Intermittent power loss

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klapool

New Member
Aug 29, 2011
68
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Wisconsin
China girl 49cc
Jamis commuter bike

Ive been riding my MB to work 13 miles one way and notice after about a mile or so the engine dogs out for a while. I can feel the sudden power loss. Then after about 25a yards it picks back up again.

After about 10 miles it does it again.

I thought it might be an air leak at the carb and checked and resealed the gasket and the mount for the carb.

I also thought that maybe it might be a fuel delivery problem so i removed the inline filter and installed a new fuel line just to be sure.

This morning, the same thing happened.

Could it be a bad cdi or plug or wire?

Dont want to be seen pushing my MB down the main avenue this after noon.

The engine has about 45 miles on it.

Any ideas?
 
Ludwig II

Ludwig II

Well-Known Member
Jul 17, 2012
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There is usually a vent in the cap. It could be partially blocked. Or have you done a real genius trick like carrying a bag on top of the tank and blocking it? Of course, I've never done that, honest, nor has anyone else here. Am I right?
 
Goat Herder

Goat Herder

Gutter Rider
Apr 28, 2008
6,237
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N.M.
Check the filter in the tank fitting inside the tank is not clogged. Also that the petcock is not clogged? These things really don't need much flow at all but these two areas can contribute.


As Two Door has often pointed out time the fuel flow to a time rate liken to 100 miles to the gallon. Drain it into a container and time the flow.
 
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K

klapool

New Member
Aug 29, 2011
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Wisconsin
So here is what I did...


I drilled a small hole in the top of the gas cap makeing sure the metal chips fell away as I drilled upside down.

Still did the same thing.

The hose from the tank to the carb is completely full and Ive never seen it drain down on WOT.

I messed with the E clip on the needle and moved it from the middle to the bottom and then to the top and finally back to the middle and never saw a change other then when I was climbing a hill and the needle was on the top clip I had no power to get up the hill.

The next thought is to replace the cdi with another china girl cdi I have in the garage.

I never saw any foaming of the fuel as I was riding which some have said it might be the issue.

Where do you all set your e clip on your needle?
 
Ludwig II

Ludwig II

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Jul 17, 2012
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I hadn't thought about the ignition, but I have known rotors go "soft" when the magnets got hot on other bikes. And electronic components can sometimes suffer from imperfect soldering as well, even if they're in working order.
 
K

klapool

New Member
Aug 29, 2011
68
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Wisconsin
So I messed around with the cdi and still did it.
Next I took out the fuel spud that the fuel line fits over on the carb. The hole in the bottom, which the needle stops fuel when its not needed, well that hole seemed auffully small. so I opened it just a bit with the smallest drill bit I could find.

What a difference!! Its like a new engine on a new bike! It really goes.

Has anyone else done this and found a difference?
 
Hoze513

Hoze513

New Member
Nov 24, 2011
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Joliet, illinois
I had about the same problem as you. Lost of power after mile. Like it was running out of gas or something. I did everything you did and it didn't work. Until I got a Fuel valve. And now that problem is fix.
 
K

klapool

New Member
Aug 29, 2011
68
0
0
Wisconsin
Hoze513 said:
I had about the same problem as you. Lost of power after mile. Like it was running out of gas or something. I did everything you did and it didn't work. Until I got a Fuel valve. And now that problem is fix.
Click to expand...

I have clear plastic hose but never saw it go empty, I think I'll change the fuel valve just in case!!! Good call!
 
MeniacleMechanic

MeniacleMechanic

New Member
Sep 4, 2012
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Virginia Beach Virginia
Ive replaced my Magneto twice already. When it becomes weak or old it wont let the plug fire properly. Making poor performance. One time i was riding and over a mile section it started to loose power and eventually just shut off and i had to pedal it home....

Theres aftermarket ignition systems to put on too.

Heres what i found after digging, give this a shot

http://www.motoredbikes.com/showthread.php?20227-Urgent-Magneto-and-CDI-Testing

http://motorbicycling.com/showthread.php?t=2118


Take a voltmeter and plug it onto the wires while its running and see if you get voltage drops when its not performing properly. i also replaced my ignition coil too
 
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Ludwig II

Ludwig II

Well-Known Member
Jul 17, 2012
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UK
One thing I do know from personal experience is that when some magnets get too hot, they lose magnetism; the cure for it was to let it cool down and the spark would return.

I wonder now, is it possible to put a rotor in a freezer for a few days and bring it back up to strength? Also, it might pay to ventilate the casing with the rotor in it to keep temperatures down.
 
G

goofyfoot2001

New Member
Aug 16, 2012
75
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South Carolina
Does your engine lose power at the same place on your journey each time? Leveling my carb made all the difference in the world. Also an ngk 7 spark plug though I'll drop that to a 6 today. I had to widen the gap on the plug ever so slightly which also made a noticeable difference.
 
R

robert.j.nash

New Member
Sep 12, 2012
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Wyong N.S.W. Australia
Ive had nothing but problems from day, 1 same sort of problems Blocked vent drill a hole the cap bike was running well then completely died, replaced the plug going again, then died blocked inline filter, replaced that and it was running brilliant going flat out 30 mph then this morning running like a dog barely going 15, cant use choke just kills motor, checked float level seemed high, reset it and felt better but same as you runs good for a while then just bos down everytime you open to full throttle ?
 
R

robert.j.nash

New Member
Sep 12, 2012
2
0
0
Wyong N.S.W. Australia
Ive had nothing but problems from day, 1 same sort of problems Blocked vent drill a hole the cap bike was running well then completely died, replaced the plug going again, then died blocked inline filter, replaced that and it was running brilliant going flat out 30 mph then this morning running like a dog barely going 15, cant use choke just kills motor, checked float level seemed high, reset it and felt better but same as you runs good for a while then just bos down everytime you open to full throttle ?
 
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