Hemi stumble/sputter on starting line ???
#1493435
08/31/13 09:25 AM
08/31/13 09:25 AM
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Joined: Feb 2012
Posts: 54 Strongsville, Ohio
Charlie Moore
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I have a '65 Coronet with a 514" Hemi, Mopar crossram with 2 Holley 770's. Footbrake car. I have tried 2 converters and the current one will only allow a launch of 2600 rpm. On the hit of the throttle the car stumbles and actually spits back thru the carbs which is visible when we try with the hood off. It will stumble for a bit maybe 100 -150 ft. and then take off like a rocket and run almost 140 mph. Now for the things we have tried are two different sets of carbs and going lean and fat with both. Different ignition wires. 3 different types of plugs. Different MSD 7al2, Compression test, Leak down test, Crank trigger, crank trigger wire, reroute crank trigger wire to avoid RF. By pass crank trigger and use distributor. We did find a broken intake valve spring and thought great that's it. Went to a track rental this past Monday ready to make some good hits and had the exact same problem. We have spoken with several engine builders across the country and they have all taken the time to listen to everything. After they have a while to think about it they have all said it sounds like everything is right. We degreed the cam a while back and we are going to check it again today just to be sure because it really acts like the intake valves seem to be closing a little late. I posted this today as it marks my 3 month anniversary since I first took this car to the track and we are no closer to a resolution. Any thoughts would be greatly appreciated. Thanks in advance.
Charlie Moore 440-846-3777
Last edited by Charlie Moore; 08/31/13 09:44 AM.
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Re: Hemi stumble/sputter on starting line ???
[Re: Charlie Moore]
#1493436
08/31/13 10:09 AM
08/31/13 10:09 AM
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Joined: Jun 2003
Posts: 52,972 Romeo MI
MR_P_BODY
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Master
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Romeo MI
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It really sounds like your accelerator pump and squirters being its right at the hit... is the pump arm moving as soon as you move the throttle blades EDIT Whats your timing at
Last edited by MR_P_BODY; 08/31/13 10:11 AM.
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Re: Hemi stumble/sputter on starting line ???
[Re: MR_P_BODY]
#1493437
08/31/13 10:13 AM
08/31/13 10:13 AM
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Joined: Feb 2012
Posts: 54 Strongsville, Ohio
Charlie Moore
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The squirters have been replaced with larger and smaller ones. The cams that push on the accelerator pump arms have been replaced and modified to give the major shot after stage rpm. Thank you for the input.
Last edited by Charlie Moore; 08/31/13 10:18 AM.
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Re: Hemi stumble/sputter on starting line ???
[Re: Charlie Moore]
#1493441
08/31/13 10:25 AM
08/31/13 10:25 AM
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Joined: Jun 2003
Posts: 52,972 Romeo MI
MR_P_BODY
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Quote:
When I try to free rev it, it will go to about 4000 rpm and stumble momentarily and then jump up.
The reason I ask if it will free rev is that will eliminate the drive line/conv... it still has the problem but less and at a different rpm.. load just makes it worse.... have you sprayed the intake for vac leaks
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Re: Hemi stumble/sputter on starting line ???
[Re: Charlie Moore]
#1493443
08/31/13 10:33 AM
08/31/13 10:33 AM
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Joined: Jun 2003
Posts: 52,972 Romeo MI
MR_P_BODY
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Quote:
I'm not 100% sure what you mean when you say spray the intake? I've heard of it, but what are you spraying it with?
Spray it with carb or brake cleaner.. it has to be a flammable product ... but if its leaking it will suck in the carb cleaner and you will hear the revs come up(its burning the cleaner like fuel)
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Re: Hemi stumble/sputter on starting line ???
[Re: Charlie Moore]
#1493446
08/31/13 10:49 AM
08/31/13 10:49 AM
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Joined: Jun 2003
Posts: 52,972 Romeo MI
MR_P_BODY
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Quote:
With this creating a super lean condition on the opening of the throttle, have you seen it start spitting back like I tried to describe?
Any time its super lean the spark tries to chase the fuel so yes its common to have it spit back and fart through the carb
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Re: Hemi stumble/sputter on starting line ???
[Re: Dodgem]
#1493448
08/31/13 11:10 AM
08/31/13 11:10 AM
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Joined: Jun 2003
Posts: 52,972 Romeo MI
MR_P_BODY
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Quote:
My uneducated guess is the problems are in the vacuum secondairees maybe opening to fast and maybe too lean or rich at first.
That could be an air bleed problem not allowing enough fuel in right away.
probably opening too fast and too lean combination??
Very well could be... but he has tried 2 sets of carbs... but that really doesnt mean much if both sets of carbs were set up about the same
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Re: Hemi stumble/sputter on starting line ???
[Re: Dodgem]
#1493451
08/31/13 11:31 AM
08/31/13 11:31 AM
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Joined: Jun 2003
Posts: 52,972 Romeo MI
MR_P_BODY
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Quote:
So he says lean and fat if it goes lean then fat it sure could be the secondairees coming open too soon lean with no air flow no initial flow from jets then maybe fat because of jetting and or air bleeds??
I took it that he jetted it leaner and fatter
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