Idles but dies with throttle

Yoshi

Yoshi

New Member
Hey CT70 fans.

I fixed up a ‘77 CT70 for my dad but am having trouble with the engine. It has a Chinese 50cc in it.

It starts up fine but dies with a bit of throttle. If you let it warm up it will run but has no power from just off zero throttle. Once going it’s ok and when you shift into second it lifts the front wheel.

I put a new plug wire and cap on last year (leftover from a car project) and maybe that made things worse?

I’m no electronics expert so.......?

Carb is cleaned, fresh spark plug, fresh gas, adjusted the clutch, not sure what to do next. I’m going to put the plug wire from my CT70 on it and see what happens. Any suggestions? Thanks in advance.
 
6

69ST

Well-Known Member
It's more than likely a carburetion problem...jet needle height adjustment, pilot screw adjustment, vacuum leak or some combination of those.

Only way I could see this being related to ignition is if the original coil were still in place, inside the frame. I am assuming that the new engine has CDI and that requires a different secondary/HT coil to match. CDI coils, typically, are much smaller than the ones found with breaker point ignition and that has to do with how they are wound. Voltage, at the plug, should be a bit higher with CDI but, the inductance value of the coil, itself, will be very different between the two types. Consider that alternator output increases with rpm and you can see how ignition output could be weak at lower rpm.
 
Yoshi

Yoshi

New Member
Thanks for the info racerx.

I thought carb too, maybe clogged low speed jet. So I cleaned the carb (no change) and then put a brand new carb in I ordered for my 88cc kit on my other CT70 (no change with the new carb either).

The stock coil is removed and the new motor has all its own electricals. I double checked all connections and don’t know what to try next.
 
N

ninjabones

Member
Similar problem. I just pulled and cleaned the carb, removed the jets, fuel screen, etc.. must have screwed something up as now no fuel is getting to the bowl. Can't figure out what the hell I did wrong. Took it apart a second time. Help appreciated (sorry, didn't mean to hijack your thread, but I was having the same problem and figured it must me a clogged jet)
 
6

69ST

Well-Known Member
ninjabones said:
Similar problem. I just pulled and cleaned the carb, removed the jets, fuel screen, etc.. must have screwed something up as now no fuel is getting to the bowl. Can't figure out what the hell I did wrong. Took it apart a second time. Help appreciated (sorry, didn't mean to hijack your thread, but I was having the same problem and figured it must me a clogged jet)
Click to expand...

That places the problem somewhere between the inlet needle/seat assembly & fuel tank. Possible causes: incorrect float height/float installed "upside down", inlet needle installed incorrectly, blockage of the fuel inlet passage, petcock incorrectly assembled, fuel screen blockage, pinched fuel line, fuel line blocked - upstream from the carb. Most of these are longshots, at best...and that's the point; you're going to find something simple - eventually.
 
kirrbby

kirrbby

Well-Known Member
You could pull the fuel line off of the carb and see if it flows freely. Then you'd know the problem is in the carb.
Also...be sure there is PLENTY of fuel in the tank to get above reserve.
Try on AND reserve, if your bike has reserve.
Gas cap turned to ON?
Try thunking the carb bowl a few times with the butt end of a screwdriver...to rattle loose a sticking float, or float needle.

I always rattle the carb and listen to make sure the float is moving inside BEFORE I install the carb on the bike.

Here's some info.
https://lilhonda.com/index.php?threads/ct70-carb-rebuild-town-time.16011/
 
N

ninjabones

Member
Is this upside down?
 

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kirrbby

kirrbby

Well-Known Member
The float looks correct, but...

I think that needle is supposed to slide INTO a groove in the float itself. The needle kinda hangs from the float...then you drop the needle into the hole AS you install the float and float pin.
Hope that makes sense. This could be what's causing the problem.
 
red69

red69

Well-Known Member
If that needle is not attached to the float, it will be governed by gravity and shut off the flow of fuel into the bowl. I can't tell if is upside down, but the needle must attach to the float, as kirrbby has stated. If that requires it being installed upside down from where it is now, do it.
 
N

ninjabones

Member
So I reinstalled and had the opposite problem. Fuel just spewed out of the drain tube, wouldn't stop. Now the needle obviously isn't closing. Maybe the float is stuck for some reason?
 
OLD CT

OLD CT

Well-Known Member
CLIP.jpg Glen , you are missing the float needle clip, it attaches the needle to the float. To let the float hang and not let the float drop all the way down.;)
 
kirrbby

kirrbby

Well-Known Member
Is that carb new? Did it come with that float needle?
Is the drain screw closed?
After you assemble the carb, make sure you can hear and feel the float moving inside, before you install the carb on the bike.
 
N

ninjabones

Member
I'm definitely missing that clip on the inlet needle shown in that photo. I also can't seem to find that part in the parts catalog. Anyone have any leads in where I can buy that clip?
 
hrc200x

hrc200x

Active Member
Isn't that clip on the needle just to pull the needle down so needle doesn't stick in the seat? I think the float is supposed to bottom out on one of the two tabs that the float pin pushes through is what keeps the float from dropping too far. When the carb is out you can hold it upright as if it was in the bike, have the float bowl off and attach a piece of gas line to the carb and blow through it with your mouth while slowly raising the float with a finger. If air stops passing through when the float is level it should be ok. If air keeps coming through, even a tiny bit, the float height is either wrong and as far as I know can't be adjusted with plastic floats, or there is something stuck in the needle/seat area or damaged needle/seat.
 
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