19 replies to this topic

[jaffercake]

hi, i have been having problems with carb overflowing for a loong time and nnothing i have tried has worked. i was runnning a hs4 carb on my 998 engine (with a stage 1 kit fitted) and it was overflowing so ibought a new float chamber lid complete with needle valve and float from mini spares and it was still overflowing, so i got my old lid and fitted washers to the needle valve so that it closes earlier but this didnt make any difference. after this i thort there might be a problem with the fuel pump (mechanical) so i removed it and tested to see if the diaphragm and everything was fine and then put it back on which took bloody ages and alot of swearing due to lack of space. after this i replaced my hs4 carb with a hif 44 carb too see if it made a difference and it ran withought overflowing though was running like crap. so i removed to dashpot to see the jet as i adjusted the mixture and i found that there was no needle in the carb lol, so i went to my garage and fetched the dashpot of another 44 carb i had which had a needle in it. i then used this needle in the hif44 carb that i had aready fitted. after this i started it up and it ran great BUT started overflowinggggg!!!!! alot of fuel is overflowing. this is where i am now. i have come up with two different solutions to this problem, could someone tell me which one is going to definately cure my problem.

1. i think the overflowing has something to do with the fuel pressure being to high and the float cant stop it so maybe an inline fuel pressure regualtor could be used to decrease the fuel pressure???

2. the second solution is the one i thort of when the overflowing first started. it is to fit an MPI fuel tank and simply run a return pipe from where the carb is overflowing back to the tank. i am thinking that this will permanantly fix my problem and is the best way to go. what do you guys/girls think?

thanks.

[Pooky]

You could try fitting a small fuel filter, it might be enough to lower the pressure enough to stop it over flowing.

[m1tch]

lol @ having no needle lol wouldn't a hiff 44 carb needle overfuel anyhow? could the jet possibly be blocked meaning that the fuel has no where to go and its all backing up?

[Cooperman]

It should not be overflowing, so you should cure this problem rather than try an alternative solution.
It does sound as though the fuel pressue is too high, although a mechanical pump won't over-pressurise the fuel system.
Try a pair of small mole grips on the rubber fuel pipe to reduce the flow rate and see if this works and if the engine still runs OK. That will confirm the high fuel pressure theory (or not, as the case may be).

[jaffercake]

thanks for the replies

its not a blocked jet as i took the carb apart and was all good.

the mole grip on fuel pipe is a really good idea, ill try it and see what happens.

if it is the fuel pressure, will i be able to reduce the pressure via regualtor? or can that only turn it up?

thanksss

[liirge]

yer a filter King Regulator will allow you to reduce the pressure

[jaffercake]

ooyaaaa i just read the new filter king regulator description on minispares and it clains to stop the overflowing of carbs as well as other things. im going to have get 1 of ebay or something because im a poor student lol.

thanks everyone. ill let u know if things go up s**t creek again

[jaffercake]

i just went out and tryd running it by blocking off the fuel pipe completely so its running on the fuel in the float. it ran without overflowing but when i open the throttle the revs decrease alot then slowly climbs up again. this has also happened previously. what could cause this? lack of oil in the dashpot? i dunno.

help please thankyou.

[jaydee]

Fill damper with oil, but at first, you dont have to use an hif44 carb on a 998 engine.
Your old hs4 will be fine.
Whats the condition of the jet and the needle? Its the needle correctly fitted to the piston? Its the foat needle valve tightened well?
If you dont have a fuel filter, its not unusual that crap goes into the needle blocking it in a stick open position.
Another check you have to do:
Remove the float lid, hold it in one hand and whistle into the fuel inlet whilist with the other hand you start to push up slightly the float. You have to feel a little resistance as the float starts to push the float needle up, and a great resistance as the float has completely closed the needle.

Edited by jaydee, 25 July 2009 - 08:35 PM.

[jaffercake]

i know but i might just keep the hif44 on. so tomorrow i will fill the dashpot with oil.
the jets clear but i dunno if i have the correct needle. how do i know which needle i have?
i have tried the blow and push on the float lid and always works fine but not when engines running. ive decided to get a filterking regulator.
then i will have to sort out the poor running.

[lrostoke]

An HIF44 is way to big for a 998, you really want a HIF38 or HS4 on there

[almichie]

are you sure you have the fuel in and overflow round the right way?? if you feed fuel into th overflow it will overflow out of the inlet. make sure its the right way round!!!

[jaffercake]

hmmmm, yeah maybe ill change the carb tomorrow, the 44 was put on for experimantal purposes lol. and yeah im 100%sure the fuel is going in the right way. ive heard that the hs4 carbs are slightly restricting on the 998 engine.

[jaydee]

hmmmm, yeah maybe ill change the carb tomorrow, the 44 was put on for experimantal purposes lol. and yeah im 100%sure the fuel is going in the right way. ive heard that the hs4 carbs are slightly restricting on the 998 engine.

Who said that? A tuned hs4 can give 1/2 more bhp compared to a twin hs2 setup.
Dont bother with the hif44.

[almichie]

hmmmm, yeah maybe ill change the carb tomorrow, the 44 was put on for experimantal purposes lol. and yeah im 100%sure the fuel is going in the right way. ive heard that the hs4 carbs are slightly restricting on the 998 engine.

you heard wrong, the hif 44 is way too big for a 998 unless you were running a turbo'd 998 anyways. the 998 runs very wel off of a hs4. if you wanted to go hif then the 38 is the way to go for the 998. the only difference being the intenal float chamber rather than the side chamber of the hs type.