DR 350 cutting out at mid-throttle

[Johnny C]

Hey all, I'm new to this forum and I tried to search first, but the search option isn't working right now. Here is the deal:
My 1991 DR 350 starts fine, idles fine, and will run smoothly up through the RPM red line if you work the throttle smoothly. However, when you hit the throttle quickly around 4-5K RPM, the engine wants to cutout. My first instinct was that the carb was clogged, so I pulled the carb and cleaned everthing, including both jets, needle valve, ect. I put it all back together and it is doing the same thing. I pulled the carb a second time and totally cleaned the entire thing a second time, put it back on and it is still cutting out. When you ride it, it will idle and make power if you run the throttle smoothly and slowly. It wants to cut out when you do hard accelerations in the middle of the RPM band when the engine is under load. I tried switching the fuel valve to different positions and it had no effect. The fuel supply seems to be fine, and I didn't mess with the float or any other settings. The plug is new,and I am thinking now maybe electrical problems? Any help is appreciated as I am beginning to lose patience.

Thanks all

[Johnny C]

I guess my symptoms are stumping everyone else too. The more I think about it the more I can't rule out carb problems. The needle jet is what comtrols the mid-range, so are there any tricks to getting the needle jet back in properly that I am not aware of? It is the kind that uses a diaphram and vacuum to raise the jet needle up out of the needle jet. I think I got everything back in the right place-jet needle, slider, e-clip, washer, spring, diaphram. What order do the washers / spacers go on the needle in from top to bottom? Thanks in advance...

[Johnny C]

Well, I just took the carb apart for a 4th time,and everything looks fine. I was able to blow into the port and push the needle jet and slide up with air pressure, just like it should when you open the throttle. Everything is clean, and yet the same symptoms when I try to ride it. It will start and idle, and will even hold high RPMs if you are sitting in the driveway. Once you try to ride it the thing wants to fall on its face and surges badly-almost wants to throw me off the bike as it cuts out. I am now leaning towards ignition problems. I will check the air box, plug, and wire tonite. Any more ideas anyone? Thanks all

[Johnny C]

O.K. Update- I cleaned the air filter and re-checked everything. The carb is clean, and every jet in the carb is the stock jet. No mods have been done to this bike, so re-jetting should not be needed. I think that the bike may be running rich around mid-throttle, and is causing it to bog / cutout. It starts right up, idles, and will run WOT, but will not respond to the throttle in the middle of the RPM band without cutting out. Once it cuts out after you blurp the throttle, the bike idles rough and wants to stall. The only thing left that I can think of is that I have a float problem. It is NOT leaking gas, so I know that the float valve is not sticking. Perhaps the float adjustment got out of whack somehow when I had the carb apart? Any help is appeciated.

[techgesture]

Sounds like ignition to me as well. I dont have as much experience with bike engines as I do with car engines, but if my truck was doing the samething, I would of checked everything you mentioned, then moved on to electrical.

Is there a way to test the ignition coil?

Also, dont rule out spark plug(s), it could be faulty inside. Replace it just for good measure.