1985 250r fmf exhaust jetting

[Auto_Demon]

Im probably going to buy a full fmf exhaust system and i was wondering what jet i should upgrade to, the stock one is 142, im probably going to remove the airbox too

[yamaha225dr]

With the FMF exhaust, airbox lid removed and stock carburetor my 250r was running a 147 main jet and stock pilot. It ran great and had no other mods done.

[Auto_Demon]

Ok, thanks

[yaegerb]

Is it a stock carb?

[Auto_Demon]

Is it a stock carb?

its not the stock carb, it says OEM STD on the side. its a flat slide carb. anyone know where to get a 147 main jet for it? or are they universal for 2 stroke carbs?

[RIDE-RED 250r]

Jetsrus.com has jets available for all Keihin carbs....


But you need to know what it is.. Being a flat slide, it should be either a PJ or PWK (if it is a Keihin). The main jets are the same for those 2 carbs. But with Keihin, pilot jets are different from one type of carb to the next.....

[barnett468]

Hello Auto Demon




Im probably going to buy a full fmf exhaust system and i was wondering what jet i should upgrade to, the stock one is 142, im probably going to remove the airbox tooits not the stock carb, it says OEM STD on the side. its a flat slide carb. anyone know where to get a 147 main jet for it? or are they universal for 2 stroke carbs?

Since your carb is not orig I would start with 3 sizes larger on the main and 1 on the pilot jet. Plus if your cylinder is not port dimensions are not the same as yamaho225dr, your jet sizes my need to be different than his anyway. It is safer to start rich then jet leaner.





PLUG CHOP In your particular case ONLY, I would jet as I suggested then install a new plug, ride it moderately from all rpm’s for 15 [30 is better] minutes then inspect plug, if it's nearly white jet up 1 more size ride for 15 minutes then run at WOT in 5th gear [not 6th] up a slight grade if possible for 3-4 seconds, then kill eng and quickly pull clutch lever in. Check plug and do further jetting according to my plug color. Others would do it differently.





PLUG COLOR - In the interest of avoiding possible plug reading bedlum I suggest you simply use the chart in the link at the bottom of my post as a guide. My method is the same used by the Kawi factory MX racing team and most other professionals I know which in general is the following:
porcelain = at least 75 % of it lite to medium tan.
Electrode = will hopefully follow the porcelain color and also have no deposits.
Outer metal plug ring = clean with no build up and lite color, black is rich on pilot.





HOW LONG BEFORE PLUG GETS MEANINGFUL READABLE COLOR
As mentioned it can take up to 45 minutes in my experience so doing a reading on a new plug that only has 5 minutes time on it can be misleading but obviously that’s the only option one has. Others experiences may vary.


Plug 1 in the chart below is ok for a street bike but slightly lean on the main for a dirt bike. Your’s should be slightly darker than this imo.

http://www.google.com/imgres?imgurl=http://modernvespa.com/pix/uploads/spark_plug_colour_810.jpg&imgrefurl=http://modernvespa.com/forum/wiki-2-stroke-carburetor-set-up-technique&h=400&w=400&sz=90&tbnid=PS4jrlt_CPdMCM:&tbnh=86&tbnw=86&prev=/search%3Fq%3D2%2Bstroke%2Bplug%2Bcolor%26tbm%3Disc h%26tbo%3Du&zoom=1&q=2+stroke+plug+color&usg=__oKzzTFUpataQjc5leQneeD4CxfA=&sa=X&ei=4r3WUfmSAony9gT904CADQ&ved=0CBoQ9QEwAA

[barnett468]

Post correction



"Plus if your cylinder is not port dimensions are not the same", should read, "Plus if your cylinder port dimensions are not the same"


"according to my plug color.", should read, "according to plug color."



I have no edit button

[Auto_Demon]

Ok thanks for the info, so i should just get like a goodie bag of jets? Haha. I went on that Jetsrus.com and looked at the jets they have for keihin carbs and the next steps up are a 145 and 148, should i get both and try both out?

[RIDE-RED 250r]

Getting yourself a good assortment of jets can be pricey, but it is worthwhile. I would recommend doing just that.

[barnett468]

Ok thanks for the info, so i should just get like a goodie bag of jets? Haha. I went on that Jetsrus.com and looked at the jets they have for keihin carbs and the next steps up are a 145 and 148, should i get both and try both out?

Sorry, I answered you 2 hours ago but it did not post.

Buy original Keihin jets only, all jets are NOT created equal.

Forget the 145, put in the 148. and 1 size larger pilot, very important.

Remember, start rich then lean as necessary. lean engine = hot engine = unhappy engine, rich engine = cool engine = happy engine, lol.

Your plug should be a 9 if it's over 75 degrees also.

[barnett468]

Post correction


"Your plug should be a 9 if it's over 75 degrees also." should read "Your plug should be a 9 if the air temp is 75 degrees or more also."