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Discussion Starter · #1 ·
I have a 1972Cb350 twin that has been chopped and dropped. Some of the electric has been replaced like the regulator and rectifier in place for new parts. My problem is that the bike looses power after the first mile or so. After about 20 min of riding I need to bring it back home because there is little to no power. I have spark and fuel. Carbs are clean, floats are set. I really think that it is an electrical issue, but I am not sure where to start to look for the issue. It was suggested that I replace the points for an electronic ignition, and that I should replace the coil. Instead of just throwing money at it I would really like some insigt ito what I could do before I start buying new parts to just replace everyting, which is what many ppl are telling me I should just do.
 

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First make dead sure the batt is new or fully charged. thats the main issue, then with the bike running and headlight off check the batt should be around 12.8 to 13v at idle. stock rectifier i assume. rev the motor to 4000 and check the batt should be 13.8 to 14. if its not you have a bad rectifier . remember headlight off during daylight on this vintage bike. unless you would like me to tell you how to wire it off of the alternator.. this is a 1st step. check and we will try from there if all is good.
 

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Discussion Starter · #3 ·
I have not checked the batt , I thought it would be good as it is a brand new sealed Harley batt they put in the full dressers, but it is worth a shot. Thanks, I'll let you know how it goes.
 

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You are more than welcome to shoot me a line, as these are problems that are easier diagnosed one on one vocally. 502-544-9386.. Doug
 

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Discussion Starter · #5 ·
Sounds good. I'll try for tomorrow.
 

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Anytime you're chasing a power loss you need to first do a compression check. You can have fuel and spark but if you don't have compression you're the 3rd leg of a 3 legged stool.
 

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Discussion Starter · #7 ·
Looks like I am going to have to replace the rings and do a bunch of other work on it as well.
 

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What were your compression readings?.............(assuming engine hot, throttle wide open, choke off)
 

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Along the same topic, as a newbie, what PSI are we looking for on a compresion test?

68 CB 350
 

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Sensei
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You want 170 or higher on a 350......Anything below 150ish is re-ring time....The engine will still run, but produce no real power below 135/140PSI....
 

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Tanks....
 

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Discussion Starter · #12 ·
66Sprint said:
What were your compression readings?.............(assuming engine hot, throttle wide open, choke off)
About 80 on the right and about 120 on the left side.
 

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Well..... There's your answer......Time for a top end rebuild.....
 

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Discussion Starter · #14 ·
66Sprint said:
Well..... There's your answer......Time for a top end rebuild.....
Is replacing rings something that I can do in my garage or am I completly done with this bike? I have been looking around, to see how hard it is for me to fix the origional motor, I have even reached out to some members on the forum. Though, I am still unsure if this is something that I can do on my own. Do I need special tools for this, or can I do it on my own? I have found the parts, I simply need to see what skill level this is going to be. Oh, and taking it to a mtorcycle shop is out of the question as there are no shops in my area that will touch anything that is older than 15 years .
 

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I will have a complete rebuilt motor in about a week, give me a shout and we can discuss. Or the second option is to bring you motor down one weekend and ill walk you through the process.
 

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Discussion Starter · #16 ·
doug350 said:
I will have a complete rebuilt motor in about a week, give me a shout and we can discuss. Or the second option is to bring you motor down one weekend and ill walk you through the process.
That would be cool. I can't wait to hear how it went! Not sure if I can get away for that amount of time though. But if I can I would surely take you up on that offer!
 

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Discussion Starter · #17 ·
It's been a while since I have been on the forum, so I thought that I would post an update on the CB350 chopper. We took the engine apart and it was in fact a piston ring. Actually, as we were removing the jugs, half of the broken piston ring fell on the floor whil my buddy quickly grabbed the other half before it fell into the case. I have the rings and the gasket set. Which I bought at Rusty Riders. Great bunch of guys and they are really helpful. I then scored an electronic ignition for the bike which I can't wait to install. Next week I'm going to take the engine to my friends home to take the ball hone to it and then get the rings installed. Then it's back together and ready for wiring. Oh, and I scored a great little tail light from Lowbrow Customs for a birthday present. Lowbrow and Rusty Riders are both located in Ohio, where I'm at so the parts come really fast. I also scored a great set of sonic cleaned, and blasted carbs to put on the rebuilt engine. Running blue see thru fuel line to accent the blue flake tank. As you can see, I've been busy on these freezing Ohio days!
 

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Discussion Starter · #20 ·
So, what we did was add new pistons .50 over then sent them out with the valves to have the cylendars professionally honed and the valves decked. I had 4 bent valves and a ovaled cylendar. Now I am within spec with factory compression. Then a new PAMCO ignition, new Mikuni VM30's from Dime City Cycles. Reused coils that were bench tested at a and purchased from a local shop. New wiring all around (it was a mess after a year on the shop floor). So basically anything that brought spark, air and fuel into this bike was FUBAR. Now it starts on one kick and idles well. When the weather clears we can ride it and put it under load to see how it performs as well as allowing the pistons to seat properly. I few test runs and then going over all the bolts in the motor to be sure they are tightened down and I should be ready to go, maybe the end of March at least that is the goal.
 
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