Motorcycle Forum banner
1 - 13 of 13 Posts

·
Registered
Joined
·
66 Posts
Discussion Starter · #1 ·
On my '73 Honda CB350g, the carborator on the right side has no compression. The left side has great compression. I have adjusted the valves to the correct tolarances. But still the bike is only running on the left cylinder. Any sugguestions would be helpful. Thanks.
 

·
Premium Member
Joined
·
5,750 Posts
Have you actually had the compression measured on the right cylinder, or does it just not fire? If it just doesn't fire, check the spark - insert a spare spark plug into the wire and hold it against the engine while turning it over. Note if there is a spark, and how 'hot' it is; a hot spark is a bluish white, with a sharp snap sound. If it's thin and purplish, the condenser is probably bad. If it's yellowish, there is something limiting the power of the spark.
 

·
Registered
Joined
·
66 Posts
Discussion Starter · #3 ·
I tested the compression and it was around 75, not sure what the units are, but it was the same on the cylinder that is working. I have good spark too.
 

·
Registered
Joined
·
116 Posts
compression test

put a teaspoon of oil down the spark plug hole and check it if your compression comes up the rings are shot :cool:
 

·
Registered
Joined
·
66 Posts
Discussion Starter · #5 ·
I rebuilt the engine and it has new rings. Ive got good compression when i measured it out of the spark plug hole. I just done have suction through the carborator.
 

·
Premium Member
Joined
·
5,750 Posts
Did you have the throttle wide open when testing the compression? 75psi is extremely low, less than half what it should be. Combine that with no suction through the carb tells me that the cams aren't timed correctly.
 

·
Registered
Joined
·
66 Posts
Discussion Starter · #7 ·
I went back and checked, my throttle doesn't return and was open a little. I've got more compression now. Haha. I adjusted the cams earlier today to the tolerances in the book. I also took the top of the carborator off, and there are no holes in the vaccum and everything seems to be fine.
 

·
Registered
Joined
·
66 Posts
Discussion Starter · #9 ·
Well I guess im not sure. How do I check to make sure it is getting there? I know it is flowing through the carb when i take the screw out at the bottom. But when the bike is running on the one cylinder there isnt any suction on the other carb...
 

·
Happy Rider
Joined
·
2,183 Posts
Try to start or if it runs do that. Not long, then pull the plug on the non running cylinder. If the plug is wet you are getting gas to the cylinder. I do this by unscrewing the plug, holding it in my hand and snapping it to wards a light colored surface such as a concrete floor. If not wet you are not getting gas to the cylinder.
You're compression measurement i believe is psi, pound (per) square inch.
 

·
Registered
Joined
·
15 Posts
WOW...I do not even know where to start.

To check for spark, just clip a timing light on ANY spark plug wire you want to test. You do not need to take spark plugs out. That is for beginners.

OK.... You put new piston rings in it . Did you hone the cylinders?
IF not it will never run right and will always smoke.
No reason to do a compression check if you put in new piston rings. They will not have had time to break in.
The throttle cable seems to have been the problem with no suction at the carb.
Suction not compression.

It is lucky you were checking the suction at the carb and found a problem with the throttle cable.
Make sure the slide is not in backwards. The cutaway has to face to the rear of the bike. Otherwise when you look into the carb and the carb is on the bike you can see the cutaway on the slide.

Make sure to check the chokes.

Have you cleaned the carbs?
You said you put in new piston rings so the carbs had to come off.
When the carbs get taken off they get turned over or shaken and debris can get loose and into the idle jets. Then it will never start or run correctly.

When you did the compression check the throttle has to be wide open. So if the throttle cable was messed up or the battery was low you would have poor compression. No reason to do a compression check if you put in new piston rings.

Many times a beginner can put the camshaft in the CB350 upside down.
You need to have someone experienced to check on that.
 

·
Registered
Joined
·
27 Posts
I rebuilt the engine and it has new rings. Ive got good compression when i measured it out of the spark plug hole. I just done have suction through the carborator.
How does one rebuild a motor and not know any more than one does? This does not add up.

carbs do not have or produce compression.

I tested the compression and it was around 75, not sure what the units are,
I hope you knew when you measured your engine parts. This is ... well I think I have said enough

KB
 
1 - 13 of 13 Posts
Top