Honda CT70H has no power

4

42653steve

Member
I have a 71 CT70H that someone else has worked on that had wrong carb and would not idle. I installed correct carb it does idle now but when you put it in gear to take off power falls off. Haven’t checked anything else like timing or adjust valves. Anyone have any ideas for me to try. Thanks
 
OLD CT

OLD CT

Well-Known Member
I know what you mean, take your time and carefully grind one side down of the feeler gauge, till it fits.;) It will be easier to find in the stack for next time.:D
 
cjpayne

cjpayne

Well-Known Member
OLD CT said:
I know what you mean, take your time and carefully grind one side down of the feeler gauge, till it fits.;) It will be easier to find in the stack for next time.:D
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I ground mine down on both sides and put just a slight bend on the end. OC is right, it does make it easier to find next time.
 
4

42653steve

Member
I found a broken wire from primary coil,reset points,new carb got bike to run. It ran for about 10 minutes with a little smoke out exhaust which is aftermarket and the bike just quit running and won’t restart. Pulled plug was all carboned up and no spark know. Leaning toward condenser is bad. Anybody have ideas on problem.
 
6

69ST

Well-Known Member
First thing, I'd want to check for spark with a new plug...just to rule out the plug itself. No, I don't think it's the plug that's just a really easy thing to check and you're probably going to need a new plug anyway. Could be a failed condenser; sometimes they die gradually. When in doubt, I like to throw new points & a new condenser at the problem...they're wear items and cheap enough to use as a diagnostic tool. If those make no difference, then it'd be time to check the coils & their respective leads.

All of that having been said, your comments about the exhaust smoke & "carboned up" plug have me wondering if the upper end is tired and in need of work. This sounds like an oil control problem and that is usually accompanied by low compression.
 
4

42653steve

Member
Think I found my at least one of my problems. The coil wire coming out of the frame was cut and someone put it back together with tape. Looks like a new coil is in order. Yikes hate doing those.
 
4

42653steve

Member
42653steve said:
Think I found my at least one of my problems. The coil wire coming out of the frame was cut and someone put it back together with tape. Looks like a new coil is in order. Yikes hate doing those.
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racerx said:
First thing, I'd want to check for spark with a new plug...just to rule out the plug itself. No, I don't think it's the plug that's just a really easy thing to check and you're probably going to need a new plug anyway. Could be a failed condenser; sometimes they die gradually. When in doubt, I like to throw new points & a new condenser at the problem...they're wear items and cheap enough to use as a diagnostic tool. If those make no difference, then it'd be time to check the coils & their respective leads.

All of that having been said, your comments about the exhaust smoke & "carboned up" plug have me wondering if the upper end is tired and in need of work. This sounds like an oil control problem and that is usually accompanied by low compression.
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Still having issues with no powe. Leaning toward rings.Any tips on checking compression and what should it read? Thanks
 
6

69ST

Well-Known Member
You want to see 150psig, or higher. Anything under 130 is weak.

Might need rings, too. Most common source of compression loss is a leaking intake valve. If it's not smoking or oiling the sparkplug it needs a valve job. Once the head is off, you'll see the condition of the cylinder walls.
 
4

42653steve

Member
racerx said:
You want to see 150psig, or higher. Anything under 130 is weak.

Might need rings, too. Most common source of compression loss is a leaking intake valve. If it's not smoking or oiling the sparkplug it needs a valve job. Once the head is off, you'll see the condition of the cylinder walls.
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Thanks appreciate the help
 
6

69ST

Well-Known Member
BTW...an easy, yet effective, compression test...


Crank the engine slowly by hand, via the kickstarter. You should feel sharp resistance on the compression stroke; if it's enough to stop the crank rotation, compression is likely healthy. At the other extreme, if it's hard to know when the compression stroke has been reached, compression is really low...too low. This is shadetree mechanic tech at its most basic but, it's simple, reliable and, with enough experience, quite accurate...as a first-step, diagnostic, tool. Not everyone has a compression tester and knows how to use it with small displacement; I've seen Z50 motors with an actual 150psi cranking pressure register 120-130psi on a different gauge, largely due to the volume in the hose (and, presumably, the gauge itself). There's also no way to adjust cranking compression pressure. OTOH, a healthy top end delivers a consistent feedback "feel" through the kickstarter.

Check the sparkplug. Do the center insulator & electrodes have normal appearance? If they're black, with fluffy/sooty deposits, there's an oil control problem. If the plug threads are oily, it's almost certain. Then, it's only a question of where the oil is coming from...valve seal, valve guide, headgasket, or rings. The head has to be pulled to verify any of those causes.

Look inside the intake port. It should be clean, gray, aluminum. If it's blackened, the intake valve has been leaking for some time. If the discoloration extends inside the intake manifold, the valve been leaking, badly, for a long time.
 
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