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Discussion Starter · #1 · (Edited)
Picked up a '72 CL175 with a spark issue. Got that sorted and adjusted the valves, cam chain, points gap and set the timing to the F mark. I cleaned the carbs and checked the float height.

It doesn't want to hold an idle. I've tried several different settings on the mixtures screws, from 7/8 turn all the way to 1 3/4 turns. I thought for a minute there that it needed more turns out because of the nearly open (barely baffled) pipes, but it soon went back to doing the same thing. Occasionally, it will get stuck at ~3,000 RPM.
I also tried going in on the idle screws until they were all the way in. I've now backed them out equal amounts.

I've read about the slides being in the wrong side. I left the slides on the cable and kept them on their respective side of the bike. And when I was syncing (by using a flash light to check slide gap at rest and at WOT), I could see what looked to me like a normal small gap at rest. Now...it IS possible that someone before me has them swapped. I DID line up the long groove on the slide with the pin in the carb(s) and the wider groove with the idle screw. I guess it's possible to still have them on the wrong side?

The air filters are old and dirty. I cleaned them off with a toothbrush (dry) and blew them out with compressed air, inside and out. They should still be OK, I would think.

I also suspect the advancer, maybe? I checked it during the tune up and the springs *may* be a little on the weak side? But that should cause it to advance early and idle high, which it isn't doing. Ditto for air leaks.

I set the floats to 22mm. I've since learned that they should be 21mm, but I don't *think* that 1mm would cause this. If anything, the fuel level would be a little lower, right?

I did see a cracked throttle tube that I will replace. But...again...not sure it's the culprit.

And while the LH bowl is leaking, the RH carb is fouling the plug.

I think I will pull the carbs again and have my friend Rick at OldSkoolCarbs do his thing. And I'll verify slides are correct and get the fuel level/float heights correct. Other suggestions?


 

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Several points here-
175's and 200's are twitchy when it comes to re-installing the carbs - it's easy to unevenly tighten the bolts to the manifolds- this can actually warp the carbs, which causes problems. Tighten one bolt a bit, then the other, then back and forth again.
The throttle cable on both these bikes is just barely long enough, and routing can cause issues.
These engines are also very sensitive to muffler changes - they NEED back pressure to run properly. Straight-through pipes will usually result in a rich condition, and fouling plugs. This seems completely counter-intuitive, but it's the way it is.
 

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Carbs need to be synced then set Correctly
For example That means 21mm floats , close enough isn't going to tune it ...1/8 of a turn out on one of the slide adjusters isnt going to tune it ...etc etc.
The trick is being precise.
The carb screw don't need to be set exactly the same to be correct but they need to be adjusted in the correct order.
Here's Steve's how to on cb175 carb setting ( there's a better version but this is the one I could find quickly )
http://www.hondatwins.net/forums/40-engine-discussion/1560-69-cb175-k3-question.html
If the bowls leaking the float is either set incorrectly , the floats got a hole ( dunk in hot water and look for bubbles) or the float valve or seat are worn or dirty
Fouled plugs could be anything from float height to worn rings

Make sure to switch the petcock off when it's not running if the overflowing carb drains into the cyclinder you'll think the oil and melt the cam and rockers
 

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Discussion Starter · #4 ·
Started to drain the gas tank this morning so I could pull the carbs and take them to Rick at OldSkoolCarbs. That's when I noticed a couple of odd things...


I noticed that I wasn't getting even flow out of the petcock outlets. And the one that was acting funny was the side that I was using to feed the RH carb.....Hmmm...
Then, as I wiggled the lever around, I noticed fuel coming out of the petcock body. Also, Hmmm...
Then, as I removed the crossover tube from the gas tank (hate those things), I noticed gas still in the LH side but nothing in the RH side. Triple Hmmm.....


Pulled petcock apart and cleaned it well and tested it by sucking through the outlets and spraying carb cleaner. Didn't really find anything.


Found the crossover tube nipple plugged up on the RH side of the gas tank. Fixed that.


Then I moved on to the carbs. I wanted to check operation of the slides/cables. I also wanted to verify that the slides were in correctly. I kept them on the same side of the bike I removed them from. BUT, I had read several threads about the slides being in backwards causing a "no idle" issue. Pulled them out and, guess what!? Yep...in wrong. The throttle cable was also routed incorrectly.


Fixed all that and hooked up my I.V. bottle for gas. Fired right up, I was able to adjust the idle and it revs MUCH better now!
I'm still waiting on bowl gaskets and a new throttle tube.
Inching closer and closer!!
 
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