Low revs stuttering

[Anarch]

Hi all,
Since last year I've noticed stuttering on the low revs - up to 3/4 000 rpm. When i keep the revs at around 2,500 rpm the engine sounds nearly like an old two stroke.
I've searched for similar threads on this forum, followed the advice there and I've:

- replaced plug caps
- checked spark plugs
- balanced carbs (Autumn)
- I've added some carb cleaner to the fuel (Profi Fuel Max) - didn't seem to help much

I think that there are two possibilities left - either the HT leads (and coils) need replacing or the jets are clogged.
Do you know how can I check whether the HT leads are faulty, and what should I use for cleaning carbs (once I open them up).

Or maybe you have some other ideas ?

Thanks

[ade the blade]

Paul.......i think your expertise in this area is needed please !!

[darrsi]

anarch try some 99 octane fuel, I noticed an improvement when I had this woe.

He should be able to run on any fuel, higher octane will just make things a bit nippier.

[red98]

cheers ade  ....i would go for a carb clean before the coils,they dont fail very often...clean the carbs with a blast of compressed air and plenty of clean cloths 

[Anarch]

Well I usually put Momentum - so it is 99 octans.
I don't have access to a compressor, and don't really fancy cleaning all the parts at a gas station -> will a compressed air spray do ?

Will there be any seals / orings that I'll most likely have to replace (would prefer to buy some earlier) ?

Thanks

[Dead Eye]

I would have thought that a can of compressed air would be good enough. Just check each jet and make sure there is no dirt / obstruction in them. I cleaned mine out with a fine needle and left them in fresh petrol overnight (no idea if this was a good or bad idea though...). There are a few O-rings on some of the jets if memory serves, but I doubt you'd need to replace them - guess it couldn't hurt though. Check out http://www.yamahascooterspares.co.uk for a full list of genuine OEM parts

[red98]

soaking in petrol is good and then in the morning just blow through them using good old man power....be surprised if the "o" rings need replacing 

[Anarch]

Thanks a lot guys Will give it a go when I have some spare time (probably early June)

[WookieoToole]

clean the idle jet and gallery and while ya on do the main jet and emulsion tube -- u will need a alkaline based cleaner and make it undiluted -- so far since november i have had 4 bikes thru with that same prob
Hope this helps

[caretaker]

air filter might need changing?

[Anarch]

air filter might need changing?

Nope, I've got a new K&N one. WookieoToole - thanks for the advice, will have a look at alkaline carb cleaners,
Should clean the carbs next week.

[Anarch]

Update - cleaned the carbs as well as I was able to - but they looked quite clean (no clogged jet screws etc).


Did balancing and replaced spark plugs today  - but I haven't noticed any improvement. The only other idea I have is replacing the HT leads with coils - I checked the spark and its colour was closer to yellow rather than blue (it was blue at the ends).

[Punkstig]

While you've got the tank off etc have a go at resetting the pilot screws, screw all the way in then back off (what is it on these 2.5 turns?) won't do any harm and you know in your head its done and they're all the same.


Only mentioned this cause it fixed my issue on the T'cat,  but for that fix I changed the settings to what was mentioned on a forum and not what Haynes said!

[Anarch]

 I followed Hayness, and put them in the same position as they were in originally - it ranged from 3.5 to 5.5 turns (by turn i mean 180 degrees).


Going back to garage now to play around with the pilot jets

While you've got the tank off etc have a go at resetting the pilot screws, screw all the way in then back off (what is it on these 2.5 turns?) won't do any harm and you know in your head its done and they're all the same.


Only mentioned this cause it fixed my issue on the T'cat,  but for that fix I changed the settings to what was mentioned on a forum and not what Haynes said!

[Punkstig]

Best not confuse things, 1 turn = 360 degrees, could easily make mistakes if you treat it any differently!
K&N filter plus aftermarket exhaust and it could probably help to experiment with the screws, probably quarter turn on all at a time!

[Andy FZS]

Correct me if I'm wrong (again) but I thought the running mixture was determined by jet and needle size and the mixture screws only set the idle mixture so a stutter at 2.5k wouldn't be effected by these. Anybody agree?

[Punkstig]

While you've got the tank off

2 minute job while you're in there!

[Anarch]

While you've got the tank off

2 minute job while you're in there!

2 minute job...  I've been trying to figure out for the last 20 minutes how to access pilot jet screw on the 3rd carb and so far no brilliant ideas.
I've got a brand new K&N filter - exhaust is aftermarket (blue flame), but having a tiny leak in one or two places (on one of the joining points near rivets).


P.S. After I readjust the pilot jet screws, should I balance the carbs again ?

[Punkstig]

Ha, well typically all photos of carbs in Haynes is of the thundercat carbs, not sure how much difference there is because I haven't had to do this yet, but will be soon!


If it helps '98- '01 is 2 turns out and
'02-'03 is 2.5! (When you get to adjust No. 3 that is!)

[Anarch]

Ha, well typically all photos of carbs in Haynes is of the thundercat carbs, not sure how much difference there is because I haven't had to do this yet, but will be soon!


If it helps '98- '01 is 2 turns out and
'02-'03 is 2.5! (When you get to adjust No. 3 that is!)

You're right 2.5 it is - checked in my Hayness as well,
I think bones in my hand shifted after 30 minuts of fidling with it and I've managed to squeeze my hand in there and set the screw on the 3rd cylinder.

[Punkstig]

We're they set correctly and equally or did you not count when turning them in?

[Anarch]

I've counted when dissasembling carbs, now changed all of them to 2.5 turns + balanced carbs and no real change.

[neilavo62]

hi,
    i also put a new K&N filter in this year and developed the same problem.
i have since put the baffles back in and it sorted the stutter out.
hope this might help..

[red98]

mmmmmmmm...had a scorpion end can on my thou....very lumpy idle and uneaven upto 3/4000 rpm,great at higher revs,put the std can back on and now very smooth,has k+n filter 

[Hedgetrimmer]

All very interesting - got a similar problem on my thou. Was much worse with open Viper can which was on the bike when I bought it. Changed to standard can, better but not right still. Have just put new Scorpion can on, as good as standard, but still not right. Problem seems to be at worst at about 3k rpm off throttle. Everywhere else, no problem. Can't work on my own bike due to shoulder problem which makes things very awkward, so sooner or later gonna have to take it in somewhere and lay out for someone else to take a look 
Pilot circuit problem?