Help with Suzuki RG150

[andrewwitham]

Hello, I bought a used 1998 RG150 on a whim today, it has WOF and rego and was cheap. I thought it would be fun to relive my youth with a two stroke bike :-) The previous owner told me it had a catastrophic engine failure (he gave me the crankcases and cylinder) and oh boy it had really let go in a big way. He paid to have new crankcases, main bearings, crankshaft with new conrod, new cylinder and piston professionally (?) installed. I think all the work was done reasonably well, sounds good, no rattles, good compression etc.

Here's the thing, it starts, runs and idles real nice, but won't make any power in the upper rev range, just splutters and misses from about 6-7K. If I give it WOT in neutral it will go to about 10-11K but sounds like it's missing. I've cleaned out the carb this afternoon, was clean as, made no difference. I'm picking it's a dreaded power valve issue. I've tested the exhaust power valve and it opens and closes ok with the motor controller, but I'm not sure the CDI/ECU is doing it's bit when it's supposed to tell it to open? I've got a service manual, the cables are set ok, but my manual has a couple of pages missing which I presume detail setting the valve cable pulley position on the shaft.

Many moons ago me and my mates had YPVS Yamahas and they cycled the power valves when the ignition was turned on, made a zzz noise. This bike doesn't do that. I'd really like to get in touch with someone who knows this model well to get some advice and pointers about where to look next.
Thanks KiwiBiker community.
Andrew

[Intruder VS]

Hi
Sorry don’t really know much about the 150’s more into Yamaha 2smokes but are you sure the carb is clean there are a lot of tiny passages that can get blocked also double check it is set up correctly 2 strokes are very fussy when it comes to carburation, Float height is very important also check needle height, check your manual and set up exactly as said not oh well that’s close enough.
While carb is off be worth while checking the reeds are good, again as per manual says

Another simple thing is the spark plug 2smokes eat plugs especially if running rich or just putting around, sometimes the plug may look ok but still be no good so would try a new one.

If you have a multimeter check the coil plug lead and also the cap.

Does the bike pull all they way cleanly into the power band at half throttle? My TZR had a similar problem after I restored it took me bloody ages to sort out, would pull no worries to redline at part throttle but full and would splutter and miss in the power band, rebuilt the carbs many times until I discovered some monkey had drilled out the tiny power jet, replaced jets and fixed.

[andrewwitham]

Thanks for your reply. I did some more work on it today. The power valves weren’t opening, they were all sticky and gummed up. They also looked like the tip of them had hit on something recently, they had burs on the end. I cleaned them up and polished off the burs with wet and dry. Reassembled and set the cables correctly. It started second kick and seemed a bit better, certainly more power and reved better, for a brief moment I thought it was right, but still not the big whoosh of power it should have. It was raining so I didn’t ride it for long. It seems like it’s way to rich at high RPM, sort of 4 strokes, but runs fine with WOT at low rpm. It is missing its airfilter, I have a stock one on order so I’ll wait for that before I do anything else. While I was cleaning up the exhaust valve I shone a torch on through the holes. I think the piston has some light scoring, probably caused by the power valve hitting on it. Not good really. I really need to strip the top end properly and see what’s been going on. I’ll report back once I know more.


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[Intruder VS]

Thanks for your reply. I did some more work on it today. The power valves weren’t opening, they were all sticky and gummed up. They also looked like the tip of them had hit on something recently, they had burs on the end. I cleaned them up and polished off the burs with wet and dry. Reassembled and set the cables correctly. It started second kick and seemed a bit better, certainly more power and reved better, for a brief moment I thought it was right, but still not the big whoosh of power it should have. It was raining so I didn’t ride it for long. It seems like it’s way to rich at high RPM, sort of 4 strokes, but runs fine with WOT at low rpm. It is missing its airfilter, I have a stock one on order so I’ll wait for that before I do anything else. While I was cleaning up the exhaust valve I shone a torch on through the holes. I think the piston has some light scoring, probably caused by the power valve hitting on it. Not good really. I really need to strip the top end properly and see what’s been going on. I’ll report back once I know more.


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You could do a plug chop at WOT while is playing up, hold it there for a little bit then pull in the clutch and hit the kill switch at the same time then coast to a stop keeping the clutch pulled in and whip the plug out if lean the plug will be white if black and wet most likely rich.

You really need to have a filter on it before doing the chop as most bikes run like crap without and in your case would give a very lean mixture which is very bad on a 2smoke

Can’t help much with Suzuki power valves but do know they have a habit of failing and dropping to far hitting the piston, do a bit of research on the inter web on that one.

