Old DT200 Powerband

[chackett]

Hey All-

Been a while since I've visited, but I have a 1986 Suzuki DT200 that runs like a top. I've spent a lot of time going through the engine and doing things like rebuilding the carbs, resetting floats, sync'ing them, etc. The oil injection on it still works great. What a great motor.

My question .. so now that it's been running great for a while, and I finally got it propped correctly, I'm noticing what I guess is a "powerband." I'll be cruising along at say 31 MPH, rpm's at 4800 ish .. then you can feel the boat lurch forward and MPH will jump up 3-4 mph and RPM's will drop a few hundred RPM. It's really like the motor has changed gears. Many many years ago when I was origionally going through this motor getting the bugs out a fellow said something like "We'll get that sucker running and just wait until you feel the powerband." I assume this is what he's talking about. However it seems to be something taht automatically happens in the motor. I don't know what circumstances bring it on, or if you can engage it "manually." I put that in quotes because I obviously understand there's no actual gear shift or button or switch or anything .. but is it a situation where like "operating at 4800 rpm for 3 minutes or more will engage powerband.?

Anyway, if anyone knows anything about this, or where I could learn more about it, that would be great!

Thanks!
Chris

[Solarman]

Sounds like more of a surging. There is no such "powerband" that this relates to, this is an indication of a problem. Generally this is related to fuel problems, more likely fuel level in one or more float bowls? slightly low float setting (causing fuel to run low in bowl) or a restriction in one or more needle valves causing same thing.
This could also be caused by almost anything, l p fuel pumps getting weak, fuel filters partially clogged, fuel regulator acting up, the high pressure fuel pump getting old/ surging.

Surging is not normal.

Good luck, post back on what you find out.

[Solarman]

Also, there is a possibility that your clutch in your prop is slipping and this would act like you described, "like it's changing gears", but again this too is not normal.

Did you buy the prop new? Do you have a prop rebuilder in your area? Many larger coastal areas have prop rebuilding shops that can re-work props.

Good luck, post back if you find out anything.

[chackett]

Thanks for the replies, I appreciate it! The motor is obviously old and any number of parts are prone to being worn out, so I can appreciate that any number of things could be causing this. I did get a new prop recently. When I bought the boat it was seriously over-propped (there's probably a thread somewhere here about it lol ). It's a 21' wellcraft center console with the Suzuki DT200 on it and I think it had a 23 or 24 degree pitch prop on it. I could never ger RPM's over about 4500 - 4800. I honestly can't remember exactly what my speed / RPM was with that prop. I went down to like a 19 I think .. now I can easily get up to 5k RPM .. although I don't stay there often. I think I've heard or read 5400 is maybe the top end for this motor.

It's been a while since I've punched my numbers into a slip calculator but I guess I'll do that and see what I'm getting. I do remember thinking the new hub seemed like it might be prone to slipping so that's probably a good place to start investigating. Thanks for the tip, I'll let you know what I learn.

Chris