Hi guys.
Im new to the forum, great one @ that.
Was hopping some more knowledgable mates on here might be able to help me out.
1st Im a big 2 stroke fan owning a 3ma TZR 250 VJ22 RGV250 and my latest MC21 NSR 250
The NSR gives me trouble starting sometimes. I can get it started in the morning with choke on after 4-5 kicks, let it run for a bit then turn the choke off.
Then ride it for a while & stop somewhere then when I try to start it when its warm it gives me trouble. sometimes Ill have to give it a bit of choke, sometime no choke but full throttle to get it to fire. Has anyone had this problem & aware of anything that may cause this problem. The bike just had piston/rings done in it bout 200 miles ago, & the carbs have been clean out twice. so I know its not a compression problem, or dirt in the jets it must be something else.
I dont seem to have this problem with my RGV.
Anyone have any advice that might point me in the right direction.
Thanx in advance.
Regards

Crank centre seal bud...

To check : When the bike is running, feel exhaust gasses with your hand at silencer end if onc side is hotter than the other...

Also read my post here : http://www.nsr250.net/forums/viewtopic.php?t=11152

Cheers
M

I also had problems starting the bike. That happened after I had tampered with one of the slow jets. The gas pulses out of the left exhaust were weaker than those from the right one.

I had cleaned my jets but it is not until I renewed them (MJ & SJ) that the bike starts at 1st/2nd kick. Cleaning jets is not always a guarantee. I also changed the carb insulator and made sure it is correctly tightened and that the airbox rubber boots are airtight.
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I too suggest the centre seal is probably past it's best. If you do a seach for that, you'll find quite a few recent threads about it.
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MC21SP Plaything
BMW F800GS Bumblebee
Triumph 9551 Daytona Big boys toy
FJ1100 Sporting relic
GTS1000 oddball

At least, try a set of new plugs,and see how that goes.

A weak battery can make them bad starters too.

Mine's a notoriously bad starter... even after it had a new crank/seals. It always has been, since (virtually) day one. (Bought with allegedly 3500kms on the clocks, 17 years ago.)
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Andy.
NSR-WORLD.COM

Please keep all responses to Forum posts on the Forum so that others may benefit.

Please DO NOT PM me for technical advice. My time is precious, and you will probably receive a faster response on the Forum anyway.

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Thanx for all the advice guyz. Well Im getting ready to install a complete HRC jet kit with Tyga high flow reeds & a set of Dog Fighter Chambers, as well as doing the wire splice as the bike is stock. So that will eleminate it being a jet problem & the plugs are getting ready to be replaced by Brisk plugs which are the best plugs Ive ever use in a 2 stroke & believe it or not Ive never fould a plug since I started using them, but this bike doesnt have them installed yet. It just had a new top end done so I know its not bad compression. I had problems in the past with a kx 125 that needed rings & was a pain to start. Im just dreading that its the Crank Seal, cause that turns a simple, jet/sparkplug/airbox problem into a major tear down & rebuild. But the only thing postive I can think of that I would gain out of the deal is that my old friend Tom Mogan (Jeff Wards old factory kawasaki mechanic) said he would do some port work on the intake & exhaust for me. Im Blessed to have him as a friend only because I use to be a test rider for him when he started a business here in FL several yrs back & built & blue printed 2 stroke dirt bikes for racing mainly pros & AMA privaters. At the time I was racing motocross in the 125 pro class & his work is top notch, he has 5 prestigious Gold Wrench awards from the AMA for his contibution to the sport for over 25 yrs now.
So the big question in whats the crank seal gonna cost & how does it have an effect on the bikes starting problem Alzazorq?
Thanx again guyz gives me some option & things to think about, but for for some reason I have a feeling that Alzazorq might be right.

The cost of the crank seal is no big deal, it's part of the center main bearing and the bearing is £37, the O ring seal is very cheap.
The issue is (obviously) fitting it as it's in the middle of the crank, I'm not going to say that it can't be done without fully stripping the crank but it wouldn't be easy, may not be wise and there's a good chance the rest of the crank isn't 100% either.

The reason it affects starting more than running is (presumably) as if the seal isn't sealing then primary compression isn't ideal, the slower the motor is turning the more the problem shows (as more mixture has time to leak through the seal) and when it's being kicked over it's turning very slowly indeed.
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Please do not PM me technical questions, if you can't find it on the Forum start a thread

rotech7 wrote:Thanx for all the advice guyz. Well Im getting ready to install a complete HRC jet kit with Tyga high flow reeds & a set of Dog Fighter Chambers

Rotech7, welcome to the forum.

