• Don't overlook our Welcome Package, it contains many links to important and helpful information about functions at VHT like posting pictures and sending PMs (private messages), as well as finding the parts you need.

    AD

cb 175: fuel or electrical issue?

LongLake

New Member
Joined
Apr 18, 2022
Total Posts
6
Total likes
0
Location
Chicago
My '72 cb 175 starts well, and idles smoothly for the first few minutes. Both exhaust pipes heat up at the same rate, and it sounds like carbs are in synch.
As soon as I run it around the block, the right side fails to burn fuel. I’m quite sure it’s getting fuel, because it smells like it. The right pipe is cool. When I pull the plug, it seems to be sparking just fine when I turn it over. I put in new plugs, but that didn’t change anything.


It seems like it has to be an electrical issue, right...?
 
Battery condition? A run around the block at modest rpm will likely only discharge the battery. These bikes have break-even charging systems that need to be revved to at least 3000 rpm to show any positive charge to the battery, so a strong battery is very important to full electrical functionality.
 
I don't think so. It's a new-ish battery, always on a tender, and I replaced my regulator rectifier to a 21st century version.
 
But have you checked its voltage after it's been off the tender for a few hours? If it's a new-ish lead acid battery it could be in decline already, and leaving them on a tender isn't always the magic bullet. Some tenders actually charge too high a rate for what is likely a 9 amp battery and can contribute to early demise. If it doesn't hold 12.6v after an hour or so off the tender then it's on the way out. Good that you went with a modern rec/reg combo but remember that the charging system is going backwards until above 3000 to 4000 rpm, so with a weak battery it often only has enough voltage to fire one cylinder
 
I will give this a try. I will be very happy if it’s this simple :)
 
Ok, so I've ruled out the battery. Bought a nice spanking new one, installed it, and it runs exactly the same. I'm determined NOT to bring this into the shop (where I'm sure an actual mechanic could fix it in 10 minutes). It's the journey, not the destination. What's the next logical thing to check? New points? Points out of synch?
 
Back
Top Bottom