Prop - 98 Montauk w/ 90HP Honda

[txmntman]

Hey folks, I recently purchased this 99 Montauk with a Honda 90 HP. boat is currently lightly loaded and only does about 31MPH. I am starting some troubleshooting, as I expected a little different performance. I really expected a little more top end speed.
* I will weigh the rig to check for water soaked foam, but doubt that is the problem.
* For those with this type of setup (I know there are some) what type props are you running?
* for those of you with this type of setup, what performance are you seeing out of your boat?

The specifics.
-speed checked by GPS, so I know that is correct.
-RPM running about 4300 at WOT
- Current prop is aluminum vortex from Michigan wheel, 13x19
-Cavitation plate is even with bottom of boat.

Thanks for your help!

 

[steelespike]

Re: Prop - 98 Montauk w/ 90HP Honda

What size and weight is the Montauk,style of hull?
Don't know the Hondas max rated rpm but my guess is about 5,500-6,000.
Your off 1,700 rpm I think something else is up Throttle opening all the way?
Check the compression,Raise the motor to a point just before venting becomes a problem.Verify the tach is accurate,Is the prop in excellent shape?

 

[Silvertip]

Re: Prop - 98 Montauk w/ 90HP Honda

You have one of three things going on. 1) Your engine is woefully overpropped (way too much pitch) or 2) the engine is not making full power 3) you have a tach that is not accurate or properly calibrated. Although there are a number of other issues that may cause performance issues those are easily checked. Among those are dirty hull, water soaked foam, not enough power for the size boat (which you did not specify). You also need to determine what diameter and pitch prop you have now. Look at the barrel of the prop or the hub for numbers. Your WOT rpm is about 1000 RPM low meaning the engine is lugging.

 

[txmntman]

Re: Prop - 98 Montauk w/ 90HP Honda

sorry, I keep forgetting there are 3 different sizes of Montauks. This is a 1998 Montauk 17 (not the Montauk 170, which came out in 2002, I think). It weighs about 980 lbs dry, but, of course, you must add the engine weight (373 lbs) and gas (about 15 gal @ 6.5 = 98) and gear (very little now, say 200 lbs with batteries, etc) Total weight in the water is about 1650 lbs.

Hull is in good shape, but is bottom painted.
I don't think the foam is saturated, but haven't yet weighed the rig.
Prop is in good shape, no dings, etc.
Have not checked the accuracy of the tach.
I believe the throttle is wot, but I have not checked that....good idea to measure that....

Thanks for all the input, folks!

 

[sschefer]

Re: Prop - 98 Montauk w/ 90HP Honda

Just for a reference point, The prior owner of my MonArk 1800 FS say's he got 45 mph @ 5975 RPM with a Mariner 100. You should be somewhere in that range also.

In order for your RPM's to drop that far off you would have to be extremely over pitched. I'm running a 13 1/4 X 17 and you should be about the same. If you're anywhere close to that then I would be looking elsewhere for the problem.

 

[DJ]

Re: Prop - 98 Montauk w/ 90HP Honda

sorry, I keep forgetting there are 3 different sizes of Montauks. This is a 1998 Montauk 17 (not the Montauk 170, which came out in 2002, I think). It weighs about 980 lbs dry, but, of course, you must add the engine weight (373 lbs) and gas (about 15 gal @ 6.5 = 98) and gear (very little now, say 200 lbs with batteries, etc) Total weight in the water is about 1650 lbs.

Hull is in good shape, but is bottom painted.
I don't think the foam is saturated, but haven't yet weighed the rig.
Prop is in good shape, no dings, etc.
Have not checked the accuracy of the tach.
I believe the throttle is wot, but I have not checked that....good idea to measure that....

Thanks for all the input, folks!

That weight is about right. Our older Montauk weighs in just about there with a 70 Johnson.

Something is amiss here. I suspect.

1. Innacurate tach.

2. Engine not producing full power.

3. A waterlogged hull. Weigh it.

 

[txmntman]

Re: Prop - 98 Montauk w/ 90HP Honda

I'll try to get it out on the water in the next couple of days...maybe then I can get some more answers...thanks, folks

 

[txmntman]

Re: Prop - 98 Montauk w/ 90HP Honda

Well, it was not a prop problem at all. I took the Whaler out for a run a week or so ago, and it would not move above idle. I moved the throttle as far as I could, and could not ever get above idle. So, back on the trailer, and to a Honda Mechanic.

To make a long story short, the problem turned out to be a problem with sludge buildup on the outside of the carbs.....the throttle would simply not move! We took the carbs off and found the inside of the carbs in relatively good shape, but the carbs would simply not allow the engine to power up. After cleaning the carbs up, and buttoning it all back together, I took it out for a run today. Top speed was about 36 mph (gps) and the motor ran great, with no hesitation out of the hole. I still may try a 17 pitch prop rather than the 19 that is on there now, but today it worked fine. I guess time will tell, but right now I'm satisfied with the engine....