[71topaz]

I have a 1971 Honda CL175 that I have been working on the past couple months. I've gotten to a point where I'm stumped and I need help. After the bike warms up on a ride it seems to drop to one cylinder or lose power. I can stop for a little while and start again and its fine. This led to think it was the coil. So I replaced the coil thinking this was the problem but it still does the same thing although it does run a little better with the new coil. I also replaced the condenser while I was at it. Before this I went through and cleaned the carbs, adjusted the floats, cleaned the tank, and checked the points and timing. The bike runs fine when its cold, its just after a little riding when it acts up. Any thoughts or ideas would be much appreciated!

 

[kbecker]

When you replaced the coil did you use new spark plugs and spark plug caps?

 

[71topaz]

I put new spark plugs but used the old plug caps. It almost feels like its some type of electrical problem that is causing it to lose power at higher rpms.

 

[66Sprint]

Sounds like a too tightly clearanced valve to me....BUT, there are lots of possibilities......

 

[kbecker]

I was thinking maybe one of the spark plug caps was bad. I think they have a tendency to increase their resistance over the years. New NGK plug caps are about $5 each. Might be worth a try.

 

[71topaz]

Thanks for the input! I'm gonna try a few more things and hope I get the problem fixed.

 

[phil71]

sounds to me like it is using up it's fuel faster than it can get more . no one ever checks this, but pull the diverted on the Petcock and make sure the "gully" is not full of gunk. Easy to miss that , even if you "think" you've blown your Petcock clean. Also, check float height. The 175 is extra sensitive to that.

 

[71topaz]

I put new plug caps and still no luck. I have another 71 CL 175 that runs perfect so I compared the two petcocks by removing the fuel lines and watching the flow into a can. They both have the exact same flow. I've adjusted the float height to ~21mm. Is this correct? The bike definitely drops to one cylinder after about 3 or 4 minutes of riding, it seems its using all the fuel in one of the bowls then it gets fuel starved some how.

 

[lowtops]

I had similar issues and replaced the same electrical parts as you. The issue was still there. I went back through everything and noticed that my float bowls had pin holes in them and were taking on gas. Also, if you are using aftermarket float bowl gaskets they can be to wide at the sides of the bowl and cause the float to hang. I cut my own gaskets for this reason. Right now I am waiting on new floats to arrive as well as a new petcock. Hopefully this week I can confirm if the new parts will solve my problem.

 

[71topaz]

I'm going to check the float bowl gasket. That may be my problem because it seems it uses about a bowls worth of gas then it starts acting up on me.

 

[kenolds]

Fuel supply could be compromised by inadequate tank venting...Next time it acts up, open the gas cap and see if it helps. Also, inline fuel filters or kinked hoses can limit flow. I have seen several carb floats with holes, but that causes flooding and overflow. Petcock (or tank) crud is likely the culprit.

 

[lowtops]

So my replacement floats came today and I installed them. This solved my issues. The bike now runs on both cylinders, and fires up without choke.
I'm not saying this will solve your problems but something to check out. I mentioned my floats had pin holes, more like cracks. I had to clean them well to see the cracks, btw.

If you guys don't mind I'm going to update my build thread, with this same info for posterity.

 

[NormanH]

I have seen this on my CL 175, the float level was the cause. As the carb warms the float and needle expand and seal causing no or little fuel to enter the bowl. Setting the float to 7/8" cured the concern.

 

[Simo]

The correct height is 21mm not 7/8"