850 double pump issues HELP!!

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hemitt

hemitt

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ok first off i got a used 850 dp and put it on a 360 thats ehh mildly built. and when i put a load on it to launch at the strip it just spit and died. ok so thought it needed rebuilding so rebuild it and same prob. well i bought a new base plate, main body, metering blocks and fuel bowls so pretty much a brand new carb well i started at 80 and 81 jets same prblm went down one by one till 70s same thing went up to 90s and belive it or not it took SOME of the stumble out but not all and ran way to rich..basicly what im asking is there sumthing im doing wrong?? i have the 50cc accelerater pumps do i need to go larger or what? i borrowed a 750 dp with 80 and 81 jets in it and it runs great is the 850 just to much for my motor or am i just not tunning it right?? im running holley blue electric fuel pump and about 7 fuel press. if you guys know something i dont please tell me if you need any more info let me know thanks
 
o and also forgot i do have jet extensions and blocked off power valves and i know the fuel level is where its suppose to be take screw out and its right below hole.. and im in colorado 4700 above sea level incase jets seemed small lol
 
Did you run a hose between the bowl vents, to keep it from sloshing over when you launch?

I used to have a piece of 3/8 hose, then cut a little vent hole right in the middle, worked great.
 
ok....if ya have blocked pv's you should be 8-10 jets larger pri/sec.

another thing is if it's coughin on ya, you need more pump shot by means of either a lager# shooter and/or more pump cam and sometime the 50cc.. like you have.

What rpm does the convertor stall at?

If 3000+stall you might wanna start with # 37 shooter and go up from there.
I tell though..on a 360, that 850 is gonna a lot of shot to smoothly transition to the mains without pop'n out the top.


on the elevation deal....just figure the 8-10 deal and then for every 1k in elevation , just go down 1-2 jets. So start 4 jets leaner than the 8-10 richer that you would need to go when plugging the pV's
 
have you adjusted the acelerator pumps?

as soon as you move the throttle the primary pump needs to squirt gas...
 
Reset it to the holley baseline jetting and start over. Make whatever necessary adjustment for lack of power valve(s).

Bad squirter set up will cause it to puke like you mentioned.
 
im running a 2200 stall not to high... the squirters are hitting right when any throttle movement is goin on so not lacking on primarys i think its the transition when launching at 2k rpms and punching it at light it just falls on its face either lacking fuel? cuz like i said when i bumped the jets crazy high (92,93) it didnt fall as hard but still coughed but ran real black smoke all the way down the track. so do i need bigger squirters in primary and sec.? is it just not giving it what it needs when i launch and hits the sec?
 
Thats kinda a large carb for that engine, I would start at box stock settings, jets, squirters, pump cams etc. If you have the power valve plugs then yes you need to go up 4 jet sizes at the least for starters. I dont have a holley book with me here at the house so am wondering about the 50cc acc pumps, we generally just use those on alky burning engines, I use 35cc pumps on my race car and smaller squirters so it will squirt longer. If its a 4 corner idle carb then set all 4 idle screws at 1 1/8th turns out for a baseline. Usually a big stumble can be tweaked out easy, the most common stumble is just fine tuning with the transition from idle to WFO. Get some clear view sight plugs too, those are the cats *** and run the rear float level in the middle of the plug, accerleration pulls the fuel to the rear of the float bowl and the jet extensions help out there too. Another trick we use is just leave the power valve plug out and use the other side for extra fuel capacity, helps keep the carb a little cooler too.
And one last trick we do is to put the 850 base plate on a 750 carb, did that with mine and it flows @ 930 CFM, smaller venturis=better throttle response.
 
ok well went to preformance shop guy told me to take 45 power vavle and put in prim. and i put 75 prim 80 sec. still got prblm...its back firing out of carb first with black smoke then caught on fire... so i think i said before i had 50cc pump but i might be wrong which ever one is the smaller im thinking 30cc?? so ima try the bigger acc. pump see where that takes things now
 
start with the 30cc [smaller pump diaphram].

It's the shooters that need to go UP IN SIZE [NUMERICALLY HIGHER]

I've done this before, I know what I'm talking about.

42 shooters and maybe the pink cam will help you big time
Also, if you hold the throttle wide open, you should be able to push the lil pump arm down another .015...
If you have 75's in the primary with a 4.5 PV [PV should be rated at Half the manifold vac reading at idle in gear] and if you have NO pv in the secondary you need to go 7 sizes bigger in the secondary.

