Help with high RPM 140 Crossflow

[joezek]

I have a 1981 Johnson 140. The lower unit was full of rust and the water pump was bad, and I hadn't figured out which prop combination I need yet for the boat I put it on. So I grabbed the lower unit that was running perfectly on my 110 Evinrude (1989) @ 5200 RPM on plane. On this 140 Johnson I'm only getting 4200 RPM and 31 mph. Same lower unit and prop runs 1,000 rpm higher and 10 mph faster on the 110 evinrude (same boat). It takes a while to get on plane, pretty weak actually. All coils are new, all cylinders are firing. Timing is set at 28 full. Compressions are now 125-135.

The plugs are coming out a little black, but never fouled. I'm also running the surface gap plugs if that makes a difference. I've gone through the carbs and set the floats, cleaned all the jets and ports thoroughly. It's a quiet and very smooth running engine, the smoothest one I've had yet, but NO POWER.

I'm trying to figure out if there's any possibility of an exhaust problem that could be creating too much back pressure. In the past I've had 2 strokes that run perfectly except at full power, and it was because of an internal water leak into the exhaust, creating a massive amount of back pressure. Incedently on pretty much all the outboards I've had, they pour a lot of water out the prop/exhaust when running to flush the engine. This engine doesn't have one droplet of water coming out the exhaust....maybe there's supposed to be some water and it's not getting there? The upper round exhaust ports are dry too, and barely have any air puffing out of them. The thermostats are also new btw.

The reeds are all intact, but I didn't pull the intake to check for reed stuffers. My 110 had the rubber blocks in there ( I added them) and had performance reeds. I also had high compression 140 heads on the 110, but not sure if that ever actually made a real difference. I don't think I need the high compression heads to get another 1,000 rpm. There's no way I need a different prop if a 110 was making that much more power than this 140 is with the same prop and lower unit. (it's a Looper lower unit originally but had it all figured out with the correct prop on the 110, was running perfect until the block cracked at on of the head bolts.

Is there a gasket under the intake that is supposed to separate the airflow, that could be causing low full power? Also, what jets should I have, maybe someone put the wrong ones in there. It has 1 5/16 carbs. One other thought is that what if it was somehow siphoning fuel from the primer lines into the cylinder, from a weak sealed line somewhere- is that common?

Whatever the problem is, it runs great except full power is just weak.

 

[racerone]

Sure is a lot of surmizing and guessing in post # 1.-------I would check the flywheel key , has to do with timing !----Remove bypass covers to inspect pistons and rings.--------Does spark jump a gap of 7/16" on each lead , yes or no ?

 

[joezek]

I'll pull the flywheel now and check the key, didn't realize that was a problem that happens on these engines. The spark is great, bright blue and jumps about an inch.

I checked the primer lines and found one going into the #1, #3 side "T" fitting that was split at the fitting. With that split, not sealed, it would probably siphon at least the amount of fuel in those "Tee" hoses until dry, but the plugs should clean up right away afterwards.

Maybe I need to make sure TDC is correct on the pointer as well.

So I'm still trying to figure out why there's no water coming out of the propeller exhaust. Is that normal? It has excellent water pressure at the **** tube and engine seems to be running cool.

 

[racerone]

If you have a hose running water is going into the engine.--------This water must exit the motor and the tell tale is not the place for that.-----------Water should be pouring out the prop if your hose is fully open.

 

[joezek]

It's going somewhere, but not out of the prop, it does come out of the imperfections at the flange where the lower unit bolts to the mid section, and from some squared sections of holes that are designed in the lower unit.

I checked, flywheel key was good, reinstalled it. Then I found true dead center (same way I do on old airplane engines) and it turns out that the degree marker was off by -2 degrees. Now my total timing is indicating 26 instead of 28, and idle is obviously -2 from what I thought it was. I don't think 2 degrees will solve my problems......

The water that exits the block, where in the block does it connect to the exhaust? Does it go through the bubble back? If it's designed to go through the exhaust, but is going somewhere else, that's gonna mess up my backpressure. Originally this engine's thermostats were severely clogged with sand when I bough the engine. I changed the whole thermostat housing with another one I had from the 110, new thermostats etc. What is the direction/flow of water through the thermostat housing? I thought the cool water went directly into the heads, then to the thermostat housing, then after leaving the housing where does it go?

On a side note, I'd like to make a flush system that doesn't require running the engine.

 

[racerone]

Water first goes to the tell tale.--------That is no indication that water is flowing properly through the block !!----------Remove both hoses from the heads.--------Start the motor.--------Do you get lots of flow out the heads ?----------Have you looked into problems with diverters in the water jackets ?

