RPM of XP150 too low?

[farginicehole]

Finally got my '89 XP150 sparking on all six - took a new timer base and power pack. Tach still acts up, so I need to figure out if it's the wiring, the tach or the rectifier/regulator. Either doesn't work at all, or works but appears to be reading 1000+ rpm higher than actual. Anyways, the motor runs very smooth now but still am only getting 40 mph top speed out of it. It's on a '91 18.5' Alumacraft 185CS walleye boat, and it has the 15x17 aluminum prop. When the tach was working properly (at least I think), I was only getting about 5000 rpm at WOT and the 40 mph. I know from reading here that I am definitely lugging the motor (if the tach reading of 5K was correct), and I'm thinking even an older 150 should be able to push this boat to around 50 mph "if set up properly". Any thoughts? Carbs haven't been re-built in about 4 years, but this was the same top speed I had right after having them re-built by a reputable pro. I de-carbed last year, and compression is good and even on all six. Any suggestions as to where I should start? Thanks!

 

[Dhadley]

Re: RPM of XP150 too low?

Something still doesnt sound right. I have basically the same motor on my Dusky, which weighs about double your boat, and we swing a 19" Turbo more than 5000. <br /><br />After you changed the pack and timer base did you check the timing? Sync & link?

 

[farginicehole]

Re: RPM of XP150 too low?

And just out of curiousity, because I know it's probably comparing apples to papayas, what top speed do you get out of your Dusky? I have a feeling this boat was never set up right from the beginning. I bought it about 5 or 6 years ago, the motor is an '89, the boat is a '91, the trailer is like a '92 or something. . . . <br /><br />No, I haven't checked the timing but probably should. That will be another "first" for me, but I have a Clymer manual, so I should be able to figure it out. When you say sync & link, do you mean the (fairly simple) procedure when you make sure the one mark (I forget if it's the short or long one) on the throttle cam lines up with the "centerline" of the follower/roller at the moment they come into contact, and also that with the throttle lever all the way forward, the butterflies are fully open (& the retaining pins are all lined up and vertical)? If so, yes. Thanks for the reply!

 

[Dhadley]

Re: RPM of XP150 too low?

Thats a good question on my top speed. I think its around 45 with the crossflow and 48 with the 60* looper. Seems like everytime we go out its too rough to worry about fast. Nothing wrong with cocktail speed though.<br /><br />Yep, on the sinc & link thats what I was wondering -- the timer base goes all the way to the stop and the carb butterflies are completely open without going past center.<br /><br />On the timing stop screw, is the bolt itself about centered?

 

[farginicehole]

Re: RPM of XP150 too low?

Yes, the timer base goes all the way to the stop when the throttle lever is in the full-forward position. As for the position of the actual timer stop bolt, I'll have to take a look later when I'm at home because I can't remember. I have not adjusted its position since I've owned the boat, but that sure doesn't mean it's right!<br /><br />I'm not familiar with what type of a boat a Dusky is. Is it a deep V, fiberglass center console? If that's the case, and you think it is about twice as heavy (really?!) you get around 45 mph, then I ought to be able to get at least that out of my Alumacraft. . . shouldn't I??? Not that it's the most important thing to me, but I want to make sure I've got the rig set up right for once, and I'll admit it is a little embarassing when I get passed by similar style boats with a lot less motor. <br /><br />Do I need a special timing light for a 2-stroke outboard, or will an automotive one work? I hope that doesn't go down as "stupid question of the week"!!

 

[Dhadley]

Re: RPM of XP150 too low?

Nothing gets classified as a stupid question. Its not allowed -- There are no stupid questions! Lol!<br /><br />Yeah the Dusky is a semi-deep V and fiberglass. Its an older one thats been redone. For a 20' boat its pretty heavy but thats good in some ways. <br /><br />But yeah, your aluminum boat should be way lighter. Thats why I was surprised that youre only turning a 17. Years ago we sold Starcrafts at the marina. We used to rig the 21 center console models with 150's (crossflows were all we had then) and run 21 SST's on them. They'd get right at 60. <br /><br />And yes, an automotive light will work just fine.

