300ex Choke Question

[hondapro300EX]

I HEARD IF YOU GET RID OF THE CHOKE YOU GAIN SOME POWER. IS THAT TRUE? IF SO HOW?

WOULD LOOK MYSELF BUT ITS IN THE SHOP RIGHT NOW. LOOKIN NICE!! POST PICS AFTER DONE.

[Trevor]

can't see it making a differance

[300ex#5]

i can't see it making a difference either...but you never know till you try

[Tri-valleyracin]

it makes it have better snap but thats it off subject 300ex#5 how do u like ur power core four im thinkg about getting one scence im sponcerd by fmf?

[TarheelRedRider]

I never ran a choke in my carbs. The power gain is very small unless you rejet. Simple fact more air more gas more power.

[big_rider]

no it dont give it more power it just make it harder to start in the winter.

[300ex73]

It only makes it harder to start in the winter, if you don't take the time to jet it properly. I've been running without a choke for a while now. And even on the coldest days all it takes to get mine to fire up is to press the throttle 3-4 times before I try to start it, and it will fire and run on the first try.

All you need to do to get it to run better from startup is to replace the pilot jet. It's the jet that controls the fuel flow at very low rpms. I recommend using a 42 pilot jet. They're available at any Honda dealer.

Just for reference, in case anyone is wondering, my jetting is as follows - 42 pilot, 138 Keihin main jet, needle clip moved down one notch, and the airscrew out between 3.5-4.5 turns. This is with a K&N filter, no airbox lid, choke removed, and Sparks X-4 exhaust. I also have the valves adjusted every so often, to help make sure it stays running like it should.

[300ex#5]

Originally posted by Tri-valleyracin
it makes it have better snap but thats it off subject 300ex#5 how do u like ur power core four im thinkg about getting one scence im sponcerd by fmf? it is great i would reccomend getting one...my cousin has a megamax and he said mine is better...are u gonna get one?

[Tri-valleyracin]

ya prolly becuse i have a slip on t4 and i like the sound but it just a slip on and i dont fell like paying 200 for a header cuse i can get a hole system for that.

[bwamos]

Originally posted by 300ex73
Just for reference, in case anyone is wondering, my jetting is as follows - 42 pilot, 138-142 Keihin main jet, needle clip moved down one notch, and the airscrew out between 3.5-4.5 turns. This is with a K&N filter, no airbox lid, choke removed, and Sparks X-4 exhaust. I also have the valves adjusted every so often, to help make sure it stays running like it should.

138 Main??? Are you stock bore? That sounds awfully rich to me. I run a 138 keihin main on my big valve 330cc, agressive MX cam, K&N no lid, and a Sparks X-4.

3.5-4.5 turns out means your too rich on you pilot. You should generally be between 1 & 2 turns out if you have the correct pilot jet in there.

I'm just being nitpicky though. If it runs great, it runs great.

[300ex73]

All of my jetting comes from actually taking the time to try different settings on the carb, starting with recommended settings I took from several different sources. Yes, I am running a 138 main, and 3.5-4.5 turns out on the airscrew. And, yes it is a stock bore. The motor itself is bone stock.

I tried running the recommended 135 main, but it cut out a little too much, so I went to the 138 main, and now it revs out almost like it doesn't even have a rev limiter.

The 3.5-4.5 turns out on the airscrew was done to help richen the mixture. If I remember correctly, the pilot jet is most effective from idle to about 1/4 throttle, the airscrew from around 1/4 to 1/2 throttle, the needle clip position from 1/2 to 3/4 throttle, and the main jet from about 3/4 to full throttle. So, basically I just adjusted each of these settings until the quad seemed to be running just right no matter how far I had the throttle opened.

Also, bwamos, if I'm not mistaken, I think the airscrew richens the mixture when being turned out from fully seated. The way you made it sound, is that turning the airscrew out from seated would lean out the mixture.

Anyways, yeah, that's how I have my carb setup, and kinda how I came about running at those settings.

[Sjorge450R]

so if i pick up a 42 pilot it will be easier to start?

[300exOH]

Originally posted by Sjorge300EX
so if i pick up a 42 pilot it will be easier to start?

Yes. I put a 42 pilot on mine and it starts much easier now. Even on the coldest days she starts right up. With the stock pilot I could barely get it started after doing pipe/filter.

