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Discussion Starter #1
Hi! This is my first time posting, but I've been lurking for a while.

I have a 1975 cb200t that does not want to idle when it's warm.

Here's some history:

It has 2500 miles and is super clean. I bought the bike at Mid-Ohio last year. It wasn't running right then. I pulled the tank and carbs and gave them a good scrubbing, replaced all the carb gaskets (it was missing the o-rings that go between the carb and the boot and the boot and the engine on both sides), and changed the oil. Still didn't run right. Tried to adjust the cam chain and broke the bolt. Doh! Found a replacement cam chain tensioner bolt (not as easy to find as I would have thought). The only way to fix that is to pull the motor. Pulled the motor, replaced the bolt, put everything back together. (The cam chain master link is impossible to find too. Any suggestions on where to get one for next time?) Set the timing, set valve clearance, changed the oil again. This took me all winter, so I figured I should give the carbs a good scrubbing again, just in case. I went through them very thoroughly.

I had the coil and wires tested - they are ok. I just put in new spark plugs. I checked the float bowl height, it's within spec. I have the idle and air mix screws set within spec.

The bike still won't idle properly. I can start it from cold and it will idle high around 3k-4k. As it warms up, the idle drops down to around 2k, and once it goes lower, it just dies. If I keep the revs above 3k, I can keep the bike running. I can ride it around and once it's moving, its runs fine, but as soon as I come to a stop, or pull in the clutch, it dies. If, while keeping the revs up with the throttle, I put my hand over the right carb, the bike falters and dies slowly and I get gas all over my hand. If I put my hand over the left carb, the bike dies almost immediately.

Any suggestions?
 

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I know this might sound silly, but make sure the choke is off, and check the carb slides. If they are backwards, it can really mess things up at low RPM's. If they are like the 175 slides then the notched side should face the air filter.

good luck.:D
 

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Discussion Starter #3
I'm pretty sure that the carb slides are in correctly (I think they can only go in one way), and the choke is definitely off.

Anything else?
 

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Clogged idle jets or passages. They are tiny and very difficult to clean. Did you really blast carb cleaner through the passage and jet or just into them?

Ken
 

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pretty sure ain't good, they can probably go in either way, make sure on one of them that the cutaway on the slide is in front. Only takes a second to check!
 

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Have you done a compression check? That comes early in the diagnostic/tune up sequence, and if you have one cylinder low, you could be chasing carb and ignition problems to no effect.
I'm only sayin'...


FR
 

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Discussion Starter #7
Well,

I checked the carb slides and they are in the right way. The only way that they could go in backwards is if they swapped sides, and I was told to only disassemble one carb at a time to avoid those kinds of mix-ups.

The idle jet and passage were thoroughly blasted. I stuck the carb cleaner straw all up in there and blasted away.

As far as checking the compression, I bought a tester, but the adaptors don't have the right thread. Any idea where I can get an adaptor with the right thread?
 

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Same place you bought the tester? I'd be willing to bet that Motion Pro makes one too.


FR
 

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Do you have pod filters or airbox?
Does it idle better when you choke it?

Check the idle set screw. Your bike's idle should be set for at hot engine, not from cold start. Meaning, you should choke it from cold start, and then set the idle when it is hot.

Check fuel lines. If you have inline filters, consider a test without them.

Then check needle position. Sounds to me like you are not getting enough fuel. lower each a notch or two, this will allow more fuel through the main jet.

Make sure your slides are returning (snapping) to the closed position (should have a wire width crack on the engine side at closed position) on no throttle. They can only go in one way.

Check that the idle set screw is not moving. Vibration can cause is to unscrew if the spring is rusted and not working.

If you have pods, consider re-jetting.

Check that all cylinders are firing. Tap their header pipes with your wet fingers when hot, and see if they are both the same temperature. If one is hot and the other is warm, it could be compression, or it could be the carbs are out of sync (one lean one rich).

Turn in your air mixture screws clockwise all the way to close. See if that helps.

Put a wire through all the holes in all the jets when cleaning. I use guitar string.

Do your tests with good fuel (new fuel) not one month old fuel. Make sure your tank is over half full.
 

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Discussion Starter #11
Right now, I don't have the filters on it, but it was doing the same thing with the stock filters on. It took them off because I've been taking the carbs on and off so much.

When I engage the choke, the bike dies immediately. I can't even get it to start with the choke engaged.

If I set the idle really high, (one to two turns out, I think it should be closer to five) it will idle around 3500, but eventually dies out. The only way I have been able to keep the bike running is to manually keep it running with the throttle, keeping the revs between 3000 and 3500 and periodically pulsing the throttle a little bit, enough to get the revs close to 4000.

No inline fuel filters on it currently. The fuel lines are brand new and the carbs are definetly getting gas, but not overflowing.

The needles are at the stock position, three notches from the top.

The slides are snapping back to closed. They are at the same height when closed, set by the idle set screw.

The idle screws are not moving, the springs are in good shape and not rusted at all.

I plan on keeping the bike stock, it's really clean, so I'm going to be running the stock filters.

Both cylinders are firing, but the left header runs hotter than the right. I'm going to be performing a compression test as soon as I can get my hands on the proper equipment.

I've played with the air mix screw before, to no avail, but I don't believe I've tried all the way in. I'll try that.

I did not use any wire when cleaning the cabs, I'll take them off and try that.

The fuel is less than a week old.

So, to recap, I need to
1) Compression test ASAP.
2) Try running the air mix screw all the way in.
3) Clean the carbs again, running guitar strings in all the holes and make double-triple sure there is nothing in there.

Things I'm also going to check:
1) Torque on the head nuts
2) Valve adjustment
3) Cam chain tension

Have I missed any thing? Any other suggestions?

Thanks for all the help so far, I really appreciate it. Eric (Krapfever) told me this place was great and he's right.
 

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You don't want to run the bike with the air mixture screw all the way in, if that's the only way it'll run then something else is wrong.

Do you have a repair manual for the bike? Reason I axe is it should give you the full tune up sequence which is generally, check cyl head torque, timing chain tension, valve adjustment, compression test, preceded or followed by the typical plugs, point gap and timing adjustments etc.

There's a good reason to follow the correct sequence, it ensures that you'll identify problem areas before you waste time trying to figure out why the later adjustments aren't working. Not trying to sound all preachy, just trying to drop the good knowledge on ya.

FR
 
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