I read somewhere that compression on these NSR250R's is about 128/cylinder, and that a top end job should be done if they're down to 100 or below with a difference of 10 or more between the two. Does this sound about right?

I've got an MC16 with 100 in one cylinder and 90 in the other

Her Symptoms:
-Hard to start when cold, 20-40 kicks! (Compression issue?)
-Hesitant between 6-7k rpm, not smooth troughout rpm range, solid after 8500ish (Carb issue?)
-Smokes like a veteran! (Comp issue?)
-On cylinder is slower to fire up than the other (Comp issue!)

So, pretty sure i have all the indicating signs haha. Thought I'd run it by you gents before I give Tyga some added income and start breaking her into pieces,

Cheers


Last edited by Flyboy on Thu Mar 01, 2007 9:41 pm; edited 4 times in total

It seems like you got a tired engine there mate ,good compression should be around 115/125,whats your metod of comp testing?was the engine warm,did you have the throttle pinned and did you stop kicking it over before a higher reading could be had,although seems like your giving your leg muscles a good workout trying to start the thing
I think the biggest mistake mc16 owners (me included) make is buying a bike that needs work that ends up costing much more than the bike is worth

IMO, even a bike with compression of 90 should still run ok if the carbs are tuned right.... I have had several friends rebuild their Yamaha 350's and still couldn't start em-ran bad-flooded one cyl.... The bike never needed rebuilt in the first place, just needed some better tuning...
Heck, my CR125 started 2-3 kicks the whole 7 years I had it and I only rebuilt it twice. Get the carbs sorted out before you tear it apart
_________________
MC21
04 NSR50R
93 CBR F2
98 CBR F3 track bike
95 VFR750
89 FL400R Pilot
90 FZR 4/600

try a new air filter for a start

Thanks for the replies!
Just pulled the carbs off, and she's got 115 MJ's and 35 SJ's. PJ is blocked off with a screw and sealant. I think i might solder it. It was leaking round the float bowl seal, so I'll need new float boal seals. Not sure if it could be float height as well? 13mm is stock for NSR and I found this one to be: 11.75mm and the other 12mm. I know its been played with as theres marks and looks as tho its been bent a few times.

I've never rebuilt this engine eh, but as far as my method for checking compression: I just kept kicking it over and over and over, and she was warm. Was my method flawed?

The Air filter looks fine, i had cleaned it before and sprayed it down with air filter oil again. Is the MC16 filter the same for all Nsr250r's?



Last edited by Flyboy on Mon Feb 19, 2007 1:14 am; edited 2 times in total

You should hold the trottle wide open while doing a compression check. The needle should stop jumping up in about 6 kicks or so. That's the way I was taught...
_________________
MC21
04 NSR50R
93 CBR F2
98 CBR F3 track bike
95 VFR750
89 FL400R Pilot
90 FZR 4/600

Check comp at WOT, kicking at at least half a dozen times. If your comp falls short, like you say 90~100, then a quick test can see if it's a comp problem.

Get your base figure, and then pull the plugs out and pour in half a tea spoon of 2 stroke oil. Refit plugs and test again. If the comp goes right up to 125 or so then you can be pretty sure it's a ring problem. The oil helps seal the rings for the first few kicks.

If the figure only rises a little bit (5psi or so) then you it's either on the money anyway, or the crank seals are toast, or there's a leak somewhere. Crank seals or a leak can be found with a leakdown test.

Your compression gauge will probably read different to mine and so on, but what you need is a base figure on your gauge on a rebuilt, run in engine. It doesn't really matter what your particular gauge reads unless it's highly accurate, as you want to measure the drop from the base "as new" figure.

Thanks Matt, SLF-951, I'll do those steps you mentioned and report back in a few days or so. Worse comes to worse, I'll be inquiring with you about makin an order Matt!

How about these carbs tho, with those settings I mentioned..could it be contributing to the trouble? I believe the carb is stock setup since it has non adjustable needles, 115 MJ's and 35 SJ's. But should the PJ's be blocked off as they are? I read the articles in the "workshop" page, but didn't specifically talk about the MC16

PICS of 'er: http://www.bikepics.com/members/canflyboy/

Appreciate it eh

Her other symptoms were:
-Would quit on me like she was running out of gas if I had run her for 5 mins at WOT (MJ issue?)
-Will start up on 1-2 kicks when warm, a bitch when she's cold tho
-front cylinder fires right away, rear spits and sputters a lil till warmed up

Keep in mind its about -10 outside and winter won't let up for another 6 weeks at least, so I can't run the dam thing unfortunately to do a plug chop. Just going on her symptoms from the fall.

