Sudden bogging/stalling after 120 miles - Motomax 250

[ADKRider]

Thursday after getting home from work, I went for a short ride and I had a sudden loss of power under throttle. Ever since then, it will idle fine at first, cut out under throttle and then won't even idle properly once warm. I have since cleaned the carb, cleaned the fuel filter, drained the gas (concerned about water), and replaced the spark plug. I am at a loss as I'm not exactly experienced with small motors or carburetors.

The picture of the fuel filter is before I cleaned it out. I got out every little bit of that black shit by blowing with my mouth back through backwards after everything was dried out.

Edit:

[Bruces]

What specs are your valves adjusted at ?

[dirtbkr188]

Did you check the jet needle to make sure it is secure under the "A-clip" and spring in the throttle slide?

[Crossbar]

What dirtbkr188 said. That acts like a lack of fuel. I'd also pull the fuel line at the carb and check you're getting adequate flow from the tank.

[ADKRider]

Valves adjusted to 0.05mm both sides. When I took apart the carb, the the needle seemed secure, but I didn't inspect it closely. Unhooked fuel line and there is a steady flow of fuel.

What is the A-Clip supposed to look like?

[Bill Hilly]

Originally Posted by ADKRider

Valves adjusted to 0.05mm both sides. When I took apart the carb, the the needle seemed secure, but I didn't inspect it closely. Unhooked fuel line and there is a steady flow of fuel.

What is the A-Clip supposed to look like?

You may have picked up a little spec of something it the main jet. I had sudden trouble out of my TBR7 one day. It was not what I would call a bog, but it wanted to cut out, land act up on anything higher than mid throttle. I ran it home on back roads, drained the carb, and some of the gas from the petcock while on reserve, because I know water goes to the bottom. I tried it out, and it still acted up. I asked about it here at ChinaRiders, and got some gas related responses ,and also was told that it may be a loose connection in wiring, or the coil may have a loose ground. I didn't see any loose wires, but I did clean some dried mud off the coil, and unhook the ground, and clean the grounding surface good, and something I did took care of the problem, and it never gave me trouble again. . I did order a coil for it, and did put it on, but my old one was working good in the mean time.
I forget about it, but my Brozz had ,and probably your MotoMax does too have a lot of pollution stuff. I unhooked, and got rid of mine, but I remember a vacuum hose that ran directly to the intake manifold, and I can't remember exactly were the other end ran, but it would have had to be some sort of check valve, or PVC valve. I would check that line, or plug it off.

[ADKRider]

Originally Posted by Bill Hilly

You may have picked up a little spec of something it the main jet. I had sudden trouble out of my TBR7 one day. It was not what I would call a bog, but it wanted to cut out, land act up on anything higher than mid throttle. I ran it home on back roads, drained the carb, and some of the gas from the petcock while on reserve, because I know water goes to the bottom. I tried it out, and it still acted up. I asked about it here at ChinaRiders, and got some gas related responses ,and also was told that it may be a loose connection in wiring, or the coil may have a loose ground. I didn't see any loose wires, but I did clean some dried mud off the coil, and unhook the ground, and clean the grounding surface good, and something I did took care of the problem, and it never gave me trouble again. . I did order a coil for it, and did put it on, but my old one was working good in the mean time.
I forget about it, but my Brozz had ,and probably your MotoMax does too have a lot of pollution stuff. I unhooked, and got rid of mine, but I remember a vacuum hose that ran directly to the intake manifold, and I can't remember exactly were the other end ran, but it would have had to be some sort of check valve, or PVC valve. I would check that line, or plug it off.

I tried cleaning my carb already, but didnt remove the jets and spray through them. I also saw a post on another forum that describes 3 symptoms of a bad coil and mine seems to be doing them. Tomorrow I'm going to try to clean the jets even better and order a replacement coil.

Anyone have advice on a coil to order? Saw amazon has Nibbi coils too, but the one I looked at was too short for Motomax.

[dirtbkr188]

The A-clip is part #7 shown in the diagram below.

[ADKRider]

Originally Posted by dirtbkr188

The A-clip is part #7 shown in the diagram below.

Yes, that whole assembly seemed secure, although I will double check tomorrow when I remove the carb again.

[ADKRider]

A clip is in place. Cleaned carb again installed the new coil. Still have the same problem.

[Crossbar]

Bummer. If you don't mind spending the money, might be worth just trying a new carb. I'm bad about parts cannoning though and I end up with a lot of spare old working stuff.

[Crossbar]

Another thought, might be worth a compression test just to rule that out. Only reason is that you mentioned that sudden loss of power while you were riding...

[CC-John]

I've come across similar problems with chinese engines on various types of outdoor power equipment. What ever they make their fuel hose out of doesn't play well with our ethanol laced fuels, and the hoses begin to "dissolve" internally. That's what all those black specs were in your fuel filter. The hose between the filter and carburetor is doing the same thing but the specs are probably jammed up in the float needle seat and restricting the amount of fuel allowed into the carburetor. That's why it will start back up and run fine for a bit, but as soon as you give 'er the beans, she falls flat on her face.

Pull the carb and remove the bowl, pull the hinge pin for the float and remove the float and inlet needle. Hold a rag over the inlet where the fuel hose connects to the carburetor and using compressed air, blow back thru the seat where the needle sits. Bet there will be a bunch more of those black flecks in your rag. Replace all the fuel hoses with an ethanol resistant fuel hose, and take 'er for a rip. Mower shops are a good source for alcohol resistant fuel line in the small sizes these bikes use, sometimes you can also find it in a well stocked auto parts store.

[Crossbar]

+1 what CC-John said. When you said you cleaned the carb, if you didn't pull the inlet needle, definitely try his advice first.

[ADKRider]

Originally Posted by CC-John

I've come across similar problems with chinese engines on various types of outdoor power equipment. What ever they make their fuel hose out of doesn't play well with our ethanol laced fuels, and the hoses begin to "dissolve" internally. That's what all those black specs were in your fuel filter. The hose between the filter and carburetor is doing the same thing but the specs are probably jammed up in the float needle seat and restricting the amount of fuel allowed into the carburetor. That's why it will start back up and run fine for a bit, but as soon as you give 'er the beans, she falls flat on her face.

Pull the carb and remove the bowl, pull the hinge pin for the float and remove the float and inlet needle. Hold a rag over the inlet where the fuel hose connects to the carburetor and using compressed air, blow back thru the seat where the needle sits. Bet there will be a bunch more of those black flecks in your rag. Replace all the fuel hoses with an ethanol resistant fuel hose, and take 'er for a rip. Mower shops are a good source for alcohol resistant fuel line in the small sizes these bikes use, sometimes you can also find it in a well stocked auto parts store.

I've only put ethanol free gas in it but I'll try it anyway and report back.

Edit: No black bits, no change.

Edit 2: New symptom exhaust cherry red after idling for only I would say 2 minutes.