1997(?) DT 9.9 2-stroke dies except at high revs

[dmicklem]

Hi,

I have an old DT 9.9 2-stroke that has recently developed a problem:

It starts easily as long as the choke is open and the throttle fairly high. Choke goes in immediately after starting.

It will keep running as long as the revs are quite high (> around half-way on the throttle). Nowhere even close to what might be described as idling.

If I turn down the throttle below about 1/2-way, it will drop in speed and die. Quickly turning up to full throttle will (usually) make it pick up again as long as it hasn't gone below some critical speed.

If I hold the throttle motionless above the minimum where the motor keeps running, the engine revs do not stay constant: it sometimes speeds up suddenly before dropping again.

I'm fairly clueless where engines are concerned unfortunately, but would welcome suggestions about what the problem is likely to be, and what I can do to further diagnose/fix.

Thanks for any help,

David

[Solarman]

It sounds like the carb should be cleaned. If you attempt this yourself, let us know. A service manual for your motor would be good to have, to know what settings everything should be at when put back together.

Without a Suzuki service manual, disassembly should include recording number of turns the idle mixture screw is set at, and what the float setting is at. As well as any other adjustment features for your motor. Then, you should take pics, of any linkages, and hoses, other connections before removal, to be sure to reconnect as it was.

Post back when able to let us know what you're going to do.

[dmicklem]

Thanks Solarman.

I do have access to a service manual that covers everything from 1988-2003 - but must admit to finding it hard to follow (full of instructions to do things "with the proper tool"). Am I likely to need any special tools - I have ring spanners/sockets/screwdrivers/other basic stuff?

But I found a YouTube video that covers taking the carburettor off a DT9.9 that looks very like mine, and it didn't seem too impossible - and knowing that it is likely to be the carburettor is encouraging.

A couple of things putting me off: the video instructed to be careful with various gaskets/o-rings. If I mess these up, are they likely to be easily replaceable? Also, what should the carb be cleaned with? Some sort of solvent?

Thanks also for the good advice to take photos of everything.

[Sealfie]

Thanks Solarman.

I do have access to a service manual that covers everything from 1988-2003 - but must admit to finding it hard to follow (full of instructions to do things "with the proper tool"). Am I likely to need any special tools - I have ring spanners/sockets/screwdrivers/other basic stuff?

But I found a YouTube video that covers taking the carburettor off a DT9.9 that looks very like mine, and it didn't seem too impossible - and knowing that it is likely to be the carburettor is encouraging.

A couple of things putting me off: the video instructed to be careful with various gaskets/o-rings. If I mess these up, are they likely to be easily replaceable? Also, what should the carb be cleaned with? Some sort of solvent?

Thanks also for the good advice to take photos of everything.

It may be that the carburator needs cleaning. However, if that doesnt work, ive had the exact same problems on a few outboards and its been an ignition problem. In my cases, one of the two ignition coils. One time I could even here a ticking sound (discharge) in one of the coils.

I usually use a compressor when cleaning the carbs, fastest way. Sometimes I clean them with ultrasound. If its noticable dirty u can for example use some diesel to help the cleaning but its probably not necessary.

[Hoosmatroos]

Cleaning in an ultrasonic bath is the best. If you don't have one available then use carb cleaner and an air compressor. I do this lots of times in a year for my customers. 9 out of 10 that your problem will be solved.

Any gasket that you couldn't re-use is replaceable. For your convenience replace them all or buy a carb rebuild kit.

You probably don't need any special tools except for a good philips srew driver en some small basic tools.

[Solarman]

As i said, before you disconnect take a couple pics each side of carb to remind you how it should look, when put back together.

Any adjustable mixture screws on front of carb, be sure to count exactly how many turns in until lightly seated closed (write these numbers down, for each carb mixture screw.).
(Some model motors had a low speed, and high speed screws).

Do Not disas-semble any linkages, only the carb bowel and jets and those parts for access. Be very careful with all gaskets/seals etc., and you may not need to replace any.

YOU should be able to soak the plastic and metal parts, jets, etc. without any worries in carb cleaner (1-gal can usually has basket for parts).

Post back when able to let us know how it's going.

[dmicklem]

Thanks for all the encouragement...

Taking the carb off was much easier than I expected (even easier than the YouTube video I found implied), and I cleaned/blew out the jets and everything I could reach. Unfortunately carb cleaner doesn't seem to be available here - probably viewed as too dangerous for mere mortals - so perhaps not as clean as it should have been.

And I wasn't able to take off the float and clean the fuel valve (which the video suggested): the pin through the hinge wouldn't shift.

Re-assembly was similarly easier than expected.

The outboard certainly runs much better now... but the problem is not completely solved. It still dies at low revs - but the point of no return is now much lower than before. Still tends to speed up and slow down when the throttle is held constant.

[Hoosmatroos]

If you can find someone with an ultrasonic tank than you are most likely resolve your issue. Remove all the jets and place it for 15-20 minutes in the bath. Temp of the bath should be between 40-60 C.

Norway is not that far from the Netherlands, drop by then I'll do it for you