2 Stroke Help Needed

[martindavies]

Hi guys,

A friend of mine has asked me to help try and fix up his nsr150rr.

I have some basic knowledge but am looking for your advice.

The bike runs fine up until 7000 rpm, and it should rev up to 11,000rpm.

Once 7000 is hit the best way to describe it is it feels like a rev limiter is being hit. Obviously its not that.

The RC valve seems to be working fine, but even if it wasnt i doubt it would stop the bike from revving.

So any ideas on where to start and what to check?

Thanks

[Crossy]

Ignition timing perhaps?

It's been a (very) long time since I worked on a stroker, but retarded timing was always a good starting point when it wouldn't rev.

Could be a clogged exhaust / air filter too.

[katabeachbum]

Ignition timing perhaps?

It's been a (very) long time since I worked on a stroker, but retarded timing was always a good starting point when it wouldn't rev.

Could be a clogged exhaust / air filter too.

when ignition is set correctly, fuel filter, fuel line, exhaust and airsupply.

still problem, pick carb apart clean and try again

[Garry]

A couple of things to consider:

1. Does the engine rev freely to high RPM when in neutral?

2. High RPM, high fuel load--what condition are the spark plugs in, gap. Is the spark good?

3. Do you have full throttle (visual check on the throttle bodies, don't just twist the throttle and think its okay)

Edited May 19, 2011 by Garry

[martindavies]

Ok have just taken off the carb and cleaned it. Wasnt blocked or dirty, I think it may have been cleaned recently.

In gear or neutral it wont rev past the 7k.

Pulled the plug (a new plug 15km ago) and it was black and oily.

Im thinking that its running too rich as there is quite a bit of smoke too, although im not sure how much is too much for a stroker

Im thinking to move the jet needle clip up one to lean it out a bit, is that a good idea? Its in the middle position right now.

Air filter is fine, Exhaust may be clogged up i dont know but to clean it out im guessing hacksaw in half the re weld?

Ignition timing... well i wouldnt know where to start with this but if its running well, nice and smooth up until 7k can i assume its ok?

Thanks very much for taking the time to help

[JeffreyMcCollum]

Just a quick note; on my NSR150 SP I have been through 2 motors by using 91 gasahol Now I only use RED pump 91

Both times I used new honda HRC crate motors

[martindavies]

Yep always use benzine.

I have tried the needle clip in various positions and its not helping.

Im thinking now that maybe its the piston / piston rings and the excessive smoke is the engine oil leaking through.

Would this cause the power to stop at 7000 rpm?

[Leckyman]

Is the gearbox oil level dropping, or the water for the coolant?

Main jet & float height ok. Could be too little fuel in the float bowl to supply enough fuel at high revs......

[Leckyman]

Also,

if you think its running too oily, you could disconnect the oil pump & put a premix in the tank & see if it improves.

[thunder30101]

Yes your losing power somewhere most likely ring or cylinder problem.

[sapi]

my rule when fixing something "always start with the easiest first"

1. replace the plug if black , B9ES or BR9ES

2. Adjust the air neddle in the carb, do it patiently

3. Empty the engine oil and replace with good one. if the oil is black perhaps long time not change or the clutch is gone

4. de-choke the exhaust. no need to cut it, 2 ways as far as i know. use blow torch or soak it in diesel oil overnight (separate between the silencer and main exhaust)

If still can't :

1. perhaps the ICM is busted, expensive to replace (2000-3000 baht)

2. when idle, engine make rattle noise (like some bolt stuck in the piston), piston and ring is gone

3. check fuel consumption, is it normal? roughly 18-22km/l. If not, piston and ring clearance is gone

4. Last solution is to take out the engine, and check one by one

edit: normal position for the neddle carb is 3 from top. idle should be 1400rpm, adjust the air neddle and idle

Edited May 19, 2011 by sapi

[martindavies]

Idle is fine, about 1500 revs. I am noticing more and more smoke each time I start it now.

I took the cylinder head off and it looks like the rings are stuck inside the piston, so i think ill start there.

Its prob been neglected for a while and rings piston would need changing soon anyway.

When looking through the exhaust port i could see as the piston passed it was leaving oil in the combustion chamber so without the oil tank or fuel tank connected thats obviously not a good thing.

