surging engine

christianava12

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Dec 18, 2008
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San Diego CA
I have a 80cc RAW engine that is on it's 3rd tank of gas and surges a lot at WOT. My first tank of gas was at the manufacturers recommendation of 16:1 and now at 32:1. I cleaned out the air filter thinking that maybe the filter was clogged from the rich mix but there seems to be no difference. When I say surging I mean it will be going and then suddenly almost completely stop pulling and just coast for about 5 seconds or so then pull strong for 5 or 10 seconds and then stop pulling and coast again, the engine never actually shuts off just not pulling very hard.

any idea's, anyone??
 
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jasonh

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Jun 23, 2008
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It sounds like you're having trouble getting enough fuel at WOT.

Do you have the screen in place on the petcock inside the tank? There is probably junk caught in it. These tanks have a lot of crap in them from the factory. I'd get a see-through inline filter and ditch the screen, after cleaning out the tank.

Also, your float could be sticking. Take the bowl off the carb and make sure the little arms move freely, and that the float is in good shape. Hope that helps.
 

Dave31

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Mar 1, 2008
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It also could be fuel foaming in the carb...check your motor mounts that they have not loosened up on you. Any notice of a small vibration?
 

captainrichhill

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May 31, 2008
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I had a problem like this and I adjusted the fuel valve while riding and I need to RESTRICT the flow a little to get maximum performance.
 

Walter F.

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Jun 4, 2008
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It also could be fuel foaming in the carb...check your motor mounts that they have not loosened up on you. Any notice of a small vibration?
Happy New Year Fair ol' buddy, got me some New Year Cheer goin', I want you to 'splain to me about this "fuel foaming in the carb"-alright I can IMAGINE an engine vibrating and maybe shaking the bowl of the carb, but in the float bowl it is air tight!!! Have you ever seen this happening inside the carb?Right after the float bowl the gas goes to the emulsion tube where it is made to bubble or foam to better atomize it. I just don't buy into this deal of fuel foaming causing "surging". What does it foam and quit, foam and quit?????? Horse Hockey-------------- Walter F.
 

jasonh

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Jun 23, 2008
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I'm inclined to agree with you Walter. The jet picks up the gas from the bottom of the bowl, so unless the ENTIRE bowl is nothing but foam (doubtful) there shouldn't be a huge issue.
 

Dave31

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Mar 1, 2008
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Well I got some video to show other wise...give me some time to get them uploaded.

Foaming in the carb is the best way to describe it. I have had lose motor mounts and the extra vibration causes a fuel delivery problem. Call it what YOU want...I will call it fuel foaming. The vibration can cause air to enter the carb...when you back off the throttle you lessen the vibration and then it runs fine. As soon as you pick the throttle back up you increase the vibration to where air gets in the carb again. Stay tuned for the vids...
 
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Sep 20, 2008
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Happy New Year Fair ol' buddy, got me some New Year Cheer goin', I want you to 'splain to me about this "fuel foaming in the carb"-alright I can IMAGINE an engine vibrating and maybe shaking the bowl of the carb, but in the float bowl it is air tight!!! Have you ever seen this happening inside the carb?Right after the float bowl the gas goes to the emulsion tube where it is made to bubble or foam to better atomize it. I just don't buy into this deal of fuel foaming causing "surging". What does it foam and quit, foam and quit?????? Horse Hockey-------------- Walter F.
laff I give it to Walter & Jason on this one!!! The fuel isn't actually "Foaming" in the bowl. The carb is unable to disperse it properly at a high harmonic...the reason...the jet needle, and main jet are doing a circle jerk that prevents the fuel from flowing through the needle as it should. Yes I checked this!!!

Jim
 

Dave31

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Mar 1, 2008
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And like I said...I call it fuel foaming...I am not saying that fuel is actually foaming in the carb. I have had the exact same thing happen. And all it was was a lose front motor mount.
 

Dave31

Active Member
Mar 1, 2008
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Here is the vids..

I noticed a small vibration but thought nothing of it. As the rpm increased, it fell flat on its face...back off throttle for a few seconds and then back on throttle would run fine until I would hit a certain RPM.

I checked EVERYTHING.. From float level to fuel filter, CDI, Mag. In the end was a lose motor mount. Tightened it up and problem went away.

FR31MB/fuel foaming - Photobucket - Video and Image Hosting
 

Technocyclist

Motorized Bicycle Senior Technologist
Jul 7, 2008
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Hmmm... could be a leaky intake gasket... or vacuum leaks in the intake.... I remember I experienced something like this and the intake gasket has deteriorated... I now changed to a better intake gasket...
 

Walter F.

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Jun 4, 2008
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Connecticut
Well I got some video to show other wise...give me some time to get them uploaded.

Foaming in the carb is the best way to describe it. I have had lose motor mounts and the extra vibration causes a fuel delivery problem. Call it what YOU want...I will call it fuel foaming. The vibration can cause air to enter the carb...when you back off the throttle you lessen the vibration and then it runs fine. As soon as you pick the throttle back up you increase the vibration to where air gets in the carb again. Stay tuned for the vids...
Seems to me that if air can get in as you say, then gas can get out and would be dripping off the carb??? Walter F.
 

TexasDav

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Aug 19, 2008
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I know that my bike had that problem and after tighing my motor mounts it fixed the problem. Now I don't have xray vision but it fixed mine and I will keep on beliving it foams
 

Norman

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Jan 16, 2008
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I wonder if vibrations get so bad that the float is being shook up and down turning off the incoming fuel and causing the carbs float chamber to run almost out of fuel?
Vibes can do strange things and if bad enough tear things clear apart. As in watching a show airplanes/helicopter ran through a harmonic vibrations testing up to the point of failure/going to jell.
Norman
What ever the cause of the problem I hope you got/get it fixed.
 
Sep 20, 2008
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The Point Beach bike I did had this problem...At upper RPM the engine would develop a high harmonic that was enough to make your bowels feel funny laff At the same time the engine would back-off.

As far as I can tell the needle is bouncing around in the jet and disrupting the fuel flow.

I found out by coating the needle with Dykem, (steel blue layout ink), and running the engine.

After the run, the Dykem was rubbed away near the tip around it's diameter. I can only assume that the needle was twizzling around in the jet. I didn't have time to fool around with a fix, the customer wanted his bike and I knew he wouldn't wind it up anyway.

I know on some of my 2 cycle motorcycles the needle was lightly spring loaded to one side of the jet.

Jim
 
Sep 20, 2008
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Clearwater, FL
web.tampabay.rr.com
I wonder if vibrations get so bad that the float is being shook up and down turning off the incoming fuel and causing the carbs float chamber to run almost out of fuel?
Vibes can do strange things and if bad enough tear things clear apart. As in watching a show airplanes/helicopter ran through a harmonic vibrations testing up to the point of failure/going to jell.
Norman
What ever the cause of the problem I hope you got/get it fixed.
Float flutter is a definite possibility...and yes vibes can cause all kinds of problems.

Jim
 

old motorbike

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Sep 21, 2008
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I believe the solution is finding someone who can balance these engines to smooth it out and that should help this problem.
 

Dan

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May 25, 2008
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Fair, you bring up a good point. With 2 strokes and mounts. Would Fuel Cavitation be a factor? no additional air would be needed and would look "foam" like. Asking, I dunno. A prop under water makes bubbles with no air present and disrupts propulsion.

After bolting down tight, would seem to fix all but is it just the "paint shaker" effect or also cavitation?