Idle changing on its own

GoldenMotor.com

cj5jeep80

New Member
Jun 8, 2014
3
0
0
maine
hello....I built myself a motorized bike using a HS 50cc 4 stroke, a 4g trans and a shifter kit from SBP....well I must say how happy I am with this set up......runs really well....I should note I have also changed out my air cleaner with the SBP cleaner.....as a result I have unscrewed the mixture screw to allow for more fuel...after a few test rides I have managed to get this thing purring like a kitten and running very smoothly at high speed...Idle has been set at 2000 rpm thanks to my tachometer...seems to run very evenly until today...I was going up a slight incline and running the bike hard 5th gear shifting to sixth gear at 7000 rpm, continued to climb the incline in sixth and reached the top and a stop sign. I gave the bike gas to continue on and it stalled immediately...I stopped on the side of the road and pull the engine cord and the bike fired up first pull but then began to climb in rpm from 2000 idle to 3 and 4000 rpm engagingal the clutch and then back down to 2000 rpm all on its own. 2000 rpm and then it would be okay for a few secs and then back up. I have read a few posts online suggesting this must be an air leak but you would think if i had a air leak the motor would run lean all the time not up and down like it is doing.....any suggestions would be great...also I tried closing my choke somewhat, the rpms drop down and the bike is ridable but there is a huge loss in power....thx
 

Patchy

Member
Aug 12, 2014
87
0
6
California
An easy way to test for air leaks is to spray starter fluid on the seals, if it revs up you have a leak, but this might not work so well if the bike changes its idle randomly..
 

cj5jeep80

New Member
Jun 8, 2014
3
0
0
maine
thx for the response....i haven't got my hands on carb cleaner in order to test for air leaks but yes this problem seems to be on and off...in fact i just returned from a bike ride ....bike started first pull with little choke.....idled normal for at least 3 or 4 mins so i thought huh...maybe the problem has gone away....i drove the bike at least 3 or 4 miles and it rode great as always.....but as soon as i stopped the motor went into the store and fired it up again....immediately it started to act up....idle climbing from 2100 rpm to 3600 rpm so i closed my choke past half way and the rpms came back down....tried riding it with the choke almost shut but it did not respond well at all so while i was driving i reached down and opened the choke to the operating position and continued back home running as smooth as ever untill i come to a stop and the idle stays up high at 3400 to 4000 rpm...If i had a air leak i dont think the bike would run so well at speed seems to be only at idle when it acts up.....Any help would be appreciated Thx
 

Patchy

Member
Aug 12, 2014
87
0
6
California
Have you checked your spark plug to see if you are running to rich or lean? When I was messing with the jets on my bike it would run weird; I'd have to hold the choke half open with my foot for it to run normally. Turned out I needed to upjet. But I'm done rambling, and I just thought of something more relevant!

How tightened is the idle screw on your carb? Mess with that, it might just need a quick turn. Also, check in the carb that when you release the throttle all the way, the slide falls pretty much all the way down. It could be stuck a little above the perfect idle position.