Struggling under load

[robotmark]

So I finally got my 1971 40 hp Johnson 40E71G up and running on the water. Based on past advice from the forums, I’ve rebuilt and thoroughly cleaned the carb, replaced the fuel pump, installed new fuel lines, new spark plugs, and a new impeller. I took it out on the reservoir yesterday morning on the back of my 1962 14′ Hydroswift runabout. Engine started right up, pumped water, sounded great, idled great. I ran it at half speed for about 15 minutes, in forward gear, just doing a lap around the lake. Then I went full throttle and it seemed to struggle, like it was pushing a boulder uphill. I did need to make an adjustment to my control cable so that my control arm could push the butterfly valve all the way open, but even at full bore I couldn’t plane or reach a decent speed.

What are the usual suspects I should be looking for? Compression? Propellor? Any thoughts are appreciated as always!

[Buccaneer]

Is the carb sync’d to the magneto correctly?
Did you try adjusting the high speed jet while underway?
I doubt it’s compression if it idles okay, but
you could have the wrong prop.

Prepare to be boarded!

[robotmark]

Yes to all above. However, I had a thought. I realized that a piece of the fuel hose that runs from the fuel pump to the carb is 1/4″, not 5/16″ like the rest of the lines. I’m wondering if that is restricting my fuel output.

[fleetwin]

What pitch prop are you using? I too, would suspect improper syncronization of that “economizer linkage”. Does it run rough at WOT, does it skip or surge? Or, does it just feel like advancing the throttle really doesn’t do anything? Any chance the mag plate is binding and not advancing fully, perhaps it is getting jammed on that shift lever interlock arm. Perhaps some debris is caught in the high speed fixed jet.

[wedgie]

Running only on one cylinder?

[jeff-register]

I had worked on a surgery table, total rebuild. It kept sticking in the up position. The inside of the hydraulic hose was releasing tiny chunks of hose hanging up the valve body. I know nothing to do with boats. Flushed the system, replaced the hose & it functioned. The inside of the hose was releasing tiny pieces of clear plasitic that looked like cigerattee pack cell a phane, Yea I can’t spell. Replace those lines please & check for old o-rings. Found powdered hose in carbs too, only wet.

[fleetwin]

jeff-register wrote:

I had worked on a surgery table, total rebuild. It kept sticking in the up position. The inside of the hydraulic hose was releasing tiny chunks of hose hanging up the valve body. I know nothing to do with boats. Flushed the system, replaced the hose & it functioned. The inside of the hose was releasing tiny pieces of clear plasitic that looked like cigerattee pack cell a phane, Yea I can’t spell. Replace those lines please & check for old o-rings. Found powdered hose in carbs too, only wet.

Well, Jeff’s post might have to do with surgical tables, but the same theory is applicable to outboards. Just disturbing all the connections, hoses, fuel pump, etc is enough to create debris that could end up in the carb.
The classic OMC example of this is those lovely plastic carb bowls on the large engines…Simply threading the brass jets in and out of the plastic bowls creates plastic debris…So, we have created debris inadvertently while cleaning the carburetor…

[robotmark]

OK, so I replaced my fuel line, no problem. The carb is super clean. However, I’m looking at the cam alignment and that may be my problem. According to my official service manual, my manifold projection is supposed to line up with the two marks you see there. When I do line those up, you’ll see that my throttle is between “start” and “slow”. Now what do I do?

[fleetwin]

Well, I’m not too concerned about the cam pick up point, your issue is at high speed. The “economizer rod/linkage” is what I’m wondering about, this is the horizontal rod that runs from the mag plate up to the carb linkage. This linkage allows full timing advance to be achieved before the carb butterfly is opened fully. It can be a little tricky to set this correctly, you almost need two people to do it…
If not set properly, the carb butterfly might not open fully at WOT…Or, if the adjustment is somehow “preloaded”, this might prevent the mag plate from advancing fully… Sorry, I don’t have the manual pages to post, but I’m sure someone will do that for you.

[bobw]

Here’s the page out of the Service Manual for the fuel saver rod adjustment.

Bob

1937 Champion D2C Deluxe Lite Twin
1954 Johnson CD-11
1957 Evinrude Fastwin 18
1958 Johnson QD-19
1958 Johnson FD-12
1959 Johnson QD-20

“Every 20 minute job is only a broken bolt away from a 3-day project.”
"Every time you remove a broken or seized bolt an angel gets his wings."

• This reply was modified 2 years, 11 months ago by Mumbles.

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