 

[jimmbo]

There's no way I need a different prop if a 110 was making that much more power than this 140 is with the same prop and lower unit. (it's a Looper lower unit originally but had it all figured out with the correct prop on the 110, was running perfect until the block cracked at on of the head bolts.
Whatever the problem is, it runs great except full power is just weak.

Exactly which Looper did the lower unit come off of? Just curious

You say the engine has spark at all 4 cylinders. Have you tested for spark at all cylinders with the timing fully advanced?

 

[interalian]

 

[joezek]

Exactly which Looper did the lower unit come off of? Just curious

You say the engine has spark at all 4 cylinders. Have you tested for spark at all cylinders with the timing fully advanced?

Yes I cranked and watched the spark while moving all the wires from the stator, timer base etc. and advancing the timing to full and to idle.....

 

[joezek]

just realized the nice flow diagram you posted, awesome perfect. So until my thermostats open, shouldn't be much water flowing if any out of the prop.

The lower unit came from a 1985 140 Looper. I'm running a 14 1/4 X 17 prop. It turned around 5300 rpm @ 40 mph with the 1989 110 Evinrude. Really want my Looper back on the boat, it brought that Mako up to plane almost instantly and reached 56 mph. Luckily I have trim tabs, that's a scary ride on a 17' Mako. The stern starts doing it's own thing and wandering left/right. At least the tabs keep the boat from launching itself , and kind of cuts through the waves instead.

 

[jimmbo]

This 1981 140, is there a chance it is a 25 inch shaft?

Are you sure it is a 140? The numbers for speed line up with what 90hp would produce

 

[joezek]

This 1981 140, is there a chance it is a 25 inch shaft?

Are you sure it is a 140? The numbers for speed line up with what 90hp would produce

The serial # on the soft plug and on the mid section is for a 140. It's got the large carbs on it too. Also has the bubble back. But yeah it's acting just like a 90, driving me crazy. It's a 20" shaft. I don't know what else to look for, it's got great compression. Maybe under full throttle, under a load in the water, one cylinder is losing spark?

 

[interalian]

If you're chasing a WOT power loss, hang a timing light on each spark plug wire in turn. With a helper piloting, aim the light toward you and look for black spots in the beam - these indicate misses.

 

[jimmbo]

Are the carbs opening fully? Have you tried running the engine with the cowl off? You say the compression is good, but I think an inspection of the cylinder walls and piston skirts may be required.

 

[joezek]

The carbs are synced and opening fully. If the compression is good you still think I need to inspect the cylinders?

 

[jimmbo]

There have been other times when people have said the engine had good compression and still had scuffed and scored pistons and/or cylinders. One other question, When was the last time the engine had a decarb, with Engine Tuner, Combustion Chamber Cleaner, or SeaFoam?

 

[joezek]

probably never lol. When I got it, it was pretty nasty. I pulled the bubble cover to get to the thermostats. The exhaust ports and bubble had about half a pound of chunks of burnt oil and carbon. They obviously never mixed the oil properly. When I measure the oil and fill it, there's never a drop of blue smoke except for the first 5 seconds after start up.

 

[joezek]

I see a lot of people doing extensive build ups and mods to older Crossflow 140's. Is there a specific reason why they're not going with the Loopers instead? I really can't wait to get my Looper up and running again sometime this year, just no comparison in power as far as I can tell. Only downside was that it shakes the boat a lot and was much louder.....- makes the wife unhappy= crappy day when she's on the boat....

 

[jimmbo]

I wonder what condition the exhaust passage is downstream. Also if there was that much carbon in the bubbleback, there is probably lots in the piston ring grooves.
When you had the exhaust cover off, did you look at the piston skirts? A lot of people look at the intake side by taking off the transfer passage covers, but it is the exhaust side of the skirt that usually scuffs/scores first
Why to people mod the 99.6 crossflow? Well with a bit of machining, and a few parts you can turn a 90 into a 115 or a 140/110/112. There is even more power available if you willing to sacrifice longevity and smooth powerband.
As for the 140 looper being jumpy. Loopers generally have a peaker torque curve than crossflow engines and some low rpm smoothness is lost, just the nature of the beast. It gives you a perfect excuse to leave the wife on shore. Wives, kids and especially Mother in laws, should never be allowed aboard. Mistresses and Girlfriends are permitted

 

[racerone]

Find a shop with a test prop or dynomometer.------Have them determine whether the motor is producing the proper amount of HORSE POWER.-----Once you know the facts you can decide what to do.