Hi everyone,
Got my 18 back on the road today but I have found it has a really frustrating misfire
At first it only seemed to be at 8000rpm +. After loads of messing and fitting new plugs, checking the RC valve positions, checked the plug cap/HT lead connection, the coil connections and cleaning the carbs its still no better. It seems only to be on the right hand cylinder (but hard to tell) this side is smoking a bit more.
I went out again and tried different throttle openings and at 1/4 - 1/2 throttle she revs to the redline as sweet as a bird through the gears. Then I tried opening the throttle 3/4- to full throttle and she misfires at virtually any revs like 5-6000rpm.
My thoughts go to either the throttle position sensor, the PGM or wildy out jetting. Its a PGM1 running 175 mains on premix which doesn't seem that far out looking at other threads.
How can I check or eliminate the throttle position sensor? Can I just unplug it? or can this do any damage to the PGM.
Any other thoughts or help much appreciated,
Ade

Sounds like its a tad rich, I had this on the lower cylinder when i was playing with the 300 on my 18. That would stubble and cough between 5k and 8k.. then clear and go like the clappers. In the end i ended up fitted power jets and running smaller mains, this gave me more control over the mid range fueling with the needle.

One way to test it.. find a hill.. ride up it with it at the point where its coughing and kill it. Check the plugs.. no doubt one of them will be wet and black.
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If I have to take the carbs off once more...

urmm, I wonder if it was running without the airbox previously??

I was just calculating the jet size increase for premix and it only works out to say 135 from 130's @ 30:1. does that stack up?

I'll try the "Hill Test" and then without the airbox tomorrow.
Cheers Stephen

All depends on what state of tune the bikes in. MC18's seem to like around 128-130 main jets (and the stock power jets) if running race pipes and a mod'ed air box. Both myself and Wayne tryed running richer only to find they hated it. Of course if youre running pre mix you will have to calculate what to add on to the 130m/j to get the same effect. With an air box 175m/js does sound very large but not unheard of.
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If I have to take the carbs off once more...

If I have to take the carbs off once more......... (Now I now why Stephen says this!!!)

I went out this morning with the airbox off (no jets available on a holiday monday) to try a plug chop whilst spluttering, and descovered that when it started to splutter, it kept on spluttering untill I'd slowed down and shut off for a few seconds. Then trying again, it reved clean to the redline for 2 gears and spluttered again.
Arh hah! maybe its fuel starvation???

Carbs off again, measured the float height and they are 20mm!!
Searched the forum and found 13mm for all NSR's and looked at the picture for height setting.

However, the floats look a little odd, as other bikes I have worked on the mould line on the float often looks parallel to the chamber face when the height is correct. On mine they are at quite an angle, then I'm thinking has someone put them in upside down ????

On mine the round part of the float is showing with the flat side up inside the carb, is this correct??

P.S. By the way the P/Jets is blocked off and is running 175 Mains

Sorted!!
It looks like it was just a case of finding how it had been set up and running before I had it.
Set the float heights correctly at 13mm, and had to run with the airbox lid removed (strangely it did not run correctly with no air box at all)

175 mains with the PJets blocked off on premix, plug chop looks good.

I want to run with the airbox lid back on (too loud), anyone any idea of where the main jet size should be leaving the PJet blocked off & premix??
What is the usual increase for running no Pjet?

Have you modded the lid? Cut the web out of the middle, and cut a whacking big hole in it. Some drill several large holes in it, I just cut the whole back end off where the tiddly intake pipes are. Makes a hole about 5 inches square.

You may find this is enough to continue using the jets you have while masking much of the noise.
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MC21SP Plaything
BMW F800GS Bumblebee
Triumph 9551 Daytona Big boys toy
FJ1100 Sporting relic
GTS1000 oddball

Forgot to mention,
I only did three miles from home and the Law pulled me over !!

They said they heard me coming for at least a mile!!

It has race pipes, but I think the induction roar was louder, so unless its a major loss to power I would like to keep the airbox standard.

You wont lose much power if any at all by keeping the air box. I managed to get just over 63bhp out of mine with an air box fitted that was very slighty modded.

I tryed playing around on the dyno with and without lids and with parts hacked off. I ended up running just 2 x 1" holes cut into the lid roof. This gave the best results. The best i saw without an air box was 61bhp plus it took an age to sort out the mid range fueling. Im sure ive gone over this before but engines love large volumes of still air which is exactly what an air box gives.
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If I have to take the carbs off once more...