Engine starts, runs, but has no power.

[Justinas]

Hey guys, I ran in to some problems with my engine and would be thankful for some help.
I recently got my engine running after rebuilding top end of it. It starts easily both with starter and kick. But sound is somehow strange, a little "klackingy". You can hear it in the video below from 2:10. As it's my first vintage motorcycle, I don't really have anything to compare it with, so if you hear anything bad, please comment on it.

The main problem is - the engine has no power. It revs really high, but when I get it in gear and give it full throttle, the revs get low and the bike barely moves. After few meter engine just dies. The bike is Honda CB 250 G from 1976.
If you have any suggestions, I would be very thankful for them!

Cheers,
Justinas


<a href="http://vimeo.com/47374551">First Engine start // Cafe Racer Project // Honda CB 250 G5 // Justinas Garage</a>

 

[teazer]

It's running on one side and not the other. Try it with some regular gas in a small auxiliary tank and check both sides for spark.

 

[Justinas]

It's running on one side and not the other. Try it with some regular gas in a small auxiliary tank and check both sides for spark.

Thank you! The right cylinder had no spark. Got that sorted out and it sprang to life!


But the left cylinder still sound strange. While left muffler gives a much deeper noise and some smoke, the left one has no smoke and the sound is like in the video - "klack, klack, klack... like. Spark plug comes out covered in black dust. Any ideas here anyone?

 

[teazer]

Let's see another video of it running on both sides at once without any other soundtrack - just the bike running for a few minutes when it's warmed up please.

 

[mydlyfkryzis]

No music and use an auxiliary tank. The bike will not run right if you try to run just of the fuel in the carb bowls. It runs out fast and changes mixture.

 

[Justinas]

So, the video. I wasn't able to capture the sound correctly, but at the end of the video, the sound difference between the pipes should be audible. In reality the right one has quite deeper sound then the left one. And overall it's very freakin loud. It's not clear in the video, but let's just say my neighbors do not like me anymore, after I started it in the morning...


Any comments. Perhaps it's all ok and just needs some milage:] But, as I said, I just don't have anything to compare it to, so any comments would help.


<a href="http://vimeo.com/50595907">Honda CB 250 G5 - Engine test.</a>

 

[teazer]

It's not easy to see in the video but is that a stock motor with stock CV carbs, pod filters and straight through exhausts? Stock carbs don't work well with pods, so they will probably need new jets and compensator jets to get that part right.

Noise is hard to diagnose, but it does sound noisy. What has been done to the motor and did it run when you first got it? G5 and its 360 siblings have a propensity to eat cam bearings, but before we go there, did you set valve clearances on both sides?

I would re-check the valves and I'd probably take the top cover off for a look inside at the cam bearings after that.

edit:
In another thread you showed the underside of the head and it looks like it had been machined and had left a hard edge around the combustion chamber. It is possible that a piston is touching the head when it runs or a valve may be touching a piston. I had a CB72 with G5 pistons that turned over easily - nothing touched, but when it ran it sounded like yours. The pistons were touching the head and that had to be fixed.

 

[Justinas]

It's not easy to see in the video but is that a stock motor with stock CV carbs, pod filters and straight through exhausts? Stock carbs don't work well with pods, so they will probably need new jets and compensator jets to get that part right.

Noise is hard to diagnose, but it does sound noisy. What has been done to the motor and did it run when you first got it? G5 and its 360 siblings have a propensity to eat cam bearings, but before we go there, did you set valve clearances on both sides?

I would re-check the valves and I'd probably take the top cover off for a look inside at the cam bearings after that.

edit:
In another thread you showed the underside of the head and it looks like it had been machined and had left a hard edge around the combustion chamber. It is possible that a piston is touching the head when it runs or a valve may be touching a piston. I had a CB72 with G5 pistons that turned over easily - nothing touched, but when it ran it sounded like yours. The pistons were touching the head and that had to be fixed.

Thank you for such an extensive answer. Damn, I see, I still have a lot of work to do.
Yes, the engine is a stock one. With non stock pod's and straight pipes. Carbs are unmodified. Here comes the first question - is there a kit with proper jets and compensator jets, that I could install myself? Or maybe there are other options for filters, which would be suitable with stock carbs? (I removed the mounts for stock filters before painting the frame :/) The problem is, there are like 5 pre1980 Honda's in the hole country of Lithuania, so parts and specialists are nowhere to be found and my only savior is eBay...


The engine was running when I got the bike, but it does sounded much better. At first I just wanted to change gaskets, but found out that cam chain tensioner was broken, so I changed that. As you noticed, head was also refurbished. I never went deeper than the cylinder heads, so don't know what condition cam shaft bearings are. Hope they are all right, because the more I touch the engine, the more problems it get's:/ Gonna check valve clearances again. If it's a problem with pistons touching the heads, because of machining, how a problem like this should be solved? Some kind of additional gasket?


Sorry for so many questions and again, thank you for any advice or comment.