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Old 08-25-2010, 02:50 PM   #1
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Default need help with a 1976 Honda CB200t...

hi all,

i'm working on a 1976 honda cb200t right now...i've got two main issues that i'm dealing with: 1) hesitation under acceleration and 2) varying engine speed at steady throttle. it seems to me like a fuel/air mixture issue (probably a too LEAN mixture?). but, just for peace of mind, i decided to give the carbs a good cleaning. I pulled them off and dipped the bodies and the jets in chem dip. washed everything out/off with clean water, sprayed everything down with gum-out carb cleaner, and then blew air through all the passageways and holes. i let them sit over night to dry out completely. today, i put everything back together. i made sure the float height was right (21mm from the gasket surface of the carb--with the gasket removed). i made small adjustments to the throttle adjustments on the top of the carbs so that the slides were starting to move at exactly the same time and moving evenly (of course, this is always in in-exact science since i was doing it mostly by sight and sound--so it's possible that this might still be an issue). finally, i set the air/fuel mixture screw OUT 1 and 1/4 turns, and got the idle down to 1200rpms by adjusting the idle screws (they wound up being out about 3 turns each). the idle was strong, and when i "blip" the throttle, it settles back down nicely. so far so good.

i took it out for a ride. on some back roads at 20-35 or 40mps, everything seemed fine. i hit the highway and opened up to 55, 60, 65 and ran it wide open for a few minutes. again, everything seemed great. when i slowed down and dropped back to 4th gear, i started to notice the two problems again: hesitation under acceleration (and general rough running) and varying engine speeds at steady throttle.

when i got it back home with the thought of trying to fine tune the mixture i realized two things:
first, i'm not 100% sure which way to turn the air screw in order to make the mixture leaner or richer. i've always been under the impression that turning the air screw IN (tightening it, turning it clockwise) REDUCES the FUEL and so makes the mixture LEANER (and vice versa with turning the air screw OUT). but--and maybe i'm just overthinking things here)--the fact that my manual (the original owners manual for the bike) calls it an "air" screw makes me wonder if turning it IN actually reduces the AIR and so makes the mixture RICHER (and vice versa). also, my clymer manual (for 1965-1978 hondas between 125 and 200ccs) says that a mixture may be made RICHER by turning the air screw IN and LEANER by turning it OUT. given this confusion (which i'm hoping to all heck that you can clear up for me), i decided to leave the air screws alone for now.
the second thing i realized is that every so often when i "blip" the throttle, i hear what i'll call a "misfire" (though i'm not sure if i'm using that word correctly in this context). essentially, it just sounds like the throttle blip has no effect on the engine and i hear a little "pop" or "poof" from the left cylinder and exhaust (at least, i'm 95% sure it's the left side where i hear it). this doesn't happen all the time...maybe 1 out of every 8-10 times i blip the throttle. i also noticed that, when looking at the coloration of the spark plugs, the RIGHT side plug was wearing evenly and had a nice (though probably a little bit light) tan color. the LEFT side plug was coloring unevenly--with half being about the same color as the right side plug and the other half being a little darker.

here's some other info that might be important: 1) my spark plug wire on the LEFT side is a little chewed and the wire can be pulled away from the cap with a little force (it does not twist/screw in as tightly or as smoothly as the right side). 2) i've got a little bit of oil leaking from the bottom of the LEFT-side engine casing--but it's nothing more than a bad gasket, i think. 3) the exhaust pipe on the LEFT side has some small cracking along the under-side seam, but i've patched it and the patch-work seems to be holding just fine. 4) i've got some oil over flow that drips from the oil over-flow tube that comes off the top of the engine and runs out the bottom (i've noticed an oil spot after a long ride for as long as i've owned the bike).

many thanks for any help/advice..
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Old 08-26-2010, 06:57 AM   #2
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You don't say if you cleaned the fuel system from the carbs back to the tank, but make sure all you are getting is clean gasoline to the bowls.

Replace the plug wires with new. Check every electrical connection and wire terminal you can find for cleanliness and tightness.

Look for broken insulation on the wiring, either by age hardening, friction against a hard point or by someone 'cutting into' the wire for a tap.
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Old 08-26-2010, 07:29 AM   #3
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Sounds a bit lean in the midrange.

The air pilot screw shouldn't affect running above idle. That's accomplished with the needle/main jet. If the needle is adjustable then set it back in the center. Check the number on the main jet and make sure it is stock.

Also check to see that the airbox is properly connected without any holes in it or loose fittings and that the air filter is clean and properly seated.
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