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Basil
04-06-2003, 12:35 PM
Tuning Question:

My 78 Spit has dual Weber 40's and a hot street cam. I'm not sure the exact specs on the cam, but its not a race cam, just a hotter street cam that Victoria British recommended with the dual Weber carbs. The car seems to have a flat spot in power and torque at higher RPMS and doesn't accelerate like I think it should. Two things I think may be at play here. First, I suspect the carbs are too rich, and second I think my timing may need to be set differently. DOes anyone have experience with this setup who could recommend the proper jets to use with my Webers (I'm at 6,000 ft altitude) and also what timing would you recommend?

Basil graemlins/crazyeyes.gif

aeronca65t
04-07-2003, 01:00 PM
Probably the most important part of timing for a car like your's is in the upper RPM range (otherwise, why have dual Webers?).

When I set my 1500 Midget (time trials car), I set the timing at 35 degrees at 5000 RPM. By the time the engine is at 5000, the distributor should be at max advance. I don't worry about timing at idle (but it's about 10 before at idle with my modified distributor).

Obviously, this can be a difficult process (who wants to have their nose up against a screamming engine?), but it's the best overall way (esp. since you have no emissions specs in NM).

Some folks invest in a degree wheel for this purpose, but I just figured out where 35 dgrees was on the front pully and made a mark there...when it lines up with "Zero" on the pointer, I'm good to go. You can play around with 32 to 36 degrees (at 5000 RPM)...soemwhere in that range should be about right.

At your altitude your stock jets are probably too rich.....but I'm not sure of about "correct" ones.

Basil
04-11-2003, 12:34 AM
Yeah, I'm pretty sure I'm too rich (and so are my carbs, nyuk nyuk). I think I'll try rechoking the webbers (I think I have too much carb on there) then re-jet them a couple sizes leaner. I also know I need to hook up my vac advance and then I'll try setting the timing as you suggest. I just know this car can run a lot better than it is.

Basil

[ 04-10-2003: Message edited by: Basil ]</p>

Dave Russell
04-15-2003, 10:01 PM
Bas,
You might find this helpful for weber choke & jet sizing.

https://members.aol.com/dvandrews/webers.htm
D

coldplugs
04-15-2003, 10:28 PM
Lots of venturi area for street use, I suspect. I'd start by installing the smallest dia chokes available and trying to get good midrange. You need some air velocity through there to pick up the fuel reasonably well. The link provided in the previous post probably has the info you need.

Also, look at:
https://www.lotuselan.net/uploads/weber.pdf

and:
https://www.lotuselan.net/publish/tuning_dcoe_carbs.shtml

The one above has info on tuning for altitude.