tootall Posted September 2, 2020 Report Share Posted September 2, 2020 Right, before I set fire to it I thought I'd ask for some advice (not on how to set fire to it, I can manage that myself) Zxr750L. Stripped years ago. Head and barrels off, new gaskets, valves lapped and gaps set. Carbs totally stripped, blasted, cleaned and rebuilt. All back together and fires up a beaut. Unfortunately it revs to over 3500 straight away. Choke plungers all closing. No throttle cable or idle cable attached. I've had the carbs off and back on again loads. Bench balanced them, even stripped and run back through the ultrasonic again. Float heights set. Never had this before. I've been assuming it's due to an air leak (poss butterfly shaft seals?) but open to suggestions (not like that). Last thing today I let it run for a bit and pulled plug leads off one at a time to see if I could narrow it down to a particular cylinder but nope. Any ideas? Going to split the rack off carbs again tomorrow and see what I can see but kinda stumped. As I said, I've done loads of carbs before and never had anything like this before Quote Link to comment Share on other sites More sharing options...
lorenzo Posted September 2, 2020 Report Share Posted September 2, 2020 is there any carbs from anywhere else you can have a try with, from a known working bike, just as a loan? They don't need to be perfectly jetted, just something that works. That'd save a load of faffing around trying to suss where & what the issue is, but, for what it's worth, that sounds like an air leak somewhere. The other alternative is the carb cleaner spray everywhere and seeing which spot you spray it in changes the running of it all. 2 Quote Link to comment Share on other sites More sharing options...
lorenzo Posted September 2, 2020 Report Share Posted September 2, 2020 Could be voodoo though Quote Link to comment Share on other sites More sharing options...
tootall Posted September 2, 2020 Author Report Share Posted September 2, 2020 52 minutes ago, lorenzo said: is there any carbs from anywhere else you can have a try with, from a known working bike, just as a loan? They don't need to be perfectly jetted, just something that works. That'd save a load of faffing around trying to suss where & what the issue is, but, for what it's worth, that sounds like an air leak somewhere. The other alternative is the carb cleaner spray everywhere and seeing which spot you spray it in changes the running of it all. Poss gonna buy another set to have a go with. Tried the carb/brake cleaner everywhere method but it's kinda hard to tell when it's revving it's nuts off anyway. 52 minutes ago, lorenzo said: Could be voodoo though Yeah, I'm reckoning voodoo myself 1 Quote Link to comment Share on other sites More sharing options...
ssray Posted September 2, 2020 Report Share Posted September 2, 2020 Sounds like a Rubber part has hardened, carb cleaner etc sprayed around the carb rubbers like loz said 2 Quote Link to comment Share on other sites More sharing options...
Alpinestarhero Posted September 3, 2020 Report Share Posted September 3, 2020 Would a smoke test help? (providing you can get a smoke machine thingy) Quote Link to comment Share on other sites More sharing options...
tootall Posted September 3, 2020 Author Report Share Posted September 3, 2020 45 minutes ago, Alpinestarhero said: Would a smoke test help? (providing you can get a smoke machine thingy) Maybe. If it doesn't then I could just inhale the smoke myself and stop stressing over it. (yes carbs been off twice more, inlet rubbers checked and graunched up tight on install, and no it still isn't right, bastard thing) Quote Link to comment Share on other sites More sharing options...
TLRS Posted September 3, 2020 Report Share Posted September 3, 2020 A bit of a stretch.. but I’ve read about some carbs/tb’s that have a coating in the bore that helps seal the butterfly. Could easily be discarded as dirt or sumptin. Any chance that’s missing? Are there plugs over de air screws? Quote Link to comment Share on other sites More sharing options...
tootall Posted September 3, 2020 Author Report Share Posted September 3, 2020 16 minutes ago, TLRS said: A bit of a stretch.. but I’ve read about some carbs/tb’s that have a coating in the bore that helps seal the butterfly. Could easily be discarded as dirt or sumptin. Any chance that’s missing? Are there plugs over de air screws? It's just zxr carbs, don't think there is/was any coating in the bores, and didn't blast the bores either. Plugs over the pilot screws? No, never has been. Even tried winding the pilots in to 1/2 a turn out instead of the recommended 2 1/4 but still doing the same. I can get it to "idle" by holding the throttle cable wheel tight shut (verified that the balancing is ok) but soon as I release it to normal shut pressure the revs just rise and rise. Bloody annoying cos it sounds dead fit when I do rev it properly, but a 3k+ idle is a bit much.... (and it doesn't stop at 3k, just keeps rising till I bottle it and hit the kill switch) 1 Quote Link to comment Share on other sites More sharing options...
