83 suzuki dt 85 with outboard jet underpowered?

[Asnyder19]

hello, recently picked up a dt 85 with outboard jet. Took it out for the first time and it acts like it's not hitting very high rpm's. At full throttle it won't even break plane with our 18 ft starcraft. Top speed was 12. Also at full throttle it acts like it might be missing. It runs pretty smooth but every once in a while the motor shakes for a split second. Almost like it cut out a little. Any ideas? Has good compression and spark and the impellerwas adjusted properly.

 

[jbcurt00]

Underpowered, by more then a little, if running in near perfect mechanical condition, which from your description it isnt.

Outboard jets are inefficient compared to comparable hp regular outboards, and at 85hp a typical OB would likely move you along ok, it too would be underpowered by a good bit. Depending on what 18ftr, they range from 120-150hp max allowable.

So, yep, underpowered.

Never owned a Suzuki, so cant help w tuning it up.

 

[Asnyder19]

I'm not sure the model of the hull. Its an 83 open bow. The in laws has a 65hp on it and moved down the lake fine. It's a light boat, I would think it would at least break plane. I'm not looking for a speed demon. Just want it to run properly.

 

[Sea Rider]

Those jet motors if not sitting at the sweet transom/motor height will perfom badly, poor water level height for internal prop to bite as intended. Can you post a side pic showing the lower leg ?

Happy Boating

 

[Asnyder19]

For some reason I can't. But from the looks of it that could be allot of the problem. Looks like its sitting about 5 inches below where it should be.

 

[Faztbullet]

The 83 Suzuki was not prop rated ...so adding a jet unit to it reduced HP by about 30%. So you take a non rated HP motor*%HP which is about 75 at prop, add a jet and reduce output to 55HP outboard performance..

 

[Sea Rider]

Just to know :

Is it a tiller steering or remote installation with manual/electric trim motor ? Was the jet slowness a gradual one or happened from day before ? Is the boat's hull perfectly clean ?

These motors runs top with the jet nozzle fully submerged, try to duplicate this motor example if the Yam has a protruding edge for water flow to pass at speed under it to achieve the best jet thrust at wot.



But firstly need to know at which lower leg height is the water flow passing by ? at wot pull head side of motor and check that out. Assume that the whole jet nozzle is not working fully submerged, if so need to lower the motor till that cond is fully met. If can't lower it any more the combo is fried, will need to shave the middle transom down a bit,

Other tech issue to have into full consideration is that if the large impeller located inside the jet housing is worn out due to extended use will lose top jet thrust.

Don't know about your Yam jet motor tech specs, need to know them and measure with a feeler gauge the distance as shown in the diagram. If the wear is excessive need to install a new impeller.

Happy Boating