G50B Runs bad after 30 minutes. Ignition?

[Superchief500]

I have thumbed through some pages here and I am unable to find what I am looking for. I have a 500 Superchief that starts throwing a fit after about 30 minutes of run time. It starts to loose power pretty bad. After it cools off out runs great for another 30. I would like to know if anyone has the test procedure/OHMS for the ignition coils and the 3 coils behind the flywheel. My suspicion is the condensers but I want to test the other coils too. If I need to replace the condensers, what would I need and where could I find them? Also the battery does not charge. Another reason I would like to test the coil behind the flywheel. A wiring diagram for the ignition system would be helpful. I know... I am asking a lot here lol but I do appreciate any help! Thank you in advance

[dave phelps]

I have 2 superchiefs that run great for about 20 minutes when its warm out and eventually will do the same thing. Are you sure its not a fuel/vaporlock issue?? I believe mine is. Or possibly the stator plate heats up and warps a tiny bit(just a theory). And one is a points fired ignition and the other is converted to CDI. The points one will fire quicker hot than the CDI engine.
Good luck with your issues and keep us posted on any findings you may come across.
Thanks
Dave

[Don]

What does it do when it's running bad? Does it have a miss or just not achieve RPMs? Does it backfire at all?

[Superchief500]

Hey Dave thanks for the reply.I never thought about the stator warping when it's hot. I think I will put it back together and check the ohm readings before I start it and after it starts acting up. There will be a difference I am sure bu it shouldnt be significant change I wouldn't think.

Thanks for the reply Don. It just loses power kinda like it is flooding out. It doesnt backfire or miss. The plugs are just a touch on the dark side, but not black and sooted up

[Don]

The G50B has a reputation of losing spark on the flywheel side when the engine gets hot and stator plate warps, but you can usually hear a partial miss. Yours sounds more like a fuel problem, maybe as simple as a stopped up fuel tank vent.

[Superchief500]

I am back. It's been awhile since I had the chance to tinker with the atex. So i took it out and about 30 minutes later, it started losing power. After i notice it starting to lose power, it's only a matter of maybe one minute and then it wont move anymore. The power loss happens very quickly. It will idle and it revs up slowly to about 3/4 of the max RPM. Then as I put a load on the motor, it falls on its face. I pulled the plugs and the left plug is dry and the right plug is wet. I am finding about a 60 degreed difference in exhaust manifold temp from side to side. The wet plug cylinder holds the lower temp. I pulled the plugs right after it acts up and both plugs show spark. Both cylinders show 120psi compression while hot. I cant hold the throttle open and pull the rope at the same time so that reading is not wide open. If I let it set for 15 minutes, it will run fine for another 15 to 20 minutes. I am not sure where to start here. Its dropping the right cylinder believe. It has a 50mm Mikuni bowl type carb on it along with some flex pipe from the manifold to the silencer. Can someone please post a pic of the stock pipe and carb? The PO has it set up this way. Thank you in advance

[Panella]

I'm not familiar with the engine.

Is there gasoline in the oil?

I had the same symptoms with a 16HP Vanguard. One of the previous owners had plugged the external float bowl vent to atmosphere with a vacuum line with a screw in the end. I assume that it was plugged for storage, as I've read that is recommended procedure, though it might have been used as a tuneup tool. When the engine warms up, increasing fuel vapors will be passed to the intake manifold via the internal vent and also possibly via increased pressure in the carburetor, which is calibrated for an open vent. The mixture becomes so rich that the mixture isn't combustible, and the engine is flooded, until enough of the fuel has either evaporated or leaked through the tiny gaps in the piston rings and into the crankcase.

I've heard that a dirty carburetor also can cause the engine to flood.

[Superchief500]

Pamela thanks for the reply. This is a 2 stroke engine. It vibrates bad enough that gas will start to dribble out of the over flow tube. At low rpms the motor doesnt vibrate real bad and the carb will stop dribbling. I dont know if this is part of the problem or not. I am hoping to learn what the stock carb is. Float type or diaphram type. I vapor lock could be an issue I suppose. I cant believe how hot this thing gets. The plastic hood can burn a person very easily

[Superchief500]

Panella.... spell check got me

[Superchief500]

Panella thanks for the reply. This is a 2 stroke engine. It vibrates bad enough that gas will start to dribble out of the over flow tube. At low rpms the motor doesnt vibrate real bad and the carb will stop dribbling. I dont know if this is part of the problem or not. I am hoping to learn what the stock carb is. Float type or diaphram type. I vapor lock could be an issue I suppose. I cant believe how hot this thing gets. The plastic hood can burn a person very easily

[Panella]

Superchief500,

I didn't notice anything too hot, but otherwise the symptoms were identical, except that I didn't have a compression tester to check the compression. Regarding the one wet plug, I was able to remove the wet one without a wrench, so a loose plug probably would explain the wet plug.

If it's running hot and airflow is unimpeded ( blower in good condition, cooling fins clean, etc.) it might suggest a lean mixture. A plugged bowl vent should run lean until the heat causes enough vapor for a rich condition.

Flooding also might suggest a bad float needle or dirty seat.

How ratty is the exterior of the carburetor? The exterior condition might suggest the interior condition. The exterior of my carburetor was filthy when I pulled it, and the interior had varnish and other dirt. I'm overhauling it.

[Panella]

Screenshot_20200701-083319.jpg

Dirty carburetor.

Screenshot_20200701-083338.jpg

After some elbow grease.

[Panella]

Although, failure to charge the battery probably indicates a problem with the stator. Have you tried a spark tester when it's hot?

Check all your wiring, too. When I recently acquired the '91 Max II, I took it for one ride on my driveway and then couldn't get it started. I cleaned the battery terminals. No dice. I looked closely at the wiring, and I found a wire that was caught behind the shifter. I taped the wire and relocated it, and it started right up.

A wire with compromised insulation might not be problematic until the engine gets hot.

In other words, check everything.

[Panella]

Panella thanks for the reply. This is a 2 stroke engine. It vibrates bad enough that gas will start to dribble out of the over flow tube. At low rpms the motor doesnt vibrate real bad and the carb will stop dribbling. I dont know if this is part of the problem or not. I am hoping to learn what the stock carb is. Float type or diaphram type. I vapor lock could be an issue I suppose. I cant believe how hot this thing gets. The plastic hood can burn a person very easily

Vibration at high RPMs might indicate loose or otherwise compromised motor mounts, though a problematic fuel mixture might also be an issue.

The carburetor has multiple fuel circuits, with separate [overlapping] circuits for idle, partial throttle and full throttle. A dirty nozzle (idle to partial throttle) might cause a lean mixture at partial throttle, and a dirty main jet might cause a lean mixture at 80% to full throttle.

A lean condition can lead to excessive heating.

You might have multiple issues here, with fuel mixture and wiring or stator (charging failure) being separate problems.

For the suspected fuel mixture issue, open up the carburetor. Inspect it for dirt and varnish, and look closely at the needle valve. If there is evidence of dirt or varnish, pull the carburetor and clean or overhaul it.

For the charging and possible ignition issue, check all of your wiring, cleaning terminals and looking for anywhere that a wire might be rubbing against anything. A compromised coil or stator might not be problematic until the engine is hot. Try a spark test with an inline spark tester when it's hot.

[racerone3]

The temp you mention certainly sounds like it is running lean. as soon as it starts running bad, reach up and unscrew the gas cap. Vent may be plugged. I would also replace all the fuel line, it could be sucking shut somewhere and starving the engine for fuel.