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Jet Eye Master
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There's only one option from here. If going leaner didn't clean it up, then it must need richer. Losing power while still having revs is a sure sign of being lean.

When the cables fixed. Keep going richer on the MJ until it gets better at 4000.
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Jack221 wrote:
There's only one option from here. If going leaner didn't clean it up, then it must need richer. Losing power while still having revs is a sure sign of being lean.

When the cables fixed. Keep going richer on the MJ until it gets better at 4000.
Hi Jack, and all, so back on the road again, everything else as before, put a 132 in and could not get it to the 3000 rpm range just splutter y as hell, 130, ok, so now its splutter y up to 4300 rpm, but as soon as it hit 4400rpm it clears & takes off.
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Leon wrote:
Hi Jack, and all, so back on the road again, everything else as before, put a 132 in and could not get it to the 3000 rpm range just splutter y as hell, 130, ok, so now its splutter y up to 4300 rpm, but as soon as it hit 4400rpm it clears & takes off.
It's the splutter at 4400rpm that needs to improve. Try 128 again.

Shouldn't be so spluttery low down. For normal too rich, up to 3000rpm it should be not so bad, then go really spluttery, until after 4000rpm, clear up, fly, then bog at high rpm.
Might be something else wrong. Choke might be slightly open, jet not seating, does happen.
Mark the throttle positions and post a video of slowly revving it from zero to max.
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Jack221 wrote:
It's the splutter at 4400rpm that needs to improve. Try 128 again.

Shouldn't be so spluttery low down. For normal too rich, up to 3000rpm it should be not so bad, then go really spluttery, until after 4000rpm, clear up, fly, then bog at high rpm.
Might be something else wrong. Choke might be slightly open, jet not seating, does happen.
Mark the throttle positions and post a video of slowly revving it from zero to max.
Hi jack & all
Well a crash course in audio/video for YouTube was a journey!
So here are the links, hopefully this all works.

I'm away this weekend so wont be able to do anything.

1 throttle position,
2 130 main jet up & down My street,
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Good job getting the videos uploaded. Scooter looks cool. Would be useful to see the rev counter better.
Seems a bit lean. Sounding tinny. What size main jet causes WOT to not rev? Or WOT to rev lower than half throttle? The 130 is revving out fairly clean by the sounds of it.
Going to need a bigger pilot jet too. Can't remember if you're running a drilled filter or a vortex.
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Also, if you could mark the throttle so that we can see the throttle position (need where the cable tension takes up and WOT on the bars, then a mark on the grip to align with those), it makes it a LOT easier to tell what's going on, too.
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Jack221 wrote:
Good job getting the videos uploaded. Scooter looks cool. Would be useful to see the rev counter better.
Seems a bit lean. Sounding tinny. What size main jet causes WOT to not rev? Or WOT to rev lower than half throttle? The 130 is revving out fairly clean by the sounds of it.
Going to need a bigger pilot jet too. Can't remember if you're running a drilled filter or a vortex.
Hi Jack
Back from work. so
yes to vortex,
Rev counter, yep I know its a bit hard to see, tried too make it visible but the sun glare was a pain, just like the wind was with the audio

yes with the 130 once you get it up to 4400rpm it clears in the gear your in, shift into the next gear and its struggles till you get it back up to 4400rpm's again away it go's.
there's some thing weird going on in the transition.

Bigger idle jet, OK, we went from bigger which was a 55/100, to a 48/100

A couple of weekends ago tried while on its stand a 140 MJ, and it was boggy as hell to get the rev up, actually it couldn't. But that's on the stand.

tomorrow is a weekend for more exploration/trials, to test/answer queries.
⚠️ Last edited by Leon on UTC; edited 1 time
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chandlerman wrote:
Also, if you could mark the throttle so that we can see the throttle position (need where the cable tension takes up and WOT on the bars, then a mark on the grip to align with those), it makes it a LOT easier to tell what's going on, too.
Hi chandlerman, I have marked the throttle, (might be a bit indefinable) blue paint pen on blue, but its there.
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Hi Jack
So with a 100AC it wont take of now till it gets to around 5000 odd rpm's and cant even get to that in 3rd
(this is all up &down my street)

