New; Problems with Jet

Hi guys, New to the site. I have a nomera 800.1 on a 40' x 14' aluminum boat lugger 6140 main engine. I am having trouble with the jet maintaing a prime. (or thats what it feels like to me) transmission in gear 1500rpm very little propultion until it suddenly bites engine gets a load and have plenty of thrust. Will also loose prime after getting it or having it for a while? any help would be great.
Thanks,
boat is at www.willamarine.com

 

First of all, check the tightness of the inspection cover, then the bolts through transom.

What version of the Lugger is it (hp @ rpm)? Any transmission? Boat weight and bottom shape?

 

Did you check for sticks or line in the jet; intake grates, shaft, stator?

 

Thanks for the suggestions i have not checked the inspection port boat is in water and inspection port will flood engine compartment if opened i know i could do it but i just bought the boat i would like to do it with the boat on the hard for first time.
It is a lugger 6140 main 500ish hp
hull is shallow v with keel coolers covering majority of bottom 14' beam aluminum
the jet is too small for the boat i only make 9 knots but i knew that pre purchase

 

yes transmission big zf dont know numbers of the top of my head and not yet sure of weight im hauling next week

 

Find some obese guys to sit at the bow with a few cans of beer.
That should give you ample time to unscrew the inspection cover and grope around for any debris.

 

Is the jet Cavitating? Does it rattle a lot while trying to prime?

 

its smooth as can be until in grabs a good prime the engine loads up and ive got good propulsion.
What im really looking for is a recomendation on a shop that you would suggest to rebuild the impeller it is 16" diameter 5 blade anyone?
Boats being hauled this weekend
Thanks

 

If it is running smoothly, but with lack of "bite", the problem is air leaking into the impeller inlet. It may very well enter from behind at low speeds, if there is a disturbence to the flow. Again, actual rpm's and speed at transition is needed for a reasonable analysis. Pictures from inlet region would help.

And, of course, DON'T MAKE ANY CHANGES TO IMPELLER UNTIL THE PRIMING FAULT IS IDENTIFYED!

 

Check to see whether your exhaust is located above waterline? Is your mainshaft of the jet under the waterline? It would be good to know the rpm vs speed you are getting on the vessel. Also before modifying the impeller you will need to know what is the maximum power & rpm of your engine, exact reduction of gearbox before modifying the impeller.

 

Well it was not a problem getting the jet to prime. I did not have any debris blocking the flow of the pump. It was not a cavitation isssue. it had nothing to do with whether or not the impeller was submerged.... It was the linkage to the transmission not allowing to thans to fully engage. I have an electronic control for the clutch. When you push the button for Ahead the lever on top of the trans moves 1/3 the distace it would if you went into engine room and engaged forward mannually. now its perfect SLAM right into gear full propultion (at idle of course).
Thanks for suggestions it was a local trans guy that suggested clocking the rpm of main engine vs shaft suggesting possibly slipping trans that lead me to discover linkage issue

 

good to hear that it is sorted, but cannot believe a jet could function with keel coolers disturbing the flow ahead of the intake. We did a new installation 4 yrs ago with a 6lp yanmar driving a HJ274 that did not go well until we made a polycarbonate cover for the inspection plate and could see and souirce the air and disturbance. Now runs perfect all day 6 days a week

 

The keel coolers dont interfere they are off the centerline and half pipes welded to the hull that only stick down 2" at most.
The boat is 40,000lbs and doesnt plane. It is a work barge i use for mooring inspection. I have lifted and moved 16,000lb granite mooring blocks with it.