DR350S Dies after closing throttle

[gregmanderson78]

Hey guys,

I just got a 1990 DR350S and I have a very confusing issue. The bike runs great. Usually starts in a few kicks when cold(sometimes even in one), and accelerates smoothly and idles fine. It also has enough power to do 2nd gear wheelies so I think everything is a pretty good shape. It has factory carb and an aftermarket petcock not sure what brand though.

there is one nagging problem. Occasionally, about 1 out of every 3 times i ride it, the bike will die when I close the throttle and begin braking for stop. The is even after I have already been riding around and already stopped a few times. It seems to also be at random when it will die. Usually I can get a started after 5 or 6 kicks following this but the other night I could not get it going again after probably 30 or 40. I gave up and started walking it down the road to the near by gas station. Once there I pulled the fuel line to verify that it was getting fuel and it was, there was also gas in the bowl. I then put the line back on and the damn thing fired right off on the first kick. This was about 15 minuets after I gave up kicking the first time.

This issue has happened with varying levels of fuel in the tank and with the petcock on both reserve and on. The one other issue I noticed is that the carb always looks like its damp or wet and I often smell gas when walking past the bike, it is difficult to tell where the gas may be leaking from. I typically shut off the petcock when I park it so it hasn't been a huge issue but I strongly believe these two issues are related.

Does anyone have any ideas?

Also I will probably be ordering a carb rebuild kit from somewhere, any good suggestions for a fair price and or good quality?

Thanks.

[gregmanderson78]

I am trying to find Carb rebuild kits on the internet. I know that the dr350 dirth version came with a mikuni pumper carburetor but my 350s does not have that. Can anyone tell me what the model of the stock carb for the 1990 DR350S was. I know it is a Mikuni cause its cast into the side of the carb but what model?

[msiddalingaiah]

It's a Mikuni BST33ss.

I would guess the problem is either a float issue or vapor lock.

Next time it dies, open the gas cap and see if that helps.

[gregmanderson78]

thanks for the info and input. Another question for you, if I am looking to go to a TM33-8012 is that automatically have an accelerator pump or is the pump an additional accessory? The reason I ask is because I found this on amazon, but it seems a lot cheaper than other places I've found and I am wondering if it does not have an accelerator pump.

http://www.amazon.com/Mikuni-Slide-Series-4-Stroke-Carburetor/dp/B001AI3JYA/ref=sr_1_1?s=automotive&ie=UTF8&qid=1342996333&sr=1-1&keywords=mikuni+tm33

vapor lock seems like the more likely of your two suggestions, some of my buddies have suggested this as well, if it was float related i think it would happen in other running conditions as well.

[Rooney140]

I have had similar issues with my 350se with the stock carb. Ran great but would die randomly, also had issues with a slow visible bowl leak. Does your local gasoline have ethanol mixed in? Is the gas more than a month or two old?

When your bike quits, turn the petcock to prime and crack the bowl drain as soon as possible to see if it is starving for fuel. On my bike gas flowed freely from the fuel line, and appeared to flow fine from the bowl drain but would slow and eventually stop after about 15 seconds. All vents were clear.

Ultimately I discovered a decent amount of ethanol induced goo in the carburetor body between the fuel inlet and the float needle. Even with the 90% blockage the bike would start and run at low speeds, but would die out after a high speed run. After sitting a minute or two the bowl would refill and the bike would run again. Carb cleaner would not disolve the goo but compressed air blew it out. We have had E-10 gas here for a while and I see issues more and more. The ethanol absorbs moisture and eventually falls out of solution with the gasoline, there are tons of articles on the internet about it.

After a tank flush I finished the carb off with a new bowl gasket, float needle and seat and related o-rings to cure the seeping. I got a kit on an auction site for less than $20. I now use an ethanol treatment and haven't had anymore issues.

[gregmanderson78]

I live in Iowa so ya, weve got ethanol here. I've got parts on the way to rebuild the carb so we will see what comes from that

[Claude Morin]

Hi,

It could also be as simple as Idle Jet too rich setting... That is consistent with your symptoms. Too rich is fine when the bike is cold but after running a while as it warms up, the mixture is too rich for idle.

Also consistent with it only happening when you close the throttle since that's the only time the bike runs solely on the idle mixture. As soon as you crack open the gas, your needle jet comes into play and your problem is not apparent...

Has this started happening all of a sudden, or has it been developing over time?

Claude

[Claude Morin]

You're on the right track anyway... A good cleaning and fresh kit usually wakes'em up pretty good. That's why I like to change my underwear everyday, dirty or not !!!

[gregmanderson78]

I just got the bike a couple of weeks ago so i don't know the history of the problem. I did get ahold of Jesse at kientech and he basically told me to take it apart and then call him. It still run decent so I'm gonna wait a week till I have parts to tear it down. Thanks for the help guys, I'll report back when I figure out what the issue was.

[gregmanderson78]

the bike dying issue was becuase of no vent on the gas tank cap, it was plugged with rubber from the PO. the Carb leaking issue was becuase the tab that the needle valve sits on was bent, and there is a stand pipe that drains the bowl so that it does not overflow. the pipe drains behind the needle drain screw so that is why i thought it was leaking from the screw, but it was really coming in form behind the seat of the needle.