need some help. on my mates bike we had a problem after the bike heated up a little bit and it was brought back to idle, the bike would get stuck at idle and wouldnt rev. only happened after about 1/2 hour of riding but he was able to get it going again from turning it off and playing with the choke. we went for another ride for 1/2 hour and could not get it to rev at all, had to ride home and get tools but we got it going again by starting it with the air filer and lid off. the other day he was riding it and ran out of fuel, so went and filled it up with 98 octane and it would not start. we pulled off the air box and filter again and got it started by moving the sliders on the carbie open and shut while starting it. we rev'd it and it bogged down and revs were laggy when bringing it up to redline. i pulled off a spark plug, it was pretty black but putting it on the frame and turning it over it sparked. so we pulled out the carbies dismantled them and cleaned them all out with carbie cleaner and an air compressor carbies went back on and it seemed to be fine, so took it for a ride and the bike got stuck at idle again when the rev's dropped. we did some reading up on here and found that some people fixed this prob by turning the 3 idle mixture screws all the way in the one turn out, we did that and it idled at 6000rpm with the throttle loosened as far as it would go. we screwed it out 1 more and it idled at 4000rpm we screwed it out again and it idled ok, and rev'd ok. we took it for a spin and going back to idle it got stuck again and wouldnt rev. he has owned it for about 2 weeks and we are going nuts because we can get it going EDIT: ive noticed its blowing abit of white smoke and using abit of coolant, but before these problems got worse the bike went really hard.
for some reason this has an electronic fuel tap. you are able to adjust the fuel flow on a screw on the tap which could be why its stuffing up?! i opened it right up and it blew black smoke and was running really rich and the idle was stuck again. i screwed it in and tryed to lean it off the bike strated reving again but then ran out of fuel eventually, i've tried a few other setting and its still weird. should i rip off the elec fuel tap and put a manual one on and re-plumb the fuel lines?
also has new plugs in it. we were able to go for a ride for about 5 mins then it died again.. doing the stuck rev thing
Well to begin with the bike should have a pump, and it should only pump when its needed. I've by passed the fuel tap on my bike (******* rubber rings) and used a Y/T pipe as a junction between the reserve and main tank, put in the filter between the pipe and pump and it runs fine. Some of the symptoms you're describing is exactly like my old problems. A valve on the carbies was snapped off and was leaking the vacuum needed to run properly. No amount of cleaning will fix that, my old mechanic, and my hard earned $200 for a dodgy job (he also managed to drop them and snap the accelerator connection, then used a cable tie to fix it.) can attest to that. Im not sure if Spark Plugs will do that to a bike, but make sure they are the right ones, dopey nutsack of a mechanic put the wrong ones in and it was burning fuel pretty quickly. Good luck with finding the problem though, i just hope for your sake it isnt a broken valve.
Charlie - it really sounds like a carby issue. so you need to make sure that 1) the float valves are not passing, 2) the float levels are good, 3) there are no air leaks in the carb to head rubber boots, 4) the air filter is fitted to the carbs properly. Also check for correct spark plugs.
ok bike has a fuel pump, reserve line goes straight to the reg then to the fuel pump. on line goes straight behind the fuel filter. noting in the carbies is broken, fully pulled them apart, again. used carbie cleaner and air compressor on everything. put wd40 on the sliders to make sure they wernt sticking. we put in CR8E plugs which im 99.9% sure are the right ones im not really sure on how to adjust the float valves or float levels the carb to head rubber boots are have no leaks, but the air box is abit loose on the boots (say 1-2mm) on my bike its tight. im sure it some sort of fueling issue. mucking around with the idle mixture screw we got it to idle good, but noticed that there was bugger all fuel running into the filter, i opened up the fuel reg to let more in and after a min on running more fuel the rev's stuck, i screwed it back in as it was running to lean it out and as the last bits drained off it was able to rev again until it ran out of fuel, but even when we have it going good down low 2-10000rpm it will bog down heaps from 10000 till redline
Mine didnt stick either, a L shaped very tiny hollow tube had snapped off of the outside, and that was leaking the vacuum. There are a few threads around here that explains this. As for AirFilter, mines always loose, might explain the **** bogging at <8000RPM, but that might be anything to do with the carbs. If you believe its fueling issue its simple to rule out: Close one of the fuel lines off (I bent my hose and placed a peg on it, similar to how u stop a garden hose whilst on the prowl), remove the other line from the tap/reg and connect directly to the filter. If symptoms persist, see your carbies.
Just above the very bottom left spring is a little tube thingy, the mechy called it a valve and it was leaking the vacuum.
The little tube thingy is the fuel feed to the starter jet. The black plunger peeking out on the other side (visible on all four carbs in the picture) is the starter jet plunger, and if its seals are worn out it will suck wind ferociously.
Don, by that do you mean that is the fuel mix adjustment for starting? I am not familiar with the 3LN carbs. I can see significant staining on those on the right, which makes me think they are leaking fuel.
still no luck with these carbs. have the same vaccum problem now on 2 engines and 2 carbs. would it defently be vacuum related or could it also be spark related? i noticed that one of the plugs lead had been pulled off its rubber bit connecting to the plug, it jammed in there and it sparks though.
The plug cap has a little brass screw, like a sheet metal screw, that bites into the lead. Trim the lead back about 1/4", then twist the cap on until it's snug.
So theory is the fizzers jet needles are at 45 degree angle and with the poor design on retaining needles square thus wearing jets oval? and on closing of throttle from high rpm creating mass vacuum when worn and or warm there pulled of there seat and over fuels the hell outta The engine flooding then down low the exup creates back pressure i believe making it hard to A. Rid excess fuels B re seat needles maybe?
@josh g these posts are more than ten years old. 30 year old carbs should be completely overhauled, including the parts you mentioned. Anything less is a waste of time IMHO