 

[farginicehole]

Re: RPM of XP150 too low?

Just stupid boaters. . . just talk to ME after a few laps around the lake at "cocktail speed"! Particularly if the fishing action is slow. . .<br /><br />Probably not half as light I'm guessing, but I get your point. Probably somewhere in the ballpark of the Starcrafts you sold, and if they were hitting 60 mph with 150 crossflows, then something is WAY wrong with my setup! Do you think that 15" diameter prop has a lot more drag than a 14 1/2"? Maybe I ought to be on the lookout for a 14 1/2 x 19 or even 21 stainless, install it and go from there? I realize I also need to get my tach issue resolved so we have something reliable to go on.

 

[Dhadley]

Re: RPM of XP150 too low?

Exactly. The tach needs to be correct as thats what we're going by. I really like the larger diameter props. They usually allow for a higher mounting or X dimension. That reduces drag. <br /><br />I would suggest we get the r's up with what you have. I'd rather do that than go buy another prop right now. Besides - we sure dont want to, at this point, put on a bigger one (more pitch).<br /><br />Is your motor mounted all the way down on the transom? I'd almost bet it is. where is the AV plate in relation to the bottom?

 

[farginicehole]

Re: RPM of XP150 too low?

Okay, well I'll try to figure out what's up with the tach as soon as possible. Do you think a rectifier/regulator could be causing the tach symptoms I described in my first post in this thread? Last night was the first outing for this year (due to the pesky ignition problems!), but last year it would either read around 5K at WOT, or it would not read anything at all, or it would jump up to 6100-6200 rpm. I always figured it was working properly when it was reading 5K, but who knows?! My ears aren't calibrated to tell the diff between 5K and 6K, unfortunately. I'll have to take a look to be sure, but I think the motor bracket is all the way down on the transom. But, I'm pretty sure the anti-cavitation plate is right about inline with the bottom (the center "rib"). Sounds like I need to get it closer to being in the ballpark, then worry about the prop last? Thanks again for your replies - I know you're a very busy man on this forum!

 

[Dhadley]

Re: RPM of XP150 too low?

Yes, the reg/rec could be the cause of the irratic readings. However, I'm reluctant to just say "go buy a new one" until everything has been checked out. After all, it could be the tach.<br /><br />Just for kicks, lets look at the flywheel. The 89 150 XP should have the 35 amp system. Look up under the flywheel at the magnets on the outer edge. Make sure they're all evenly spaced and not loose.

 

[farginicehole]

Re: RPM of XP150 too low?

Yeah, me too because they are pretty expensive! Yes, it does have the 35 amp system, and the magnets are all very secure and evenly spaced (doesn't even look like they've ever been repaired). I'll try and check out the connections and stuff this weekend and get back to you.<br />Edited: I guess rect/reg's aren't all that bad at around $160 - I was thinking they were $100 or so more than that. I'll check back in next week - have a great weekend!

 

[Dhadley]

Re: RPM of XP150 too low?

Sounds good. I'll be away this weekend myself so dont think I'm ignoring anybody if I dont respond.

 

[walleyehed]

Re: RPM of XP150 too low?

I might be able to add some insight to this...I have an 18ft Starcraft, fairly heavily loaded with trolling motor up front, 3 batteries and about 26 gallons of fuel. I have a 2.5L 200 Rude with XP heads and I can turn 6200 with a 15X17, and still have a touch to go...a 19 puts me about 5850, and I can turn a michigan edge 22p about 5600 with a speed of about 56-57...slight chop I can get 58MPH. The edge we've been told, acts simular to a 20P Raker.<br />Here's the kicker...#1, I'm at close to 4000ft above sea-level-about 12% less power than rated...I also have a bit over 8" of set back and am 3-1/2" higher than level with transom.<br />If it weren't for Dhadley, I would likely have it in the second hole, mounted directly to the transom, burning ALOT more fuel at a much slower speed and in the market for a 250HP...