I will prob drop the whole engine out, take it to a shop to be possible re bored and have a new piston fitted.

Whilst they are at it ill ask the to check the carb over.

Ill let you know how it goes, once i have figured out how to remove the engine

With the engine out will be able to tart up the frame a bit and give it a good degrease.

Thanks a lot for the replies

[sapi]

just helpfull link:

http://www.smellofdeath.com/lloydy/piston_diag_guide.htm

http://www.spark-plugs.co.uk/pages/technical/diagnosis.htm

http://www.dansmc.com/MC_repaircourse.htm

open the gear while u at it.

[dumball]

To me this sounds like you have a common 2 stroke problem when too much oil is getting into the cylinder , the rings have nothing to do with this as there is no oil in the crank-case other than that fed by the oil pump , unless the oil pump is stuck in the fully open position , leave it alone . It is not normal for changes to be needed in the carb if the machine was running satisfactorily prior to the onset of your current problem , changes will not affect the oil contamination on the spark plug .

The problem is most likely to be a worn or broken crank=case seal on the clutch side of the engine , I have even found them blown out of position , this will allow transmition oil to be sucked into the engine , hence the increase of smoke from the exhaust system .

[Richard-BKK]

Check for broken gaskets, it's not uncommon that a “higher” performance two-stroke is blowing a gasket, and I not necessarily mean a cylinder gasket. A two-stroke also creates high pressures under the piston to push out the exhaust... if somehow that pressure is not enough a two-stroke engine will have performance problems in the high revs...

[dumball]

='Richard-BKK' timestamp='1305817031' post='4434972']

Check for broken gaskets, it's not uncommon that a "higher" performance two-stroke is blowing a gasket, and I not necessarily mean a cylinder gasket. A two-stroke also creates high pressures under the piston to push out the exhaust... if somehow that pressure is not enough a two-stroke engine will have performance problems in the high revs...

I am afraid your diagnostic skills are a little amiss , the engine in question is suffering from excess oil in the cylinder and combustion chamber , which in turn alters the stoiciometric balance of the fuel mixture and also lowers the octane value of the fuel being burned . Just because the engine is of a higher performance character , it in no way entails it will be more susceptible to blowing a gasket in any particular joint on the engine , I have built literally hundreds of high performance engines of an extremely high standard during my 60 + years in the racing circles of several countries with multiple provincial and national champion riders . It is obvious that without the particular machine within at least ear shot , true diagnostics are or can be a little hazy .

[martindavies]

Going to drop the engine out today, If I can I will post some pictures.

Thanks for the replies

[KRS1]

Idle is fine, about 1500 revs. I am noticing more and more smoke each time I start it now.

I took the cylinder head off and it looks like the rings are stuck inside the piston, so i think ill start there.

Its prob been neglected for a while and rings piston would need changing soon anyway.

When looking through the exhaust port i could see as the piston passed it was leaving oil in the combustion chamber so without the oil tank or fuel tank connected thats obviously not a good thing.

I will prob drop the whole engine out, take it to a shop to be possible re bored and have a new piston fitted.

Whilst they are at it ill ask the to check the carb over.

Ill let you know how it goes, once i have figured out how to remove the engine

With the engine out will be able to tart up the frame a bit and give it a good degrease.

Thanks a lot for the replies

when you get the carb checked make sure the jets are 142/45 if i recall correctly these are the stock sizes. (or it may have been 145/42) anyway its around there, nothing below 140 or 40.

I think the bike may be suffering from more than one ailment, run the bike on premix like someone else mentioned and disconnect the 2t and see if it helps. If it does the 2t pump needs to be worked on, its usually a gasket. KRR 150's are notorious for this with more and more accumulated smoke the longer it sits. When the 2t gasket goes the flow of 2t becomes much higher because there is a loss of vaccum to keep the oil back.

When the pump goes bad and the bike gets smoky, the first thing a thai mechanic will do is adjust the 2t to be too lean, then they'll burn out the pipe, finally theyll rejet too small, then change the crankcase gasket, then they eventually get to the 2t pump and change the entire pump instead of replacing the gasket. Somewhere along theyll consider the piston rings and try to think of something else because its too much work !

