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1990 DR350S Cuts out at about 5500rpm...

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Hi Guys,

Bought this bike from a kid for $700.

He had the follwoing done which may impact, and he never could get the bike running again!

- High-Compression Bore kit installed (He couldn't give me the model, size or nothing...)

- Power Trap Muffler

- Low resistance air Filter.

So far I found the follwing issues:

- Timing was off one link - Fixed, released tensioner and did two full rotations to be sure...

- Needle clip was missing in Carburator, so needle was just laying in bottom... Got clip, installed at stock position and throroughly cleaned the carb.

- Fuel Petcock vacuum leaked. Replaced.

Then I could start the bike, but it was barely reaching 2500 rpm before cutting out. I noticed the CDI produced an odd Blue and VERY bright spark. Measured all coils, all in spec. so got a new CDI

Now the bike idles great and runs great up to about 5500 rpm where it cuts out (when just in neutral). The cutout point is very sharp... fine to 5500 then nothing...

Would the mods above require a Main Jet increase that drastically? If so, by how much would be good increase recommendation considering the rpm at which it seems to get starved (5500).

Or should I look elsewhere altogether?

ALMOST THERE !!! VERY EXCITING!! (Please help... :devil:)

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If you are running an open air box and an aftermarket exhaust, you definitely want to change jetting. What carb is on your bike, CV or the pumper carb?

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It's a Mikuni CV 33mm. I believe it's the stock carburator.

While I had it open, I cleaned it and made sure all circuits were free (I had to use a guitar wire to clean out the starter circuit, which worked great.

I also replaced the float, needle and seat, upper vacuum diaphragm and few other parts that came in the kit. I don't know what's currently in the Carb for a main jet, I assume stock. I placed the needle clip at stock position and made sure the float was at proper level (1mm down from bowl gasket via a clear pipe as per Mikuni recommendations.

I am just perplexe that jetting would cause the thing to cut off completely at 5500 rpm. It's not the typical flat or sputtering.

Just wondering, is there ANY timing adjustment to be made other than the CAM mark? I know the CDI takes care of everything. My coil resistance values are within spec... But could they have installed a coil wrong or something that could cause my timing to be bad, or is it really a "It only goes one way" deal. It almost feels like I'm running out of advance as I get into the high rpm.

BUT, jetting might be it. Just not familiar at all with these...

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Does it run if you go up to 5500 RPM and then reduce throttle?

Do you have spark beyond 5500 RPM?

If it stops completely and requires a restart, it could be a CDI/spark problem or maybe a flaky kickstand/kill switch.

The CDI has a high RPM cutout around 10,000 RPM or so. That shouldn't be a problem, but it's hard to tell from here.

One way to check is to remove the spark plug boot and lightly connect the spark plug wire to the plug.

Once the engine is running at idle, pull the wire back and watch the spark jump from the wire to the plug.

Increase RPM and see if the spark is good beyond 5500 RPM.

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