Engine idling too fast (not throttle stop issue)

[D O G]

Hi, now that I am on the brink of resolution of my brake problems (new caliper to be fitted this eve), it's time to turn my attention to its other problems.

Bike is a 1990 GS500E

First one on the list is the idle. Essentially when coming to a stop, the engine refuses to idle below 3,500 rpm of its own volition.

You can make it idle properly by loading the engine (foot on brake, let clutch out slightly), and initiating the revs to drop below 3,000, at which point they fall to normal idle steadily over a couple of seconds.

[As an aside, they would in fact fall so low that the engine would cut out, but can 'correct' for that with the sligtest throttle - not going to treat this until I can resolve the initial problem].

It does this all the time, not just if it gets hot - it did it this morning in the pissing rain after a minute's ride.

I know it is not the throttle stop, as I adjusted this to set the idle when it was idling around 1,250rpm. I have fiddled with it a bit, but that only affects the idle once the revs have dropped.

I also know it is not a sticky throttle cable - I inspected these a couple of weeks back and there was no problem.

What would you guys check?

My thoughts are that it could be the fuelling - reason for this is that I also get shitloads of backfiring/popping when under engie braking situations.

It could also be the electrics, there is clearly something wrong with these - see separate thread.

What does it sound like to you knowledgable chaps? Thanks!

[Timmeh]

Usually if the engine is hanging up and won't drop to idle a carb balance will fix/better the issue.


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GSXR400 x2 | '94 RVF400 | '93 TZR125 4DL (again)
20:22:30 BLUEX5: i would love to be forced to undergo a**l plugging with different sizes
20:48:18 Temeluchus: comp you hunk of smouldering homos3x you

[Timmeh]

Either that or the choke circuit is sticking open/leaking.
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GSXR400 x2 | '94 RVF400 | '93 TZR125 4DL (again)
20:22:30 BLUEX5: i would love to be forced to undergo a**l plugging with different sizes
20:48:18 Temeluchus: comp you hunk of smouldering homos3x you

[steo]

I had an old Kawasaki gt550 that used to do something similar, it would tick over really lumpy at low revs & if you adjusted the idle screw slightly, it would then scream it's head off. I had the carbs balanced & still no different.
A guy in kawasaki said that they all did that once they got old or had high mileage & the way to resolve it was to overhaul the carbs with a new carb kit. It's a pain in the tits but you do get used to keeping the bike ticking over using the throttle.

[Kickstart]

Hi

As above, but also check for air leaks (eg, cracked inlet manifolds, cracked fuel tap vacuum pipe).

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[D O G]

[Kickstart]

Hi

The Scottoiler relies on carb vacuum to open a valve and allow oil to flow when the engine is running. Possible there could be a problem there.

The pipe from the intake to the fuel tap is just some small bore fuel proof pipe. While it does have to put up with a vacuum it should only be a small one, so I doubt any vacuum specific pipe is required. Doubt any car place like Halfords would have any suitable pipe small enough, but suspect any small bike shop probably has a few lengths around (ie, something like fuel pipe for 50cc bikes).

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing