Help with proper jetting

[Awk08]

that's not a stock head making 150+ psi.

 

[chuey_316]

That's what I was thinking. I'm wondering if a previous owner milled .30 or so off, and that's why it hasn't been running right.

I was running 87 octane. Yesterday I had maybe a 1/4 tank, and I mixed in a gallon of 93, and it seemed to run better. Still a bit choppy on the top end, and not as fast as it should be, but low end and mid range is there. Didn't get to do a gps wot run, but I'm hoping to get out again tomorrow.

May end up pulling the head to have a look, but not till winter. Gonna salvage what little bit of halfway decent weather before the snow starts to fall.

Still need to do a warm compression test. I'm curious to see what the #'s are when the engines at operating temp.

Would the milling/higher compression affect jetting?

 

[chuey_316]

Found yet another thing throwing of my jetting. The previous owner didn't seal the pipe to the flange at the head after rebuilding the top end. Bought a stick of high temp permatex and sealed it up, just have to wait for it to cure before taking it out.

So I think I have everything addressed that was affecting the jetting, just not sure whether the higher compression has an impact or not.

So what I've got is:

Full FMF
Tors delete
Mixing 32:1
Stock carb
Elevation 761'
250, 270, and 290 mains

 

[Awk08]

throw that 290 in and plug chop, that'll be close depending on current temps
if it's in the high 30's like it is here, it may want richer jetting.
what works at 60-80 degrees will fry at 30-40-50 degrees, you must keep up with changing temps

 

[chuey_316]

It's 50ºF here. Put the 290 in, moved the needle clip to the 3rd position (was in the 2nd), and adjusted the mixture screw to 2 turns. I'll be going out in the next hour or so. I'll grab a new plug and do a chop today.

 

[chuey_316]

So I started it up, and it idled ok, but when riding it ran like crap throughout the whole throttle range. I removed the lid, and it seemed to help, but still wasn't running too good. Did get a chance to do a chop though. Did a wot run, but couldn't get past about 7/8 throttle or it would lose all power, as if the fuel were off.

Put the old plug back in, and it did it a few times at different throttle positions as well. Definitely had less power over all, and would randomly bog.

 

[chuey_316]

I see that the FMF site calls for a 260 main, with the snorkel removed, and outside temps at 70º. It's 45-50º here, and while it wasn't running perfect with the 270, it did seem worse with the 290. Could the jetting be too rich? Maybe Try the 270, lid on, snorkel off, and 93 octane?

I have my baby grandson today, so I can't do anything right now. If the rain holds out until his mother gets homes, I'll mess with it. I'm on vacation this week and would like to get it buttoned up soon, so I can ride before giving my time back to the man.

 

[Awk08]

start at the bottom and work up, get each correct before moving up to the next jetting range.....

check float height: https://www.blasterforum.com/threads/float-heights-and-how-to-adjust-them.50565/

set airscrew: https://www.blasterforum.com/threads/adjusting-your-airscrew-pilot-jet.51060/

needle in middle clip position

then try the mains again, should be in the 270-300 range

 

[chuey_316]

Can't find my digital caliper, but I'll check the float height when I do.

I put the 270 back in, adjusted the air screw back to 1 1/2 turns out, clip in 3rd position. I put the lid back on, but took the snorkel off. WAY better. Still seemed to break up a small bit at full throttle in 1st-2nd when I first took off, but after that it ran pretty good, and pulled nicely. Sounded like I was revving out pretty good as well, but I wasn't able to get to top speed with the space I had. Was definitely running stronger. Had enough in it to drift corners on pavement. Looks like just a bit of fine tuning now.

Once I check the float height I'll report back. Then if the weather is decent someday this week, I'll do another plug chop. How did the pic I posted look to you? I'm slightly color blind, so I don't trust myself to gauge it.

After it's all dialed in I'll have to address a couple other issues, but that's for a different thread.

Thanks for the help. It's appreciated.

 

[chuey_316]

Got to go back out today. Runs so much better. I think it's a touch lean on the top end, maybe one size. The trails I'm riding are mostly tighter though, and I rarely get past 1/2 throttle.