KE125 exhaust firing, sneezing, power loss

lgajohnymac

I have a problem and looking for ideas. Bike is a 76 KE125, less than 800 original miles. Everything is original. Slight rusting on outside of tank, inside looks good, I couldn't see any rust in there looking from the cap. The header looks like it rusted and was repainted. The fuel oil pump works, I have not confirmed the flow rate, but as much as I have been able to ride it, I don't think its a problem.

Here is what is happening with it. Bike starts fairly with the choke in a sweet spot. It will idle. after warming, it idles fine as well off the choke. After warming up, it will only go 1-2 miles before I get a sudden power loss, backfire and sneezing. The bike also will not start again for several minutes, but repeats the symptom quickly. Also, the bike is not throttling up from idle cleanly. It seems to bog a bit, and does not seem to wind through the rpms without a lot of rough running. However I was able to get it up to about 45 mph before the symptoms appear. The acceleration seems about right for a 13hp engine.

I have pulled the carb, and inspected it. Its very clean, as one would expect on a bike with less than 800 miles. I looked at the timing, and it is firing a small bit before the indicators line up with an ignition timing light. I adjusted it a bit, and it ran worse with the timing in both directions, so I returned the timing to where it was before. Fuel delivery is good, spark plug gap was verified. I did not note a plug problem with lean or rich mixture of oil in the fuel.

Any suggestions?

Rizingson · Posted: Fri Jan 13, 2012 8:20 pm Post subject:

I would guess that it is running out of fuel. Check for full stream at petcock. Also it is quite likely that the float level setting is too low or valve may be sticking. This would also cause the lean backfiring etc.

lgajohnymac · Posted: Sun Jan 15, 2012 7:12 pm Post subject:

Thanks, but I am not convinced. I guess it wouldn't hurt to disconnect the hose from the petcock and see how fast it flows. It does have a clear gas line, and when I switch it to the run position I see gas run down the hose. Well, when it did stop, I was about a mile from home. I pushed it all the way back occasionally stopping to try and start it. I would think even a low flow would have time to fill the float bowl after pushing for a couple minutes. And the sticking float likely to free itself after a few rigorous kicks on the starter. Its entirely possible I closed the petcock each time I went to pushing the bike after stall. I doubt I would actually...

Rizingson · Posted: Mon Jan 16, 2012 10:47 am Post subject:

Because my first post on your issue is brief (sent from my Iphone), I'll try to clarify better hopefully!. First of all most statements in your analyisis definately indicate fuel issues which I believe you should address first, but also there are symptoms of another problem, namely bad crank seals (bogging down trying to accelerate and hard starting when hot)
A vintage bike with 800 miles isn't the same as a 2 yr old bike with low miles. The lenght of time sitting without being run, is the key element in seals drying up or if not properly laid up, carb jet problems etc.
You could certainly take a plug wrench with you on the next ride and after you can't restart it, pull the plug and lay it across the engine and check for spark, thus eliminating any electrical issues. (I don't believe you have any)
Next you could run some crankcase air pressure/vacuum tests on the seals to see if that is a problem. (procedures can be found on this forum or elsewhere on the internet) Crank seals provide a rubber seal around the crank shaft. Over time, the rubber dries up and no longer makes a seal. When the engine heats up is when the problem shows itself most dramatically. Seals also can be destroyed if end bearings wear and can't stabilize the crank. (unlikely with 800 miles)
Now what I'd do first is verify the fuel flow by removing the line at the carb and inserting into a container and be certain it isn't just dribbling. Next I'd take the carb apart and verify passages through jets and immulsion tubes are clear (hold up to light and physically look through them) If dirty clean with soft wire kit made for that purpose, no need to buy a rebuild kit (especially an aftermarket brand) which would probably cause more problems. Make sure float height is correct and isn't catching on gasket and valve freely drops after being closed. Also pay close attention to the enrichment plunger valve adjustment. It must be able to close and seal when in the normal position. (This is not a choke, and the proper use for starting is different than a choke) Throttle MUST be closed for the enrichment circut to help start a cold engine. If you can't close it or it doesn't seal, after warm up the bike will bog down and die also. (there is no sweet spot, just mis-adjustment or faulty seal)

lgajohnymac · Posted: Mon Jan 16, 2012 11:13 am Post subject:

Wow thanks for the detailed response. I'll spend some time on this during the week and see where I get. Follow up when I get some more info.