9.9 vs. 15 hp Evenrude difference

[cropduster21]

I am considering buying an Evinrude outboard that I'm told is a 15 hp but it has 9.9 decals on the cover. (used on small lake with 10hp max restriction.)

With the cover off, how can I tell if this thing really is a 15 hp?

thanks, Cropduster21

 

[ezeke]

Re: 9.9 vs. 15 hp Evenrude difference

Generally, the carburetor has a larger throat - different part number. The 15 runs to higher RPM.

See LeeRoy Wisner's article near the bottom of the following web page for detail once you know what year/model you are talking about:
http://www.wisnersinc.com/Fishing Information/Fishinginfo_main.html

 

[wbeaton]

Re: 9.9 vs. 15 hp Evenrude difference

Check the model number on the transom bracket. No one ever goes to the trouble of replacing the transom bracket or the id plate. Sometimes people will cover it over or remove the plate, but not usually. The model number will start E15 if its a 15 hp or E10 if its a 9.9 hp. Let us know what you find.

 

[Sandhammaren05]

Re: 9.9 vs. 15 hp Evenrude difference

Carburetor is only difference. For that reason, 15 hp carbs go for $50-$200 on Ebay.

I am considering buying an Evinrude outboard that I'm told is a 15 hp but it has 9.9 decals on the cover. (used on small lake with 10hp max restriction.)

With the cover off, how can I tell if this thing really is a 15 hp?

thanks, Cropduster21

 

[wbeaton]

Re: 9.9 vs. 15 hp Evenrude difference

Carburetor is only difference. For that reason, 15 hp carbs go for $50-$200 on Ebay.

That was only true for about 3 years in the mid 1970's.

 

[Sandhammaren05]

Re: 9.9 vs. 15 hp Evenrude difference

No, at least through 1989 the only difference is carb. Check the Bombardier/Evinrude parts list on the web to verify it.

That was only true for about 3 years in the mid 1970's.

 

[Patate]

Re: 9.9 vs. 15 hp Evenrude difference

No, at least through 1989 the only difference is carb. Check the Bombardier/Evinrude parts list on the web to verify it.

yep,

heads are not the same in 1989 and on.

and...

Quoted from Mr Wisner website:

You will note that there were 3 different ongoing 15 hp modifications. (1) The 15 hp from 1974 to early 1987, with just the different carburetor. (2) The added leaf valve shim in 1979. (3) And the added tuned exhaust system in 1981, which also included the 2 previous modifications. The 1979 parts manual lists a shim, part #325038 to go between the leaf valve & the stop for the 15 hp only. This shim sells for $2.94 each. It is carried on up into 1992 for the 15 hp, which apparently allows the 15 hp to breathe a little better. These leaf valves are the same for all motors they are used on.

 

[Sandhammaren05]

Re: 9.9 vs. 15 hp Evenrude difference

Leaf plate shims are a minor change, no change in hp (I found no advantage in using them on my record setting 75 after OMC made them available and APBA approved them). Check out the 1974 (!) parts list and you'll find a tuner on both the 9.9 and 15 hp models, that's where a good fraction of the hp on that small motor comes from. It's the carb that adds the 5 extra hp over the 9.9.

yep,

heads are not the same in 1989 and on.

and...

Quoted from Mr Wisner website:

You will note that there were 3 different ongoing 15 hp modifications. (1) The 15 hp from 1974 to early 1987, with just the different carburetor. (2) The added leaf valve shim in 1979. (3) And the added tuned exhaust system in 1981, which also included the 2 previous modifications. The 1979 parts manual lists a shim, part #325038 to go between the leaf valve & the stop for the 15 hp only. This shim sells for $2.94 each. It is carried on up into 1992 for the 15 hp, which apparently allows the 15 hp to breathe a little better. These leaf valves are the same for all motors they are used on.

 

[iwombat]

Re: 9.9 vs. 15 hp Evenrude difference

This topic comes up all the time on this forum. Do a search and check out the old threads. Bottom line - carb throat/jet size is only one difference. Is it THE difference? That's up to you to decide.

 

[JB]

Re: 9.9 vs. 15 hp Evenrude difference

It is clear that over the years the differences change. Getting a 50% increase in HP is not likely to be a simple matter of changing a carb.

 

[wbeaton]

Re: 9.9 vs. 15 hp Evenrude difference

No, at least through 1989 the only difference is carb. Check the Bombardier/Evinrude parts list on the web to verify it.

I think you need to look at the parts lists. I just happened to be looking at the parts list two days ago for a 1986 Evinrude 15 hp I'm working on and noticed that it shows a different exhaust than the 9.9 of the same year. So I guess if you ignore the exhaust tuning and leaf valves then, yes, the carb is the only difference.

Back when the 9.9 and 15 hp were only separated by the carb difference the 15 hp under performed. In fact, I've heard it said, but have no proof that it outputted more like 13 hp.

 

[Sandhammaren05]

Re: 9.9 vs. 15 hp Evenrude difference

You're right, even in 1981 there was a different tuner on the 9.9 and 15. However, on the 1981 25 and 35 the tuner is the same, the only difference is carburetor. That's a 40% increase in power, which is pretty close to 50%.

I think you need to look at the parts lists. I just happened to be looking at the parts list two days ago for a 1986 Evinrude 15 hp I'm working on and noticed that it shows a different exhaust than the 9.9 of the same year. So I guess if you ignore the exhaust tuning and leaf valves then, yes, the carb is the only difference.

