Two T Troubles

[twotakt]

Posted some Q's relating to this problem in another section but thought I may get some more suggestions here.

The bike is a 1995 Suzuki RG125F which had a broken top end. I rebuilt the top end using a RGV250 barrel (same bore size as the 125) and replaced the powervalves. I also gave the carburettor a good clean and replaced the spark plug and the battery. The cylinder is getting fuel/oil and a spark but it still won't start.

Occassionally it'll fire and begin to start then it dies, weird eh?

I'd love to get this bike on the road to lend to the Mrs' so she can learn to ride but I need to get it running first.

Any suggestions/advice on what could be causing the problem would be greatly appreciated. Also have I missed anything?

I know its something blatantly obvious that I've overlooked.

Thanks for your time,
Jack
____________________
R.I.P. Tareree Shiimi, 1985-2008

[2006 _p1]

What does the plug look like?

Try adjusting the air/fuel mixture

[iooi]

[twotakt]

The new plug looks relatively clean still, just a bit wet with premix.

The ports are slightly larger on a RGV250 cylinder but otherwise they're exactly the same.

Ta,
Jack
____________________
R.I.P. Tareree Shiimi, 1985-2008

[2006 _p1]

Have you tried a new plug? If you keep trying to start the bike and the plug keeps getting fouled up with premix it will eventually kill the plug.

[twotakt]

Yea, tried two brand new plugs but still the same symptons. When I do take the plug out its clean although wet and it gives a strong consistent blue spark.

Ta,
Jack
____________________
R.I.P. Tareree Shiimi, 1985-2008

[2006 _p1]

Oh. Normally if you have it in the engine long enough trying to start it with no luck they usually die. And some time a spark out side the engine dont mean its going to spark in the engine.

My bike was playing up and it had a great spark but wouldn't fire up. New plug and she started first kick!

Have you tried Air/fuel mixture?

[twotakt]

Serious!?

I hope it's that easy, the good spark flippin' deceiving me. I've got another brand new plug so I'll give a go now. I'll be back in 15mins or so and let you know how I get on.

Ta,
Jack
____________________
R.I.P. Tareree Shiimi, 1985-2008

[twotakt]

Tried and unfortunately didn't work, the bike doesn't even fire now

Ta,
Jack
____________________
R.I.P. Tareree Shiimi, 1985-2008

[petemell]

The new cylinder may be a different compression to the old one with it being from a different bike. This could be stopping it from starting.

[twotakt]

I using a RGV250 cylinder, which has the same stroke length and compression as the RG125f. The ports are in the same position on both models except that the RGV250 ports are slightly larger. The reason why the ports are smaller on the RG125f is (apparently) to provide more torque, something which is not needed on the RGV250.

The RGV250 is essentially a twin cylinder version of the RG125f so all the engine components are the same.

Ta,
Jack
____________________
R.I.P. Tareree Shiimi, 1985-2008

[Kickstart]

Hi

Port sizes will affect the jetting a bit, but realistically not enough to stop it firing up.

Check the reed valves are in place and sealing correctly. Also check the ignition timing (although probably not this as it was presumeably fine before it went pop).

All the best

Keith
____________________
Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[twotakt]

Yea, will check the reed valves at some point but need to remove the oil pump to do this . Busy with revision at the moment, but am collecting information on possible solutions now so I could try them all out when I've got time.

I suspect the ignition timing is ok as the bike was running fine before it blew up. However it had been sat out in all weathers for about a year before I bought it off the Mrs' uncle. Weathering process likely to affect anything as to make it stop running?

Thanks again,
Jack
____________________
R.I.P. Tareree Shiimi, 1985-2008

[StealthDJ]

Did you say previously that you'd had to replace the powervalve servo aswell? Are you sure it's talking to the controller properly?

I'd maybe try removing the servo and fully opening the powervalve, before trying to start it.

It won't pull worth a damn if you try to ride it, but it should run and rev freely.

Other than that, I'd be looking for causes of fuel starvation, though it doesn't particularly sound as though that's the issue either. Have you definitely got a fully charged battery on it, by the way?
____________________
Current garage: VFR800 FI-W | RD500LC YPVS | SV650 K2 | MZ TS250/1 | MZ ETZ251 | BSA WDB40
Previous notables: H100 S2 | CB250NA/B | CB250T | GT250X7 | Z650 B1 | SR650
Still owned, but long gone: RD250LC | CB750F2 SOHC | C50

[twotakt]

Yea, I've had the battery on the charger and all is well and the cylinder is also getting fuel. Compression feels good (judged by the feel on my hand).

I've tried openning the p/v's and starting the bike but it still experiences the same symptons.

Ta,
Jack
____________________
R.I.P. Tareree Shiimi, 1985-2008

[StealthDJ]

Ruling all that out, last time I had a bike that did that, it was because the jetting was all over the place (well, I was actually running a carb from a 500 suzuki twin on an MZ 250 single. *Everything* was wrong).

Given that the plug's wet, maybe it's running horrifically rich? There's a few possible causes for that - a stuck float / flooding carb being one.