TLRS Posted September 3, 2020 Report Share Posted September 3, 2020 On a TL there’s a screw the cable wheel sits against. I guess to avoid slamming the butterflies in the bore. Bit of an open goal maybe.. but easy thing to check. Quote Link to comment Share on other sites More sharing options...
tootall Posted September 4, 2020 Author Report Share Posted September 4, 2020 8 hours ago, TLRS said: On a TL there’s a screw the cable wheel sits against. I guess to avoid slamming the butterflies in the bore. Bit of an open goal maybe.. but easy thing to check. Same on the carbs, but it's backed right off. Carbs coming off again today and splitting the rack to see if I can see what's up 1 Quote Link to comment Share on other sites More sharing options...
hawkati Posted September 4, 2020 Report Share Posted September 4, 2020 throttle cable interference? maybe at the handlebar end? Quote Link to comment Share on other sites More sharing options...
tootall Posted September 4, 2020 Author Report Share Posted September 4, 2020 53 minutes ago, hawkati said: throttle cable interference? maybe at the handlebar end? Cable not fitted. I reckon air getting in around butterfly shafts Quote Link to comment Share on other sites More sharing options...
Damnthistinleg Posted September 4, 2020 Report Share Posted September 4, 2020 Fucked 'O' rings on the float valve seats? That's my 'go to' investigation for carbs that although seemingly correct, are misbehaving quite badly with fuelling. That and the butterfly shafts/bushes. Quote Link to comment Share on other sites More sharing options...
tootall Posted September 4, 2020 Author Report Share Posted September 4, 2020 10 minutes ago, Damnthistinleg said: Fucked 'O' rings on the float valve seats? That's my 'go to' investigation for carbs that although seemingly correct, are misbehaving quite badly with fuelling. That and the butterfly shafts/bushes. Going to order some new float valve kits, but having a mare trying to find butterfly shaft seals Quote Link to comment Share on other sites More sharing options...
426hemi Posted September 4, 2020 Report Share Posted September 4, 2020 This company is very good for spares. https://www.nrp-carbs.co.uk/ 1 Quote Link to comment Share on other sites More sharing options...
spannerman Posted September 4, 2020 Report Share Posted September 4, 2020 Somewhere in the back of my mind I recall something similar, can't remember what bike but the inlet rubber clamp to carb was interfering with the throttle mechanism spun it round and it was sorted. sometimes it's just oddball stuff, have a check 1 Quote Link to comment Share on other sites More sharing options...
svingel Posted September 5, 2020 Report Share Posted September 5, 2020 Stupid question maybe, but can you check if the butterflies closes fully? Visually? Hold them up towards the light etc Quote Link to comment Share on other sites More sharing options...
TriGGer Posted September 9, 2020 Report Share Posted September 9, 2020 Has this had the float bowl vent done J? Quote Link to comment Share on other sites More sharing options...
tootall Posted September 9, 2020 Author Report Share Posted September 9, 2020 20 minutes ago, TriGGer said: Has this had the float bowl vent done J? All emissions guff removed/vacuums blocjed/vent running to right side of airbox. It's something I've done tbh cos it ran ok before the strip down. Quote Link to comment Share on other sites More sharing options...
VeeTeeArr Posted September 9, 2020 Report Share Posted September 9, 2020 Can you detect any individual exhaust header warming more quickly than the others from cold or can you pull the plug caps one at a time, something to narrow it down to one cylinder. Quote Link to comment Share on other sites More sharing options...
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