77. I'll probably put the 80 in and start from there also. When I'm trying a different carb I like to put them back to stock specs and eliminate any changes someone else may have made. I left the 77 jet this time though but I don't see that as the problem. I will go to the 80 just to start from stock. I'll post my results.

Look forward to the results, could be a good idea to start that way.
My thought is the convertor is loose, your cruise speed falls under its full lock up and when you tip the throttle the convertor flashes, motor goes lean during the flash/free rev or however you wan to describe it. Every car I've ever had with 3800 stall, mostly turbo action stuff, always needed a big shot AND the power valve either removed and jetted up 8-9 sizes (pri/sec square jetted) or pv setup 2" below manifold vac in gear.

 

[MOPAROFFICIAL]

Sorry if I'm pestering you that's not my intent. If you read it the problem is at cruise speed and ease into the pedal, not off idle. I think you misunderstood the problem.

No big then, all is fine.
We don't know what gear he runs with that stall, don't know if its a tight or loose convertor or the make... But we're all just offering our thoughts as to why, not as to who's right or even psychic.lol

 

[340doc]

Its been a couple weeks and I want to thank everyone who tried to help. Long story short, I put the pink pump cam back on and tried the different holes. That did the trick. I've never had a Holley so sensitive to a pump cam adjustment. Thanks again, great support here.