Mariah and Barefooting

[Grillzy]

I have a 91 Mariah. Love the boat. But today I decided to try barefooting again. Wife says it topped out at 36mph (no gps) with me footing. I am approx 160lbs it was just fast enough, barely. The boat does everything else I want but now I'd like footing again. My son was footing for the first time today behind it but he is 130lbs. Any suggestion on getting more top end and not loosing the bottom or over rev?

[cadunkle]

What prop is on it and what is your WOT MPH and RPM?

[Grillzy]

Supra WOT 2.jpgSupra WOT 3.jpg

Taken today. About 3/4 tank of fuel and just my wife and I in the boat. Prop is 3 blade numbers and writing on the prop are 19117, Michigan, NI-BRAL, 3 90 cupped, 14RH14. Not sure if anything other than the dia of 14 and pitch 14 right hand is needed. I did gps speed and the speedo on the right correct one one, the left needs to be replaced. I did hit 37mph gps and speedo on the second pass but that was at the end of the run of lake.

[cadunkle]

Not sure what ratio is in the gear reduction trans but your around 1 MPH per 100 RPM which is typical for how these are usually propped.

I'm concerned about the low RPM. You should be getting 4400-4600 RPM WOT. Are you significantly above sea level? Check timing , should be 8*-10* at idle and 30*-32* by 3000 RPM. Check that your throttle is fully opening the carb butterflies and that the secondaries are opening. Check tune up items if it hasn't been done in a while. That engine is down on power for some reason, 14x14 isn't over propped particularly with gear reduction trans.

[Grillzy]

Ya pretty sure 1:1 on the tranny. The 4500 rpm range is what i was expecting. south eastern Ontario Canada so no not above sea level by much. motor runs perfect so not sure about timing. Motor idles at 900 rpm. Engine was converted to electronic ignition before me. Motor does not smoke etc. Approx 750 hours and well cared for. Maybe the throttle is not opening up completely? How to check that? push throttle down then see if i can hand push more at the carb? I like to wrench some but don't know anything about carbs. Maybe something like throttle cable stretch? Thanks

[zroe]

You probably need to replace the secondary diaphragm, you are probably only using two of your four barrels in your carb because the vacuum secondary isn't opening. I have the same problem currently and will let you know if the secondary diaphragm fixes it, but it may be a week until I can work on my boat and get it out for a test drive. The secondary is only $15 on Amazon or you can buy a full carb rebuild from O'Reilly auto that comes with it for $60


Sent from my iPhone using Tapatalk

[Grillzy]

Zroe. This is great info! You have the same boat motor carb? Guess I should check the numbers on the carb and order a kit.

[zroe]

I have a PCM351W with a Holley 4160 series carb. You need to look on the "air horn" for the actual model number. Mine is 75009-3 and I got a Holley TricKit 703-28 which includes the secondary diaphragm and is meant for the marine carbs. It cost $42 at Oreilly Auto. Haven't had a chance to put this in yet to find out if it works but I think it will because if the secondary doesn't open at WOT you are only pulling air through half the carb so it is almost like running with the choke on.... I'll keep you posted if it solves my issue.


Sent from my iPhone using Tapatalk

[zroe]

So I tore the carb down and one thing led to another, not to mentioned we moved! I am a bit embarrassed to admit I left the bowls on the carb cleaner to long and took off the factory coating I found a new carb for $62 as a back up but I plan on still putting the original back together to see if there was any improvement. Sorry it has taken so long to reply. I'm actually doing a small (for now) rebuild of the floor after removing all of the wet foam so it might be a few more weeks before I am on the water.


Sent from my iPhone using Tapatalk

[Grillzy]

Sad to say due to a crappy weather last summer the boat was in 3 times. I know sad. First launch this year starter was done. Its now replaced. Hope to get the boat in the water this week to see if secondaries are opening.