Jetting advice
 

Hi

Can some one start me in the right direction with jetting. As a recent 4 stroke convert, I have limited experience with 2 stroke jetting, other than getting my son's RM85 to run properly.

Bike: 2010 EC300 6 days, Gnarly pipe, just replaced the stock piston with Wossner kit, and cleaned out the top end which was a bit coked up. Left the base gaskets at 1.1mm to match the exhaust port height. I didn't have the correct thickness of solder so I haven't checked the squish yet, but I know that this bike has been maintained as stock rather than modified so it would probably benefit from being reduced.

Jetting is currently stock
38mm AS2
N1EF clip 1
MJ 165
PJ 35
#7 slide

Riding - Based in Cyprus. Anything from fire trails to real gnarly single track and dried river beds
Winter 15-20 deg C, 0-1000m
Summer 20-30+ deg C, 0-2000m
Humidity typically around 65%

I haven't ridden it since blowing the dents from the pipe and replacing the piston so the symptoms may have improved, but it was bogging at the bottom end, not pulling cleanly until PV opening. At 50:1 it was blowing unburnt oil out of the exhaust and smoking lots. I was advised to swap to 60:1 which cleaned up the exhaust but I would feel happier running 50:1 for a bit more engine protection. Plug was black and a bit oily.

I'm not looking for jetting perfection at the expense of regular adjustments due to temperature and altitude changes. Instead a good working setting that can cope with temperature and altitude changes, improve running and also fuel range.

Parts availability in Cyprus is a bit patchy so I will probably have to order in from UK or mainland Europe. So far I have tracked down suppliers who can send me standard Keihin needles and the Yamaha needles; I have drawn a blank on the Suzuki needles.

So can someone start me off with advice for a minimum order - a needle, couple of mains and pilots that will get me sorted.

Thanks in advance.

The needle is the problem.

Order Suzuki RM250 needle: NEDJ
Part: NEEDLE, JET (NEDJ) (13383-37FM0)

42 NEDJ#2 (second from top), and 172 main jet.

You might want to grab a 168, and 170 main jet as well to test with, but start richer.

That will get you much closer to where you want to be.

Thanks Jakobi. The Suzi part number made the difference and I have managed to track down a supplier.
Will the pilot be ok at 35?

Edit - I'm assuming the 42 is pilot?

Yes, Jakobi is recommending a 42 pilot jet. The 35 you currently have will be too lean with the NEDJ needle.

As above :D

Thanks for the advice guys. New needle and jets ordered and on their way to me.

https://www.jdjetting.com/xcart/home.php?cat=15

Maybe just trying to keep it simple, but I have used the above with no problems. Gives you needles, pilots and mains with chart. Has worked spot on for me in Arizona.

Thanks to the joys of international postage I am still waiting for the NEDJ to arrive but I do have the jets. I am hoping the needle arrives this week as I have a race next weekend and I need to get rid of the off idle blubbering, excessive fuel use and almost non-existent idle.

My other alternative is a N3CH which i was given today. Any recommendations for jet sizes and clip position with this needle?

The other problem is that while I can spare some time to swap them over any testing is going to be very limited, especially since I will also need to clean the filter, change tyres and attempt to straighten the side stand after another rider attempted to park his bike on top of mine today - strangely enough the stand does not support the weight of two bikes plus a rider :(

40 N3CH#3 178 main.

Thanks. I might have to hope that the NEDJ turns up because I haven't got a 178. I will be able to get hold of a 175 though - close but I don't want to run lean.

Just checked details again, given you've been running a 165 main with the N1EF you'll probably have no issues with a 175 main with the N3, or probably even down as low as a 170... based off your current main being OK.

The H diameter might be a bit rich still though, and especially with a 40 pilot. 38 may be closer.

Waiting on the NEDJ should get you closer quicker, I think.

Thanks Jakobi. You are a legend.

I'll give it a couple more days for the NEDJ to arrive then use the N3CH if it doesn't. I have mains in 172 and 170, pilots in 42 and 40 so should be able to find something that will be an improvement on the N1EF for the weekend and swap for the NEDJ when it arrives - sods law says this will be the day after the race. I doubt I will be spending much time on WOT, if any, so if the main is a size off optimum I should be OK.

Well the NEDJ arrived before the enduro and I fitted it on #2 with the 42 and 170 but quickly swapped back again. It started fine and the initial throttle opening was crisper but beyond 1/4 throttle the engine would quickly foul the plug and stop running. I didn't have time to play with it but I suspect it wants the needle dropping to the 1st clip and a smaller main.

It seems that my bike needs a leaner jetting. I still have to set the squish, which is probably a bit wide, so I don't know whether this is the reason.

I think I might have just identified my problem. The original owner was insistent that the bike used to run beautifully with the current jetting so I started wondering whether there might be another problem.