Back when the 9.9 and 15 hp were only separated by the carb difference the 15 hp under performed. In fact, I've heard it said, but have no proof that it outputted more like 13 hp.

 

[wbeaton]

Re: 9.9 vs. 15 hp Evenrude difference

Those are completely different motors than the 9.9 hp. However, without looking at the parts lists I know the 1981 had a different lower unit than the 35 hp, which gave up 2 hp. The 35 hp also became the 30 hp with no real changes in 1985 as the motor became prop rated. The 25 hp gained the thru-hub exhaust in the same year and remained the same hp rating. I believe there were other differences between the 25 and 30 hp, but I'm not sure without looking at the parts list. The air intake may be different between them. I'm not going to look it up. Either way, the carb was not the only difference between the 25 and 35 hp either.

 

[CATransplant]

Re: 9.9 vs. 15 hp Evenrude difference

No, at least through 1989 the only difference is carb. Check the Bombardier/Evinrude parts list on the web to verify it.

You are incorrect.

 

[jauguston]

Re: 9.9 vs. 15 hp Evenrude difference

I don't know what other differences there are but on my '92 15 Evinrude the ignition module is different in that the rpm limiting is set for the 7000 rpm engine power rating. I have mine propped for 7100 rpm with one person in my 14' Crestliner Jon boat. 25 mph.

Jim

 

[Sandhammaren05]

Re: 9.9 vs. 15 hp Evenrude difference

Gearcaes on 25 and 35 became same in 1981. OMC did not rate at prop in 1985 (!), the 30 has a smaller throat carb than the 35. Racers in GT-Pro class know that the 20,25,30, 35 powerheads are all the same, the 25 and 30 have smaller carb than 35, the 20 has smaller carb and also intake manifold restriction. Yes, the carb is the only difference between 25 and 35 hp OMC (I go up to 1989).

Those are completely different motors than the 9.9 hp. However, without looking at the parts lists I know the 1981 had a different lower unit than the 35 hp, which gave up 2 hp. The 35 hp also became the 30 hp with no real changes in 1985 as the motor became prop rated. The 25 hp gained the thru-hub exhaust in the same year and remained the same hp rating. I believe there were other differences between the 25 and 30 hp, but I'm not sure without looking at the parts list. The air intake may be different between them. I'm not going to look it up. Either way, the carb was not the only difference between the 25 and 35 hp either.

 

[Sandhammaren05]

Re: 9.9 vs. 15 hp Evenrude difference

Oil: should be 25/1, not 50/1 with standard OMC/Bombardier oil in any John-Rude turning 6500-7000 RPM. To stay with 50/1 in that RPM range, use the new E-Tec synthetic oil, XD-100. I have friends racing the older looper V-6s in Formula One using that oils successfully at 9000RPM at 50/1.
OMC 'rated' the 15 for 6000-7000 RPM but th motor was not built to turn that RPM at 50/1 oil ratio. I'm rebuilding a 1981 model right now that has tiny hairline score on the crak journals, although the rod bearing surfaces look ok.

I don't know what other differences there are but on my '92 15 Evinrude the ignition module is different in that the rpm limiting is set for the 7000 rpm engine power rating. I have mine propped for 7100 rpm with one person in my 14' Crestliner Jon boat. 25 mph.

Jim

 

[freddyray21]

Re: 9.9 vs. 15 hp Evenrude difference

Oil: should be 25/1, not 50/1 with standard OMC/Bombardier oil in any John-Rude turning 6500-7000 RPM. To stay with 50/1 in that RPM range, use the new E-Tec synthetic oil, XD-100. I have friends racing the older looper V-6s in Formula One using that oils successfully at 9000RPM at 50/1.
OMC 'rated' the 15 for 6000-7000 RPM but th motor was not built to turn that RPM at 50/1 oil ratio. I'm rebuilding a 1981 model right now that has tiny hairline score on the crak journals, although the rod bearing surfaces look ok.

50:1 is fine for any motor post 1964. 25:1 won't hurt them but is not necessary.

 

[CATransplant]

Re: 9.9 vs. 15 hp Evenrude difference

Oil: should be 25/1, not 50/1 with standard OMC/Bombardier oil in any John-Rude turning 6500-7000 RPM. To stay with 50/1 in that RPM range, use the new E-Tec synthetic oil, XD-100. I have friends racing the older looper V-6s in Formula One using that oils successfully at 9000RPM at 50/1.
OMC 'rated' the 15 for 6000-7000 RPM but th motor was not built to turn that RPM at 50/1 oil ratio. I'm rebuilding a 1981 model right now that has tiny hairline score on the crak journals, although the rod bearing surfaces look ok.

You're just full of misinformation. Look...most people here aren't racing. They're using their outboards in a normal fashion. The 15 hp outboards specify 50:1. If you're not racing, that works just fine. If someone mentions racing, then your advice might make some sense. For normal use, users should follow manufacturer's recommendations.

 

[Sandhammaren05]

Re: 9.9 vs. 15 hp Evenrude difference

Racing has nothing to do with it, it's about RPM and lubrication. Any OMC or Mercury running normal oil and turning over 6500 RPM needs double oil, but the new synthetic oil can be run at 50:1. Are you a mechanic? I am. I've seen the cranks on 15s after high RPM at 50:1.

You're just full of misinformation. Look...most people here aren't racing. They're using their outboards in a normal fashion. The 15 hp outboards specify 50:1. If you're not racing, that works just fine. If someone mentions racing, then your advice might make some sense. For normal use, users should follow manufacturer's recommendations.