[bwamos]

Originally posted by 300ex73
Also, bwamos, if I'm not mistaken, I think the airscrew richens the mixture when being turned out from fully seated. The way you made it sound, is that turning the airscrew out from seated would lean out the mixture.

I'm 110% positive turning out the air screw leans it. The Keihin's have an air screw. Some others have a fuel screw.

The pilot jet adjusts the fuel at idle. The air screw adjusts the air.

That's why you start the adjustment at the seated position. (richest), then turn it out until it stops increasing idle speed (14.7:1 a/f mix), then turn it back in a 1/4 turn or so for saftey.

The air screw needle clogs the air bypass pathway to richen the mixture, and opens it up to lean it out.

It's jsut all about the ratio.. if it runs well, it runs well.

I'm just seeing that your pilot is too rich. (you should be running a stock pilot w/o motor work), And you leaned it out to the point that it actually affected you'r full throttle circuit to a point that it required a larger main jet than normal.

I don't see your setup actually needing more than a 132 main jet, stock pilot, 2.5 turns out, and the needle up 1 position from stock.

The pilot jet and air screw affect Idle - 25% (the pilot is the fuel, the air screw is the air for the bypass circuit)
The Needle and Needle Jet affect 25% - 75%
The Main Jet effects 75% to full throttle.
Obviously there is overlap as well.

Check out Duncan Racing's jetting guide for jetting Keihin Carbs.
http://www.duncanracing.com/techfaq/Tech_keihin-carburetion-jetting.phtml

In short your jetting is probably correct in compensating for the larger pilot. Not, trying to knock your jetting job at all. Just trying to figure out why you'd be running the same jets as I am with a full blown 330cc. (I still run a stock pilot on my 330cc.) I found that the stock pilot was actually a hair too large for the stock motor on the 300ex.

As a note, nothing above was meant to be condecending in any way. If you knew me, you'd know it's not my style. I tend to not be very charismatic in my posting though, lol.

[300ex73]

Well, the recommendation for the 42 pilot came from Sparks. I think FMF (I know, not the greatest pipes, but I was curious and had too look up jetting for a friends wheeler) and prolly a couple of others also recommend the 42 pilot. As well as the starting point for my main jet. They recommend the 135 main. But like I said before, it cut out too much with the 135. And the airscrew setting, I based off of the 3.5 turns out recommended by Dynojet. I'm pretty sure my airscrew is only about 3.5-4 turns out. But until I put in the larger pilot, it wouldn't run at idle until it was completely warmed up. I've got a funny story about that one too.

As far as what I said about the airscrew on the carb, that's something I was told by my mechanics. I figure they know quite a bit more about them than I do. They're both semi-pro GNCC racers as well as awesome mechanics and engine builders, so any advice they give me, I usually take into consideration.

And I know that it sounds like my jetting may be too rich, but I've done about as much testing as I can. I've even had it on the dyno to check it, which I need to do it again very soon(long story), and when they are doing an air fuel check on it, they very slowly roll on the throttle instead of just hammering it on. I also normally check the plug between rides. Anything less then how I have it set now, usually left me with a white, or very light grey color on the plug.

And yeah, I've seen the charts and diagrams that show the effectiveness of each part of the jetting at each point in the throttle opening. I also know about the overlap of each, which helped a lot. I didn't just go and throw in the first thing that sounded good. I've spent countless hours trying different settings, and this is the one that has worked the best for me.

It actually has enough pull, that I can stand in fourth gear and hammer it, or sit and use the clutch a little, and pull the front wheels without having to pull on the bars. If I use the clutch a little, it'll also do it in fifth. The thing that I like the most though is that I can consistently beat my friends piped and jetted 400 in a 300 foot drag. And I know this one isn't really a case of better rider, considering he's pretty well the one that taught me how to ride. It also runs really well when just putting around, at about any rpm. The only thing I wish I had right now, is an extended swinger. I lost a race to a mostly stock, piped 300, simply because I couldn't keep from wheelying out.

[300exOH]

I'm running a 42 pilot/135 main because that's what sparks recommended for the X4 on mine as well. My engine is stock otherwise. I'm hoping to get some dyno time though to make sure it is right.