1975 70hp Evinrude stalling problem

[acam]

I have a 1975 70hp Evinrude. I just got it running after it sat for a while, at least 3 years. I had cleaned the carbs as part of restoring it to running status. I took out the idle orifices and sprayed cleaner in there and in the vent holes and bowl drain hole. That made it so it would run on its own (without gas squirt), which it previously had not, though poorly as described below.

It starts with choke on, runs, but starts to die a few seconds later until I put the choke on again for a moment and then it revs back up. Seems like it is not getting fuel all the time but does when I choke it. If I play with it I can get it running in an RPM range a bit above idle pretty smoothly with no load and without having to choke. But after maybe 30 seconds running well at that speed it starts to slow down then dies. It is really hard to keep it running at idle even playing with the choke. It almost seems like the idle speed is set too low (but I realize it could be due to lower fuel sucking at low speed). I can get it to rev up to high RPMs when I open the throttle and it seems to run fine then.

Any suggestions on what I should try next?
Is there a way to test the fuel pump?
What should I look for on the fuel lines? Will a loose clamp cause this?
It has 3 lines to the pump, supply, outlet, and one from bottom of intake manifold. Is this correct?

 

[durban]

Re: 1975 70hp Evinrude stalling problem

i would check fuel pump diaphragm & possible sucking air some where

 

[BonairII]

Re: 1975 70hp Evinrude stalling problem

Run a clear fuel line from fuel pump to carb(temporarily). If air is getting in...you'll see bubbles in the clear line.

 

[acam]

Re: 1975 70hp Evinrude stalling problem

@BonairII & @durban:

Thanks for your help. Do my symptoms sounds like a bad fuel pump/FP diaphragm?

FYI, went out this morning and bought new 1/4 ID fuel line and replaced the line from the intake manifold to the fuel pump and put metal hose clamps on it. I am assuming that is the vac/pressure line that runs the fuel pump, right? It looked suspect. Fired it up and it definitely runs better and will idle now!

The problem now is that the motor sounds like it is running at a pretty high RPM at idle (no load, neutral, only earmuffs, it is on the trailer). What kind of RPM should that be running at idle with no load?

Also, I have access to an older auto volt/tach/dwell meter. It has a needle dial, mode selector switch, number of cylinders selector button (either "4-8" or "6"), and cable with red and black connection clips at the end. How do I use that on a 3-cylinder O/B to measure RPM? Where do I connect the red and black clips? Can I I set it to 6 cylinder and double/half the reading to get the correct rpm? Which should I do, double it or cut it in half?

Thanks again for your help.

 

[BonairII]

Re: 1975 70hp Evinrude stalling problem

@BonairII & @durban:

Thanks for your help. Do my symptoms sounds like a bad fuel pump/FP diaphragm?

FYI, went out this morning and bought new 1/4 ID fuel line and replaced the line from the intake manifold to the fuel pump and put metal hose clamps on it. I am assuming that is the vac/pressure line that runs the fuel pump, right? It looked suspect. Fired it up and it definitely runs better and will idle now!

The problem now is that the motor sounds like it is running at a pretty high RPM at idle (no load, neutral, only earmuffs, it is on the trailer). What kind of RPM should that be running at idle with no load?

1/4" line should be fine, but 5/16ths is prob better.

According to the manual...set rpm to 1000-1100 in neutral.

When on the water, I believe the idle should be 650-750rpm idling in gear

 

[acam]

Re: 1975 70hp Evinrude stalling problem

Thanks BonairII.

The 1/4" fit the nipples so I went with that. Took the spring out of the old line and put it in the new one and it worked slick.

After playing around I finally figured out that the high rev was due to the throttle not going all the way back down. It turned out that the connector on the end of the throttle cable had slipped a bit and eventually came all the way off as I was playing around. I loosened the set screws, slid the cable back into the little hole, tightened, and it was fixed.

Then I had to play around with getting the motor to run in the right RPM range at idle. A few adjustments it I got it.

