35hp w'outboard jet model Q, low WOT rpms

[mphelle8vld]

35hp w'outboard jet model Q, low WOT rpms

I have an 1983 Johnson 35hp, model #J35ECTS, mated to an outboard jet model Q. It will only rev to 4900rpm and while it pushes my 1648 jon 20mph, I've been reading that lugging the engine will lead to an early demise. Anyone out there have a similar setup or ideas?

 

[mphelle8vld]

Re: 35hp w'outboard jet model Q, low WOT rpms

Re: 35hp w'outboard jet model Q, low WOT rpms

Just wanted to add what I've checked so far, the rpm's were verified with a optical laser tach, comp. was 130 in both cylinders, rebuilt the carb, linked and synched several times, timing is set to 30btdc at wot, even removed the powerhead to check for carbon build-up in the exhaust (clean), and then as a last resort installed a friend's spare 30hp powerhead and got the same rpm result!, about 4900. <br /><br />Outboard Jet Inc. supplies the Q series pump for all OMC 20-35hp motors, so if a 20hp should be able to spin the impeller to 52-5400rpm, one would think the 35 could. I've spoken with an engineer at O.J. who didn't think that running at 4900 would hurt the motor, but I've read alot of posts that say otherwise. Any thoughts out there?

 

[MCM]

Re: 35hp w'outboard jet model Q, low WOT rpms

Re: 35hp w'outboard jet model Q, low WOT rpms

Hi, prop choice can effect the rpm's & overall performance of your boat/motor, i e: prop size/pitch vs. total boat weight. See this link:<br /><br /> http://www.maxrules.com/fixproptip.html <br /><br />Also see<br /> http://www.props.net/ <br /><br />Mike

 

[MCM]

Re: 35hp w'outboard jet model Q, low WOT rpms

Re: 35hp w'outboard jet model Q, low WOT rpms

Hi mphelle8vld, Sorry about that last post, I should have read it more closely.<br /><br />I did find this web site that can give you a lot of info on outboard jets.<br /><br /> http://sites.state.pa.us/PA_Exec/Fish_Boat/boatcrs/jet/jetboard.htm <br /><br />Mike

 

[dajohnson53]

Re: 35hp w'outboard jet model Q, low WOT rpms

Re: 35hp w'outboard jet model Q, low WOT rpms

mphelle8vld: Did you ask the guy at Outboard Jets if there were any changes in the setup that might increase RPMs? My outboard jet happens to run within factory recommended specs (about 52-5500). But I have experimented with both the trim and the height.<br /><br />I have both a trim/tilt and a hydraulic lift. I notice that just as with an outboard prop, trim can affect rpms as well as hull trim. You might try changing the trim - whether you have electric trim or just the pin adjustment. <br /><br />That said, the jet performs best when trimmed way in so the intake is close to the hull. If the lift is too low, the motor lugs a little - and lifting it just shy of the point it ventilates does increase RPMs. I believe this is the recommended set up. If your outboard is mounted a little low, you might try inching it up and see if that helps.<br /><br />One final note - although I don't think either will increase RPMs. Make sure your impellor blades are sharp. Outboard Jets publishes a guide for sharpening. It's easy, but do the bevel correctly. Also, there are adjustment washers to adjust the clearance between the impellor and the wear sleeve. Again, Outboard Jets publishes a guide for doing this - easy to do. Good luck and let us know what you find out and/or accomplish.

 

[dajohnson53]

Re: 35hp w'outboard jet model Q, low WOT rpms

Re: 35hp w'outboard jet model Q, low WOT rpms

PS: what is the recommended RPMs for your engine? I know that this can vary quite a bit from engine to engine, sometimes as low as 5000, sometimes as high as 6000.

 

[mphelle8vld]

Re: 35hp w'outboard jet model Q, low WOT rpms

Re: 35hp w'outboard jet model Q, low WOT rpms

Thanks for the quick responses. The data plate is stamped 5200-5400rpm. I found that keeping the motor trimmed all the way in results in the most speed. The leading edge of the foot is even with the bottom of the transom so it only cavitates in a really hard turn. I've played with the loading of the boat to get it up on plane easiest, and while the boat is fast enough for the rivers I fish, I don't want to lug the motor. Outboard Jet recommended raising the impeller with the shims, reducing the effiency of the pump, which gave me about 50rpm but really made the boat sluggish. They also said I could have the trailing edge of each fin on the impeller machined off incrementally and then rebalanced. This seems like a stretch considering the 20hp is supposed to be able to spin this pump.

 

[the machinist]

Re: 35hp w'outboard jet model Q, low WOT rpms

Re: 35hp w'outboard jet model Q, low WOT rpms

One thing I had on a 40 hp was my first jet, I was trying to adjust the shifting linkage at the motor to mate up with neutral on the control lever. It will probably never work out right. What I found was that unless the clamshell snaps up tight against the jet housing on forward, some water pressure as you are going forward will get under the front of the clamshell & force it back slightly. When this happens, you are in effect placing the clamshell back just enough to get a partial reverse thrust. This will definatley slow the boat down & I am sure also effect the RPM.

 

[mphelle8vld]

Re: 35hp w'outboard jet model Q, low WOT rpms

Re: 35hp w'outboard jet model Q, low WOT rpms

Thanks for the thought machinist, it was brought up by O.J. but I've checked it since I get the same result with the boat strapped on the trailer backed into the water with me operating the controls back at the motor, looking for just that type of thing during my testing. I appreciate your insight, if anything else comes to mind, I could use the help.

 

[mphelle8vld]

Re: 35hp w'outboard jet model Q, low WOT rpms

Re: 35hp w'outboard jet model Q, low WOT rpms

^Any last thoughts before I fish this rig to an early grave via lugging?

 

[mphelle8vld]

Re: 35hp w'outboard jet model Q, low WOT rpms

Re: 35hp w'outboard jet model Q, low WOT rpms

^This is a follow-up on my low rpm problem. I've always used high octane fuel in 2 strokes thinking it would aid in reducing potential detonation, after reading several posts on octane, I drained the tank and lines and refilled with 87 octane(no ethynol) The rpm went up to 5450 almost immediately. The slower burning high octane really had a negative impact on my small outboard, hope this helps others.

 

[MCM]

Re: 35hp w'outboard jet model Q, low WOT rpms

Re: 35hp w'outboard jet model Q, low WOT rpms

That's definately something to remember

 

[ozarkrivers]

Cant believe months worth of research led me to this simple of a fix... Thanks alot guys!! Shes runnin great now! And i have a 76 35 hp with a jet also. About how fast does yours run?

 

[GA_Boater]

This is 12 years old, too old to re-open.

Closed.