[andrewwitham]

You could do a plug chop at WOT while is playing up, hold it there for a little bit then pull in the clutch and hit the kill switch at the same time then coast to a stop keeping the clutch pulled in and whip the plug out if lean the plug will be white if black and wet most likely rich.

You really need to have a filter on it before doing the chop as most bikes run like crap without and in your case would give a very lean mixture which is very bad on a 2smoke

Can’t help much with Suzuki power valves but do know they have a habit of failing and dropping to far hitting the piston, do a bit of research on the inter web on that one.

The new airfilter arrived today. I fitted it and a new plug, the correct one according to the manual, B8ES. It had an Iridium plug in it with a protruding electrode, BPR something (cant remember the number right now). Went for a short ride. Much better, still got a flat spot in the midrange, but pushed through it into the power band. Not bad, not 36HP as it should be, but pretty good. I did meddle with the float height a couple of days ago as the carb was pouring fuel into the cylinder, so I will reset/lower the float level again and test ride again. I reckon the power valve is still sticking/slow to open as it takes a concerted effort to get the revs and power up into the band. If I keep it there it’s ok (which means riding very fast all the time), but once it drops below the band it’s difficult to get it back up there. I read articles about people taking to their power valves with Dremels to chamfer/ free them up and avoid piston damage. I think I understand why. How to you adjust the power valve position when you have an oversize cylinder and piston? There appears to be no way to move it back in the bores?


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[Intruder VS]

The new airfilter arrived today. I fitted it and a new plug, the correct one according to the manual, B8ES. It had an Iridium plug in it with a protruding electrode, BPR something (cant remember the number right now). Went for a short ride. Much better, still got a flat spot in the midrange, but pushed through it into the power band. Not bad, not 36HP as it should be, but pretty good. I did meddle with the float height a couple of days ago as the carb was pouring fuel into the cylinder, so I will reset/lower the float level again and test ride again. I reckon the power valve is still sticking/slow to open as it takes a concerted effort to get the revs and power up into the band. If I keep it there it’s ok (which means riding very fast all the time), but once it drops below the band it’s difficult to get it back up there. I read articles about people taking to their power valves with Dremels to chamfer/ free them up and avoid piston damage. I think I understand why. How to you adjust the power valve position when you have an oversize cylinder and piston? There appears to be no way to move it back in the bores?


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Having the correct air filter should make a big improvement over none also check the airbox is sealed with no air leaks anywhere.

Mid range could be mixture where one jet in the carb overlaps the next, normally If its a smooth flat spot with no missing just a flat feeling I would say a lean spot.
Could also be something to do with the power valve tho as mid range revs is probably about the time the power valve starts to open. From memory the power valve is not a big mission to remove and check everything is correct as per the manual, as said before I know the RGV250 has a bad habit of dropping the valve causing it to hit the piston and making a big mess. May be a similar set up to the 150 so you could check out on line

Sounds like you are heading in the right direction if she’s running better, can be like banging your hard against a concrete wall sometimes, best thing I found is do research and learn as much about it as you can.
Also I’m only trying to give pointers so up to you to do what you will with the info and disclaimer time, if she self destructs its all on you!!! So don’t me.

Cheers

[andrewwitham]

Having the correct air filter should make a big improvement over none also check the airbox is sealed with no air leaks anywhere.

Mid range could be mixture where one jet in the carb overlaps the next, normally If its a smooth flat spot with no missing just a flat feeling I would say a lean spot.
Could also be something to do with the power valve tho as mid range revs is probably about the time the power valve starts to open. From memory the power valve is not a big mission to remove and check everything is correct as per the manual, as said before I know the RGV250 has a bad habit of dropping the valve causing it to hit the piston and making a big mess. May be a similar set up to the 150 so you could check out on line

Sounds like you are heading in the right direction if she’s running better, can be like banging your hard against a concrete wall sometimes, best thing I found is do research and learn as much about it as you can.
Also I’m only trying to give pointers so up to you to do what you will with the info and disclaimer time, if she self destructs its all on you!!! So don’t me.

Cheers

Looks a bit lean. I shall get cracking with resetting the float height this afternoon.


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[Intruder VS]

Don’t for get to set the pilot screw adjustment if it has one set to manual specs, even tho it mainly controls idle and a little above the pilot jet still supplies fuel no matter what throttle position you are in.

If screw at front of carb in for rich out for lean, if at rear in for lean out for rich

[Intruder VS]

Don’t for get to set the pilot screw adjustment if it has one set to manual specs, even tho it mainly controls idle and a little above the pilot jet still supplies fuel no matter what throttle position you are in.

