1952 Evinrude 7.5hp - I have no Idea What the issue is

[Personius1976]

Ok, so I have been out and about several times on the lake this year, and one day I was scooting along, and all of a sudden my '52 Evinrude 7.5hp engine decided I was not worthy of full throttle. I had it running at almost full throttle, and it slowed to about 1/4. I wasn't even touching the thing. Then, if I throttled up or down the speed would not change.

In the process of tearing apart the motor, I discovered I had one fin of the impeller that was bad (replaced), but I am doubting that is my problem. Other than that, everything looks fine and dandy.

It almost sounds like it is a fuel or airflow problem. I am also really disliking the copper fuel line and was looking for suggestions on what to change that assembly out with.

I can add pics if needed.

 

[tashasdaddy]

Re: 1952 Evinrude 7.5hp - I have no Idea What the issue is

have you check spark and compression? if that is good, i would look at contaminated carb, or fuel supply.

 

[F_R]

Re: 1952 Evinrude 7.5hp - I have no Idea What the issue is

have you check spark and compression? if that is good, i would look at contaminated carb, or fuel supply.

Especially the spark. It should be capable of a 3/16" spark with ease. Partial power like that is almost always due to running on one cylinder. The carburetor and fuel system feeds both cylinders. Bad coils are extremely common on those motors. Have yours ever been replaced? If not, they are way past due. In fact, the replacements might be past due if it has been a number of years.

 

[Chinewalker]

Re: 1952 Evinrude 7.5hp - I have no Idea What the issue is

Also - check for beads of water on the spark plugs - could be a blown head gasket.

If the copper fuel line is clean and not kinked, it should be fine .
- Scott

 

[Personius1976]

Re: 1952 Evinrude 7.5hp - I have no Idea What the issue is

Ok......

So I tore into the motor, replaced plugs, cleaned carb, cleaned fuel tank & line, have good coils, great spark. While running in neutral, she fires off like a champ. Once it is put into gear, it is a complete 180. In low speed she runs ok, but after about 1/2 throttle she throttles up no more.

I have no problems starting the engine, usually goes on the first or second pull.

 

[Chinewalker]

Re: 1952 Evinrude 7.5hp - I have no Idea What the issue is

Have you checked the head gasket? Compression? Your motor will run and sound "fine" on one cylinder, but will lack power. Look for any evidence of water beading on the spark plugs...

 

[Personius1976]

Re: 1952 Evinrude 7.5hp - I have no Idea What the issue is

What is the "Home Remedy" way to check the compression?

 

[lindy46]

Re: 1952 Evinrude 7.5hp - I have no Idea What the issue is

What is the "Home Remedy" way to check the compression?

Not sure what you mean by "home remedy" - just get a compression tester at an auto parts store - very useful, and necessary tool to have if you work on old outboards. By the way, how do you know your coils are good? By good spark - did you test with a spark tester or just see that the plugs are firing?

 

[F_R]

Re: 1952 Evinrude 7.5hp - I have no Idea What the issue is

You need to do what you should have done in the first place before doing all that work. You need to find out which cylinder is not firing and then find out why it isn't firing. The quickest, simplest and cheapest way to find out is to remove and ground one spark plug wire and see how it runs. Then do the same thing with the other one. Chances are it will run the same with one wire grounded, but won't run at all with the other one grounded--that is the good one.

Now that you have figured out which one is not firing, go the next step. Check compression. Check ignition, including the spark plugs and 3/16" spark. Check for water in the bad cylinder. If none of the above, it could be a broken reed valve, but that is fairly uncommon however that 7.5 does do it once in awhile.