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DR350 w/ Thumper Racing 435 kit. Anyone get the stock carb to work?

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After many years of faithful service in stock configuration, when the motor got really tired I decided to rebuild it and do a thorough refresh of the whole bike. New chain and sprocks, new front rotor, FMF Q pipe and sent the motor to Thumper Racing to have them rebuild it top to bottom and install the 435 kit.

Got it back and put it all together, including the jetting they provided for the carb (yes, I tore the airbox a new one as they suggest). I searched around here on the other 350 big bore threads, but it doesn't look like anyone else even tried to make the stock carb work. Is this a lost cause? I would think I'd be able to at least get the bike to run with it, but it won't run below 2k. If you are lucky enough to get it to start you can keep it above 2.5k on the gas. Between 2 and 2.5, it is tough to keep it going. If you try and let it idle it just dies. I've tried both the kit jetting (140 main and 40 slow jet) and the stock jetting (135 main, 37.5 slow) and tried the pilot screw from 1 to 3 turns with both jet combos. None of that helped.

If you think I should just ditch the carb, a recommendation for a specific substitute would be much appreciated. A friend of mine is pushing me to get the Keihin FCR39, and there is one recommendation I've seen for a Mikuni TM36, but in neither case did anyone try and justify how they arrived at that decision, which I am interested to hear.

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Are you running the street model CV carb? If so, I would suggest you dump it and get a dirt model pumper carb. If you're running the pumper carb then you just need to keep messing with it, my DR435 runs great with jetting change and airbox mod.

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Yes, I've been trying to get the stock street model carb to work.

Do you know what jetting you've got in your carb? The jets Thumper Racing sent me were for the dirt model carb, so I am guessing the 140 main/40 slow would be a good starting point.

Is the suzuki dealer the only source for the dirt model carb?

Hmm. Normally when I check eBay there is nothing, but there is one on there right now. Any idea what these things usually go for?

Thanks!

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Before you do anything ... Check you valves ... If they are tight ... the engine will hang at a HIGH IDLE AS YOU HAVE DESCRIBED ... once this is done ... your (what you believe to be) carb problems will be gone. The CV carb ... setup correctly ... is still a good option ... with no money spent

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Yes, I've been trying to get the stock street model carb to work.

Do you know what jetting you've got in your carb? The jets Thumper Racing sent me were for the dirt model carb, so I am guessing the 140 main/40 slow would be a good starting point.

Is the suzuki dealer the only source for the dirt model carb?

Hmm. Normally when I check eBay there is nothing, but there is one on there right now. Any idea what these things usually go for?

Thanks!

I'm not 100% sure of my jetting, it's whatever Jesse at Kientech.com suggested. You can get those carbs on Ebay for around $100, I've got one for sale now but it's pending sale. If you do change you will need the intake manifold, the rubber boot between the carb and airbox, and maybe throttle cables.

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Before you do anything ... Check you valves ... If they are tight ... the engine will hang at a HIGH IDLE

The motor was just completely rebuilt by Thumper Racing. The valves are new and correctly adjusted. The engine doesn't hang either. If you shut the throttle it dies quite promptly.

I do wonder if something is wrong other than the carb though, but if the bike runs fine at high rpm/high throttle opening, there isn't much I can point to as a likely problem. I would have though that although the stock carb might not make the best power, it would at least be workable. But if no one is using it in this configuration, it is hard to get advice for it.

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Well the 435 should run just as well with the street carb as it did before you put in the bore kit, assuming you were using the same pipe and airbox.

Yes, you do want to change to the pumper carb, but you need to find out what is keeping the bike from idling now, a new carb wont fix that. Check the stuff that was messed with when it was rebuilt. Double check the valves, yes and look for an intake leak. Make sure the carb boots and manifold are tight and not ripped/leaking. Spray wd-40 at the carb and manifold while it tries to idle and see if it clears up. If so you have a vacuum leak.

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Made some time this weekend to work on it. Replaced the o-ring on the head side of the intake boot just to make sure nothing was leaking in there. Confirmed that the carb was in good shape and that the valves were adjusted properly.

After a bit of trial and error I found that it worked best with the smallest slow jet I had, and full lean on the pilot screw. That seems strange since the guys who sell the big bore kit AND the pipe both say go richer. Even though I got it so it would idle (if you call 3k an idle) on the choke, it won't idle at anything less than full choke. Getting it so I could take both hands off the bike and it would still run was a big improvement, since now I could move around the bike and comfortablyl mess with the pilot screw, or check vents or whatever.

Next up, smaller slow jets.

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There's an annual ride coming up this weekend. I've done it like 4 years in a row now and it is a good deadline to get me off my * to fix the bike. Eventually I got suspicious that the float needle was not sealing. After replacing it the bike started acting in a more predictable way. Before, it was inconsistent and seemed rich, probably due to a fuel level that was too high. After, it would only run on full choke which said it was lean, which finally made sense, since the big bore and the pipe should both want more fuel.

The big bore kit came with a 40 slow and 140 main. The 40 is probably about right. Maybe a 42.5. There's a 145 main in the bike right now and it still seems lean. At this point I am stoked because it looks like I'm close enough that there is plenty of time to finish fine tuning it before the ride this weekend.

Just thought I'd follow up on this in case anyone else runs into the same problem and is searching for results.

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Did you adjust the idle circuit? The CV carb has a brass plug over the fuel screw which needs to be drilled out so you can adjust it. See the full airbox mod instructions at Kientech.com for details. This should at least get you in the ballpark for jetting with the 435. Maximum Suzuki also has a lot of info on jetting the 350 with various mods.

BTW, if you have an electric start SE model, the FCR carb will not fit as the starter motor is in the way. I learned the hard way and went with the mikuni pumper.

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The idle circuit is being adjusted for each change, yes. I was very suspicious of the whole low speed circuit because of the way the bike was acting, so it has been shot full of solvent and compressed air many times. It's all good and now that the float needle works small tuning changes actually do what you expect. I could tell the 40 pilot is too lean and the 45 was too rich, although the mixture screw could compensate pretty well for either.

Looks like the 42.5 pilot and 145ish main are going to be about right.

As for the other question, the kit and pricing are described in an online catalog:

http://www.thumper-racing.net/cgi-bin/ez-catalog/cat_display.cgi?45X362143

It cost about $90 for me to UPS the motor to them from California. The cost is very reasonable to have them do the work. They also put in new valves for me as the originals were toast, so that made it a bit more expensive, but again it seemed very reasonable.

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That site hasn't been updated in a while. The catalog they sent me has prices about 10% higher. And they've replaced the 435 kit with a 441 kit. Pretty much the same otherwise.

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