Holeshot repaired - Now Surging

[Darrenkmac]

Thanks to the help from this forum I was able to fox my holeshot bogging down problem on my 94 Evinrude Intruder 175. After replacing my warped carb bowls and rebuilding them with new kits I was able to get on plane easily yesterday. I am however still having the issue of surging. An example would be that if I am running at exactly 3000 rpm, about every 20 seconds or so my engine will surge up to 3400 rpm for about 5 seconds and then settle perfectly back at 3000 rpm. This was happening before I fixed the carb problem by the way. When I had the carbs down for cleaning I noticed that the idle screws were set at 12 turns out from soft seat. From what I have read online, that seems a bit high ? I had changed the spin on fuel line filter and cleaned the cone filter screen at the motor as well. Am I starving it of fuel or air perhaps ? I have good compression and I am using the Champion QL78YC plugs gapped at .030. Any ideas on why my engine surges ?

 

[webbd]

Multi-cylinder, multi-carburetor engine, this might not be the situation...

But - when my lawnmower surges, it means it has a stuck needle-and seat in the carburetor. It might be worth a look to make sure all of your needle/seats are clean and floats are working properly.

- DW

 

[Darrenkmac]

Multi-cylinder, multi-carburetor engine, this might not be the situation...

But - when my lawnmower surges, it means it has a stuck needle-and seat in the carburetor. It might be worth a look to make sure all of your needle/seats are clean and floats are working properly.

- DW

They should be clean. I just cleaned them thoroughly and set the floats.

 

[Chris1956]

That sounds like a fuel delivery problem. You might check the vapor pump. The vapor pump in conjunction with the OMS pump are responsible for supplying the carbs with enough fuel to run at any speed.

In addition check all fuel line connections, the antisiphon valve at the fuel tank and the tank breather. Anyfuel restriction will be an issue. You do have 3/8" ID fuel lines, right?

 

[Chris1956]

One more thing, the fuel mixture adjustment screw on the carbs only affects idle mixture. At RPMs above 1200 or so, it has no effect.

 

[racerone]

Test run with another tank and hose.------Test run with a timing light to see if spark returns on one cylinder when motor RPM goes up.

 

[Darrenkmac]

That sounds like a fuel delivery problem. You might check the vapor pump. The vapor pump in conjunction with the OMS pump are responsible for supplying the carbs with enough fuel to run at any speed.

In addition check all fuel line connections, the antisiphon valve at the fuel tank and the tank breather. Anyfuel restriction will be an issue. You do have 3/8" ID fuel lines, right?

Yes, 3/8 fuel line. However, the line has a quick connect with a check valve. I think that I will change to just a 3/8 barb.

 

[Darrenkmac]

Yes, 3/8 fuel line. However, the line has a quick connect with a check valve. I think that I will change to just a 3/8 barb.

I also cleaned the vapor tank and checked its float.

 

[Chris1956]

OK, did you check the vapor pump?

 

[Darrenkmac]

OK, did you check the vapor pump?

I will take a look at it. I noticed while running that when I ran through small wakes of other boats that the rpm would change and rev up. I have it trimmed up but not in such a way as to starve the intakes.

 

[Chris1956]

The vapor separator cover must seal to it's body. A new gasket may be in order.

Air leaks there are the same as air leaks anywhere in the fuel line.

 

[Darrenkmac]

The vapor separator cover must seal to it's body. A new gasket may be in order.

Air leaks there are the same as air leaks anywhere in the fuel line.

I will look at the gasket as well, thank you. I talked a local boat dealer and he told me to change the gaskets behind the reeds. He also said that a bad powerpack could cause surging. Do these things sound right to any of you ?

 

[Chris1956]

The surging you describe sounds like a fuel delivery issue. You could try pumping the primer bulb at high speed and see if it collapses or if the motor runs better. That will cinch it as a fuel delivery problem.

if the primer bulb collapses, the fuel tank vent is likely the culprit.

 

[oldboat1]

I will take a look at it. I noticed while running that when I ran through small wakes of other boats that the rpm would change and rev up. I have it trimmed up but not in such a way as to starve the intakes.

sounds like that could be a ventilation issue -- trimmed too far out or motor not mounted low/deep enough on transom.