Details on 425

[phantomshafter]

After 30 years of dreaming about it, I have my idea of the perfect street rod motor running, in my first car, a 1950 Chevy. It's a 1970 292 six, with a Model E and a 425 on a Holley throttle body/single 4bbl intake, big cast iron headers, HEI, 10.5:1 flat top pistons. Everything in the engine is new. I bought the 425 used/rebuilt from a buddy who has been into propane for 35 years. It starts and runs great, will rev right up sitting with no load. But out on the road when I stab the throttle, it lays down, and sort of burbles. A couple of guys have said sounds like lack of fuel under power. I think I need to see an exploded diagram of a 425, or info on how to tune one. The big bolt on the front doesn't seem to have any effect on behavior of the motor, whichever way I turn it. When you look down the throat of the 425, you can see the end of the bolt, but there's no butterfly or anything attached to it. It is set at 10 deg initial advance, and about 7 deg mechanical. The motor behavior is the same whether the vacuum advance is hooked up or not.

[phantomshafter]

Since posting my inquiry, I have gotten a chance to look down the throat of another 425, and low and behold, there is a plate on the end of the adjusting bolt! So, I may be flooding my motor out at full throttle. I'll switch mixers this weekend, and report on the results.

[Frank]

The power mixture bolt just restricts the amount of fuel flowing through the mixer at high air flows. The plate has to be there for the adjustment to work.