Weber 36 IDF jetting

[karolp]

Hi i need some input on carb jetting.
Engine is 1755 (90x69 nikasil cylinders), 8,4:1 cr, c35 cam, stock valve heads slightly ported, 009 ignition, 10 deg. btdc static advance.
After initial break in and first 300 km i checked plugs beacuse i have a feeling that it runs a little bit too rich - whilie quickly upshifting at higher 4500-5000 rpms it bangs and fires from exhaust muffler. Otherwise motor runs great.

My carbs are alfa romeo weber 36 idf with 30 venturis and:
f11 tubes
52 idle
135 mains
190 airs

Should i go leaner on mains? bigger air jets? Any advice will be apperciated.
Thats how my plug looks - click the link it should open in new window:

[modok]

If you know what conditions of throttle position and RPM you need more or less fuel I'm pretty good at figuring out how to make the carburetor do that.

BUT

I have had very poor luck guessing what jets somebody else's engine needs beyond a starting point. I'd say you are started already. Should work good enough to drive.
Backfiring on decel is not necessarily a real problem. They always do that, some more than others, and some mufflers do it loud, some keep that quiet.
if severe it is usually an exhaust leak or an excessively short tailpipe is the problem.

And those extendo-cock spark plugs and modern gas both make it real hard to do plug reading.
BUt it can still kinda work.
Gas is more clean so it does not color as fast as old days....so, what you have to do is run the engine "in the condition" you want to check for a good 20-30 seconds, then kill it, pull a plug and look DEEP in there. Might need to find a long hill or whatever and no traffic to even do that.
My guess...that plug says your mixture is correct at least half the time but beyond that who knows.

[oprn]

I love my AFR meter. Worth every penny in time spent tuning and confidence that I know what the mixture is at a glance at any rpm and engine load.
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We had the stone age, the bronze age, the industrial age and now we are in the age of mass deception and mind control for corporate profit. (The mass media age)

[karolp]

Just FYI i got my engine dyno tested with AFR probe (no graph overlay).
It turns out, that my jetting with 125 mains is at least ok. WOT afr on dyno was 13.2:1 at 4000+ rpms, light load at criuse rpm 16:1 - not too lean?

What do You think on dyno results?

[Alstrup]

Looks quite ok for a mild engine.
Wrt jetting. Lean or not. I would encourage you to find a 043 905 205, 113 905 205L or This https://www.ebay.com/itm/144084822102?hash=item218c1fe856:g:iNYAAOSwpCtg0bcu Rebuild it and make the timing curve your engine wants. Then you have the vacum advance on cruise and then 16-16,5 on cruise is no problem
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https://www.thesamba.com/vw/forum/viewtopic.php?t=435993

[karolp]

[Alstrup]

[karolp]

First dist i found in my shed. As far as i understand, recurving distributor is about adjusting the max advance limits, changins springs and/or altering weight of those little weights or wahtaever it is called. But figuring exact amount without special machine seems like hit or miss.