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MX-18 135 merc setup problems

DougA

DougA

New member
Hello all: My MX-18 with a 135 merc will not plane with three people aboard with a 19P prop. I've been using a 17P aluminum merc which has been repaired and I suspect is now more in the 18P range. With this 17P I get a decent, but not great, hole shot and top out at 43mph (GPS) WOT. To compound the problem, my tach is not working properly and have been told by a tech that it needs a very expensive, $300+ part in the ignition to repair. I also suspect that my trim is not working as it should. (I've heard that these may be related issues).
I had the carbs re-built last year, compression checks, the whole nine yards but has not helped. I tried the Piranah composite props with basically the same results. Their 17P gave me a slightly better hole shot but only 35mph WOT. I recognize that as a performance boat the Checkmate hulls are different and therefore have different setup standards than set forth in the engine manual and other books. An example is, where should the tilt pin be set for my boat? I am probably not optimizing my performance with the cav plate at and level with the bottom of the hull.
I need a good hole shot for skiing but also hope to get a better top end. As I said, it's an amazing dog with a 19P and only three aboard!!
Any and all comments are welcome. I've already learned a ton in just two days or reading these forums!

Thanks!

Doug
 
Just as a reference, my 115 pushes my 17' boat to around 48 mph (speedo that was almost dead on GPS at 35 mph) with a 19p at 5200 rpms. I needed to get the rpms up over 5500, so it has a 17p on it now and hasn't been run WOT yet. I also have about 7" total setback and a manual jackplate raised about an inch right now, but the cav plate is still below the V. My boat has a small pad (about 3") and a 10-12" notch in the transom. I'm not sure what the MX18 has for pad, notch, etc. I run the trim pin in the 2nd to 3rd hole from the top depending on load. For speed runs, I just move it up until I get too much slip with the prop to try to get the bow up.

I have lots more experimenting to do, and hope to borrow a GPS one day to do it. I need to get the most out of what I have and then get a good prop if I figure out what pitch works best. I think power trim will be a necessity to use a jackplate (especially a manual one) to be able to get going without slipping and then trim back up.
 
Thanks for the reply: Sounds like you're in the same ballpark performance wise as I am but may be trimmed out better. My 19P works great with one aboard or two lightweights but bogs down with any more. I just looked at my trim pin and it's in the second hole from the bottom! Could be part of the problem.
I'm not familiar with the term "pad", is that the top of the transom where the motor is mounted?

Thanks!
 
You want that 1350 to turn 5500-5800 no less. Make sure the timing and linkages are right on. Run premium and 40:1-trust me
 
Thanks Kary: I'll try a tank of premium. How did it and going 40:1 change you're performance with the 1350?
 
Not for performance

It is for longevity of the motor. These old motors don't care much for lower RPMs under load on 87 octane.
 
Could that partially be why the engine seems to "bog down" at take off? What prop do you run?
 
You run a 1350 on an MX18 and I have one on an MX15. Big difference in setup. I have a couple props I run. a 22 pitch chopper and a 24P chopper. You are running a through hub which is a good ski prop. The bog on takeoff sounds like your linkages and timing are not in synch. It takes about 3 steps of back n forth adjusting to get these perfect. When they are right, you shouldn't have any bog in it. The prop selection may be an issue also. It gets expensive picking the right prop. When I am trying to get setup right, it usually takes for to find the perfect setup. Then someone can recommend something from that perfect setup. The problem with yours is there aren't any other MX18s runnin a 1350. Big boat old setup. I usually have 2 props- one for buzzin round the lake, then another for flat out haulin with no kids..

I am not a pro at this, but have had a few boats and am never happy with the setup when I get them. Always gotta run better and faster. PM your number and maybe we can get it done quicker than zaoppin posts on here...:)
 
Remember that motor is only about 90-110Hp at the prop so for speed your not doing to bad. Your 19 may be a tad overpitched as with your 17 and if your motor is really buried it may not ventilate enough to let it spin up.
 
Thanks Blizz! I agree. I don't think the trim has been working and now my tilt is not working either. Just clicks when I press "up/out and "up" and nothing when I press "up" when underway or otherwise. "in" works fine. Next stop is the repair shop!
Doug
 
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