Hello all, I've recently become the owner of a early 70s era CT70. When we first got it about a week ago, we fired it right up with some new gas, a quick check of the oil, and spark plug and a little persuasion from bump starting. It ran great for about 2 days , then died and since then I cant get it started to save my life. I've been reading all the expert answers you folks know about these little bikes, and I've tried everything that you sugest, but with no success. I've tried the whole carb thing(dissassembly,soaking in carb cleaner, cleaning all jets with a wire,cleaning screen, blowing everthing out with compressed air, and re-assembly),checking and adjusting the points, setting the valve lash, I've even replaced the fuel lines. I get good spark, and some backfiring thru the carb and exaust.(I have the air cleaner out for now). Any ideas would be greatly appreaciated. My 2 young boys cant wait to get back on it!
Newbie cant get it started
- Thread starter JohnE
- Start date
Did you lube the points cam so they didnt close back up, ck for .015-.016 gap, open carb drain and turn gas on so you can see it run out so your sure carb has gas in it, sand inside of magneto flywheel so its not rusted along with edges of coils, make sure screen in carb that acts as a filter is clean, ck valve lash for .002 ? Try a new plug in it, you may have fouled it by flooding it. Thats all I can think of right now, it should run. If you dont have the skinny feeler gauge just open the lash up so it has a little you can feel. The fact that you had to push start it makes me think the lash closed up. Maybe kick it over with plug out first to feel with finger if it has compression first, if not open lash up. Someone smarter then me will come up with whatever Ive forgot to mention. Good luck with it
Points seem the most likely problem but, you say the engine has good spark. Still worth checking, it's possible to have spark even with a too-narrow point gap. That would alter the timing somewhat. It's the backfiring that has me wondering. A jumped timing chain could cause that.
However...you mentioned that the bike had to be bump started; that won't compensate for a timing chain problem. It could compensate for a blocked idle circuit in the carb. Check the plug for signs of flooding, if it's dry then try a few drops of gas down the carb slide and see if that will get it started. If it does, then you know there's a carb blockage somewhere. If the carb is functioning normally, the points are correctly gapped and you've got spark, then pull the cam cover and check the cam timing. With the "T" mark on the flywheel at 12 o'clock, the crankshaft keyway should be pointed at roughly 9 o'clock - directly inline with the bolt that retains the cam chain roller and the center of the cam. The cam sprocket "O" mark should be aligned with the timing mark at the top of the head such that the crankshaft keyway, cam chain roller bolt, cam centerline and cam sprocket "O" mark together form a straight line...if the cam timing is correct.
Problems such as this can seem much worse than they actually are. The reality of the situation is that these engines are relatively simple and so are the problems. Most of the time it's either a problem with fuel or spark. Timing and valve clearance issues are far less common and low compression will be obvious.
However...you mentioned that the bike had to be bump started; that won't compensate for a timing chain problem. It could compensate for a blocked idle circuit in the carb. Check the plug for signs of flooding, if it's dry then try a few drops of gas down the carb slide and see if that will get it started. If it does, then you know there's a carb blockage somewhere. If the carb is functioning normally, the points are correctly gapped and you've got spark, then pull the cam cover and check the cam timing. With the "T" mark on the flywheel at 12 o'clock, the crankshaft keyway should be pointed at roughly 9 o'clock - directly inline with the bolt that retains the cam chain roller and the center of the cam. The cam sprocket "O" mark should be aligned with the timing mark at the top of the head such that the crankshaft keyway, cam chain roller bolt, cam centerline and cam sprocket "O" mark together form a straight line...if the cam timing is correct.
Problems such as this can seem much worse than they actually are. The reality of the situation is that these engines are relatively simple and so are the problems. Most of the time it's either a problem with fuel or spark. Timing and valve clearance issues are far less common and low compression will be obvious.
TrailPunisher
Member
I would also check for a partially sheared flywheel key. This would alter the timing