The Carb Dead zone

[robracer]

Help......whilst riding I have found a carb problem between 5000 & 6000 rpm whilst rolling on the throttle there is hesitation? fouling / lack of acceleration / flat spot for a few seconds... this only happens when rolling on. If I give it heaps the prob seems to disapear, same if there is a gear change & the revs are higher. My question is: can there be some sort of notch or worn spot on the main jet / needle or some other part, due to the bike constantly being ridden between 5000 & 6000 revs.
Any Ideas

[Nanna10r]

Hey Rob your not running shell Optimax in it are ya, that will junk up the carbies if it sits too long.
Cheers Brett

[ttc]

Try LRP.. works for Yankee

(only joking - do not put it in ya bike:P)

[Smitty]

hmmmm
I see a carb and fuel system clean as a starter
and at the same time....
replace/clean air filter, new plugs
and please adjust throttle cables
btw
you got an aftermarket can on it?
got a jet kit in it?
let us know

cheers

[Yankee]

BP ultimate or whatever they call it.... uh, Optimax! that's it... yeah, good stuff! I was starting to get some "rough" running probs.... have used this new petrol (for me) and she has a new lease on life!

[Barrabob]

Dont forget a carby balance as well, helps with throttle response no end.

[robracer]

Its got a yoshi can but no idea if its been rejetted
so this doesnt help with determining the prob.
The note is a bit fluffy on deceleration (no backfire) so it might not have a jet kit. The fact that it is only within a small range of revs suggests its not a brand / type of fuel prob + I have changed brands & it has done the same thing

Mabee a carb clean is a good start as suggested.

Was thinking of having the carbs done as well as valve clearences at the same time as there is a slight valve noise when the bike has ben running a while....... (44000k's)

[MadKaw]

If it has a yoshi can it should have been rejetted, it may not have been and that could be the problem.
If it has a dynojet kit fitted they had a tendancy to produce a flat spot at lower revs in that model. In can be minimised by a good tuner so I'd suggest you get it on a dyno and have it checked.

[mfzx6r]

I agree with the " after market can" suggestions.


mario

[icebreaker]

sounds like you just might have picked up abit of gunk into one or 2 of the jets, perhaps.. maybe running low in reserve perhaps.. *shrugs*

could just need a good service, with a tune and balance also.

My ZX2R originally had a similar problem at about 12K up, and you pretty much couldn't red line the bike, cause it just started surging, spitting, farting and carrying on.. Unfortunetly they swapped the carbs with another ZX2R they had on the floor, and that fixed, so i will never know what the problem was..

Good luck with it.

[Aussie Ninja]

Float levels wrong mabye? I had my carbies off about ten times getting them right after my pipe and jet kit. First it was too rich down low and bogged then I went the other way and it hesitated when opening the throttle at higher revs. But I'd go with some Motul fuel system cleaner first. It works a treat.

[FuTAnT]

Carbs can be a rats nest of problems, but you can systematically work your way through it.

As people have already suggested, try putting a fuel system cleaner through it first, and running on BP Ultimate or Optimax as these have small amounts of cleaner in them as well, which will reduce the deposits and shite in your induction and combustion chamber area.

If you want to start playing with the carbs, it's best to first make sure your valve clearances are correct (If they're out, it can 'cause incorrect vacum readings when you go to balance the carbs).

Once that's done, try balancing first, to see if this helps. If not, then I'd go the way is dismantling and finding out what's going on. It's possible that the emulsion tubes may also be worn if you're consistantly running the bike at a certain rpm range. All the normal things should be checked, but give them a really good clean out (possibly a few times) then reassemble. Make sure the needles are in good condition and not leaking fuel. Reset the float levels and go from there. Replace all the little internal o-rings as you go as well. Of course, if the bike hasn't got a jet kit, then I'd talk to an experienced tuner and see what they reccomend, as well as having it fitted or fit it yourself, but you'll need dyno work to get it dialled in. Depending on who it is, they may not need a "dynojet" kit and might just get the exact parts you need (as a side note, the jet kits come with all sorts of jets that you don't need, that can be got around by a decent tuner just putting in what needs to be put in).

Anyhoo, enjoy, see what happens. Go through the process and see what results occur. Post it up and perhaps some more people might be able to help you out.

[aardvark]

I had a problem with my VH Commodore once. It had a worked 253 in it (went like a cut snake) and one day it decided to develop some fuelling problems.

It was having problems running so I adjusted the idle mixture etc which seemed to fix it for about 10 minutes, then it stopped and wouldn't start again.

So, I poured a splash of petrol down the throats and fired it up, only to find on exiting the vehicle that the top of the engine was on fire and a flame about 4 foot high was coming out of the carby.

Very amusing.

[icebreaker]

Who said cops aren't dickheads... ROFL


Mind you i was having probs with my '76 celica.. Fully worked, 32/36 DD Weber.. back fired through the carb.... nice flame out the carby as i recal... And who's head was over the top...

[mfzx6r]

Mind you i was having probs with my '76 celica.. Fully works,.

wow did it have enough guts to pull that skin of the rice custard !! ??? hahahaha junk car junk motor




mario