Gas feed problem with 1974 Evinrude 70hp..

Hi everyone.

I'll try to just get straight to the point here. We've been having trouble getting this engine to run right for quite a while(couple years), but I think we may have gotten it narrowed down to just a gas feed problem now. Anyway, we took the boat out on the lake yesterday and it starts and idles fine but when you go to accelerate then it starts to fall on it's face quite a bit. However, when someone is pumping the primer bulb it seems to help and almost eliminates the problem. Although as soon as you quit pumping, it loses power almost immediately. Does anyone know what could be causing this? I'll list the things that we've checked and/or replaced below.

1) Replaced gas lines at engine
2) Replaced spark plugs
3) Compression is good
4) Carbs have been cleaned
5) Primer bulb replaced near gas tank
6) Forward & reverse cables replaced
7) Screen in filter looks good

I should also mention that I've been told to look for a fuel pump on the engine but I can't seem to find one. Does this model have a fuel pump and if so, where is it located? Any info/suggestions would be greatly appreciated. Thanks and let me know if you need more information on anything.

Re: Gas feed problem with 1974 Evinrude 70hp..

welcome to the forum.

That filter screen you checked - the thumbscrew is screwed directly into the center of the fuel pump.

Look on iboats for a pump rebuild kit, about $12, get some gasket cleaner and permatex #2, half hour later you'll be good to go.

And next time don't wait 2 years, we can narrow it down lots faster than that!

Re: Gas feed problem with 1974 Evinrude 70hp..

Sounds like a fuel pump. Follow the hose from the primer bulb thru the cowl then it will lead to the pump.Jerry

Re: Gas feed problem with 1974 Evinrude 70hp..

jtexas said:

welcome to the forum.

That filter screen you checked - the thumbscrew is screwed directly into the center of the fuel pump.

Look on iboats for a pump rebuild kit, about $12, get some gasket cleaner and permatex #2, half hour later you'll be good to go.

And next time don't wait 2 years, we can narrow it down lots faster than that!

Click to expand...

jerryjerry05 said:

Sounds like a fuel pump. Follow the hose from the primer bulb thru the cowl then it will lead to the pump.Jerry

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Thanks for the information, jtexas & jerryjerry05. I see the fuel pump now and have ordered one of those kits. I'll pick the other items up soon and let you all know how it goes.

Haha, yeah I won't be waiting that long again to seek help -- thanks to this great community.

Re: Gas feed problem with 1974 Evinrude 70hp..

Well after replacing the fuel pump kit the problem unfortunately didn't seem to change very much if at all. It almost seems like it's sucking air in somewhere and smothering it out. You must accelerate very, very slowly to full throttle or it will smother out and die. I tried pumping the primer bulb again and sure enough it helped but ONLY when pumping it. I'm gonna make sure all the lines and whatnot are blown out and cleaned but I'm sure they already are. Do you all have any more ideas on what the problem might be? Thanks.

Re: Gas feed problem with 1974 Evinrude 70hp..

positive the carbs are right and you rebuilt the pump rightand got the parts in the correct way could try swapping with a known good used part or buy a new one i m sure that the pump is still your problem or stuck inlet needles or floats that the pushing of the bulb helps fuel flow in.

-nate

Re: Gas feed problem with 1974 Evinrude 70hp..

The fuel pump is a lift pump and needs a pure column of fluid to move the gasoline to the float bowls in your carburetors. Any air leak at all in the system will cause the fuel pump to fail to perform properly. Additionally, the pulse line to the pump must be airtight.

The ventilation of the fuel tank must also be adequate or the pump cannot work.

You might want to try using a new portable tank with new fuel line, fuel and oil, to eliminate the possible problems there from further consideration. In the meantime look for air leaks, and a fuel leak is an air leak, too.

Re: Gas feed problem with 1974 Evinrude 70hp..

positive the carbs are right and you rebuilt the pump rightand got the parts in the correct way could try swapping with a known good used part or buy a new one i m sure that the pump is still your problem or stuck inlet needles or floats that the pushing of the bulb helps fuel flow in.

-nate

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I'm pretty sure everything is right that you listed.

The fuel pump is a lift pump and needs a pure column of fluid to move the gasoline to the float bowls in your carburetors. Any air leak at all in the system will cause the fuel pump to fail to perform properly. Additionally, the pulse line to the pump must be airtight.

