Loss of high RPM spark?

Norman

LORD VADER Moderator
Jan 16, 2008
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check your wiring look for a hair of a wire that's not wrapped and grounding or a loose connection on all wiring look very close at this could even be a tiny bare spot in the wiring touching the frame and grounding out. Plug wire tight at both ends. O resistance on the plug wire check it with an ohm meter. and unhook the kill switch it might be grounding out due to vibs at higher rpm. Plug good and tight and is it clean and not gunked up?
Check your air cleaner it might be a little too oily and last is your throttle slide all the way open when you are wide open. Just some of the things that come to mind. Do each check one at a time, ride it to check if you found the problem. Step by step if you do 3 or 4 things at once you will not know which worked if you do get it to run right.
Is your permix the right mix? and not old. The float could be causing you fits too if your float is set too low. Got a fuel filter in place? fuel valve all the way on. the chicken poo filter in the tank might be gettin gummed up and starving it for fuel at high rpm. I know my fuel valve has a sweet spot that if its not right my engine will act like its cutting out at high rpm. I don't think your fuel cap is not venting cause all of mine leak fuel so its venting on mine you couldn't be that lucky to have a good sealing fuel cap could you? You see a little fuel leaking out if you fill it up that will let you know your tank is venting .rotfl hope some of these ideas will help.
 

Skyliner70cc

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Mar 8, 2008
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Pablo, what are your symptoms? Too often, the high speed jet (at sea level not at my altitude) cannot supply fuel fast enough at full throttle/full engine rpm and engine cuts out. This cut out feels like loss of spark but isn't.
 

Pablo

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Dec 28, 2007
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Pablo, what are your symptoms? Too often, the high speed jet (at sea level not at my altitude) cannot supply fuel fast enough at full throttle/full engine rpm and engine cuts out. This cut out feels like loss of spark but isn't.

That's exactly what happens. Bike starts easy, idles fine. Wick it on, bogs and dies. I thought it needed more fuel so I went richer (lower the clip) and seemed to make it worse. I will try moving the clip to the top to see what happens.....if I move it to the top, change to a new spark plug and it bogs and dies at full throttle and the plug still very wet, to me this kinda say it's a spark problem.

Norm - I methodically checked MOST of the stuff you write - but I feel like making a list and checking stuff off with notes! :D:eek:;)
 

Skyliner70cc

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Mar 8, 2008
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Did you replace the chinese spark plug and spark plug wire? I had a spark plug fail 2 weeks ago, it fired only every 3rd revolution. Had other plugs fail where the electrode cracked or separted in the plug.

The clip on the spark plug often falls out and the plug is loose causing intermittent spark when engine is vibrating most at full throttle.

Some tips, hope they solve your issue.
 

Norman

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Jan 16, 2008
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Pablo you got a buddy with a good engine ignition coil box to try? Did you take a look at the mag coil under the cover the wires could be damp or the soldered connections might be lose or you could have some metal particles touching the wiring and occasionally shorting things out. You haven't washed the bike off or got it wet lately did you? Out in the cold and then brought into a warm place or vice verse.
Lowering the needle will lean it and rasing the needle will make it richer
But you said the plug is wet and it cuts out if it aint the cdi black box it must be fuel related.
I don't have the ohm reading on the cdi maybe we will get someone to jump in that has these reading handy. If not I could check mine and get back to you.
Don't give up.
Norman
 

Pablo

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Pablo you got a buddy with a good engine ignition coil box to try? Did you take a look at the mag coil under the cover the wires could be damp or the soldered connections might be lose or you could have some metal particles touching the wiring and occasionally shorting things out. You haven't washed the bike off or got it wet lately did you? Out in the cold and then brought into a warm place or vice verse.
Lowering the needle will lean it and rasing the needle will make it richer
But you said the plug is wet and it cuts out if it aint the cdi black box it must be fuel related.
I don't have the ohm reading on the cdi maybe we will get someone to jump in that has these reading handy. If not I could check mine and get back to you.
Don't give up.
Norman
Thanks Norman - to know me, "give up" is not in my soul or genetic make-up!:)

My bike buddy is to far away - about 100 miles - but we had discussed swapping carbs, cdi's, etc and such, just to see.

Please - I would love the ohm readings on the coil.

I will open the mag coil area and have a look-see.

Indeed - moving the E clip up lowers the needle and makes it leaner.
 

Pablo

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What resistance #'s do you guys get?

Code:
CDI pack        GOOD     Mine
Black to Blue 1150kΩ   7.6 meg Ω
Black to Plug 2.6kΩ     2.17K Ω
Blue to Plug  1150kΩ    OPEN
 
 
Magneto
Blue to White 327Ω    349Ω
Black to Blue 327Ω    347Ω
Black to White 2.1Ω   2.1Ω
Black to Gnd 0Ω        0.3Ω
Blue to Gnd  327Ω      347Ω
White to Gnd 2.1Ω     2.3Ω
 

Pablo

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Dec 28, 2007
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Bad Cdi Unit?

Blue to Plug 1150kΩ OPEN
Can anyone measure this one only? I even took the spark plug wire out and measured from the screw to the blue wire and it was a solid open circuit. Dunno if I have a problem with my CDI or this is a circuit state???? Ghost0 is getting about 1.2 MegΩ.

Thanks in advance!
 

Pablo

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Dec 28, 2007
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Please measure....

I have no idea how to read it, but when set on 200K, I get 42.6.
When on 20K, I get 8.9.

Both are blue to plug.
Wow - thanks - another data point. We all get different numbers.....but a pure open doesn't seem right. There must be a diode in there.....and of course some capacitors.....

Others?

I'll probably just buy a new CDI unit, even if I keep one as a spare.
 

paul

Well-Known Member
Dec 23, 2007
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i am going to do the same thing. i hear over and over people haveing problems with thier bicycle engine and it ends up the cdi is bad
 

Pablo

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Dec 28, 2007
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Never mind....I got home from work and I reversed the meter leads and got 7.6 meg on blue to plug...so there is some type of diode in there...I think the CDI unit is OK

It started happy as a lark. Sounded good......warmed up slowly jiggling the choke, could rev it OK with choke.....engine warm.....choke almost all the open........give it gas.........gagging low buuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuu bowaaaaaaaaaaaaaaa dies. Start and repeat. I think it's the carb.....I tried to get it hot, but it takes awhile......
 

deacon

minor bike philosopher
Jan 15, 2008
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I happen to agree, I always thought it was. It sounds too much like the problems I had at first. It seems anytime you pull that manifold, you need to just replace the gasket. That's what happened to me. I pulled it and tried to reuse the old gasket. Never did seal so I had to reinstall a cereal box manifold. Clean off the old one carefully so you get a clean flat surface for the new one.