2001 90 hp surges

[jackcaptjr]

Hello all. I am currently sitting in Mexico and am having trouble with a well maintained 90. Symptoms are:
Surges under full power with about a 5 second frequency.
Primer ball stays firm and pumping while it is running has no effect on symptom
Starts and idles fine
Seems fine in nutral rev-up

I thought fuel problem so have done the following:
Replaced internal filter and spin-on external filter
Replace primer ball and checked and or replaced all lines to the internal tank
Checked tank pick-up
Checked all fuel line connections
Removed and cleand carbs....... they were not dirty but are now clean with all jets clear.

Could use some help
Thanks,
JR

 

[sschefer]

Re: 2001 90 hp surges

There's about 100 things that it could be. You've done most of the simple stuff but there are a couple you missed.

Water in the fuel (probably courtesy of E-10 gas).
Old spark plugs.

Where was the last place you got fuel? I'm suspecting either old/bad gas or water. Replacing the plugs is just something you can do to eliminate them from the equation and make them easier to read.

You should also put a fuel/water separating filter in the fuel line. It's become sort of defacto standard with today's fuels.

 

[jackcaptjr]

Re: 2001 90 hp surges

Thanks for the input. I did forget to mention that the plugs are less then a year old but installed the new spares just in case. Fuel was ruled out by testing with a seperate can if gas. I did use the old primer ball fuel line during that test but have since replaced that line.

I have talked to a local Merc guy and ha wants me to run a full throttle test with the boat still on the trailer, dunked in the water, and when the engine bogs to place my hand over a carb input. If the engine picks up speed tells me that is a lean carb. If all 3 further stumble then she is not running lean. Sounds like a reasonable test so will do this AM.

I have also rotated a new switch box through all 3 with no changes in symptoms.

He has indicated that it could be the stator somehow effecting the timing. I don't have a timing light here but he wants me to at least check the voltage output from the regulator.

At least the wind is up and I haven't missed much of a bite.

JR

 

[ENSIGN]

Re: 2001 90 hp surges

If you do decide to do this test Make sure you have the lanyard tied to yourself!!!

 

[jackcaptjr]

Re: 2001 90 hp surges

Hello all,

Just wanted to report back in on the positive results of the carb test. Turns out that the upper carb did in fact pick up power after being blocked off for a couple of seconds. this indicated that the upper carb was running lean. The other two stumbled when covered and did not recover to full song when uncovered. Indicating they were working properly.

Pulled all three carbs off and field stripped them all..... again. This time I payed special attention to the upper carb. The only area where I found any gunk was in the fuel well in the center of the bowl. This is a critical area and just a little gunk will cause problems. Cleaned this area and all of the jets and tubes. Used 15lb fishing line to clean the small tube that runs from the well to the upper section of the carb.

She is now running back at full song.....43.3 MPH @ 5200 and doesn't miss a beat.

Thanks for the inputs,
JR

 

[Texasmark]

Re: 2001 90 hp surges

Glad you got her fixed. Something in the back of my mind tells me that the setup on these triples carbs is not identical. I can look it up if you want; I have the serv manual.

I have a '02 90.

Mark

 

[jackcaptjr]

Re: 2001 90 hp surges

All is well in San Carlos as Short Stack is running great.
As to the carb set up, these carbs are very simple with only one idle mixture adjustment. All 3 have the same fixed jet size and float levels. The throttle rod I left alone.

Cheers and thanks

JR