Several bikes have 'engine racing' problem at stoplight, at idle

[ClareQuilty]

Its a bit odd, but I've had about 3 bikes develop the same problem all at once, to varying degrees - basically the problem that, though the bike would idle fairly normally at start up, it began 'racing' at idle once the bike had been driven 'at speed' for a while. One old Honda Nova had this problem VERY severely, basically revving flat-out when stopped, and another old Nova and a Honda Smile had the problem less severely.

I'm wondering what causes this sudden change? Is it the floats in the carburetor? Or the idle setting screw? When I stopped by a bike-shop with the flat-out revving Nova they just set the idle down, but I'm not sure this has really fixed the problem, and I'm just curious what caused these to all develop the same problem at once - the return of 'cool weather' in Isaan (about 58-60 for a low at night), or maybe bad (gasohol) gas? I try to always put 'real benzine' in, but never feel 100% sure the stations sell honestly.

[thrilled]

Many times when the engine gets hotter,the engine RPM's tend to go up.Nothing to get alarmed about.If it troubles you take the bike in the shop and they will low them for you.

[kaorop]

dont listen to the above, there is a problem

its usually an air leak, sometimes the carby slide and carby are worn so much they let more air in,

common on older 2 strokes, dungdungdungdung instead of dung........dung.........dung

but all 3 bikes? that'd have to be some very bad luck

the cooler weather combined with fuel might be the cause, as thailand doesnt change its fuel formula during the year to compensate for colder temps.

sell the 3 and buy 1 new....

[papa al]

Throttle cables sliding freely?

Ghosts?

[mania]

The fact that you suddenly have 3 bikes doing this ( All carbureted I assume )

would likely point to atmospheric changes which in fact we are having now in Thailand since

it is the so called cool season.

It cannot really be much else since again you said 3 bikes it is unlikely all would suffer the same

symptom. As such I would just adjust & not worry

If you would like to tune it yourself....

Start with warm engine....raise idle with the idle screw till 2000 rpm

Once idling clean at 2000 rpm adjust your air screw adjustment till you have highest idle

Once that is done go ahead & reduce your idle screw to idle at 1200 or so rpm

little more or less if you like.

If your 3 bikes is showing no other symptoms than what you mentioned (faster idle once warm)

this is all it likely is.

PS: If you get no idle changes while adjusting the air screw you likely have clogged pilot jet.

Which could happen if you fill all bikes at the same place/time & got some dirty bottom of tank fuel?

Seems like a stretch though

PSS: Does the bike bog or cut out at all if throttle is opened quickly while this condition is occurring?

Edited December 14, 2014 by mania

[ClareQuilty]

"sell the 3 and buy 1 new...."

No thanks, love these old two-strokes, don't much like the newer bikes. I'll have the carbs checked out next week, post here what's the outcome.

Edited December 14, 2014 by ClareQuilty

[yankee99]

Air leak imho and if it is be careful because this will cause a lean condition and lead to catastrophic failure

[Shurup]

On all 3 at the same time??? Dunno, maybe you filled them up with Lao-kao?

[ktm jeff]

CQ , i know the age / standard .of your bikes , and there will be wear on the throtte slides The slides may also be sticking if there gummed up , or cable is rusting / sticking..All 3 bikes at the same time would suggest poor / dirty fuel or water contaminated fuel. Try sticking (no pun intended ) to Shell fuels. With the cold / damp weather there is also more water it the air , possibly causing "carb freezing" , where the water forms frost / ice , and freezes carb butterflies open. A fuel additive would solve this if you can get it - Silkolene Pro FST. Air leaks also possible , but on 3 bikes the same time ?. Please keep us posted .

[ClareQuilty]

CQ , i know the age / standard .of your bikes , and there will be wear on the throtte slides The slides may also be sticking if there gummed up , or cable is rusting / sticking..All 3 bikes at the same time would suggest poor / dirty fuel or water contaminated fuel. Try sticking (no pun intended ) to Shell fuels. With the cold / damp weather there is also more water it the air , possibly causing "carb freezing" , where the water forms frost / ice , and freezes carb butterflies open. A fuel additive would solve this if you can get it - Silkolene Pro FST. Air leaks also possible , but on 3 bikes the same time ?. Please keep us posted .

Fuel wise, I've just been avoiding gasohol.. I'm not sure whether Shell stations around here sell 'real benzine'. I'll take a look. Its a good theory as I've been using super cheap 'benzine 95' from a local non-brand station on the recommendation of my mechanic who was encouraging me to avoid gasohol (stating that PTT benzine is often actually gasohol put into the wrong tank).

[ktm jeff]

To effect 3 bikes , im thinking its water . Some old and rusty underground tanks in small "mom&pop" fuel stations leak water in due to poor vent systems , high water tables , poor water run-off design or dodgy owners adding it .I only suggest Shell , as their stations worldwide seem to be well managed. With your need for Benzine , and your specific location , you may not be afforded such a choice. I presume your bikes run additional in-line fuel filters ?. Have the float bowls and / or tanks drained ( you may then see the water - and may be able to seperate it ) and try another ( better run ? ) station. The fuel additive Pro FST may be found in motocross type shops.

