The OMC Cross Flow Thread

Thank you very much for your reply sir. I’m sorry for the lack of information. To add more specific details:

-Yes I’m wondering what would be the recommended RPM to run this 2.6 XP engine at. I know there’s a an originally published range but it seems most 2 stroke outboards with experience have been recommended to be run higher.
-My specific engine is an original low hour unmodified Evinrude 2.6 XP, 1984. These engines had no power rating but were based on the 235 hp engine, just guessing maybe 250?? It’s on a 1984 Checkmate Sportfire, very small, 16 ft, custom ordered package, boat rated for a max of 140hp. Original receipts and manuals.

Hope that helps!

No problem…I actually have the same motor. The OEM Service Manual says that the Full Throttle Operating Range (for 2.6 models) is 5000-6000 RPM. The manual also says that the RPM Limiter Powerpack limit (for 2.6 models) is 6200 RPM. As for the actual HP, if it’s bone stock, my guess is 235 - 240 but that’s just a guess. Others should be adding their opinions and knowledge which may conflict with the numbers I’ve posted but that’s ok…I’m citing what’s in the OEM manual but that info might be dated…

In my experience with crossflows you just wind em out until they go no higher. 6-6500ish

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Originally Posted by LakeFever

In my experience with crossflows you just wind em out until they go no higher. 6-6500ish

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for a v6 you need to avoid the critcal speed zone 6400 to 6600 i think it was?

2.6 GT XP made more power than a 235.

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Originally Posted by powerabout

for a v6 you need to avoid the critcal speed zone 6400 to 6600 i think it was?

2.6 GT XP made more power than a 235.

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It's 6200 to 6300 rpms. It is believed that there was a harmonics event that would sometimes result in a broken crankshaft.

My very successful engine set up for when I was drag racing was 30* of timing and removal of the rubber bump stop only when actually racing, which will give an additional 2-3*. Relieved exhaust with a Bobs snout and the midsection cut out to match it (it's a lot of relief). Red Holly fuel pump set to 7psi. Carb floats lowered 1/8" from level with the carb body. I ran #67 jets in 75-85* weather. I forgot what I did with the air bleed jets, but I remember that it was really important for good initial throttle response and getting out of the hole. Check your carbs for full throttle and synchronization.
Stick to the stock timing or a little less for just screwing around on the lake and always run midrange to premium fuel. Never run old fuel and make sure you have a water separator. These last 2 points may be the most important. I've seen 7200-7300 rpms while prop testing, but my 24" drag props always ended up topping out the engine at 6700-6800 rpms.

I actually have a 1985 service manual that covers this engine and kinda forgot about looking in it for the speed spec, but I know experience has many times taught guys that the 2 strokes like to run faster than the originally recommended range, usually to avoid things like pre-detonation and pits in pistons etc. I want to protect this engine and get the best performance out of it without modifying it. And so you think the power isn’t much more than the 2.6L 235hp
model?

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Originally Posted by 97mirage

No problem…I actually have the same motor. The OEM Service Manual says that the Full Throttle Operating Range (for 2.6 models) is 5000-6000 RPM. The manual also says that the RPM Limiter Powerpack limit (for 2.6 models) is 6200 RPM. As for the actual HP, if it’s bone stock, my guess is 235 - 240 but that’s just a guess. Others should be adding their opinions and knowledge which may conflict with the numbers I’ve posted but that’s ok…I’m citing what’s in the OEM manual but that info might be dated…

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My previous reply was meant to be a reply to 97mirage, I’m still figuring out how the website and threads work!

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Originally Posted by john j 80 viking

It's 6200 to 6300 rpms. It is believed that there was a harmonics event that would sometimes result in a broken crankshaft.

My very successful engine set up for when I was drag racing was 30* of timing and removal of the rubber bump stop only when actually racing, which will give an additional 2-3*. Relieved exhaust with a Bobs snout and the midsection cut out to match it (it's a lot of relief). Red Holly fuel pump set to 7psi. Carb floats lowered 1/8" from level with the carb body. I ran #67 jets in 75-85* weather. I forgot what I did with the air bleed jets, but I remember that it was really important for good initial throttle response and getting out of the hole. Check your carbs for full throttle and synchronization.
Stick to the stock timing or a little less for just screwing around on the lake and always run midrange to premium fuel. Never run old fuel and make sure you have a water separator. These last 2 points may be the most important. I've seen 7200-7300 rpms while prop testing, but my 24" drag props always ended up topping out the engine at 6700-6800 rpms.

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Thanks for all the good tips! I don’t think I’ll do any mods like you did for racing but I’m going to go through the engine timing, sync, rebuild the carbs, those little brass hose barbs (check valves or orifices), replace all hoses, etc. I already rebuilt the fuel pumps and replaces the fuel
lines to the engine and those to the pumps. Actually, I plan to add a NOS OMC period correct remote mounted spin-on water separating fuel filter. I doubt I’ll see much water but those little screens on the fuel pumps wouldn’t seem to catch much. I always run no-ethanol rec fuel which here in Michigan tends to be 91 octane.

Question for you guys, I’ve always been thinking about getting an ultrasonic cleaner for doing carbs., any of you guys use one? Do you recommend this or not? And recommendations on brand and size? Can you damage these carbs using one? What fluid do you use? I saw where one guy used gasoline. What about diesel fuel? I use that in my parts washer. With stubborn stuff I use OMC Engine Tuner, special ordered a gallon and keep it in a metal gallon paint can, but it’s very harsh and may be too much for an ultrasonic. Thanks in advance. I appreciate the knowledge from you experienced guys.

