1985 250 Big Red - Jetting Recommendations?

[cosmohawk]

Hey there...first post...

Alright, I've got an '85 250 Big Red, stock carb + jetting, UNI Filter (stock airbox and lid), and I just added a new full DG RCM exhaust with aluminum can (from a 250X).

Started it up, and after warming up, noticed it didn't want to accept throttle off idle, and while running it, would backfire on decel. Now, I know it is running lean with the exhaust addition...but I was looking for suggestions as how to specifically change the jetting?

Has anyone else made this same change to their 250ES or 250X, and what exact jetting changes did you make to get it running A1? What changes did you make to the pilot jet, main jet (size increases), air mixture screw (in or out), and raising the needle one notch?

Thanks for any info...and yes...I have read the thread on jetting. :cool:

[Mondexbrute]

so was the 250X exhaust a direct bolt up or did u custom fit it? I have a Cobra full exhaust, UNI airl cleaner & a snorkel on my Big Red, changed the main jet from a 130 too a 135 & the slow jet from a stock 38 to a 42 & it runs perfect!

[tri again]

that sure sounds familiar but its been a while for me.

jetsrus.com may have parts if you aren/t near any cities

[cosmohawk]

Well, I had been looking for the aluminum cobra system for the 250ES, but it seems to me that they only made it for the 200X, 250SX and 350X models...all the rest just got the shitty black steel systems.

I bought the full DG RCM off of Ebay for $100 (brand new - still in the original box from back in the day)...knowing it was for the 250SX, but I checked the OEM exhaust #'s, and the can assembly is the same, and I know that the two bikes are basically the same...so I kinda figured that it might just bolt up, with the exception of one rear mount.

Got the system on the bike, bends were where they should be (perfect), header pipe length was perfect, mounts on the can looked to be in just the right place (not what I expected)...but...once I got it fitted...both rear can mounts were about 1 inch away from where they should be (250SX must have a longer frame). I resorted to making a rear hanger bracket (top can mount) for it to be solid...and it is mounted solid.

Looks great, sounds awesome, and is just a fraction of the weight of the beastly stock system.

Thanks for the jetting ideas...so you didn't move the needle up one notch? Should I go to a 40 primary first, or 42?

[Mondexbrute]

sure would like to see pics of that exhaust system on your Big Red!

Check out JetsRus.com the jets are cheap so buy a few different sizes to play with!

[cosmohawk]

Yeah, I've been looking for an assorted box kit of KeiHin jets...because I'm usually changing things around in all of my hondas...and they all take they same style pilot and main jets. No luck yet...still have to order them individually at around $10 to $15 a piece.

I'll wheel her outside and get some pics. :cool:

[cosmohawk]

Well...here you go, finally...got the carb rejetted properly as per your recommendations...went from a 38 to 42 slow (pilot) jet, and a 130 to 135 main jet. Not sure about the air mixture screw...when I took it out it was at 1.5 turns out from seated...manual calls for 2 turns out as a basic setting, so I reset it at 1 3/4 turns out. Any ideas if this is good, or should I just set it as per the manual description?

Here are some new pics from yesterday...took it for a rip through the field across the road...works a lot better...but now it's obnoxiously noisey! Not too sure if I like that or not...time will tell.

Thanks for the help.

http://www.3wheelerworld.com/attachment.php?attachmentid=102261
http://www.3wheelerworld.com/attachment.php?attachmentid=102263
http://www.3wheelerworld.com/attachment.php?attachmentid=102265

[Thorpe]

:wondering Now, I dont mean to be rude... But that is a real nice original BR... Why did you want to put a Cobra or other aftermarket exhaust on it?