The NSR had a nikasil coating or whatever its called, so if you bore you'll lose the coating. If i recall correctly it uses a sleeve and you can get one of those oversized in .25 / .50 / .75 / 1.0 for under 1000 baht.

If you think its the crankcase oil, start the engine and stick your hand behind the exhaust, you'll be able to tell easily.

[martindavies]

Idle is fine, about 1500 revs. I am noticing more and more smoke each time I start it now.

I took the cylinder head off and it looks like the rings are stuck inside the piston, so i think ill start there.

Its prob been neglected for a while and rings piston would need changing soon anyway.

When looking through the exhaust port i could see as the piston passed it was leaving oil in the combustion chamber so without the oil tank or fuel tank connected thats obviously not a good thing.

I will prob drop the whole engine out, take it to a shop to be possible re bored and have a new piston fitted.

Whilst they are at it ill ask the to check the carb over.

Ill let you know how it goes, once i have figured out how to remove the engine

With the engine out will be able to tart up the frame a bit and give it a good degrease.

Thanks a lot for the replies

when you get the carb checked make sure the jets are 142/45 if i recall correctly these are the stock sizes. (or it may have been 145/42) anyway its around there, nothing below 140 or 40.

I think the bike may be suffering from more than one ailment, run the bike on premix like someone else mentioned and disconnect the 2t and see if it helps. If it does the 2t pump needs to be worked on, its usually a gasket. KRR 150's are notorious for this with more and more accumulated smoke the longer it sits. When the 2t gasket goes the flow of 2t becomes much higher because there is a loss of vaccum to keep the oil back.

When the pump goes bad and the bike gets smoky, the first thing a thai mechanic will do is adjust the 2t to be too lean, then they'll burn out the pipe, finally theyll rejet too small, then change the crankcase gasket, then they eventually get to the 2t pump and change the entire pump instead of replacing the gasket. Somewhere along theyll consider the piston rings and try to think of something else because its too much work !

The NSR had a nikasil coating or whatever its called, so if you bore you'll lose the coating. If i recall correctly it uses a sleeve and you can get one of those oversized in .25 / .50 / .75 / 1.0 for under 1000 baht.

If you think its the crankcase oil, start the engine and stick your hand behind the exhaust, you'll be able to tell easily.

Hey KRS1,

How would I know the difference between the oil being burnt at the exhaust end?

Would the crankcase oil smoke look or smell different to the 2t oil smoke?

Cheers

[KRS1]

Both ...but it may be hard to tell unless you know what to look for, check the jet sizes , it will have the same effect if they are too big.

When it hits 7k does it stop climbing, stutter, become lathargic or increase slowly?

The bike wouldnt happen to be black with white stripes would it? I have a friend that likes to get other people to do the dirty work for him ..

Edited May 20, 2011 by KRS1

[martindavies]

Both ...but it may be hard to tell unless you know what to look for, check the jet sizes , it will have the same effect if they are too big.

When it hits 7k does it stop climbing, stutter, become lathargic or increase slowly?

The bike wouldnt happen to be black with white stripes would it? I have a friend that likes to get other people to do the dirty work for him ..

Nope not black and white

I have put the bike back together as I didnt have the tools (jack or axle stands) needed to drop the engine so i put everything back in cleaned.

Still exactly the same.

If I warm the bike up, and give it WOT it will climb quickly untill 7000 rpm. from there. Its a stutter, like its hit a rev limiter. Could possible sound like its 4 stroking not 2 stroking anymore if that makes sense. It doesn't rise any further or increase at all. And thats free revving or in gear.

Its strange that up until that point the bike runs great. Could leave it the way it is and have a nice runner but from 7k-11k is where the fun is!

So the exhaust isnt clogged, air filter is ok, carb cleaned. New plug. When pulled after 5 mins of running its black and oily. Same as when I looked inside the exhaust and exhaust port. Thick black oily sludge.

Silly question but in regards to the jets how do I tell what size they are?

[Semper]

Ignition timing perhaps?

It's been a (very) long time since I worked on a stroker, but retarded timing was always a good starting point when it wouldn't rev.

Could be a clogged exhaust / air filter too.

when ignition is set correctly, fuel filter, fuel line, exhaust and airsupply.

still problem, pick carb apart clean and try again

It's a CDI system, or whatever they call it. You don't have to set the ignition on a electronic thing.

