Type 1 jetting problem (I think)

[advokat]

I just built a 1904 (74 x 90.5) with a web 119 cam, dual spring ported and polished heads with 40 x 32 (or 40 x 35-I forgot which) valves. Exhaust is a merged 1 5/8" header with a fat boy. 009 dist. Carbs. are dual Dell 36's.

Engine is just barely broken in and I will be doing a valve adjustment as early as this weekend.

Anyway, in low to mid rpm's the car runs smoothly and pulls really well. When the rpm's get higher, though, it loses a lot of power and runs much less smoothly.

It is also a complete bitch to restart quickly after a good long run that heats things up. After some cool down time, it fires right up.

I've been told that I have a vapor lock problem that could be from my fuel line being too close to a heat source-or-that my poor running in the top end is causing a lean condition and the engine to run hot and that is causing the vapor lock condition.

Either way, those that I have spoken with all seem to think that I need to consider new main jets and/or venturis. The CB Perf. Dellorto book seems to say my mains and vents are too small.

The guy I bought these carbs from says they are factory jetting specs.-which should mean 30mm vents with 122 mains, 60 idles and 50 acc. pump, 180 air. I am thinking about bumping up the mains to 140 and not messing with the vents at all unless my problem persists.

Can anyone give me some insight here as I have never had to tune dual carbs. like this before.

Sorry for the frickin' novel, but I am trying to give complete information here.

Thanks

[havik180]

I'm no professional but arent 36's a bit small for a 1904 w/ a cam and head work ?! I would think that that may be part of the problem,but I am unfamiliar with the specs of that cam.

I found these "formula's" in the back of a book by Keith Sume :

carb size = Sq root of (cc per cyl, x max. rpm) divided by 40

choke dia. = carb size x 40 , divided by 50

main jet = choke dia. x 4

Maybe somone who knows better can chime in about these figures !

[advokat]

I went ahead and bumped up the mains from 122's to 130's, but left everything else as is.

After a good ride today, I had great improvement throughout all rpm levels and with no sluggish or poor running. Pulled smoothly and well right on into the high rpm's.

Thanks for the input.

Rick