1974 evinrude 115hp running question???? Help!!

[adm1476]

I have a 1974 Evinrude 115hp that starts and runs, but only at high idle. It appears to be only running off the bottom carburetor. I have done a compression test, and compression is good on all 4 cyl. I have rebuilt both carbs, and I have also tried swapping out the top carb with another one that I had around. Same thing it is only sucking from the bottom carb. I need to know what could be causing this?

 

[Boat Doctor1]

check carbs fuel lines & where line enters/ feeds fuel into carb. also- check needle & seats in carbs & esp.= the lower high speed jets-that are buried in the area behind where the float bowl drains are !! These jets are brass & will corrode shut! Dont screw these up with a plain screw driver trying to remove them!! use the proper tool made for these to remove! Your likely dealing with a fuel delivery problem to carb/s!

 

[adm1476]

I don't think it is a fuel delivery problem. I took the carbs off my 76 85hp which runs excellent, and put them on the 115 and it does the exact same thing. Only runs off the bottom carb. That is what I thought it was at first also. Even after I put the carbs back o my 85 it still runs excellent. So I am pretty sure the carbs are not the problem. I even swapped in a 3rd carb that I had around that I rebuilt first, same problem. I can block off the front of it with my hand and it makes no difference at all in how the motor runs.

 

[racerone]

Are orange wires going to the correct coils ?

 

[emdsapmgr]

That engine will seem to run ok when running on only 2 cyls. Once you put it under load is when you need all 4 cyls firing. (like when it's floating in the lake) Check to be sure you have spark on all 4 plugwires.

 

[F_R]

Bad power pack??? Bad sensor???? Does it have 7/16" spark on all 4 cylinders?

 

[adm1476]

no it has 13/16 spark plugs on all 4 cyl. I changed the power pack too and it didn't change anything. I will actually check for spark on all 4 cyl. Never did check that.It doesn't run ok it only runs at high idle. Probably 3000rpms or more. As soon as I start it up it revs high and stays there.

 

[emdsapmgr]

When that engine idles, both carb butterflys are supposed to be completely closed. The idle air goes thru the small holes in the butterfly plates-that's enough to let it idle. If the "sync and link" is off, (if the carb roller has too much contact with the cam,) the butterflys may be slightly open. If so, you can get a high idle when the throttle handle is in neutral. It's also possible the butterflys on one carb are closed and the other is slightly open. Pull the airbox cover off and double check to insure that they are both completely closed. If not, get out the factory manual and so a "sync and link." When the engine is running and the airbox cover is off, put your hand in front of both carbs. As if you are going to cover the carb throats with your palm. You should be able to determine if you have any suction through the top carb-should be the same as the bottom.

 

[adm1476]

I have tried what you say everything is synced properly. When I put my palm over the carbs only the bottom carb is effected. When I cover the top one nothing happens at all. no suction. I did this with 3 different carbs. All did the same and all work fine on my other engines.

 

[Bosunsmate]

Whats compression like?
Looked at the reeds?
Top seal gone?

 

[emdsapmgr]

You've taken compression readings. What are the actual results?

 

[adm1476]

The compression was within 5 lbs on all 4 cyl. Don't remember exactly what the psi was it was a while ago. I have not checked the reeds. How do you check the reeds? I can see them somewhat with the carbs off. How do I check the top seal? I am a car mechanic, not a 2 stroke mechanic so I am not all that familiar with outboards.

 

[racerone]

Each carburetor bore feeds only one cylinder !--------Cylinders are completely independent of each other as far as the air is concerned on this motor.-------It seems strange to have no suction on both carburetor bores !!!!!

 

[Bosunsmate]

So you are saying you only have suction on one out of four bores? (yet even compression)
Cool, i cant wait to see what is causing this.
Can you post a video and hold a dollar bill in front of each carb by its corner so on a good motor it would be tried to be sucked in.
Doing that means we can see if you are getting any back flow too

 

[adm1476]

This motor is a 4 cyl. It only has 2 carbs on it. So that would be 1 carb for every 2 cyl. And yes when it is running and I block off the top carb with my palm nothing happens. When I block off the bottom carb. It tries to stall out. The bottom carb has suction. The top carb does not.

 

[Bosunsmate]

ok two carbs then, well top seal, inlet reeds and internal ring on crankshaft that separates the cylinders may of gone.
Enjoy:joyous:

 

[emdsapmgr]

The normal compression on that engine should be in the 125 lbs per cylinder. Is yours close to that figure on all 4 cyls?

 

[racerone]

It is odd that you have 2 upper cylinders with no " suction " on one of these motors.---Remove one drain plug on the upper carburetor and operate the primer bulb.---Does fuel pour out ?-------------The design of this motor is 4 seperate cylinders with a common block and crankshaft !--------Each cylinder is fed from one carburetor bore.-----Air that goes in the top left carburetor bore only goes to the # 1 cylinder.----- air that goes in the top right bore goes to # 2 cylinder.

 

[adm1476]

I am going to do some more investigation. I am going to put it on my stand and check some more stuff.

 

[Roj115]

I am a bit late coming into this thread but from what I've read, it hasn't been ruled out that this is not a spark problem. Am I right?

I own and have maintained an identical engine (a '75 Johnson 115) for 40 years. I have diagnosed and corrected all sorts of problems over the years.

If spark problems have not been ruled out, it is not worthwhile to speculate on what may be causing problems on the fuel side. In my experience, problems on the spark side are much more likely than problems on the fuel side. If the motor starts and runs, it is getting fuel so I think a problem on the fuel side is unlikely.

If the motor starts and idles but doesn't have any power at high/full throttle, it sounds to me most likely that you've lost spark on 1 or 2 cylinders. Note that a spark plug with a cracked insulator can spark normally at idle but will ark through the crack under load. I have seen that happen before, although admittedly it was on my car.

If you can only make about 4500 rpm at WOT when you could normally make 5500 rpm, you might very well have no spark on 1 of the cylinders.

To find which one, unplug each of the spark plug leads one at a time and try starting and running the engine. If you disconnect a working cylinder, the engine will run much worse. Rule that one out. If you disconnect the one with the problem, it won't make any difference unless you have a situation where the plug is working ok when not under load but doesn't when under load.