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: https://youtu.be/7XCC_Lr3dJs?si=84UnWiotnZpgIc0r

[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]

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]

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.


https://imagizer.imageshack.com/img924/1964/cc9kcs.jpg

[ADKRider]

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


https://imagizer.imageshack.com/img924/1964/cc9kcs.jpg

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]

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.

[CC-John]

The exhaust glowing red would indicate a very lean mixture, or a restricted exhaust. If this bike has a catalytic converter in the exhaust, it could be partially blocked. Try disconnecting the exhaust from the engine and fire it up momentarily to see if it will take throttle. Don't run it for a long period with the pipe disconnected as it's possible to warp the exhaust valve.

[Thumper]

My Templar is doing the same thing. I suspect pilot circuit lean issue. I need to pull the carb and take a look. HOT exhaust, and won't idle after warmed up.

I am sure it is a carb problem. I have a spare to swap in, so I will probably do that.

[ADKRider]

The exhaust glowing red would indicate a very lean mixture, or a restricted exhaust. If this bike has a catalytic converter in the exhaust, it could be partially blocked. Try disconnecting the exhaust from the engine and fire it up momentarily to see if it will take throttle. Don't run it for a long period with the pipe disconnected as it's possible to warp the exhaust valve.

Same behavior. Dies immediately.

Check around the intake manifold at the head and at the carburetor for vacuum leaks. Also check the vacuum hose port on the manifold better yet if you havent done it plug the port off with a rubber vacuum cap. That hose goes to that emmisions control valve. The red glowing exaust pipe is a sighn of extreme lean condition.

There shouldn't be any vacuum leaks as all bolts are tight, all hoses connected, but if you show me which hose you mean (i assume the one connected to EGR?) I'll try it.

My Templar is doing the same thing. I suspect pilot circuit lean issue. I need to pull the carb and take a look. HOT exhaust, and won't idle after warmed up.

I am sure it is a carb problem. I have a spare to swap in, so I will probably do that.

Let me know how it goes. txpowersports is sending a carb and CDI but they haven't given me a tracking number yet

[CC-John]

If that engine has an EGR system on it, a dirty EGR valve that won't close all the way can cause the symptoms you're having. That type of problem was pretty common on older carbureted cars and trucks.. Pulled and cleaned many an EGR valve back in the day to correct lean idle or stalling right off idle. The EGR valve is supposed to only open when the engine is at a high enough RPM to handle it without stalling or bogging.

Honestly, the best thing you could do is to just delete all that emission control crap to prevent ongoing problems as those parts age.

[ADKRider]

If that engine has an EGR system on it, a dirty EGR valve that won't close all the way can cause the symptoms you're having. That type of problem was pretty common on older carbureted cars and trucks.. Pulled and cleaned many an EGR valve back in the day to correct lean idle or stalling right off idle. The EGR valve is supposed to only open when the engine is at a high enough RPM to handle it without stalling or bogging.

Honestly, the best thing you could do is to just delete all that emission control crap to prevent ongoing problems as those parts age.


I had deleted it at one point during this saga, but was concerned about causing buildup in the cats In my exhaust. Can safely say that is not causing it because It was off of my bike for about 3 and 1/2 days of this.

That said, a future project of mine will be deleting the cats, deleting the EGR, and installing a nibbi carburetor.

[ADKRider]

Replace the carb and CDI as per txpowersports instructions. Same issue. Time to wait another 3weeks for them to ship more parts. I'm so effin fed up with this shit. It's goddamn brand new.

[Thumper]

Replace the carb and CDI as per txpowersports instructions. Same issue. Time to wait another 3weeks for them to ship more parts. I'm so effin fed up with this shit. It's goddamn brand new.

I've been real busy with prepping the house for painting (carpentry) and garage door rehab. Finally got time to work on the carb. I installed a back up carb after rejetting it and it is doing exactly the same thing. Won't idle but midrange is great.

So I will check the valves now. Should have done it yesterday before putting the gas tank back on !

[ADKRider]

I've been real busy with prepping the house for painting (carpentry) and garage door rehab. Finally got time to work on the carb. I installed a back up carb after resetting it and it is doing exactly the same thing. Won't idle and runs like crap.

So I will check the valves now. Should have done it yesterday before putting the gas tank back on !

In my case the valves were the first thing I checked. While waiting on txpowersports, a couple coworkers who regularly work on small motors said to I should try checking compression. I'm completely at a loss. Lol

[Thumper]

Just checked exhaust valve. I need to verify I am on the intake TDC and check the intake valve.

I am starting to think I need to adjust the airscrew. It is on the airbox side, so should need to close that screw a little bit for more fuel.

It misses at idle, won't keep idling if I lower the tower to get a normal idle rpm (1200 to 1400rpm). But the responsiveness off idle is excellent and midrange seems fine. This is a new PE28 I got as a back up. Stock exhaust and intact airbox, so this carb should match well. I rejetted (main 120 to 125 and pilot 40 to 42). I am at 1 1/2 turns out, will try 1-1/4 and see if it gets better.

[Thumper]

Those valve are really stable in the 172-FMM (Templar X). They were right where I left them 6 months ago.

But closing the airscrew a half turn smoothed it out. Nice idle, instant and strong response to throttle twist. I should have known it was a minor carb adjustment needed.

[ADKRider]

Those valve are really stable in the 172-FMM (Templar X). They were right where I left them 6 months ago.

But closing the airscrew a half turn smoothed it out. Nice idle, instant and strong response to throttle twist. I should have known it was a minor carb adjustment needed.

I wish that were the case with mine lol. I'm starting to think there's something bigger wrong with mine than just a simple part swap will fix.