The Stovebolt Site Forums The Shop Area The HiPo Shop now i've done it, how to time it?

Well, I've gone and done it now! I've up-graded my "54" 1/2 ton by installing Patrick's 3:55 to1 ring&pinion, added the modified 2-ring Saginaw, rebuilt the 235 with a 3/4 mild cam, ballanced it, hardened the valves, added the dual intake&exaust manifoldes..... Now..... to time it! The carbs where built as a pair with the # 57 jets replaced with #51's. I haven't done anything with the power valve springs yet. I'm still trying to find its sweet spot in timing. I've been told by some that the vaccuum advance unit is no longer useful and I've tried timing it with and w/o but even at 20 degrees advanced, it still stumbles off the dime. Me thinks I'm dealing with too many variables at once here for me to see a clear path to a good tune. Any advice?? Timmer,you where wise to sneak up on your project in stages.

Are you still running the stock distributor? If so, you should hook the advance back up. The stock disributor's advance curve is setup to run with a vacuum advance. If you do not want to run a vacuum advance. I'd suggest getting a Mallory unit from Patrick's. Set it up with a 3rli Hyfire control box (no ballast) and about 10-15 degrees advance. Should run fine with setup.
Perhaps some of the other 'Bolters can shed some more light on what options are availible for a system with a vacuum advance that would work with the cam you have. By the way, I'm running the same setup on my '55.

Its been my experience that the 235 with the Howard 3/4 cam and the dual carbs don't like a lot of timing. Try stock timing and hook up the vac advance.

Seems like 51 jets are kinda lean. I think you are bogging from too lean mixture.

Wrenchbender; If my #51 jets are too lean, should I be able to se evidence on my plugs of too lean a mixture? They don't look like the classic starved color.

Sorry, I am not too familiar with the dual carb setups, except on a VW.

Is the stumble off idle, or only under load?

In my experience with my Q-jet, an off idle stumble would be fuel related. Are the floats in the carbs set too high? Are the carbs synchronized?

What kind of carbs are we talking about? A pair of Rochester single-barrels?

I've had a good deal of trouble in the past with the original Rochester 1BV off my '66. They use a piston-type accelerator pump. Over time, the pump chamber gets worn and the piston will no longer seal, even if it's replaced with a new one. That could explain your stumble right from the get-go.

Might I reccomend a pair of Weber ACHs? Excellent design with ball-bearing throttle shafts, and every jet is easily accessable, making for a very tunable carburetor.

Flunky1,
At 1299 feet at Tonasket, Wash you may be about right for your main jets .o51. Where is the color change on the ground? The further it is towards where it is welded near the threads the leaner it is. You know the main jet size is correct when the color change is 1/2 way to the tip.

52PU; Thanks for the color code tip. I'll use it. Also Gearhead66; I'll ask some pointed questions to my carb rebuilder. They are indeed Rochesters, and the core's petigree is unknown. As you see "saved a 48"; you are sniffing up the same trail as the other hopless cases. May we never be cured!!! Must go pick some tree ripened preaches to bring me back to the other world.