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Old 24th March 2009, 20:04   #1
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Default Hanging RPM Issue

My brain is in safety mode, meaning overheated and has crashed temporarily.. so please think for me

Hanging RPM can be cased by lean jetting, air leak and rich jetting. The first two possibilities are ruled out, so only richness prevails. But why?

Hanging RPM means, I let go off the throttle but the RPM don't drop fast enough when the bike is coasting in gear, when i pull in the clutch it drops fast enough.

It has happened before while sorting out the jetting, but it hasn't happened with the present setup till this evening. It was fine this morning, but it rained in the afternoon and the bike was in the rain. RPM were hanging when i rode back home after the bike got wet in the rain.

What could cause this? Wet filter? Anything else... I'm very tired for thinking & investigations...help is mucho appreciated!
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Old 24th March 2009, 20:05   #2
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Is it possible that the accelerator cable has gone tight.
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Old 24th March 2009, 20:15   #3
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Quote:
Originally Posted by bblost View Post
Is it possible that the accelerator cable has gone tight.
No it's free enough, i checked, moreover RPM fall quickly once i pull the clutch.
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Old 24th March 2009, 20:35   #4
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If it was a prob within the engine, shouldn't the revvs drop even slower when the clutch is disengaged. Since there is no load on the engine.

I feel its just the momentum of the bike that is causing this.

Shan2nu
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Old 24th March 2009, 21:02   #5
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Actually if the revs fall off like normal when clutch is pressed, then we can safely eliminate any engine problem.
Get your carb serviced, my friend had similar problem, was traced to slider top and sorted out.
There is something wrong with fuel and not even the filter ( IMHO )

Clean the carb, replace any part if required in carb and this would be fine.

Same problem in my Zeus was traced to poor quality fuel that damaged some rubber seal in carb.
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Old 24th March 2009, 21:38   #6
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Dirty filter? You diagnosis is right.
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Old 24th March 2009, 21:59   #7
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Quote:
Originally Posted by Shan2nu View Post
If it was a prob within the engine, shouldn't the revvs drop even slower when the clutch is disengaged. Since there is no load on the engine.

I feel its just the momentum of the bike that is causing this.

Shan2nu
Yes exactly So am at peace.

It could be momentum and the rains combined together. Engine is being turned over by the wheels keeping the pumping action up and prolly the rains could've washed out the lube in cable and throttle housing causing a little bit of stiction and combined effect is hanging rpm.

bblost, eventhough i dint feel any resistance to the throttle movement i went ahead and lubed the cables well! Now i can feel it to be a lot smoother. Prolly it will solve the issue.

Quote:
Originally Posted by aaggoswami View Post
Actually if the revs fall off like normal when clutch is pressed, then we can safely eliminate any engine problem.
Get your carb serviced, my friend had similar problem, was traced to slider top and sorted out.
There is something wrong with fuel and not even the filter ( IMHO )

Clean the carb, replace any part if required in carb and this would be fine.

Same problem in my Zeus was traced to poor quality fuel that damaged some rubber seal in carb.
I service the carb myself man, and i've been using an aftermarket carb since many days. Parts have to be imported if any needs replacing, carb is fine. Fuel, fuel filter etc are all okay since the problem wasn't there in the morning. So prolly it's engine pumping + tiny bit of stiction as pointed out by shantanu and bblost. Will find out tomorrow. Have lubed the cable very well.. or i can say the i have filled up the bouden with oil Hehe..

Quote:
Originally Posted by crazydiablo View Post
Dirty filter? You diagnosis is right.
I checked the filter, it was not wet.. atleast it dint feel wet. I have cleaned the filter last weekend, so filter is clean. I dint open and check for wetness coz it's a fight to get it back on, as it's a stretch fit..

Here's a pic how i have stretched it over the carb mouth. It's an R1060. Pic is not new so it may seem dirty in the pic.

Picasa Web Albums - Crank - Karizma Diary

Hoping it's the cable coz i don't want to remove the filter anytime soon!

Last edited by Sankar : 24th March 2009 at 22:06.
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Old 25th March 2009, 03:32   #8
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Sankar I had been facing this issue on my zma since long.
Bike used to run perfectly with the air fuel mixture screw removed,but then it didnt idle.
I had tried tuning from various places,multiple times but to no avail.
I got the carb replaced(got it off a crashed bike for cheap),and somehow its 95% fine now
Points of failure for this issue according to me are.
1)Play in Carb Slide.
2)Incorrect Air fuel mixture setting
3)Improper routing of accelerator cables.
4)Problem with choke cable.

I doubt if this has anything to do with a dirty filter.

Last edited by akshay4587 : 25th March 2009 at 03:34.
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Old 25th March 2009, 09:50   #9
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Unfortunately the hanging RPM issue is still there. Throttle cable is as free as it can be.

Akshay, 1) there always has been a bit of play in the carb slide even from brand new, but since it's a flat slide with slide blocks there are two sealing points on either slide. The slid rings just off idle even from brand new.
2) Possible, but the hanging RPM issue manifested itself all of a sudden after the rain last afternoon, it was fine yesterday morning.
3) Throttle cable is routes with few kinks as possible and it's free moving.
4) It doesn't have a choke cable, choke is closed.

Now to check the filter for dampness and put some fuel in the tank. It was nearing reserve. Theoretically low level in the tank (when it was nearing reserve but i was on mains) can cause hangin rpm when the flow cannot keep up with usage leaning out the pilot. I was riding mostly at off idle and midrange.

Btw, how much did you pay for the carb?
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Old 25th March 2009, 09:56   #10
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Quote:
Originally Posted by Sankar View Post
Unfortunately the hanging RPM issue is still there. Throttle cable is as free as it can be.

Akshay, 1) there always has been a bit of play in the carb slide even from brand new, but since it's a flat slide with slide blocks there are two sealing points on either slide. The slid rings just off idle even from brand new.
2) Possible, but the hanging RPM issue manifested itself all of a sudden after the rain last afternoon, it was fine yesterday morning.
3) Throttle cable is routes with few kinks as possible and it's free moving.
4) It doesn't have a choke cable, choke is closed.

Now to check the filter for dampness and put some fuel in the tank. It was nearing reserve. Theoretically low level in the tank (when it was nearing reserve but i was on mains) can cause hangin rpm when the flow cannot keep up with usage leaning out the pilot. I was riding mostly at off idle and midrange.

Btw, how much did you pay for the carb?
Oh now i remember that you are running on slide carb.
Sankar,since your bike was parked in rain,water might have got into the carb,and you may need to Drain/Clean it,as water seeps in easily through fuel tank cap in a zma.

Damn as I type this my bike is also parked in rain since last night

I got the carb for 1.7K,new one costs 4K+ i guess.
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Old 25th March 2009, 11:23   #11
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Yep, i'll clean the bowl when i reach home.
I put the bike in reserve and checked the problem seemed to have come down. But after i refuelled it came back again, again i put it in reserve but still hanging RPM. Puzzled!
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Old 25th March 2009, 11:37   #12
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Does this bike have a TPS?
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Old 25th March 2009, 12:12   #13
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It used to, now it doesn't. Removed it long back.
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Old 25th March 2009, 17:33   #14
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Had the similar symptoms in my classic pulsar, it went away with a few tweaks to the air screw and the idle adjustment nut. It too started during the monsoons for me. Don't know if I got lucky!
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Old 25th March 2009, 18:48   #15
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Bike is allright now...no problemo I dint do anything to it. After i filled `er up with fuel it has been fine. Low fuel level around pilot jet that caused this, thats the conclusion. So next time when the RPM starts to hang i know it's about to get into reserve
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