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  #1  
Old 04-23-2006, 09:11 PM
party340 party340 is offline
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Default Need help with double pumper tuning

I just put a 800 holley double pumper on my dart and the thing bogs for about a half of second and then pulls hard. It doesnt matter if its first gear or 4th gear low or high rpm, the lag time is about the same. The cab is bone stock with a 30 cc pump on the front and 50 cc pump on the secondaries. The squirters are 31 in the front and rear. I thought that maybe it was pumping to much gas so i tried a 25 squirter in the rear and it ran worse. Do I need bigger squirters? If so about how big ( just ballpark). I also have another 50 cc pump i could put on the primaires or would that be too much? I've never messed with double pumper carbs before so I'm at a loss. The engine is a 340 with a 242 at .050 cam, ported 360 heads, rpm intake, 3.91 gears, headers, 4 speed, and run's mid 12's at 112. Also, its been a while since i've changed the plugs, could this cause the problem also? Any input would be greatly appreicated.
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  #2  
Old 04-23-2006, 10:49 PM
Crank Crank is offline
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the squirters are to small go up 1 or 2 sizes and make sure your pump shot is adjusted properly you may need to change the cams go to holley's web site they have a trouble shooting and adjustment area on the site.
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  #3  
Old 04-23-2006, 11:01 PM
Crank Crank is offline
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btw pull the plugs check color then check your vacume presure if carbs stock it proubly has the wrong size power valves in it.
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  #4  
Old 04-24-2006, 11:43 AM
dart662dp dart662dp is offline
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carb may ba a touch big for the motor combo. maybee stick with 700-750 dp. have tinkered with 800-850 on similar built 340s with the same intake, 692dr dart body w/3.55 gears in the past and always boggy down low.
thing was/is happiest with a 670-700 cfm carb. it went nuts with my 650 dp on it, but i'm keeping that one!
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  #5  
Old 04-24-2006, 01:08 PM
Kevin Garceau Kevin Garceau is offline
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carb is way too big. You may not ever get the bog out....too much air for that little motor to suck up
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  #6  
Old 04-24-2006, 06:37 PM
B1owner B1owner is offline
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Before you take it off and buy another carb, try getting the 800 to work properly. No, the carb isnt too big. 340s love alot of carb. If you dont believe me, keep tuning the carb and see for yourself. It could stand to be a little smaller, but it should work really well. Is this an 800 spreadbore? Hope not. If it is, youll need about a 40 squirter in the secondary side.
But if its a square bore, here's what Id do. If its hesitating just off idle with only the primaries, go up a size of two with the squirter till its gone. It should quit after a couple size bigger. And if its bogging olny when it goes to the floor, try the same with the secondary side ...like a 32 or 35 or even a 38. go up till it quits hesitating.You can also play with the pump cams, but I never seem to get anywhere doing that. Also, make sure you have fuel coming out both squirters when you touch the pump arms, because alot of folks put the carb bowl gaskets on backwards and it blocks the fuel delivery hole. Keep us posted.
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  #7  
Old 04-24-2006, 11:09 PM
party340 party340 is offline
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Thanks for the input folks. I'd be lost without this website. Theres nothing like getting advice from mopar gear heads all over the country. Any hoot, once I get past the hesitation and I go through the gears the car does feel faster than with the 3310. The car also runs fine if I roll the throttle, its just when I nail it hard I get the hesitation. I'm going to order a 35 and a 37 squirter and see how that works. I will not be able to play with the car for another 2 weeks but as soon as I do I'll post on the results. Thanks again.
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  #8  
Old 04-24-2006, 11:52 PM
dart662dp dart662dp is offline
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when you nail it hard, hard transition from one constant vacuum, to a big drop in vacuum due to throttle blades suddenly opened, and motor starving for fuel because the vacuum is too low to pull fuel through the boosters =lay down bog, this happens with big carb on little motor, then when the rpms get up a bit, it starts pulling more vacuum, pulls fuel, and takes off, "kick in the pants" feeling. a LOT of pump shot may help, try two white cams. basically, too much plenum area opened too soon on too small of a motor causes boggs and lay downs. run some volumetric efficiency #s with the big carb, versus a smaller one.
hate to say it, but a big single plane and some more cam/compression and some 4.30 or 4.56 gears might be needed to get the 340 ready for 800 cfm.

we tried the 850 dp on my buddies 340 and same results no matter what, so we save the carb for the 452
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  #9  
Old 04-25-2006, 02:05 PM
beepbeepsrule beepbeepsrule is offline
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When tuning Holleys keep in mind that the squirters control the duration of the pump shot. The same amount of fuel will reach the plenum each time, this is determined by the pump chamber volume (30 or 50 cc's). The smaller the squirter the longer the duration, larger squirters let it in faster.

