can I get more out of a Johnson 30hp

I purchased an 2003 30hp Johnson and noticed you can turn the older 25's into 30 and 35's. Can this be done with a 2003?

Bump, anyone?

How are they doing this? Boring out the cylinder and installing a bigger piston?

[url=https://tinboats.net/forum/viewtopic.php?p=348987#p348987 said:

huntinfool » 16 Apr 2014, 18:11[/url]"]How are they doing this? Boring out the cylinder and installing a bigger piston?

Click to expand...

No. Alot of OMC motors from late 80s to late 90s have the same block. The carb and intake manifold are the only difference.

I turned my 1990 Evinrude 20 into a 30 HP by adding first a new intake manifold then a new carburetor.


I'm not sure if you can do it on that year - you'd have to reference part numbers and look at diagrams. If anything were different, it'd be a larger carb.

I do a lot of this. The 30 already has the big carburetor. There's not much left to do on it. Make sure you don't over-prop it. The engine needs to rev to around 5500-5800 to make its power. Add extra oil for continuous full throttle duty.

Nitrous

[url=https://www.tinboats.net/forum/viewtopic.php?p=349098#p349098 said:

Plasticmotif » Yesterday, 13:58[/url]"]

[url=https://tinboats.net/forum/viewtopic.php?p=348987#p348987 said:

huntinfool » 16 Apr 2014, 18:11[/url]"]How are they doing this? Boring out the cylinder and installing a bigger piston?

Click to expand...

No. Alot of OMC motors from late 80s to late 90s have the same block. The carb and intake manifold are the only difference.

I turned my 1990 Evinrude 20 into a 30 HP by adding first a new intake manifold then a new carburetor.


I'm not sure if you can do it on that year - you'd have to reference part numbers and look at diagrams. If anything were different, it'd be a larger carb.

Click to expand...

True, but the 30 has a higher rpm rev limiter than a 20 or 25. Probably have to change the ignition module to one made for a 30 to get the extra rpm or you are not really getting 30 hp. I'd love to convert mine, but the carbs are very expensive and hard to find.

I'm running a jet on it, so I'm losing power already.

Have you mounted the jackplate and jet motor to the towee? https://www.toweemarine.com/ There isn't a lot of easy hp to add to that powerhead but it should be plenty of motor for that craft if you keep it light. Resist the temptation to add a 24v TM or electric start. I would recommend one of those cheap digital tachs that wrap a wire around a plug lead. https://www.ebay.com/itm/Hour-meter-tachometer-jet-ski-boat-sea-doo-polaris-3d-outboard-kawasaki-js-650-/321377385261?pt=Personal_Watercraft_Parts&hash=item4ad395bb2d&vxp=mtr#ht_769wt_758 Post some photos!

Dropped her off in Michigan today to have the jack plate installed and water tested. Starts cold on a pull and a half so i will resist the e start for now. I got a used terrova 55lb TM for a song so no 24v for me, i should stay nice and light.

[url=https://www.tinboats.net/forum/viewtopic.php?p=349290#p349290 said:

mphelle » Yesterday, 21:58[/url]"]Have you mounted the jackplate and jet motor to the towee? https://www.toweemarine.com/ There isn't a lot of easy hp to add to that powerhead but it should be plenty of motor for that craft if you keep it light. Resist the temptation to add a 24v TM or electric start. I would recommend one of those cheap digital tachs that wrap a wire around a plug lead. https://www.ebay.com/itm/Hour-meter-tachometer-jet-ski-boat-sea-doo-polaris-3d-outboard-kawasaki-js-650-/321377385261?pt=Personal_Watercraft_Parts&hash=item4ad395bb2d&vxp=mtr#ht_769wt_758 Post some photos!

Click to expand...

[url=https://www.tinboats.net/forum/viewtopic.php?p=349283#p349283 said:

Nohasslekindaguy » 18 Apr 2014, 21:36[/url]"]

[url=https://www.tinboats.net/forum/viewtopic.php?p=349098#p349098 said:

Plasticmotif » Yesterday, 13:58[/url]"]

[url=https://tinboats.net/forum/viewtopic.php?p=348987#p348987 said:

huntinfool » 16 Apr 2014, 18:11[/url]"]How are they doing this? Boring out the cylinder and installing a bigger piston?

Click to expand...

No. Alot of OMC motors from late 80s to late 90s have the same block. The carb and intake manifold are the only difference.

I turned my 1990 Evinrude 20 into a 30 HP by adding first a new intake manifold then a new carburetor.


I'm not sure if you can do it on that year - you'd have to reference part numbers and look at diagrams. If anything were different, it'd be a larger carb.

Click to expand...

True, but the 30 has a higher rpm rev limiter than a 20 or 25. Probably have to change the ignition module to one made for a 30 to get the extra rpm or you are not really getting 30 hp. I'd love to convert mine, but the carbs are very expensive and hard to find.

Click to expand...

I was wrong. The 30 does not have a higher rev limiter, it just operates at a higher rpm. 20 to 30 hp motors have a 6100 rpm limiter. Sorry for any confusion.

This may sound stupid but I upgraded my Gamefisher 9.9 to a 15 HP by comparing the parts manuals of each to determine what factory parts were different. In the end it was a larger carb, new reed plates, and a slightly different exhaust that were changed. Seemed to work as my 9.9 would get 10 mph and my 15 HP gets closer to 13 mph.

All I am really trying to say is I'd look at the parts catalog for the 30 and 35 to see if there's a lot different. Sure, takes some time but you may be able to just buy the parts you need for the upgrade...or at least see what's different and how cost prohibitive it is.

In 1986 outboard rating methods were changed. Engines had to be rated at the prop...not the powerhead. As a result, 35hp engines became 30hp. You can find references to 35hp engines after that, but these were military issue. The 35hp was only nominal. Like the commercial engines(45hp,55hp) the extra 5hp was just in the name.

Checking parts lists is the way to tell for sure. That, and taking them all apart and looking at the parts. The 30s built 1986 and after were equipped the same as the 35s 1985 and before. The 2003 30hp is at the top of the pile. It is the equivalent of the earlier 35hp engines already.