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Old 08-03-2005, 07:05 AM
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Accelerator pump pullover

I've been working on a customers 2.2 Mopar circle track application and I've been trying to debug a high RPM miss he's encountering. The engine gets to 5500 ok but when it approaches 6000+ it starts missing. What I've noticed is that it begins pulling fuel out of the accelerator pump squirters and fuel starts splashing out the vent tube. At this point it begins missing from the extra fuel. The carb is a 350cfm two barrel. Float level is good, the vent has the plastic duckbill, the squirter is the standard type w/o the extensions. Any thoughts on how to prevent the pullover condition and why it's splashing out the vent.

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Old 08-03-2005, 07:10 AM
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fuel

Is the small steel seat under the squirter still there????

I have seen carbs do this when that is missing...

keith
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Old 08-03-2005, 07:46 AM
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Yes it's there. Keith I also tried a straight type squirter that's supposed to be anti-pullover. My next thought is to keep going down with the squirter size to try and minimize the effect. It's a 28 right now.
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Old 08-03-2005, 07:49 AM
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leak

how about the brass insert that it seats into,,, Is that in good condition???

also is the vent open???

keith
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Old 08-03-2005, 08:21 AM
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Not sure about the brass insert. The vent is open, right now it has the plastic "duckbill" attached to the metering block that extends into the bowl. I might also try more spacer under the carb to deaden the signal.
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Old 08-03-2005, 09:37 AM
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Squirter Pullover

Is it actually pulling fuel out of the squirter, or is coming out from vibration? Vibration is extremely common on the 4cyl engines. If it's coming out of the vent tube as well you're probably looking at a vibration problem, and you need to look into some type of isolators.
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Old 08-03-2005, 10:00 AM
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Vibration was something I was thinking about. I might try to extend the vent tube a bit. Isolating the carb might be an option, not easy but an option none the less.
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Old 08-03-2005, 10:09 AM
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Quote:
Originally Posted by engineczar
Vibration was something I was thinking about. I might try to extend the vent tube a bit. Isolating the carb might be an option, not easy but an option none the less.

Very common on 4cyl race engines.
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Old 08-03-2005, 09:13 PM
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Some stainless steel wool rolled up and inserted loosely into the vent tube will stop the splashing from there, I agree that vibration is your problem. I think you will find that a set of heavy duty support straps that hold the intake manifold and bolt to the head (or ideally lower on the block) will reduce the frequency of the vibration and stop the nodal peaks that can occur whenever a hanging piece of metal is excited by vibration.

When you fabricate the straps make them heavy duty or they can vibrate causing other problems, round tubing with heim joint ends look cool and work well but angle iron bent and welded to fit has worked for me too. You may have to drill and tap holes in the intake to find a place to mount the support straps (the closer to the carb mount the better). I would use at least 1/2" fasteners, any less and you could shear the bolts...yep the vibration is that severe.

Remember the intake is a sizable chunk of metal hanging off the block, add the carb and fuel inside and I'll bet your looking at 30-40 pds floating there. the mounting bolts are heat treated too so they are like spring mounts and the gasket a flexible seat. You may find that removing the gasket and going metal on metal (with non hardening sealer doing the sealing duties) will help immensely also. I'm willing to bet your misfire is due to an intermittent vacuum leak at the intake manifold gasket interface from the vibration too.

Check it out.
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Old 08-04-2005, 06:35 AM
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Quote:
Originally Posted by 4 Jaw Chuck
Some stainless steel wool rolled up and inserted loosely into the vent tube will stop the splashing from there, I agree that vibration is your problem. I think you will find that a set of heavy duty support straps that hold the intake manifold and bolt to the head (or ideally lower on the block) will reduce the frequency of the vibration and stop the nodal peaks that can occur whenever a hanging piece of metal is excited by vibration.

When you fabricate the straps make them heavy duty or they can vibrate causing other problems, round tubing with heim joint ends look cool and work well but angle iron bent and welded to fit has worked for me too. You may have to drill and tap holes in the intake to find a place to mount the support straps (the closer to the carb mount the better). I would use at least 1/2" fasteners, any less and you could shear the bolts...yep the vibration is that severe.

Remember the intake is a sizable chunk of metal hanging off the block, add the carb and fuel inside and I'll bet your looking at 30-40 pds floating there. the mounting bolts are heat treated too so they are like spring mounts and the gasket a flexible seat. You may find that removing the gasket and going metal on metal (with non hardening sealer doing the sealing duties) will help immensely also. I'm willing to bet your misfire is due to an intermittent vacuum leak at the intake manifold gasket interface from the vibration too.

Check it out.

GREAT points. We've also had a very good luck using a heavy durameter rubber as an issolator between the carb and intake.
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Old 08-04-2005, 07:15 AM
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Thanks for the ideas. He's racing it again tonight so I'll have more feedback tomorrow. This is his backup engine and I want to get all these issues resolved for his primary engine.
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