Correct Jetting Please

[heenimeeni]

Sirs, I have 1998 KDX 200 H4. She has some mods:

Full FMF Gold Series Gnarly Pipe and Rear Silencer
Boysen Rad Reed Valve with Pro Carbon Reeds
K&N KA 1287 Air Filter
Lightweight Racing Piston

I run the bike on 99 Octane fuel with a 50:1 mix

The bike is in immaculate condition having only done 5,800 Miles from new!!

The bike tends to feel a bit strangled up the upper of the rev range and does not seem to rev out fully.

I would like better throttle response with fully revving out motor.

I suspect that I need to adjust the carburettor setting s and have some jetting changes made????? The bike is running a stock carb.

Your advice would be priceless.

Cheers Guys

[Julien D]

There are no shortcuts to jetting, but to start with some recommendations we will need to know what jets are currently installed. I would also recommend mixing more oil than 50:1. 40:1 is as little oil as I feel comfortable running in any 2 stroke.

[scheckaet]

check my sig

[cornishwrecker220]

i would ditch the k & n air filter for a twin air , UNI air filter or no toil as the k & n is a solid caged filter & difficult to wash/clean & oil & in my opinion not very good for a dirt bike as very little foam (single layer) .. i`m with julien regarding oil mix...40.1 ..check your jetting spec with the factory settings & go from there, usually its just a case of a small tweek here & there with the needle & jets fresh plug filter & fuel & away you go

[heenimeeni]

Thanks guys for the advice.
Well the carb is stock and has never been tampered with at all. I have installed a new plug two days ago which means the bike starts first kick although the weather is 20 degrees C at the moment which helps. I am not using the choke and only just turning the throttle a bit to start it.

The advice concerning the air filter I will take on board. I do remove it regularly and use K&N cleaner & oil ONLY. This filter is only about 40 hours old. When I bought the bike it had a stock filter in it!!

I noticed on the FMF web site they were recommending a 32:1 mix!!?? would this be correct? I see that you recommend a minimum of 40:1

The previous plugs were coming quite black and not the lovely Mocha colour you suggest I should achieve scheckaet!! I read with great interest your sig on this and the quite lengthy process to heaven.

Taking account of the mods that I have put on the bike and the fact the card is till in 'factory' settings is there anything I should do immediately to get the benefit of the pipe and Boysen Rad Reed Valve? I.e bigger jet etc?

[robertotjr]

In my humble opinion 50:1 is quite alright for premix. I`ve been using it for more than 7 years now. Oil has advanced quite a bit in the last 10 years, especially with the syntetics oils. If you are using mineral oil i would stick to 32:1 or 40:1 but if you're using syntetic 50:1 is ok.

[heenimeeni]

With regards to the oil robertotjr I am using fully synthetic racing oil which is very expensive I can tell you. I have run the bike on this for over one year and the previous owner ran it on this from new!! So..... what to do????

[Julien D]

The "advances" in oil are more marketing hype than anything else. All the way up until the KDX stopped production in 2006 Kawi was recommending 32:1 in the service manual. And that wasn't "32:1 if you're using conventional oil, or XXX if you're using synthetic." It was just 32:1, period. This is my personal opinion, and should be taken as such. I would, however, point out that it has been shown repeatedly that there is absolutely no power to be gained by running less oil in your mix. So unless you are more concerned about emissions and a couple bucks worth of pre-mix than you are the longevity and performance of your machine, 50:1 or higher just doesn't make much sense.

If the carb has never been messed with, it is most likely quite rich. You'll need some smaller jets to start playing with the jetting. It's a very methodical process, and there really aren't any shortcuts. 155/45 is a generally safe starting point for most 200's, assuming that the bike is in sound mechanical condition (no air/oil leaks, good compression, etc).

[robertotjr]

The "advances" in oil are more marketing hype than anything else. All the way up until the KDX stopped production in 2006 Kawi was recommending 32:1 in the service manual. And that wasn't "32:1 if you're using conventional oil, or XXX if you're using synthetic." It was just 32:1, period. This is my personal opinion, and should be taken as such. I would, however, point out that it has been shown repeatedly that there is absolutely no power to be gained by running less oil in your mix. So unless you are more concerned about emissions and a couple bucks worth of pre-mix than you are the longevity and performance of your machine, 50:1 or higher just doesn't make much sense.

I don't mean to start any discussion that I'm sure have happened before, but if you check every manual for newer 2 strokes they all gonna tell to mix 50:1 or less. Kawasaki was recommending 32:1 because they were too lazy to make new manuals and just kept copying the old ones.(just like they did with their bikes)
And about marketing hype involving the advances in oil you can check for yourself, just dip your finger in mineral oil and rub it on your thumb and then do the same with syntetic oil and see the difference.

I've been using less oil not because of "more power", but because of fouled plugs. Whenever I used more than 40:1 I would stop 2 to 3 times to change plugs or clean one.

[Julien D]

Its nothing to do with lazy. The newer euro 2t oil recommendations are based on emissions, not performance. And yeah, this subject has been beat to death. Everyone has their own ideas about it. As long as what you are doing works for you, keep doing it.

