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Question: Moped accerlation problems??? points for best answer?

(Posted by: Matthew on 2010-02-25 04:40:46)

Hi I bought a yamaha jog r 50cc 56 reg, it has 8, 500 miles on it and the problem I have with it is that it gets stuck at 20mph. What I mean is when I accerlate it will hit 20 mph with ease then it appears to bog down and slowly work its way up to 30mph, once its on 30 mph or above it is fine and if i keep it at 30mph or above the throttle response is great. Once the speedo indicates below 30mph the throttle response is bad and slowly works its way up. I want to get the bikes throttle response like it is at 30mph. I have ridden my friends mopeds and theres are all standard and dont pause at 20mph they just keep going. West london yamaha have carried out the following on repairs to my bike: - Glazed the variator - New Rollers (All parts replaced are standard) - Stripped and cleaned the carb - Checked compression - New air filter - new spark plug - test ridden It also is terrible at going up hills, I know its only a 50cc but honestly it bogs down and wont budge unlike on a straight road, any ideas as to what it can be

Posted by: Blessy on 2010-02-25, 04:43:43

Sounds like you might be running either rich or lean. Take the air filter out completely and see if that helps or makes it worse.

Posted by: dazza_ea on 2010-02-25, 04:45:16

Yep.. your throttle response is due to your variator washer being dented.. if it is restricted, then deresrict it, if it is derestriced, then you need to change the variator washer.. if i can remmber correctly. and your poor acceleration is due to your rollers. if you have rollers that are light, you will have very good acceleration, but lower top end speed. and if you have to heavey rollers, then the acceleration will be terrible and in some cases it wont move as they are too heavey.. but you will have higher top end. hope this helps.

Posted by: Mikey B on 2010-02-25, 06:34:58

Ok...you do have a problem as even for scooters, acceleration to their top speed still tends to be quite fast. A 20-30mph top speed is also unusual, even on a 50cc scooter. To me, it seems that the highest possibility, is that the variator rollers are too heavy. Find out what the standard roller weight is, and compare them to your variator rollers installed now. On the front/ side of the roller, a weight should be stamped. For example; '6gram' If the rollers installed now are heavier than standard, take it back to the dealer and begin asking questions as too why. Heavy rollers increase top speed and slow acceleration. Lighter rollers have the opposite effect. Reemember that this is upto a point. There will become a point where the rollers are too heavy or light. If the rollers aren't the problem, then it may have been de-restricted poorly and/ or de-restricted then re-restricted. In the case of re-restricting a de-restricted scooter, the carb jets may not have been changed back to the standard jetting and may be too large for the requirements of a restricted engine. If the jets are too small on a dep-restricted scooter then install bigger ones. Both os these issues will cause the carb jetting may be off by a substancial amount. If this is the case, find out what the standard jet size is and compare to the jet currently installed. If the jet is too small, then this may preventing your scooter from running properly If none of these things are the case, then the problem lies deeper. Return to the dealer and ask questions... Hope this helps, good luck and ride safe ---Mikey B--

Posted by: guardrailjim on 2010-02-25, 07:19:07

May need a top end rebuild (cylinder, piston & rings). 8,500 miles on a 2 stroke 50cc engine is way over due for a rebuild. 2 stroke engines can give false compression readings. Ask your Yamaha dealer to make a visual inspection and service specification measurements of the top end. You've tried all the obvious repairs, now it's time to perform deeper inspections.