March 9, 20188 yr Hi all, Ive been working on my 2006 beta rev 3 trails bike for days now trying to find the cause for an issue im having. Bike runs and idles ok although the exhaust does pop a little but im unsure if this is normal with it being a two stroke. The issue im having is that when i rev it up even on the stand and in neutral, the bike takes way longer than expected to return back down to idle. Ive chased a whole host of potential problems and I cant seem to find any faults. ive checked the airbox for cracks or holes and found none, ive checked the airbox to carb rubber boot and found no issues there and then ive taken the carb apart and cleaned out all the ports by spraying carb cleaner down them and cleaner comes out of the ports(at the other end). Ive checked and resealed the carb to engine rubber hard boot too and that seems fine. throttle cable seems fine although the snap back at the carb (mikuni) isnt as sharp as i thought it would be but it does shut quickly. The research i have done suggests air is coming in somewhere but i cant see where?or how? Does anyone have any suggestions to what it could be?
March 9, 20188 yr its probably running too lean.... just richen up the bottom end a little at a time and see if it helps....
March 9, 20188 yr Author 1 minute ago, thall1 said: its probably running too lean.... just richen up the bottom end a little at a time and see if it helps.... How would i do this? I think the mikuni i have only lets you regulate the air
March 9, 20188 yr if its a fuel screw then open it up to increase the fuel, if its an air screw then close it up to reduce the air - reduces the air to fuel mix ratio..there plenty on this site about setting up these carbs.....I think there are some mods that can be done as well....
March 9, 20188 yr Worth checking crank seal - flywheel side - for air leak. Can give similar symptoms.
March 9, 20188 yr Author 53 minutes ago, lsv said: Worth checking crank seal - flywheel side - for air leak. Can give similar symptoms. Crankshaft seal/bearing or did you mean the crankcase seal? Sorry if thats a stupid question im a complete novice here
March 10, 20188 yr It’s not the air before the carb that influences engine run down from acceleration, its the air that can be drawn in from other areas including the throttle slide. So as suggested by others, crankshaft oil seals, crankcase drain bungs, cylinder base gasket, carb air leak after throttle slide( engine side), breather pipes blocked, kinked and incorrectly routed. Popping at the exhaust could be ignition incorrectly set, possibly crankcase containing excess fuel residue, the list goes on.?
March 10, 20188 yr 1 minute ago, section swept said: It’s not the air before the carb that influences engine run down from acceleration, its the air that can be drawn in from other areas including the throttle slide. So as suggested by others, crankshaft oil seals, crankcase drain bungs, cylinder base gasket, carb air leak after throttle slide( engine side), breather pipes blocked, kinked and incorrectly routed. Popping at the exhaust could be ignition incorrectly set, possibly crankcase containing excess fuel residue, the list goes on.? You can experiment with richening and weakening the mixture by adjusting the carb needle. This may also be very worn as will the main jet allowing too much fuel in and hence the engine trying use up the excess fuel. This would also cause the engine 4- stroke and try to bog down. Are you using a manual? I ask as it appears to me that by asking how to alter the mixture you are not that experienced. Please take that comment with the good intentions meant by it, we all learn something new each day and this forum and it’s members have a wealth of experience to share and to learn from???
March 10, 20188 yr hello, check the slide needle to make sure it is held in place properly. if the hold down clip is missing the needle will slightly rise out of the emulsion tube allowing excess fuel to be delivered to the engine at idle and cause the engine to not return to idle quickly. the needle has to be positively held or the vacuum created at idle with the slide closed attempts to pull fuel thru the main jet and feeds the motor with excess fuel at idle.
March 10, 20188 yr Author 10 hours ago, section swept said: You can experiment with richening and weakening the mixture by adjusting the carb needle. This may also be very worn as will the main jet allowing too much fuel in and hence the engine trying use up the excess fuel. This would also cause the engine 4- stroke and try to bog down. Are you using a manual? I ask as it appears to me that by asking how to alter the mixture you are not that experienced. Please take that comment with the good intentions meant by it, we all learn something new each day and this forum and it’s members have a wealth of experience to share and to learn from??? Im certainly not very experienced. I have all the manuals for the bike but it never covers much in detail. I have a screw only for air and a screw for idle speed. The bike doesnt cut out or even change engine note even when the screw is all the way theres not much i can do there till i find the problem. Will be removing the fly wheel this week and changing the crankshaft seal just to rule it out
March 10, 20188 yr Author 10 hours ago, scifi said: It might have the additional flywheel weight... looks like a small discus. . I never thought of this! I will check it when I can get it off next week
March 12, 20188 yr No need to strip the cover off to check. If there is a plastic spacer between the casing and the cover, it should have a weight on.
March 12, 20188 yr On 10/03/2018 at 10:12 PM, mattmahon10 said: Im certainly not very experienced. I have all the manuals for the bike but it never covers much in detail. I have a screw only for air and a screw for idle speed. The bike doesnt cut out or even change engine note even when the screw is all the way theres not much i can do there till i find the problem. Will be removing the fly wheel this week and changing the crankshaft seal just to rule it out Hope you get to the route cause of the problem. Lube the oil crankshaft seal lips with either two stroke oil or a smear of silicon grease. Good luck, let us know how you get on??
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