The pump cam determines the strength of the pump shot over the duration of the shot. In general there are 3 profiles.. 1.) More fuel at first then less, or 2.) Even amounts of fuel for the whole shot, or 3.) Less fuel at first then more at the end.

DP's are not as tolerant regarding the proper CFM range for the cubes and RPM range. Also not as wide of a usage band, meaning hard to tune just one way for strip AND daily street use

My experience with 383's and 440's is they want a 31 or 33 squirt off the green cam, which gives more at first then less at the end as the main jets begin to flow. An 800 dp is pretty large, really designed for a 440+ engine with an open plenum intake and full 36-38 degree timing all in by 2200rpm.

Vehicle weight and Rear gears can also affect the carb tuning. As an example a lightweight Duster with 4.56 gears and good torque converter could probably take an 800 on top of a healthy 360, whereas a Newport with 3.23's would bog with it on a 440.

A thermoquad can flow UP TO 800, and anywhere in between which is nice, the same carb can literally be used on a 318 or a 440. The Holley flow rate is what is says, and needs to within the range of the intended cubes/powerband/vehicle application demands.
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  #10  
Old 04-25-2006, 06:34 PM
mgreen2994 mgreen2994 is offline
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Default double pumper

party340 do yourself a favor put a vacum guage on the motor about 1100 rpm and check the reading. bet it will need a 4.5 power vaule
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  #11  
Old 04-26-2006, 03:34 PM
mrjack10 mrjack10 is offline
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How do you tell if the power valve has blown, due to backfire ?
I had problem with backfiring last summer and have a 750 3310 Holley
(vacuum). what are the most common signs ?
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  #12  
Old 04-26-2006, 04:38 PM
dusterrcr dusterrcr is offline
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It will dump a ton of gas in the motor due the rupture in the diaphram-ie--wont idle,black smoke,black plugs-etc--etc Keep in mind if you've got this going on.Your dumping raw gas in the oil too.Not good for the bearings.Pull the dipstick see if oil is black and smells like gas.
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  #13  
Old 04-26-2006, 09:26 PM
beepbeepsrule beepbeepsrule is offline
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Yup, the fuel bowls will drain down until the fuel pressure drops, LOTS of raw gasoline odor. Nasty problem.

Hey Party340, meant to mention the ignition system, not sure what you have from your posts ...... need a good one. Sometimes a carb change can show a weak ignition setup. If the carb is setup up a little off AND the ignition is not up to par it can feel like all carb problems.
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  #14  
Old 04-27-2006, 01:30 AM
mrjack10 mrjack10 is offline
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Ok....I don't recognize any of that, no idle problem no gas in oil, maybe it didn't break then. Somebody wrote here at the forum that it always will break when backfiring. Maybe I was lucky.Thanx!
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  #15  
Old 04-29-2006, 06:29 AM
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ttraut@unlockit ttraut@unlockit is offline
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Default Backfires don't cause power valve failure...

Quote:
Originally Posted by mrjack10
Ok....I don't recognize any of that, no idle problem no gas in oil, maybe it didn't break then. Somebody wrote here at the forum that it always will break when backfiring. Maybe I was lucky.Thanx!
I had heard that too when I was in the market for my 850 DP; Holley's website that their "new" (5-8? years old) design prevented that from happening and it's old talk that keeps coming up.

I'm doing this from memory so you may want to check out the FAQ section on their website.

Terry
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  #16  
Old 05-07-2006, 05:40 PM
party340 party340 is offline
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What a difference a little tuning can make!! It doesenst even feel like the same carb. It's not 100% but its pretty close. There is still a very slight hesitation when you nail it hard but it's almost unnoticible. Here's what I did.

First i changed the plugs and cap. No difference

Next I changed the secondary squirter from a 31 to a 37. Felt a lot better but still had some hesitation.

Next I put a 50 cc pump on the primay and went from a 31 to a 37 squirter. Runs like a champ.

I was reading somewhere about shimming the springs for the squirters so I think I'll try that next just for the hell of it. Thanks everyone for your advice, espically B1owner!
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  #17  
Old 05-11-2006, 08:25 PM
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what ever happened to the demon/holly tuning guide Don put up?
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  #18  
Old 05-12-2006, 11:50 AM
70_A66 70_A66 is offline
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Party340:
You can shim your accel pump arm springs if they "give" too much as soon as the accel arm moves. I have done this using flat washers. Just make sure you recheck your clearance with the linkage opened up to WOT.
I believe that Don now sells the Demon tuning book.
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