It has a new piston, the dents blown out of the exhaust and silencer repacked so that was all ruled out.
I got a bit more analytical about how the bike was running - bogging at low revs but clearing higher up, regardless of throttle opening, suggesting it could be something other than jetting.
I had an idea, did a bit of googling which supported it, then pulled the reeds. Bingo! 2 of the petals are chipped along the edge - just enough to affect the seal and allow a little leakage back to the carb at low air velocity.

Nice work! That'll do it for sure.. and you'll never out jet a mechanical issue!

Swapped the reeds and running better. Still rich and blubbering below 1/4 throttle but the lack of power at lower revs due to air leaking back past the reeds has gone.

Dropped in the NEDJ#2 and 42 pilot today and it pulls a lot cleaner. Still a hint of hesitation just as the throttle is opened but only given it a quick beat up the road and back so far. Centre and earth electrode much cleaner but still looks sooty on the outer ring. Out for a run tomorrow so I'll see how she runs and check the plug when I get back.

Since you fixed the problem try putting your settings back to where they were in the first place and try it. Previous owner claimed it ran great, right? I have an N1EF needle with a #7 slide in my 05 ec250 and have no problems down low. No bobble and pulls like a 4 stroke. Hope you get it ripping good!

Been a while but haven't been able to get out much due to other commitments.

The NEDJ#2 was working well with 165 main and 42 pj with fuel consumption improved and pulling much cleaner than before.

I was able to wind the idle screw out a turn which allowed the air screw to come into play - previously it had no effect as so much air was coming past the slide.

So I was pretty happy with it until I went for a ride up in the mountains (around 1000m, 30C) at the weekend. The bike was almost unrideable with very little pull until the power valves opened. On hill climbs (long steep fire breaks) the I was struggling to keep the bike on the pipe in 2nd when it should have been able to fly up in 3rd or more. On technical climbs it was even worse as once it came off the pipe it wouldn't even pull up in 1st and I was unable to get up stuff that should have been well within my capability.

Back down the hill and normal service is resumed so it was nothing more than a bit of altitude sickness. I have dropped the needle to the #1 today which has removed the last bit of hesitation as the engine comes on pipe but that is close to sea level. No idea whether this will be enough back up in the mountains.

I am wondering whether the NEDJ needle is more sensitive to altitude changes than the stock needle - is that possible? I also think I will need to get a leaner needle than the NEDJ for riding up in the mountains (up to 2000m) since I am already on #1. I don't know whether I just need to get a needle which is a clip or 2 leaner or change the diameter or taper, and what about the main? Advice please...

In my current stock I have the NEDJ, the stock needle and N3CH which I haven't tried yet.

TIA

Was it getting rich at altitude? or was the added load from climbing causing it to lean out and lack torque? These engines do make more 'grunt' with a bit more fuel. I have tried going leaner many times and you get a very responsive snappy power delivery which feels great under low loads and on fire trails, but once you get in the hills it falls flat.

It might not be the problem you have though, but keep an open mind to it.

If you haven't had the squish reduced, that's where I'd be looking. Makes the engine much more consistent and resistant to changes in temp, humidity and elevation.

I don't think it was leaning out from added load while climbing as it was also suffering on the roads.

I do think you are right about the squish though. One of the first things I did was replace the piston since this had never been done and was at around 350 hours. I removed 2 base gaskets but was unable to measure them as they tore when I lifted the barrel. On reassembly I used what I thought was similar thickness gaskets and chose the thickness to set the piston level with the bottom of the exhaust port on BDC. If I have used thicker gaskets I will have opened up the already wide stock squish band. This has got to be a priority.

Found time to do a bit of tinkering and jet swapping this afternoon. Fortunately I have a km of 10% gradient twisty road at the end of the street so I am able to give the bike a pretty good run to test out the effects of any jetting changes with the engine under load. Going up on the main definitely made things worse with the bike struggling to pull until it hit the power band, much like it was at the weekend. #1 on the needle is also giving the best response.

For the moment then I can't do any more with the jetting as I am as lean as I can go without getting more brass. Since the plug looks spot on now, and my jetting is leaner than most of the settings in the database, I don't think that is necessary.

I'm back up the mountain at the weekend so I will see how it works then.

Next stop will be checking and correcting the squish.

If you get the squish down to somewhere useful, like 1mm, you will need to cut area out of the chamber or the compression will be several orders too high. But super worthwhile

Had a revelation today.

Was up in the mountains again and the bike was definitely better that last week but still lacking in mid-range before it came on pipe. I had all my brassware with me this time though and swapped back to the N1EF#1 and 35pj. Of course this brought back the bobble up 1/8th throttle which the NEDJ had removed but after that the bike was so much better. Where I had been struggling with to keep the revs up high enough to prevent the bike bogging, once I got through the initial off idle bobble the bike pulled much stronger and was much more controllable coming on the the pipe.