With my midlife crisis in overdrive, I’ve bought a race prepped 1989 NSR250.
(Like most people of my vintage, all my first {dirt} bikes were 2 stroke. That carried over to RD350LC, RZ350, and a fragil RGV250)

Problem.
I’ve tidied the bike up, put a new battery in etc.
The bike starts easy, sounds good, rides up and down the street ok, and when warmed up really seems to go well when “on the pipe”, then after a few 1st/2nd gear runs, it dies.
If I had to guess, I’d say it sounds like its out of fuel. After a little while I can repeat the process.

The new plugs look nice - not wet after the dying episode. BR9ECM - $25 each!
No issue with fuel flow from the tank. (Blocked breather etc)
The RC valves seem to operate normally. (Tried the test with the TPS disconnected)
The fuel was a bit old. 25:1 that I had lying around for my VMX bike. (It was 50/50 “98/100LL)

I’ve drained all the fuel, and will try again with fresh fuel today.
I’m planning to run PULP 98 at 32:1 with Motul 800 - any issues? (I don’t want to start an “oil thread” but am happy to take advice)

Basically: it runs strong for 2 or 3 1/4 mile passes, then dies when doing the 5th U turn, almost but not quite like a kill switch issue. More like fuel.

Thanks for any suggestions. I will report back.


Last edited by skypig on Sun Dec 10, 2017 12:43 pm; edited 1 time in total

I’ve removed and stripped (didn’t separate or remove slides) the carbs.
There was some detritus in the bowls, and likely in some other, more critical places.

The bike starts first kick and seems to run strong.

The better idle has allowed me to more accurately track down the original issue.
It cuts out when moving the bars -almost certainly a shorting kill switch/ignition wire.

A few questions if anyone cares to assist.

1. The air screws were bottomed out. I’ve set them at 1 1/2 turns out and intend on trying to fine tuning them from here. (Nothing unusual on these bikes I need to know about?)

2. On each carb, on what appears to be a breather (vents to the slide) there has been a short tube, and #150 main jets installed! See pic. Can anyone shed any light on this?

3. The installed jets are MJ 128, PJ 38 are they ballpark? (stock airbox, 2 extra holes, currently no filter*, Tyga chambers.)

4*. No air filter. This is not what I’m comfortable with. I can make one no problem, but haven’t got the support screen (17212-KV3-000) anyone know where I can get one (Or other parts?) The local Honda Shop can not help, at all.
Is the extra (slight) resistance a reason that the filter would be commonly removed. (Track use only) Any insight appreciated.

You can find the stock settings here:

http://tech.nsr-world.com/nsr250/all-nsr250/nsr250-stock-carb-settings.php

I don't allow specific jetting discussion on the public forums because every scenario is different, and I have had problems before with readers blindly using settings that have caused failures.

To me it sounds like someone has removed the air correction (quite why, I don't know!), hence the jets in the "breather" pipes.

It's difficult to improve on the standard setup, and extremely difficult to troubleshoot someone else's attempt to do so! My advice would be to reset to standard settings, including air correction/airbox, and go from there. It may sound like a terrible get out clause, but in the majority of cases, the stock setup just can't be beaten.
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Andy.
NSR-WORLD.COM

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I completely understand the restriction on publishing jetting specs.
Thanks for the stock settings info.

Anywhere I can get a diagram of the carb venting system?
The parts manual shows a few T pieces (missing from my system) and a 4 way which I have got.

I suspect the short tubes with the main jets should be hooked in with the other vents that go to the solenoid thing?

The tiny pics in the manual I found on this site, seem to have the vents go from one side of each carby to the other side..

As you recommended. I’d like to get it back to “stock” as possible.
Not easy without some good diagrams, and/or help from some experts.

Do guys usually run a filter element on race bikes?
Any recommendations for trying to buy NOS parts online?

Sorry for all the Questions.
Thanks for any help.

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Andy.
NSR-WORLD.COM

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Thanks for the diagram. It should be helpful.

Even though my bike was sold to me as a 1989 MC18 II, is seems to have a frame number from the MC18 (mark I), PGM-III ignition (Mark II), carbs with pilot jets and no “power jets” (MC28?), and only a single air solenoid.??

A true “voyage of discovery for me......

1987 MC16 Pre-PGM (28mm TA10 carbs/no power jets)
1988 MC18 R2/4J Mk1 PGM-I (32mm TA20 carbs with power jets)
1989 MC18 R5/6K Mk2 PGM-II (32mm TA21 carbs with power jets)
90-93 MC21 PGM-III (32mm TA22 carbs with power jets)
94-97 MC28 PGM-IV (32mm TB10A carbs with power jets)*

*TB10A carbs are very different to MC18/MC21. (TA20/TA21/TA22 all look very similar. The MC16 TA10s are a similar design to the TA2x series.)

A single solenoid would usually indicate a 1988 R2J/R4J.

The 1987 TA10 carbs are the only carbs without provision for power jets.

TA2x and TB10A all have power jets, however they can have blanks fitted as part of the HRC setup.

TA20/TA21/TA22 are all interchangeable, but they ARE NOT a simple direct swap for one another.
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Andy.
NSR-WORLD.COM

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I’m away at work and can’t check things (till after Xmas)

Do they all run pilot jets? (I might have been misled by a description I read)

Interestingly, I found a reference on the TYGA site about the air vents running 140 main jets to replicate the function of HRC carbys (which vented via a similar size hole) Might explain the setup on mine.

I didn’t see any power jets when I was removing and cleaning the jets. Might be blocked off (as part of a HRC setup) or I might not know what I’m looking for.

What is the recommendation for airfilter/airbox for Track only use? (Currently stock airbox, two extra holes, no filter.)

They all run pilot (slow) jets. TA2x carbs as standard are #38 across the board.

The power jets are hidden under a large alloy screw in the float chamber. Careful removing the screw. They are easily damaged.
_________________
Andy.
NSR-WORLD.COM

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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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