[Lickey]

MD, take the exhaust off and remove the air filter, fit some ear plugs and start it up, does it rev better now? if so, replace the filter, still revs good? re-fit exhaust, back to 7k revs? you say the exhaust has been cleaned out, ok, lets take that for gospel, Strokers need exhaust back pressure to run nice, but that back pressure can expose a leaking crank seal,

this simple test should show up the problem. dont worry too much about the oil you see in the exhaust port, the pump is delivering at full throttle opening and the engine is not reaching it, normal..

[Semper]

Just a quick note; on my NSR150 SP I have been through 2 motors by using 91 gasahol Now I only use RED pump 91

Both times I used new honda HRC crate motors

As you know, the SP needs 95 octane.

[Semper]

Ok have just taken off the carb and cleaned it. Wasnt blocked or dirty, I think it may have been cleaned recently.

In gear or neutral it wont rev past the 7k.

Pulled the plug (a new plug 15km ago) and it was black and oily.

Im thinking that its running too rich as there is quite a bit of smoke too, although im not sure how much is too much for a stroker

Im thinking to move the jet needle clip up one to lean it out a bit, is that a good idea? Its in the middle position right now.

Air filter is fine, Exhaust may be clogged up i dont know but to clean it out im guessing hacksaw in half the re weld?

Ignition timing... well i wouldnt know where to start with this but if its running well, nice and smooth up until 7k can i assume its ok?

Thanks very much for taking the time to help

I find this very hard to believe. If it don't rev 7K in neutral, there must be a serious problem. A hole in the piston?

[KRS1]

Both ...but it may be hard to tell unless you know what to look for, check the jet sizes , it will have the same effect if they are too big.

When it hits 7k does it stop climbing, stutter, become lathargic or increase slowly?

The bike wouldnt happen to be black with white stripes would it? I have a friend that likes to get other people to do the dirty work for him ..

Nope not black and white

I have put the bike back together as I didnt have the tools (jack or axle stands) needed to drop the engine so i put everything back in cleaned.

Still exactly the same.

If I warm the bike up, and give it WOT it will climb quickly untill 7000 rpm. from there. Its a stutter, like its hit a rev limiter. Could possible sound like its 4 stroking not 2 stroking anymore if that makes sense. It doesn't rise any further or increase at all. And thats free revving or in gear.

Its strange that up until that point the bike runs great. Could leave it the way it is and have a nice runner but from 7k-11k is where the fun is!

So the exhaust isnt clogged, air filter is ok, carb cleaned. New plug. When pulled after 5 mins of running its black and oily. Same as when I looked inside the exhaust and exhaust port. Thick black oily sludge.

Silly question but in regards to the jets how do I tell what size they are?

The numbers are stamped on the jets

Just how thick is that black sludge? Honey or milk?

Try and take a picture of the RC valve position at 7k rpm please. Just want to make sure its not choking. Speaking of choke, make sure the chokes not on.

[Semper]

Interesting. My money is on the RC Valve.

[dumball]

'Semper' timestamp='1305921628' post='4437749']

Interesting. My money is on the RC Valve.

80% for sure it is the crank-case seal , easy to replace if you have the tools and some idea of how to use them , all of the symptoms point to it including the black heavy oil coming out of the exhaust exit .

[martindavies]

The black stuff is more like honey.

Choke is not on, and the RC valve is working fine. I have the owners manual and have checked all the movements / specifications against it. Also while the head was off it was cleaned, made sure it was moving freely and then rechecked once I put it all back together.

I cant see any numbers stamped on the jets? Maybe im missing them but I can buy new jets of the numbers you recommended and try that out. I cant imagine them costing a lot.

One other thing I noticed was when looking through the exhaust port at the wall of the piston whilst turning the engine over slowly a slight amount milky coloured oil on the piston walls below the rings. Is this normal or point to something else?

[Richard-BKK]

Milky-colored fluids suggest a gasket is leaking... cooling liquid mixes with oil and create the milky color you see... As the two-stoke oil mixed in the petrol is probably not enough to create the milky looking fluid you likely have also engine oil leaking... Time to split the engine and replace all gaskets...

Edited May 21, 2011 by Richard-BKK