Hi all. Newbie here. Having trouble getting my stock 92 mc21 nsr250r se to start, cold or hot weather makes no difference. Got a service from a reputable service centre about 1.5months ago and everything was running beautifully until I took it for a 250km ride last weekend. On the way back I just made it to a fuel stop before I ran it completely dry. The next morning; no start.
She sounded like she wanted to go i.e. revs pop up to 1k then died. I left the bike for about 3hours and then tried again. After about 20mins of kicking and up and down a hill I finally got her to fire. Ran fine, wit no pops or back fires, but when ever I applied some choke the revs would drop dramatically.....
With the knowledge I found on previous posts (thanks so much to all of you) i was able to get the carbs off and cleaned, that is a first for me so I feel that much closer to my bike. All carb inside components seemed to be ok i.e. float height, no blockages etc.
She fired 4th kick and i was chuffed with myself. However, next morning same issue as it has been for the last 4days.
Got the carbs off again today and adjusted the air screws back to stock (1.5turns) they were at 2 1/4 lhs and 2 2/3 rhs. took her for a run and all seems ok but the choke still causes the revs to drop.
The only other thing to note is that sometimes when I am riding at a constant speed and I close the throttle the revs hang for a while until i touch the breaks at which time the revs drop...... Also spark and compression seem ok.
As I have said I am a newbie in regards to the mechanical side and have read so many post to try and figure out this problem, but I think I am getting bogged down with all the possible causes and with my limited knowledge I am unsure of where to turn. Plus I don't want to take it back to the shop, I want to learn how to do this myself. So I am sending out an S.O.S to all other NSR lovers, please help. If you need more info just give me a yell.

If it is holding on to revs then your pilot jets are blocked and this would explian why it wont start either. Strip the carbs again and clean them again, use a compressor if you can.

Thanks for the reply epa police. When I had the carbs off the first time I took out all the jets one-by-one and cleaned. Don't have a compressor but used my lungs. Little bit of black gunk came out of one of the jets but the rest seemed clear. I'm in nz, no garage and its gunna get dark soon so may have to be a tomorrow arvo affair. will get the carbs off again and have another pock around albeit genitally. Any other thoughts on why the choke is not working as it should?

How old are the spark plugs? What about the fuel in the fuel tank? Have a look in there and see if your tank is rusting away while you are at it. Any fuel filters? Check those too.

What sort of volts are you getting on your battery? I don't think that would be it, but no harm in checking too.

Don't undertand what you mean about the choke. On my mc18, I only use the choke for cold starts. Fire it up, with the choke on it should idle around 3k. I let mine warm up on the choke for about 1 min then close the choke and the bike will idle at around 1200 rpm. You shouldn't need to touch the choke again. Are you saying that when you apply choke when the bike is hot the revs drop? Does the bike idle in the first place? Have you got a fuel filter in-line? I had this problem, whithout a fuel filter, some gunk from the 20year old tank would clog up the float needle. Carbs off, clean, run fine, more gunk, carbs blocked again. A fuel filter fixed it no worries. Have you checked your coil connections? Pitted or corroded/loose connectors can produce some funny symptoms. Checked your battery voltage? Should be 12.5 v rising to around 14.5 volts at 2000rpm. All of these can make an NSR hard to start. Good luck!

Plugs are 2 days old. had a set of br8ecm changed back to 9s. as for the choke: can't start the bike with the choke on. when i do get it started it idles really roughly (rpm fluctuates) so try and put the choke on ramp up the revs but it drop below 1k and wants to stall. pvan340 your start up sounds much like mine was a week ago. I learnt how to warm it up a while ago, would leave it idling for way to long and was fowling the plugs.... lesson learnt.
Wanted to replace the battery anyway, not sure on the voltage will borrow a multi-meter in the coming days.
Fuel Filter???? Hope this is not a face-palm moment: fuel line seems to have a clear bit of tubing in the middle joining the line. thought it was an in-line filter or something. may have to check that.....
thanks for your time guys...

follow the choke lever to the cable that goes to the carbs. Check that things move back and forwards.

