Thread: Cant get my CT to run (carb or head issue)

So I tried to start my CT up today and it will start, but it will not run off choke. The valves were lapped in and they seat nicely. The piston and rings were changed and the cylinder was honed. I have a brand new carb on it too.

What happens is I can start it and it will run on choke, but as soon as I take it off choke it bogs out. So I tried to richen the carb a little and it does the same thing. I did a leak down test on this CT a few days ago and it was just blowing air out the exhaust so thats why I lapped the valves. It was burning a bunch of oil at one point, so thats why I bought a new piston and rings.

I recently rebuilt my brothers SL70 and replaced the piston and rings and other things, but did not touch the head. His bike starts first kick without the choke and idles immediately after. Its frustrating that I can get one engine to run like new, but my CT runs like its been sitting in a junkyard for years.

Any insight to my situation would be greatly appreciated.

My answer to this problem is to have the valve seats cut and then bore the cylinder. Let me know what you guys think

I really dont think you have internal engine problems like valves not seating or piston not sealing. First off where do you have all your adjustments on the carb? What slot is the needle clip on, what kinda air filter, air screw position, idle screw position, good seal on both sides of the intake manifold?

I would bet if you took that carb off the SL and put it on your CT it would run fine.(just to see if it's carb related)
Most of the time the carb is the issue with poorly running bikes.
This is where I would look first.

"Brand new" carburetor tells me its aftermarket? Agree with BJ & Mr. H in that would be my first suspect. What is its jetting?

I agree with BJ and MH...That has to be the issue and Brian's suggestion to check by switching carbs is a great idea...That will save you a lot of time. HA!!...Didn't see you posted that Harry!

Alright, well with your suggestions I went down to mess with the carb and it turns I didn't have the idle set right. Its was hard to get the SL and the CT to sound the same... in turn, run decently the same. The SL has an original exhaust, but the baffle is out of it so its free flowing and loud. The CT has a cheap repop exhaust and it is really quiet and restrictive. But now the CT starts first kick without choke, and it idles. I'm going to try it again tomorrow morning when its cold again and see what it does.

This is the carb I have..
CT70 1969_KO_THRU_1977 "STANDARD" REPLACEMENT CARB_READ (300011)

If anyone has some good tuning tips with it, let me know. I think I have it good now, but I cant ride it until tomorrow to make sure. Its always good to know what carb settings work for other bikes though.

If that has the #72 main jet (as shown in provided link) that will have to be changed to a #58 or #60.

yea a #72 MJ is way to big for these bikes..i acnnot even see a reason to ever run such a size on these bikes

Originally Posted by Flash

If that has the #72 main jet (as shown in provided link) that will have to be changed to a #58 or #60.

Why does he say they work for the CT's then? I have the honda hot cam in my bike right now and (dont know if it did much), but I ported and polished the head to help for better flow. So far the bike started first kick again this morning and idled immediately after without the choke. I can rev it up and it will rev smoothly and drop back to idle nicely.

What main jet did the SL70's have?