Son's Reiju MRT 50 SM - 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.
So, I've had the exhaust off and looked up inside. Can't see any holes in the skirt but for a relatively new piston, it doesn't look like it's in good shape to my eyes, see video.
https://youtube.com/shorts/1Y6Rw0EqYYc
And there is what looks and feels and smells like oil in the exhaust port.
New piston and rings? I already have a spare cylinder head which it came with.
https://youtube.com/shorts/1Y6Rw0EqYYc
And there is what looks and feels and smells like oil in the exhaust port.
New piston and rings? I already have a spare cylinder head which it came with.
SuffolkDefender said:
So, I've had the exhaust off and looked up inside. Can't see any holes in the skirt but for a relatively new piston, it doesn't look like it's in good shape to my eyes, see video.
https://youtube.com/shorts/1Y6Rw0EqYYc
And there is what looks and feels and smells like oil in the exhaust port.
New piston and rings? I already have a spare cylinder head which it came with.
A compression test would be the next step , piston looks to be in the correct way .i always used to do a light premix of petrol and oil on a new bore just to make sure which makes for a smokey bike for a while and a oily exhaust .https://youtube.com/shorts/1Y6Rw0EqYYc
And there is what looks and feels and smells like oil in the exhaust port.
New piston and rings? I already have a spare cylinder head which it came with.
I’m not clear if it is running well at full throttle or not. If so the following may help.
Changing the main jet won’t affect the midrange, if the main jet needs to increase then the needle jetting will need to as well.
Try richening the part throttle by raising the needle. This done by moving the circlip on the needle down. Move it one notch and if it improves things a bit then keep going down.
Ideally you would fit a larger needle jet to achieve this but I appreciate that they may not be readily available.
Changing the main jet won’t affect the midrange, if the main jet needs to increase then the needle jetting will need to as well.
Try richening the part throttle by raising the needle. This done by moving the circlip on the needle down. Move it one notch and if it improves things a bit then keep going down.
Ideally you would fit a larger needle jet to achieve this but I appreciate that they may not be readily available.
SuffolkDefender said:
So, I've had the exhaust off and looked up inside. Can't see any holes in the skirt but for a relatively new piston, it doesn't look like it's in good shape to my eyes, see video.
https://youtube.com/shorts/1Y6Rw0EqYYc
And there is what looks and feels and smells like oil in the exhaust port.
New piston and rings? I already have a spare cylinder head which it came with.
Don't discount the exhaust as being the problem. https://youtube.com/shorts/1Y6Rw0EqYYc
And there is what looks and feels and smells like oil in the exhaust port.
New piston and rings? I already have a spare cylinder head which it came with.
My Son had a Gilera RCR50 (6 speed Minarelli engine) on which I fitted a new cylinder & piston when we got it because it was worn out, it ran fine for a while but then would occasionally bog down.
Cleaning the oil out of the exhaust out would cure it but there were parts of it that weren't easily accessible and after a while it bogged down again.
We fitted a new performance exhaust (road legal with the restrictor in the manifold) and with the restrictor removed, plus an increase in jet size to the carb it was totally transformed, I followed him on my 916 and he got it up to around 60mph at one point.
In fact after we sold the Gilera when he 'upgraded' to a YBR125 he told me he wanted it back because it was faster, at least acceleration-wise.
Edited by catso on Tuesday 17th February 09:52
We haven’t even begun to scratch the surface of jetting 2 strokes - we’ve still got atomisers, pilot jets, slide cutouts to confuse matters
And to the OP if you get it going properly remind your lad to fide with his fingers hovering over the clutch lever - can save a lot of grief if and when it seizes
And to the OP if you get it going properly remind your lad to fide with his fingers hovering over the clutch lever - can save a lot of grief if and when it seizes
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