 

[farginicehole]

Re: RPM of XP150 too low?

If it weren't for Dhadley, I would likely have it in the second hole, mounted directly to the transom, burning ALOT more fuel at a much slower speed and in the market for a 250HP...

So it sounds like Dhadley advised you to get a jack plate maybe? I was gone most of the weekend, so didn't get to run my boat. Actually, a buddy and I made it to the launch last evening for a little musky fishing, and I'm not kidding that we had the trailer/boat in the water, I had the motor started, and was motioning for him to back me the rest of the way in when the downpour came. My cavitation plate is lined up with the bottom of the boat, which I thought was right. . . would you guys suggest I try raising it up an inch or so? Guess I should probably figure out the tach problem first, but since I'm only getting 40 mph, I'm sure my rpm is way low! Sounds like your rig is very similar to mine, except your motor is bigger by 50 hp.

 

[MGuckin]

Re: RPM of XP150 too low?

1) Fix the tach first.<br />2) Verify tach.<br />3) If rpm's still low, with existing prop, jack motor 1 hole (increase x factor) or so at a time until handling is unstable. Keep in in mind, you want the RPM to max out about 5800 - 6000 and still be able to handle the hull with your normal average load (weight).<br />4) Then consider new prop if needed. Largest diameter possible.<br />I suspect you will end up with a prop in the 21" range.<br />I have an 18' Starcraft aluminum semi vee swinging a 21' on a 84' Rude 150 hp.<br />Dh helped me set this boat up 2 years ago.

 

[farginicehole]

Re: RPM of XP150 too low?

Okay, but I think I can only go up about 1.5 inches or so with the mounting bracket on the engine. It looks like it is in the "all the way down" position now, however. Looks like I just need to take out the top two bolts, loosen the bottom two, and maybe use a hydraulic floor jack or something to lift the engine up. Does this sound right? Will try and fix the tach first though. How do I know for sure if my rectifier/regulator is bad?

 

[MGuckin]

Re: RPM of XP150 too low?

This would be much easier with a manual for you to follow along with. Hopefully you have 1.<br />Been awhile but I'll give it a shot. I think I got this right but if I am wrong, I know I will be corrected.<br />1) Engine in water or test tank "not on muffs".<br />2) Check and note battery voltage with key in off position. Must be 12.5 volts or lower. If it isn't, disconnect the charge coil connectors and crank the motor in short bursts (don't start it yet) until voltage has dropped down enough then reconnect the charge coil.<br />3) Disconnect battery cables - negative first.<br />4) Hook a 0 - 40 ammeter in series between battery side of starter selenoid and the rectifier/regulator red lead.<br />5) Reconnect battery (positive first)<br />6) Start engine and run @ about 4500 rpm. Ammeter should read full output. After running a bit, amp output should drop and voltage should settle around 14.5 volts.<br />As far as lifting the motor, you are dealing with almost 400 lbs. Do not jack up the motor, lift it but again we need the tach working correctly first. When the time comes, should you decide to jack this, make sure you seal the mounting bolts.

 

[farginicehole]

Re: RPM of XP150 too low?

Thanks Mike. Yes, I have a Clymer manual for the motor, and I'll have a look and compare to your procedure. When you say "0 - 40 ammeter", do you mean to have the ammeter set on the 40 amp range? If so, does "full output" mean it's supposed to actually read 40 amps?! Guess I'll have to rig up some sort of hoist to lift my motor when the time comes.

 

[MGuckin]

Re: RPM of XP150 too low?

Set it where the scale will read what the system is designed to put out. It should read what the system is rated at which in your case is 35 +/-

 

[walleyehed]

Re: RPM of XP150 too low?

Or....you can just check batt voltage with a DVM before starting...after start, run up to 2000RPM and check batt. voltage. If it's working it will not be higher than about 15.1 volts.