SU issues

[allgearnoidea]

Hey. Long story short, my A series 1340 has developed a misfire at around 5500rpm and above. Ive replaced all the usual suspect electrical stuff but the miss remains. I have now turned my attention to the weber 45. Not being a weber expert I have replaced it with a hif44 which was removed from a mate’s working 1380 about 4 months ago. I’ve done this to see if the misfire persists with the su. Now, I cant even get the thing to start, there’s not even cough, theirs is a spark, but I think fuel is failing to get out of the float chamber? The carb seems to be in serviceable order,(and yes ive connected the carb up correctly) ive had a gander inside the float chamber and had the piston/needle off, all seems ok? Im running an electrical pump/regulator still set up for the weber. Any ideas please..on either problem..

[blitzracing]

IF you have fuel coming out of the float chamber either the input fuel pressure is too high although from what I remember the of the mini pumps they stop when the max pressure is reached, so the pump SHOULD STOP with the ignition on after the float chamber is full. Otherwise the float height is wrong, the float has punctured, or there is muck on the float valve seat if the pump keeps ticking.

[allgearnoidea]

Its a solid state fuel pump and as far as im aware is always pumping. the float chamber is filling up as it should and the float is cutting the fuel when its full as it should,the problem is thereafter.
Oh and ive just had it running with the weber back on so there is a problem with the su. Ill have flush it out or something.

[Pigeon]

If you take the suction chamber and piston off so you can see down into the top of the jet, is there fuel in it?

Could be some dirt or a dead spider or something has got into it while it was not in use. (The spider wouldn't have been dead when it got in, of course, I mean it was alive at the time and then died in there.)

[Pumaracing]

allgearnoidea said:

Hey. Long story short, my A series 1340 has developed a misfire at around 5500rpm and above.

Take the rocker cover off and see if you have a broken valve spring.

[davepoth]

It'll be an ignition fault I think. The spark isn't strong enough for proper ignition at high revs.

[stevieturbo]

Although if he cant get it running with an SU...one of the simplest carbs in existence.

Maybe it's time to find a mechanic.

[allgearnoidea]

Yeah, have you seen my name pal! Its just pissed me off by trying to solve one problem ive introduced another in the form of a fked carb, i had reason to believe fuel was getting through, when i removed the su and manifold there was a collection of dashpot oil overfill sitting in the manifold and i 'assumed' it was fuel. my fault i know. i reckon the reece fish is simpler anyway.

[duncancallum]

SU's very simple but its like a lot of things the simpler they look the more complex it is.

Have you got it running on the SU?

I have to say at 5500rpm I would of thought more towars an electrical fault.