Cylinder Drain Check Valve Location - '79 Evinrude 70 HP

[gobbleme]

I've been trying to diagnose an over consumption of fuel issue, on my 1979 Evinrude 70 HP. It seems like it's using way too much fuel for the amount of time it's running, and it spits fuel out of the intake of the carbs while running. My manual suggests testing the cylinder drain check valve... But it doesn't really explain what or where it is. It also suggests that not all models have this check valve. I've found a couple of hoses coming off of the intake manifold, but I don't think either are a check valve. One is the vacuum line for the fuel pump and the other seems to be some a vent line that connects to the air box.

So my question is: Does my engine have a cylinder drain, and where is it located? Any info would be appreciated.

Thanks!

 

[Joe Reeves]

Having started in the trade with OMC back in 1960 and retiring in 1991, and being a serious minded tech.... I have never heard of a Cylinder Drain Check Valve.

What are you calling excessive fuel usage?

That engine will bur 6 gallons of fuel at full throttle in about 45 minutes...... In cruising range (go to full throttle, then back up to roughly 3/4 throttle) 6 gallon would last about 1 hour & 45 minutes.

 

[mrcj001]

With fuel coming out of the carbs like that tells me there is a float issue.

 

[gobbleme]

Having started in the trade with OMC back in 1960 and retiring in 1991, and being a serious minded tech.... I have never heard of a Cylinder Drain Check Valve.

What are you calling excessive fuel usage?

That engine will bur 6 gallons of fuel at full throttle in about 45 minutes...... In cruising range (go to full throttle, then back up to roughly 3/4 throttle) 6 gallon would last about 1 hour & 45 minutes.

Maybe my terminology isn't correct, but the manual says to use a syringe and some isopropyl to test. I can double check the wording in the manual when I get home tonight. And if it can burn 6 gallons in less than an hour then maybe my fuel usage isn't excessive. The motor is new to me, and with all the fuel coming out of the carbs I assumed the usage was high. I have had a no start issue when the engine is warm (say sitting for an hour or 2 after running hard) and am trying to track it down to a fuel issue. There is definitely lots of fuel coming out of the engine (both from the carbs, and the exhaust) when it is not starting.

As for the floats, they are all new with new needles and seats, but taking them off and checking the levels is on my list of things to check.

 

[mrcj001]

yes check the floats.....when you re-assemble the float, needle and seat, be sure that the small wire the needle hangs from doesn't get caught or pinched with the float hinge assembly. Its easy for that small hanger to get caught there causing a stuck open float.

 

[Joe Reeves]

Do the basic troubleshooting......

Remove all spark plugs.
Check the compression... what is the compression psi of all individual cylinders?
Plugs still removed... check the spark which should jump a 7/16" air gap with a strong blue lightning like flame... a real SNAP!. Does it?
********************
(Spark Tester - Home Made)
(J. Reeves)

Most auto part stores have "air gap" spark testers... OR..........

You can use a medium size philips screwdriver (#2 I believe) inserted into the spark plug boot spring connector, then hold the screwdriver shank approximately 7/16" away from the block to check the spark or build the following:

A spark tester can be made with a piece of 1x4 or 1x6, drive a few finishing nails through it, then bend the pointed ends at a right angle. You can then adjust the gap by simply twisting the nail(s). Solder a spark plug wire to one which you can connect to the spark plug boots, and a ground wire of some kind to the other to connect to the powerhead somewhere. Use small alligator clips on the other end of the wires to connect to ground and to the spark plug connector that exists inside of the rubber plug boot.

Using the above, one could easily build a spark tester whereas they could connect 2, 4, 6, or 8 cylinders all at one time. The ground nail being straight up, the others being bent, aimed at the ground nail. A typical 4 cylinder tester follows:

..........X1..........X2

.................X..(grd)

..........X3..........X4
**********************

Since you've re-worded your post problem.... (fuel coming out of carburetors when the engine is not running).... the carburetors possibly are flooding. If so, clean and rebuild them as needed.

