i have an '86 250r that i bought receintly, it had an LRD ajustable exhaust,K&N air filter, and the air box lid removed.My problem is when i first get on it, it had a dead spot and then takes off like crazy, it happens every time i nail the gas.I took the carb apart and clean it all out but still same thing. the jet that was in it is a 148, the honda manual says it should be a 150 and i think it should be bigger then that with my mods.Should i increase my jet size or try something else????I live in new jersey so im not in a high altitude or anything.
Let me know what you think guys.
thanks,

Quad040

 

First, check the needle on the carb. Start with it in the stock position which is the 3rd notch.
The stock main jet size on an 86 is a .150. If you have a pipe on it, go up one or two sizes. An open air box, up one or two more. Aftermarket air filter, go up more. For each thing you do to improve air/exhust flow, you need to change main jet size.
Jets for stock carbs are
.150
.152
.155
.158
.160
.162
.165
.168
etc.
Go up several sizes. Do a plug check. Warm the engine up, ride for a short while. When you go for high rpms, does it kinda "blubber"? If so, go down one jet size. When it quits "blubbering" at high revs, its close. For a plug check, after warm up and ride for awhile, hit high revs, pull in the clutch and shut the engine off. Pull the plug out. It should be a light brown color. If it is, you will have the jetting right. If it's black and wet, it's too rich. If it's white, too lean. You will not hurt your motor running too rich, but you will cause damage by running too lean.
Remember, jetting can be affected by air temp, humidity, and elevation. Also the fuel/oil mix you are using.

 

Just for comparison:

I have an 87 250R with a Paul Turner pipe, rad valve, Uni-filter, stock carb, air box lid ON and I run with a 162 main jet. I am in Illinois (don't know the elevation off hand). I would say you are running a little lean right now.

Trapper pretty much covered it all but I thought I'd throw in my $.02.

 

thanks for the help guys, the only thing im not sure is that my repair manual for the '86 trx 250r says the stock neddle setting is the 4th notch not the third, are you sure its the third??

but i will try your jetting suggestions,
thanks
quad040

 

I have an 86 with an FMF gold series fatty pipe,power core 2 silencer,porting,and a uni filter with the airbox lid removed.I am running a 150 main.I didn't change the needle postion.It runs alittle rich without the airbox lid and about right without it.

 

I put a 152 main jet in and it was loading up like crazy, wouldn't even idle, so i moved the needle from the 4th clip to the 3rd and its much better, but im gonna try going up to a 155 and see what happens.


quad040

 

Good idea. Try the .155 jet. If you have the needle in the 3rd slot, try it out. Do the plug check. I realize I may have been wrong about the needle setting for a stock 86, but some of jetting really is just a crap shoot. You will have to setup everything for your individual ride and conditions and it sounds as if you're well on the right track. Good luck and have a good time!

 

Trapperb1,

When testing the needle and pilot jet, do you do plug runs? Just like testing the main, except at the appropriate throttle position?

 

Hey Mike!
Wondered if you lost my email addy.
I don't do plug checks for anything but the main jet. If your ride is running good on low and mid range, it's probably alright. I only do plug checks for main jet. I do pull the plug every once-in-a-while just to see the "overall" condition. That gives me an idea of what to do. Most riding is done in the mid-range (for me anyway).
I know you're coming out to Glamis soon. Hope you have a good time and take lots of film! You may not have time to take pics, but you should be ready for them when you can.

 

Trapperb1,

Checking the low and mid ranges are seat-of-the-pants, and obviously the main is a plug chop. Good deal. Thanks.

Glamis is (January) 25-28! I can't wait. Our friends have arranged for a 250R and 400EX between my brother and me. How about that!

You'll bet I'll take lots of film. Santa brought a digital camera for Christmas. Even with a few video clips, which I'll do, I can probably take 60+ pictures! Hopefully I can take that many. Check my website January 28 for the pictures. I'm not going to waste any time posting them.