RD250LC 4500 to 6500 rpm stutter

[markrd250lc]

Hi All,

Looking for a bit of advice, i brought a 250LC in November 2020 that had sat in the previous owners living room for 7 years, good original condition, standard except JL pipes (Allspeed lookalikes).

Got her up and running before Christmas with a basic carb clean, new plugs etc, moted, and done about 300 miles on her but there was a huge splutter/flat spot about 4500 to 6500 rpm then she goes well.

So over the last couple of months i have tried/ changed new carb needles , pilots 2.0 to 22.5, mains 190/200/210, needle clip position all, and every combination of inc air screws!!

Today fitted new Tourmax float needles/seats , removed brass balls, stripped and cleaned the carbs/ choke and now all clean, did notice a weep from the head gasket so i changed that as well.

And now it pulls better from tickover to about 4500 splutters/misses until 6500 then pulls like mad (for a 250LC) until 10,000.

The engine has done 15500 and had never had the head off until today.

Starts fist/2nd kick and will pull to 100mph if kept above 6500 , plugs are a nice brown colour.

I have put everything back to stock except the JL pipes.

It feels like its running on choke when it splutters.

Where should i look next ??

Thanks
Mark 

[ajh]

I have same problem on my 350lc. Not sure if its same on 250 but the early 4l0 carbs needed a modification to the air correctors to re route the passage outside the inlet tract - Im just in the process of doing that to mine. hopefully it will fix it because Im out of ideas after that
The Yamaha service bulletin is published on the forum several times, should be able to search for it

If not relevant to 250 then air corrector jets just being blocked might be the problem

[Tobyjugs]

I think i've read a few threads on this forum about the JL lookalike Allspeeds being difficult to jet and people complaining about flat spots.

[markrd250lc]

Hmm i did wonder about the JL Pipes, i might fit the standard pipes and try that, going to ultrasonic the cabs as well ....... once i work out how to use the thing !!

thanks for your input.

Mark

[geoffb]

Non standard air filters will cause this type of spluttering issue as well but you did mention everything else is stock.

I fitted RamAir filters to my 4L0 and it took a while to get the jetting right but bigger mains and pilots has made it much better.

[rigga]

If it feels like its choking at that point, its probably running rich, try dropping the needle/raise the clip one notch and try again, it helped on mine when I was running LC carbs

[markrd250lc]

Funny enough i just took the top of the air box off went round the block and its better ..................but then the head gasket failed again (sham bits) time for genuine gaskets.

[midlifecrisisrd]

Deffo sounds like a midrange fuelling issue

You said you tried 190/200/210 jets

What was standard?

Steve

[markrd250lc]

Jun 13, 2021 12:05:26 GMT 1 midlifecrisisrd said:

Deffo sounds like a midrange fuelling issue

You said you tried 190/200/210 jets

What was standard?

Steve

190 standard with 20 pilots (standard) when i changes to 200 mains and 22.5 splutters more until 7000 then pulled to 11000 but was unridable, going to pulled the motor out paint the head and barrels and fit genuine gaskets and rings if i can find standard genuine rings, will ultrasonic the carbs as well .

[midlifecrisisrd]

Try 180's first and see how it feels as it sounds rich, especially in the midrange

Steve

[tony2stroke]

If its at a certain throttle position then its jetting, but if its at a certain rev range with different throttle positions then its something else.

[markrd250lc]

So quick update, i fitted new rings/ head/base gaskets (all gen yam) fitted reed spacers and boysen duel reeds, removed and cleaned behind the brass balls and the splutter is .................the same , but past 6500 goes really well better than before.
so today i moved the carb needle clip up one ( lean ) and it was much better only minor stuttering so moved it up again (one from top) and the stutter has gone and she goes very well but now from idle to 3500/4000 rpm it feels like its running out of petrol (full tank) so would this mean i need bigger pilots ( 2.0 at present) but i do have 22.5. i have adjusted the air screw from 1 1/8 to 1 3/4 and everything in between and no difference

thanks

Mark

[Tobyjugs]

Hi Mark, be very carefull about dropping the needle down that far. It might help cure the stutter but It could also make it too lean a little further up. Your heading into seizure territory. At the very least do some plug chops at 1/4 throttle or better still get it on the dyno bank with an experienced 2Stroke man with or without a gas analyser.

[markrd250lc]

Jul 24, 2021 18:04:01 GMT 1 Tobyjugs said:

Hi Mark, be very carefull about dropping the needle down that far. It might help cure the stutter but It could also make it too lean a little further up. Your heading into seizure territory. At the very least do some plug chops at 1/4 throttle or better still get it on the dyno bank with an experienced 2Stroke man with or without a gas analyser.

Thanks Mr TJ i did think it may be to lean, going to try the bigger pilots ( when it stops raining) and drop the clip back down one again , worst case it goes bang so 375cc convo will be ordered 

[muttsnuts]

lift your needles back to mid clip position (3rd groove) and drop to 180 main, then try it, leave the pilot at 20, air screw should only be 1/4 to 1/2 turn out (no more despite what the book says), then try it and see how that goes

[markrd250lc]

Just waiting on new needle jets as I'm assuming they are worn as the needles were banana shaped , then I'm going to reset to standard, i will also order some 180s, and try that with the clip mid way.
i cant remember all this faff in the 80s , short can Microns , 240 mains no issues 
Thanks
Mark

[marknet]

Where are you getting the needles and which ones

[stusco]

Aug 6, 2021 17:45:41 GMT 1 markrd250lc said:

Just waiting on new needle jets as I'm assuming they are worn as the needles were banana shaped , then I'm going to reset to standard, i will also order some 180s, and try that with the clip mid way.
i cant remember all this faff in the 80s , short can Microns , 240 mains no issues 
Thanks
Mark

I think we just put up with the splutter and rode round it (slipped the clutch) all part of the charm😁