Jet sizing for 84 250R?

[HerculesEngine]

Hi all,

A while back I picked up my first pinger, an 84 250R. Well I've been out of school a couple weeks now and finally bolted the old girl together runs great (new top end)... with the airbox cover on. However, with the airbox cover off plug reading shows a very lean mixture... go figure. Adjusting the main needle position did not help any.

Anyhow, I plan to jet it with these changes and modifications:

K&N filter with outerwear

Boyesen Reeds

DG Expansion chamber and silencer

.060 over with Wiseco Piston

Air box cover off

The R idles great, so pilot jet is likely the last of my worries. What size main jet should I start messing with? Any insight appreciated. THANKS!!

[Chevy200s]

I dont know, but I've been having similar issues, anyone have any information?

[88 Turbo Coupe]

Run a rich mix and a larger main for break in. Lean is bad

[88 Turbo Coupe]

BTW When does it lean out? At mid or WOT or both??

[HerculesEngine]

Thanks for the response Turbo Coupe. I've already given it a break in period, I mixed Amsoil a bit heavy, 32: 1, with the airbox cover on, made sure I had a BLACK plug. Probably 2 hours worth of running rich.

Anyways, I adjusted the main needle position to furthest down (least fuel.) This was with the air box cover on. Brown plug, all was happy and well.

Now I remove my airbox cover, totally different machine. Rode it around the yard for about 3 minutes, come back and pull the plug, white. Seems now that I may be upgrading the pilot and main. Running a #50 pilot and #130 main, I beleive this configuration is stock. 1/8 throttle and less, out of 1st gear, seems to be underpowered. Mid and WOT yield a very white plug. In all 3 situations the plug was white.

[88 Turbo Coupe]

What carb are you using? A stocker?? Too small. Engine starving for fuel. I run Mikuni and Bing. Most of the problems are usually a too small main. What is stock on your carb? I would jump at least 70 sizes up on the main to start with your setup. Don't keep riding until you dial it in. Hate to see your racer die early due to lack of fuel!!!!!!! I never had a white plug. Your causing major damage! Run dinosaur oil instead of synthetic until you figure out your jetting. You have alot into the engine setup with your mods. Somtimes you have to do a mod at a time then jet it accordingly. You are at the top of the hill with your setup. (Well almost, lol) Difficult to dail it in that way. Fatten up your fuel delivery and run 20:1. Smoke out of your pipe is a good thing. No smoke, BAD. BTW put your main needle and pilot back to stock and start from there. Are you lean at idle? If no then leave your main needle alone. Usually idle problems and off the line acceleration require a needle adjust. I try not to idle my r too long. It loads up. Pilot is what I would mess with last. Do the main next.

[HerculesEngine]

Hello Turbo Coupe,

Got ahold of a selection of Kehin main and pilots. I went from stock configuration to the following: With a #148 main and a #55 pilot the machine is performing well. The plug is properly colored at a dark brown. I figure I'm close if anything, any thoughts?

BTW I have not "ridden" the machine running lean as mentioned, I guess I was a bit misleading. I have not honestly ridden the machine since installing the new top end. More so 2 passes up and down my yard and then checked the plug. In my younger years I remember 2 close friends of mine blowing up their Ski Doo snowmobile due to lean mixture, so I knew better than to beat on it or ride it.

I've heard as much as 10 to 15 sizes larger; am I honestly looking at at least 70 sizes larger??, just want to make sure that wasnt a typo.

Here's a little background just to clarify:
I bought this wheeler, kid complained of low compression, I received the machine in pieces. Bore guage showed that the bore was out of round down by exhaust ports. Sent the jug over to a friend's, was taken to .060 to compensate for lower wear. Unfortunately when I bought the wheeler the kid specifically said that the incorrect jet was installed by a local part- time ATV repairman. Apparently he didn't know enough to put in a larger jet with the machines mods. Needless to say these aftermarket components were installed at the time I purchased the machine. I knew I was in for a fun time trying to figure out jet size. Well after a little trial and error I've figured it out and it seems to be running decent.

Hopefully this gives some more insight to this situation. Thanks again for your help so far appreciate the info.

[88 Turbo Coupe]

What I do is use a 20;1 mix and jet the main for a good burn. Don't use synthetic oil. ifyou want to run 32;1 then go up 2 sizes on the main. It works for me. Or get a larger mm carb. I have a 38mm Mikuni on my 82R 300cc. It takestime to get it right but well worth it. I went 10 sizes larger on my main.