Power loss, reduced power, wot, high speed power loss

mgladden2

New Member
Aug 10, 2008
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Las Cruces
www.markgladden.com
Hi everyone,

I bought a dresser black from spookytoothcycles in bisbee arizona and mounted the pk-80 kit on it. i broke it in nice and easy, and after a few weeks I was happily able to cruise at a constant 28-30mph, with a nice clean engine sound and good strong WOT/powerband performance.

The other day I took it for a slightly longer ride, but still under 20 minutes, and out of the blue I started loosing power / experiencing power loss at full throttle / top speed. The engine would suddenly bog down for a bit, then after reduced throttle, would pick up for a bit, then bog down again, etc.

I've read tons of posts, tried a hundred different things, and the best I can tell is that the carburetor reservoir is not sufficiently maintaining enough fuel to get pulled up by the jet. (But it used to do this, at least for the first few weeks??) I notice when I mess with the tickler while riding the problem will sometimes go away for 10-20 seconds, but it always returns.

I've read about drilling out the inlet to allow more gas to get in, but I worry I'll end up with a leaking inlet and have to replace the whole carb. I'd like to avoid doing that if possible. Besides which this problem didn't occur for a few weeks during which time I could WOT with no problems at all. I've tried adjusting the fork that pushes down on the floater (both upward and downward bend adjustments), I've tried adjusting the c-clip, I've tried cleaning all filters (tank, main line filter) and checking all points in the carb for clogs. I'm beginning to think that the tickler itself may letting air into the reservoir, and ultimately causing fuel foam to build up, which might push the float higher than it really should be and/or might prevent the jet from being immersed in sufficient fuel.

Has anyone else encountered this problem on an 80 engine? Any solutions that ultimately made it go away for good? I really hope this isn't how the bike will be from here on out. 20-24mph sucks when you're used to cruising right at or below 30mph.

Mark
 
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jasonh

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Jun 23, 2008
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Longmont, CO
Have you checked your spark plug yet? Tighten all bolts on motor? (head studs, intake and exhaust manifolds...) is the air suction at WOT pulling your choke on a little bit (happens to me)?
 

mgladden2

New Member
Aug 10, 2008
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www.markgladden.com
Tighten all bolts on motor? (head studs, intake and exhaust manifolds...)
Thanks, Jason. I was just getting on here to write...

I fixed it!!!!!!!!!!! I routinely tighten all of the bolts before a ride, but apparently I hadn't tightened the motor mounts enough -- doh! I re-seated the motor to pitch it forward a tiny bit more, then snugged the mounts good and solid. The problem is not only gone, but now I'm easily cruising at 31mph!! It seems so strange that loose motor mounts would cause this problem, but I guess the vibrations were bad enough to make it an issue.

God it's such a relief to solve a problem after you've been tinkering with it for four days!

Ride on,
Mark
 

wizzizer

New Member
Sep 8, 2008
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Seattle
i'm having this same issue and now that i see the fix, i did notice some extra vibration last time i rode er. i'll check my mounts and give it a whirl. thanks!
 

wizzizer

New Member
Sep 8, 2008
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Seattle
okay, so i checked my motor mounts and they were tight (i tightened them as much as i could anyway just to be sure) so i guess thats not the problem.

the weird thing is that if i go uphill (one that would normally bog the motor) it starts firing correctly and pulls just fine, but when on flat ground at wot it misfires (i think thats whats happening) and will not clear out and rev.

i'm at a loss. i even tried a bigger mainjet but that didnt help any.
 

Bikeguy Joe

Godfather of Motorized Bicycles
Jan 8, 2008
11,843
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up north now
You sound like you have too rich a mixture and the engine is four cycling when it's not under a hard load. Move you needle clip up one notch and try it.
 

Bikeguy Joe

Godfather of Motorized Bicycles
Jan 8, 2008
11,843
236
63
up north now
To the OP- if the mounts are loose and the engine is vibrating around a lot, it will cause the fuel to froth in the float chamber, and it will cause the problem you had. It make a sporadic lean condition. Hitting the tickler holds the float still and lets the float chamber fill up better.
 

wizzizer

New Member
Sep 8, 2008
14
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0
Seattle
thanks bikeguyjoe, i moved the needle clip up to the highest slot already but that didnt help either. but i think i will try a smaller main and see if that helps (i would put the stock one back in but i tried drilling it out and went waaay to far so thats not an option) but i dont know what the stock size is for the "80cc", anyone know? thanks!
 

wizzizer

New Member
Sep 8, 2008
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Seattle
cool. i have some dellorto jets that i can use in lieu of redrilling.

btw-someone on this forum said you cant redrill them but i will check the thread youve suggested. thanks!
 

Biker Mike

New Member
Mar 21, 2008
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Cropwell Alabama
okay, so i checked my motor mounts and they were tight (i tightened them as much as i could anyway just to be sure) so i guess thats not the problem.

the weird thing is that if i go uphill (one that would normally bog the motor) it starts firing correctly and pulls just fine, but when on flat ground at wot it misfires (i think thats whats happening) and will not clear out and rev.

i'm at a loss. i even tried a bigger mainjet but that didnt help any.
check the factory intake gasket as well. It gets saturated with fuel and oil, it then expands and may interfere with the flow to the cylinder. It also covers half the inlet hole on the jug. I just removed the gasket and used blue sealer. :bike2:
 

wizzizer

New Member
Sep 8, 2008
14
0
0
Seattle
i replaced the intake gasket on day 2 cuz it was oozing and seemed to be disolving entirely. so i bought some gasket material onto which i traced the manifold and cut with an *exacto, it worked out good so i think i'm ok there.

*hole punches are easiest for cutting the bolt holes.
 

2old2learn

New Member
Sep 17, 2008
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okay, so i checked my motor mounts and they were tight (i tightened them as much as i could anyway just to be sure) so i guess thats not the problem.

the weird thing is that if i go uphill (one that would normally bog the motor) it starts firing correctly and pulls just fine, but when on flat ground at wot it misfires (i think thats whats happening) and will not clear out and rev.

i'm at a loss. i even tried a bigger mainjet but that didnt help any.
I had a very similar problem on my HT engine after about 150 miles. I had to lower the clip on the needle to make it run richer at Wide Open Throttle, WOT. Suddenly instead of being limited to 20 mph now I can run at 30 mph. I'd have never thought it would make that much difference. I had tried to go the other way thinking it was too rich at first. Trial and Error.
 

mgladden2

New Member
Aug 10, 2008
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Las Cruces
www.markgladden.com
I still think it's your motor mounts. Uphill would cause the engine to vibrate differently against the frame. I would try to completely unbolt then re-seat your engine. Also, change from factory threaded rods to M6 x 50 and M6x25 threaded bolts (get some lock washers). Good luck!