Hi hi just about to start upping the boost the engine has been rebuilt and done about 1000 miles the carb rebuilt with the kit not had much to do with carbs just want to know witch jet to drill out in what order and what increments to go up in any help much appreciated got an afr gauge its at 12.3 ish on 15 psi at wot .
First thing - I would stop booting it as you are very very lean. Far too lean on WOT
If you have a look at the guides ( articles ) on here you can find what you need
( example )
What revs is that at???
12.3afr @ 1bar/wot is fine, assuming o.e c/r, ignition timing, etc.
Trusty was running a wot afr of 12.5 for years.
If no det' is present, then all is good
I need my eyes testing !
I could have sworn I read 12.3 on idle and 15 on WOT
Hi it's 12.3 at 15 psi at wot it's got wossner pistons with a lower comp ratio a piper 285 cam at 4degrees advance on verneir no det revs at about 6500 what is the best way to go about tuning the carb thanks
Originally Posted by andybond
I need my eyes testing !
I could have sworn I read 12.3 on idle and 15 on WOT
Been a long day mate??
120 main jet
1mm air corrector
1.3m second stage
I use this for 18 psi. With no pinking/det
Correct me of I'm wrong Mart... Just learning myself.
Different horses for different courses, every engine will be different and need different things.
There's no set pattern with carb (re)jetting I'm afraid.
Hi thanks for the info i understand each engine is differant just didnt know witch jet to start drilling first and in what order to adjust the afrs to suit the boost
2nd stage enrichment cct for boost/wot. You shouldn't really have to touch the other jets.
Drill the 2nd stage out a bit at a time, start off at 1.2 then up to 1.3mm. Next step for more fuel is to make the air corrector smaller.
I think at 18psi, i made the acc slightly smaller, and drilled second stage to 1.2mm @ wot i had afrs in the region of 11.7
Prefect example! On my brothers engine with a full T25(18psi) low comp pistons and a 285 camshaft we needed
1.3Mm second stage
1Mm a/c
Standard main
This gives 12.2 afr @WOT upto 7k rpm
Thanks for the reply going to start this afternoon with 2 nd stage and take it from there
Hi drilled the 2nd stage out to 1.2 and im getting 11.7 at wot now is it just acase a case of upping the boost a little at a time and enlargneing the 2 stage to match or will i need to mess with other jets thanks
..
The bowl on mine emptys at 7k in 4th. Is it a case of different ac to change this If I was to up the boost... Sorry for hijack lol
If you are emptying the bowl you need to make the needle jet bigger, 2.0mm plus. You can buy them but you can drill them if your carefully, if you decide to drill it do it by hand and then try to press the bearing back into to it turning it at the same time to remove the swarf and help it seal, other wise it may leak and your back to square one with a problem.
just bear in mind 2nd stage is a fixed bush (therefore you cant make it smaller) (easily). Therefore i prefer to make the ACC jet smaller to begin with.
Do you think for high boost tuning, I would be better buyin the goodies and taking it to scoff??
your car was fine in 1st/2nd/3rd
Just the top of fourth, you already have a 2mm needle valve, a phase 1 pump (better for higher boost). New fuel filter, so unless your pump is tired.
Only things left to try are removing the little gauze filter in the carb fuel supply fitting or getting your mits on an ajustable fpr, or slightly larger needle valve.
Tuning on the road can be difficult but not impossible.
Basically yes, you need to also take into account det/pinking, no set threshold for this occuring I'm affraid, an easy and cheap way to listen for it is to plumb a stethoscope in off the cylinder head. Even with this it can still be difficult to pick out the noise it makes. Det can destroy an engine in no time.
There are some great articles on carb tuning in the articles section that will probably answer most of your questions at first.
theres nothing better than diy tuning imo.. at least then should you change engine etc your not gona loose the tune as you have the skill/ability to do it again yourself.. For the less confident though scoffs the only guy id ever approach.
Back in the day, I drilled out & threaded the bush to take an air corrector/1st stage jet - That makes it totally flexible then, although not much point drilling the jet/original bush past ~1.3mm anyway, unless other 2nd stage mod's have been carried out.
As I mentioned above, for boost/wot fuelling no other jet should be/has to be touched
To the OP; if the float chamber is emptying, you either need to up the fuel pressure, but not so much that the float/needle valve won't then close against the raised pressure, or open up the needle valve, but again, the extra flow might cause problems with float operation, which is why some people have problems after fitting the 'German Ebay' 2mm needle valve.
Cue the main jet cover plug mod'...
Posting Permissions
Reply With Quote
