Hi,

I seem to have a bit of a problem with the NSR.

The bike runs and start's fine , with very good performance, but after a while it loses power throughout the rev range.
This can occur from 1/2 hour after start up onward's, sometimes switching the bike off and restarting can restore power for a while.

The plug's are a good colour.

Tonight I pulled the carb's, to check what jetting the bike has and check for internal blockages. All seem's fine.

Main's; 128.
Power; 55, both carb's.
Slow; 38.
Pilot; 1 and 1/3 turn out.

I believe stock Power jet's should be 70/75 is this correct?, where can I get them and how do you remove the flaming thing's that ers in , (tried (gently) a pair of mole grip's(??? ). They're going nowhere!!!).

On inspecting the TPS connector, some corrosion was evident on the terminal's, I tried a multimetre and struggled to get reading's, after a bit of a cleanup I could get ascending and descending resistance reading's when opening the throttle.
I'm hoping this cure's my problem (well one of em! ) sound likely?

Is any info available to check/set the TPS?

Bike is running stock exhaust's with wire splice (which didn't seem to make much difference!).

Any advice or opinion's greatly appreciated.

Regard's Phil


TRX 850
Honda 400/4
NSR 250 MC21

OOOps.

The item's I described as being the power jet's are actually the air jet's !

I've just checked the POWER jet's 72 for left carb and 75 for the right carb.
I would have expected the rear (left) cyl to be running the bigger jet.

Of course it alway's helps when you know what your'e looking at when trying to diagnose a problem!!!

Just been out for a run, bike still seem's to go better for first 1/2 - 3/4 hour. Perhaps better than it was tho.

Regard's Phil

If the TPS is not working correctly then power loss can result.

The resistance readings should ascend and descend smoothly. If they don't they try soaking the thing in WD40 or similar over night.

the TPS has a major effect on ignition timing and can either cause very poor performance or can actually blow things up as we've found in the past!

Funny that it runs fine at first with bad connection ? How is your charging system ?

Thanx for the replies guy's.

I was clutching at straw's with the TPS, but I was figuring there may be connection through the corrosion when cold but engine heat may increase resistance giveng a duff, if any reading. Thing's also seem worse in damp or wet condition's...
Of course I could be talking complete crap!!!

I've just been out for a good long(ish) ride, performance seemed to be consistent throughout the 1 3/4 hour blast.
Here's hoping.

BUT....

With performance now consistant over a period of time, the bike is noticably lacking in the 5 1/2 to 8000 rpm power band, poor acceleration and quieter engine note (Kapow above 8500 tho!).
As I've mentioned jetting is stock, For the power jets is it correct that the left (rear) cylinder run's the smaller -72 jet, while the front run's the larger 75 power jet?

Also the Needles are marked J3LC,

If I understand correctly there are three sizes of needles used, A, B and C. Size B being standard and (my) size C being thicker, hence leaner mid range = less power and tractability.

Is this correct, if so are B needles available and can they be used with the needle jet's currently fitted?

Hopefully I'm getting there....
Many Thanx,
Regard's Phil

PS The battery's new and charging system ok, I tried trickle charging and running with no light's, in case there was slight power drain causing the PGM to go Doollally (technical term).

Didn't make a scrap of difference!!!


'01 TRX 850
'93 NSR 250 MC21
'76 Honda 400/4

Run a compression test when cold, then after the power drops off. Power will drop off after a while if your rings are worn, or the top end has high mileage. Just another suggestion.
_________________
Mike

Check your power valve & servo are working. The needles only come in a jet kit, they can't be used alone as the needle jet and holder are differnt then stock.

You should find the needles are different in each carb, not that I suspect it has anything to do with your problem, just letting you know as you are rummaging around in the carbs checking settings.

As previously mentioned, do some compression checks - one hot, one cold. It sounds very much like a possible case of "fair wear and tear", and due a top-end rebuild.

Poorer performance in the wet would certainly suggest corroded terminals somewhere however, so a good clean and check of everything you can lay your hands on (don't forget the earth [ground] points too). Corrosion and/or damp can indeed cause more resistance in different circumstances, and then possibly failure, and lead your fault finding astray!

Andy.
NSR-WORLD.COM

Hi guy's,

I did a couple of compression check's just after I got the bike, both cold and partially warm, both cyl's running at about 130 psi, so I don't suspect much is wrong.

As I've mentioned there's nowt wrong with the performance once the tacho hit's about 8K right up to the red line, it's ok upto about 5500 rpm too, it's just the bit in between!!!
Which is is why I'm now wondering what else it can be, lean midrange???

I'm now thinking my problem has been twofold;

1, Cleaning the various connector's seem's to have cured the power drop off that I was experiencing after the bike had been run for over 1/2 to 3/4 hour, and in particular in the wet.

2, There is a distinct lack of oomph between 5500 - 8000ish rpm, which is why I'm now wondering if the bike is running lean between these points?
The bike does instantly take off at about 8 grand though


I've now got the (borrowed) pipes off power valves are correctly adjusted and "slide" freely on their shaft.
When I stop when the bike is running crap (actually doesn't run badly, just lack's performance) and blip the throttle the valves seem happy enough rocking, doin' their stuff.

At the moment I haven't a clue what's wrong......

HELP!!!

I take it the carb spec's I've given are correct for a stock bike.

Any more Idea's greatly recieved!!!

Thanx, Regard's Phil

How sure are you that it's stock?

Might be worth a trip to the dyno to have it checked - a siezure isn't pretty!
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MC21SP Plaything
BMW F800GS Bumblebee
Triumph 9551 Daytona Big boys toy
FJ1100 Sporting relic
GTS1000 oddball

Hi,

I was starting to thing along the same lines. A trip to the dyno was on the card's anyway, I was hoping to have it sorted first and use the dyno as final confirmation that thing's are ok (or not!)

Speaking or which, can anyone recommend a knowlegable 2 stroke dyno guy, In the Cleveland/ N.York's area?

There is one in Malton and one in N/allerton, both about the same distance from me.

Anyone used them?

As for the bike being stock, with the exhaust's off, some porting work look's to have been carried out on exhaust and transfer port's.

It look's as though detonation ring's may be fitted to the head's, though it's bad to tell.

It's a crackin' bike but can't live with it like this. I'd sooner sort it than sell it!!!

Thanx all,
Regard's Phil

Yam TRX 850
Honda 400/4
Honda NSR 250