stumble

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the twister
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stumble

Post by the twister » Fri Nov 03, 2017 7:40 am

I am running a 355 sbc with tunnel ram and 2 1050 dominators, car used to run great but previous owner had carbs rebuilt and car now has a stumble off the line, i replaced the floats with wedge type and that helped some, Is there a trick to setting up these carbs to run them sideways? it seems now that maybe the front jets (left side since mounted sideways) are getting uncovered under hard g's. would jet extensions help? that would only move the jets out and not back. I know that pro-stocks have run them like this forever but no one will tell you anything.The holley people dont know ...

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Re: stumble

Post by mag2555 » Fri Nov 03, 2017 9:05 am

How the Hell high a rpm are you spinning this 355 t motor that you need 2 1050s? !

And everything is the same with this car now but for the rebuilt and indifferent position Carbs?

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Re: stumble

Post by the twister » Fri Nov 03, 2017 6:14 pm

launching at 7400,shifting at 8600, finish line around 9-9200, supposedly nothing else has been changed but the rebuild on carbs, have installed qft wedge floats, has helped some but still acts like starved for fuel 30-40 ft out and after shifts, (4 spd lenco) new magnafuel 500 pump, #10 line to reg,#6 to carbs, #130 inlet valves, car was running 5.80's before i bought it, best i ve had is 5.91 with one carb but cant get the rpm's or mph with single carb

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Re: stumble

Post by fdicrasto » Fri Nov 03, 2017 7:15 pm

Rear mounted fuel cell and pump? What is your bypass pressure set at for return line? A #10 line running to front regulator has need for very stout pressure and flow which that pump is capable of delivering. G forces on several pounds of fuel in that #10 line can create issues if not properly compensated. Just one of several areas of possible problems.

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Re: stumble

Post by the twister » Sat Nov 04, 2017 4:36 am

I have the pump pressure set at 25 lbs at the reg, i have been told i need to set this up as a 2 line system( return line to tank) so that the fuel will be continuesly flowing to the reg. Yes the pump is mounted at the tank in rear with reg mounted in front of carbs

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Re: stumble

Post by mag2555 » Sat Nov 04, 2017 6:50 am

Well it sounds like your set up good to over come the G force lunch pressure reduction , and If the motor is not falling on its face on the top end then I would have to say that since the Carbs are the only thing that was touched that they are the issue, and it's likely in the Accel pump circuit area or the transistion circuit in the Carbs.


Are the gaskets all the right ones and in the right way on the Carbs?

Is this a 2 circuit or a3 circuit Dominator?

I spent weeks of time at the track once on a brand new 3 circuit Dominator that ran great but for at lunch!
I finally gave up and got a 2 circuit model!

One other thing to concider is that if your tune is better then the passed tune and your now making more power you have then turned up a problem that was there before , but never quite showed it's ugly Head all the way!

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Re: stumble

Post by the twister » Sat Nov 04, 2017 6:27 pm

I am thinking about fabbing a single 4500 top for my tunnel ram and get a new 1475 holley , That way one carb mounted conventionally, I know my engine will handle the cfm's, this engine loves lots of air..

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Re: stumble

Post by F-BIRD'88 » Sat Nov 04, 2017 8:04 pm

Tunnel rams are not intended to run only 1 carb.
They all want 2 carbs.
Any 1 carb setup will never run as good as a 2 carb setup.
if the thing was good before it will be good again/
Something is different about the carbs now.
Talk directly to the shop that did the carb service.
Find out what they did.
2x 1050 Dominators is not too much carb and you don't need to switch to a single carb. That is not the fix.

The stumble may not even be the carbs at all.

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Re: stumble

Post by the twister » Sun Nov 05, 2017 3:58 am

I did switch to a single carb(a different 1050 mounted front to back) and dart intake, car ran good with no stumble only wouldn't turn the rpm's ( 1000 less) and mph fell off 10-15. car ran 6.0's pretty consistantly but I know there"s more there.I made some homemade 90 degree jet extensions (90 degree grease fittings rethreaded and tapped with straight jet ext's screwed in) this has moved the front jets right next to the rear jets, also had to use bowl extensions to make these fit without hitting the floats. Going to test this afternoon if the weather permits. Only issue with this is it makes the carbs so long side to side that my hood wont fit now (scoop not wide enough) , so this wont be a permanent solution.I looked up the correct gasket #"S AND WILL CHECK THEM BEFORE RUNNING.Sometimes we take for granted that someone else has done the right thing and maybe they haven't.

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Re: stumble

Post by jmarkaudio » Sun Nov 05, 2017 9:40 am

What do your plugs look like? What heat range? What fuel?
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Re: stumble

Post by F-BIRD'88 » Sun Nov 05, 2017 11:42 am

Try turning the fuel pressure at the carbs DOWN. Of ten LESS fuel pressure at the carbs ( but plenty fuel FLOW volume) is just BETTER.

if the fuel pressure regulator(s) is mounted IN FRONT of the carbs you don;t need or want high fuel pressure at the carbs. When the floats get upset at launch or on shifts excessive high fuel pressure at the carbs plays HAVOC like stumbling.
Carbs like flow VOLUME not fuel pressure. High carb fuel pressure causes many problems. Turn it DOWN and reset the floats. If the pressure regulator is not IN front of the carbs, move it. Ya you should have a proper return style fuel system.

If you put the fuel cell and pump in front under hood you eliminate all these issues
and the bad effects of excessive high fuel pressure trying to overcome G Forces.
A consistant steady 5psi fuel pressure at the carbs is plenty.
The carb floats will control the fuel a LOT BETTER. Try it.

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Re: stumble

Post by the twister » Sun Nov 05, 2017 4:32 pm

just made a test pass, then rained out, 90 degree extensions with bowl extensions didnt make any difference, didnt have hood on and noticed a lot of fuel spray coming from slosh tubes on bowl vents, maybe this was because hood was off and siphon effect on tubes? car runs great except on launch and shifts so I believe engine can and will handle the 2 x 1050's if I can get a handle on it

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Re: stumble

Post by F-BIRD'88 » Sun Nov 05, 2017 5:03 pm

Were the anti fuel slosh baffles/whistles removed when the carbs were rebuilt?

Anti spill bowl vent tube hose extensions and the bowl vent baffles/whistles may help
on launch and shifts. Combine with less fuel pressure at the carbs. ( reset the regulator and reset the carb float setting too)
Less fuel surge and spill when the floats get shocked on launch and shifts.
Adding a anti surge float dampening spring can help with float surge too.

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Re: stumble

Post by the twister » Mon Nov 06, 2017 6:05 am

bowl whistles were shortened but I replaced them with 2 in ones, there is a lot of fuel coming out of my bowl vents when this is happening ( i have put clear tubing about 6 in above the carbs with 4 i/8 in holes in them at the top) I ran it w/o the hood and lots of fuel sprayed out the tubes and over the top of the car, not sure if this was slosh or siphon effect from no hood and scoop, I dont think this much fuel is coming out with hood on as there is no fuel on the engine after making a run

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