My first Suzuki DR350 rebuilt. Need jetting help

[Raptorforme93]

Hello, Im 16 and today I finally completed my first engine rebuild and it was on my 97 DR350. I put a whole new top end it after the old one dropped a valve. So anyways I got it running and rode it around for a few and it runs great. It just needs to be jetted. Im not sure whats in it right now (ill look tomorrow) but what would you guys recomment for mains and pilots? The engine has an 89mm JE piston with stock compression and stroke and a slip on FMF exhaust. I live at like 50 feet above sea level. Any and all help is appreciated. Thank you

[jcalis]

Make sure your airfilter is clean and correctly oiled before jetting the carb.

Stock pilot jet should be fine. Adjust the idle mixture screw and the idle speed knob for best smooth idle ~ 1600 rpm. The idle mixture screw is located under the carb, in front of the carb bowl. It normally has a metal plug covering it if no one has removed it already. You should get a good idle setting about 1-2 turns out from the lightly seated position. Try to leave the mixture adjustment a bit on the rich side for good throttle response off-idle.

Stock main jet is a 127.5. With an aftermaket exhaust and a modified airbox (airbox top cut open) you should use a main jet in the 135- 137.5 range. Look for a good strong pull in the upper rpm range at WOT. keep going up in jet size until you start to get an intermittent skip at WOT. (too rich). Go down one jet size.

[Raptorforme93]

stock pilot jet is going to be ok with a 9mm over bore? I kinda assumed the bigger the piston, the more fuel it will need. Is this not true??

[jcalis]

Sounds crazy but you may find a smaller main jet works better with the larger bore, assuming it was jetted correctly with the stock bore. The larger piston creates higher velocity through the carb and picks up more fuel.

I would try what you have and also one size smaller main. See which one works better.

[Raptorforme93]

Well the thing is that it took my like 30 kicks to get it started. It my my first start on the build and I kicked and kicked with the choke on and off and it didnt even sound like it was close to catching (no backfires or double rotations) and I was going to kick it one more time then go inside and on that last kick it fired up. But after running it and riding it around for a few minutes it ran good but again it would not start. This time it would atleast sound like it was about to catch and was backfiring some. I think that it had trouble starting because of the jetting. Also while it idled for about 30 second, it would stumble every few seconds

[drrick]

double check your valve adjustment.

when valves are out of adjustment it can be hard to start.

good luck.

[Raptorforme93]

Good point. I didnt think of that. Does anyone know what the valve clearences are supposed to be on a 91 head? My manual is for the head of a 97...

[TN2Wheeler]

Good point. I didnt think of that. Does anyone know what the valve clearences are supposed to be on a 91 head? My manual is for the head of a 97...

Service manual says Intake .002"-.004" and Exhaust .003"-.005" for the '91

Later models were .007"-.009" on the Exhaust. Clearance should be set cold.

[Raptorforme93]

Alright thank you very much. Does anyone know what the stock jetting is? It looks like mine is 37.5 pilot and 113 main... Does that sound right? The main was very hard to read the number. Also, does anyone know how a larder piston effects jetting? Thank you very much for all the help!!

[jcalis]

Stock is a 37.5 pilot and a 127.5 main. Most people open up the airbox and can use a 130-135 main instead.

Larger piston usually needs a smaller main jet size. Larger piston creates higher air velocity through the carb and picks up more fuel.

[Raptorforme93]

I do run with my airbox lid on. The previous owner had like an 87 or 88mm bore and had the jetting that I said and it started and ran great. Ill get a few sizes smaller and a few sizes larger. My pilots are ok though right?

[jcalis]

Pilot jet should be fine if you can get a good stable idle with the mixture screw between 1 and 3 turns out. Any more or less would tell you the jet is too large or too small.

I don't think you have a 113 main however. The standard Mikuni jet sizes come in "2.5" increments. Like this: 125, 127.5, 130, 132.5, 135, 137.5, etc.

[Raptorforme93]

It was really hard to read the main numbers so I dont doubt it. I know that there was a three though so it was probably a 130 something. Thanks for the help man