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Discussion Starter · #1 ·
Hey all!

First post - just got my 1975 CB200 off craigslist last weekend from a guy in NH (I'm in Boston). The bike had been rode something around 15 miles since 2011 (so 15 miles in 8 years!) so is a bit of a project. At first, it wouldn't start.... because there was no petcock! I ordered a replacement, and while waiting I cleaned the tank thoroughly. Put the petcock on (and a new battery), and decided to gamble, and it fired right up. I was able to ride it around the neighborhood a few miles to get it warm as-is with seemingly no issues.

Next up I wanted to check out the carbs I tore them off last night, as during/after the warm-up ride, I noticed that there was gas dripping through the overflow ports. I cleaned the carbs up, reset the float height, cleaned all the constituent parts, and put it back together. Had to take air filters off to do this, got them back on tight enough and they don't look that dirty so probably don't need replacements. No leaks after that! Great news. But then, I noticed that I had perhaps over-corrected - the right carb now must have been off in the other direction, as the exhaust pipe was punching out cold air with no moistness to it - not firing anything! I adjusted the float a bit before taking it out today, and got it in a spot where it'll feed fuel.

The above is *everything* I've done so far - any omissions should be interpreted as "I dunno, it was probably in a garage in New England for the last decade". Now, here's today:

Starting it cold this morning, I lowered choke towards the ground (that's open, yeah?) and fired it up. No problem, and it idled around.... let's say 2,500/3,000 - still way too high. I ****ed with the carb adjustment screws, starting in the "proper" start position then quarter turning each at a time to see the effect. To be honest, nothing really profound seemed to change when doing that. As I was getting it warmed up, and just letting it idle in neutral in my yard, it kept climbing in RPM and so I lifted the choke to close it up to compensate (hitting on limits of my knowledge about proper choke operation here). I jumped on and went on a cruise for about an hour around town, putting ≈15-20 miles on it. As I had it out in town, it just stubbornly kept climbing and ended up getting to a resting idle reporting at 6,000 - how accurate are the tachs over the years on this? I lifted the choke all the way to close it, but now, say I'm at an intersection - I put it into first, lift the clutch and transfer to throttle, and it'll just start sputtering - as if I'm stalling it. If I close the choke the whole way, it'll just shut down (perhaps obviously?), but even a little open, and I just don't have any power to pull on the throttle without it just quitting on me.

So that's where it's at right now - I tried adjusting the carb adjustments while it was warm after the ride but again, they didn't seem to have any appreciable affect whatsoever. Would love advice at this point, and if there's any folks on the forum in the Boston area, would gladly trade a good meal or repair fee to help figure this one out - I'm very eager to learn more but don't know where to head from here!
 

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Sensei
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OK....Choke arm up is choke closed (choked) and arm down is choke open (normal running).....
I suspect you have an air leak causing the run-away idle (and this is somewhat common).......
I've discussed my fix several times on group here, but it would be easiest for me if you would simply phone me while you are at the bike.....
540-525-5199....
 

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Also, check the splitter junction box on the throttle cable. The CB200 cable is just barely long enough to do the job, and it's easy for one of the "split" to come out of the junction when you take the tank on and off.
 

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Discussion Starter · #4 ·
OK....Choke arm up is choke closed (choked) and arm down is choke open (normal running).....
I suspect you have an air leak causing the run-away idle (and this is somewhat common).......
I've discussed my fix several times on group here, but it would be easiest for me if you would simply phone me while you are at the bike.....
540-525-5199....
Thanks for the offer! I'll give you a call tomorrow when I'm working on it again.
 

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Discussion Starter · #5 ·
An update on this thread!


I got a carb rebuild set, replaced the brass and gaskets, and got some viton o-rings that fit the intake boots. I'm fairly sure the o-rings are working now, as I can spray carb cleaner and get little/no reaction when doing so, *and* my engine idles safely without shutoff at 1200/1500 RPM without issue, *and* playing with the carb screws actually has an effect on how the engine runs now - if I screw both the larger/upper screws (not the one closest to the bowl), the engine dies, for example.

New problem! If I run it at anything less than ≈3,000 RPM, and give it any throttle, the engine will just shut off. It almost has the opposite from intended behavior - the more throttle you give, the slower the engine chugs, until it just dies. If you run it over ≈3,000 RPM, it'll work fine, but it's a loud/high idle. Another thing - if you open the choke all the way (all the way down), it'll red line on idle - if you close the choke (all the way up), it dies. If you *just* have it a tad down from the top, that's where I can get it to rev at ≈1250-1500 RPM. Probably still an air leak? What are the next diagnostic steps here for the long weekend, folks?
 

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Sensei
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OK....
IF your float levels are properly set at 21 mm,
and IF your mixture screws are set 1 &1/4 turn out from GENTLY bottomed,
and IF your slide/needle assemblies are in the correct carbs (cut-away towards air cleaners),
and IF the throttle-stop screws are NOT holding the slides up too far (about 1/32" to 1/16" on the non-cutaway side of the slides)
AND it STILL revs past 2500 with the choke fully open (choke arm down),
YOU STILL HAVE AN AIR LEAK........
You CANNOT set idle until engine is warmed and choke is fully off.....

Some Possibilities:
warped manifold and/or carb flanges (even with new o-rings)
cracks in rubber manifold
Bad seal at vacuum ports in manifolds
bad seal at head gasket
Intake valves too tight, burnt, or warped or otherwise not perfectly sealing
Stripped spark-plug threads
 

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Did you put the slides in the right way around? beveled side faces the air cleaner.
 

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Discussion Starter · #12 ·
It's basically there! For the curious, here's the things that were wrong:

1. Slides were not in correctly - in the right sids, but not actually sliding down into their cylinders
2. Cable adjusters were *all the way* unscrewed, which meant that the slides had huge huge gaps. Screwed the cable adjusters all the way in and then set.
3. O-Rings on intake boot (piece between carb and engine) were worn out and flush with the engine, replaced with 28x3mm o-rings from an oring website - will replace with OEM parts next week when they come in.
4. Spent way too much time working inside the carbs when I should have been paying attention to other parts
 

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Discussion Starter · #14 ·
Oh and also for posterity - 66Sprint is a hero. He (extremely patiently) walked through all the steps here and got me on the right path. He thought of all the problems and delivered all the right answers. If you *ever* have a problem just call on him!
 
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