1991 Stratos 290SF Not great speed

Okie1985 · Wednesday at 4:03 PM

I have a 1991 Stratos 290SF, with a Johnson 1992 200GT, it runs good, starts right up every time, sounds good when running, but with just me(140lbs) and 1-tank of fuel(20gallons) once trimmed up I can only get about 42mph out of it. Is that just all these engines produce, or are they some things I could try ? I feel like it should have much more top speed. It has a stainless prop, the numbers on the inside of the prop are 391290 15x17…..but stamped on the outside of the prop is 521642 which when I google that number it says it’s a 19 pitch

Bondo · Wednesday at 5:05 PM

Okie1985 said:
I have a 1991 Stratos 290SF, with a Johnson 1992 200GT, it runs good, starts right up every time, sounds good when running, but with just me(140lbs) and 1-tank of fuel(20gallons) once trimmed up I can only get about 42mph out of it. Is that just all these engines produce, or are they some things I could try ? I feel like it should have much more top speed. It has a stainless prop, the numbers on the inside of the prop are 391290 15x17…..but stamped on the outside of the prop is 521642 which when I google that number it says it’s a 19 pitch

Ayuh,........ Welcome Aboard,........ At what rpms,..?? what's the motor's redline,,..??

Okie1985 · Wednesday at 5:07 PM

I apologize that is something I should have had prior to making this post, I will know for sure Saturday, but last time I had it out I believe it was about 4800rpm and I believe the redline was around 5800-6200

Bondo · Wednesday at 5:11 PM

Okie1985 said:
I apologize that is something I should have had prior to making this post, I will know for sure Saturday, but last time I had it out I believe it was about 4400rpm and I believe the redline was around 5800

Ayuh,...... Up at the top of the prop forum is a thread that tells you what you need to know, to optimize yer rig,.....

Okie1985 · Wednesday at 5:32 PM

I also just verified from a pic I took while out a couple weeks ago that at WOT it was running 5,000rpm

Bob_VT · Thursday at 9:06 AM

Your motor MIGHT NOT be hitting on all cylinders. I have a V4 Johnson and with one spark plug not firing - i was only able to get 4300 rpms..... figured that out and now I am back to 5500 rpm. Outboards ALWAYS sound right but often are not firing on all cylinders. Best tool is a timing ligt to check each individual plug. Testing cost's nothing

Okie1985 · Friday at 5:56 PM

I do have a timing light that I keep on the boat, and I have checked all cylinders to make sure they are all firing. And at least that part is good

Bondo · Saturday at 4:11 AM

I believe the redline was around 5800-6200

Ayuh,....... If so, yer lugging the motor, risking burnt pistons at only 5,000 rpms,.....

Okie1985 · Saturday at 5:58 PM

Took it out today, at full throttle from an idle, takes about 30-45 seconds to get on plane, and max speed was 34mph @4700rpm trimmed up pretty high, used my depth finder to verify mph from the boat Speedo. Even after it gets on plane, it takes some time to get to top speed. Tomorrow I will do a compression test and post the results

Okie1985 · 2025-06-22T08:41:35-0600

Did a compression test this morning after getting the engine warmed up, these are the results, all plugs appear to be burning the same, nothing odd visually

jimmbo · 2025-06-22T09:57:00-0600

Plugs look horrible. Running very Rich?
Does the Ignition System produce a Spark that will jump a 3/8" gap for every Cylinder?
Some will say the Compression Numbers are too Low... Might be the Gauge, though.
How long have you owned this Motor?
BTW, the prop is a 17, that stamped Number is likely an Work Order# from a Rebuild Shop

cyclops222 · 2025-06-22T12:18:27-0600

Buy new plugs AND reset the gap to what it should be. If you break the white insulator ? Have to replace it.
Has any ignition parts been correctly replaced ?

Okie1985 · 2025-06-22T13:11:46-0600

When I put these plugs in towards the end of the summer last year, of course they were brand new at the time, there was no difference in the way it ran before/after the replacement. Plugs are gapped at 0.030 which is what the manual says is spec

Okie1985 · 2025-06-22T13:21:03-0600

jimmbo said:
Plugs look horrible. Running very Rich?
Does the Ignition System produce a Spark that will jump a 3/8" gap for every Cylinder?
Some will say the Compression Numbers are too Low... Might be the Gauge, though.
How long have you owned this Motor?
BTW, the prop is a 17, that stamped Number is likely an Work Order# from a Rebuild Shop

The compression for this engine shows to have a spec of 85-90 psi(this engine has low-compression heads) it was my dads boat and he has been chasing this issue for a while now. He has replaced many parts on the engine with the same result.

jimmbo · 2025-06-22T22:31:02-0600

Looking at the Plugs, I would say the Carbs, need some attention:
Are the Floats set correctly, and not lacking Buoyancy
Are the Metering Jets correct and properly tightened?
Correct Gaskets, O-rings in place?
Is the VRO/MRO Pump working Proplerly?
Is the Enrichment System for Cold Starts working correctly, and not passing Fuel when it shouldn't?
Is the Sync between Spark Advance and the Carbs set correctly?

1991 Stratos 290SF Not great speed

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