round trip 60

hey all,

i just rode my moped on a 60 mile round trip, now this may not seem like alot but heres the story. now the roads i traveled on were all 40 and up. and my lil moped was being passed by every jackass out there. it took me 50 mins to get to manassas from springfield,va. the bike performed flawlessly exept the fact that at high speeds(40) the bike would be at max rpm and it would start to kinda four stroke while popping. the pipe was all tight. and when it started four stroking i put my hand down and undid the air box. it stopped four stroking but it still ran rough and it had a slight popping to it. i wonder what the problem is? hey, since i know the estimated miles and the exact time couldnt i find put my average mph? what would the formula be for this? well feedback is greatly apreciated

Re: round trip 60

Chris Robertson /

The generally accepted theory we have about mopeds that suddenly start four stroking after running for a while is that fuel mix is getting kicked back into the air filter through the carburetor. After a while, the filter becomes so saturated that it begins blocking the air flow (thus enriching the fuel/air mixture). Too much fuel results in four stroking. Taking the air box off will not make your moped work better because your engine requires the resistance the airbox creates --indeed many people find their top speed <i>drops</i> when they remove their airbox.

You didn't mention what kind of moped you ride, but PA-50's are notorious for four stroking at top speed. If you let us know a little more about what you ride, and what conditions caused the four stroking (i.e. how long you were riding, what kind of fuel mix, etc.) we might be able to tell you how to fix the problem.

To figure out your average speed (in mph) take the distance you travelled (in miles), and divide it by how long it took (in hours --e.g. number of minutes divided by 60). You said it was 30 miles one way and that it took you 50 minutes. This would work out to 30 miles / 0.83 hours = 36 mph.


Re: round trip 60

I don't know about your bike, but miles per hour is pretty easy to calculate.

mph = Miles devided by Hours

Re: round trip 60

i have a tomos targa. i took my air box out because it would four stroke. the point is that the engine started popping. the day before i left i took the bikes cylinder off and cleaned everything up. one thing that i noticed was that there was a lot of carbon on the head and the pison and the exaust port had a lil more that the last time i cleaned it. all these parts had no carbon on then before i advanced the timing. could this be the reason for the carbon? and another thing... the piston had a brown is yellow kinda color on it. this color was found right after the rings and in the middle of the rings. does this mena my rings are dead? or could this be because i put a new piston in it and the new piston/ rings dont match my cylinder exactly. the cylinder had no scratches along with the piston.could the new piston be the reason for the popping? any more feedback.


Check your compression

Chris Robertson /

Hi Mike:

What color is your spark plug?

Buy/borrow/use a compression tester and measure how much compression you are getting.

I think if your timing is too advanced you can get problems with the engine bogging at high speeds.

I'm not sure what the discoloration on your piston means...


Re: round trip 60

Hi! If you don't solve it with what you've tried so far,try replacing the spark plug with one that's one heat range lower.At that high an r. p. m. ,the spark plug can get hot enough to predetonate the mixture,causing a slight backfire or popping.BYE!

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