Power Problem at Throttle-Up

[Speedy4]

Hello Everyone,

I am having difficulty with a 1975 Evinrude 135hp after about 2k RPMs. I have recently bought this motor so I have no history with it. This was my first in the water run with it:

Cold starting is a little difficult. Starts, shuts off. Once warm after about 2 or 3 minutes the motor starts and runs at an idle and warm-up position. It will go into gear and maintain low rpm under a load. When I increase to half throttle the motor start to "sputter." Increase throttle more and the motor shuts off. Bring the throttle back and it easily starts back up and idles.
Playing with the throttle, back and forth quickly, i did get the motor to come up to full RPM, the boat to plane, and stay at High rpms for a couple of minutes. The motor ran smoothly. After backing off the throttle it went back to the sputter and was unable to duplicte the good running condition again


Things I have done:
Water Pump has been Changed
Carbs have been rebuilt (Soaked in Kerosene for 2 days, used HP Air and all orifices looked clear)
New gas at a 50:1 ration (tried 2 different tanks)
Pulled each plug wire off while running at an Idle and part throttle, each dropped in RPM and picked back up when reconnected.
Compression is 115-120psi all cylinders

What I had noticed:
The fuel tank throttle ball seemed to be very stiff, more than what I have seen with other motors.

When i disconnected the fuel line hose from the tank, I got a really good spraying. Under a lot of pressure.

The spark plugs are NGK BUHXW-1. Came with the motor, the champion plug listed in the manual is not available anymore according to the champion website. In fact champion does not list a plug for the motor.

Took the fuel pumo apart, noticed some almost steel wool like wire in the valves. Diaphram, springs, look ok.

Changed the fuel pump out with a known good one. Though again I can't find a sierra rebuild kit or a sierra replacement one for this motor, not listed. so I am guessing the one I am using will work. 18-7820 which is for a 140 hp V-4.
Haven't had the boat back in the water yet, been raining.

Any thoughts or suggestions?

Thanks In Advance!
John

 

[kynolan2183]

Re: Power Problem at Throttle-Up

My thoughts

Sounds fine on the primer bulb.

Check that the tank is venting ok

Check the link and sync. If you need instructions I have those in a PDF or JPG

Check that the link between the throttle and the timing is not loose. There are little plastic pieces that hold the connector bar and those break over time.

Look at your throttle connections and you will see a bar that connects to a piece under the fly wheel. This is the connection bar I spoke of above.

Also in the link and sync. This piece under the fly wheel should start to move at the same time as the throttles start to move.

I think that this problem is normally caused by the engine not getting enough fuel (my experience) thus I would back the idle down alot and reset the cam follower on the carb /carbs to have the butterflies open a little more.
It is best to do this at a boat ramp with the boat on the trailer.
When you can throttle her up to any part of the throttle and she doesn't die then you are on the money.
Use your starting lever to help you keep her on idle and set the idle screw then.

Good luck let me kow if you need more help

Kyle

 

[Speedy4]

Re: Power Problem at Throttle-Up

Kyle,

I have the manual but thanks for offering the files. I haven't done any carb sync or spark advance adjustments yet. Though looking at the linkages, everything thing seems to be moving ok. But that is going to be my next step.

With the pressure in the fuel line and the debris in the fuel pump valves, I was just wondering if it was possible to pressurize the tank on the piston downstroke if the valve did not seal correctly. I did not have the tank cap loose to vent at first and how I noticed it.

I was thinking fuel also, but so far what I have come across with this motor has been "shody" work from whomever did it in the past. Wrong screws, lost parts, ect ect.. So I do not know what was adjusted or played with.

What gets me is that it did run ok for a few minutes. So I maybe wrong, but I would guess all the mechanical linkage adjustments would be ok, and the problem would be fuel or spark related?

It is going to be a couple of days before I can put it back in the water again to try, raining here next few days.

Thanks for the help.

John

 

[jtexas]

Re: Power Problem at Throttle-Up

That you can nurse it up to WOT makes me think your most likely culprit is in the timing/throttle linkage kyle described - the throttle cam should have a mark on it, and it has to hit the roller right on that mark, where the timing advances before the throttles open - just a tiny bit early & she'll fall flat on acceleration.

 

[kynolan2183]

Re: Power Problem at Throttle-Up

On my 70 hp I had the same problem. No power on throttle up
Don't mess with any of the timing adjustments until the very last thing, because it is a pain to work on the timing when you are at a boat ramp.

I am really thinkiing that this is a link and sync problem just like mine,

I actually ended up with the throttle butterflies being open a little more than I thought that they would be with the roller just ahead of the mark as the fellow above described.

But, once I then set the idle she was dead on.
You really can not do it without it being at the boat ramp because you can't rev it up without a load, IE (driveway).

On these two strokes they are different than the old 4 stroke Briggs. They like to run rich not lean at idle and mid throttle.

So adjust the roller on the cam to the point that she actually is reving up from it when you start it and then back it off with the idle speed adjustment screw.
In most cases the idle will not go down just because you turned the screw you will need to use the starting lever (up, down real quick) to pull the linkage back.
In some cases you may even need to adjust the cable to the start lever.

Kyle

 

[kynolan2183]

Re: Power Problem at Throttle-Up

One thing that you asked about was the pressure in the tank.

I would say you are running on a older metal tank more than likely.

I have two of them and they will get pressure on them, it is because of the way they are designed. The valve only allows air in not out and temp changes will cause the pressure.

On my two plastic tanks I don't have that issue because of the cheap open vent system they use.

Kyle

 

[ob]

Re: Power Problem at Throttle-Up

UL77V or L16V Champion surface gap plugs is what is recommended for your engine.They're available.

 

[Ed in North Texas]

Re: Power Problem at Throttle-Up

For What it is Worth: I had 3 mechanics get into the spark plug issue (on my '73 135hp) with me this year, and they tell me the plug OMC speced for this engine originally is the Champion QL77JC4 (not a surface gap plug), which is still available (or at least I bought 4 of them at NAPA about 2 months ago). One mechanic says the surface gap plugs are just fine, 2 say stick with the gapable QL77JC4. I don't know whether either is better than the other, but the original specified plug is apparently still available.