The other is that the pilot jet might be blocked, so fuel is being sucked through the main jet instead, which will make its fuelling appear all over the place. You said you've cleaned the carbs, but if you've got access to one, I'd consider bunging the jets in a sonic cleaner. Unleaded fuel left for a year in a carb goes pretty nasty.
____________________
Current garage: VFR800 FI-W | RD500LC YPVS | SV650 K2 | MZ TS250/1 | MZ ETZ251 | BSA WDB40
Previous notables: H100 S2 | CB250NA/B | CB250T | GT250X7 | Z650 B1 | SR650
Still owned, but long gone: RD250LC | CB750F2 SOHC | C50

[twotakt]

To be honest I just cleaned the carb just using a Air compressor and nothing more. Unfortunately I haven't got access to a sonic cleaner but I've got some proper carb cleaner (spray can). I've also heard that soaking it in coca cola is a good way of cleaning it as well.

Ta,
Jack
____________________
R.I.P. Tareree Shiimi, 1985-2008

[2006 _p1]

[petemell]

It could be just the choke jet or plunger that is blocked or faulty.

[twotakt]

Why the bike needed to be fixed

Bought the bike as a non-runner from the Mrs' Uncle for £70; the powervavle had broken and fallen into the barrel (a common problem on these model bikes using the 3 piece AETC system).
He said it happened when he was trying to race a BMW, what a doughnut eh?.

On removal the piston and the barrel were both badly scored and the exhaust bridge was particularly f**k'ed. One of the powervalves was severly damaged as well. Apparently the bike ran really well before it went pop, but he did admit that he abused the bike in terms of redlining it constantly. He confirmed it was pretty quick and stated that he had 100mph indicated on the clocks quite regularly. To the best of mine and his knowledge the bike is completely standard and un-tuned.

Why I'm using a RGV250 on a RG125f

So I now needed a good barrel, I had two options:

Replate/weld original barrel: ~£150
New Barrel: TBA

When someone offered me a very good conditioned RGV250 barrel and a RG125f bottom end for £42 (including postage) I couldn't refuse. I didn't buy this RGV250 barrel as a performance mod at all, I simply bought it as a far cheaper alternative to having to get my original barrel replated. Also the RGV250 barrel is the only non-original part on the bike; I got the idea from many members of www.rgv250.co.uk and this forum. They stated that: apart from slightly larger port sizes the RGV250 barrel is the same as a RG125f barrel and thus it can be used on a RG125f.

EDIT: Using RGV250 Piston/rings with the RGV barrel

Now back to Pete

Please can you justify your statement:

"I think you may have bent the con-rod"

Can anybody else confirm/reject this statement?

Ta,
Jack
____________________
R.I.P. Tareree Shiimi, 1985-2008

[Kickstart]

Hi

While possible, I would expect it to run (maybe badly) even if this were the case unless really bad.

Presume you have checked the big end / mains for play when the engine was appart.

It might be worth doing a compression check. Just in case you have snapped a ring off when reassembling the top end (I have done that before, then spent ages trying to start the bike).

A 2 stroke bottom end is pretty tough normally.

Personally I would try a little "Cold Start" in it. Don't need massive amounts, but likely it will get it to fire up.

All the best

Keith
____________________
Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[twotakt]

Yea, I checked the big end for play when replacing the top end and everything was within specifications. I doubt anything would be wrong with the bottom end anyway as the bike has only covered 15552miles.

I'll see if I can borrow a compression tester from my mate, if not anyone from Bristol got one that I could borrow/hire? I'll also just phone my Dad now to see if he's got any cold start in work.

EDIT: Cold Start is en route home

Ta,
Jack
____________________
R.I.P. Tareree Shiimi, 1985-2008

[petemell]

Is the inlet and outlet manifold clamps for the carb done up tight? There should be a little bit of life, even if it just coughs once or twice.

[StealthDJ]

While I don't know about RGs in particular, if the bore, stroke and port timings are the same between the 125 and the 250, there's no reason it shouldn't run. It may not run *well*, but I'd expect it to run - It's certainly a trick used on various Yamaha two strokes.

Personally I'd be looking to give the carb a damn good clean (not just compressed air - that won't cut it if the old fuel has turned to jelly). I'd also be looking at the ignition system - putting the pickup coil etc from the broken engine on to the replacement.
____________________
Current garage: VFR800 FI-W | RD500LC YPVS | SV650 K2 | MZ TS250/1 | MZ ETZ251 | BSA WDB40
Previous notables: H100 S2 | CB250NA/B | CB250T | GT250X7 | Z650 B1 | SR650
Still owned, but long gone: RD250LC | CB750F2 SOHC | C50

[twotakt]

To be honest, the bottom end was pretty f**ked, the main bearing is completely gone and I don't know what else.

The barrel was in extremely good condition, I took it to a couple of mates to check it out (including Rob who races MX and owns Kellaway Motorcycles, Bristol) who all said it is in very good condition. So I'm more than happy to use it, however if I did need to get my original barrel replated then I think I would just break the bike as I don't think the investment would pay off. I've only spent £320 in total (including the bike) on the bike and I've got many spares for it (including brand new parts which could be sold again). So I'd prolly at least come close to breaking even if I sold it all in parts (parts can fetch quite alot due to them being quite rare). But if I rebuilt it after a replate it would cost ~£450 and I doubt I could sell the bike for that either in parts or whole.

EDIT: Busy with exams this week, so will clean carb on the weekend and have a look at the reed valve. If it still doesn't work then I'll swap over the ignitions, failing that.......its getting broken for spares

RE-EDIT: No cold start as friend of my Dad's in his work said it's a big no no, especially in 2 strokes. wtf? is what i said.......what do you say to that?

Ta,
Jack
____________________
R.I.P. Tareree Shiimi, 1985-2008