If screw at front of carb in for rich out for lean, if at rear in for lean out for rich

Oh and that’s for Mikuni carb

[andrewwitham]

Oh and that’s for Mikuni carb

So I raised the float height to where I think it was before I meddled with it. Doesn’t leak so I’m picking it’s about right. Took it for a 20 minute ride and it’s still not right. The ride gave me time to try some different stuff and I convinced the power valves are still sticky. I managed to get it into the power band and as long as I kept it there, even changing gears, it went really well. Once it dropped off the power band I had to let it come back to idle before it would make any power. I’m going to take the cylinder off and inspect everything properly. Need to get some gaskets too.


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[Intruder VS]

So I raised the float height to where I think it was before I meddled with it. Doesn’t leak so I’m picking it’s about right. Took it for a 20 minute ride and it’s still not right. The ride gave me time to try some different stuff and I convinced the power valves are still sticky. I managed to get it into the power band and as long as I kept it there, even changing gears, it went really well. Once it dropped off the power band I had to let it come back to idle before it would make any power. I’m going to take the cylinder off and inspect everything properly. Need to get some gaskets too.


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Could be sticky power valve if it has plenty of top end power and none down low the valve may be stuck in to open position. The valve stays closed to lower the exhaust port which gives more low end toque and only starts to open at the start of the power band.
If everything checks out mechanically and you still suspect power valve you may have to start looking at the electric side, Servo, controller and check cables aren't binding.

[Intruder VS]

Found some old posts

https://www.kiwibiker.co.nz/forums/s...uki-rg150-Help

https://www.kiwibiker.co.nz/forums/s...short-on-power

https://www.kiwibiker.co.nz/forums/s...ning-on-RG-150

[andrewwitham]

Could be sticky power valve if it has plenty of top end power and none down low the valve may be stuck in to open position. The valve stays closed to lower the exhaust port which gives more low end toque and only starts to open at the start of the power band.
If everything checks out mechanically and you still suspect power valve you may have to start looking at the electric side, Servo, controller and check cables aren't binding.

I know the servo is working because I’ve watched it open and close the power valve, when I set it up upon reassembly yesterday, but there is a spring on the power valve shaft to protect the gears on the servo if the power valve jams up. Despite all my fettling and deburring yesterday the power valves still feels notchy and I’m picking that the servo protection spring is struggling to slide the power valves as they don’t slide that smoothly. That’s why it seems to struggle to get into the power band, cos the valves aren’t sliding nicely. And then the power valves stick in the open position and it’s gutless at low/mid RPM. After I let it fall back to idle it makes good low to midrange power. If I can get some gaskets I’m going to thoroughly inspect the power valves, power valve bores and the cylinder and ports. I reckon there’s something (like a bur) that I can’t see from the outside in the power valve cylinder bores.


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[Intruder VS]

Any luck with the investigations into the power valve yet?

[andrewwitham]

Any luck with the investigations into the power valve yet?

I had the top end off today, all looked pretty good. No obvious massive issues. Piston is new and cylinder looks mint. Crank and conrod is also brand new, as he previous owner promised. There was some very light scoring on all four "corners" of the piston skirt (light cold seize/pick up, probably me thrashing it when cold) but nothing that would really affect compression much, certainly not enough to cause the issues it has. I cleaned up the piston skirts and cylinder with some 80 grit wet and dry, washed it thoroughly, lubed up with some two stroke oil. For good measure I gave the power valve bores a bit of a touch up and the valves too. One of the screws in the power valve assemble had come loose and worn a groove in one of the power valve plates. I fixed this with some washers and locktite. It will not move again. Funny, it wasnt like that last week when I removed them to have a look. They move super easy now, no sticking, but no slop either. Happy with power valve motion and servo etc. All working as it should. Cables are correctly adjusted as per service manual. I took it out for ride and it was pretty much the same, boo hoo :-( . It was really low on fuel and I only filled it up on my last test ride, probably done less than 50Km's. It took 10 litres of fuel. When I got home I thought about it running really rich, you know that 4 stroking noise that they do. I sell chainsaws and know that noise well. So when I got home I tried turning the choke on to see what happens. Exactly nothing happens. Pulled the plug, looked rich as. I reckon the enricher/choke has issues. I'm going to read up and see what's going on with that. I have a couple of custom CG125's just for fun round town, and if I got to this point with one of them it would be new carb time, except instead of $30 from Aliexpress, it's $200 off ebay, which aint gonna happen.