1957 Evinrude 7.5 Compression

[Dizz]

Hello to all,just found this forum.
Hoping to bug you a little over this old 7.5 I just picked up from a guy at work that said it ran good.I was going over it before trying to run it,checking points&such.i noted a couple possible problem areas.According to my local dealer,it needs at least 100lbs comp cold.I noted 68-70lbs on both cylinders with throttle fully open.It was very even,just maybe low.I checked my later model 8 Johnson,and 15 Evinrude.They had 110 and 120lbs.I also checked the carb on the old 7.5,and it was clean.I gapped the points@ .o20",and filed them a little.I then hooked up gas,loosened cap,pumped button till tight,choked and it started 2nd pull.I had to turn fast carb screw in till it was just out 1/4 turn to get it to accelerate.I set low speed out 1.5 turns.
after I ran it 10 minutes or so,it seemed to run fairly good.I`m hoping to try it on water in a week or so,I had it in trash can tonight.The last fella put a water pump&head gasket on it.
My question is does it have a good chance of running good with this low of compression,and does the lack of compression have something to do with having to turn fast carb screw in so far&will this keep fuel pressure up?I also noticed a high pressure water leal at maybe a freeze plug,it was on right rear of head on bottom,maybe .5 in diameter.If any of you work on these old moters,appreciate any tips!Thanks,Dizz

 

[wbeaton]

Re: 1957 Evinrude 7.5 Compression

Your compression is fine. I have a 1956 7.5 hp with compression in the 60's that runs great. You can't set the carb in a barrel. You can get it close enough, but you need to have the motor under load to set it right. I find my 50's OMC's like the high speed jet set around 1/2 - 3/4 turns.

When you had the inspection plate off the flywheel, how did the coils look? Did you see any cracks in them? Have they been replaced? If not they will need to be.

The welsh plug on the underside of the head often corrodes. Pop it out and replace with a new one.

Your fuel mix is 24:1 using 87 octane gas and TCW3 outboard motor oil. Plugs are Champion J6C.

 

[Dizz]

Re: 1957 Evinrude 7.5 Compression

Thank`s for the reply,sounds good!Looks like I found the right place for sure.My spark sounded&looked white&strong.My coils looked good,they were green& one looked new&the other was more faded green but I could tell for sure it wasen`t real old.It had the plugs you mention gapped@.030".The gas was from last year according to the fella I bought the motor from and it was kept in inside.When I 1st pumped some gas from hose by pushing plunger it started pure oil.Then it looked&smelled strong.I also noticed some tiny black specks running gas on paper towell.Hose looks old but good on outside,but I think it`s breaking down on inside.I will replace hose .
Where do I get that welsh plug from,any Evinrude dealer?
Thanks again,Dizz!!

 

[tashasdaddy]

Re: 1957 Evinrude 7.5 Compression

super dependable engines. here are carb settings:
Carburetor Adjustments - Two Adjustable N/Vs)
(J. Reeves)

Initial settings are: Bottom high speed = seat gently, then open 1 turn out. Top slow speed = seat gently, then open 1-1/2 turns.

Setting the high and low needle valves properly:

NOTE: For engines that DO NOT have a shift selection, obviously there is no NEUTRAL position. Simply lower the rpms to the lowest setting to obtain the low speed needle va /lve adjustment.

(High Speed) Start engine (it will run pretty rough), shift into forward gear, take up to full throttle. In segments of 1/8 turn, wating for the engine to respond between turns, start turning in the bottom high speed needle valve. You'll reach a point whereas the engine will either start to die out or spit back (sounds like a mild backfire). At that point, back out the needle valve 1/4 turn. Within that 1/4 turn, you'll find the smoothest setting.

(Low Speed) Slow the engine down to where it just stays running. Shift into neutral. Again in segments of 1/8 turns, start to turn the top needle valve in. Wait a few seconds for the engine to respond. As you turn the valve in, the rpms will increase. Lower the rpms again to where the engine will just stay running. Eventually you'll hit the point where the engine wants to die out or it will spit back. Again, at that point, back out the valve 1/4 turn. Within that 1/4 turn, you'll find the smoothest slow speed setting.

When you have finished the above adjustments, you will have no reason to move them again unless the carburetor fouls/gums up from sitting, in which case you would be required to remove, clean, and rebuild the carburetor anyway.

 

[wbeaton]

Re: 1957 Evinrude 7.5 Compression

You can get the welch plug anywhere they sell outboard parts. I usually just pick up a couple extras (among other tiny parts) whenever I order parts online or from my dealer. If you go to the dealer, take the old one with you for comparison.

If you are getting bits of deteriorated hose in your gas then you should also clean out the filter in the glass bowl under the carburetor and, of course, change the hose.

 

[F_R]

Re: 1957 Evinrude 7.5 Compression

There is another welsh plug on the bottom of the head. Get another one for that while you are at it. Same size. Get at it by removing the lower rear motor cover. No need to pull the head. Most any mechanic will have a dozen of them in his junk drawer, leftovers from carburetor kits.

 

[Dizz]

Re: 1957 Evinrude 7.5 Compression

Thank`s all all usefull imfo,and that carb fine tune was great!
On the 2 hose gas line system,do you still loosen cap when you are runnning in boat,or just keep it tight?It seems that maybe this system might push air in tank,pressurize and force gas back out?it would seem the lid would have to seal in this type system,or maybe the air works a little pump in tank??I`m guessing the air line out of engine block uses piston blow by to make air,or maybe reverse piston air flow.

