Prop or carb??
 

I have a 1993 Mariah 2350Z with a Mercruiser 454 and Bravo 1 outdrive. I run the boat on Deer Creek reservoir (elevation 5400 ft). We usually have about four people in the boat, and one towed. Recently, we seem to be short on power, in thyat we can't get my son fully up on skis. He weighs about 220 lbs.

I am running a 15 x 15 4-blade stainless steel prop. The engine was recently tuned, fitted with new spark plugs, the timing set, and the carb cleaned out. I use stabilizer in the fuel.

When we pull out of the hole, it is sluggish, and I have to set the throttle a little lower than max as it tends to backfire a couple of times on max. Once it gets going, the speed builds up pretty well and we soon have to back off the throttle to avoid over-revving. We keep the rpm below 4800, but it would easily exceed this if we let it.

It has trim tabs, and we can improve the take-off by putting the tabs down to begin with, then ease them off as it starts planing.

The speedo doesn't read true, but if I let the speed build up on 4800 rpm, my son will bounce on the surface and cartwheel several times when he comes off the tube.

My younger, lighter (160 lb) son gets on the skis and we have to back off the throttle a long way to avoid him getting a lot of air on small waves.

So, after all that preamble, here is the question:

Do I need to adjust something to avoid the back-firing, i.e. the carb?

and:

Am I running the right prop? This is the one that came with the boat when I bought it used. Is it worth trying to polish it. I had it refurbished to take out the dings, and it has a dull matte finish.

The engine doesn't smoke, and the oil is a decent color (new when the engine was refurbished). The out-drive oil is clean, and the prop doesn't vibrate if I run it on the trailer (with water intake).

We are not speed freaks, and would prefer a good torque for hole shot with speed limited to 30-35 mph. At the moment, we don't know our max speed, but it seems pretty good and we back off the throttles once up to a good ski and tube speed just to keep the rpm down to 4800 in bursts and 4000 for longer periods.

Any advice is welcomed.

Thanks

Clive

Re: Prop or carb??
 

If most of your boating is tubing/pulling skiers & wakeboarders then that 15" 4 blade should work ok at 5400 ft. Yours sounds like a carb problem and likely a rebuild is in order.

Re: Prop or carb??
 

I.don't.pull my kids faster than 20 or so on the tubes...

Re: Prop or carb??
 

Auyh ,
There is a speed limit of 25 mph at most lakes I go too.
I don't pull any faster than 25 with the kids , sometimes I'll sneak the speedo to about 33 mph with the brother in law on a tube though.:yes_grin:
It ain't no fun biffing it off a tube at 45 mph for most people.
Water becomes concrete at that speed.:(

Re: Prop or carb??
 

Wow. I didn't realize that. Thanks for the heads up. I guess that's why we have been passing everyone. I did find the tubing a little painful on re-entry. I'm a little old for bouncing off the surface and cartwheeling on the water.

Re: Prop or carb??
 

Agreed! :eek_animated: Ouch!

Re: Prop or carb??
 

I took the boat out yesterday and the engine quit after about 5 minutes. Had to get a tow back. I ran it at home before leaving for the lake, with the water hose attachment. It ran fine and I let it run for about 10 minutes to charge up the battery. On the way to the lake, I stopped at a gas stn and put in $100 worth of ethanol free gas. This is the first time I have put the ethanol free gas in as I learned of its existence at $4.00 per gallon, from an employee at O'Reilly's. After it quit on the Lake, we could get it to start, after a long crank, and ran a few seconds then stopped again. Also, if I opened the throttle, it sounded weak. It made symptoms of fuel starvation. When we got home, I pulled the fuel pump and checked the lines were free. Also, that the diaphragm pressurized the out line. Just remembered my chainsaw did same thing with gas from same stn. Could it be water in gas?