1975 CB200t Project (with a question)

[WarwickE36]

Hey all,

Just bought my 6th Honda CB

This time around it's a CB200t...

Bought it as a non runner for $150.

With a Carb Clean and Points Cleaning it fired right up.

I was able to source the front brake caliper parts I was missing and rebuild it. I also replaced the front brake cable as it was completely bound.

I also replaced the clutch cable while I was at it.

The front tire was roached as well, so I bought a Michellin tire and a new tube as well.

Right now I have a fairly solid running little 200t. I did have some holes on the underside of the left exhaust, which was disappointing as they looked very solid upon a cursory check over. I was able to JB weld a couple of plated on an completely seal them back up, the repair is not visible when mounted, which is nice.




On to my question...

I was pretty diligent about cleaning the carbs the first time through. I made sure to clean all the passageways and made sure the jets were spotless, emulsifiers and all. I am however having a bit of an issue with a cold start idle. The choke seems to have no affect on the running at idle. I pulled the air filter boots and made sure the slides are operating correctly and they are. The bike will idle at 1,200 rpm when warm but won't hold an idle cold with those carb settings regardless of choke position. The Spark plugs are new and the ignition timing is spot on. The battery is fully charged as well. To run it now I turn the idle stop screws in 1/2 a turn and let it warm up for a few minutes, then i turn them both back 1/2 turn and it idles at 1,200 rpm as it should. I have the mixture screws set at 1 1/4 turns out and I have tried adjusting those to make it idle when cold but it just wont. I also checked for leaks at the intake boots on both sides of the carb, no issue that I can tell. I have double checked throttle cable routing and operation, both seem fine. The only thing I haven't done is vacuum sync the carbs and I forgot to set the cam chain tension (shame on me I know). Any thoughts???


The only odd thing I found is if I turn the mixture screw in on the left side the idle goes up, even fully in it goes up to 3k rpm...if I do the same on the right side, it will eventually quit. Shouldn't they operate the same? To me maybe that says float height is off on the left side? or both....

Thanks for viewing and I appreciate any input.

Hopefully this winter I will have time to either resto-mod or build a fairly gnarly little cafe bike.

 

[WarwickE36]

Re: 1975 CB200t Project...Update

Bump to add a few things I did today,

I wanted to check a few things off the list so I started with the basic tune up stuff. Some of this I did before but wanted to double check.

1. Set timing (I must have been high on exhaust fumes when I did it the first time because it was pretty far off) Bike has a lot more pull now.

2. Set points gap to .014"

3. Set Cam Chain tension

4. Pulled carbs and check float height. No adjustment needed. 20mm

5. checked all jets and passageways, all clean.

6. Cleaned the mounting surfaces between the carbs and head. Added a thin layer of silicone so ensure there were no air leaks.

7. Re-installed carbs and checked slide height for anything obviously off. Both measured very similar with a quick "stick a drill bit in test"

8. Re set the carbs in accordance to the manual. (Left carb still rev's up the more I twist in the mixture screw... right side still dies when I do the same)

9. Tried balancing the carbs by ear. I am able to hold a steady idle when warm like before.

Choke still seems to have no or very little affect on idle. Starting to feel pretty stumped. I did notice on the airbox side of the carbs it looked like someone maybe used a die grinder inside the carbs in the area where the choke slides up and down. Its possible it's supposed to be like that but the two sides didn't look the same. Perhaps someone modified the carbs?

Thanks again for viewing.

 

[carnivorous chicken]

Just a thought -- have you looked through the back end of the carb to make sure that the choke is actually engaging when you put it on? And that all the parts are there? I can't remember if its this way on the CB200 -- I thin I am thinking of some Cb350s -- but some chokes also have a spring-operated mechanism that opens with more pressure. If that's the case, and the spring is missing, the door is missing, etc., your choke isn't going to function.

 

[carnivorous chicken]

Rereading your last paragraph, although it doesn't make much sense, it's possible that a PO somehow screwed it up but I'm having a hell of a time thinking why.

 

[WarwickE36]

Thanks for the reply Angry Bird. The choke does drop down as it should. In fact if I pull the choke up all the way the choke plates will fully block the entire carb body causing it to stall. I have tried setting the choke 9/10ths of the way to full and the revs don't really come up at all. Viewing them with the airbox boots off, they are about 1/16" from fully closed.... equal on both sides.

My only other thought is that the tach isn't reading accurately... and that 1,200 RPM is actually lower than it appears. I think that's pretty unlikely. Only reason I even consider it is that when I bought the bike the inner part of the tach cable was missing entirely. I took a spare cable from a 350 twin I had and used it.

I can try and snap a pic of the carbs with the airbox boots off and see what you think. It's frustrating because the bike runs great when warm... idles smoothly and runs great through the RPM range and at all throttle positions. It just doesn't make sense that it doesnt like to idle when cold.

My other thought is that I took some sand paper to the points to get it started initially. I did set the gap to spec since then but I wonder if spark isn't quite right causing a weak idle. I may just buy a point set for good measure.