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Post by Graham on Jun 15, 2012 10:27:31 GMT
Okay my bike starts fine now, full choke from cold, half choke once running, slowly coming off choke as it warms up but it is very reluctant to rev up cleanly. If I give it too much throttle it just bogs down & dies. I'm having to build the revs up by feathering the throttle. It will reach hight revs eventually but between tick over & high revs it is not happy at all. I have stripped the carbs more times than I can remember now & tried standard jets with cone filters & with standard air box, slightly bigger jets (108's) with cone filters & with standard air box but still the same symptoms. I am hoping that someone will suggest something I have overlooked now as I'm running out of ideas. Anyone?
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Post by Crusty on Jun 15, 2012 11:38:21 GMT
At a guess, I'd say not enough fuel. Mine starts without choke every time, regardless of the time of year, with just a touch of throttle.
Float heights wrong?
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Post by Crusty on Jun 15, 2012 12:09:40 GMT
Has anyone near you got a working bike you can borrow the carbs off?
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Post by fatbloke on Jun 15, 2012 12:10:51 GMT
Check if the airbox to carbs and carb to head rubbers are in good order. Sounds like its sucking air in somewhere. Just had the same isses the the LC, the pipe joining the carbs on the choke side had perished but you couldnt see where it was leaking. Replaced it yesterday and it ran fine last night. Hope you find it soon, Fatbloke.
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Post by Crusty on Jun 15, 2012 12:23:06 GMT
Check if the airbox to carbs and carb to head rubbers are in good order. Sounds like its sucking air in somewhere. Just had the same isses the the LC, the pipe joining the carbs on the choke side had perished but you couldnt see where it was leaking. Replaced it yesterday and it ran fine last night. Hope you find it soon, Fatbloke. Funnily enough I was just stood in my back garden considering this very thing. A temporary solution would be to liberally coat the outsides of the rubbers with a layer of silicon sealant. The sealant would block any hole and cure the issue (unless the leak is at the mating surfaces, you could always put some fresh there when you reassemble, just remember that petrol will disolve it in time). If it works, buy some new rubbers. if it doesn't peel the silicon back off...
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Post by fz750horse on Jun 15, 2012 12:39:36 GMT
I notice you say you put 108 mains in there - which manufacturer? I ask because as far as I know Mikuni don't make 108s, they go 100, 102.5, 105, 107.5 etc. Different manufacturers' numbers don't tally up because some refer to the size of the hole, others to the flow rate. 108 Dynojet mains, for example, would likely be about 100 in Mikuni numbers. Good luck.
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Post by Graham on Jun 15, 2012 20:26:45 GMT
Thank you all for your thoughts on this. I have been busy replacing my temporary all thread for actual exhaust studs today so not done anything more about the poor running issue. The only people I know with FZ's are all on here crusty. My airbox rubbers were a bitch to get on when I first put this bike back together nearly 2 years ago but I did the boiling water thing & they seem to be playing ball still. Not sure about inlet rubbers but sure I would have noticed if something was dodgy about them. Will have a closer look tomorrow. I bought a set of carbs for spares with the 108 jets fitted. The seller (ebay) said they were dyno jet ermmm jets but I wouldn't have a clue to be honest. Just thought I would try a different set to see if it helped. I will have another crack at it when I'm in the mood for taking my bloody carbs off again.
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Post by Crusty on Jun 15, 2012 21:12:29 GMT
Well, I've got shit to do this weekend and next weekend, but if you haven't got it sussed I'll have to consider a trip up to your place the weekend after. You're doing all the work though...
I would suspect the intake rubbers over the airbox ones. Mine weren't on the carbs when I first got it and it started alright.
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Post by Graham on Jun 16, 2012 21:13:17 GMT
"Think" I may have sussed out the problem. Stripped & cleaned the carbs again today (force of habit now) & made a few adjustments to the intake clamps so they grip the rubbers a bit tighter. Sort of knew it wasn't going to solve anything but wanted to eliminate everything I could. Whilst reving the engine again I noticed flames coming from the exhaust as it was popping & spluttering which I took to mean unburned fuel escaping from the combustion chamber/s. Plugs were new so I decided to take a look at the caps. The screw fitting inside one of the caps has snapped off so I'm guessing I was getting an weak/intermittent spark. It's still not 100% but a much needed step forwards which could mean the difference between life & a very violent lump hammer type death for my bike this weekend. I think once it is running something close to how it should I will be on the hunt for bigger jets as I'm determined to fit the cone type filters.
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Post by Crusty on Jun 17, 2012 7:55:14 GMT
The circuit for the plugs goes through pairs of them so you wouldn't have had a cylinder with one weak spark but two. Running on only two cylinders would explain a lot.
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Post by Graham on Jun 17, 2012 8:23:00 GMT
It was only 1 plug cap broke mate so 1 plug misbehaving. Guessing it was running on 4 whilst ticking over, breaking down under load then working again as I eased the throttle off slightly.
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Post by Crusty on Jun 17, 2012 8:43:15 GMT
It was only 1 plug cap broke mate so 1 plug misbehaving. Guessing it was running on 4 whilst ticking over, breaking down under load then working again as I eased the throttle off slightly. You miss-understand. It's a single coil that connects to two spark plugs, with the engine block completing the circuit. If you loose one of the pair, the other side is lost as well as the circuit is broken. Here's a link to a GSZR ignition, but it's essencially the same as an FZ. 3.bp.blogspot.com/-3AUdHZF5xs4/T8a__QLkU1I/AAAAAAAAAIg/BVGnPop3xX0/s1600/Suzuki+GSXR+Ignition.pngThe coils and spark plugs are on the right hand side. As they are,in essence, a separate circuit of their own, if you break any part of it, both spark plugs lose thir spark. This diagram isn't 100% accurate as the earth points on the HT circuit are wrong.
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Post by Crusty on Jun 17, 2012 8:59:27 GMT
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Post by fz750horse on Jun 18, 2012 12:20:38 GMT
I'm not sure about an open circuit cap knocking out both cylinders on the coil. Surely that would mean that removing the plug cap from No1 would also cut out No4 . I've had a bad HT lead cause problems, but only on the cylinder it was connected to. A fault in the low tension side would certainly affect both cylinders though.
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Post by Graham on Jun 18, 2012 13:16:29 GMT
I'm not getting in to an argument with anyone but fairly sure it was only missing on 1 cylinder?
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