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Discussion Starter · #1 ·
Hey guys,
Been trying to get my 1972 CB175 up an running reliably and have been having issues time and time again.
To begin with background, I rebuilt the engine over the winter including new seals in the bottom end, new oversize piston and rings with cylinders bored to spec, valves and head were taken to a machine shop and re seated and head cleaned, new cam chain. Engine has ok compression (dont have exact readings right now and my compression gauge is not very accurate). Engine does not leak oil at all and smoothly rotates, I've run it enough now that the rings should be seated.
Issues I have had thus far:
- Rebuilt the original carbs and could not figure out why they kept leaking no matter what I did. Floats were not sinking and level was set correct. I suspect it was a cheap bowel gasket or something as the gaskets swelled up. Either way I could not figure it out and was fed up so bought the set of chinese carbs on ebay.
-When the bike first ran it only ran on 1 cylinder. Checked timing and it was off so I tried to set that as good as I could. Issue here was that when I set the timing for the first rotation it would be spot on and then rotate the engine for the second spark in 360 degress and it would be off. It was explained to me that this is just how these old bikes are and was told to split the difference. So currently one spark is a bit advanced and the other is a bit late.
-Suddenly now the chinese carbs are leaking fuel when the petcock is turned to the "on" position. Worked on them last night and seemed to get it fixed but then when riding the bike today the left carb was pouring out fuel everywhere again.
Current Issues I'm looking to address:
Right now the bike will start and run ok for about a 5 min ride it goes through all the gears ok but not perfect. Then after about 5-10 mins of riding the bike gets extremely sluggish and cannot get it to rev past 5000rpm while in gear. Bike can hardly limp home and starts popping and backfiring. Let alone the fuel leaking out of the left carb due to the float valve being screwed up somehow I am mainly wondering if anyone can help me figure out what is going on with this bike.
It seems to run better when in neutral and the plugs were very black so I've ordered smaller main jets to try and fix that. In the meantime I took the air filters off to try and get some more air in there to lean it out. Took the bike out for a ride and it was doing great and thought I had it fixed! Then suddenly the bike goes into sluggish mode again and popping/spitting and hardly can make it home at only 20-30 mph.
Any help would be greatly appreciated. Sorry for the long post but needed to explain as much as possible.
315937
 

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I wonder if the filler cap vent is not working ?

Try taking the cap off next time it goes sluggish, see if there's an in rush of air into the tank.
 
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Spark advancer free and working correctly?
 

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Discussion Starter · #7 ·
Still trying to work this bike out. Last thing I tried was going down to a 90 main jet instead of the 95, seemed to help a bit I thought but still had the 15 min into the ride problems.
Found out the fuel tank was not as clean as i thought so last week I bought some evaporust and treated the entire fuel tank etc and cleaned the carbs. Now the fuel is much cleaner and can rule that out as an issue. Took the bike out today for a spin after cleaning the spark plugs and making sure clean fuel going into the float bowels. Bike Ran very poorly off the get go this time... Wow after all the effort to clean the tank the darn bike runs even worse! It was able to drive a bit for 3-5 mins and then the same problems returned. Bike got extremely sluggish and limping my way home popping etc.
I took the plugs out and they seemed ok. Not as black as before with these new 90 size main jets. And the coils still had spark so I'm really stumped...
Wondering if anything else could be my issue besides fuel?? is there a chance my coils are bad even though they still spark.
After the bike died and I got home I tried starting it after 5 mins and wouldn't even fire up again so took a break working on it for the night. Really stumped right now how the bike seems to get worse and worse.
Any ideas? The gas cap vent is not an issue as it leaks gas out like crazy. Need to find a new cap as this one does not work correctly even with a new seal.
 

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Discussion Starter · #8 ·
I wonder if the filler cap vent is not working ?

Try taking the cap off next time it goes sluggish, see if there's an in rush of air into the tank.
haha yes it works. Too well actually. Doesn't hold gas in at all.. Need to find a new cap as my new seal doesn't even work.
 

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Discussion Starter · #9 ·
Update for anyone interested in knowing what the problem was.
Its been a long process rebuilding this motorcycle and getting it inspected for street legal registration and then to find out it had issues after running for 15 mins or so. Now I have finally gotten the bike running flawlessly (fingers crossed). Took it out for two 30-45 min rides today and it never skipped a beat, hitting all the gears and revs up to redline perfectly.
What I found to be the main culprit was actually my ignition coils. I never considered it to be an issue because when checking for spark before and after the problems it always still had spark. Either way, I eventually just bought a coil recently to rule it out and sure enough, bike ran better than it ever has! Was a blast and rewarding process to see this bike I had in bits finally working as it should! I'm using the Chinese carbs but got them dialled in with 90 main jets, stock air filters, and CB200 OEM exhaust mufflers. Now that the bike is running great I will be making her look better in the coming years, but for now will ride and enjoy! Thanks for the help everyone.
 

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Update for anyone interested in knowing what the problem was.
Its been a long process rebuilding this motorcycle and getting it inspected for street legal registration and then to find out it had issues after running for 15 mins or so. Now I have finally gotten the bike running flawlessly (fingers crossed). Took it out for two 30-45 min rides today and it never skipped a beat, hitting all the gears and revs up to redline perfectly.
What I found to be the main culprit was actually my ignition coils. I never considered it to be an issue because when checking for spark before and after the problems it always still had spark. Either way, I eventually just bought a coil recently to rule it out and sure enough, bike ran better than it ever has! Was a blast and rewarding process to see this bike I had in bits finally working as it should! I'm using the Chinese carbs but got them dialled in with 90 main jets, stock air filters, and CB200 OEM exhaust mufflers. Now that the bike is running great I will be making her look better in the coming years, but for now will ride and enjoy! Thanks for the help everyone.
Really glad you figured it out. I'm starting the process of restoring a 1973 CB360.

I'm sure it was great feeling to have figured out the issues. Have fun!!
 

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Discussion Starter · #11 ·
Really glad you figured it out. I'm starting the process of restoring a 1973 CB360.

I'm sure it was great feeling to have figured out the issues. Have fun!!
Yes i am very glad! I was starting to think the bike was cursed or something.. but was a good learning process for me to diagnose and re test each time and learned some carb jetting along the way as well.
Love these bikes and will be doing a 350 for sure in the future!
Good luck to you on your bike!
 

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Yes i am very glad! I was starting to think the bike was cursed or something.. but was a good learning process for me to diagnose and re test each time and learned some carb jetting along the way as well.
Love these bikes and will be doing a 350 for sure in the future!
Good luck to you on your bike!
Thank you. Bike is 90% disassembled.
316060


I'm having difficulty locating this part. Not certain if other bike model can be used.
 

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Discussion Starter · #13 ·
Thank you. Bike is 90% disassembled. View attachment 316060

I'm having difficulty locating this part. Not certain if other bike model can be used.
Nice job! Oh wow, that looks rough. I'm sure you should be able to find one of those. CB360's were pretty common bikes but I wouldn't be surprised if the 350 fork ears work as well. I'm sure someone on here with more 350/360 knowledge would know!
 
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