Performance Question

[JSMoore]

I run a 1997 Evinrude 90 SPL, (E90TSLEUA), on a 19ft center console boat. The motor runs absolutely flawless at all speeds. Compression is 120, + or - a pound or two in all four cylinders. It's propped for 5200 RPM at WOT and typical loads. And, I get about 30 knots on the GPS.

Sounds OK. But, this rig has always seemed just a little "sluggish", some how. The boat is rated for a 115. And, I'm sure a re-power to a 115 would light the fires a little brighter. But, that ain't an option.

However, a buddy offered me a set of carbs off his locked-up 115. The carbs are exactly the same as mine except for the bore. Now.... I know changing the carbs ain't going to turn my motor into a 115 because of the differences in the exhaust side of the thing. But, I would think it might open it up & give it just a little bit more "umpfh". So, my questions are: Do y'all think a set of 115 carbs on this 90 would make any NOTICEABLE difference in power? If there would be some difference, would it be enough to justify the expense of cleaning & kitting the 115 carbs and installing them on my motor? Would it be likely that I would have to re-jet the 115 carbs? Or..... perhaps it would be best to just let well enough alone?

I appreciate any educated opinions y'all might have.
Thanks!
JSMoore

 

[coolbri70]

Re: Performance Question

works on a 9.9 to a 15, but the exhaust was done too. not sure if its the same on the v-4 or not, but am curious to hear as i have an 85 that would be nice to get a little more out of

 

[boobie]

Re: Performance Question

As long as it's running as good as you say, leave it alone and save some $$$$. You wouldn't notice that much difference in the performance anyway.

 

[trendsetter240]

Re: Performance Question

Not sure how much of a difference it will make but carb kits are cheap. Only two carbs on those crossflows and I think the kits are about 17-18 bucks each. So for 40 bucks and a little elbow grease you might see a bump in performance. Then again you might not.

 

[emdsapmgr]

Re: Performance Question

The first thing to do is to consider changing the prop to a lower pitch. At 5200, the engine still has some rpm's left to give. Normally, it should top out at 5500. So, go down one size on the prop so that the engine runs right at the top (5500) of the "normal" rpm range. You will gain 10% more torque from the engine.

 

[Faztbullet]

Re: Performance Question

You might see 5 hp gain with carb switch which might add a 1 mph to speed.....

 

[Bob_VT]

Re: Performance Question

Since your motor is already a prop rated HP motor...... I doubt you will feel any gain and might even hurt the economy.

Perhaps a complete carb overhaul..... a new prop to raise your top end rpms........ and possibly a set of boyesen reeds but the best gains will be felt from a prop change with clean carbs

 

[JSMoore]

Re: Performance Question

As long as it's running as good as you say, leave it alone and save some $$$$. You wouldn't notice that much difference in the performance anyway.

Yep! That's kinda what I've been thinking, too. "If it ain't broke..... Don't fix it!" I can't see where opening up the intake side without opening up the exhaust side would make that much difference in power. But, I had to ask. And, I do appreciate the comments and suggestions!
Many Thanks!
JSMoore

 

[Chinewalker]

Re: Performance Question

Definitely downshift on the prop. 5200 is too low. 5500 would be the minimum. My 1983 Johnson 90 is propped for about 5700-5800 (as per my local Johnrude tech's advice).

 

[boobie]

Re: Performance Question

I'll go along with the prop switching provided your tach is accurate.

 

[nwcove]

Re: Performance Question

maybe the prop is a bit low in the water also??