[DualSportBiker]

PT sell 95 benzine. Esso have dropped it nationwide, and upcountry is more varied... My 2007 GS requires me to use benzine...

[ll2]

several gremlins!

[ktm jeff]

Several gremlins ?. CQ,s bikes always have gremlins , but now they appear to be breeding. . EDIT , PTT stations would be my 2nd choice.

Edited December 16, 2014 by ktm jeff

[alco]

I had a similar experience a while back with my old 2 stroke motor. In my case it got worst to the point that the engine is dieseling when put in idle, means it run on its own even without a spark, like i hit the kill switch and pull out the spark plug wire and it is still running at high rpm! the motor seems to run fine but 'engine racing' problem always appear whenever i pull the clutch or in neutral. i pull out the cylinder head and found the head gasket warped. so i thought it could be an air leak on the cylinder head that happen when the engine is really hot and causes the metals to expand allowing an air leak. i also found substantial amount of carbon deposits on the cylinder head and top of the piston. carbon deposits can glow red hot and cause similar problem. i fixed mine by cleaning up the carbon build up and replacing the head gasket. i have two old two-stroke motorcycle and both had this problem in the past. i strongly suggest to have the mechanic pull out the cylinder head for inspection/cleaning..

[ClareQuilty]

PT sell 95 benzine. Esso have dropped it nationwide, and upcountry is more varied... My 2007 GS requires me to use benzine...

Yeah I stick to PT benzine quite strictly with the car and with my 'favorite' bikes, but with bikes I rent out or otherwise don't care so very much about I fill up at this mom-and-pop station - its only something like 37 baht per liter for their benzine, but the mechanics have told me 'its really benzine'.

I can now report having gotten the last of the three bikes back and all are fine now - the two better ones I had a full 'carb cleaning' and resetting of the mix, idle and so forth at a trusted mechanic (70 baht for each one), and they're running very sweetly now with no over-revving. The last bike is such a rough looking old beater I've resolved to spend no money on it, so I just stopped off when it was revving and had another shop set the idle down (free) and it seemed to do the same trick. The idle's now almost too low, but its showing no tendency to over-rev at idle after long trips (8-10 kilometers).

Edited December 16, 2014 by ClareQuilty

[papa al]

'its really benzine'.

Color?

[ClareQuilty]

'its really benzine'.

Color?

It is a bit hard to tell peering into the tank hole, but it seems to be a reddish color.

[papa al]

Benzine is red.

95 gasohol is orange, which might appear reddish in the dark tank.

Put some in a clear bottle if you want to know.

PM me your bank number and I will transfer 70baht so you can get the carb cleaned on the beater bike.

" ...long trips (8-10 kilometers)." 5 5

Edited December 17, 2014 by papa al

[ClareQuilty]

PM me your bank number and I will transfer 70baht so you can get the carb cleaned on the beater bike.

" ...long trips (8-10 kilometers)." 5 5

Haha, good point, about the 70 baht. About the short trips, well believe me, these little 105 cc Honda Novas aren't exactly intended for driving from town to town, more for just putt-putting around inside the town. They are reliable, enjoyable little bikes for what they are, however.

The awful beater I mentioned, though it cost only 3,000 and I've been stingy with repairs/fixing up, it still starts easily every time, drives well, and has good brakes (dual disk brakes). What makes it a 'beater' is that it has a little bit of a noise in the engine... I'm not sure what causes it, but its kind of 'clattery', and the mechanic said this engine is unrebuildable because of whatever that is that makes it sound this way. However, it runs fine and has very adequate power (about as much as my other Nova which runs/sounds normal).

[kaorop]

I had a similar experience a while back with my old 2 stroke motor. In my case it got worst to the point that the engine is dieseling when put in idle, means it run on its own even without a spark, like i hit the kill switch and pull out the spark plug wire and it is still running at high rpm! the motor seems to run fine but 'engine racing' problem always appear whenever i pull the clutch or in neutral. i pull out the cylinder head and found the head gasket warped. so i thought it could be an air leak on the cylinder head that happen when the engine is really hot and causes the metals to expand allowing an air leak. i also found substantial amount of carbon deposits on the cylinder head and top of the piston. carbon deposits can glow red hot and cause similar problem. i fixed mine by cleaning up the carbon build up and replacing the head gasket. i have two old two-stroke motorcycle and both had this problem in the past. i strongly suggest to have the mechanic pull out the cylinder head for inspection/cleaning..

5555 warped head gasket? thats a new one, sorry for the 555

most old 2 st used a copper head gasket that doesnt mind being warped a bit

you can use them again by heating it up till just glowing and dip it in water, annealing, makes it all soft and malleable.

most newer bikes use a tin gasket with a few ribs and a sealing compound on both sides, which can also be re-newed if need be.

they also flex and wont be 100% "flat".

cheers