Any 2-stroke clever pants here?

aardvark · Post by **aardvark** » Wed May 31, 2006 4:30 pm

I recently purchased an RD250 with the intention of taking it racing. It hadn't really been given the proper thrashing it needed over the years and has a bit of a problem.

The bike blows, no wait, make that billows, white smoke! It also leaks oil where the exhaust headers meet the barrel. When you give it a decent rev the smoke turns a lightish grey. When you take off in first it really bogs down when given too much throttle, it then starts to rev before bogging down at about 5,000 rpm. If I hold the throttle at 5 grand it eventually clears and takes off.

Suspecting a dodgey oil pump I removed it (not going to need it at the track when I run premix). I changed oil the oil and put some premix 25:1 in it. The problems don't seem to be any better.

Anyone with half an idea?

Smitty · Post by **Smitty** » Wed May 31, 2006 5:44 pm

Jase

when I have played with 2strokes with similar maladies
it has turned out to be the main bearing seals
or worn piston/ring assemblies.

and my memory sez ....
I have heard the first to be an issue with highmileage/thrashed RD250s
whch you fix thru reco'ing crank with new seals.

long time since I played with 2strokes
.....'cept for my Victa!

Plaz · Post by **Plaz** » Wed May 31, 2006 5:46 pm

Still have a feeling it needs a set of rings mate.

mike-s · Post by **mike-s** » Wed May 31, 2006 5:50 pm

Firstly i'll assume you've pulled the carby apart and rebuilt it with new seals, rings (if its high km's especially) and emulsion tubes (important bit to replace in old bikes, worn emulsion tubes are a very efficient way of getting a bike running out of tune). I'd guess that there is a rich point in the carby somewhere, or a shot plug (MAYBE).

Assuming all the above has been sorted, can you experiment and see if you can find a definitive point in the throttle opening where it goes from bad to good/ good to bad, that way you get an idea which part of the throttle circuit your dealing with, which gives you an idea where to mess with the tuning.

Try lookin up that tuning guide i made mention of a few months ago when my bike first shat itself carby wise. The same principles should apply for the tuning of your 2 banger. Tune from WOT and work your way down the circuits

As a hint, tuning priority goes WOT / main jet -> needle taper -> needle body -> pilot jet.

greenmeanie · Post by **greenmeanie** » Wed May 31, 2006 6:26 pm

Not sure about 2t road bikes but dirt bikes run anywhere from 32:1 up to 40:1.

mike-s · Post by **mike-s** » Wed May 31, 2006 6:27 pm

30 seconds with google gave about 5-6 sources that indicated 25:1 for the rd250

Smitty · Post by **Smitty** » Wed May 31, 2006 9:46 pm

mike-s wrote:30 seconds with google gave about 5-6 sources that indicated 25:1 for the rd250

AFAIK
most 2blow motors are happy on 25:1
or maybe a tad richer (but not leaner with the oil)

hth

Glen · Post by **Glen** » Wed May 31, 2006 9:59 pm

greenmeanie wrote:Not sure about 2t road bikes but dirt bikes run anywhere from 32:1 up to 40:1.

You betcha. So long as it's a good synthetic oil 40:1 is pretty standard. The serious blokes run 50 or 60:1 (but rebuild motors often). We always run 40:1 in the young blokes race bikes with Motul Oil plus dropped the needle 1 step and run a smaller main jet. Did 2 top end rebuilds a season and a bottom end and everything was pretty sweet.

aardvark · Post by **aardvark** » Thu Jun 01, 2006 11:39 am

Thanks guys. I will check all those things over the next few days.

I was thinking it might have a blown head gasket. What are your thoughts on this?

mike-s · Post by **mike-s** » Thu Jun 01, 2006 3:04 pm

*points to magic 8 ball*

NovaCoder · Post by **NovaCoder** » Thu Jun 01, 2006 3:51 pm

Even if it's not the problem you'll want to de-coke those pipes of yours Jimmy m' lad.

Fill them up with kero with a rag shoved in one end, stand them up for a few hours and see what comes out.

aardvark · Post by **aardvark** » Thu Jun 01, 2006 4:10 pm

mike-s wrote:*points to magic 8 ball*

Ahh thanks. Solved all my problems, including those that aren't bike related.

NovaCoder wrote:Even if it's not the problem you'll want to de-coke those pipes of yours Jimmy m' lad.

I did think of doing that, I just havent gotten around to it. The pipes are caked in oil so I guess that could be causing a good part of the problem.

plane · Post by **plane** » Thu Jun 01, 2006 4:28 pm

Plugs, plugs and more plugs......

I had three RZ's in my younger years (2x250, 1x500). I used to keep a couple of different sets of spark plugs in different temperature ranges and swapped them according to the ambient temperature.

Starting with the kiss principle, have you changed the plugs for a hotter/newer set?

In my (untrained) opinion, it doesn't seem like fuel is being burnt properly (hence oil leaking at the pipe). If the problem still persists, then it will probably be the crank shaft seals, but if you don't eliminate the plugs as a cause of the smoke you may perform a rebuild for no reason.

If the old girl hasn't been flogged for a while, be prepared to run a few sets of plugs through her.

Cheers,
Pete

aardvark · Post by **aardvark** » Thu Jun 01, 2006 4:36 pm

plane wrote:Plugs, plugs and more plugs......

I did think about changing the plugs, so pulled them out. They were nearly clean enough to eat your dinner off of (if you were a really little person with a tiny little meal.... )

Anyway, the moral of the story is, I didn't bother changing them.

mike-s · Post by **mike-s** » Thu Jun 01, 2006 5:58 pm

id say for the hell of it, change them, you never know, they could be failing under load, it's happened to another chappy on here before *looks towards Vinnie*