(Carburetor Float Setting)
(J. Reeves)

With the carburetor body held upside down, the float being viewed from the side, adjust the float so that the free end of the float (the end opposite the hinge pin) is ever so slightly higher (just ever so slightly off level) than the other end. And when viewed from the end, make sure it is not cocked.

That engine should start within six revolutions, hot or cold.

 

[jimmbo]

I've been trying to diagnose an over consumption of fuel issue, on my 1979 Evinrude 70 HP. It seems like it's using way too much fuel for the amount of time it's running, and it spits fuel out of the intake of the carbs while running. My manual suggests testing the cylinder drain check valve... But it doesn't really explain what or where it is. It also suggests that not all models have this check valve. I've found a couple of hoses coming off of the intake manifold, but I don't think either are a check valve. One is the vacuum line for the fuel pump and the other seems to be some a vent line that connects to the air box.

So my question is: Does my engine have a cylinder drain, and where is it located? Any info would be appreciated.

Thanks!

If you are referring to a crankcase purge drain, you engine doesn't have one. Instead it recirculates the crankcase condensate to bearings supporting the crankshaft

 

[jimmbo]

That engine will bur 6 gallons of fuel at full throttle in about 45 minutes...... In cruising range (go to full throttle, then back up to roughly 3/4 throttle) 6 gallon would last about 1 hour & 45 minutes.

That's not much worse than what our 63 40hp burned per hour. In reality, it would be better mpg wise as it would have pushed the boat faster, and thus further

 

[flyingscott]

Is the fuel pouring out or being spit out in drops. If it is drops, it is not abnormal for those motors to do that out of the carb.

 

[gobbleme]

Is the fuel pouring out or being spit out in drops. If it is drops, it is not abnormal for those motors to do that out of the carb.

While it's running it's spitting the fuel out. It slowly accumulates and then will drip down out of each carb. It's definitely not pouring out, but you can see the accumulation of it when it's been running and you take the engine cover off.


Thanks everyone for the advice. Sounds like I have some troubleshooting to do - Float heights, compression, and spark test - I will post my results when I have a chance to do it.

 

[flyingscott]

While it's running it's spitting the fuel out. It slowly accumulates and then will drip down out of each carb. It's definitely not pouring out, but you can see the accumulation of it when it's been running and you take the engine cover off.


Thanks everyone for the advice. Sounds like I have some troubleshooting to do - Float heights, compression, and spark test - I will post my results when I have a chance to do it.

That is normal that is why the the air box has the drain hose on it. The drain hose recycles that fuel back through the motor. That issue will usually show up the most at an idle it goes away as the rpms go up. That is also why there are gaskets on the carb side and cover side of the air box to contain that fuel . What RPM are you running wide open you want to be as close to 5500 as possible. What kind of boat is it on? What do you use the boat for? If it is skiing and tubing with a lot of start and stops kiss your fuel mileage goodbye regardless of the motor.

 

[gobbleme]

That is normal that is why the the air box has the drain hose on it. The drain hose recycles that fuel back through the motor. That issue will usually show up the most at an idle it goes away as the rpms go up. That is also why there are gaskets on the carb side and cover side of the air box to contain that fuel . What RPM are you running wide open you want to be as close to 5500 as possible. What kind of boat is it on? What do you use the boat for? If it is skiing and tubing with a lot of start and stops kiss your fuel mileage goodbye regardless of the motor.

My tach isn't working so I don't know what RPM's I'm reaching at WOT. It's also on my list of things to troubleshoot/repair lol. The boat is a 15.5' Crestliner Muskie - Mid 70's fiberglass Trihull. I use it for a bit of everything: Tubing, fishing, and cruising.

 

[flyingscott]

edit

 

[flyingscott]

How does it run? If your tach isn't working look at the rectifier.

 

[gobbleme]

It runs great for the most part. Usually idles well but will occasionally start to die out if it's been idling for a long time (like trolling). Top end seems to run great. Sometimes has trouble going from idle to high RPM's; seems to bog down and run rough if you ease it into the higher RPM's, almost feels like it loses a cylinder. This is usually when the engine is colder, and is short lived. Keep giving it throttle and it seems to sort it self out.

 

[flyingscott]

The motor dying when trolling is usually the idle is to low. You need a tach.