'99 F100 Fuel Issue

[SeaDouble]

Hi guys, I have a '99 F100 that sat for a little over a year with gas in it before I recently bought it. I changed the oil, thermostat, and water pump, siphoned the old gas and changed the 10 micron h20 separator filter, then filled with 89 octane and a can of seafoam. Took her out this morning, and she was running great at low and high rpms, but a little rough in the middle. I ran her for about 10 minutes at 4000 rpm and we were cruising along nicely when all of a sudden she bogged down & I stopped. From there she didn't want to go past about 1800 rpm, any higher and she would start to miss out pretty bad and act like she was going to stall.

So I know I should clean the carbs & replace the filter in the engine as first points of attack, but I'm worried about it and can't do anything until tomorrow. Does it sound more like a clogged filter, dirty carbs, all of the above, or something else? I'm really hopeful that it's not serious.

I should add that the engine still runs very smooth at idle, and up to about 1800 rpm, which makes me hopeful that I did not blow a piston or anything too serious. Am I being overly optimistic?

Any input is greatly appreciated.

[99yam40]

I would check compression or do a leakdown test on the cylinders to make sure the motor is still in good condition.
and make sure the alarms system works as it could be going into RPM reduction but the buzzer is not sounding

[SeaDouble]

Compression was just checked last week and was 215-225 in all cylinders. Overheat alarm works as well.

I will check compression again to make sure that no damage was done today.

I have not had a chance to pull it off and look, but I was thinking that maybe the water separator could be full of water restricting the flow of gas through the filter. Possible?

I will be able to investigate later tonight.

[200090tlry]

When you changed water fuel seperator

Did you bleed line of air? Sometimes a simple thing

[99yam40]

Compression was just checked last week and was 215-225 in all cylinders. Overheat alarm works as well.

I will check compression again to make sure that no damage was done today.

I have not had a chance to pull it off and look, but I was thinking that maybe the water separator could be full of water restricting the flow of gas through the filter. Possible?

I will be able to investigate later tonight.

Does this motor have water detect ion on the onboard filter? Check to see if it has wires to it

[SeaDouble]

No, it does not.

[99yam40]

I would clean the carbs and run it on a portable tank and line to make sure there is not a problem with you on board ones. You may need to have the carbs balanced with special manometer once cleaned

[SeaDouble]

Did you bleed line of air? Sometimes a simple thing

Actually I think this was the problem. It seemed that there was some air in the line, but i won't be sure that it was the culprit until i can test it on Wednesday. The previous owner did not have a priming ball rigged in the line, so when I replaced the h20 separator I just topped the new one off with gas before screwing it on, which I'm sure left some air in the line. I installed a priming ball and bled the line at the carb. I will report back after testing it on Weds.

I replaced the fuel filter inside the cowling and it was dirty but not clogged. I dumped the h20 separator and there was no water, but a little bit of light translucent neutrally buoyant sediment (maybe some bits of varnish from tank/lines?). Neither filter seemed to be what caused the issue.

If this fixes the issue, but it still studders in the mid rpm i will go ahead and get the carbs cleaned and possibly balanced.

Thanks for all of the input guys.

[SeaDouble]

So I was able to take the boat out tonight for a test, and it's improved but there's still an issue. The boat runs great from idle up to 2100 rpm, and above about 3600rpm but rough and sputtery in between. It even stalled once accelerating through that mid range. Once you get up past 3600, though it runs totally great.

Any ideas?

Thanks!

[rodbolt17]

time for a carb job and check the fuel pump diaphram.

[SeaDouble]

Thanks guys. You are all barking up the right tree.

Dirty/clogged venturi jet in one or more of the carbs was the verbal diagnosis from my local yamaha shop based on my description of the symptoms. Advised to do a shock treatment of ring free and to run the engine in the rough range to see if it can be cleared that way. If that does not fix it, clean carbs myself and then take it in to have them rebalanced.

[rodbolt17]

are you NUTZ
you already suspect a clogged jet.
clogged jets make LEAN A to F ratios.
difference between an oxy acetylyne welding set up and a cutting set up.
LEAN.
however its your motor.
snake oil it vall you wish.
just pray an ex valve wont smoke or a hole appear in a piston while snake oiling.

[SeaDouble]

Well I thought the same thing until I talked to this guy - a Yamaha dealer.

I specifically asked if there was a risk of blowing a piston while doing this and he said not with a 4 stroke.

Obviously you think otherwise and that it's bad advice. Maybe he wants to see me back with a blown motor for a big service bill. He sure seemed like he was honestly trying to help me out.

[rodbolt17]

you have 4 little engines sharing a common crank.
all go the same speed all at the same party.
not all have to get along.
myself I would speack to actual techs not parts or sales staff.
yes virginia
4 strokes lean out and burn ex valves,detonate holes in pistons just like they do on automobiles.
only modern autos typicall are efi and have knock sensors or you can hear the ping.
your F100 has no knock sensors and you will never hear the ping as it destroys a cylinder,piston,piston rings or a valve.
your call though.

[SeaDouble]

Well the bummer of this is that this guy is the service manager and a tech. I thought he was helping me out. Even gave me a free bottle of ring free.

Now I'm afraid I need to find a new shop.