mixture and timing questions

68notch Casual Dubber

32 posts · joined May 2003 · 12 Nov 2004, 6:55 pm

#262637

Can someone suggest if the carb jet sizes need to be / can be changed when a big bore kit has been installed? For example I've gone from 1600 to 1776 running dual solex 32pdsit's in a type 3. Although this will only be temporary I want to make sure that the mixture is not lean.
Also, does the compression ratio and bore size affect timing or is that only related to the cam? (it's stock)
Thanks very much for any help!!
JT

AdrianH Officially Full-On Dubber

257 posts · joined Mar 2004 · 12 Nov 2004, 7:11 pm

#262652

High compression may require you to reduce the advance you run, dependant on cam and combustion chamber design.

You can check your mixture by reading plugs. Find a hill, run up it (in the car) switch it off without reducing revs. Anything 2000 and under will be idle jet, 3 - 4000 plus will read your main jets. Black sooty is rich, nice brown is on the money and white is lean.

68notch Casual Dubber

32 posts · joined May 2003 · 12 Nov 2004, 7:16 pm

#262660

Thanks mate!
Yep, I guess it's all in the plugs :-) Will check 'em. If it's lean then what jets can or should be changed?
Also curious if semi-hemi heads and low compression would indicate that timing should be retarded, advanced, or would stay the same as what the book says. (Idiot's guide)
Cheers!
JT

Bizarre Moderator The artist formerly known as blue74l

12,787 posts · joined Aug 2002 · 12 Nov 2004, 8:30 pm

#262716

For the money you have invested go for a drive and get it dynoed.

You are at Dural - not that far from Penriff.

Go and see Mike at CBB. Get it dynoed and find out if it is lean rich or what ever.

Futue te ipsum!!!

68notch Casual Dubber

32 posts · joined May 2003 · 12 Nov 2004, 9:50 pm

#262771

Cheers Blue!
Can't see the point in having it dyno'd before the turbo is fitted. Also, I would like to have a chance to run it in b4 thinking about a dyno. As you might have guessed I am very much a hands on person when it comes to my Dub. Just want to be sure that it's going to run well and remain reliable until such time as I am ready to "soup it up".

AdrianH Officially Full-On Dubber

257 posts · joined Mar 2004 · 13 Nov 2004, 5:46 am

#262903

With plugs you can read each cylinder, with an a/f meter you get an average of all cylinders, and there can be differences.

68notch Casual Dubber

32 posts · joined May 2003 · 13 Nov 2004, 5:03 pm

#263223

I agree especially with dual carbs!
How will I know if I am running too advanced?
The idiot's guide suggests that timing is quite different on an aircooled engine compared to a watercooled one meaning that I couldn't just run as much advance as I liked until it was just short of pinging. Any comments?

Bizarre Moderator The artist formerly known as blue74l

12,787 posts · joined Aug 2002 · 13 Nov 2004, 7:33 pm

#263308

68notch wrote:IHow will I know if I am running too advanced?

It will ping

Futue te ipsum!!!