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Huw

su problem

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hey everyone

 

got a small problem in that my front carbie is acting normally (sucking like a vaccuum cleaner!) but my back one has almost no suction at all. thus I'm getting a funky idle.

 

I'm currently looking for an air leak somewhere, but have spent 2 days tightening and clamping with no luck.

was wondering whether anyone would have any suggestions?

 

I am running headers but we were pretty careful when we mounted them to avoid a leak. (and they're a bastard to get at!!)

 

cheers

Huw

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is the butterfly in the rear carbie opening the same as the front one? maybe the bushes on the buterfly shaft are worn out bad on the rear carbie.

 

Ash

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you could spray some kind of liquid around the suspect carbie to try and find and airleak (aerostart for example will make it rev up if its getting sucked in.

 

Couple of things to maybe check - level of the damping fluid (generally auto trans fluid or similar) in the dashpot of the carbie? It might be possible that your diaphragm inside is flapping up and down madly...

 

Also, have you tried fiddling with the idle air screw on the second carb? Or is it controlled by a balance mechanism off the first, like the crappy Hitachis? If it has its own idle air screw, try turning it anticlockwise two turns, and see if anything changes... If it doesn't go back to the original position, then try two turns the other way - usually though anticlockwise is 'lean', or allows more air in.

 

The only other thing that comes to mind is possibly a blocked idle jet - maybe try pulling them out one at a time (so as not to mix them up :P) and blowing through them to make sure they're clear. CAUTION: do not stick wire down the insides of them to clear them. use compressed air, and/or dip them in petrol to clear them, or if its really desperate, try some fishing line - carefully. The brass is very soft.

 

Failing that, try just ringing a carbie specialist - SU's are pretty common and pretty simple, so any problem you're having should have been encountered before many times, and they may be able to give you specific directions. I can think of many things to play with inside the carbie, but at the moment I can't think of a way to connect them to your fault....

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think i got it....

well just before work i started playing with the individual throttle adjustment screws a bit more, have equal air flow now, but still doesn't seem quite right......think I'll go through the full tuning process tomorrow.

 

will get the aerostart tomorrow and check for leaks..apart from that the carbs should be ok as they were fully rebuilt and bushed a couple of months ago (and haven't been used since)....

anyway, thanks for the help.

 

Huw

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it sounds more like tuning issue, but after doing zedophiles test. if its not that....

 

most likely, air leak.... theres actaully a carby cleaner product... mostly like WD40, but more for carbies, use that before tuning to clean it up a bit... intructions are easy rev the car to around 2k, then spray in the intake of both carbs, and it will free up parts etc, if things are stuck,,,,

 

i also found atf the best fluid for my 240z Su's///

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