Vintage 57' Evinrude 7.5 High-Speed quitting...

[frustratedboater]

I have a vintage 1957 Evinrude 7.5 hp motor, model #7522, that is quitting completely after 23-25 seconds of wide open throttle. I can putter around with even slight throttle and runs very well and smooth, but as soon as I bring it past that, the motor boggs down, and quits. It will start with a very short choke pull when pull-started.

I have gone through the carb 4 times with the same results. The carb has a new kit on it, needle packing, etc.. I had blown out the low fuel circuit and also the center of the bowl and out through the fixed jet, and also the center bowl jet is clean. I have even looked through (with light) to make sure that my high speed needle is unobstructed and clear. I took the dime shaped plate on the top where the low speed needle intersects and the low fuel circuit is clean through out.

Am I missing something? I am usually pretty solid with these small carbs, but this one really has me! Every possible passageway is blown out with air and is clear. Is there something, or somewhere else I should be checking? Any assistance would be appreciated.

~FB~

 

[racerone]

Fact---" carburetor problems " usually turn out to be something else.----------------Is the sintered fuel filter clean ?----Does spark jump a gap of 1/4" or more , yes or no ?----Are you running with the pressure tank or with a fuel pump ?----What does a compression test show ?

 

[tomhath]

Sounds like it's running out of gas; either pressure tank or fuel pump. It could also be ignition, condensers or coils, but the fact that it dies completely instead of just dropping a cylinder makes me think fuel delivery.

 

[frustratedboater]

Yes, it still has the original set up (Pressure tank). I was, personally, leaning towards the fuel delivery myself because that is classic of a carb running out of fuel. When I ran the motor and it died, I lifted the side of the cover and checked the glass sight bowl and it was full. But, that doesn't mean the fuel bowl is, but the glass was. Thinking about that, I don't remember there being any blockage from the glass bowl, at the bottom, to the fuel bowl. With the pressure in the tank, I would safely assume that it was pushing it through...

Yes, the fuel bowl filter was initially missing, but I did purchase another and it is currently in place, but left the original gasket in place because I had assumed it would come with the kit. The rubber showed signs of slight cracking, but it does not leak.

I did check for pressure by loosening the cap of the tank and there is plenty of pressure release happening and does hold pressure as well. I had released the cap a few days later after a previous trip and hissed out pretty good.

As for the spark, it is throwing a strong blue spark and over a 1/4"...

 

[frustratedboater]

Pressure is 50-54 in both cyl's...

 

[F_R]

That is low compression if your gauge is reading right. But never mind that for now. It starts and runs, so it isn't a compression problem. Tell ya what---my vote is the sintered fuel filter is partially clogged. If not that, then the screen filter at the bottom of the pickup tube in the gas tank. If it were me, I'd temporary remove the sintered filter as a test. If it runs full speed without it, you know that was the problem. If not that, on to pulling the top off the tank.

 

[frustratedboater]

I had purchased a brand new carb bowl filter (that copper/bronze ring) so it isn't that. I never thought of the pressure tank pick-up screen, but that is a difinate possibility. I guess I can both, change tanks (I used to collect them and have 4) to see if the same problem happens, and pull out the innards of the tank and take a peek. That just might be it, cause everything else down the line is clean as a whistle!

Thank you!

 

[oldboat1]

Guess I would be inclined not to mess with the current tank for now, if it's holding pressure. But good idea to try a back-up tank, hose and connector, and see if there is improvement. Could also be something as simple as a plug wire or unreliable wire to coil connection. (Maybe revisit prior magneto work.) I think with low compression numbers, you could be dropping a cylinder and stalling out on the remaining one -- maybe not able to run on one cylinder. That might be particularly true if spark is at all weak.

Also might need a head gasket, particularly if any history of overheating. (Assume it's not currently overheating.) If past use in salt water, worth pulling the head anyway to clean out the passages, then resurfacing and replacing with new gasket. Might see an improvement in compression.

I run a 16:1 mix on my 7 1/2, 24:1 on the 10 and 18 -- have a number of tanks, like you, but end up using one known good one most of the time. Think it's laziness (nice to rule out potential tank issues when doing any troubleshooting or tuning -- or running, for that matter.)

 

[racerone]

Is the lower unit binding up ?

 

[frustratedboater]

The lower unit was rebuilt with all new seals and gaskets and is fine. Everything is to spec and operates correctly. I am leaning more towards fuel than mechanical. When I was picking up all my duck decoys yesterday I was in and out of gear for about 10 minuites with no problems of stalling and ran smooth. When I was motoring back to the ramp I gave it high-speed throttle again and quit after 20-25 seconds, which tells me it is fuel. It seems like I was draining the fuel bowl. I am going to try the pickup screen inside the tank and see what that looks like.


I don't know... I should be getting real close!

 

[HighTrim]

I too am leaning towards the filter (don't rule out a new one). Remove it completely, and try again.

As Frank stated, try a new tank altogether. Pick up could be clogged, anti siphon valve partially stuck closed, etc....

However, you are skipping past some other very good thoughts. Racerone had a good point. That motor has a spring loaded shock absorber in the gearcase, under the water pump. When they fail, even partially, they will bind up and cause resistance, killing the motor. Sometimes you cannot get them fired with a faulty one, sometimes it will kill it. It should measure about 6 3/4" long when removed. If you see damage or burning to the bottom of the bearing housing, you know what is wrong.

