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Discussion Starter #1
I was out running the bike around for a few minutes the other day and it took a crap on me.

It started when I went to take off in first and put load on the bike, it wanted to fall flat on it's face. ran fine, then started loosing power, aggressive popping under throttle, and would have a tough time restarting. Then when I would get it fired back up, there would be little to no then tons of power, or very sluggish...no smooth power delivery.

xtremly erratic with no consistency.

I don't think it's fuel delivery or any air intake issues. I did not have the bike fired up for that long, so I don't think it was overheating.

sounds like shit as well, not as crip as it did a few miles back. I think it might be electical due to the unpredictable nature. would a bad coil cause this, or do they fail consistently?
 

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You might want to take a compression test on the cylinders before you start chasing an electrical problem. It is a quick test and will tell you if your motor is A-OK. If the compression test is good, then move on to check your fuel system (dirt in your carb or fuel filter). Again this is a quick test. After you have eliminated motor and fuel - then start looking at your electrical starting with your timing (points??), sparkplugs and finally coil.

From the description of your problem, any or all items listed above could be the cause. Problem tracking is a process of elimination - one step at a time.
 

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Discussion Starter #3
compression crossed my mind, but i just rebuild the cylinders with a hone and new rings. I'll do a test as a process of elimination.

Do you do compression tests on a warm or cold engine??
 

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First thing you need to do is establish a baseline. Take the time to do it right instead of just using the shotgun approach and hoping that you hit it. Set your timing, even if you just did it, check it again. Replace your plugs, even if they look OK, change them. Adjust your valves, even if you just set them, check them again, they may have loosened or tightened up if you just did the top end. Check all your electrical connectors from the ignition switch and kill switches, points and coil wires. When you have all this done, then you can start looking for specific issues such as coils or compression. Otherwise you can end up chasing a non existent problem like compression that is actually a tight valve.

Good luck, but diagnosis is a very reasoned methodical endeavor that easily goes astray.

Ken
 

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You can check your compression with a cold engine. As the notes above indicate, have a plan to check out your engine in a system type fashion. In my option, start with compression, check your valves settings, Plugs (don't forget to read them and check for fire on the plugs, move to the fuel section and then your ignition and electrical connections. Each of these checks is quick to do and may also indicate more clues on your real problem. The main objective is to leave nothing out and have a systematic method for checking the major components to help determine your problem. Leaving out something (just because it's brand new) really opens you up to missing the real problem...
 

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Discussion Starter #6
sounds good, i'll do a simple tune up on her to make sure the basics are in smooth working order.
 

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Discussion Starter #7
quote:Originally posted by cb175guy

sounds good, i'll do a simple tune up on her to make sure the basics are in smooth working order.
Valves are good
Ignition is perfect (light goes on right at the "f" mark)
condenser is new
point looks strong
plugs worked, but put new ones in,
ignition has spark
Carbs are clean, good flow to each carb.

I can't for the life of me find the adapter for my compression gauge. I might have lent it to a friend, and it never returned....grrrrr
I'll post up my compression readings once I get them....
I am assuming there will be a slight difference in readings since i will be testing compression on a cold engine.
 

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Discussion Starter #8
So i could not retrieve the adapter for my compression gauge so I made on out of a rubber stopper. Compression was at 100 on each side.....

not good.

Just does not make sense. The bike has 5K miles on it and I honed the cylinder and put new rings in. That should have done the trick. Any other suggestions how I would loose compression.

This was done on a cold motor
 

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Try adding a tea spoon of oil to each cylinder and re-try the compression test. If the compression goes up, then your piston rings are more than likely either not seated yet or the rings were not positioned correctly when installed. (The split of the rings should have been positioned 180 degrees from each other.) If there is no change in compression (with the oil added) - then your valve seats are more than likely your issue. I would say your compression should be up around 125 to 150. Based on what you have been saying here - it's looking like your valves need a little TLC.

I am having a similar issue with one of my cb's - I'm thinking my #2 exhaust valve is sticking open. My compression test of that cylinder is down around 95 (the other cylinders were all up around 125). When the engine gets up to operating temp, I'm hearing popping thru the exhaust and noise from that cylinder at idle... My fix will be to replace the engine with one a rebuilt one off my work bench that's ready to go and rebuild that one that's in the bike.

Your fix might be to pulling the head and having the valves rebuilt and or checking your cylinders and rings.
 

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Discussion Starter #10
great advice, thanks. I'll try that this weekend, but right now....

It's beer thirty, and my GF is looking might fine in my sweatpants....
 

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Discussion Starter #11
I went out and bought a new fitting for my bike and ran the compression test again with something more acurate than a rubber stopper.

Cold motor, wide open carbs, off a rolling "bump start"

150 right side
150 left side

with and with out a little oil in the cylinders.

When I rebuilt the motor, I flipped the head over with the valves still in it and filled the combustion chambers with acetone to check for leaks. no leaks. My new compression test would support my findings.

Here is a video of the bike

SO......i'll fire up the bike again today and see what I can find out. I am still guessing it's the coil or some sort of short somewhere in my electrical system.
 

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Discussion Starter #12
fired her up, sounds great. I have the headlight somewhat disassembled so i think there was a short somewhere in that area. I put shrink wrap over the ends that were exposed, and the bike is back to normal....I feel like an idiot for not even thinking about that.....duh

At least she got a tune up out of it all
 
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