NC35 Racebike Carbie Issue - fuel in bowl, not in cylinder

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Suzuki416
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Re: NC35 Racebike Carbie Issue - fuel in bowl, not in cylinder

Post by Suzuki416 » Fri Jan 04, 2019 10:56 am

Rohin,

I just want to check what I'm reading - you don't think the bike is running on 4 cylinders, yet will rev to 12,000 unloaded... I'd suggest the mains are working fine - lol

I'll assume you guessed the misfiring cylinder was number 2 by the temp of the exhaust pipes?

I'd look at your idle jets on all the carbs & absolutely re-synch them..

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Re: NC35 Racebike Carbie Issue - fuel in bowl, not in cylinder

Post by RoninZX-10R » Sun Jan 06, 2019 7:59 pm

Hi Suzuki416, yeah that's exactly right. When it's idling, and revving it a little to warm up the engine, it'll only run on 3 cylinders, number 2 won't fire for some reason (confirmed only from the temperature of the header pipe). I had the bike on a dyno yesterday and it ran fine all the way up to redline, so my guess is it's out of balance. I've borrowed a mates carbie sync tool so I'll have a look at that in the next couple of days.

I'm assuming when I sent my carbies out to get ultrasonically cleaned and set up for racing that they may have accidently turned the synchronising screw. I'll report back in a few days...fingers crossed I'll have it sorted quickly!

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gavins
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Re: NC35 Racebike Carbie Issue - fuel in bowl, not in cylinder

Post by gavins » Tue Jan 08, 2019 1:51 pm

Have you checked the float height as well? Have had similar issues with one cylinder not firing until it's warmed up and revved out - turned out to be the spark plug in my case.

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Re: NC35 Racebike Carbie Issue - fuel in bowl, not in cylinder

Post by RoninZX-10R » Wed Jan 09, 2019 11:25 pm

Hi Gavins, yeah the float heights have been all checked and adjusted. I've swapped the spark plugs to other ones, but that didn't make a change, so I'm hoping it's the carbies being out of balance. Haven't had a chance to get onto it yet unfortunately.

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Re: NC35 Racebike Carbie Issue - fuel in bowl, not in cylinder

Post by RoninZX-10R » Tue Jan 22, 2019 8:18 pm

So I finally got around to balancing the carbies and strangely enough the exhaust header pipes on the front cylinders (2 and 4) remained much cooler than the rear 2. I was able to get all 4 carbies balanced equally, so this has really confused me as I assumed that once the carbies were all equally balanced everything should be idling evenly.

I might change the spark plugs again to a different set (have done this previously, but they may have been dodgy as well?). Any other ideas from the 400 experts???

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Re: NC35 Racebike Carbie Issue - fuel in bowl, not in cylinder

Post by gavins » Wed Jan 23, 2019 10:11 am

Worth checking the HT leads and plug caps and seeing if you're getting a nice spark.

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Re: NC35 Racebike Carbie Issue - fuel in bowl, not in cylinder

Post by magg » Wed Jan 23, 2019 8:29 pm

When did this problem start?

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Re: NC35 Racebike Carbie Issue - fuel in bowl, not in cylinder

Post by RoninZX-10R » Fri Jan 25, 2019 2:32 am

Gavins, I've checked the spark and it looks to be fine. Yesterday I swapped spark plugs, HT leads and coils but it didn't make any difference.

Magg, the problem started during the last round of racing back in August. Once the revs got up to around 11,000-12,000 rpm the motor wouldn't rev any higher. During the day I had a look inside the petrol tank and saw the remains of a cockroach! I then assumd that a part of it might be blocking some carbie jets or the fuel hose causing starvation at high rpm. I stripped the tank and flushed it out, as well as cleaning the carbie, but to no avail. I then swapped bikes with a mate who's pretty good with these bikes, and he thought it was an electrical issue and suggested adding the resister at the ECU just in case the lack of speedo was causing some sort of problem. I've added the resister and also sent the carbies off to get ultrasonically cleaned. Since getting the carbies back it's not been able to idle on cylinder number 2.

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Re: NC35 Racebike Carbie Issue - fuel in bowl, not in cylinder

Post by magg » Fri Jan 25, 2019 10:56 pm

If the speedo has been removed and the engine could be revved higher than 5500rpm then the speed limiter has already been bypassed and thus the resistor you added at the ecu would have no effect. No speed limiter at start up usually results in a 5500rpm rev limit.

So at the start, the engine idled ok but would not rev beyond 12,000rpm. You suspected blocked fuel flow, there is no filter fitted to fuel tap?

After cleaning tank and carbies it runs to 14,000rpm but will not idle on 4 cylinders. You have balanced the carbies, do they all pull the same vacuum as the rpm is increased from idle. If not then I would suspect one or more has an air leak that is masked at high revs.

Worse case scenario, a compression test to ensure there is not underlying mechanical problem. Was the loss of performance at the last race meeting sudden and dramatic?

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Re: NC35 Racebike Carbie Issue - fuel in bowl, not in cylinder

Post by RoninZX-10R » Thu Jan 31, 2019 9:16 pm

Hi Magg, sorry for the late reply (I took an extended Australia Day long weekend). Regarding the resistor, that was my understanding that it would limit the engine to 5500rpm, but my mate has experienced issues at various revs that the resistor has fixed (may have been coincidental but at least it removes that from the equation).

At the last round it was really difficult to start first thing in the morning. Once started it idled fine although I didn't think to confirm all cylinders were firing as I was busy getting ready to go out on track. From the first session it wouldn't rev to redline, only to around 11-12,000rpm. I checked that there was fuel flowing from the tank, which it was, but I suspected some of the dead cockroach may have caused a blockage which may be limiting fuel at full revs.

When I had the carbies cleaned and tank flushed out (no more cockroach!), I put the bike on the dyno and it ran well, except it wouldn't idle on cylinder no. 2. I have since balanced the carbies at 1,400rpm but noticed when the revs were increased to 2,500rpm the balance was out. Would this indicate an air leak from the carbie-engine rubber boots or something internal within the carbies?

I turned the engine over a couple of days ago and now it's only running on 2 cylinders...FARK! Number 2 is firing, but 3 and 4 are not. A mate has said he'll try to locate his RVF ignition module to see whether my one is playing up (more so to confirm that's not the problem).


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