Su related problems. Help much appreciated.

[Henry]

Hi All.

Been using the sj all weekend and it ran great! Come today after running it dry of fuel (the fuel pump did not kick in) it has become very bad in the low rev range.

Dont get em wrong it ticks over smooth as you like, at about 800 RPM, it revs round the clock and isnt down on power.
However sometimes when starting off from a stand-stil and giving it the beans it has a massive flat spot and will just do nothing apart from decrease in revs. Its almost like you have to feed in the throttle to get any response from it. I have tried turning up the fuel pressure a bit but nothing changed?

Any suggestions would be appreciated as i carnt for the life of me figure this one out!

[Edweird]

Have you tried a hammer? It is an SJ after all.

The only thing I can suggest is making sure the fuel is reaching all the points of the carb it should be. Possibly check the butterfly? It might be sticking when you slam your foot down too quickly, or possibly the engine's not getting the fuel it needs when you want the umph, but you said you'd adjusted the fuel so...

[Henry]

Hi Ed.

The Su (non standard carb) opperates on a piston. When you accelerate it pulls the piston up and lets more fuel into the chamber. This piston has an oil chamber to controll the speed at which it comes up to allow more fuel to come. It could be that the low oil level is letting it rise to fast and flooding the engine.

I will have to check the oil level tomorrow. I have turned the fuel pressure up by 0.5 PSI. It made no difference but i will have to turn it down as i do not have a fuel return like the standard carbs and pumps. So effectively what ever goes into the carb has to be used

[muddy kev]

hi henry,
r u sure its carb? and not ignition?
r say been using all weekend was that off road? poss wet in cap?
what sort of distributor have u got? electronic or points?
if points could be condensor or broken centrifugal weight spring?
cheers kev.

[Henry]

hi henry,
r u sure its carb? and not ignition?
r say been using all weekend was that off road? poss wet in cap?
what sort of distributor have u got? electronic or points?
if points could be condensor or broken centrifugal weight spring?
cheers kev.

Hi Kev.

Yes im pretty sure its the carb, all the ignition is in GWO and is free from any mud, or water ect. This weekend has been road miles and around home. I have an electronic distributor and everything is ok. I have taken that off and cleaned with emry cloth and wd40.

Henry

[muddy kev]

does sound like carb then. may be worth having a real close look at the needle. make sure it moves nicely and no flat spots on the needle its self. also i'd have a good old spray around the carb area with some carb cleaner while shes running to check for air leaks.
cheers kev.

[ScottieJ]

I'm not too clued up on SUs but i'd imagine they have some sort of jets in them??? maybe some crap made it through the filter and is blocking them? it does sound like it a fueling problem when it's running at idle? presume you've checked your fuel filters matey?

[Henry]

Hi scott.

Yes the fuel filter is fine, nice and clean and full up. What i might to do is put a filter after the pump too. The current one is just in front of the fuel pump.

And the idle is fine, its just when you hit the power that it dosent know what to do

[Tramp]

Hi scott.

Yes the fuel filter is fine, nice and clean and full up. What i might to do is put a filter after the pump too. The current one is just in front of the fuel pump.

And the idle is fine, its just when you hit the power that it dosent know what to do

are you still using the original fuel filter on the chassis leg by the back wheel? when mine did what yours is doing (on the standard carb) i just changed that filter,

[Henry]

No Luke i have an in line fuel filter before the fuel pump like so.




That is all clear. It then goes all the way down the chassis with a flexible pipe, straight into a fuel pressure regulator then into the carb.