115 hp evinrude won’t throttle up under load

[79Invader]

I have a 1979 115 hp evinrude that came on a project boat. The motor fires up without much hesitation, and seems to run great out of the water on the muffs. Revs good in gear and doesn’t sound like it has any misses. In the water under load, it doesn’t plan the boat (16 foot tri hull) in under wide open throttle. I noticed the starboard side cylinder bank was noticeably warmer than the other (starboard side wasn’t too warm, seemed like perfect temp) but the port side was definitely colder. Not sure where to go as the carbs look decently clean, although obviously that doesn’t always tell the whole story,, where should I start? Maybe a problem with the timing advance? I’m new to larger size outboards. I should also note all 4 cylinders have good compression (>125). Any input is greatly appreciated.

 

[racerone]

Perhaps coil ( orange ) wires or plug wires on one side are wrong / reversed.-----And yes that motor will run nice on a hose on 2 of 4 cylinders.----Check for spark on all leads.

 

[79Invader]

Racerrone, just pulled the plugs. The port side (left) cylinder bank had one fowled plug. Interesting

 

[racerone]

Post actual compression numbers.----Check that orange wires are going to the correct coils.----Check fuel pump diaphragm too.

 

[JerEazy]

Definitely check for spark with a tester - not just a look. Some do the “pull a wire at idle” test - but that doesn’t give a good read.

What RPM does it rev to?

Does it rev to that RPM smoothly and then not go higher?

 

[79Invader]

I have tested the compression myself and can tell you all 4 read 125 to 130. I’m not sure exactly what RPM since this boat wasn’t fitted with a tachometer from the factory. But if I had to take a guess it wouldn’t be any higher than 2500, it wasn’t racing by any means. I wouldn’t call it a smooth rev to its max RPM either, as it wanted to die as soon as I put it in gear, pretty much had to gun the throttle to keep it running. Also, I tired “bumping” the choke while it was running as fast as it would go, and it hates the choke, would almost instantly stall if I bumped the electric choke switch.

 

[79Invader]

Okay so, while it’s idling with the choke off it doesn’t want to rev if I push the throttle arm down. Push the manual choke to the halfway setting, and it wants to rev and is very resposive. This seems like a carb issue, but which part of the carb? Should I just take them apart and clean them?

 

[79Invader]

Okay so, while it’s idling with the choke off it doesn’t want to rev if I push the throttle arm down. Push the manual choke to the halfway setting, and it wants to rev and is very resposive. This seems like a carb issue, but which part of the carb? Should I just take them apart and clean them?

 

[IDFISHER]

As mentioned above, test for good spark on all cylinders first. I have a 3 cylinder outboard that would fire up and run and rev up and sound relatively normal while on the hose on one or two cylinders but once you put it in the water it would not plane out. Got that squared away and now it runs great on all 3.

 

[79Invader]

Update: Strong spark on every cylinder, tested with a tester and everyone had no problem jumped a 7/16th gap. So I tore the carbs off, dropped the bowls and the bottom carb bowl was very dirty with lots of debris, while the top one wasn’t spotless wasn’t as bad. What’s the chances of the jets being clogged? The high speed jets are the ones the protrude into the bowl, correct? And are there other jets? “Low” speed? Thanks for all the info everyone, greatly appreciated.

 

[racerone]

The nozzles stick into the float bowl.-----The high speed fuel metering jets screw into the float bowl horizontally.---They are about 5/8" long.-----They are often hard to find for some folks.----They are way in behind those drain plugs with the 7/16" bolt head.

 

[79Invader]

So the high speed jets are in this hole? I removed a flat head machine screw from this hole, not a 7/16 hex bolt.

 

[racerone]

Yes, way inside..----I forgot that some use a different drain screw.

 

[79Invader]

Okay sounds good. I’ll run some wire through there along with some carb cleaner. Any other passageways I need to give special attention?

 

[79Invader]

Here’s a picture of the dirty bowl. Seems like this would be enough to restrict fuel flow, eh?

 

[racerone]

I really do not see any dirt in that bowl----Or should I say that I have seen much worse.