Speed/rpm of a johnson 150 carb'd eng. on a dusky 20ft'r

[Jquest]

I've been trying to figure things out with my engine for a time now. Basically...it won't go over 5k. Just hovers around it. I believe I've covered all my bases. Other than idling a little rough and high (900 in gear)... it runs fine. <br />The question is....in flat conditions I can get my boat up to 40 knots(gps says). This is for a 150 matched up with my boat. Does that sound about right? Remember...Duskies have one of the heavier hulls around. Their site says 3100 pounds for my boat. From their site....I should get "5250 rpm at 45.2 knots". This is done with a 150 ficht. They used to have a page with carb'd Johnsons and I could swear they mentioned 37mph, but they don't have that page anymore. It looks like they go with a SS prop that is "Diameter/Pitch: ....... 14 3/4" x 19" and don't believe in the 5500 that everyone suggests.<br />NOw...their performance chart tells you how they do the test with the boat. They don't, however, mention a T-top which I added to my boat during Christmas. That would produce addional drag. So it sounds like my boat is doing what it should be doing under my conditions. Does this sound right? I guess the next step would be to put a different prop on my boat to get the rpms up?

 

[Seasport]

Re: Speed/rpm of a johnson 150 carb'd eng. on a dusky 20ft'r

Hi Jquest<br />I have a 2001 150 V6 running a SS 14 3/4" x 19" (SST II)on a 20' fibreglass boat. So a similar set up to yours. My boat is lighter than yours. Hull weight is meant to be 750Kg (1700 lbs) but with fuel etc. I'm probably quite a bit more than that.<br /><br />I too max out at just over 5000rpm and get about 42-43mph (36-37 knots). I haven't played around with the rig setup. I bought the boat from a reputable dealer and presume they set it up correctly.<br /><br />Experts in this forum say ideally you should pull more than 5000rpm (like 5800rpm). As you know, factory specs are max revs from 4500-5500.

 

[Jquest]

Re: Speed/rpm of a johnson 150 carb'd eng. on a dusky 20ft'r

Mighty kind of you Seasport. Thank you for helping me out!!! I'm glad you also have a johnson like mine. THere can be no doubt now.

 

[walleyehed]

Re: Speed/rpm of a johnson 150 carb'd eng. on a dusky 20ft'r

jquest, what part of the 5500RPM do you not believe???? That it "should" be that high?? or it "won't" go that high/??

 

[Dhadley]

Re: Speed/rpm of a johnson 150 carb'd eng. on a dusky 20ft'r

I have an older 20 Dusky also. We've run about every OMC motor on it you can imagine from a V4 to V6. No V8's -- yet. Its a mid 70's model and very heavy. No T top though. <br /><br />With the 60* 150 I run a 3 blade 14 1/4x19 Turbo or a 4 blade 14 1/4x19 Turbo and turn about 5700-5800. With the 150 crossflow I turn a 14 1/4x17 3 blade Turbo about 5800. Obviously its a little slower.<br /><br />We do have a hydraulic jackplate so switching between the props is easy. I think youll be amazed at how high you can run your motor with a decent prop. Dusky is very famous for mounting motors too low. They're more concerned about not having venting problems than engine life.

 

[Jquest]

Re: Speed/rpm of a johnson 150 carb'd eng. on a dusky 20ft'r

Originally posted by walleyehed:<br /> jquest, what part of the 5500RPM do you not believe???? That it "should" be that high?? or it "won't" go that high/??

I'm not sure anymore my friend. I've tried everything. I've brought an Ignition analyzer and checked the timing and it's dead on. I've checked everything. About the only thing I haven't done is....mess with the carbs. I won't do that cause I'm not experienced. And with the searched i've done on the forum....I've seen a bunch of nightmares where people get the boat back and it runs even worse.<br />I live in Miami. Boating Capital of the world. I guess my last choice is to take it to a wrench with a Reputation and see what they tell me. One thing on the prop. I'm not sure what I have. I got these numbers from the hub on the prop. What do these number signify? IT looks like I might have a 20" prop instead of a 19?<br />Stileto 20317 01417<br /><br />EDIT:<br />Ok...I called Dusky. The lady on the phone looked through her books and told me I should have a 15X17. Does that sound right or what do you guys recommend as far as having the right prop?

 

[Dhadley]

Re: Speed/rpm of a johnson 150 carb'd eng. on a dusky 20ft'r

Thats a 17 Stiletto (2=Evin/John hub, 0= V6, 3= 3 blade, 17= pitch in inches). 01417 may be a shop number if it was ever reworked. And that can be good or bad.<br /><br />You should be zinging that up pretty good. Unless its just plain burried. Have you tried raising the motor?

 

[Jquest]

Re: Speed/rpm of a johnson 150 carb'd eng. on a dusky 20ft'r

Originally posted by Dhadley:<br /> Thats a 17 Stiletto (2=Evin/John hub, 0= V6, 3= 3 blade, 17= pitch in inches). 01417 may be a shop number if it was ever reworked. And that can be good or bad.<br /><br />You should be zinging that up pretty good. Unless its just plain burried. Have you tried raising the motor?

Thank you Hadley. It looks like I definately have something going on with the motor. I'm gonna take it to a shop and have them look at it. Then I'll get the correct prop for it.

 

[Dhadley]

Re: Speed/rpm of a johnson 150 carb'd eng. on a dusky 20ft'r

I hope they do find something wrong. If they dont they'll do all the things youve already done. They may even hook it to a propshaft dyno. If its Ok then theyll just sell you a smaller prop.<br /><br />I think youd be money ahead to raise the motor and see what happens. I doubt the dealer will want to do that. If you go up and the r's come up then you found the restriction.

 

[Seasport]

Re: Speed/rpm of a johnson 150 carb'd eng. on a dusky 20ft'r

Dhadley, just how many more revs would you expect to gain by raising the motor each hole position? What are the main problems caused by having the motor mounted too high? With my current motor set up, the prop starts to ventilate if I trim the motor right out (not sure if it is actually ventillating but I get more of a rooster tail out the back of the motor and I can hear a definite change in motor sound). I've had no problems with the prop letting go on corners.<br /><br />Jquest & I seem to have the same situation in maxing out about 5000rpms (as have a few other 150 owners who've posted here). Like Jquest I've checked timing & lync & sync is spot on. My motor runs like a top and hole shot is fine.