Two-stroke scooter bogging?

[oldguy]

Ive got this problem with my little 90cc 2 stroke scooter, Its starts and runs sweet, idles fine and revs freely up to a certain point.
When I first take off down my drive it seems all is well, then soon as I give it a bit of throttle it bogs down till I back off, its not missing or anything like that, it just bogs down till I back off the throttle.
I put a new plug in, pulled out and cleaned carburetor, washed and cleaned air filter, and still no joy still doing the same thing.
It runs fine two a point where the auto clutch starts to engage, or if i lift the back wheel off the ground so it has no load on it, it starts to bog at about half throttle.
Its got me beat.

Any help advice would be much appreciated.

John

[iranana]

What kind of carbs are in there? I'm assuming they're the round slide type? I was recently having issues with my RD, and I thought was it bogging down when taking off, but after research and tinkering I found it to actually be running too lean on the pilot jet/air screw. I think half throttle is governed by the needle/needle jet. 3/4 to WOT is where the main jet comes into play. Try raising or lowering the needle by one clip and see if that makes any difference. Raising the clip leans out the mixture (raises the air/fuel ratio), lowering the clip (towards the pointy end) enriches it.

[oldguy]

What kind of carbs are in there? I'm assuming they're the round slide type? I was recently having issues with my RD, and I thought was it bogging down when taking off, but after research and tinkering I found it to actually be running too lean on the pilot jet/air screw. I think half throttle is governed by the needle/needle jet. 3/4 to WOT is where the main jet comes into play. Try raising or lowering the needle by one clip and see if that makes any difference. Raising the clip leans out the mixture (raises the air/fuel ratio), lowering the clip (towards the pointy end) enriches it.

i took this vid may help

[oldguy]

pic of top half of carburetor

[Katman]

Possibly a blocked exhaust. What does the exhaust gas flow feel like when you rev it?

[paturoa]

Assuming this is a recent change, and that it has run fine previously. Done any other changes lately?

I'd try another plug first, though doesn't sound like a plug issue. What "colour" is the plug?

Thoughts are

- is there enough fuel flowing into the carb? In the vid it bogs when the load comes on and seems to recover.
- blocked zorst, builds up back pressure when revs?
- air leak between the carb and head that only leaks when very sucky?

[sgtp]

air/vac leak, but good luck finding it

My scooter developed this same issue, but I could not get it to rev up enough to move out of a parking space before it bogged down (didnt die, just lost all power) I though I blew out the rings or burned a hole in the piston, because it happened immediatly after a 4-500m blast down a 70km zone on my 2 stroke 50cc upgraded to a 80cc. First I played around with the carb and filter, then I broke it down to inspect the barrel/piston/rings. All looked well, but I was in there so I swapped the rings anyway. When put together it was the same issue. I was done messing around with it myself, so I brought it to a shop and asked for a compression test and look over. They said it held 130-140 psi, so that wasnt the issue. They ended up putting a used carb they had laying around and the scoot was back to its usual imperfect but running condition. My guess was that as the vac pressure increased or sustained itself for long enough, some gap is working open and leaning things out.....again, good luck finding it. I've played the game of using RTV on every conceivible point of failure, or emptying a can of CRC on the carb, etc, but never found it. I've since put the stock ECM back in so I am limited to ~55km. It runs fine now, nice tan color on the plug, etc......but on a hot or 100% humidity day, its a dog, lol

[awa355]

My 100cc 2t also bogs down within the first 30-50 metres of opening the throttle too quick when cold. If I take off at a slower pace then there is no problem. It runs fine at any speed after that initial burst. At 11,000k's the scooter still has the original plug in it. When the exhaust came off two weeks ago for a new rear tyre, The mechanic said there was no carbon build up, the colour was spot on.

[oldguy]

What kind of carbs are in there?

Mikuni

Possibly a blocked exhaust. What does the exhaust gas flow feel like when you rev it?

checked exhaust flow seams good, removed exhaust and check port all good there as well, thanks for the advice worth checking

Assuming this is a recent change, and that it has run fine previously. Done any other changes lately?

I'd try another plug first, though doesn't sound like a plug issue. What "colour" is the plug?


Thoughts are

- is there enough fuel flowing into the carb? In the vid it bogs when the load comes on and seems to recover.
- blocked zorst, builds up back pressure when revs?
- air leak between the carb and head that only leaks when very sucky?

Gas flow looks good, pulled the fuel hose off carby while engine was running gas flow nice and steady. there is a vacum hose that runs from the carb to the tank if that was blocked or not working there would be no fuel flowing to carby I pulled it of to check. and block with my finger and fuel flow stop till I reconnected it.

air/vac leak, but good luck finding it

My scooter developed this same issue, but I could not get it to rev up enough to move out of a parking space before it bogged down (didnt die, just lost all power) I though I blew out the rings or burned a hole in the piston, because it happened immediatly after a 4-500m blast down a 70km zone on my 2 stroke 50cc upgraded to a 80cc. First I played around with the carb and filter, then I broke it down to inspect the barrel/piston/rings. All looked well, but I was in there so I swapped the rings anyway. When put together it was the same issue. I was done messing around with it myself, so I brought it to a shop and asked for a compression test and look over. They said it held 130-140 psi, so that wasnt the issue. They ended up putting a used carb they had laying around and the scoot was back to its usual imperfect but running condition. My guess was that as the vac pressure increased or sustained itself for long enough, some gap is working open and leaning things out.....again, good luck finding it. I've played the game of using RTV on every conceivible point of failure, or emptying a can of CRC on the carb, etc, but never found it. I've since put the stock ECM back in so I am limited to ~55km. It runs fine now, nice tan color on the plug, etc......but on a hot or 100% humidity day, its a dog, lol

Is there a way to ckeck for air leaks?

My 100cc 2t also bogs down within the first 30-50 metres of opening the throttle too quick when cold. If I take off at a slower pace then there is no problem. It runs fine at any speed after that initial burst. At 11,000k's the scooter still has the original plug in it. When the exhaust came off two weeks ago for a new rear tyre, The mechanic said there was no carbon build up, the colour was spot on.

I was thinking of trading it in on a new Suzuki125 till this happened it had been running sweet.

[Premature Accelerato]

Try taking the baffle out of the exit end of the exhaust. Its often carbon build up in that, not the exhaust port or the rest of the exhaust that causes power loss. Burn off any carbon with a blow/gas torch if you have one. It makes a shit load of smoke but needs to be done from time to time. A wire brushing will help but burning it off or even sandblasting is better.