Check your airfilter, open up the box, check the intake tract, airfilter element and then put it back on. I usually put the lower half onto the carbs, make sure that is secure, the place the element, the element holder and then fasten the top of the box. It makes sure you get a proper seal.

So you suspect an air leak as a possibility?.... have a new air filter as of the service date. but will check when i have it apart tomoz. Any other problem spots for air leaks?

Side Note, nxrsr20: any ideas on cost of freight from melb to auckland for a bike. have another mc21 back in aus(near bendigo), has a busted up front due to a taxi thinking he could nip in front of me at 50k/hr. would love to get it over here for parts or rebuild project.

For a mechanical newbie you know a fair bit of stuff

I don't really suspect an air leak, that would be causing revs to rise, not hard to start issues (unless you haven't seated the carbs).

Dumb question, but how reputable is the service shop? You trust them enough to know that they changed everything for you? The NSR airfilter is not something that any shop would have on hand unless they made one from a foam piece.

hmm I will chat to a few kiwi work mates and see if they have carted anything over the ditch back home. Bugger about the Bendigo bike, is it really worth shipping over though?

Definitely a newbie but as I said have seen so many posts, just with no hands on knowledge. My dad is a mechanic but when ever I walked into the garage, tools and profanity would fly my way, so that kind of scared me off mechanics until now haha.

The shop did a good job with the service, made a new air filter for me from foam. Really dont think its their workmanship, thoughts are leaning towards a blockage somewhere after your comment about the fuel tank. Tank looks ok, good steel colour throughout, but i did run it near completely dry, could have still been some nasties floating about.
There was one part of the carbies that i could not get off: there is 2x star screws on the engine side(i think), what is behind that? went to get the right tool for removal but they were charging $60NZD for a set, no thanks bro.....

As for the the aus bike: just wanted some parts off it that weigh quite a bit so maybe cheaper to get it all over rather than posting individual items.
Thanks so much for your time and suggestions mate.

Woop woop woop. just went out, started first kick . 10degrees outside and she has been sitting for 4-5hours. fingers crossed for tomorrow morning.

I can't remember the part with the special tool on the carby, maybe someone else can shed light on that.

Since you are not using a standard air filter, check your jetting and adjust if necessary. You check your jetting by doing a plug chop, discussions on jetting is not allowed in this section of the forum (forum rules), but folks are more than happy to help in other ways.

Ok, so bike started ok in the morning. Cold so i tried some choke, same result: revs dropped below 1k. Performed regular warm up procedure wit no choke. Once warm, revs were jumping from 1k to 2k, gave her a bleep revs dropped to 1.25k then jumping started all over again. Revs really rough but no stall so off to work.

On the way home I tried what i thought was a plug chop: high revs up a hill then hit the kill switch.looked at the plugs and they were a tan colour = lean, but i have the air screws set at 1.5 turns as per stock set up??????? day temp was about 15degrees. Maybe an air leak somewhere? took the air box off and the filter the mechanics made was really rough, with gaps around the edges in some places, but the box itself has a good seal. carbs and box seem to both be seated correctly..... Started her and the same rev jumping was going on.......

Only other thing to note was the front cylinder: at idle it was 'off beat' compared to the top. with a little throttle both seemed to 'pop' in time.

On both carbs: main jet = 128, Jet to the left = 38........

Frustratingly intrigued!!!!!
Please help, Gods of NSR knowledge!!!!!

Sounds like you are on the right track. You need to get your hands on a multi-meter and check the voltage at idle and as the revs rise. Sounds like it could be electrical? Get some contact cleaner and start taking connectors apart and giving them a clean. Will help you get a good handle on the NSR electrics and give you a chance to do a bit of preventative maintenence.

One story I have heard....

Has your tank been lined with anything? Read somewhere of some of the tank lining lifting around the fuel pickup in the tank. Full tank, lining floats, as the fuel drops, lining falls over the fuel pickup, fuel starvation, poor running as a result! Just a suggestion while you have the tank off checking other areas!!

Good luck!

thanks pvan340, have had the carbs off and cleaned 3times so far, getting familiar with it quickly. electrics are the next step i think. contact cleaner available from most auto shops? Might get the the tank drained and check the pickup. does the mc21s have a mesh filter at the tap?
thanks again