Johnson 110, Lurching/Dying Off At High Speed

[great_white_fisherman]

The engine runs pretty well, except that between 3/4 and full throttle, it will lurch. Speed will drop for a second then return for a few seconds and repeat. It doesn't do this, or at least far and few between, when below 3/4 throttle. A search revealed it could be the fuel pump is weak or a bad coil causing misfires.

The fuel pump idea sounds like just the ticket based on how it behaves at higher speed. But before I go buying a $600 part, $200 on Amazon or eBay, I was thinking perhaps a bad fuel filter could be to blame. Replaced fuel hose with one off my other boat and it has an inline filter barely a few months old. The one inside the cowling looks original and being an 87 model.....ya. Two fuel filters would be redundant, yes? I can remove the inside one, insert a hose coupling and I'm good to go to see if that's the issue?

Otherwise, if that idea doesn't do it, what could be the problem?

Note - I have the VRO disconnected at the harness and the hose because of reading on another thread that they can destroy a motor if they go bad and that usually the first sign it has gone bad IS destroying the motor. I don't want to take that chance so I'm sticking with 2 stroke gas in the tank....could that be the problem?

 

[jfoulk84]

I would always try to replace a filter before a pump before buying the parts. Much cheaper for the filter. Simplest (albeit not safe for long term) way to test would be to bypass the filter and go open it up. Just make sure there's no junk or debris in your tank. You have the inline filter for anything big. If it works, problem solved. If not, replace the filter anyway and get the pump.

 

[great_white_fisherman]

It's got 2 inline filters. One on the fuel line and the one on the inside of the cowl. So i figure double filters is unnecessary

 

[oldboat1]

Why double filters? History of fuel problems? Double filters may be too restrictive at high throttle.

When the hull changes angles, contaminates (incl. water) can come within reach of the tank intake.

 

[great_white_fisherman]

No I don't think it's a history of fuel problems. I think it's more like the normal protocol to have a filter on your fuel line coming from the tank both for peace of mind and being able to see the fuel. So I'll go ahead and remove the inner filter and put a coupling in it's place. That particular filter is no longer available anyways. It has a 90 degree nipple and the replacements I could find when I searched the part number were all straight nipples which wouldn't work with the way everything is routed under the hood

 

[great_white_fisherman]

I removed the filter and replaced it with brass fittings. I cut the old filter open to see what it looked like inside and it was clean. No signs of junk build up. So it wouldn't appear that this filter is the problem. Perhaps clogged jets in the carb? Can those be cleaned without completely tearing off the carbs?

 

[great_white_fisherman]

I got her to run right. Maybe....

I found some info on anti siphon valves causing this issue so while waiting on the replacement, I removed the valve and replaced it with a quick connector. It ran full throttle and I disconnected it when I stopped in order to prevent back flow. Worked great!

When I got the new one in, I blew through it and it had just as much resistance as the old one! We'll find out but I fear I may be back to square one. Would this indicate a weak pump not able to overcome the valve?

 

[racerone]

Fuel pumps are driven by crankcase PRESSURE pulses.-------There may be issues there.-------How does the motor run when your assistant operates the manual pump ?

 

[great_white_fisherman]

It ran great so that was unnecessary

 

[great_white_fisherman]

I'll give that a try if I do end up with the same issue though

 

[great_white_fisherman]

Good news! I don't know what was wrong with the other siphon valve but this one did the trick. Runs great, holds prime, the whole 9 yards. Next up is the charging system :/