My advice would be before you start bolting on all the fancy stuff (Chambers, Reeds, Jet Kits) you make sure your foundations are solid.
A bottom end check & rebuild can seem daunting first time around, but once you get into it it's not so big a deal. If you have a mechanically adept friend, get them around to help.
If you subscribe to the forum, you get access to the very useful workshop manual.

Before you strip the engine, a crankcase leak down test will confirm all 3 crank seals integrity, you can search the forum as there are loads of posts on this subject.
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Rich
MC21 Track Bike / RS250 NF5 'Spencer', NX5 'Cadalora' & NXA 'Aoyama' / RS500 / Two Brothers Racing RC30

i can confirm what RichG has said and the general consensus on this forum in that the motor really is easy to strip down, having just done it myself for the 1st time so dont be affraid to give it a go.

RichG wrote:

rotech7 wrote:Thanx for all the advice guyz. Well Im getting ready to install a complete HRC jet kit with Tyga high flow reeds & a set of Dog Fighter Chambers

Rotech7, welcome to the forum.

My advice would be before you start bolting on all the fancy stuff (Chambers, Reeds, Jet Kits) you make sure your foundations are solid.
A bottom end check & rebuild can seem daunting first time around, but once you get into it it's not so big a deal. If you have a mechanically adept friend, get them around to help.
If you subscribe to the forum, you get access to the very useful workshop manual.

Before you strip the engine, a crankcase leak down test will confirm all 3 crank seals integrity, you can search the forum as there are loads of posts on this subject.

Thanx guys.
Im mecanically inclined. Ive been in & around 2 strokes my whole like & done almost all my own work on my bikes, when I raced motocross I use to tear down & rebuild my motors all the time just for experience & to learn more about the internals of the 2 stroke motor itself.
So I know I can handle the teardown & rebuild, but the manual; will come in handy to have by myside incause I run into something Im having an issue with.
My one question is as long as there isnt any bearings that are pressed on there should be no problem for me. I fell confident about tackleing the job. & when I 1st got the bike I wanted to focuse on tunning, jetting & chambers, but my attention now is to go thry the whole motor to make sure everything down stairs is sound, new & tight. The only weekness I have is in the tunning department I usually go to my mechanic do all that for me cause he has the dyno & the equipment to make quick changes to see what works & what dosnt with different bolt on goddies.
After all that has been done Ill worry about the upgrades & the tunning asspect of the hobby. Trust me I have no problem waiting. having a bike that puts out 65 HP is great but with a motor that could potentially come apart, theres no point in it & know that for sure & agree with you 100%.
So once Ive gone thru everything & fell comfortable that I have a good foundation Ill work on the other goodies.
@ least thats the plan I have @ this point.
The one thing Im concerned with is that my mechanic told me if Im gonna do the lower end I might want to consider doing the crank as well. well thats an extra $450 & I dont see how a bad seal could cause that much damage to a crank. I mean if I have to replace it I will, but I would like to avoid that if @ all possible as thats a good chunk of change to drop down.
Thanx for all the advice guys & appreciate your input. The only questiuon I do have is where would I go to get a leak-down test done on the bottom end?
Is that something that can be done @ a dealership & does most bike repair shops have the equipment to do the same? Thanx

Knowone got back to me on if they think I will need to replace the crank just because the crank seal is bad ..?
I can replace all the lower end seals for a couple hundred. But a crank is gonna cost $500.
So anyone on here have had this experience & tell me if they swaped cranks or ran the same one in there?
I just wanna do whats best, but Dont want to spend unnecessary money on the rebuild.
Thanx

You can have the crank rebuilt, incorporating new seals - assuming the crank is straight (or can be straightened).

I had the crank out of my 18 without dropping the engine. Only took a couple of hour. May as well have a look and see whats what. Better than waiting for it to lunch it's self for the sake of a few hours with a wrench.
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it wouldn't be fun if it was easy!

dunkenb wrote:I had the crank out of my 18 without dropping the engine. Only took a couple of hour. May as well have a look and see whats what. Better than waiting for it to lunch it's self for the sake of a few hours with a wrench.

No the engines comin out of the bike. Im gonna go thru everything. The cylinders are getting sent to Tom Morgan for porting as well as the flyweel to get lightened up.
I just dont know what condition the crank is gonna be in & if I will need to buy a new one. I dont know how much damge can get done to a crank that has a bad seal on it. & the other un answered question is, how long has the seal been bad?
If the crank is damaged or bent & has to be fixed for what thats gonna cost I might as well get a new one if it looks bad.
I just want to go thru everything from top to bottom & make sure everything is correct before putting it back together thats all. Then I can worry about my bolt on upgrades after I know the motor is fresh...Its just money money money with our hobbys aint it ..