Car and Bike Talk
- Thread starter cachsux
- Start date
rod
Retired 22 years
I do have a problem that is bugging me to no end. I have a 1988 Yamaha 50cc scooter that has about 1,800 miles on it that for some reason will idle just fine and mid-range runs good but at full throttle (under load or not) it falls on its face to the point it dies. If you let up on it it starts running again. So far I have replaced the fuel cock (the filter in it was really dirty) that didn't help. Cleaned the carb-that didn't help. Put a brand new carb on it-that didn't help and just the other day I put a new set of reed valves in it -that didn't help. I'm at a loss as to what to do next other than to scrap it and sell parts off it. Its been a great scooter and has hauled my fat ass -a case of beer and a 20 pound bag of ice at 30 mph many times at the races. Any suggestions?
rod
Retired 22 years
I think my next step is to see if it needs new rings. Thankfully the parts for that thing are fairly cheap. (Its the shipping that kills you). The reed valves were like 7 bucks and came in a little envelope that a 50 cent stamp could have been enough to cover it but oh no--10 dollars shipping and handling.
rod
Retired 22 years
its a brand new carb.
Could still be out of adjustment. I have a 2-stroke Mantis that drives me nuts setting the carb.
Ask @1BROWNWRENCH.
rod
Retired 22 years
I've adjusted both the old and new carbs until I've about wore out the threads. Nothing seems to help getting a top end out of it.
rod
Retired 22 years
without air box
with factory air box
with aftermarket K & N style air cleaner
Nothing makes a difference.
Shiftless
Well-Known Member
What does the plug look like?
Me? First thing I would check if the main jet isn't clogged up and the needle is in the right position. I would check fuel flow.
You may have debris or restriction in your fuel delivery that is causing the problem.
If not?
Your asking a lot out of that little motor. Top end maybe? Crank seals? I guess I am assuming its a ringadingee motor??
rod
Retired 22 years
new plug
needle is in the same position on on the new carb as it was on the old one.
I've checked for a kinked fuel line
new fuel cock with new filter
Is it possible the rings are bad?
1BROWNWRENCH
Amatuer Malthusian
Possibly the crank seals are leaky
1BROWNWRENCH
Amatuer Malthusian
Spark is good at the top? Weak ignitions crap out as revs and load rise.
Shiftless
Well-Known Member
So do I have this right, at mid range up it goes into a "BOG" mode till the motor stumbles but it recovers when you throttle out?
Do you have the old plug? If so what does it look like? Plugs speak volumes.
I know its a new carb but float height can cause this effect also. Could your old one have been and this one sticking or improperly set height?
A compression check is pretty simple check with out costing money.
If all that seems good then maybe your ignition or CDI system needs a check?
If you were in California I would also be asking how old the gas is! Stuff just SUKS out here. I have gone to all electric mower and weeder equipment the stuff just kills carbureted engines and goes bad SO FAST!
rod
Retired 22 years
The old plug looked dark but wasn't that bad of condition. It was dry when removed. The old one wasn't that old before it was replaced with a new one when this problem started. Being it is a 1988 I burn nothing but real gas in it--no ethanol and the gas is fresh. The last time I had it in for a tune up at the local Yamaha dealer it cost about $125 and I shutter to think what those bandits would charge if they actually had to get into it. Maybe its time to part it out. Thanks for all your help guys.
Shiftless
Well-Known Member
Just keep tinkering with it. U got nothin to lose!
If it has been a gradual over time issue happening? Probably a bore and or new crank seals.
If it came on suddenly?
Sometimes its "OH shift, how did I miss that" like a piece of something got in the tank and is floating around in the fuel tank and once flow of fuel gets going it rides over the petcock? You know that Stuff u generally don't expect!
Good Luck!
If it has been a gradual over time issue happening? Probably a bore and or new crank seals.
If it came on suddenly?
Sometimes its "OH shift, how did I miss that" like a piece of something got in the tank and is floating around in the fuel tank and once flow of fuel gets going it rides over the petcock? You know that Stuff u generally don't expect!
Good Luck!
rod
Retired 22 years
I'll continue to fix on it until it is broke beyond repair. I'm good at that.