Did the compression test on my MC16, carbs off of it both times and engine cold:

Without oil I get:

Front: 108psi Rear: 100psi

With a tsp of 2 stroke oil in each cylinder, I get:

Front: 110psi Rear: 125psi

(Not able to do a plug chop till this snow melts, prob another 6 weeks or more , I don't know anybody else in Winnipeg with an NSR either! ha)

Thoughts on these numbers?..
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I'm going to stick with my original thoughts on you have more of a carb issue than a worn engine issue. I'm not saying you couldn't use a rebuild, but you should be able to get it to start and run better..... I'd put money on if you do rebuild it, you still will have problems.

Steve
_________________
MC21
04 NSR50R
93 CBR F2
98 CBR F3 track bike
95 VFR750
89 FL400R Pilot
90 FZR 4/600

[quote="Flyboy"]
How about these carbs tho, with those settings I mentioned..could it be contributing to the trouble? I believe the carb is stock setup since it has non adjustable needles, 115 MJ's and 35 SJ's. But should the PJ's be blocked off as they are? I read the articles in the "workshop" page, but didn't specifically talk about the MC16

[quote]

So if it were a carb issue, given that the PJ's were blocked off, should I change the SJ's or MJ's out for larger ones? I checked the needle and its non-adjustable, and the float bowl heights weren't the same and off by only 1 mm..
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You should identify the carbs first.

Check the Technical Resources section for standard carb settings.
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Andy.
NSR-WORLD.COM

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Am I missing something here??? I have yet to receive my bike, and hopefully I won't be into the carbs right away.... Jim just rebuilt it anyway...So I know nothing about these particular carbs. But the "PJ" is the small jet.... right. Any carb I'd ever touched only has two jets, pilot-main.... so what on your carb is blocked off??? The choke feed???? That would be the other pick up in the bowl on any carb I've ever had my hands on.
I'm looking through the manuals that Jim sent me and they look like a pretty normal set up, besides the slides. But I can't read any thing since they are all writen in Japenese so I cant be for sure....
But if what I'm saying were the case.... You would have one hell of a time getting it to start.... And in those temps, you'd be lucky to get it to start at all.

Steve
_________________
MC21
04 NSR50R
93 CBR F2
98 CBR F3 track bike
95 VFR750
89 FL400R Pilot
90 FZR 4/600

Andy wrote:You should identify the carbs first.

Check the Technical Resources section for standard carb settings.

Hey Andy, here's my specs:

Keihin TA-10A - D type (read of side of carb set)
MJ's - 115
SJ's - 35
PJ's - 2 blanks (blocked off with screw)
Float bowls heights - 11.75-12mm (instead of 13mm stock, will fix this)
Needles - Stock, non-adjustable
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SLF-951 wrote:Am I missing something here??? I have yet to receive my bike, and hopefully I won't be into the carbs right away.... Jim just rebuilt it anyway...So I know nothing about these particular carbs. But the "PJ" is the small jet.... right. Any carb I'd ever touched only has two jets, pilot-main.... so what on your carb is blocked off??? The choke feed???? That would be the other pick up in the bowl on any carb I've ever had my hands on.
I'm looking through the manuals that Jim sent me and they look like a pretty normal set up, besides the slides. But I can't read any thing since they are all writen in Japenese so I cant be for sure....
But if what I'm saying were the case.... You would have one hell of a time getting it to start.... And in those temps, you'd be lucky to get it to start at all.

Steve

Thanks Steve, yea these carbs have got a Main Jet(MJ), a Slow Jet(Pilot/SJ) and a Power Jet (PJ) Or at least, this is what I gather from:

http://www.nsr-world.com/tuning/250-tuning/carburation%20index/carburettors/

I haven't been trying to start it, the bikes not even outside eh, its in the livingroom...right where the wife doesn't want it !
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