RG125F 1994 (is that a bucket?) issues

[marlow]

Hi guys, I've resorted to cybering all the way over here from Blighty (don't hold that against me) as getting much feedback on any forums based on my bike or country is nigh on impossible. I don't know if people just think I'm so thick that they can't be assed taking me seriously or what, but here's hoping I can get feedback from some 2-stroke racers who know everything!!

Not long rebuilt my whole engine, standard sized replate, new big end and crank trued by PJME (reputable UK company) and so forth. Tons of running issues though, it seems after taking months to fix one, another one instantly arises. It feels as though it's stuff experienced people would have sorted in a day!! Yet here I am a whole year later.

My current issue is a weird cutting-out/spluttery/surging (not sure on the best describing word for it) problem right as max power is coming in, just as powervalve has fully opened around 10,000rpm onwards. Pretty sure the valve is opening as and when it should (altho setting it correctly seems to be another can of worms no one dare talk about ) and I've messed with a few different main jets which has made zero difference. I've tried messing with no air box, half an air box and other altered carburrations, no difference. It feels electrical.

Is there any way I can test the HT lead/coil/CDI and whatever else is involved for faultiness? Or is it a case of having to just replace and hope? Has a brand new spark plug btw

[Henk]

Not a bucket but the street stock guys might know.
Usually easiest way is replace and hope. First thing I'd do is try another spark plug, have had new plugs faulty straight from box, after that switch out the plug cap and lead if it unscrews from the coil, froth at point on it gets harder / more expensive unless you can find someone with the same bike that you can steal the parts off to swap them out.

I'm not all that talented a mechanic or a two stroke guy by the way.

[Kickaha]

Pretty sure the valve is opening as and when it should (altho setting it correctly seems to be another can of worms no one dare talk about )

How is it set on those?

Does it work off cables or centrifugal from the crankcase?

[marlow]

Not a bucket but the street stock guys might know.
Usually easiest way is replace and hope. First thing I'd do is try another spark plug, have had new plugs faulty straight from box, after that switch out the plug cap and lead if it unscrews from the coil, froth at point on it gets harder / more expensive unless you can find someone with the same bike that you can steal the parts off to swap them out.

I'm not all that talented a mechanic or a two stroke guy by the way.

Funnily enough it is a brand new sprk plug in there, but the old one before it was fine so I can try that again. There's a few coil/lead/cap set ups on ebay for around £15 at the moment so that at least wouldn't be too expensive.

How is it set on those?

Does it work off cables or centrifugal from the crankcase?

Yh it's a servo/cable system but the Suzuki manual is the absolute worst! No Haynes was ever made for these bikes and it shows.

This is my post from another forum.



Reverting back to this in the manual, and someone made a thread on this before, I just found it today (despite searchinng months ago) and it's been archived and closed.

So those notches 3 aligned with 4 is exactly how my bike appears whilst switch off. Take exhaust off and see that this is the FULLY CLOSED position. The manaul states above, that these marks should align when you have connected the wire test, turned the ignition on then off. When you turn the ignition on with wire connected, it opens the powervalve to FULLY OPEN. I know this becuz whilst in this position the valve will not open any further using a socket and ratchet. Also feeling up exhaust port tells me this. Then, when you turn the ignition off again, the valve stays in the fully open position. So why on earth is the manual stating to align marks 3 and 4 while the valve is fully open?????????

For the record I've revved it to 10k and the valve does appear to open fully, so this seems to confirm it isn't restricted, however I've no idea if it's doing the correct stuff down low and mid. What I do know is the valve stays shut and doesn't move until 8,000rpm, which to me isn't really where mid range starts. The bike pulls decentish from 6 to 7, but has a pretty s***e flat spot and struggles getting from 8-10, and this is where the apparent "blend" point takes place. Incidentally with pulley in the blend position, one blade (I think the brand new one I bought) seems blended, but the other valve I think middle blade slightly protrudes downward into the port, only by a gnat's, but either way, getting your finger hard up against the piston to feel blending is very hard, unless you've the skin sensitiviy of a girl then you can't really feel it accurately. But then I don't know how much play or tolerance is going to make how much difference. When it comes to port timing I thought even 0.01mm is critical?

This s*** is so confusing and still no proper detailed layman's explanations for it anywhere.

[Drew]

Only simple thing I can think of is battery voltage. The power valve operation used to go all over the show on RGVs if the battery was poked or the charging system not working right.

[Asher]

I was thinking of low voltage before I read Drew's comment. My RGV250 would almost hit a wall at 9k rpm if the battery wasn't fully charged. I don't think the power valves are the issue but just disconnect the cables and cable tie the Pully in the full open position and take it for a ride and see if it comes into power at 10k rpm like it should

[FastFred]

What I do know is the valve stays shut and doesn't move until 8,000rpm, which to me isn't really where mid range starts. The bike pulls decentish from 6 to 7, but has a pretty s***e flat spot and struggles getting from 8-10,

picture posted upside down ... ???????

Probably not relevant, but interesting. Dynograph of NSR125 cylinder. Blue line is the valve fully closed, Red is the valve opening progressively to the fully open position.

[marlow]

The battery is literally brand new last week, correct one for the bike I'm pretty sure, 12v etc.

