Can't get bike running right!!

yooper trooper

yooper trooper

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Feb 28, 2020
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I'm at my its end!! Bike was a one or two kick machine....ran great! After sitting for few months it has become almost impossible to start and if it does start it runs like crap!! I have difficulty getting it started, runs for a short while then stops. Restarts are all but impossible. Pops, sputters and sometimes kicks back. Compression is good, carb (mikuni vm 34) seems ok. It has a TRI spark ignition which Im starting to suspect. It has spark but timing seems to be the problem. Suggestions please.
 
yooper trooper said:
I'm at my its end!! Bike was a one or two kick machine....ran great! After sitting for few months it has become almost impossible to start and if it does start it runs like crap!! I have difficulty getting it started, runs for a short while then stops. Restarts are all but impossible. Pops, sputters and sometimes kicks back. Compression is good, carb (mikuni vm 34) seems ok. It has a TRI spark ignition which Im starting to suspect. It has spark but timing seems to be the problem. Suggestions please.
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It's possible that the Tri-Spark rotor has come loose. Just redo the static timing and both self-tests to confirm or eliminate Tri-Spark problems.

It's also possible that the Mikuni is clogged in some way or that the enricher plunger's rubber it perished; or, that you have water condensed in the tank.
 
Also possible the TriSpark is getting ready to take a crap. It can pass the tests and still be on the way out. Takes a while for them to completely die. I know this for a fact.

Bad gas as mentioned will also do it. StalBil helps in the tank of a bike that sits.

Turn the fuel taps off and remove the float bowl plug with a container that can catch the fuel under it. Open the taps and let some fuel run through. Shut the fuel taps and reinstall the float bowl plug. Open the taps and see if it will start with your normal cold start procedure. Typical troubleshooting stuff.

Try retiming it. If that doesn't work refer to my first sentence.

And yes Mikuni carburetors are hard starting if the choke plunger rubber is shot, but they can still be started.
 
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concours said:
"sitting for few months"

Ethanol fuel corrosion deposits have clogged your idle circuits.

Common problem.

What is your skillset regarding carburetors?
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Pretty good..............all cleaned up and set. Tank drained and fresh gas added.
 
Schwany said:
Does that mean it's running right now or that it had fresh gas in it, and it did not make a difference?
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Sorry for delay, computer stopped also!!! Still not able to start the bike. Has compression, plugs are cleaned and has spark. Ran the TRI Spark test and passed. Right plug mush dirtier than the leftas result of short run yesterday, very sooty. Compression on right side was lower than the left.
 
yooper trooper said:
Sorry for delay, computer stopped also!!! Still not able to start the bike. Has compression, plugs are cleaned and has spark. Ran the TRI Spark test and passed. Right plug mush dirtier than the leftas result of short run yesterday, very sooty. Compression on right side was lower than the left.
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How's the battery voltage? Test with a load like a headlight bulb. Sometimes bad batteries show a full voltage until loaded when the voltage drops substantially. After ethanol fuel problems, battery problems are the next most likely failure from sitting.
 
Another vote for checking the battery properly.

Followed by fitting NEW spark plugs.

If it’s still not right then it’s almost certainly carb blockage related.

This is assuming that the bike was running fine until parked up and nothing was done to it whilst parked.
 
Fast Eddie said:
Another vote for checking the battery properly.

Followed by fitting NEW spark plugs.

If it’s still not right then it’s almost certainly carb blockage related.

This is assuming that the bike was running fine until parked up and nothing was done to it whilst parked.
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It was running perfectly.....nothing done prior to now. Choke lever was stuck in on position and I had great difficulty freeing it up. Took carb apart and cleaned everything up. Choke is now free. I'm starting to suspect faulty float needle or float height setting. Charging up battery today and buying new spark plugs.
 
yooper trooper said:
It was running perfectly.....nothing done prior to now. Choke lever was stuck in on position and I had great difficulty freeing it up. Took carb apart and cleaned everything up. Choke is now free. I'm starting to suspect faulty float needle or float height setting. Charging up battery today and buying new spark plugs.
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yooper trooper said:
It was running perfectly.....nothing done prior to now. Choke lever was stuck in on position and I had great difficulty freeing it up. Took carb apart and cleaned everything up. Choke is now free. I'm starting to suspect faulty float needle or float height setting. Charging up battery today and buying new spark plugs.
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My money is on something in the carb not being as clean as you might think it is.

The most likely cause is so,ething related to ethanol fuel sat festering away whilst parked.
 
yooper trooper said:
Took carb apart and cleaned everything up. Choke is now free.
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On Amal's the pilot jet has to be drilled out, its a small jet and no amount of carb cleaner sprayed down the pilot jet will get the jet back to size. I can't see any other similarly sized jet acting any different. So either get a new pilot jet or find out the drill size to drill out the current one. A 25 Amal flows 25cc of petrol in one minute and is a 17 thou hole and you use a 16 thou drill to clean it out.
 
Single 34mm Mikuni gents. Amal troubleshooting is irrelevant.

Try opening the throttle all the way and kicking it over 4 times key off. Then turning the key on and try to start it normally throttle closed or as closed as you can get it while trying to start the engine. That is how I had to start my engine when the choke rubber hardened after nearly 3 decades of not being ridden. You more than likely will need to keep the engine running with throttle until it warms up enough to maybe idle.

By the way, my Norton sat in the corner of the garage for 27 years and started with two Mikuni carburetors on it after cleaning the white powder out of the float bowls. No clogged jets. Yours should not be clogged after only a couple of months with fuel in it.

As I mentioned previously the TriSpark can still be messed up even if it passes the tests. They stop passing the tests when they are completely dead or not wired correctly. The TriSpark will start an engine with less than 12V, but it is not recommended to use a battery that won't hold 12V with the lights turned on not running. The battery information is in the manual that comes with the TriSpark.
 
Schwany said:
Single 34mm Mikuni gents. Amal troubleshooting is irrelevant.
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Ethanol does the same blocking of small jets on all carburettors, my Keihin carb on my KLF300 and my Briggs carbs all need their pilot jet probing for clean starting every one or two years.
 
Didnt mention year of bike, glass fibre/resin tank perhaps? Modern fuel will dissolve resin in such tanks. Leading fouled carb jets and even accumulated build up on intake valves. You did mention one side lower compression, and a sooty plug.
 
Habe you checked coil primary resistance against Trispark specs? I believe <=3 Ohm is their spec.
 
I now turn the taps off and allow the motor to empty the carbs , then a month later its a one or two kick affair, before it was two or twenty kicks , nothing in between ,,,,,,,,,,
 
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