BTW, I used that old automotive tach/dwell/volt meter that I mentioned above. After 2 hours of searching on the Net and a lot of people saying (incorrectly, I believe) that it could not be done I figured out that I could use it set on 6-cylinder and then cut the reading in half to get accurate RPMs. I attached it to the terminal block where the gray tach wire comes off (and alternator output comes in). It seemed to work great. I finally got it reading about 2000-2100 RPMs at idle (1000-1050 actual RPMs). Do you see any problem with that method?

 

[ACAMS]

Re: 1975 70hp Evinrude stalling problem

I knew you would figure it out .... How did you come about your name?

 

[acam]

Re: 1975 70hp Evinrude stalling problem

So I went to float test it yesterday and it is back to its old tricks. It does not run well at low speed or idle. I have to keep choking it every few seconds and then it comes back to run strong for a few more seconds, then fades. Seems obviously to be a fuel flow problem. Once I open the throttle a ways it revs right up, gets on a plane quick, and runs great; seems to have good power.

I realize that there are a bunch of things I can check from fuel tank to carbs but I was wondering if these symptoms point to something more specific. I know we said it could be the fuel pump but since it runs better at high speed, requiring more fuel, I would think that is counter-indicative. Is my deduction correct or is it backwards?

Also, is it possible that this could be a gas tank or gas line issue? I am using an old Evinrude 6-gallon portable tank. When I pump the bulb I can hear sucking/blowing sounds at the fitting where it attaches to the tank. Is that normal/OK? A small amount of fuel sometimes leaks out too. One thing that was different from when (I thought) it was running well on the trailer vs not running so well in the water was that the fuel tank was up on the gunnel when it was on the trailer, about even height with the motor. In the water it was on the floor, maybe 12-16 inches lower.

 

[BonairII]

Re: 1975 70hp Evinrude stalling problem

Also, is it possible that this could be a gas tank or gas line issue? I am using an old Evinrude 6-gallon portable tank.\

The tank and/or fuel can definitely be the problem(including the bulb). Always replace EVERY last piece of fuel hose on new(to you) motor. Old line will deteriorate and foul carbs....and will leak at the fittings causing poor idle etc.

I'm a fan of plumbing the fuel line directly to the fuel pump(bypassing the quick connect fitting). Also replace the fittings at the tank.

Buy yourself a new fuel tank. Old tank invariably have varnish and/or debris in them.

 

[acam]

Re: 1975 70hp Evinrude stalling problem

So I tried a new tank and gas hose and it does not leak. That may have helped a bit but it did not fix the problem.

So I pulled the fuel line that goes to the carburetors off and cranked the engine to check flow. It flows.....but what is the flow supposed to look like? It was a constant stream but it pulsates a bit, which I would expect because the fuel pump cycles through push and suck as the crankshaft rotates. But when I pump the priming bulb on the hose the gas gushes out in a wide stream, albeit intermittent. Can you describe what the flow should look like when cranking? Should it look like a garden hose?

Also, I THOUGHT I saw some posts that alluded that a good fuel pump should NOT let fuel through when the priming bulb is pumped but I was not 100% sure. Is that correct? Even when the line to the carburetor is off?

 

[acam]

Re: 1975 70hp Evinrude stalling problem

So I tried a new tank and gas hose and it does not leak. That may have helped a bit but it did not fix the problem.

So I pulled the fuel line that goes to the carburetors off and cranked the engine to check flow. It flows.....but what is the flow supposed to look like? It was a constant stream but it pulsates a bit, which I would expect because the fuel pump cycles through push and suck as the crankshaft rotates. But when I pump the priming bulb on the hose the gas gushes out in a wide stream, albeit intermittent. Can you describe what the flow should look like when cranking? Should it look like a garden hose?

Also, I THOUGHT I saw some posts that alluded that a good fuel pump should NOT let fuel through when the priming bulb is pumped but I was not 100% sure. Is that correct? Even when the line to the carburetor is off?