DSP TI exhaust

I just installed a DRD hotstart and I just had a thought...that should make a perfect tuning tool. If you lean it out a little with the hot start and it gets better, you'll know you're too rich and if it gets worse, you should expect better performance with a richer jet. Anyone tried using the hot start as a tuning tool and have any tips?

I have a 1999 YZ400, I just purchased a new DSP TI Exhaust this past weekend. I am having a hard time jetting the bike right. Stock it was a 45 pilot and 175 main, 1 3/8 out on the air screw.

I went to a 180 main, and 2 1/2 turns out on the air screw. Its bogs when I wack the trottle wide open hard from idle. and its also having a hard time running less then 1/3 throttle it kind of lugs down low ( does not have the snappy crisp sound to it )

Im going to try a 48 pilot today ( picking it up on the way home )

I did know if anyone else is running this setup ?

I Live in Massachusetts, and the sea level is LOW ! like 100 feet or so. Temp this past weekend was about 50-60.




Nothing will help you more than a little "trial and error."

An aftermarket pipe will often require richer jetting (larger pilot, larger MJ, maybe one clip position lower on the needle - raising the needle for more fuel to come in).

The first thing I would try is to get rid of the bog down low by tweaking the fuel screw IN (leaner) until the bog goes away, or you get a hanging idle (blip of the throttle and it doesn't come back to idle in a second or two). If you get the hanging idle and the bog is still there, you've gone too lean and smaller pilot jet isn't going to help. If you never get the hanging idle, then you can try going one step down on the pilot jet. You can convince yourself you are doing the correct thing by also tweaking the fuel screw OUT (richer) and seeing if things get worse. If they get better, then you KNOW you need a richer (bigger) pilot.

OK so far? Make sure you do all of this with a warm bike and NOT just on the stand in the garage. Take it for a spin.

Now, it is a simple matter to also pull out the needle and change the clip position which will affect your 1/3 throttle position running greatly. I would try richer first since you added an aftermarket pipe (clip goes on next lower position). I've found the easiest way to do this is to loosen both carb clamps (air box and intake), and just pull the carb loose (I take off the seat but leave the gas tank on). Leave everything else on. Your carb will just hang there. Then you can loosen the two top allen bolts and pull the top cap off. From there you can get to the allen bolt and spring that holds the needle in. Loosen and remove that, then you can use a small pair of needle nose to grab the needle out.

Hint - a good way to make sure you don't lose the clip when you change the position is to put the needle/clip inside a sandwich baggie. Then work from the outside of the baggie. If you drop the clip - no biggie, it's in the baggie! :)

Please reply with your results!

And BTW - bbeakley is right, if you pull the hot start while running you lean things out. If it runs better you know you need leaner. Same with the choke. If you pull the choke while running and it runs better - you know you need richer! This is a coarse way of checking things and requires some good hand coordination though (unless you have the Dr.D hot start!)

[ April 09, 2002: Message edited by: skthom2320 ]

$28 for a pilot jet!!!!

Your dealer is taking advantage of you.

Do you have a Honda dealer? Those'll work too. The pilot is a standard Kiehin pilot. Take your old one in, they often have a box with a selection of jets. I paid $5 for the last one I got, the one before that was free since I was buying a bunch of other stuff (filter oil, etc.).

$28 bucks for a pilot jet :) I sure hope your dealer ment $2.80, if not I wouldn't go back to that dealer. I got one from my dealer for about 3 bucks. Look out! Good luck on the jetting.

$2.80? I'm getting ripped off! I paid almost $5 for mine! Will it never stop (dealers ripping you off)?

Great feed back, I was going to try a 48 pilot yesterday. But the dealer did not have one in stock, plus the price was scary @ $28.00 ! I did not move the needle clip yet, but i was reading in the YZ400F1 manual last night and they say you can tune the carb from 1/3 to 3/4 throttle with just adjusting the clip !! I really dont want to spin out the air screw much more then 2 3/4, as i hear guys have had them vibrate out :) But i was thinking about getting a longer spring at the hard wear store and replacing it with the stock one to add more pressure to the air screw so it wont back out on me.

Thanks for all the feed back, i will be working on the bike thrusday night after work. I will post my results then.

I know ! I almost fell onto the floor... Then get this he told me that was racer discount too :) But i have a feeling he might have looked at the wrong part, or ment to say $2.80 But I think my reaction would have made him double check it ! :D

I will be jetting the bike tomorrow after work. I will let you guys know how everything turns out !

My plan is this,

Give the carb a good cleaning, and check to make sure everything is working right ( pump, and sensor )

Then im going to drop the needle to the 4th postion, and put my air screw at 2 1/4 out.

I will tune the air screw from that point.

I will also make sure i have the bike good and warm :D

[ April 10, 2002: Message edited by: DJDMX46 ]

Well, I finally got to work on my bike this past weekend ! But never got the chance to start it up :) I pulled a real dumb a$$ move... I got the right pilot jet from my dealer.. for 8 bucks :D and he also told me that was racer discount.... cough cough bull shi* cough cough...

But once i got everything back together in my shop, I look on the floor next to my little crash cart that I always put all my parts into.. Whats that sitting thier, DAM IT I left the little plastic neck that snaps around the main jet off..

So needless to say I have not started up the bike yet to see if all my changes have helped or not...

I will have a update soon....

Thanks again for all the in put.


Be careful when using the hotstart as a troubleshooting tool. It introduces an unfiltered air path to the carb/engine. I wouldn't do it out on the track or in very dusty conditions. JMHO. :)

man, you guys buy jets. some service departments will trade them. they have build up a colletion over time. its just like trading shims.

I have the Yosh Ti pipe and header (DSP is made by Yosh). Back when I was searching for jetting specs a guy told me to start from stock. As it turned out all I have done is change the needle position/air screw and I run race gas. Bike runs like a top.


First test at the track this past Saturday ! I did not get a chance to test out the jetting before race day, so i was letting the dice roll with what everyone had told me.

This is what i went with



AIR SCREW 2 Turns out

Temp was 65 on saturday, and the bike ran AWESOME ! I might have to turn the air screw in a tad. But throttle response was great and the power was smooth..

See pic below, from saturdays race :)



Hey BigLou,

Actually, the hotstart does pull in filtered air. The Dr. D hotstart pulls air through the airbox, and the Ty Davis hotstart should have a piece of filter material in the opening.


I like those pics! Did you paint your hubs blue (or anodize)? Please let us know what you did because that looks killer! Later,


Garrett, the rims are Anodized and the hubs are painted. A freind of mine paints helmets and just started doing the hubs last year.

I will try and take some better pics for you. They have the yahama Logo painted on the inside of them too.


Cool...let me know when you take some pics!


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