If you are fouling plugs, your jetting is poor. You can run 20:1 without fouling plugs if you take the time to jet for the mix.

[Tedh98]

If you are fouling plugs, your jetting is poor. You can run 20:1 without fouling plugs if you take the time to jet for the mix.

+1

I've been running 32:1 for years now and never fouled a plug. I'd rather have more oil than less.

Actually more oil = more power due to better ring sealing. But of course you have to have it jetted correctly.

[bufftester]

If you are fouling plugs, your jetting is poor. You can run 20:1 without fouling plugs if you take the time to jet for the mix.

+1

Actually more oil = more power due to better ring sealing. But of course you have to have it jetted correctly.

+1 +1

Premix oil is not the reason you're fouling plugs, it's all jetting, and there is no "magic" combo, or shortcuts. Take the time, do it right. Pick a fuel/oil ratio, jet to it and stick with it. 50:1 might be good for a weedeater, but that's precious little lubrication. Oil-presence in the engine is a function of the operating rpm. You can run 50:1, and the oil-presence at low rpms will be sufficient lubrication, but start revving to 4K and above and its the same as running your truck with only 2 quarts...yeah it'll run, but you are causing damage. Without delving into the "synthetic vs non" quagmire (though I will rant a pet peeve--you do know that synthetic oils are not 100% synthetic, right? they are more non synth than they are synth, but if you buy the media claims ), the bulk of work done with synthetics is to increase the oils viscous life, in other words make it stay slippery longer, not make it more slippery period. And regardless of how good, if there's not enough oil to lubricate, it's going to end badly eventually. Just my .02...Besides the woods need a little blue smoke to let them know someone's out there enjoying nature lol.

[diymirage]

[robertotjr]

Its nothing to do with lazy. The newer euro 2t oil recommendations are based on emissions, not performance. And yeah, this subject has been beat to death. Everyone has their own ideas about it. As long as what you are doing works for you, keep doing it.

If you are fouling plugs, your jetting is poor. You can run 20:1 without fouling plugs if you take the time to jet for the mix.

I did not know that. I am young (25yo) so what I`ve been saying is what happened to me during the 10 years that I ride my KDX. I`m pretty sure you guys know a lot more about KDX`s than I do. If you guys are saying that oil does not foul plugs, and my jetting is right for my conditions(I don`t have any bogs or flats in acceleration) it could probably be the crappy gasoline from my country. I always used 32:1 with mineral oil and when I changed to synthetic it started to foul plugs. I talked to some people about it and they told me to reduce my premix. When I did that it stopped, so I assumed it was the oil.

But anyway, thanks for the info.

[diymirage]

now might be the time to start trowing around spark plug numbers aswell

[heenimeeni]

Ok guys so there is a great debate about the premix quotient .

1.So I will take the advice that more oil is better than less so I will change to the 32:1.

2.My plugs are coming up very black even with 50:1 premix so I guess this is because the carb is stock and never has been messed with?

3. it is running rich and I am guessing this is preventing the engine from revving out completely??

4.Final recap: Full FMF Gnarly with SuperCore Silencer, Boysen Rad Reed Valve Conversion, Boysen Pro Carbon Reeds, K&N Air Filter (I know, I know and this will be changed), Wiseco Racing Piston. Stock Carb at factory settings!!!!

5.Julian D suggested: 155/45 is a generally safe starting point for most 200's, assuming that the bike is in sound mechanical condition (no air/oil leaks, good compression, etc) Well I bought this bike as it had amazing history with it from New. I am only the Second Owner!! (remember this is an H4!!). The mileage is fully documented with only 5,500 Miles in total!! The engine is in amazing condition as it has never been raced, just some gentle green laning and mild road use (Previous Owner Usage). No oil leeks, No air leeks and my local mechanic said he could not believe the condition of the engine and the bike as a whole taking account the age - A1 perfect was his comment.

6. Now SPARK PLUGS!! I am running the manual recommended NGK BR8ES ( 0.74 gap) - any other ideas on this would also be welcome

So allowing for the above would it be fair to start with Julian D recommendation?????

[Tedh98]

So allowing for the above would it be fair to start with Julian D recommendation?????

Yes

[heenimeeni]

So allowing for the above would it be fair to start with Julian D recommendation?????

Yes

Ok this will be first port of call.

Apart from changing the Air Filter to a No toil or similar should I be considering any other modifications to the air box? I ask this prior to changing the jets??

[Tedh98]

Yep , definitely do your modifications first and then jet last.

[cornishwrecker220]

regarding the air box lid i would just remove the `snorkle` from the top of the lid ...some people on here would say remove the whole lid completely but i perfer to leave the lid on personally...with the jetting the first thing i would do is raise the clip on the needle to position number 2 ( 2nd from the top.. 3rd is standard ) this would lean the jetting slightly , if still blubbery then go down 1 size on your main jet ..i notice you are running a rad valve?...these require to lean both the main & pilot jet so you your probably looking to run a 42 pilot jet rather than the stock 45...i recon with a new air filter, plug & fuel mix of say 32.1 or 40.1 & snorkle removed your jetting will be around the 42/40 pilot & 150/152 main mark.. air screw is between 1.5- 2 turns out .. let us know how you get on