Engine surging

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dwarfy

dwarfy

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Was out with my mate today and towards the end of our run his engine started surging. He would hold the throttle steady and the engine would rev in surges on its own. Not heard of this before but my thoughts were either an air leak or defective carb. The clunk was clean and at the bottom of the tank and the air filter was also clean.

Any ideas anyone :confused::confused:
 
im guessing air leak also.
grab the carb and give it a stern wiggle, look for any movement. carb and manifold to cyldinder should be snug as a bug tight. any movement (not wiggle movement, but acutal movement) is a sign of loose bolts.

check intake manifold, carb, exhaust and cylinder bolts, and also the spark plug. all of these can/have come loose while running. i always make it a habbit of occasionally checking each of these to ensure they are tight.
 
both my engines were doing the same thing, i did a carby swap on one and it didnt do it again, but could only test briefly before my clutch spring died.

sounds like an air leak or something in the throttle linkage, check receiver battery voltage and if anything appears to be sticky in the linkage.
 
i had suggested the servo cause i had that happen to me before. the servo would start going hay wire then stop then start again.
 
+1 WITH fOXY,tIM AND tRIP,GOTTA BE AN AIR LEAK.iF THE ENGINE IS HUNTING LIKE THAT ITS NORMALLY DOWN TO A BUST GASKET OR LOOSE MANIFOLD.
j.

Oops,caps lok but I cant be bothered typing again.
 
Lets not forget the crank seals & bearings might be worn. How old is the engine? when was the ring last changed?

A long shot and unlikley but I known a faulty spark plug give similar symptons.
 
also, check ya battery packs! ...sounds daft, but about a year ago i had ver similar problem.. the throttle would glitch, in turn the engine would surge.

I Tried all sorts, new reciever, spark plug, throttle linkage, air leaks etc... in the end i had 2 battery packs & they BOTH had dodgy connectors, when the engine was running the vibration would cause the battery connection to hit & miss in turn causing the throttle to glitch!. I only found out after i decided to try a new battery pack as a last resort thinking that there was no way i would have 2 dodgy battery packs!! how wrong was i lol :(
 
you can watch your servos. if they are slightly moving with the surgeing. then its probalby an electronic glitch happening. but easy way to find out, leave everything off, and fire up the motor (be sure T/B servo is at idle).

if it is surging with the elecs off, its an airleak somewehre. if it only does it with the elecs on, keep your eye on the t/b servo looking for small movement.
 
how have you got it wired up? do you have an on/off switch or do you just hard wire straight to the reciever with no switch? (this is the method i use as switches are prone to going faulty if bashing in muddy/dusty areas etc).
 
Mike1970 said:
Lets not forget the crank seals & bearings might be worn. How old is the engine? when was the ring last changed?

A long shot and unlikley but I known a faulty spark plug give similar symptons.
Click to expand...

crank seal is what did it on my cy. we replaced the carb and crap on the way to figuring it out. was still doing it. the cy 26 in the 4wd vw conversion.
 
We checked the servo for glitching and it was fine - no movement at all. It only does it at half throttle upwards and is fine a tick over but it sounded lean to me so I suggested an air leak to him. He will have to strip it down and rebuild it.
 
if its doing it at only higher RPMS, then that leads me to think its being cuased by the higher case pressure at the higher rpms.


I would check cylinder gasket, spark plug, and crank bearings/seals.... if it was the carb or intake, chances are it would happen thruout the rpm range. if i t was the exaust same thing. but the case gaskets, cylinder gaskets, and oil seals are what i would suspect considering your only seeing it at the higher rpms.

cylinder gasket would be 1st guess (may just be Loose Cylinder bolts too). then oil seals. get to the clutch shoes, and see if they have any up/down movent while on the crank.
 
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