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HELP!! question on jetting?
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Posted by: mak400ex

hey guys i just ordered a Dyno jet kit, i need to know what size of jet to use with a FMF megamax slip on.

has anyone jetted a 250 with this pipe on there before? and if so did you like it?

i know there is already a thread on here kinda about this..but it got a little off topic..mines coming in soon and i need to know. so please help

Posted by: tedwilley

Read '250EX Performance FAQ' thread for starters (the first page anyway). It has pretty much everything you need to know. Jetting is slightly different for every engine, even though they may be the same engine, much less with different exhausts and filters.
Also, I recounted my setup, borrowing from the FAQ thread, in the thread 'any1 ordered this before' It's near the bottom of the page. You need to be careful and keep track of what jet got put where. It makes it easier to do the fine tuning if you remember what you did each time.
Tools:
10mm combo wrench
00 Phillips screw driver (be careful with the Phillips screws on the carb, snug tight is good, don't strip the head!)
1/4 flat screw driver
Diagonal pliers to pull the body clips out (carefully there are soft!)
Needle nose pliers for the hose clamps and the keeper for the needle jet (just look at it and you will see how to squeeze to release the keeper)
Follow Ryan's instructions in the 250ex Performance FAQ thread!
The first jetting took about 45 minutes, the last two times about 25 minutes start to finish.

Posted by: mak400ex

it says all the sizes are not for Dyno jet..and plus he doesnt have FMF in there..

Posted by: JBacon

To tell you the truth we didnt have to jet at all on my moms 4wheeler. Honda said we didnt have to...

Posted by: JBacon

To tell you the truth we didnt have to jet at all on my moms fmf megamax. Honda said we didnt have to...

Posted by: hillclimbingrec

well. On my recon it ran Perfect with out jetting! i moved up a size then down and the stock jet was the majic one. so i would see how your quad runs 1st with out jetting. If it runs like crap. then bump it up a size, and keep doing that. if it Still runs like ****. start at the stock size and go down. well.. at least thats what me, and my freinds all do. Or you could go to FMFracing.com( i think thats there website) and they have a little chart to help you.

Posted by: bwamos

quote:
Originally posted by mak400ex
hey guys i just ordered a Dyno jet kit, i need to know what size of jet to use with a FMF megamax slip on.

has anyone jetted a 250 with this pipe on there before? and if so did you like it?

i know there is already a thread on here kinda about this..but it got a little off topic..mines coming in soon and i need to know. so please help

Read the instructions?

http://www.dynojet.com/pdf/Q110.pdf

Stage1 airbox lid = on
Stage2 airbox lid = off

Posted by: bwamos

quote:
Originally posted by mak400ex
hey guys i just ordered a Dyno jet kit, i need to know what size of jet to use with a FMF megamax slip on.

has anyone jetted a 250 with this pipe on there before? and if so did you like it?

i know there is already a thread on here kinda about this..but it got a little off topic..mines coming in soon and i need to know. so please help

Read the instructions?

http://www.dynojet.com/pdf/Q110.pdf

Stage1 airbox lid = on
Stage2 airbox lid = off

Posted by: tedwilley

Well, sometimes a leaned out engine will run satisfactorily without a lot of back firing.
However, air cooled engines do not like running more than just slightly lean, because they do not have a robust cooling system, e.g. water cooled. A water cooled engine is more tolerant of lean fuel mixture. (in the end they don't like lean mixtures either). The back firing is worse the hotter the engine, too.
'Your results may differ', but having more than a little experience modding air cooled engines, I prefer to rely on recommended data for a particular engine, backed by spark plug reading. That's what i base my peace of mind upon.
Just keep in mind, the exhaust valve won't 'burn' for sometime, depending on how hard you push it.
But, it will eventually burn from running too lean. Eventually so will the intake valve, because they work together on the exhaust stroke. The exhausting gases help pull in more air/fuel mixture, another benefit of a properly tuned pipe
If it works for you, cool. Just don't believe that it always works that way.
Perhaps, some of the aftermarket pipes are not moving as much air as others. If you open the exhaust with the stock air intake, it is only louder. That's all. Intake and exhaust work together and are to be modified together, along with an increase in fuel supply. That's how it works.
It is simple physics and chemistry; more air requires more fuel. That fact is not up for debate.
I am NOT trying to be a 'doom sayer', I just want you to realize that just because someone validates an 'easier' way, doesn't make it so.
Not trying to dis anybody, just the facts ma'am..

Posted by: homemadebrownie

run a 96 or 98 main and u just have the best results and leave the pilot stock

Posted by: jrafter

running a curtis sparks full and K&N on my kids 250ex

97.5 main and had to sim the needle jet because we didnt have a dyno jet needle.

runs great

Posted by: Honda10

Ok, I live in florida and I am installing An HMF full system, K&N, outerwears and, no airbox lid. and I was wondering if buying 120-130 jets off jet-r-us.com would be a good range of jets to buy. I was also wondering if I needed a new pilot jet and what I should do with the fuel mixture screw.

Posted by: Honda10

can someone help me with my last post?

Posted by: Honda10

Anyone?

Posted by: tedwilley

I am at ~200 feet above sea level, same exact pipe/filter setup . Stock pilot, 112 main, needle on 3rd slot, fuel screw 2-3/4 turns out.

Posted by: Honda10

Thanks for anwsering, But i dont understand, kluchbuster250 is running the same setup but he has a 125 main

Posted by: tedwilley

Altitude is very important. Also, every engine is slightly different.
Jetting that works perfect at sea level will be increasingly richer as the elevation goes up. The air is thinner, needing less fuel.
What works great at 1000' will become leaner as you go down in altitude, more air density needs more fuel.
Additionally, remember that the different jets operate in different throttle ranges.
Idle (pilot) jet: idle to 1/4 throttle
Needle: 1/4 to 3/4 throttle ( most of the engine's range)
Main: 3/4 to wide open throttle (WOT)

The fuel mixture screw affects the idle mixture. Usually this adjustment will get rid of mild popping on decel. When you let off the throttle, you go from using the needle or main jet to the pilot jet.

Posted by: Honda10

So the jets that I listed are good? I wouldnt need a new pilot jet would I?

Posted by: FoxHondaRider

quote:
Originally posted by Honda10
Thanks for anwsering, But i dont understand, kluchbuster250 is running the same setup but he has a 125 main

Every engine is different. They are cast molded so there are many flaws inside. The casting flaws are what makes each quad different. 2 quads that came from the same factory on the same day could have slighlty different HP/Torque numbers.

Posted by: jrafter

quote:
Originally posted by Honda10
So the jets that I listed are good? I wouldnt need a new pilot jet would I?

i would think the jets you listed would be kinda rich

my kids 250ex has a full curtis sparks and kn and has a 97.5 main stock pilot and it was the needle jet that really needed the adjusting.

i didnt get a dyno jet kit so we had to shim the needle jet.

i think it would have been cheaper to get and dyno kit than all the jets and a/f screw.

Posted by: Honda10

I am buying the jets today or tomarrow I need to know a good rage of jets.

Posted by: jrafter

you should order a dyno jet kit because i has an adjustable needlejet and the tool to adjust air/fuel screw

and all the jets you will need...you shouldnt need a pilot jet the stock one is pretty big.

i tried every jet from 95 -112 and ended up with 97.5

but the needle jet was the one that really had to be worked with and an adjustable would be what i want.