Help diagnosing problem on 1974 CT70

[zack_novak]

I recently got a 1974 Ct70 project. Got her running the next day and noticed a few problems. I have tried two carbs, and the bike will run with either. The OEM one will be getting a rebuild soon.

Anyways, when the bike is stopped, I can rev the motor up fairly high. I then shift into first, and it will go maybe 5mph at the most. Shift into second, then maybe another 4 or 5 mph. Shift to third, and the engine will begin to bog. I have a feeling this is the clutch but I am not 100% on that.

Background info: Clutch never rebuilt, carb never rebuilt, stock engine size, adjusted valves/points, etc.

If this is indeed a new culprit for a clutch rebuild, can someone point me in the right direction of getting the parts? Do I just need friction plates and the RH side cover gasket? Should I get HD springs?

Thanks

 

[cjpayne]

I would first try seeing if the air cleaner is clogged or the air inlet tube is crushed. Second, try seeing if the exhaust/baffle is clogged(just remove the baffle anyways). 3rd, replace condenser/points, set points to .016, and clean/check stator condition. I damaged a stator removing the flywheel once and it caused some weird stuff to happen.
When my 3speed clutch was slipping, it caused the motor to rev high while not wanting to gain speed. Save your self the time, trouble, and basic BS, and just go ahead and replace the discs, plates, and springs. H.D. springs can't hurt, especially if you plan later to increase the output of the motor.
If the RH cover has never been off(it really REALLY needs too be, to clean the spinner and screen), you will definitely need the gasket and a razorblade. To make clutch maintenance easier, replace the screws with hex heads. I've done that with my points cover also. As for the clutch parts, OEM will be fine(don't forget the clutch spinner gasket). For the HD springs, I would post in the Tech Area for the best place to go. Someone like Fatcat would definitely know the best place.

 

[b52bombardier1]

You might get lucky and try to adjust the clutch. It's easy enough to do but I would still do as suggested and clean the spinner and the oil screen very soon.

Rick

 

[kirrbby]

Air filter, points, and plug would be my first thoughts. Condenser, dirty carb or float height.... what you really need is what has been suggested here many times before, a complete, by the book, tune up. These bikes are 40 years old, if you don't know you're bikes history... just do it.

 

[cjpayne]

......I then shift into first, and it will go maybe 5mph at the most. Shift into second, then maybe another 4 or 5 mph. Shift to third, and the engine will begin to bog.

Sounds like the symptom of the classic prank...........banana in the tailpipe.

 

[69ST]

A slipping clutch would manifest as...well...clutch slippage(!) From what I read in your OP, cj's B.I.T. theory is slightly more plausible. Joking aside, the engine would rev higher while the bike goes no faster - not bog. I'd also expect starter slippage, which wasn't mentioned. Sounds to me like the clutch and two different carburetors have been all but ruled-out already.

Sounds to me like the engine is completely gutless and the big question is: "why?". There aren't many possibilities:

1. Low compression
2. Lean mixture
3. Timing (cam or ignition)
4. Restricted breathing

#1 seems unlikely, as low compression is incompatible with easy starting and decent idle quality. You didn't mention exhaust smoke, which suggests adequate ring sealing. Could be a leaky valve. Is the intake port blackened?... tuliped intake valves are relatively popular with these motors. I'd give it a rudimentary compression check. Turn the engine over slowly, by hand. Sharp resistance should be felt as you reach the compression stroke.

#2 is also unlikely, since swapping carbs makes no difference...unless there's a vacuum leak. That, however, would cause hard starting and idle problems.

#3 has been partially covered. However, I'd start by checking the point gap, resetting it if needed. If your points have closed-down enough to be the problem, you'll know instantly once they're re-gapped. New points may be needed but, the existing parts seem to be working well enough for the moment. Doesn't take much to foul points and, like a bad condenser, you're far more likely to get a no-run condition. If the cam timing has jumped by a single tooth, which is nowhere near as rare as a partially-failed condenser, it'd manifest as the symptoms you described.

#4 could be on either the intake or exhaust side. For testing purposes, I'd simply pull the end caps from the airbox. If there's no difference, time to look elsewhere. 40 year old foam that's deteriorated, or just plain clogged, wouldn't be unusual.

 

[zack_novak]

I'll check all of the recommendations tomorrow morning (12 am right now, cant run it anyways). I believe it was racerx who mentioned the starter slippage. If you kick it hard, it'll slip. If you kick it slow, it wont. I had to put the head back on so there's a chance I skipped a tooth on the cam sprocket.

I also took out the baffle today. I started the bike and a big puff of carbon came out. I'm guessing the exhaust flow is already increased.

Regardless, I only paid $50 for the bike so even if its just barely running I'm happy for now. It's a good start.

 

[OLD CT]

Glad i came late to the party,#3.

 

[Boomer3]

I had the same symptoms on one of my bikes. It ended up being that my cam chain was loose and slipped a few teeth. I readjusted the timing and it ran great. (I replaced the cam chain and cam chain tensioner a few days later) Just my two cents!