I don't think it's pv issue either but can someone confirm what that manual is saying is wrong? Becuz when you run that test it turns the valve to open position yet it's saying to align the mark furthest left which is the closed marker. As you can see here, there's a second mark to the right, between the cables that this manual mentions nothing about anywhere. It would make sense to me that it's THIS marker that needs to align with the housing notch when it's fully open. As it happens though it can't even get that far when you physically open the valve to maximum by hand so what it's meant to line up with I've no clue. I believe the RGV250 has 3 marks that all align with the notch from closed to blended to open.



Still not had a chance to do anymore work as it's doing nothing but piss down over here, literally the wetest coldest spring we've had and that's saying something for this dump!

[jellywrestler]

vent for gas cap blocked or missing, as the thing uses motion lotion it needs air to come into the tank otherwise it can cause a vacuum

[TZ350]

... can someone confirm what that manual is saying is wrong?

Totally agree with you. The manual is obviously wrong. Not the first time for that to happen.

Do the test with the wire to earth so the servo goes to the fully open position and adjust the cables to get the PV blades fully open by looking/feeling up the exhaust.

A small discrepancy between blades is not that important and the closed position is not that important either so long as the blades don't protrude far enough into the exhaust port to catch the piston/ring. Check for that with the test wire out and the PV fully closed by looking up the exhaust and carefully turning the motor over by hand. To make it easier, take the spark plug out, leave the plug in the cap and earth it to protect the CDI.

[marlow]

Thanks for the tips TZ350. I already know the blades are safe as I'm 200 miles run in now on the new engine. But I was told on RGV.co.uk forum that the important part of the pv's is the blend point. I think it's about as close as it can get anyhoo.

Well, major progress made, it was the chuffin spark plug!!!!

Unbelievable, a BRAND NEW spark plug I had in there since engine rebuild, exactly as standard, NGK BR9ES, and the whole time it's been a dud. I swapped it back for the old one that came with the bike and hello rocketship!! No more splutter, screams round to 12 (then hits a brick wall) and even ironed out a few flat spots. How can a brand new plug be a dud? I got it off ebay but still. Over 6 months ago now I can't even trace where it came from.

But sadly bad news. Went out on it tonight still with the 180 MJ but realised to replace the airbox lid first, cruised about 20 miles out of town with two mates, was giving it way more on the way to a pub meal than what I was on the way back, however just appraoching 5 miles from home it pretty much blew up....or something, I thought heat seized. It died mid thrash, the first beans I'd given it for the past 20 mins so it wasn't currently hot, temp gauge hadn't gone past 1/4 all night either, and I thought i was going on to reserves. But I'd put a tenna in it there's no way it's used that!! It kept running for a bit gradually slowing to a halt then I noticed it was 4/5ths up the temp gauge. Let it cool and tried to start but there's no compression, engine turning over real fast like it does with no spark plug in it. Hoping it was just a too lean MJ and it's holed piston, cuz if it's anything else like rings or exhaust bridge issue then I can't be doing another replate and not know wtf it did this for.

Running too lean doesn't bugger rings does it? There was no clattering around from the engine, just a gradual dying as if it was heat seizing but like I say now no compression. Knew I should've done a friggin plug chop before venturing out..but at the same time all the caburation below thrash range has needed leaning off big time, needle max lean and still struggles to tickover so a leaner pilot required. Can a Nikkon or any aftermarket spanny cause this change? Where bottom range needs leaning but top range needs richening? Bizarre...

Had an absolute calamity being recovered, had to call a half cut mate out and he brought a 7 seater that we pulled every muscle squeezing the bike into the back of. Fun fucking times these 2-strokes eh

[marlow]

VERDICT





Platiung ripped off from just above both exhaust ports, bit hard to see it with bright reflection of powervalve. %mm ish corner of piston gone/melted, partly welded to side of barrel. And nice lean spark plug there, obviously overheating has caused this right? Cheers my friend to suggesting I put a 180 MJ in it.

Can someone please explain how my needle needed leaning off to the max or it wouldn't tickover even with air screw fully out and tickover screw fully in, and is still in need of a leaner pilot, but yet leaning off the MJ has cost me another £300+? Ok coming down from the standard 200 to 180 is a bit much, but does that look like 0.2mm worth of over leanness?

[marlow]

And bit strange how it's broken down where it has on the piston, it even looks as though the pv's have been caught but how/why? They haven't come anywhere near the piston/rings for 200 miles they wouldn't just decide to now. If overheating due to leanness has cause it then why hasn't it holed the piston, isn't that what overheating usually does? Why would the overheat attack that particular side and not the other?

[marlow]

Woaaah hold up, mistake made, eyes deceiving me, can't even get a prognosis right!!

I don't THINK there's any plating missing. It was the shape of the exhaust port and the background of the darker pv section that mde it look that way, but on closer inspection I don't think any plating has gone. Phew! (if that's right).

So I need an emrgecny piston, assuming I can just scrape the welded remnants of previous one off the barrel there, I have another question.

What exactly is the difference between the more expensive Vertex and Wossners, around £100, and the cheaper ones? Mitaka are around £50 but there's kits on ebay for as little as £25. Is the main difference weight? I mean how many miles difference in longevity or how much difference in performance are we talking here?
Also the cheaper pattern ones only say "to fit 56mm bore", they don't state the actual size like Vertex/Wossner do. It's problem?

[F5 Dave]

Woosner are great but the Mitaka ones are quite serviceable for a road engine. I'd be concerned of too cheap, may be copies.

Detonation at ex port of piston is too lean. Drain cleaner powder on a damp rag can help remove ally from bore but be super careful it is dangerous.