Also then tried a 55/100 idle jet, that made things terrible, wont idle (even with the mixer & idle screws both fully turned in) and just spluttery as hell and wont take off at all, shithouse.
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Leon wrote:
Hi Jack
So with a 100AC it wont take of now till it gets to around 5000 odd rpm's and cant even get to that in 3rd
(this is all up &down my street)

Also then tried a 55/100 idle jet, that made things terrible, wont idle (even with the mixer & idle screws both fully turned in) and just spluttery as hell and wont take off at all, shithouse.
This sounds better. Reduce the main jet until it all cleans up. Easiest way to do this is hold it wide open. And see how high it revs out to. If way over rich, this will be under 7000rpm. If it revs much higher than this, there's something else wrong.
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Jack221 wrote:
This sounds better. Reduce the main jet until it all cleans up. Easiest way to do this is hold it wide open. And see how high it revs out to. If way over rich, this will be under 7000rpm. If it revs much higher than this, there's something else wrong.
Hi Jack, sorry about the slow getting back, life stuff happens.

So at MJ 130 wouldn't get above 5000rpm
128 wouldn't get above 5700rpm
125 wouldn't get above 6200rpm
122 wouldn't get above 6500rpm
at about this stage the engine suddenly made an awful noise and lost compression, so Im going to drop it out and strip it down and rebuild it (when I get a spare moment)

Ill let you know what I find
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Jet Eye Master
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Leon wrote:
Hi Jack, sorry about the slow getting back, life stuff happens.

So at MJ 130 wouldn't get above 5000rpm
128 wouldn't get above 5700rpm
125 wouldn't get above 6200rpm
122 wouldn't get above 6500rpm
at about this stage the engine suddenly made an awful noise and lost compression, so Im going to drop it out and strip it down and rebuild it (when I get a spare moment)

Ill let you know what I find
You're having some awful luck. Something catastrophic going on at 6000rpm off load is highly unusual. Sure your rev counter is not set to read half rpm? If it were actually 12000rpm this would make perfect sense.
Will be interesting to see what happened. If the conrod snapped it's definitely an rpm thing.
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Leon wrote:
Hi Jack, sorry about the slow getting back, life stuff happens.

So at MJ 130 wouldn't get above 5000rpm
128 wouldn't get above 5700rpm
125 wouldn't get above 6200rpm
122 wouldn't get above 6500rpm
at about this stage the engine suddenly made an awful noise and lost compression, so Im going to drop it out and strip it down and rebuild it (when I get a spare moment)

Ill let you know what I find
Were you riding it or was it on the stand?
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orwell84 wrote:
Were you riding it or was it on the stand?
Hi orwell84
It was on its stand, as that's how I interpreted what jack was instructing me to do with this diagnostic process. put mj in rev it out see what rpm's it get to, then step down, do all over again. just like he said.
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Jack221 wrote:
You're having some awful luck. Something catastrophic going on at 6000rpm off load is highly unusual. Sure your rev counter is not set to read half rpm? If it were actually 12000rpm this would make perfect sense.
Will be interesting to see what happened. If the conrod snapped it's definitely an rpm thing.
Hi jack yep to that,
in regards to rev counter I was monitoring rpms with both the onboard & a strobe/rpm light
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Jet Eye Master
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Leon wrote:
Hi jack yep to that,
in regards to rev counter I was monitoring rpms with both the onboard & a strobe/rpm light
Can't imagine what happened. Circlip came out? 6000 rpm is crusing speed. Can hold that all day long. If it was over 12000 rpm you would know it. With a full finned flywheel they whistle like a jet engine.
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Leon wrote:
Hi orwell84
It was on its stand, as that's how I interpreted what jack was instructing me to do with this diagnostic process. put mj in rev it out see what rpm's it get to, then step down, do all over again. just like he said.
Yeah, I snagged a piston ring revving it on the stand, but it was over 8500 rpm.
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