The spark will jump to the engine fin if I hold it a little away but if I put it right on engine it will not fire what does this mean this problem has been with this bike for over a year I cannot figure it out. Also how do you get the thottle needle to seat all the way down in the carb just cannot get it to all the way down and what is that little clip for that kind of looks like a letter A was told that fits at bottom of spring to hold needle down. Hope someone hear can help me out. With this 1970 ct70.
spark will jump to engine fin
- Thread starter yuke
- Start date
Can't believe on the 3rd plug I put in I have fire as I should now I just have to figure out how to get the needle to seat in top of carb the bike is running at full thottle have to slow it down with the choke.
cjpayne
Well-Known Member
Try turning the carb slide 180deg and see if it slips in. Make sure your twist throttle handle is all the way forward.
OLD CT
Well-Known Member
Sounds like your part way there with spark. Is your air fuel screw 1 3/4 out from lightly seated? You want to put the tiny needle clip in the middle groove of the needle,to start out with. The W clip is just under the throttle spring and sits in the bottom of the round throttle slide. Once that's back together i would check for fuel flow at the drain screw.spray a little shot of carb cleaner and see if it fires. Is it a fresh plug?
Thanks for all the quick replys after doing some more reading and searcning I realized I was putting the w clip in totally wrong when I installed it the correct simple way of just laying it in the chamber on top of the needle everthing went smooth as silk and she started 1st kick. It does idle a little erradic kind of like it haw a cam in it. The c clip is on the top ring on the needle I think which lets the needle sit the furthest down in the carb making it the leanest setting I think. I might try to move it a little down to make it a little richer if that would make it idle a little smoother. This is one great site to keep these great little bikes running. This ct was the 2nd among many bikes I have had over the years exact right down to the color red. Thanks for the replys.
Your understanding of jet needle clip position is correct. And, richening the mixture, as you're contemplating, is probably a good idea...especially considering the oxygenated pump gas we have to live with.
However, the main jet and jet needle only affect operation above ~1/8 throttle and should have little to no impact on idle quality. If it does, you've got a blockage issue on the pilot circuit. For now, I'd suggest richening the idle mixture, via the pilot airbleed adjusting screw. Try turning it clockwise 1/2 turn. That should make a big difference...hopefully giving an overrich idle mixture; that's a good indication that the carb is flowing fuel as it should.
You might have a vacuum leak...loose bolt, failing gasket and/or O-ring. The air filter element could be dirty, or dying. Pull an endcap off the airbox; if the idle quality changes, especially if is speeds up, the air filter needs attention.
However, the main jet and jet needle only affect operation above ~1/8 throttle and should have little to no impact on idle quality. If it does, you've got a blockage issue on the pilot circuit. For now, I'd suggest richening the idle mixture, via the pilot airbleed adjusting screw. Try turning it clockwise 1/2 turn. That should make a big difference...hopefully giving an overrich idle mixture; that's a good indication that the carb is flowing fuel as it should.
You might have a vacuum leak...loose bolt, failing gasket and/or O-ring. The air filter element could be dirty, or dying. Pull an endcap off the airbox; if the idle quality changes, especially if is speeds up, the air filter needs attention.
Now I dont have spark again this is my 3rd plug this is driving me wacky any one have any thoughts as why these plugs seem to be going bad so fast when I was holding the spark wire yesterday I really got zapped so I know there is fire at end of spark wire just not jumping the electrode when it is grounded on engine fin and probably why it will not start.
cjpayne
Well-Known Member
This is starting to sound like one of those electrical problems that comes and goes:102:. The engine needs a good clean grounding to the frame. Sometimes the grounds will will pass a continuity test, but when under load(alot more voltage/current) the contacting surfaces aren't clean or tight enough. I wonder if the ignition switch grounding to the frame could be causing this too.
Yea CJ this is crazy I m ust went out again and now I had spark and the bike started but it idles very rough and erratic I did a continuity test on the heads offboth frame bolts and it seems good. The way I guess to really get a better ground would be to drop the engine a bit to really scrape around there to make a better ground. I have had this problem ever since I bought the bike do not know what the po screwed up before me I know he messed with the carb and put an intake valve in it. But he said it was done professionally by mechanic. I might try to take out s,ow jet and make sure it is open and give carb a good cleaning although I do not think this is the problem for my erratic idle.
I did run a wire from engine to good ground and there was no differance. It seems that if I keep trying and trying eventually I will get spark on the electrode of the plug while grounding it to the engine fin. I'm wondering if the rectifier could be causing my trouble. I sure hope I figure this out soon as it is driving me bananas. I know my battery is weak but I know these bikes can run with no battery so I figure that should not be my problem right? I think the next thing I am going to do is clean out the carb and see if that will make it run a little smoother. I did take notice that if I turn the petcock off and let it run out of gas right before it stops it gets smooth and idles faster leading me to think that maybe my float level on my carb is causing the rich mixture and erattic idle.
cjpayne
Well-Known Member
Is there any fuel coming out of the carb weephole too? That would also point to a float/needle valve problem. I assume you already tried the air/fuel mixture screw. You can also try running a jumper from the stator plug directly to the coil wire plug(bullet connector) to eliminate any coil problem. I think the rectifier only bleeds off voltage and the battery is just a buffer to keep from frying the headlight. This persistant problem would be driving me nuts too.:102::43:
kirrbby
Well-Known Member
Points and condenser #1. Dirty carb #2. When these old bikes stop runnin, these are the most common problems. If you haven't cleaned the carb yet, that will be a very good thing to do. Including flushing out the tank and fuel lines.
cjpayne
Well-Known Member
Never hurts to do a by the book tune up first. Why didn't I think of saying that?
I have tried all of these things already it is really strange in that if it has no fire at plug electrode when grounded to engine fin if you hold the plug away a little bit and make the spark jump enough times eventually you will get fire there. Had the bike running yesterday ran fairly well except a little rich and idled erattic when I was going to start ripping into carb to clean I then had no fire and back to square 1. It baffles me in that the spark is at end of spark plug wire always but will not jump electrode when grounded on engine fin but at a later time w/o doing or turning anything off or on you will have spark there. I wish I could track this down in a simple manner as I am not that good with a meter. Maybe is there anyone close to me that could help me work on this I am in eastern pa. near allentown.
birdmannn101
Member
Yuke, I know you said that you already switched the plug out several times. I had this very same problem on the C102 Super Cub I restored. No one would believe me when I said the spark jumped from the side of the plug to the frame and a long distance too but it wouldn't spark where it is supposed to. I was running a resistor plug and didn't think that could be the problem. I looked up the original plug and switched it out and never had the problem again.
b52bombardier1
Well-Known Member
Maybe a broken, intermittent plug wire? Bad spark plug cap?
I would also check coil resistance because it might be changing due to an internal broken wire that gets intermittent contact as the coil heats up. Coils rarely fail in this manner but you are in "Doctor House" territory now with this bike.
Rick
Two CT90 and two ST90 bikes
I would also check coil resistance because it might be changing due to an internal broken wire that gets intermittent contact as the coil heats up. Coils rarely fail in this manner but you are in "Doctor House" territory now with this bike.
Rick
Two CT90 and two ST90 bikes