Jetting time

[rd400canuck]

I followed the jetting chart from the tech library. Really like that... seems like the easiest to follow.

Seems like, at 50f, my bike wants the stock 25 pilot at half a turn out. When I had the 27.5 in it I turned it to 2 turns out and it revved higher. I'm guessing when it's warmer out I might be able to turn the air screw out a little more.

[rd400canuck]

Maybe I was wrong about the 25 pilot being the right one... I went for a ride today at 1/2 turns out and the needle in the middle. I was doing mostly steady 40-45 mph for 10 mins or so. When I got home I thought the engine felt hot so I pulled a plug and was certainly running lean. Hard to tell exactly because the plugs were dark colored before I set out but they were defo lighter, and not brown in any sense.

I wanted to ask... it seemed to me at that relaxed pace I was barely into the throttle.  Maybe 10 - 15% is felt like. Does needle position have much effect at small openings or does the pilot play a big part in riding like this?

[SUPERTUNE]

I did say to use bigger pilot's... don't worry if you need the air screw out past 2 turns.
Chuck

[SoCal250]

I wanted to ask... it seemed to me at that relaxed pace I was barely into the throttle.  Maybe 10 - 15% is felt like. Does needle position have much effect at small openings or does the pilot play a big part in riding like this?

Pilot

[SUPERTUNE]

Thanks for that Russ!
Your our home encyclopedia!!
I forgot about that one and didn't have it saved on my computer...
Chuck

[Yamaha 179]

Take a piece of light colored duct tape and wrap around the throttle housing.  Then pick a spot on the hand grip next to the tape where you can make a noticeable mark.  Then use a magic marker and make four marks on the duct tape corresponding to throttle opening: 0 - 1 - 1/2 - 3/4 - F.  That way you will know which jet range you are working with. 
Lyn Garland

[rodneya]

I followed the jetting chart from the tech library. Really like that... seems like the easiest to follow.

Seems like, at 50f, my bike wants the stock 25 pilot at half a turn out. When I had the 27.5 in it I turned it to 2 turns out and it revved higher. I'm guessing when it's warmer out I might be able to turn the air screw out a little more.

2 turns out the pilot was good, why did you go smaller?

[rd400canuck]

I followed the jetting chart from the tech library. Really like that... seems like the easiest to follow.

Seems like, at 50f, my bike wants the stock 25 pilot at half a turn out. When I had the 27.5 in it I turned it to 2 turns out and it revved higher. I'm guessing when it's warmer out I might be able to turn the air screw out a little more.

2 turns out the pilot was good, why did you go smaller?

When I put a 30 in after the 27.5 seemed to be lean after I leaned the needle the off idle got weaker. I suspected the 27.5 was the right one but I wanted to start over so I went to the stock 25 and put the needle back in middle position. Honestly the off idle to 1/4 really seemed the best with the 25 at 1/2 turns out so I convinced myself it was good until I pulled the plugs after that 10 min ride. TBH the bike ran better than ever before with no dips or peaks in output when I open the throttle.

I didnt realize that the pilot jet played such a major role in 0 to 1/4 throttle. Now that I see that chart that Russ posted I see it plays a very big part in the steady cruising speeds around 45mph. I swear... to keep it at this speed it feels like I am only opening the throttle 15% of the way.

Today I will also mark the throttle positions like suggested so I can see where I truly am while testing

Thanks gain everyone... keep you posted.



I'll put the 27.5 back in and start the process of air jet adjustment testing again to see where it revs the most.

[SUPERTUNE]

I followed the jetting chart from the tech library. Really like that... seems like the easiest to follow.

Seems like, at 50f, my bike wants the stock 25 pilot at half a turn out. When I had the 27.5 in it I turned it to 2 turns out and it revved higher. I'm guessing when it's warmer out I might be able to turn the air screw out a little more.

2 turns out the pilot was good, why did you go smaller?

When I put a 30 in after the 27.5 seemed to be lean after I leaned the needle the off idle got weaker. I suspected the 27.5 was the right one but I wanted to start over so I went to the stock 25 and put the needle back in middle position. Honestly the off idle to 1/4 really seemed the best with the 25 at 1/2 turns out so I convinced myself it was good until I pulled the plugs after that 10 min ride. TBH the bike ran better than ever before with no dips or peaks in output when I open the throttle.

I didnt realize that the pilot jet played such a major role in 0 to 1/4 throttle. Now that I see that chart that Russ posted I see it plays a very big part in the steady cruising speeds around 45mph. I swear... to keep it at this speed it feels like I am only opening the throttle 15% of the way.

Today I will also mark the throttle positions like suggested so I can see where I truly am while testing

Thanks gain everyone... keep you posted.



I'll put the 27.5 back in and start the process of air jet adjustment testing again to see where it revs the most.

Don't put too much emphasis with the air screw for this. Do it by how it runs and idles when riding and coming back to idle.
I've run 30 pilots no problem.
C

[rd400canuck]

I actually just noticed it not settling into idle after a mall throttle blip if I went to 1.5  turns out with the 27.5's. I ended up at 1 turn out and went for a ride with throttle positions marked.... for sure just taking it easy and not really going faster than 50mph I rarely pass 1/4 throttle and once i am at a steady speed I am closer to 1/8 than 1/4. OK, so now Ive learned the pilot jet is more than just for idle and immediately off idle like I always thought it was for.

I did notice a little surging when closing the throttle and coasting to a stop from around 40mph. Nothing crazy, ive felt worse but there was still some... does this indicate lean pilot setting or is the normal for completely stock RD400?

Should I am to eradicate the mild surging?

[SUPERTUNE]

Most stockers have some surging.
What pistons did you use?
C

[rd400canuck]

Orig Yamaha's

[SUPERTUNE]

That helps a little.
Stock oem RD400 C, D and E models pistons used a burp notch in the bottom of the piston exhaust side skirt to help alleviate low speed surging by burping to the exhaust port at top dead center.

Banshee, Wiseco and Wossner do not use the oem Yamaha notch.

Chuck

[SUPERTUNE]

Another trick to do when rebuilding the carbs is I drill out the airjet ball then tap for a 5mm x.8 setscrew, to replug, then drill out the air jet and tap for a real Mikuni removable air jet with a 4mm x.7 tap then I use a .7mm air jet over a .5mm stock pressed in jet. this helps run a 30-32.5 pilot jet and helps the surging with a stock baffle mod.
C

[rd400canuck]

ok, I went out farting around town and I went went from 1 to 1/2 turns out and the surging at closed throttle has just about disappeared. Once I get used to the bike like this I'll try the 30 again and see if 1/4 and below throttle improves. Its kind of hard for me to tell sometimes the difference can be so subtle.

I did something really effing stupid today. I was using a 3-cell lipo as a stand in while I was doing all the wiring over the last couple weeks. I totally forgot it was in there and 10  mins into the ride I was sitting at a turning lane waiting to turn and flames started shooting of from under the seat and around the oil tank. I assumed it was fuel and I panicked because there was no way I could put this fire out and I was sure my bike was going to burn to the ground and create one hell of a scene. I pushed the bike to the corner and it dawned on me that it was the battery so I opened the seat and there was a huge fire under it. Black smoke everywhere. I knew there was a chemical fire in the battery bay and if I didnt get it out it was going to burn my bike to the ground. I reach in quickly 2 or 3 times and pull out chunks of flaming lipo. Im so pissed off with myself :(  Could have been very bad.

Effed up my finger tips. Doesnt look too bad but hurts like a mofo.