Scoot idles and revs great... on the big stand

[scootnewb]

Hello Everyone,

My scoot ran like crap after it became extremely cold here for a couple of days and the throttle froze. Since it warmed up,  the scooter never ran right.

It would pop and bog when giving it some throttle I thought maybe something got messed up with the plug or maybe the needle in the carb froze and broke (yeah that is kind of dumb).

So while it wasn't running right, I decided I may as well change the oil, I also replaced the big wonking paper element fuel filter I had with an inline one and ran new fuel lines and tried again. No different. I changed the plug and added Seafoam to the gas tank, no different.


I ordered a new Keihin and some other things thinking I would learn to rebuild the old one, anyway I got the new carb it came 33/88 and inspected it for debris it was good and should be good with the stock air box but no different. I checked the gas for water, .  

It may have a small layer at the top but I can't really tell.

So I jetted it 33/95 and popped on an after market air filter. This set up is when it always ran best. On the big stand with wheels off the ground it idles and revs out. Really responsive, but if I put the back wheel on the ground it wont move, the engine bogs and pops then seems to suck in air loudly as it dies. 

TLDR

Scoot idles and revs great with rear wheel off the ground. When rear wheel is on the ground, it dies when giving it any amount of throttle, bogs, sometimes pops and you can hear air being sucked or blown from the air filter as it dies. 

Please help, I am starting a new job soon, am poor AF and need this for transportation.

[lilpinny]

You have an air leak somewhere. The freeze might have cracked a line or a part on the intake.

[scootnewb]

Hmm. I also replaced the intake. All new fuel lines, fuel filter, carb. I don't use any vacuum lines. The outlet on the intake manifold is sealed off.

[lilpinny]

It's in there somewhere. Put the bike up on it's stand with the rear wheel off the ground and mist around the engine with starting fluid and see if you find a spot where it wants to rev up. Thats a good way to start hunting down the leak.

I have the same problem with a Vespa I have. It'll run only with the choke on. Turn the choke off and it'll die. That's a good example of it running rich to make up for the extra air the leak is introducing. If I ride it around the block it'll eventually make that air whooshing noise you mention and it'll die. I still gotta find that leak... pretty soon it'll be summer

[scootnewb]

Ok, I will try it tomorrow when the Sun is out. Is there anything else I can use besides starter fluid to check?

[lilpinny]

Brake cleaner, maybe carb cleaner ( the spray) Anything that will ignite and burn clean ( so no aqua net hairspray) Try to keep the spray out of the air intake. That'll make it rev like it's supposed to. Won't tell you anything.

You can so blow a bunch of smoke around it and try to see where it's sucking it in. Like a big vape cloud should show you pretty quick.

[scootnewb]

Excellent. I have brake and carb cleaner on hand. Man, I'm trippin' out on it cause the fuel system just goes from the tank to manual petcock, to fuel filter into the carb and like I mentioned the only outlet on the manifold is sealed off. I think that will be the first place I check. If by chance there isn't a leak do you know what else it could be?


Thanks 

[lilpinny]

Also make sure you look where the intake hits the head. A lot of times the intake doesn't sit flush and it's hard to see. I know I had to file the edge of my intake into a 45 degree angle to get it to sit flush.

[lilpinny]

Feb 13, 2019 21:59:26 GMT -5 scootnewb said:

Excellent. I have brake and carb cleaner on hand. Man, I'm trippin' out on it cause the fuel system just goes from the tank to manual petcock, to fuel filter into the carb and like I mentioned the only outlet on the manifold is sealed off. I think that will be the first place I check. If by chance there isn't a leak do you know what else it could be?


Thanks 

It's an airleak... Untill it's not. But it sure sounds like a leak. those leaks don't have to be very big at all. Could be a pin hole. Finding them is not always easy. Could be in the carb. Could be many places.

Then after that it's the other side of the lean condition, fuel starvation. But look for a leak first.

[scootnewb]

Thanks man, I need to get this thing running badly. I was thinking about messing with it now but the neighbors may get upset.

[scootnewb]

I checked for leaks with the carb cleaner. If there are any the carb cleaner didn't expose them. I misted up and down the fuel line, around the carb and around the engine and the idle was steady. In fact it idles better than it ever did. I am going to try a larger pilot and main and see what happens. Nope. Dang, if I put the wheel on the ground, and give it gas there is a loud air sound that comes from the air filter. Like it is madly sucking in air. I might have to bring it to the shop. And to think I wanted to get a Grom clone and put a 190 motor in it. Like that would have gone well. 

[lilpinny]

Keep us posted.

I bet that slurp is the leak rearing it's ugly head.

[scootnewb]

I'm going to check the valves tomorrow when it's a bit warmer.

[scootnewb]

If there is an air leak, I can't find it. So I checked the valves and the exhaust valve seemed like it was all the way closed. So I adjusted both to .05mm (stock head).

When I brought the piston up to TDC there was a strange, IDK like slosh sound, I don't remember hearing before. But I usually remove the spark plug when I do that. This time I didn't.

I may have left the ignition on cause the battery was dead so I can't test it. I removed the kicks start lever because well, the kick start itself is a huge POS and I've had to replace it twice if I kicked more than 5 times in a row.

TDC
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IIRC









WEW
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[scootnewb]

Well, I can't figure it out and I don't want to spend more money on it. It seems like a money pit since I can't wrench well enough to completely rebuild it nor do I have the proper space. I am literally going to throw it away. Then pick up a new 2t and