engine valve to piston clearance problem

Well, you should have had plenty of that......

 

Hawg, The hilborn unit is quite flexible and takes the shape/angle of what it's bolted to.We changed heads once and had to reset the cross linkage to achieve balance--must have been a slight angle or height difference.
Thats the beauty of using the flowmeter(uni-syn) you can see slight differences in flow.When its real even the idle,throttle response, and restart will be impressive.

 

Root, I agree with ENGINENUT. I don't know that much about the Hilborn specifically, but I know a little about fuel mixture problems. A mid-range stumble comes from the fuel system, rich or lean. I fought the same thing trying to get a Holley spread-bore carb to work. Mine was getting too much air until it came up on the cam, then it pulled hard.

 

Oh yeah, get yourself a new set of valve springs and check the cam clearance with Play-dough. I don't think you have a big problem there.

 

I don't suppose you could have fuel puddling or loading up somewhere that gets upset and sucked in when the car launched? What about uneven cylinder temps causing fuel to drop out of suspension on one or two cylinders? Or maybe fuel sloshing in the tank on launch is causing an air bubble to get sucked into the feed line? Just tossing out random thoughts since you seem to have all your other bases covered...

 

The tank is the same tank that ran with this engine since 1960 or so. I opened up the vent line to a 3/8" opening as well.

I'll hafta investigate the butterflies.....thanks for the input.

 

I would stck with the fuel theory. It has to be something really stupid. Check everything, I mean everything. Hope you get it figured out.

 

About the cam...Since you are changing it, did you measure the valve lift on the mystery cam while you had it installed?

The reason I ask is because if your new cam has any more valve lift, you are probably going to have to either run thicker head gaskets or fly-cut the pistons.

 

Bass, yeah we have a rough estimate. It was about .510". The pistons are fly cut but we may hafta go a little deeper. There's plenty of material inthe pistons still...

 

Where's your fuel tank? The fuel level needs to be above the pump inlet. Supposedly Hilborn pumps won't suck, fuel needs to be gravity fed to the pump inlet.

 

This was my thought, could the initial launch G-forces be causing a lean condition after launch? I agree the stumble seems to be fuel related and not ignition.

 

Do you have a fuel pressure guage in the car? If not get one. That would be the best way to confirm this theory.

 

looks like to me, maybe valve springs are too weak for the rpms you are trying to turn or you need to relive the pistons where you are having the interferrance, if the decks arent square, you will only have a couple cyls
not happy,
worn valve guides may also cause at full lift some deflection in them to hit close piston to valve clearance

dont look to be lean to me.

good luck

 

The tank is a vertical tank and it is mounted about 6 inches higher than the pump. The tank is also the tank that was with this engine in the 60's. It ran with the tank until 76 or so.

 

Good luck Root...keep us all updated on this one...more than one of us will surely benefit from all of this....Thanks