I would just run a PV if possible in both the primary and secondary and then square up the jetting, as in same size jets primary/secondary.

You should get a holley book and read the sht outta it.
 
Unless that 360 is making more than 600 hp that 850 dp is to much carb.the problem is not to much gas so much as to much air. A 750 carb should be lots.Adding more gas is just a bandaid for to much air.1wild&crazyguy is right. Buy a book on holley carbs.
 
hemitt said:
ok well went to preformance shop guy told me to take 45 power vavle and put in prim. and i put 75 prim 80 sec. still got prblm...its back firing out of carb first with black smoke then caught on fire... so i think i said before i had 50cc pump but i might be wrong which ever one is the smaller im thinking 30cc?? so ima try the bigger acc. pump see where that takes things now
Click to expand...

That carb takes 80 jets square (all around with PVs F&R), if you block them off (either end) run 88 jets as a baseline, that carb should have NO problems on its factory cams/squirters, there should be a 31 & 30cc with pink cam (#1 hole) up front & a 50cc pump with a brown cam & 31 or 33 squirter out back, for some reason your going "lean" on the transition.

And when your trying to make changes to a carb, make "little" ones, not "BIG" ones. If i was there i'd have that carb singing, as long as it hasn't been jacked with too much or is all screwed up. A 4781 850dp is a very simple carb, there fairly straight forward, easy to tune, really it sounds to me like its all fucked up in the metering.
 
cuda20 said:
Unless that 360 is making more than 600 hp that 850 dp is to much carb.the problem is not to much gas so much as to much air. A 750 carb should be lots.Adding more gas is just a bandaid for to much air.1wild&crazyguy is right. Buy a book on holley carbs.
Click to expand...

If your reffering to the "issues" he's having I disagree, if that carb is in its tune it'll run fine on there, it won't spit or pop back, i don't care if its on a slant 6, sure i agree its too big, & it won't run "as strong" then it would with a smaller carb, but if its "in tune" metering wise it'll be very drivable, just sounds like the metering is off somewhere & he doesn't know were to look to fix it.
 
ok so i took the squirters out of the 750 which is 35 prim.squirter 28 sec i tried it wit PV and still fell on its face. so i took Pv off and blocked it ran 79 prim 80 sec jets it seemed to help with the bigger squirters but still fell just not as bad so buy a kit of squirters and play with that or am i just wasting money on the 850??
 
ok got tired of playing with the 850 so just ordered a 750 proform carb any advise on what jets i should start with or anything i should do or nothing i should do?
 
not sure if i wanna sell it just yet i got a 440 going in my duster this winter so i think ima try it one more time on that and see how it runs with more HP. but if im going to sell it ill let you know
 
hemitt said:
ok got tired of playing with the 850 so just ordered a 750 proform carb any advise on what jets i should start with or anything i should do or nothing i should do?
Click to expand...

You could have tuned that 850, you were still WAY too lean with those jets &^ the block offs, i told you 88 square with block offs, but now you ordered a 750 proform "carb" & your already wanting to change the jets lol, leave the jets alone, not trying to sound like a hard *** here, but it seems you don't have much experience with carb tuneing, so you don't need to be jacking around changing jets, if your getting a "complete carb" leave the jets alone & start out with what comes in it, & if your just getting the MB, it will come with jets & air bleeds, read the instruction thoroughly!!
 
my 750 proform on a pretty built and aggressinve cam'd 367 uses 72 and 82 jets along with a 37 and 35 squirter. I have a PV in just the front and it's a 6.5. 30cc front acc. pump and 50cc rear


Also I had on a Quick Fuel Tech. 850dp with annular boosters with the same jets, 50cc pumps, and same PV and it absolutely loved it, it would swallow both carbs from idle to WOT without a hesitation anywhere, took a lot of time to tune these in and I'm not done playing with pump cams yet.
 
well the only reason im saying playing with the jets u gota think im at 4700 above sea level ur prbly at sea level so your stuff comes pretty close mine stuff comes for sea level so i havta to play with the stuff. yes ima throw carb on when i first get it to see where its at and how close/far off i am but im sure the jets are gna be for sea level....sooo if anyone thats NOT at sea level have any adivse on where about there at on jets squirts etc wigsplitter74 are u running at sea level? kinda seems about right where i need/should be?
 
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