850 Ultra XP lean bogs when secondaries open

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Demonx2 said:
Now I recall - you taught me that video trick!! It helped me when I was working to solve my stumble.
Your fix is not counterintuitive. You lengthened the pump shot with the smaller shooters to cover the lean hole until the main circuit could catch up. Pretty straightforward theory but takes a lot of trial and effort to get it right!
Click to expand...

Thanks and agree.
We all go for the bigger squirter, because it stumbles AKA it needs more fuel......not it needs Less squirter for more time. We want to change the cam to get that extra time, and you can get a little bit more........but they are more for shaping the squirter curve in city driving( in my opinion). When you wack it to the floor, the shape of the cam curve DON'T MATTER! It will start to squirt and will stop when the pump is empty.
 
Cudafever said:
Thanks and agree.
We all go for the bigger squirter, because it stumbles AKA it needs more fuel......not it needs Less squirter for more time. We want to change the cam to get that extra time, and you can get a little bit more........but they are more for shaping the squirter curve in city driving( in my opinion). When you wack it to the floor, the shape of the cam curve DON'T MATTER! It will start to squirt and will stop when the pump is empty.
Click to expand...
Absolutely correct! And hence why the position 2 on the cam may matter depending on where you whack it to the floor from!!
 
Just went thru the same issue with a 950xp
Had to up the squirter‘s and replace the 30cc pump with a 50
 
I run 50cc on both ends in my 850.

Edit: got my cars confused. The 850 has a 30cc pump on front and 50cc on rear.
 
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I run a BLP BX4 1.59" 4150 main body, 1050-1100 cfm according to BLP on my 434" small block and run 30cc pumps on both ends.
 
there is many reason why one eng won't stumble and another one will.

Mine reared it ugly head when i when from a 3000 stall converter, that had next to nothing for resistance below 2200 rpm. Too, a 4200 stall converter that had the same load or resistance, on the eng, at 1500 rpm that the 3000 stall convert had at 2200 rpm.

Hope that made sence.....................

Even thought it stalled at a much higher stall it put a load on the eng at a much lower rpm and caused the bog that i struggled with for 2 years.
The carb didn't change, only the conditions.
The 850 demon, never even as much as a wispier of a bog until the new converter was installed. Which stalled Higher.:realcrazy:
 
Pump shot can be one of the hardest things to get right. Takes time, patience, and a slew of cams, nozzles, and maybe a bigger pump. That’s your issue though. Put the jetting back to normal.. I recently worked on a 340 dart with a 750. Guy has driven the car for 20 years with a stumble on the secondaries. A few hours and several hole shots later the stumble was gone and the car picked up significantly at the track. I ended up with a big shot on the back of that carb to get it to transition. Pump arm adjustment is also critical, 90% of the carbs I work on have the adjustment screwed up.
 
On the traditional 850’s(1.56 x 1.75), I often end up with quite large squirters...... like 40-47.
Anything over a 35, and the hollow screw should be used.
With downleg boosters they’ll usually need the 50cc pump on the rear.

I believe the XP850 is a 1.56 x 1.69 carb. I’m not really a fan of that configuration. It’s like the old “830” .
Less of a pronounced Venturi.
I prefer the smaller Venturi and larger throttle bore arrangement(HP950).
 
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