The OMC Cross Flow Thread

[James45157]

some where in my basement i have the specs on thr 2.6 gt was 265 hp at 6250 rpm they came with single stage carbon reeds good for 10 hours we were told to change them after 10 hours of hard running when you got them set up right they were fast for there day

[john j 80 viking]

ok thanks for the suggestions on the jets John. I’ll wait til I get into the engine and figure out what jets I have first and then ask guys to see who might have what.

so I will only know the engine is 4 stroking really is that it runs like **** at wot? And that’s because it’s so rich and cylinders are so full of fuel they can’t fire every time at tdc? So basically I’m probing for that condition, overfuelling and then backing off until it fires on every stroke? You basically want to feed it as much as fuel as you can (and retard timing to about 26 to 28 deg)? Just making sure I understand the idea. I find this stuff interesting!

It sounds like you have it. Much earlier in this thread I copied an old Land and Sea catalog. There is an excellent graph and description of all jetting conditions in relation to power output and the risk of jetting too lean. For every 10* of air temp you should jet up or down one jet size. I usually raced with 67's in my carbs, and for skiing and screwing around on the lake with my buds I would run 68's or 69's. With the fatter jets when the weather would turn hot and very humid it would 4 stroke at wot. A benefit was that if it turned cooler, like into the 60's, I wouldn't have to rejet and my boat would rip. The last use of my boat every year is usually the Connecticut River Run 3rd weekend in October. The morning is usually in the 30's or 40's. I put in 70 or 71 jets in for that. My motor isn't some super sensitive race motor, it's just a stock 235 with the good heads and plenty of exhaust relief.
I guess the moral of this story is that if you jet fat you will e a le to use yoj boat in almost all conditions without worrying it you are too lean for todays air temperature.

[john j 80 viking]

I just realized that those pictures of the Land and Sea catalogs that I posted were victims of the great photobucket dump. I will repost them today.

[john j 80 viking]

---

I can't seem to flip this, but this is a great explanation of how jetting is done and why.

[wolfgangb]

Since it was mentioned earlier. What is the physical difference between C and D jets?
I admit that I have used them interchangeably.

C Series for metal carbs, D Series for the plastic carbs - DO NOT MIX THEM.

[sootypipe]

---

I can't seem to flip this, but this is a great explanation of how jetting is done and why.

Hey, thanks for finding that and attaching it. Very good article and I like the explanation. Makes sense but I’ve never read anything like that before. That does help since I play with a lot of 2 strokes.

[sootypipe]

C Series for metal carbs, D Series for the plastic carbs - DO NOT MIX THEM.

Wow I haven’t even seen an engine with the plastic carbs!

[sootypipe]

Hey guys I was curious what my engine actually said for timing especially since the 1985 service manual has no timing specs listed in it so took some pics…

[sootypipe]

One more, having trouble, doing this with my phone!

Btw I’m going to have to fix the hood emblems and paint. I hate the pinstriping and the missing 2.6.

[racer]

Engine is a 1984

[john j 80 viking]

Man, those were great engines.

[BarryStrawn]

Did you note the numbers on the stern side of each ignition pack?

[James45157]

looking at your pictures are you sure you have a 2.6 because the 2.6 xp had a difference lower unit your does not look like what we had from omc

[97mirage]

That’s a great looking engine. I love those things!!!!

[BLisBack!]

In addition to the fine advice that has already been posted... I would add...

Get yourself a length of Water-and Steam-Resistant EPDM O-Ring Cord Stock McMaster #9616K17 and replace those water diverters immediately! I've had two motors stick pistons from that crappy vacuum hose OMC used when they swelled and blocked all water flow down that side of the block. Also, go aftermarket on the ignition. If you've ever seen the schematic of an OMC powerpack (and could understand it) you'd never leave the dock. The slightest variation from the stator charge coils and trigger base will cause those packs to miss fire. I had a timer base go bad at WOT and it was the most horrible sound I'd ever heard. Thought I split the motor down the middle! I can't believe the motor actually survived it. Also, there's an air bleed hole at the top of the head gasket that when it clogs (only 1/8" diam) from sea a shell, gasket material etc. it causes a hot spot. Drill another one about 3/4" to the side of that one.

As far as power, second biggest power maker (1st being more compression) is getting weight out of the pistons. The Merc guys will have an orgasm if they can get 15g out of their reciprocating assembly, and there's 150g to be had in those stock pistons if you use a CNC machine, at least half that if you do it by hand or bridgeport mill. Keep in mind it will all be power under the curve, no rpm increase, those motors with that 3x2 front half will only go low 7K as has already been said. Maybe 7400 with the wind at your back and jacked to the moon.

-BL