150 crossflow wot rpm

[jy118lfd]

My used 150 crossflow project is running. Wot rpm is 4200 with a 14 1/4 21 prop on a 19 aquasport center console 3/4 tank of fuel and one person. I know I need 5800 the motor runs smooth with no noticable miss. Compression after the run was 87 to 92 psi on all cylinders cold. Is this my problem? I have to do a link and sync but I did not have my old timing light and my advance light dosent work on this. I also have the recirc system blocked. Should I hook this up? I will check wot timing on sat. Do I need to change prop? any ideas will be greatly appriecated

 

[Dhadley]

Re: 150 crossflow wot rpm

You have a lot of motor issues to look at first (sync & link -- timing etc) but youre close on the prop. <br /><br />First I'd verify the tach setting. Make sure its on position 6. Then verify that its hitting on all 6 at wot. With a crossflow we almost always end up with a 19" prop on those boats. They can take some pretty high X dimensions too. We like the 19 Stiletto unless you have a jackplate and then we like the 19 Turbo. <br /><br />If your fuel tank is forward of center and under the deck, like most from the factory, thats going to hurt with a lot of fuel. About the only thing -- short of moving the tank -- you can counter that with is setback. <br /><br />Verify your tach and motor before getting too excited. I had a 19 with the little cutty cabin. Lots of weight forward and the same motor you have. I used a 19 Stiletto and it spun up just fine. Even all the 19' CC we rigged used a 19" prop unless it had a V6 looper. Now that was a fun ride!<br /><br />Good rig, you'll like it a lot.

 

[jy118lfd]

Re: 150 crossflow wot rpm

Thanks, the tank is about center and it is about 40 gals under the console. I am not to concerned with top speed the 40 is fine with me I just dont want to lug the motor. I am going to check the timing and link and sync on monday as I work 24hr shifts and am stuck on overtime on sat. I will post with the results. Should I get a 19 prop or wait and try the other things first. This is my first time tring to set up an outboard correctly. I only have set up stern drives and they are alot like cars. I just want a reliable setup and was a little worried about the compression.

 

[Solittle]

Re: 150 crossflow wot rpm

Hold off on the prop for a bit. Where is the cavitation plate relative to the bottom of the hull? We need to get a sense of where the motor is mounted on the transom.

 

[jy118lfd]

Re: 150 crossflow wot rpm

Cavatation plate is even with the bottom of the v I still have two holes to go up on the mount. I am going to do one thing at a time so I will check the timing and the sync check and post the results. But I wont replace the prop yet. Thanks. The motor is also mounted directly to the transom (no jack or setback) It is a 20" shaft on a step down on the transom I will try to post a pic on monday eve.

 

[jy118lfd]

Re: 150 crossflow wot rpm

Also boat jumps on plane rather quickly just does not get rpm at wot. Just a little more info

 

[jy118lfd]

Re: 150 crossflow wot rpm

Went out yesterday timing was 23degrees set to 28 did link and sync ran wot 42mph at 4100rpm. I think the tach is wrong it was set on the wrong setting and when I set it to 6 cyl it was over 6000 rpm at wot.When I set it at 8 cyl it read the closest as it was 5200 at wot. I am going to replace the tach and retry.I think its a four stroke tach. No miss at wot but loaded up slightly at idle in no wake zone. Should I set up the recirculation system as it is looped with hose right now?

 

[Dhadley]

Re: 150 crossflow wot rpm

Yes, that sounds like the wrong tach. Lets not worry about anything else right now but the tach. If we make more than one change at a time we will lose our baseline.<br /><br />Good info.

 

[jy118lfd]

Re: 150 crossflow wot rpm

I will change the tach first, then retest without changing anything else. Will post after test

 

[jy118lfd]

Re: 150 crossflow wot rpm

By the way, prop slip calculator 4200 rpm 1.86 gear ratio,21 pitch prop, slip comes in at 6% totally unrealistic. 5200 rpm comes in at a believeable 24%

 

[jy118lfd]

Re: 150 crossflow wot rpm

Went out today 19 pitch prop (borrowed) New tach set on 6p rpm was 4200 at wot. Of course I left my gps home no speed. In the ocean was able to get 5800rpm wot for about ten minutes. I went back about 1 mile then turned around and went the other way I did this about 5 times each time got about 5800 fully trimed out. When I came in I went through the inlet (no wake) then in the river could only get 4200 but it felt the same. I will go out on sunday and test with gps. But in the ocean it was a bumpy ride and maybe I have a loose connection somewhere. Does anyone know what wires could cause this. Also if the motor was high speed misfiring wouldn't I feel it? It doesen't miss at all through the rpm range now that I hooked up the recirc system and replaced 3 check valves. Thanks for everyones help!

 

[jy118lfd]

Re: 150 crossflow wot rpm

Dhadley I had it out today and tried a 15x17 prop that I had lying around. 5100 rpm and 44 mph holeshot was unreal. My question is I can trim all the way up and not lose prop bite. It knida rooster tails and you can see the water spray from the cav plate come out at a 45 degree angle. I still have 2 holes to go up How much rpm can I expect to get by raising the motor? Also the 15x 17 has no vent holes in it should I add these?<br /><br />I also checked my tach with a fluke meter and it reads right so I know rpms are accurate. <br /><br />I will also say that the 15x 17 is an omc prop and the other props I tried were hustler, all alumnium. What is funny is that I went from a 141/4 21 to a 19 pitch and did not change rpm at all. The hub seems rather large and it looks like it could create quite a bit of backpressure on the exhaust. I dont know if this was the problem but to go to the 17 and get 900 rpm seems like alot. <br />If I can get it to rpm right I will be tempted to go and get a stiletto like you said

 

[jy118lfd]

Re: 150 crossflow wot rpm

bump