For reliability and long as possible service, good fuel, timing set to 26*, never overprop (probably not possible with your small boat). Overall timing needs to be set under a load at 5500 rpms. I would lap the flywheel to the crankshaft taper. Check the crankshaft seal and make sure the bearing cap bolts are tight. Also make sure there aren't any loose magnets inside of the flywheel. These motors are getting old and the magnets do pop off. I would go up 4 jet sizes from stock because there is so much alcohol in fuel now compared to the 80's.

I really don’t know for sure if the XP has any more horsepower than a stock 235 but others might. And I don’t know anything about the ultrasonic cleaners. I’ve never used them. I do like to run Sea Foam in every tank to keep the fuel system clean. I always run 93 octane in all my motors. Good luck.

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Originally Posted by john j 80 viking

For reliability and long as possible service, good fuel, timing set to 26*, never overprop (probably not possible with your small boat). Overall timing needs to be set under a load at 5500 rpms. I would lap the flywheel to the crankshaft taper. Check the crankshaft seal and make sure the bearing cap bolts are tight. Also make sure there aren't any loose magnets inside of the flywheel. These motors are getting old and the magnets do pop off. I would go up 4 jet sizes from stock because there is so much alcohol in fuel now compared to the 80's.

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Yep, I remember setting the timing on my 175hp crossflow with a borrowed test wheel at the boat launch. The onlookers thought I was crazy. No one even knows how to work on anything or tries.

What is factory timing? I tried to find it in my manual but I couldn't find the spec anywhere! Really bothers me. The OMS manuals from that era are so horrible. Is 26 deg advanced? What does that do for the engine?

Are the magnets riveted on? If they are on, do you see them starting to come off or are they just on or off? That sounds catastrophic. Should I be mixing up some epoxy as a preventative measure or something??

Jet sizes...I run only rec fuel with 0 ethanol. Do I then even need to bother with changing jets? I don't have experience with that. Where do you get your replacement jets from?

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Originally Posted by 97mirage

I really don’t know for sure if the XP has any more horsepower than a stock 235 but others might. And I don’t know anything about the ultrasonic cleaners. I’ve never used them. I do like to run Sea Foam in every tank to keep the fuel system clean. I always run 93 octane in all my motors. Good luck.

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Thanks bud. It will be a little project next year. I'm excited. I have never seen one of these engines. I'm wondering in stock form how fast thing thing is going to push that 16 ft Checkmate!

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Originally Posted by sootypipe

Yep, I remember setting the timing on my 175hp crossflow with a borrowed test wheel at the boat launch. The onlookers thought I was crazy. No one even knows how to work on anything or tries.

What is factory timing? I tried to find it in my manual but I couldn't find the spec anywhere! Really bothers me. The OMS manuals from that era are so horrible. Is 26 deg advanced? What does that do for the engine?

Are the magnets riveted on? If they are on, do you see them starting to come off or are they just on or off? That sounds catastrophic. Should I be mixing up some epoxy as a preventative measure or something??

Jet sizes...I run only rec fuel with 0 ethanol. Do I then even need to bother with changing jets? I don't have experience with that. Where do you get your replacement jets from?

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Originally OMC had spec the timing at 30*. They later reduced it to 26*, I'm sure to reduce warranty issues. You should be confident timing your motor to 26*. The magnets are epoxies on. They get a little rust behind them and pop off. You could do some plug checks to check that your jet size is ok. If it were me, I would still go up a few sizes. Not sure where to get jets anymore, now that OMC is gone for good it seems.

I would say 26 degrees max on a heavy boat, premium fuel ONLY. And that depends on the heads and cranking compression.

My XP and mod 235s were 128 to 130 psi. I set them at 26 degrees and ran them a bit rich.

And RPMs. LOL!!! Yea, there is a range where there is a harmonic vibration. As said in the 6300 to 6500 range. But I found the old 235s/2.6 motors could run 7,000 on a light boat all day if you tune it right. Even with cast pistons and stock rods. Just blow past the "no go zone!" and let her rip!

https://www.youtube.com/watch?v=_rHWWiMiA4U

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Originally Posted by Forkin' Crazy

I would say 26 degrees max on a heavy boat, premium fuel ONLY. And that depends on the heads and cranking compression.

My XP and mod 235s were 128 to 130 psi. I set them at 26 degrees and ran them a bit rich.

And RPMs. LOL!!! Yea, there is a range where there is a harmonic vibration. As said in the 6300 to 6500 range. But I found the old 235s/2.6 motors could run 7,000 on a light boat all day if you tune it right. Even with cast pistons and stock rods. Just blow past the "no go zone!" and let her rip!

https://www.youtube.com/watch?v=_rHWWiMiA4U

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Well, this is a 16 ft Checkmate Sportfire, only thing heavy about it is that it has 2 fuel tanks (a 19 and 21 gal).

Well let me get the thing all tuned and carbs rebuilt and ignition dialed in. Then I’ll play with props and see if I’m daring enough to get it past 6500!! Haha!

About carb jets, anyone know what size the stock ones are? Have any OMC part numbers for replacements that are larger in size? What about buying a really nice/expensive (not Amazon junk) micro drill set) to drill them out? Can you get a good enough finish?