help solve problem

Howitt

New Member
Jun 7, 2008
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I am having a problem with my 80cc motor. When travelling at WOT the engine sounds funny. It has a nice hum to it but every few seconds there is a brief almost purring sound. I also seem too lose and gain speed while maintaining the same throttle position. Does anyone have a suggestion to a possible cause?
 

gadgetman80

New Member
Jul 2, 2008
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Mio MI
Is this when it is cold/warm/hot? When I was messing around with nitro r/c cars, I noticed when they got hot and the mixture was lean, they'd fluctuate at WOT. Keep in mind, I don't have one of these engines "YET", but if I'm off base I hope someone can correct me.
 

Ilikeabikea

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Staff member
Jan 27, 2008
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Mine does that too. A wot it fluctuates. Norman soldered and redrilled my main jet yesterday. I've been having lots of company over the weekend so I haven't really got to try it out yet. I rode it once yesterday but didn't have time to let it warm up good. As soon as I can really ride it I'll let you know how it does..............................
 

Venice Motor Bikes

Custom Builder / Dealer/Los Angeles
Mar 20, 2008
6,615
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Los Angeles, CA.
I think your fuel mixture might be fluctuating between slightly rich & just right.
My "Bomber bike" was doing the same thing!
Try dropping the carb needle down one notch, (C-clip UP one notch) & see if that helps.
Also make sure to upgrade your spark plug, wire & boot, & solder your coil wires!!
 

Howitt

New Member
Jun 7, 2008
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I moved the clip up one notch but the same problem is happening. I am going to go out and replace the plug and wire today. I was reading some other posts and I'm thinking that the problem might be caused by the main jet being too small, I think replacing it with a larger one ( .80mm ) might solve the problem.
 
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imdhulk

New Member
Jun 1, 2008
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i desperatly need help... i finally put together my moter kit.. i rode it for 2 days with no prob.. this morning i tried to get her started but she wouldnt start... i peddle to get the motor runnin but it just wont start..can some one please give me advice before i lose my mind.. im not miachanically incline.. i dont know what the **** im doing... my brother inlaw put this gadget together..and has no time to help.. he said to come to this forum.. can some one please help
 

imdhulk

New Member
Jun 1, 2008
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i just finnished putting my motor kit togather.. rather my brother in law did.. it was runnin for two days ... i tried to get her started but she wouldnt... i peddled my buns off but no start.. what can be the prob... i m not mechanically inclined. i do not no where to begin to look for the prob. can some one please help me befor i lose my mind.:confused::confused::confused:
 

Dave31

Moderator
Staff member
Mar 1, 2008
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The first thing you can try that's the easiest is diconnect the kill switch..some of these switch's will ground themself's out.

If that don't work, you want to check for spark...before you do that check all you wire connection's for the CDI and make sure they are still connected.

To check for spark I use a spark plug ignition tester..



This can be picked up at any local auto parts store...you can also make one with a good plug...alligator and just solder the clip to plug

Norman has a cool one that is much simpler to make...
http://motorbicycling.com/f4/tester-ignition-207.html

Be sure to pull the plug out to turn the motor easier...or just pull your plug and hold it next to the motor to check for spark...this is a little hard for me since you have to hold the plug and turn the motor at the same time..

If you got spark...then you need to see if you are getting fuel....crank the motor for a little bit then pull the plug out and see if it's wet with fuel.
If not...check the screen in the petcock...check to be sure float is not stuck in the carb bowl..

hope this help's get you going :ride2:
 

Ilikeabikea

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Jan 27, 2008
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If you didn't put an inline filter on the fuel line you could have trash in the carb. These tanks can have crud in them. Check the simplest stuff first. If you don't have fuel and fire it won't run................................
 

Skyliner70cc

Member
Mar 8, 2008
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Very common problem. Not enough fuel at WOT. Problem can be too small jet, needle clip height, or what I think is slightly more common: carb float not properly adjusted from factory.
 

Howitt

New Member
Jun 7, 2008
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my carb is slanted about 15 degrees because the throttle cable doesn't fit under the top tube of my bike, would this cause a problem with the carb float?
 
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Skyliner70cc

Member
Mar 8, 2008
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I don't think 15 deg is enough of an engle to cause problems. I'd adjust the float and then increase jet diameter. In addition, the more oil you put in your fuel, the less available gas you have to burn per unit volume of mixture. Try a 40:1 mixture using a quality synthetic or Maxima 927. Running 16:20-1 is just too much oil and can be effectively leaning your mixture out.
 
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Bikeguy Joe

Godfather of Motorized Bicycles
Jan 8, 2008
11,843
236
63
up north now
You may be having a problem because the flost chamber is not level. It is designed to have a little extra fuel at lean angles, but since it's constanly "leaning" you may have a little fuel starvation goin on there. Have you tried ajusting your float arms upward a little?

16-20:1 IS too much oil. 24:1 is recommended for a reason...these are ancient tech piston ported engines and they also have really sloppy tolerances. The highest I'd go is 32:1. And that's at your own risk.
 

imdhulk

New Member
Jun 1, 2008
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good morning all... so far this forum has helpd me some what with the minor problems i had...one recent prob. i had was my air filter fell off as i was on my way to work. i realized it when i was trying to chain my bike up to get a bite to eat. i retreaved the air filter cap about 2 miles back. it was slitghtly damage. the bike will not run now with out it. the cap is the only thing that fell off.. any suggestions.. any home aid remedies out there i can use to get her back on the rode??
 

Bikeguy Joe

Godfather of Motorized Bicycles
Jan 8, 2008
11,843
236
63
up north now
Did you find the filter element or just the cap? You need both. Try making a new one from an air filter element for a mower and fix the old cap.