The ventilation of the fuel tank must also be adequate or the pump cannot work.

You might want to try using a new portable tank with new fuel line, fuel and oil, to eliminate the possible problems there from further consideration. In the meantime look for air leaks, and a fuel leak is an air leak, too.

Click to expand...

Well, today I noticed some fuel actually squirting out around the fuel pump so I disassembled and resealed with more permatex - fixed that problem. Also there is a tiny hold on the back of the fuel pump that was shooting out liquid - fix that after the reseal of the pump. Next I noticed that the gas lines were clamped with zip ties instead of metal clamps which was causing a bit of a fuel leak - so I replaced those with the two available clamps that I had on hand. The vacuum line (which is the same as pulse line, right?) is the only line that's still clamped with zip ties - however they look secure but I will replace them with clamps when I get them. So after resealing the pump and clamping the gas lines I started it up without any trouble in a barrel of water to test it and it idled and throttled up almost perfectly. However when it was throttled you could hear a kind of stutter in it's rhythm...like it wasn't smooth but certainly not bad either. Anyway, we thought we would try it out in the lake and see if we made any progress but unfortunately it would hardly start once we got it in the water at the lake. Once we did get it running then we would have to idle it higher than usual in order for it to not just die completely. We then tried to very, very easily ease it into gear and it would die right away. Needless to say we had to load it back up and it's back to the drawing board. I don't understand why it started and ran decently the other day even with the old fuel pump and leaking line...yet today it would hardly start and even go into gear without dieing.....what the heck?

It's hooked up to a vented plastic tank that appears to have adequate venting.


I'm thinking of trying the portable fuel tank with new gas/lines asap.

Re: Gas feed problem with 1974 Evinrude 70hp..

zipties are factory spec - they will hold until the hoses get old and stiff, at which time they need to be replaced.

make sure the throttle butterflies are all parallel.
make sure the choke plates are parallel and completely open except when the choke solenoid is engaged.
Idle speed in neutral with lower unit submerged should be 950 to 1000.

Re: Gas feed problem with 1974 Evinrude 70hp..

jtexas said:

zipties are factory spec - they will hold until the hoses get old and stiff, at which time they need to be replaced.

make sure the throttle butterflies are all parallel.
make sure the choke plates are parallel and completely open except when the choke solenoid is engaged.
Idle speed in neutral with lower unit submerged should be 950 to 1000.

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The butterflies are all parallel.
The choke plates seem to be working properly.
I don't have a tachometer gauge for the boat atm..=/

The engine seems to run fine when it's out of the water and hooked up to a hose in the yard. Seems to idle fine and throttle up without a problem. However when you get it in the water it will usually start up and idle but it sounds like it's smothering when idling in water...and as soon as you try to put it in any kind of gear it will smother out and die almost immediately. Very rarely now can you get in in gear and barely chug along without it dieing. I recorded a short video clip of it idling and throttling up in the yard...maybe some of you could take a look at it and see if it sounds 'normal'. Any help is appreciated. Thanks.

Re: Gas feed problem with 1974 Evinrude 70hp..

good idea, the video.

It appears to me as though the timer base is not moving at all when you throttle up. It's supposed to be linked to the throttle lever, and start its motion just before the throttle valves start to open.

What this does is to advance the spark, from TDC at idle to 19? BTDC at around 75 to 80% of full throttle. Without it, the opening up the throttles will rev the motor all day long, but it can't make any real power when you put a load on it.

If the timer base is sticking because of dirt or grime or whatever, obviously you want to clean it out until it'll move smoothly. But if you see what could be epoxy that has melted and dripped down, that means your flywheel has heated up at some point. If a magnet loosens and shifts even a little, it throws off the timing of the engine. But I wouldn't pull the flywheel unless & until you get some symptoms of bad timing.

The roller should be covered with a plastic (nylon?) bushing - hard to tell but it looks kinda like it's missing. That will affect the timing of the spark advance/throttles.

Just in case, I went ahead and identified the idle set screw. Adjusting that screw should only move the timer base - all the idle RPM adjustment is accomplished with spark timing, the throttles are always closed until you move off idle.

What we're talkin bout here is "link & sync", the process of synchronizing the throttle linkages with each other and with the spark advance. You really need a manual to walk ya through the step by step, too many variations year to year for a person to remember 'em all and type out here.

