High idle - intermitently

Hi Guys,

I have a problem that has developed recently (last two days) that I
would like your help with. The bike is a 1996 RGV 2stroke.

When I stop at a set of traffic lights, the revs will come down to
4000rpm and not to the usuall 1600rpm. If I blip the throttle, it will
usually return to 4000, but sometimes down to the normal 1600.

What is interesting, is that when it rests/idles at 4000rpm - if I
move the throttle only slightly, it starts to rev up (ie, If it were a
cable issue, I would expect there to be some slack in the cable before
it starts reving up from 4000rpm, but it doesnt).

If I drop it into gear, slowly release the clutch until friction
point, the revs will drop down and then idle at 1600rpm like it should
- sometimes returning to 4000, but usually not when I pull the clutch
back in - so it can be forced to drop its idle back down to normal -
dont understand why?

I have checked the choke, and it is operating corerectly and the choke
is not on when this behaviour is present.

Sometimes, the idle is just fine, as if nothing is the miss.

So, what are the possibilities?

I guess it could be;

*a sticky throttle cable
*a sticky throttle lever on the carb
*something amiss with the idle screw - but not likely, since it
returns to normal sometimes
*a crack or hole somewhere in the fuel lines allowing more air in
somewhere (help on this one please)
*loose carb boot, allowing (extra) air to be sucked into one cylinder?

What I have also found is that when I start it first thing in the
morning, with no choke as usual, the revs seem lower than normal (like
1400) where usually it revs upto around 4000 for around a minute than
drops down to 1600 as normal.

Is it possible that this is as a result of a foulling plug?

I have had the tank off a few times, to do things like clean the
powervalves, balance the carbs and removed the airbox (for access to
he carbs), so it is possible that I have bumped something or worked
something loose.

What i am afraid of, is causing the bike to run lean and doing some
engine damage.

The bike seems to run sweet at anything other than idle.

Cheers, James
Kurrajong Australia.

 

In aus.motorcycles on 13 Sep 2004 21:45:11 -0700

Vague 2 stroke memories say "air leak". Meaning check carby rubbers and
exhaust pipes and gaskets.

Zebee

 

yep what she says

look for air leaks

 

crank seals

 

Yep. Airleaks it is.

Most likely culprit are the rubber intake manifolds.

Had you done anything to the bike just before the problem first became
apparent?

 

Yep, split the cases.

 

Zebee said....

Yep, and a great way to add that extra hole to the piston......

 

[high idle revs]

Most likely cause, IME.

With the engine idling (doesn't have to be at high idle at that moment), spray
some WD-40 or similar on the boot. If the revs change there's an air leak.

--
// Rik Steenwinkel '85 R80ST Skippy bike
// Enschede, Netherlands '91 R100GS/PD The Great Unwashed
// N 52.2158 E 6.88589 '90 K75C Kommutabike
// "Far away is only far away '81 MZ TS250/1+LSW Badkuip
// if you don't go there" '79 Honda XL250S TBD