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Caltransboy

1999 Suzuki DR350 carb jetting

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Just want to pass on a tip For jetting a carburetor on my DR 350.

The first few times I pulled the entire carburetor off which is kind of a pain in the neck.

I found that if you just loosen the clamps on the intake and the airbox rubber snorkel, and undo the rear brake master cylinder reservoir. The carb will turn sideways and it’s EASY to takeoff the float bowl to change the main jets or a pilot jets. (15 min)

 

Also I’m running a DG pipe with a modified airbox on mine and I am already up to a 145 Main Jet, Stock pilot jet 37.5, and One nylon sham underneath the needle.

 

It runs really good on the low end and mid range but is just a tad lean because I can’t seem to get it above about 7 1/2 thousand RPM in sixth gear. Should go to 8500

I’ll try going up one more size on the main and see if I can get the extra RPM?

The bike just might be struggling to haul my Fat Ass around....Or it’s That damn CV carburetor that the slide doesn’t open up all the way ???

 

Any thoughts??

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That’s interesting!! I was figuring since the tachometer redline goes to 8 1/2 it should rev to 8 1/2
Thanks for the info

I’m going to try one larger size up on the main jet and if there’s no improvement I’m gonna say I’m spot on with what I have now. The mid range and lower end are perfect...

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Hate to say this but the lack of top end is because you are way too big on the main.  Any more than about #132 will seriously affect peak power.  To "solve" the requirement for a richer mix when opening up the airbox you need a thinner (richer) aftermarket needle, Dynojet works. 

 

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Hate to say this but the lack of top end is because you are way too big on the main.  Any more than about #132 will seriously affect peak power.  To "solve" the requirement for a richer mix when opening up the airbox you need a thinner (richer) aftermarket needle, Dynojet works. 

 

Thanks for the input. I’ve tried a series of jets in this ranging all the way from 130 and now To 145. When I had the 132 and 135 in it it ran like a turd. So far it seems to be running good with the 145 jet in it? I got it up to 8000 RPMs today and couldn’t use much more anyway?
I like your idea of going with a Dynojet kit. Except I already have a pretty wide assortment of pilots and main jets.

So here’s another question? I have a CV dirt carburetor from an earlier model which has a different linkage system but other than that it all looks the same as mine. What I’m thinking about doing is taking its tapered needle and replacing my stock needle which doesn’t have any adjustability to see how that works? Do you have any thoughts on making the switch?
It only take about 15 minutes to do but I don’t want to start chasing ghosts. I also don’t want to spend $50 for a jet kit if I only need the needle.
Like I said, it’s running pretty good now and the plug chop only shows it’s a little bit rich.

Again, thanks for your input

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Thanks for the input. I’ve tried a series of jets in this ranging all the way from 130 and now To 145. When I had the 132 and 135 in it it ran like a turd. So far it seems to be running good with the 145 jet in it? I got it up to 8000 RPMs today and couldn’t use much more anyway?
I like your idea of going with a Dynojet kit. Except I already have a pretty wide assortment of pilots and main jets.

So here’s another question? I have a CV dirt carburetor from an earlier model which has a different linkage system but other than that it all looks the same as mine. What I’m thinking about doing is taking its tapered needle and replacing my stock needle which doesn’t have any adjustability to see how that works? Do you have any thoughts on making the switch?
It only take about 15 minutes to do but I don’t want to start chasing ghosts. I also don’t want to spend $50 for a jet kit if I only need the needle.
Like I said, it’s running pretty good now and the plug chop only shows it’s a little bit rich.

Again, thanks for your input

So just to clarify I have twoCV carburetors. One is from a 1991 or 1992 dirt model That has the tapered needle with the adjustable clips, and the other is from a 1999 enduro with no adjustable clip but I’ve been running a small nylon shim under it

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The UK model came with an adjustable needle, but even raising it right to the top did not make the mixture rich enough. The "cheap" fix is to go as big on the main as you are personally happy with and adjust the needle to suit, and accept some top end power loss.

Some folk don't rev their engines much and won't notice, its over about 7000rpm that it shows.  With the right jetting the DR pulls willingly right round to 9000rpm in all but 6th gear.

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like caltrans, also tried a range of mains (have big box, see bellow :) ) and MINE was happiest / pulling highest speed by GPS with a 140, your bike could be different and its totally fine. In another 350 forum people seem to be happiest with "anything" from the stock 127.5 up to 145... You are absolutely right about sorting the main first, but in my case 132 was still lean, also by plug reading. 

indeed, as the dyno run shows, the engine can rev to 9000 but not sixth gear, past the power peak at 7500, but that was exactly the question from Caltrans that i tried to answer: why it doesnt pull to 8500 in 6th...

interesting that early CV models had 135 stock, before going down to 127.5, because of emissions, see item 21

https://www.ronayers.com/oemparts/a/suz/50d3aa98f8700220d0b71fbf/carburetor-model-l-m

 

jets.jpg

Edited by turboguzzi
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Thanks for all the input guys. I think I have it just about figured out. Currently I have:
145 main jet,
37.5 pilot jet,
one shim under the needle,
One and a half turns out on the fuel mixture screw.

Yesterday I put one more shim under the needle to raise it up what would be a notch. That gave me a little bit of hesitation and gurgling at around 3000 RPM.
I switched it back to only one shim and no more hesitation.

The information provided about revving in six gear was really helpful. Coming up through the gears I can redline every shift. But when I get it into six gear it just seems to Plateau at about 8000 RPM which is about 85 miles an hour.

So again, with the modified airbox with the Uni filter, and the slip on DG pipe I’m really close!!!
I might try going up or down one size on the main to see if it gets better or worse, and if I don’t see any improvement I’ll go back to the 145 and call it good?

After I get it all set...I’ll probably try putting in the modified slide, (1/8 inch holes) the modified shortened spring, and the adjustable needle that I have on that OTHER carburetor. If it doesn’t work out I’ll still have all The original stuff to put back.
I’ll start another post about drilling the slide and cutting the spring ♂️

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