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Discussion Starter · #1 · (Edited)
Hello all, as you may know I was in the process of rebuilding the top end of my cb200. I got the head professionally cleaned and valves lapped. I installed new piston rings, new gaskets, including head gasket. Cylinders honed. I got the bike fired up and running for a day. It didn’t run too well but figured it needed carb tuning.
To my disappointment, while riding the bike had the same problem as before the rebuild, it would bog out and misfire at like 7k rpms and then it died out entirely, needing to be pushed home. After that I tried starting the next day and it didn’t want to start. I finally got it going and I noticed blackish smoke out of right exhaust. It also filled my garage with a smell. Im not sure what it was but it didn’t smell good. Anyway the bike wouldn’t idle and it ran horrible. Like it was completely strained.
So now I pulled the motor again and checked the smoking cylinders valves, the exhaust valve and port is completely black. The other cylinder is still pretty clean with a little black. What does this indicate!?!? Mind you this head was completely pristine before the first start. And compression read below 60 for both cylinders.
IMG_7346.JPG IMG_7347.JPG
 

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Discussion Starter · #3 ·
IMG_7351.JPG IMG_7349.JPG IMG_7353.JPG

This is what the cylinder in question looks like and valves. What is the burnt looking ring at top of cylinder? Could the head gasket have failed?


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Discussion Starter · #4 ·
Your carbs are messed up. Running way too rich.
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Good to know. But I think something else occurred. Could something just carb related cause this? And what else can I do to adjust carbs? My air screws are set to spec, and I adjusted floats.
 

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Repeat after TOOLS:

Your carbs are messed up. Running way too rich.

The black ring at the top of the cylinder is soot from excess/unburned fuel. It correlates with the space between the top ring and the top of the cylinder.
 

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Discussion Starter · #6 ·
Repeat after TOOLS:

Your carbs are messed up. Running way too rich.

The black ring at the top of the cylinder is soot from excess/unburned fuel. It correlates with the space between the top ring and the top of the cylinder.
Makes sense. Good to know my piston rings are working! But what actions should I take to correct it? And that wouldn’t explain bad compression though?
 

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Have you gone through the carburetors? What is the airfilter, exhaust configuration, stock or pods-open exhaust? This is suspect of being over jet-ed on the one side or the timing way off. Sounds like you are confident the top end is OK. Put it together and start trying to tune it. Check the jet size and float levels.
 

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How do you know you had "bad" compression? Black soot and smoke is caused by a rich condition. You need to thoroughly clean your carbs, replace any O-rings, and missing/damaged parts.
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Discussion Starter · #9 ·
Have you gone through the carburetors? What is the airfilter, exhaust configuration, stock or pods-open exhaust? This is suspect of being over jet-ed on the one side or the timing way off. Sounds like you are confident the top end is OK. Put it together and start trying to tune it. Check the jet size and float levels.
Carbs are rebuilt. Stock exhaust. And unfortunately stock air filters which Im sure are restrictive. I was confident top end was good but after the black smoke and really rough running, including the right exhaust being louder than the left. Then It wouldn’t start. So I was worried something was wrong.
 

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Discussion Starter · #10 ·
How do you know you had "bad" compression? Black soot and smoke is caused by a rich condition. You need to thoroughly clean your carbs, replace any O-rings, and missing/damaged parts.
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I did a compression test and this was the result. IMG_7339.JPG
Same for both cylinders. I just rebuilt and cleaned the carbs. All jets new. I will replace the o rings between carbs and cylinders, thats one thing I never did.


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You have the throttle open or carbs off when you checked compression?

This is just after the rebuild before the rings have seated?

Your crappy running condition could've been electrical(coils) or your plug crapping out and putting you on one cylinder?
 

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Discussion Starter · #12 ·
You have the throttle open or carbs off when you checked compression?

This is just after the rebuild before the rings have seated?

Your crappy running condition could've been electrical(coils) or your plug crapping out and putting you on one cylinder?
Yes, Throttle open. Im aware numbers are lower after a rebuild but that low?! Thats about 100 psi low isn’t it? And my ignition coil is brand new. Along with condensor and ignition points, and about 4 sets of spark plugs. Im really at a loss.
 

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Discussion Starter · #13 ·
Im sure my ignition timing is off. But don’t understand how to fix with the lamp. And not sure if that would give me so many issues.
For those helping me out thank you! And a little background of my initial problem,
I would ride the bike for about 10-20 minutes and eventually it would start misfiring. If I up shifted to go to lower rpms it would get better but then immediately misfire again. It would break up very bad, and this was mostly out of only right cylinder. I could feel it stop firing then fire. Completely on/off and then the bike would die. Almost like it wasn’t getting fuel. The next day it would start fine, then same issue after riding. The bike would completely misfire after 7k and wouldn’t rev higher. After the rebuild on my first longish ride, the same issue happened, but felt like both cylinders were having the bogging. Then it died and a day later the bike didn’t want to start and then heres my issue now.


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Missed about 3 posts while I was typing!:evil:

Your original symptoms sound like fuel starvation, possibly due to a plugged fuel cap vent.
 

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If that is all the compression it had, it would not have ran. Have you checked with a different gauge, or even tried that gauge on another small engine? Some gauges will not read correctly on a small engine.
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Discussion Starter · #17 ·
If that is all the compression it had, it would not have ran. Have you checked with a different gauge, or even tried that gauge on another small engine? Some gauges will not read correctly on a small engine.
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Im thinking the gauge is bad. Its harbor freight. My second one from them. The first one before the rebuild also read about 60. I think their gauges are no good. Ive read on small motors people added 40 psi to their number to get actual compression.
 

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Oreilley has them in their small engine section. I use 1/4" size. I'm sure there are other options, but they're a mile or so from me, so it's a quick trip
 
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