Son's Reiju MRX 50 - Lack of power
Discussion
Bought my 16yr old son his first moped the other day. Absolute bargain, 8k-mile 73 plate Reiju MRT 50 SM for under £500 (not MRX as per subject)
Now, of course it's a steal because there's an issue with it.
It blew up last autumn and the previous owner, a friend of mine, fitted new piston/rings, head etc and put it back together and now it wont go over 15mph or so.
I have refitted the derestricted exhaust it came with, modded the CDI by removing a particular black wire, fitted a main jet size 90, and she starts and runs fine but there is a serious midrange lack of power. At idle it's fine, and once you're moving it'll rev to about 12k quite easily, but there's nothing in the midrange and as a result, the slightest incline pushes the engine back into the midrange, you can feel the power drop off and you end up downshifting to 3rd or 4th.
Years ago I had a TZR125 which was derestricted and that had sod all midrange and this was due to the way the YPVS system worked, opening this valve and closing it; but in mine because I didn't have the kit it was just fully open all the time so unless you were revving the nuts of it, it was gutless.
This feels just the same but AFAIK there is no such valve in this model.
So ... I expect this is a fuel/air mix issue, but I'm wondering if anyone else has any ideas or experience with this?
And yes, I know derestricting makes it illegal, but frankly I'd rather have him riding at 45-50mph on our B-roads if he is going to ride, instead of stuck at a traffic-menacing 31mph with frustrated drivers trying to get past at inopportune moments. So please, spare me your thoughts on that matter. I'm just trying to get it to work properly, because in this format it should be capable of 50mph or so and it's not happening.
Now, of course it's a steal because there's an issue with it.
It blew up last autumn and the previous owner, a friend of mine, fitted new piston/rings, head etc and put it back together and now it wont go over 15mph or so.
I have refitted the derestricted exhaust it came with, modded the CDI by removing a particular black wire, fitted a main jet size 90, and she starts and runs fine but there is a serious midrange lack of power. At idle it's fine, and once you're moving it'll rev to about 12k quite easily, but there's nothing in the midrange and as a result, the slightest incline pushes the engine back into the midrange, you can feel the power drop off and you end up downshifting to 3rd or 4th.
Years ago I had a TZR125 which was derestricted and that had sod all midrange and this was due to the way the YPVS system worked, opening this valve and closing it; but in mine because I didn't have the kit it was just fully open all the time so unless you were revving the nuts of it, it was gutless.
This feels just the same but AFAIK there is no such valve in this model.
So ... I expect this is a fuel/air mix issue, but I'm wondering if anyone else has any ideas or experience with this?
And yes, I know derestricting makes it illegal, but frankly I'd rather have him riding at 45-50mph on our B-roads if he is going to ride, instead of stuck at a traffic-menacing 31mph with frustrated drivers trying to get past at inopportune moments. So please, spare me your thoughts on that matter. I'm just trying to get it to work properly, because in this format it should be capable of 50mph or so and it's not happening.
Edited by SuffolkDefender on Sunday 15th February 10:00
SuffolkDefender said:
It s a possibility I guess. Not a big job to check on a 2 stroke.Why would that affect it this way?
If the piston is in wrong the transfer ports will not be feeding fuel into the cases correctly . Easiest way to check is by removing the exhaust and looking up to the cylinder , if you can see the holes in the piston skirt its been fitted wrong .tegwin said:
As above... I would also check
1. That the piston rings are fitted correctly and not broken
2. That the reed valve assembly is not damaged (assuming this engine has one).
3. Possibly check the carb but its less likely than the above.
Thanks, will also check. It just had new reed valves fitted by previous owner. 1. That the piston rings are fitted correctly and not broken
2. That the reed valve assembly is not damaged (assuming this engine has one).
3. Possibly check the carb but its less likely than the above.
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