Holley Lemans 715 Problems

One potential problem is too much fuel pressure. The stock float settings go with stock fuel pressure which was somewhere around 5 psig (don't remember exactly but that is close). Many of the pumps today have springs that meter to way more than that like up to around 12 to 14 psig.

If all else is correct I suspect excessive fuel pressure for the float settings.

 

If the car still idles with the screws bottomed, there must be fuel
leaking into the manifold. I had this problem on my 67 Shelby
and it was the float level on the secondary side. Replaced the complete
bowl with another one with correct float level and the problem disappeared.
Another problem it could be is a broken power valve or misadjusted
secondary plaps, i.e. they are a tard open and drags down fuel.
Texas Swede

 

Has it ever run well? What jets are in it. Was the carburetor off the shelf new when you got it. In my 289 I have 10:1 compression. 351 heads tri-y headers. cobra intake and the C7 le-mans cam. It cost me 300 dollars of dyno time to find out that the factory spec jets were the best ones.. 2 or 3 numbers in either direction was a big mess. My car has a lumpy 900 rpm idle but it runs like a champ all the way to 7 grand.
these cars are a lot more fun when the run well...
good luck!
jimbo

OOPs! ....sorry I just re-read your post and saw you mentioned the jet size.
When I drive around town my exhaust pipes get black and sooty. When I get it out on the road and run the piss out of it it cleans up...

 

IIRC, in order to set the floats on carburetors with "LeMans" bowls, you have to take the bowels off the carburetor, turn them upside down, and then set them so that they are parallel with the ground. The reason for this is that they do not have an externally adjustable needle and seat or a bowl sight plug. Before you go doing that, let's get that procedure confirmed by someone who has a rebuild instruction sheet handy.

 

I don't think pop-riveting holes in throttle plates is a good idea. If one of them gets loose, you could have a big problem as it gets sucked into the engine.

 

I believe 1/2" for front float and 3/8" for rear float is the specification for GT350s. I made a permanent gage with one end 0.500 and and 0.375 on the other.

Note: Using these float levels on an original Cobra (leaf spring cars) will create several problems as engines in Cobras sit in the chassis at a different angle than in a Mustang chassis.

 

Dan is correct with the measurements on the float levels.
Please remember though, that they are from the float to the
top of the bowl. Many people makes the mistake to measure
them from the bottom and the levels will be too low.
See picture.
Texas Swede

 

First, check the float level. If that doesn't help try the procedure below.

I had a similar 715 problem several years ago, i.e. idlling with the low speed screws closed. It turned out to be the secondary throttle plates were open too far at rest. Try turning the secondary throttle plate adjustment screw until it is not in contact at all. Then open the idle screws to the stock setting. Finally, turn the secondary throttle plate adjustment screw until a reasonable idle is achieved.

I doubt a stock style fuel pump is putting out over 6 lbs., but it is worth checking if the float level, etc. check out OK.

Z. Ray

 

my cousins 67 shelby had this problem. brand new everything. no amount of tuning changed it. it was stopped when i took the manifold off and put sealant around every hole rather than just the water jackets as recommended. problem has now gone (sooted plugs and soot out the back). however, the fact you can put the screws all the way in and it still runs suggests fuel leaking

 

I know I'm a knoob, but I think it could also be a vacuum leak. I'll be interested to hear what the final problem was on this...

 

did you try turning out the secondary plate screw until the engine dies, etc. as I outlined above?

Z. Ray

 

Have you tried using a vacuum gauge while tuning your car? Again, I realize I'm new here, but if the idle screws have no affect on the engine idle, then it sounds like un-metered air some where, or bad valve timing. A vacuum gauge would be a useful tool here I think.

 

Check out Holleys web site and read about the power valve it said that if you turn the screws all the way in the car should die , If it stillruns then you power valve is bad. It also said to check you engine vacuum and it tells you how to see if you have the right power valve.

Mike