Topic: CL175 carb puzzle

[paulages]

1970 CL175. my lady's bike. it had been sitting in a friend's garage for a year or two after several people had failed in attempts to tune it up. i arrogantly blurted, "eh, we'll have it running in an hour!"

got it back to the shop, pulled the carbs, disassembled them and dropped them in the ultrasonic tank, and set about adjusting the tappet clearances, point gap, and timing. half hour goes by, ready for the carbs, and on reassembly i discover that someone has installed 2 left slides, so that the cutaway on the right carb was facing backwards. AHA! that must be the problem, right?

i located a new slide, reassembled, and it started great... but the problem still persists: the right carb idles by itself (with the other plug wire pulled) at about 5000 RPM. there is slack in the cable, the slide is bottomed out all the way, no air leaks in the manifold or at the airscrew. the float height is set properly. all jets and emulsion holes are clean as a whistle. i borrowed a carb off of another CL175 and the bike runs like a champ.

i cannot for the life of me figure out what is causing the high idle on this carb. any ideas? i'm truly stumped.

[speedy_the_drummer]

This may not be why, but it may be why.

On my CL350 I had that problem and it was a bad carb boot. It was letting air in and shooting the rpms up.

But I'm still fairly new to bikes, but it sounds like a possibility.

[paulages]

This may not be why, but it may be why.

On my CL350 I had that problem and it was a bad carb boot. It was letting air in and shooting the rpms up.

But I'm still fairly new to bikes, but it sounds like a possibility.

no air leaks...

[bwaller]

At thirteen I had an S65 and big bro had a 68 CB175 twin carb. Only kept the 65.

It sounds like the left carb doesn't cause issues? I wonder about the slide or the needle. You switched right carbs and it was fine. did you try the slide & needle from that carb in yours?

I'm sure you didn't overlook that side idle screw but sounds like the slide is different or there is damage to the carb bore (slide groove pin burred?) preventing the slide from closing. I'll go look for a carb. 

[paulages]

At thirteen I had an S65 and big bro had a 68 CB175 twin carb. Only kept the 65.

It sounds like the left carb doesn't cause issues? I wonder about the slide or the needle. You switched right carbs and it was fine. did you try the slide & needle from that carb in yours?

I'm sure you didn't overlook that side idle screw but sounds like the slide is different or there is damage to the carb bore (slide groove pin burred?) preventing the slide from closing. I'll go look for a carb. 

as far as i can tell, the carb bore looks fine, and the slide closes the same as the other three functional carbs in the shop. as far as the needle and slide are concerned, they are identical, not to mention the fact that the needle/main shouldn't be doing anything at an idle, right? ...unless the needle was REALLY in the wrong position and allowing fuel to pass it, but the clip is in the same position as the other. 

[malcolmgb]

Had a similar problem with my CL, if I tightened the carb tight to the manifold it distorted the carb body and slide stuck part open (high RPM) just had to back the bolts off, the 'O' ring still sealed the inlet so no air entered. The bike has recently landed in the UK so that is one of the jobs when I get it home. Suspect an oversize 'O' ring has been fitted, may cut a gasket to fit between carb and manifold to fill gap created by 'O' ring if that makes sense.

[bobjohnson]

Jets the same size in both carbs? Maybe someone swapped the main/idle jets in the bad carb, and your dumping a load of extra fuel into the cylinder?

[paulages]

the carbs are lightly tightened to the manifold (know this problem from amals..), and the jets/slides are identical from carb to carb. i can't believe such a simple carb has stumped me so much.