Also when I was checking compression,after getting 68 in top,and 70 in bottom cylinder,I then put some engine oil in spark plug holes&tested again.it made no change.with worn rings this will usually bring it up.I guess these motors maybe started with 70lbs or so when new??
Thanks again all,and I would like to mention a couple issues with my 91 model 15hp Evinrude a little later.
Regards,Dizz

 

[tashasdaddy]

Re: 1957 Evinrude 7.5 Compression

the cap should be tight, the button pushes gas to the carbs, for start up. once started the engine pumps air into the tank, forcing gas out to the carbs. that's why it is called a pressure tank. if the tank won't hold pressure you can get rebuild kits. there are 2 types, tank with black plastic button use one, tank with metal button uses another. parts are available at laingsoutboards.com

 

[wbeaton]

Re: 1957 Evinrude 7.5 Compression

I believe these motors came out of the factory with 120lbs, but they manage to run at much lower compression than that. I have a couple other 7.5's with compression in the 70's and 80's.

I'm glad the carb setting fixed your problem. Enjoy your motor.

 

[JayM001]

Re: 1957 Evinrude 7.5 Compression

I own a number of old OMC outboards ranging from late 50s to late 60s/early 70's, 6hp to 35hp. I don't run 25:1 in any of them - modern synthetic oils are much better than the old "natural" oils so 50:1 works just fine. This advice originally came from my local OMC dealer and I have proven the advice to be valid over years and hundreds of hours of use.

 

[samo_ott]

Re: 1957 Evinrude 7.5 Compression

Yikes. I wouldn't run 50:1 in anything that didn't have roller bearings in it. (around '61 on)... but to each his own I reckon! OMC recommended 24:1 up till '64 or so I believe it was.

 

[Dizz]

Re: 1957 Evinrude 7.5 Compression

Thanks again all,the gas that came in the can with this motor was very rich,as the water in the barrel looked like it had pure crude after 20 minutes or so of running.I`m gonna try in this weekend.
Regards,Dizz

 

[tashasdaddy]

Re: 1957 Evinrude 7.5 Compression

the reason for the crude in the barrel is the build up in the exhaust housing. you could try doing a decarb on the engine, that might bring the compression up also.

 

[steelespike]

Re: 1957 Evinrude 7.5 Compression

The 7.5 is all friction bearings.I wouldn't run 50:1.The motor was originally listed at 16:1.The old 10 hp had some roller bearings in the crank with the center bearing and the rest friction and was listed at 24:1.
I wouldn't go less than 24:1 with the 7.5.

 

[Dizz]

Re: 1957 Evinrude 7.5 Compression

Good imfo steelspike.tashdaddy,could you explain what the decarb procedure is?

Also,1st I heard of the pressure tank.to ask a dumb question,how do you know if tank is not holding pressure.Would it loose pressure at trolling speed&you would have to prime time to time,or would you loose pressure @ high speed,or maybe cause other stalling problems?with the can setting in the sun in driveway,it was leaking a little gas(full tank)around big cork gasket.would this mean it won`t hold pressure?
To anyone:
I have a late model Evinrude 8HP that planes my Alumicraft 12/36 jon boad with 2 people&gear if the guy in front moves to front seat after it comes out of water.Do you think this old 7.5 will come close to that,or would the low compression cause a similar HP loss??
Regards&many thanks,Dizz

 

[tashasdaddy]

Re: 1957 Evinrude 7.5 Compression

if you tank is leaking around the gasket, it's leaking, need new gasket laingsoutboards.com. should be close to the 8 hp.
the way i decarb those engines: by a can of seafoam, in the tank, 3/4 gallon of premixed gas/oil, 3/4 can of seafoam. the rest of the seafoam goes in a spray of squeeze bottle. remove the air silencer from the carbs, start engine, make sure you have good water source, run engine until it get to operating temperture, kill engine, remove plugs, and put a liberal amount of seafoam directly in to cylinders, let sit for 15 minutes. now restart, ( it's going to smoke) let it the engine settle down, now spray seafoam directly into the carbs, until the engine almost stalls. keep this up until out of seafoam or the engine, quits smoking. you can just add regular premix to the rest in the tank. also changed the plugs afterwards, you will be amazed at what the water looks like when finished. wash lower unit.

 

[BoatBuoy]

Re: 1957 Evinrude 7.5 Compression

Tank gasket, Sierra 18-2887, $4.65, right here at iboats.

 

[Dizz]

Re: 1957 Evinrude 7.5 Compression

Thank`s guys will try.I`m wondering if I can make that gasket from regular cork gasket material?Thanks,Dizz

 

[samo_ott]

Re: 1957 Evinrude 7.5 Compression

You possibly could make it, but is it worth the $5? And when you shred the old one taking it off what are you gonna use for the template?

 

[Dizz]

Re: 1957 Evinrude 7.5 Compression

Hey tashasDaddy,I was at the last stage running engine &spraying seafoam in engine when I noticed it started hitting on just one cylinder,thought the plug fouled.Wrong,after new plug still no fire to bottom plug.
This motor had one new looking coil,and one much older,but it was not cracked on outer coating.this is the plug not firing,the older coil.points opening fine,assuming it just picked this moment to fail.Does this sound reasonable?Going to the local OMC dealer in morning.
Regards,Dizz