Twin DT 200's die only under midrange operation....

[R_Andersen]

I have a boat with twin 1989 DT 200's. The boat sat for about 4 years before I got it but the motors had been properly winterized when it was put away. I have since changed the impellers and have both motors runnign again.<br /><br />The problem is that both motors run great in neutral and will idle perfectly all day long in gear. As soon as you accelerate above idle, both motors want to die. They just bog down and shut off. If I rev up both motors in nuetral and as soon as they come back down to about 1200 rpm, put it in gear and accelerate hard I can usually get both motors to stay running and then the boat will run fine above 3800 rpm. I drove around for about an hour and had no problems at all as long as I stayed above 3800 on both motors. As soon as I slow down to below that rpm, both motors bog down and stall out. They will both then restart immediately and idle perfectly again. <br /><br />I ordered carb kits and am going to rebuild the carbs but it seems odd that the motors will idle fine and run fine over 3800 rpm, but will stall out at anything in between there....<br /><br />Any advice would be appreciated.<br /><br />Thanks,<br />Rob

 

[fridays]

Re: Twin DT 200's die only under midrange operation....

Pull your carbs and clean them. Properly winterized doesn't mean pickled for long term storage. Engines start up and run on the idle jets which are seemingly clean. Off idle the mid-range is controlled mostly by the emulsion tubes which have little holes which are most likely clogged. Top end runs off the main jets as well as the tubes and idle jets. Bite the bullet, clean your carbs, live happily ever after.

 

[murphy1]

Re: Twin DT 200's die only under midrange operation....

My engines were doing the exact same thing. It's a pain that you have to do twice the work having two engines and all, but like the previous post said, pull the carbs and clean them. Don't do a half a$$ job like I did either, or you'll be pulling them again to clean. Use compressed air and carb cleaner and a paper clip and go through every tiny hole thoroughly. It'll take some time since you have 6 carbs to do, but I did it for the first time a couple weeks ago on my 1987 dt200 and it runs like new again.

 

[R_Andersen]

Re: Twin DT 200's die only under midrange operation....

Thanks for the info guys. I'm 95% sure the carbs are the problem but I just wanted to check. I have 6 carb kits arriving today so I'll be doing a few carbs a night and hopefully I can get the boat back together for the weekend. <br /><br />-Rob

 

[ThomWV]

Re: Twin DT 200's die only under midrange operation....

Try this first, each carb has two large brasss plugs. one on each side of the bottom of its float bowl. These are the main jet carriers. Remove them (they are screw slotted). The main jets screw into their ends and will be easy to spot when you remove the plugs. Clean them out and reinstall them and try it again. They are at the bottom of the float bowl and that is where the crap settles and sets up, they get clogged up if the engine is not used and the bowls were not dranined (not normally done with winterizing) before storage. <br /><br />Thom<br /><br />Thom

 

[R_Andersen]

Re: Twin DT 200's die only under midrange operation....

Well, I rebuilt all 6 carb's and now the motors run fine for about 3-5 minutes and then one or both slows down to 2500-3000 rpm. If I sit for a few minutes they run fine again for another 3-5 minutes. I'm not getting any water flow or oil alarms so I doubt it's an overheating problem. I'm pretty sure it's a fuel starvation problem, so I'm going to look over the fuel bulbs and fuel tank vent's to see if the problem might be there. <br /><br />Any other advice would be appreciated.<br /><br />-Rob

 

[jim dozier]

Re: Twin DT 200's die only under midrange operation....

Check to see if the engine(s) revlimiter is being activated by the oil flow sensor or the temp sensor.

 

[R_Andersen]

Re: Twin DT 200's die only under midrange operation....

It's definately not the oil sensor or water flow sensors. The rev light does not light on either gauge so I doubt that is the problem.<br /><br />-Rob

 

[ThomWV]

Re: Twin DT 200's die only under midrange operation....

Fuel pumps.

 

[murphy1]

Re: Twin DT 200's die only under midrange operation....

When I had that problem, in addition to cleaning the carbs I had to replace my throttle position sensor on the lower carb. I also had a cracked, what I think was, a vacuum hose on the port side of the engine going from the bottom to the top of the engine. I noticed the engine ran well when i disconnected the throttle position sensor, so I replaced it and she's back to normal now. So that was my problem when I had the same scenario as you.

 

[R_Andersen]

Re: Twin DT 200's die only under midrange operation....

Originally posted by ThomWV:<br /> Fuel pumps.

Would bad fuel pumps cause this type of intermitent problem where it runs ok for a few minutes and then starts to die. Then it will run good again after sitting a few minutes?<br /><br />-Rob