CT-90 - Tune up all the way around

[Allistah]

Hey all --

A little history first.. This 1979 CT-90 was my step-fathers. He bought it after he got cancer because he always wanted one so he bought one before he got too sick to ride it. It's pretty clean and wasn't beat down much at all. I don't know how long the points/condenser have been on there or any thing else about the maintenance. Before he died he gave it to me. I want to make sure I keep it in tip top shape for him. It's a great bike.

I think I've got the timing thing down now and it seems to run better. Things still aren't exactly perfect though and I want to make sure I give this thing all the attention it deserves. Here are my questions:

1) When it idles, I hear like a knock sound, it's not loud by any means, but I hear it a bit if I listen close. I would think I would hear a smooth purring engine. When I rev it up a bit I don't hear it, only when it idles. What am I hearing?

2) It has a tendency to sound like it misses a fire every 5-10 seconds as well. Kind of like the key was turned off for a split second. Any ideas on what is causing this?

3) I charged the battery but not for too long (about two hours) since I didn't want to cook it. What voltage should it be when it is fully charged and it has stabilized? What is the minimum voltage I would want to see here after it has settled down over night?

4) Is there anything else that I can do to this thing to make sure I've got all my bases covered? I was it to start as easy as possible and I want it to run perfect. Should I be looking to make sure the valves are adjusted properly as well or does that usually not cause these kinds of problems?

5) I made sure that the battery was charged and it seems to be holding a charge at 6.11v. I didn't let it charge too long as I didn't want to cook the battery. If the battery is well charged, what voltage should it stabilize at?

I've looked at the points and the surfaces look a little discolored. I'm going to buy a new set along with a condencer, and a new coil wire splicer kit just in case the plug wire is old and contributing to the problem(s). No idea how old this stuff is and I'm sure new ones would take out the possibility of them contributing to the problems above.

Thanks for the help guys,

-Allistah

 

[jesse8931]

sounds like your timing is off by 1 or 2 degrees also take the carb apart and clean good make sure all the jets are clean and see if that helps and replace the points and condenser

 

[Allistah]

Thanks..

Is using a timing light the most accurate way to set the timing? I have one and it is easy to hook up so that isn't a hassle for me. I think the manual said to time it when it was at 1300rpm. When it's at 1300 rpm I should make it so the F mark is exactly on the mark on the case?

 

[jesse8931]

Thanks..

Is using a timing light the most accurate way to set the timing? I have one and it is easy to hook up so that isn't a hassle for me. I think the manual said to time it when it was at 1300rpm. When it's at 1300 rpm I should make it so the F mark is exactly on the mark on the case?

not sure never had to time mine maybe some one can help on that but mini ran rough till i rebuilt the carb i clean it with Yamaha carb clean if you cant get it at a local dealer then order it here Yamaha Carburetor Cleaner 32 oz. - ACC-CARBC-LE-NR not sure if they ship outside the usa if you get it then follow this guide
VJMC- Craig Faith's Magic Carb Cleaner

 

[Allistah]

I have a gallon can of that parts cleaner stuff. You take it all apart and set all the parts in the basket and let it sit in this thing for 30 mins or something and then clean it up/blow it out with compressed air to make sure all the little fuel circuits are open. I'll do that in the meantime when I'm waiting for the points and condenser.

 

[jesse8931]

thats should help on that my ct90 just needed carbs cleaned

 

[Custom]

a healthy battery should stablise around the 6.2-6.4V mark. The knock sound at idle could mean your bottom end need rebuilding, new points, plug, oil change and setting valve clearences should be done as a part of any major going over on a bike

 

[Allistah]

I took the carb apart today and cleaned it all up. Still has the same issues. I'll wait till I get the new parts and install those and see what happens. I'll reply to the thread when I get to that point. Probably not until this weekend at least I'm guessing.

 

[Allistah]

Hey guys,

I got the new points, condenser, plug wire and boot installed. I set the timing using a static timing method and it was spot on the F <--> Case mark. I also set the gap on the points to .35mm as recommended by the book. I forgot to buy a carb rebuild kit, but I did pull it all apart and go through it to make sure nothing was clogged. I let all the parts sit in a part cleaner and then I blew compressed air through all the holes and even put strands of wire though the tiny holes in the jets to make sure they weren't plugged.

What should I use as a starting point on the air mixture jet? The book says about 1-1/8 turns out but if I give it throttle just a little to fast it will caugh and fall on it's face and die. Starts right back up. I put a tach on it and adjusted the mixture until the idle speed went up to about the max it would and then re-adjusted the idle speed down to 1300rpm.

I also noticed that when it sits there and idles it is still doing that "miss" or a slight caugh every 10-15 seconds or so. Here are my new questions:

1) The service manual I bought says that if I have a dynamic timing system in the bike to use a timing light. How do I tell if my bike has one or a static timing system?

2) It seems when it's running "better" I have to have the air mixture screw turned out like 2-3 turns which doesn't sound right to me. Any idea on this one?

I have not checked the valve adjustment yet - could that cause something like this? I'll try and do that tomorrow just to make sure it's where it should be.

Thanks for the help guys, this is getting on my nerves.

-Allistah

 

[Allistah]

Ok, here is where I'm at:

I adjusted the valves this morning and took the carb apart again and let it soak in carb cleaner to make sure it was clean. Replaced the O-ring on the carb side and put a new gasket on the manifold side. The book says to have it idle around 1300 but it has trouble down there. If I set the idle to 1400 things are very smooth and I don't get the problems.

The only problem that is left is when I give it throttle quickly, it wants to die. It's like the sudden drop in vacuum makes it die. If I don't gun the throttle quickly it's ok and runs great. It shouldn't want to die and fall on it's face if I gun the throttle should it?

Here is what I've replaced so far:

Points
Condenser
Cleaned carb twice to make sure
Adjusted valves
Replaced plug wire and boot
New spark plug
Set timing with timing light F mark is exactly on the case mark
Timing advances to advanced timing mark as it should near 2600rpm

Anyone have any ideas what I could be missing here? I'm wondering since it's not a brand new engine that I should advance the timing a tiny bit to see if that would help?

Thanks,

-Allistah

 

[Custom]

try adjusting your air screw a 1/4 turn at a time and give it a rev at each adjustment

 

[R_dub]

If you havn't done so already, make sure to tear down the whole air filter assembly with the plastics and check for major dirt build up or any other foreign material that might be in the air intake system. I good K&N or UNI filter along with a proper carb mixture adjustment might help the engine not die when you give it a lot of gas. An origonal honda air filter is also great.
As for the 'knocking sound', that might be the piston skirt slapping the cylinder. You may want to look into replacing the rings and/or having the cyliner sleeve re-honed.
Hope I could help a little
-R-dub-