Okay, I have a problem with my son LT80, been trying to figure it out but no luck yet. Here are some of details:
· Put in new top-end (compression is @ 150psi)
· New reed
· Clean and boiled the carb
· Clean air filter
· Brand new gas
· New plug and gapped it to spec
· New starter (after market on Ebay)
· New battery (Walmart)
· New petcock (after market one that has on/off/res)
Here is the problem I am having. Engine is cold, I would choke the carb and it would fire right up. Soon as it starts, it would rev to the moon. I would close the choke and rpm would drop to near normal. It would run for about 5 sec and just die. If I choke again, and start it up it would start right away and rev really high again until I close the choke. Been playing with the idle adjustment but so far no luck.
For the idle screw, where would be a good start for it? All the way in, 1 to 2 turn out…??
Also, after a few starting of the motor the circuit breaker would trip and I would need to reset it. What would cause the breaker to trip so often? I only crank it over like 3x and the breaker would trip.
I am going to order a carb rebuilt kit next.

 

IMO: A carb kit isn't going to fix it.
When it's revving to the moon, is the machine trying to move? If you leave the choke on does it eventually slow in rpm's? If you leave the choke on does it warm up and run correct?
Maybe try lowering the needle.

I think the starter may be drawing too many amps.

 

IMO: A carb kit isn't going to fix it.
When it's revving to the moon, is the machine trying to move?
[TN09] Yeap, it wants to run away

If you leave the choke on does it eventually slow in rpm's? If you leave the choke on does it warm up and run correct?
[TN09] No, not really. If I close the choke after it has started, the rpm would drop to near normal but won't idle. I would blip the throttle to keep the machine from dying. After about 20~30 seconds, it would just die even if I pin open the throttle. It almost sounds like when you are draining gas from a carb on a 2-stroke bike. Can of like when you would shut off gas to the carb and you would let the bike idle, just about when it run out of gas in the bowel the rpm would increase.

Maybe try lowering the needle.
[TN09] The needle is in the middle position. I can try this.

I think the starter may be drawing too many amps.
[TN09] Purchased the starter on Ebay. I just have to be careful not to crank too much, don't want to fry electronics on this bike. I dump enough money into this bike already.

Do you think I might have an air leak somewhere?? Bike is driving me nutts!!!!!!

 

It sounds like it has an air leak between carb and the cylinder (It's sucking in extra air, leaning the air/fuel mix, causing it to rev, the reason it slows down when the choke is on is because with the choke closed, it limits the amount of air going into the carb richening the air/fuel mix back to where it should be... is it a two-stroke, cause it could have a crankcase air leak?

 

Air leak: Yes. Sure could be.
Try spraying carb cleaner around the intake altho they don't usually leak there.
I'm thinking main/crank seals.
FYI: on a LT80 carb, the choke lets more fuel in. It don't have a flap that closes like bigger carbs.

 

If the choke lets in more fuel, that would explain why the motor is revving so high when I first start the bike. Like I had mentioned before, if I close the choke after it fires up the rpm would drop to near idle. I will double check the needle position and if I put the slider/needle in correctly.

If the main/crank seals need replacing, that would require to split the case, which would be too expensive since I would need the help from my local mechanic.

 

Hello...


Are you sure the throttle barrel is in correctly? I remember rebuilding my daughter's carburetor some years ago when I first started working on ATVs (have worked on small engines for 35 years, but never got into ATVs until a few years ago). After "completion" of the rebuild I had the same thing happen---I had the throttle barrel in backwards and it was holding open and racing--luckily I had the rear up on jacks and there was no problem.

Hope this helps...

Keep us posted!

Tom

 

Hi Tom,
Thanks for the suggestion on the carb slider. For this carb, the slider only can go in one way. I wish it would be this simple of a fix...lol

It almost sounds like the motor is running out of gas. If I choke it, it would fire right up but would rev really really high. Close the choke and rpm would drop to near normal. Would blip the throttle to maintain idle then after 20-30 secs, it would just die like there is no gas.

But you know, gas and air leaks are very hard to tell apart. I will keep you guys posted on what I find.

 

"If the choke lets in more fuel, that would explain why the motor is revving so high"
But it shouldn't want to run away.
"If the main/crank seals need replacing, that would require to split the case"
Not so. The seals simply pry out and push in. You would maybe need help to pull the flywheel tho..
Seals are like 3 bucks each.

Maybe the barrel is in backwards..

 

“But it shouldn't want to run away.” Can you please explain why it should not want to run away?

“Maybe the barrel is in backwards..” Which barrel are you referring too?

“Not so. The seals simply pry out and push in. You would maybe need help to pull the flywheel tho..
Seals are like 3 bucks each.” Maybe I can save this bike if I don’t have to split the case. I hate to give up on the bike since I have invested so much money and time already. Plus it is for my son to ride, so I am trying not to disappoint my son by not being able to fix it.