OMC Tech: Crossflow Jets

**DieselDood** · 05-09-2020, 12:53 PM

The whole story... in case it matters... but more info usually isn't bad.

Last fall I horse traded for this "77 175" with a 150 cover. The trim tag said 77 175, but immediately it was found that the water pump was NOT a 77. It's the 79-84 style. I brought it home in a snow storm.

So I installed a new water pump. I also immediately checked compression. Never ran it, just checked it. If it had a bad hole, I wanted to know. All read 95psi. Ok.. good to go. A little low.. but hey.. it should run out.

I added some fuel and the carbs didn't pee everywhere so.. what the heck, I fired it up on Ears and it ran pretty good, Idles perfectly. Took it to the lake in the another snowstorm. 2800-3000rpm. Ok... winterized it and I'll mess with it later.

*All test drives I HAVE been able to get up on plane... but I had to either turn hard left to a Uturn or a complete circle to get the RPM up*

I cleaned out the garage and made it fit... I went through the carbs and found they are the 1 5/16. Nice little upgrade. I then checked spark and had 1/2" jump. Checked timing 7 and 20. Ok so off, I reset to 4 and 25 since I couldn't run it under load. All should be good.

As soon as the ice was off I tried again. Backed in, fired it up and once I could walk away I let it idle and parked the truck. Idled perfectly all while I was gone. Took it out and... Same. 2800-3000rpm with a 21P prop. Ok... maybe it needs a lower prop. Threw my 19P on. Same deal 2800-3000rpm. OK WTF.

Checked fuel pressure. 3psi max. Ok.. ordered rebuild kits for the pumps. They arrived and rebuilt. Rechecked. Still 3psi. Removed the pumps and installed a Delphi Electric pump and all new lines. 3.5psi. Ok... so my 25 year old gauge has failed and reads low. 20 years as an automotive tech... I've never seen a bad Delphi pump out of the box. I also cross referenced the number on the CDI box... looks to be an 84 and older.

At this point I also borescoped the motor and found it to have the 3.5 bore but .040 over Wiseco pistons

Test drove.. Same issue.

I brought it home and rechecked timing. Good, but no load. I rechecked compression. 95psi. Ok. Recheck spark, good. Ohm check everything. Found the middle cylinder to have 73ohms. Spec is 15-50. Ok. Timer base is bad. I have another motor with a timer base (88 year), stator, etc. For fun I pulled the airbox and turned the pump on, then opened the butterflies. Not a drop. So the needle and seats are working properly.

Swapped the timer base, flywheel, stator, voltage regulator and wiring harness. Retest. All good. Jumps 9/16" spark. So now the motor has the 87-88 Electrical system on it with 8000RPM CDI packs.

Test drive. Same issue. Was told to try my 23P 4 blade Ballistic prop that is a smaller hub so it passes exhaust over the top and can help. Test drove... Same issue.

Pulled the motor cover and found the case halves leaking. Dissassembled and resealed the case halves.

Test drove 18 hours later... Now it won't get on plane and doesn't want to idle very well.

So here we are. I rechecked everything last night. Compression has come up to 100-105, spark still jumps 9/16 gap. Timing reads 4 and 25.
I pulled the carbs down and found the large Jets.

so...as Paul Harvey used to say... "Thats the REST of the story"

**DieselDood** · 05-09-2020, 01:08 PM

Also.. not that it matters... but it was what lead me to thinking about overfueling... In my.... 5 test drives... I've gone through 15 gallons of fuel. I know Xflows are thirsty... but this seems excessive to me.

(Hull is a Skeeter SK1700, bass boat. When on Plane with the 21P I did see 51mph, but the tach was dropping out. By ear it sounded like 6k, so I think other than "getting up" it should spin a bigger prop)

**FMP** · 05-09-2020, 01:17 PM

Since it got worse the last time it ran something is degrading. Everything checks out, flywheel magnets to the right wires and boots on the plugs?

I was going to ask if someone forgot the tuner after rebuilding LOL.

And other than jetting the big side, the low speed is setup right.

**DieselDood** · 05-09-2020, 01:22 PM

When I switched Flywheels I checked the magnets... and wished I could run the other flywheel... lol the one that was on it the magnets were captured, this one has the "moveable" magnets, but all were in place as they should be.

Actually for fun last night I checked not only cylinder 1 for where it was firing, but cylinder 2 as well since the flywheel is actually marked for it. Both are right on.

It got worse after it "lost" air when I resealed it (my thoughts)
I was hoping to find something dirty in the carbs after laying them on their backs on the floor during the case split, but I didn't find anything.

I wish it was a tuner... or even Fuel injected. I'd be much better off in this diag process!

**FMP** · 05-09-2020, 01:32 PM

Is it possible the fuel pump could spill into the case if valve or seal was going bad?

**DieselDood** · 05-09-2020, 01:33 PM

I guess possible... but I don't see anything that could do that other than the "choke" solenoid, and with the butterflies open I didn't see anything coming from those ports.

I'll reassemble and recheck though!

**FMP** · 05-09-2020, 01:38 PM

I had both pumps tear new junk aftermarket diaphragms on the small side after a few hrs. Poured fuel in the midrange and lower and leaned out up top. Moral of the story, only buy the quality, even if the other only what they have in stock.

**DieselDood** · 05-09-2020, 01:41 PM

The pulse pumps are gone and the intake ports are capped off. I'm running a Delphi Electric pump 4-7psi and 73GPH currently, or I'd be looking at that as well

**FMP** · 05-09-2020, 01:55 PM

And you've metered all the coils, checked the plug wires solid core.

So back to page one. Might as well pull the transfer covers and check the rings for rebound. Maybe someone only hung one ring per piston. Haha

**DieselDood** · 05-09-2020, 01:56 PM

With the compression climbing... is pulling those covers needed? I've gained 10 psi since I've started messing with it

**FMP** · 05-09-2020, 02:15 PM

What plug wires are on it?

**DieselDood** · 05-09-2020, 02:19 PM

I have 2 coils on order that match the 86-88 ignition system because I have 2 that are from the 84 and older ignition system. I cut and spliced the wiring so the new snap on style harness clips into a connector, so the harness isn't damaged.

I thought they may be an issue, but both of the old coils ohm out within spec.
The newer style coils all ohm out within spec also.

I know I shouldn't mix them... but they all jump that 9/16 gap with bright blue spark.

Tuesday I should have everything the way it was intended.

**FMP** · 05-09-2020, 03:15 PM

So solid core conductor spark plug leads, all 6
https://www.marineengine.com/parts/i...mc/0582365.jpg

**DieselDood** · 05-09-2020, 03:29 PM

I have 2 of these coming on Tuesday:
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

Those are the coils I already have and these are the plug wires I have on 4 cylinders currently. They all measure 0.01ohms. I had an 85hp Crossflow last season, which is why I have 4 of them.
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1