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Post by mikezs on Jun 5, 2013 7:04:58 GMT -5
Hi All, I've got a problem with my scooter. It's been de-restricted for a couple of years and would happily get up to 36ish mph (I'm happy with it) while driving on the flat and keep it way above 30 up hills. More recently (last month or so) it's been struggling to get up to 30 and will drop down to the early 20's up hill! But when cold (when first using it for the day) it gets up above 30 pretty quickly and makes noticeably more power than when hot. This leads me to believe it's something engine/fuelling related, so I adjusted the mixture screw to make it slightly more lean (1/4 turn) and it didn't make a difference. Tried making it richer (1/4 turn past original other way) and it wouldn't start. Back to normal (I marked the screw with a sharpie) it's running as before, so I don't think it's a fuel issue. If I let it cool for 5 mins and run again after it's been hot/slower, the power picks back up breifly. I don't know where to go from here. My options are, from what I can see: - Check all variator, rotor, rollers, clutch & belt for wear and tear (rollers are approx 4k miles old and belt is original, done 9k)
- Top end rebuild with new gaskets/cleaning. I've already ordered a gasket set because it's about £5 and im not afraid to take stuff apart
- Carb rebuild. I'm wary of this one as it seems that it's quite sensitive to change and I may have to re-tune.
I'm looking for everyone's infinite wisdom about what my next step should be, and what you suspect my problems are! I'll keep it updated with what I try and post some pics of mildly interesting stuff. Cheers! |
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Post by 90GTVert on Jun 5, 2013 8:09:17 GMT -5
 to the forum. After a couple of years, it's time that you go over the whole CVT anyway. www.youtube.com/watch?v=2EjW-iSP-Q8If you have a compression tester, do a compression test. It's also time for a valve adjustment if you haven't done one in that time. www.youtube.com/watch?v=s0K-ytyjOFgYou shouldn't really need to rebuild the carb, but it may need a thorough cleaning. If you clean it out, there's no need to re-tune simply from the cleaning. Just turn the mixture screw in, counting how many turns it takes till it seats gently. Write that down. Now you can take it out and clean there and when you're ready to reinstall the screw you can set it were it was. If you take the needle clip off for any reason, note it's position as well. The jets will simply screw in snug, no adjustment to them. You shouldn't really have to install different sized jets if it's ran well for a couple of years and you haven't modified anything. |
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Blowin Smoke
Scoot Enthusiast
Posts: 289
Location: Port Orange, Fl
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Post by Blowin Smoke on Jun 5, 2013 8:51:18 GMT -5
I would visit the carb first.If it runs ok cold and not hot it would indicate to me that your main/high speed jet is partially blocked. The air/fuel screw will have no effect on top speed, it is for the idle/low speed circuit.When the engine is cold and the enrichment circuit is active you have a higher fuel flow to the cylinder creating the issue you described.
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Post by mikezs on Jun 5, 2013 9:01:25 GMT -5
There's 3 screws available on the carb that don't take it apart: 1. High/fuel air mix in the middle 2. Low/idle near the back/airbox side 3. Drain screw, right at the bottom I've been adjusting the one slap bang in the middle of the carb .jpg) Is this correct? That picture is of my actual carb |
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Post by 90GTVert on Jun 5, 2013 15:56:06 GMT -5
The one on the right should be idle mixture/speed. The center/top should be idle speed. The bottom should be the drain.
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Post by mikezs on Jun 6, 2013 3:41:08 GMT -5
So both screws that aren't on the bottom adjust the idle? One the ratio, and one the quantity?
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Post by 90GTVert on Jun 6, 2013 6:41:00 GMT -5
Yes, the mixutre screw will richen or lean the idle circuit, working with the pilot jet. Since it's on the inlet side, it should richen when turned in and lean when turned out. The center screw should protrude inside the carb and hold the slide open more as it's screwed in to raise idle with a greater throttle opening. It's the standard setup for scoot carbs.
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Post by mikezs on Jun 6, 2013 7:32:28 GMT -5
Thanks for the insight! I'm very new to working with scooters. I'm used to fuel injected cars and DOC motorbike engines.
I'll be rebuilding the top end (mainly for fun, but partly for inspection). New spark plug, belt and rollers too.
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Post by 90GTVert on Jun 6, 2013 12:13:39 GMT -5
Good luck with it and let us know if you have any more questions.
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Post by mikezs on Jun 21, 2013 4:32:39 GMT -5
Update!
I took the CVT cover off, inspected the belt. Looks completely mint still. Ordered a new one anyway and will install when I make a variator holder.
Dismantled the carb fully (they're very intricate!) cleaned everything (although the inside was spotless) and reassembled. No change with lack of power (sadface!)
I've come to the conclusion it's the piston rings (after ruling everything else out!) so I got a new piston/rings and will install tomorrow. Had to use circlip pliers to get the rings on, even though lots of youtube videos show it being done by hand, so I'll report back how I get on!
Thanks to everyone who's posted their problems and solutions on this board (and others).
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Post by mikezs on Jun 21, 2013 4:35:13 GMT -5
Yes, the mixutre screw will richen or lean the idle circuit, working with the pilot jet. Since it's on the inlet side, it should richen when turned in and lean when turned out. The center screw should protrude inside the carb and hold the slide open more as it's screwed in to raise idle with a greater throttle opening. It's the standard setup for scoot carbs. I've just re-read this explanation after taking the carb apart and it's brilliant. Before I had opened it up and looked at each of the components this description was like a different language! |
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Post by 90GTVert on Jun 21, 2013 10:14:19 GMT -5
Hope that gets it.
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Post by mikezs on Jun 23, 2013 9:24:31 GMT -5
Changed over the piston yesterday. I've not run it in yet, just down the road to make sure it was ok, but already feels better! Most of the time was spent getting the old cylinder gasket off! After inspecting the piston, I'd say the rings have failed    |
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Post by mikezs on Jun 23, 2013 9:42:05 GMT -5
Some notes:
There's actually 3 rings on this piston, an extra octagonal one goes under the bottom ring. The rings also have an orientation (mine had a T to indicate the top). You wont be able to get the piston in the barrel if the rings aren't lined up to the pin properly, so make sure they're in the right place and don't force it.
Double check the circlips are in their grooves and the gap is away from the edge slots. If they come loose they will smash around above the piston and damage the head.
Give the cylinder a really good clean with carb cleaner, a scouring pad (in horizontal motion to not ruin the honing) and then another clean and wipe with a clean cloth. Check it with your fingers, it should be perfectly smooth.
This piston has actually got EX stamped on the top to denote which side of it is the exhaust side, but also has the rings on the back so they dont catch in the exhaust port.
All went well, took me about an hour and 40 mins in total.
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Post by 90GTVert on Jun 23, 2013 10:00:29 GMT -5
Nice! Glad you got it and thanks for sharing some notes/tips.
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