But bottom line, you want to get the carb throttles sync'd up and horizontal (not beyond) at WOT. Find the mark embossed on the throttle cam (the part that contacts the roller) - the cam needs to hit the roller right on that mark.

You'll have to fine-tune the idle speed with the lower unit submerged - the backpressure on the underwater exhaust makes a difference of a couple hundred RPMs. Just set the idle to where it will run smoothly *in gear* in the water.

Re: Gas feed problem with 1974 Evinrude 70hp..

Thanks for all the info, jtexas. I'll look into all this asap and let you know how it goes. It definitely sounds like the problem. In the meantime I'll put some better photos of the engine up here so you can get a better look at it. The plastic cap does appear to be missing that you spoke of...not exactly sure where you would find a replacement but I suppose it could be ordered off here or somewhere online...

Also, do you know what the screw above the idle set screw controls? (Best seen in images 1 and 2)

Sorry about all the 'beginner' questions but this is the first boat I've ever worked on so it's a pretty new experience for me and I appreciate all the advice.

Boat engine images:
Image 1
Image 2
Image 3
Image 4
Image 5

Re: Gas feed problem with 1974 Evinrude 70hp..

that's your WOT stop screw, set it to where it stops the throttle lever when the throttle butterflies are horizontal.

Re: Gas feed problem with 1974 Evinrude 70hp..

jtexas said:

that's your WOT stop screw, set it to where it stops the throttle lever when the throttle butterflies are horizontal.

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Alright, thanks.

I took another short video clip of the linkages where you can see the timer base is indeed not moving at all. I thought seeing it 'semi first hand' would be better than just writing it out here. It's explained with better detail in the video clip below(Sorry the audio is kind of low - you may have to turn up your speakers a bit):



Here's the engine running in a test tank and we're attempting to put it into gear but it dies immediately as you can see (You may want to turn your speakers back down for this one):




It appears the spring that's in the fixture where the timer base and throttle linkages connect is good and for the most part clean. Any ideas why it isn't moving at all? Thanks.

Re: Gas feed problem with 1974 Evinrude 70hp..

you pulled the timer base back -- it's s supposed to start out back, and move forward. the rubber stop that it's resting against now - that's what stops it's forward travel.

I'm not sure what year is shown here, but see the how the cam and throttle lever are angled back more than yours in neutral? (ignore the yellow arrow)



My boat's at a storage yard but I'm going to have it here tomorrow, prepping for camping later in the week. It's a '79 - very little difference in appearance and the linkages are all pretty much the same. Then I won't have to work from memory.

Any chance you could get your hands on a manual - the "link & sync" procedure is pretty specific, model to model.

Re: Gas feed problem with 1974 Evinrude 70hp..

If your timer base is indeed resting against the stop screw when the engine's idling, the timing is messed up. When you pull the timer base back, that retards the timing.

Your idle timing spec is 0? TDC.

Check the Engine FAQ section of iboats, there's a thread on setting your WOT timing at cranking speed.

Re: Gas feed problem with 1974 Evinrude 70hp..

Thanks for all the information, jtexas. With the little experimenting I've gotten to do so far, when the timing base is pulled back it does indeed idle down the engine - almost to where it will eventually cut off. Otherwise, the timer base is resting against the rubber stop at all times. I do see how all the linkages are angled back more in that picture. I ordered a manual and it should be here Thursday and I'll have to take some time to look at it. I'll check that thread you mentioned. I haven't had a lot of time to work with it much lately but I appreciate you sharing your knowledge and I'm sure I'll have more questions. Thanks again.

Re: Gas feed problem with 1974 Evinrude 70hp..

look for air leak in all seals on engine,use carb cleaner to spary with,engine will change pitch

Re: Gas feed problem with 1974 Evinrude 70hp..

check for air leaks on all engine seals & gasket,use carb cleaner,pitch of engine will change when you find air leak.

Re: Gas feed problem with 1974 Evinrude 70hp..

rx_morph said:

Also there is a tiny hold on the back of the fuel pump that was shooting out liquid - fix that after the reseal of the pump. QUOTE]


I may be mistaken but I think that hole needs to be open so air behind the diaphragm will escape when the diaphragm moves.
If fuel comes out then there maybe a bad seal in that area or a hole in the diaphragm.

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