I have a hesitation at 2500 rpm when I get on it hard. The engine is a 454 LS7 with a tunnel ram and two 600 Holley's. I am running an MSD with the timing locked out at 38 degree's. The engine has 12.5 to 1 compression, so I run 110 race fuel.
The thing runs great other that the hesitation.
Any ideas on what may be causing this or what to check? Thanks
[img]http://free.***boat.net/gallery/Gearhead_Garage/Other_Equipment/IM000173.JPG[/img]
Hestitation could be from many different sources. If it has all of a sudden just started to happen, I would say that a vacuum leak is in order. Otherwise the accelerator pump diaphragm may be collapsed or bad.
Otherwise check the fuel filter.
Call me if you need to some help
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-Ty
I run 850 double pumpers and for me it was a simple tuning procedure that solved it. I changed the accelerator pump cam on the secondaries to a more aggressive position which then gave me a quicker shot of gas and help solve the hesitation I had when transitioning into the secondaries.
Accelerator pump is the problem. Sounds like you need double pumpers. I do not know if you can change the accel pump cam to work that late or not. That manifold gives a very poor signal to the carbs. If those are vac secondaries, you might try a stiffer spring so the secondaries do not flop open.
Most of the time a hesitation is caused by a fast increase in air flow but the fuel flow lags slightly. That is what the accel pump does. It gives a squirt of fuel until the main metering system catches up. That manifold gives a poor signal to the carb. which multiplies the problem.
What you say makes sense, it is when the secondaries kick in that it hesitates. The secondaries are vacum. The hesitation has always been there, but I am just now to the point of dealing with it. Where it's a problem is crusing around at 2000 rpm and when I step on it hard it has a hesitation before it really takes off. The carbs were freshened up this sping, but I just now have enough seat time to start running a little harder.....Thanks for the help.....
Your problem is in the primaries, at 2000 the secondaries are closed, you don't have enough pump shot to cover the hole when you stand on it. What size are the shooters??...
GofastRacer:
Your problem is in the primaries, at 2000 the secondaries are closed, you don't have enough pump shot to cover the hole when you stand on it. What size are the shooters??...The above post is right---order some larger nozzels and go with a 50cc diaphrams---the tunnel rams need a big squirt when u first hit it---if u can't find local, go with summit or jegs--regular holley stuff--
[/QUOTE]The above post is right---order some larger nozzels and go with a 50cc diaphrams---the tunnel rams need a big squirt when u first hit it---if u can't find local, go with summit or jegs--regular holley stuff--[/QB][/QUOTE]
Yep, going with the larger diaphragms did it for me. It's a long way down from the top of a tunnel ram!
The problem is not with his current set-up but with an issue that had started to plague him at 2500RPM or so.
Possiable problems??? Busted accelerator pump diaphragm, power valve busted or incorrect, or even a vacuum leak in the baseplate.
Do not increase the pump shot or squirter sizes...those types of mods are not used for correcting issues that arrise when you have been running great before....
Also note- according to the pics he already has 50cc shots, from the looks of it...
Like I said in our phone conversation...plug the powervalves, increase the primary jets, and eliminate the powervalve concerns. If the problem is still occuring, check the accelerator pump diaphragm for a collapsed umbrella. Make sure your check ball or umbrella seal is in place and functioning, and lastly....Pray there are no vacuum leaks within the primary throttle shaft. Any loose wobbling conditions are vacuum leaks waiting to happen.
-Ty
[ August 12, 2002, 10:10 PM: Message edited by: Hotcrusader76 ]
I will give it a try this weekend and let you know how it goes.........Thanks for the help and ideas!
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