Other thoughts.

Float swollen and catching. Carb gasket catching float (seen this on aftermarket gaskets). Seat partially clogged. Inside fuel lines clogged. Fuel fitting plugged.

 

[frustratedboater]

I appreciate all the possible areas to check and will give me something to look into. Many times the simple can be over looked! Along with the carb kit, the needle & seat were replaced and checked each time I went into the carb to clean & blow out ports just in case.

Out of curiosity, what are other ways in telling if the shock absorber is defective? Does, or will it come apart? Does it spin (if broken) in any way? What are all the symptoms of a 'broken" shock absorber?

I am using this motor on a 12' LOWE, flat bottom, duck boat and it won't quite plane off. I thought it might... Perhaps, it's keep it from really taking off?

I might just consider splitting the block, replacing the rings, and honing out the cya's this winter. I am trying to sell off my dad's Honda 4-Stroke 15hp (BF15A) and put a 9.9 on it. This was a temporary motor that I took off the rack, and besides, the whole package has that old vintage look...

 

[F_R]

No Title

When the shock absorber breaks, it grows in length, becoming too long for the space it is in, That causes it to bind up. It may only be noticed under power, but eventually you can count on it being hard to pull the starter cord due to the binding in the lower unit.

I'll still believe it is the filter in the carburetor till you try taking it out. Hey new ones can get stopped up too.

 

[frustratedboater]

I appreciate the image and the info on the absorber, it helps! The only reason why I am ruling out the bowl filter, is that, 1-it is brand new, and 2-I have never seen sediment in the glass bowl and I've taken it out each time and sprayed air all through it, but I will clean it again just to double check. What is really weird is that the sight bowl is full when it runs out. I wish I could see into the carb...

I split the handle from the pressure tank today and the pickup screen is very clean, gasket looked intact, and nothing seemed out of order. I will have to replace all the gaskets though. I will spend more time tracking the path of the fuel while I have the tank handle out: up the tube, through the tank handle, check the double line to & through the connector, then the fuel lines to the carb and the jets once again. It would be great if something obvious popped out!

 

[F_R]

OK, you described the filter as a "copper/bronze thing". I'm not sure I know what that means. The only ones I know about are made of thousands of tiny balls fused together. Is that what you have? They are notorious for partially clogging. That's why I keep harping on the subject. As for the glass bowl being full, that is not normal. Well, it is normal if you have been mashing hard on the tank primer. But otherwise, those things run almost empty. Don't try to understand it, just believe. Something about capillary action or something. If is running full, all the more reason to suspect a clogged filter. I realize you are skeptical, but I've worked on thousands of those motors. They fed my family for over 20 years,

 

[oldboat1]

Alternatively, the bowl filter might be OK, but carb is not feeding correctly. If the boss gasket is missing from the high speed nozzle, for example, the air/fuel mix might be affected -- maybe fuel remaining in the glass bowl is a symptom. I think a missing or damaged gasket would likely lean out the h.s. mix (air entering the nozzle) -- conceivable that could cause stalling at high speed, particularly if the engine has other issues. Just a thought.

 

[frustratedboater]

Yes, that is exactly what I have purchased. I had purchased this motor 8-10 years ago and has been sitting in my basement and decided to consider this 7.5, until I found a 9.9 for my boat. So, given my experience with these little motors, I knew to make sure I had blue spark, a clean functioning carb, and a sealed lower unit.

So, when I was digging a little deeper in all the gaskets that I would need, I noticed that there was that bronze, "tiny balls" filter missing from the diagram, and decided to replace what originally should be there. The rubber gasket that it mounts to, didn't come with the carb kit, or with the filter, so I left the original in place. That original gasket was swollen towards that filter and slightly cracked and couldn't get it in place, so I gently trimmed that with an exact knife (I know that is contrary to best practices). I will replace it someday, but it does not leak.

Hey, I really appreciate you keeping on harping about this cause I'd like to get this behind me. I will look at this filter and see what comes out of it. I am going to use a glass jar and swish it around in clean gas, so I can see if there is anything semi-transparent that comes from it, than just the obvious, which I can't see. I believe that I am going to take a better look at the tank and drain it, and blow the lines out and clear out all the handle passageways, while I wait for my tank gasket to come in.

Thanks again, and I'll let you know what I come across...

~FB~

 

[F_R]

You still don't seem to understand. Those things get partially obstructed and still look like new. They never were meant to be cleaned--only replaced. Some guys claim they clean them with carb cleaner or something, but I remain skeptical. It is almost impossible to get the goop out from around the balls inside where you can't see it. Hey, who knows--maybe somebody sold you a "cleaned" one as new. Stranger things have happened.

 

[64osby]

How does the supply line look? Any cracks or dry rot?

 

[frustratedboater]

No, the motor did not come with it and perhaps, that is why it was missing, because it brought problems..?. I purchased the filter along with the lower unit seal kit and carb kit. It is brand new!

The supply line is a new double hose line and fresh fuel.

I was thinking about it on my way to work, is there a glaze, or coating that I should have soaked off before installing? I doubt it, but in this case, you never know...