2000 Johnson 250 hp ( not a FITCH ). I keep wanting to think it’s sucking air somewhere. Runs good from WOT to around 8 mph, then it wants stall. You pump the bulb primer and it smooths out for a few minutes then it starts again. ( Note: it’ll idle all day in the yard on muffs. ) It was acting this way when I bought the boat last spring.
Everything is new from the tank to the motor: fuel filter - seperator - new fuel lines - primer bulb replaced twice - new fuel pump new fuel rail - new fuel lines on all carbs. Can see no fuel leaks anywhere.
I’ve got an Atwood glass fuel filter on it - I’ve noticed air in the filter even when it’s idling. That can’t be right - there should no air in the fuel delivery system. But I’m at the end of ideas from where it’s coming from.
Motor fires right up after it stalls - no problem there. Like I said, if you catch it stalling and get to the primer bulb it’ll smooth right out ( primer bulb oriented w\arrow up with flow up fuel ).
I thought about putting an electric Holley red fuel pump between the primer bulb and motor to have positive fuel pressure all the time toward the motor.
I’ve been fighting this issue for 9 mons… I’ve posted this problem before without many ideas. Any ideas will help at this point.
Try posting this on iboats.com if you don’t get alot of responses here. If you are lucky a member called rodbolt may respond.
84’ 18 Privateer
08’ Yamaha 90
There are always greater fish than you have caught, always the lure of greater task and achievement, always the inspiration to seek, to endure, to find.
Is it a carburated model? Have you replaced the primary fuel pump? This a small square pump on the side of the block and it driven by crankcase pressure. It has a rubber diaphram in it. If it the diaphragm gets hard the crankcase pulsations at or near idle aren’t quite enough to overcome the added resistance so fuel pressure to the carbs drops. When it is working good it is a very low pressure, like 1-2 psi so it doesn’t take much pressure loss to cause a problem. It sound like that when you pump the bulb you fill the carbs bulbs up, but the slowly empty because of a lack of fuel and the problem reoccurs a few minutes later.
I it okay to have air it the sightglass filter. If you had an air leak you will see bubble entering the sightglass and the air leak would be worse the higher the speed.
There are always greater fish than you have caught, always the lure of greater task and achievement, always the inspiration to seek, to endure, to find.
Do you have three fuel filters in this setup? Atwood, water seperating and engine mounted filter. Maybe all of this filtering is putting a restriction in the fuel flow at slow/idle speeds. If your water seperating filter is a 10 micron you shouldn’t need the atwood. Try taking this out of the setup the next time out.
84’ 18 Privateer
08’ Yamaha 90
There are always greater fish than you have caught, always the lure of greater task and achievement, always the inspiration to seek, to endure, to find.
quote:Is it a carburated model? Have you replaced the primary fuel pump?
Yes, it’s carburated. It had a VRO fuel pump system on the motor when I bought it. As you thought of, I also thought it was the diaphram so I just replaced the VRO fuel pump with a new non-VRO fuel pump. I pre-mix the fuel now.
The problem didn’t follow the old pump off the motor - same problem existed after new fuel pump installed.
quote:Oh yeah, I forgot to mention that running on muffs vs. in gear on the water requires less fuel so maybe why you don't have an issue on muffs
I know - I just mentioned that to show it’ll idle on muffs - so at idle speed in the yard everything seems to be ok. After a long run out it seems to act up the worse but runs good on the long trip in…
quote: Do you have three fuel filters in this setup? Atwood, water seperating and engine mounted filter
I have the Atwood water sep. ( 10 micro I believe ) and the Atwood inline fuel filter. I don’t know about a third engine mounted filter. Where would be it mounted ? There’s nothing between the glass Atwood and the fuel pump. Is it somewhere else…?
cummins
you are sucking air somewhere
find that location, and you will fix your problem.
you could have a leak anywhere between the pickup tube in the tank, and the clear filter you are seeing the bubbles in
quote:you are sucking air somewhere
find that location, and you will fix your problem.
you could have a leak anywhere between the pickup tube in the tank, and the clear filter you are seeing the bubbles in
I haven’t checked the pick up tube in the tank…never thought of it.
quote: Hook up a portable tank to your engine it will tell you if you need to be looking at your motor or boat side.
I did that but just on muffs in the yard. It showed the motor side was good ( and I believe that ) but that isn’t a true indication since the problem doesn’t show it’s self until you’re at trolling spd…
quote:ditch the glass in line filter, they create more problems than they fix, you're probably sucking air from that point
I’ve been told to get rid of the glass filter twice pretaining to this problem. It’s good as gone. Should I replace it with another fuel filter or just not replace it and use the water \ seperator alone. Someone mentioned two filters might cause fuel restriction @ low RPMs.
I think it’s an air leak like ChrisV said and it could be from the glass filter or the pick-up tube. It’s sucking air somewhere or there wouldn’t be air bubbles in the glass filter.
you can use one of the white inline filters to splice the line where the glass filter was. They are usually listed as the replacemnt filter for use on the engine(merc, Johnson, Evinrude, Sierra selss them listed by fuel line size. You really don’t need the additional filter, but I don’t think it will hurt. Anything that has Moeller written on it, throw it in the trash and replace it with a good brand. What type of primer bulb did you use? The Johnson/Evinrude is the best one available
Hook up a portable tank to your engine it will tell you if you need to be looking at your motor or boat side.
This is a very good start. This way you can figure out where to start. I am going through a similar issue and it is very very frustrating. I feel your pain.
Have you removed (not replaced) the anti-siphon valve? I had a very similar issue this summer - ran great north of 1500 RPMs; stalled out quickly when running below that. Turned out that I had a bad ASV. The ball moved freely when you pushed on it but it had just enough resistance that the engine couldn’t crack it at low RPMs. Anyway, I removed it and the engine has been great since.
I had a similar problem on my little whaler with a 60 bigfoot. I have had the problem since I bought the boat two years ago. I had already changed out the tank, hose, bulb - everything twice, but after reading this post I checked around the internet. Several people said the same thing - What made the difference was an OEM Mercury bulb. I put it on, and shortened the distance between the bulb and the tank. Runs like a champ. Thanks for the help.
quote:Have you removed (not replaced) the anti-siphon valve? I had a very similar issue this summer - ran great north of 1500 RPMs; stalled out quickly when running below that. Turned out that I had a bad ASV. The ball moved freely when you pushed on it but it had just enough resistance that the engine couldn't crack it at low RPMs.
My tank two inlets for two motors - I have only one motor. We put the fuel line on the other inlet after inspecting both fuel pick-up lines. Both picks ups looked good. Looked like someone had already taken the ASV out before we owned the boat.
quote:What made the difference was an OEM Mercury bulb. I put it on, and shortened the distance between the bulb and the tank. Runs like a champ. Thanks for the help.
Discovered a bad bulb yesterday… Atwood bulb had a leak at the factory crimp - just enough to suck air. You could see the air accummulating in the glass fuel filter when idling - it would take about 5 mins to get enough air in the filter to effect the idle. That falls right in line with the idle\trolling spd. stalling issue.
Also a high pressure fuel leak ( when the bulb is squeezed ) at the auto primer fuel line ( has the red lever on it ). You couldn’t have seen that with one person - someone had to be looking for it when someone else primed the motor. If it’s leaking fuel anytime - it’s sucking air. I hope we fixed the problem.
To all, thanks for the ideas and suggestions… We’ll see what happens.
Cummins,
Read with interest your letter about the boat motor…I have been fighting the same problem with my 2001 70 horse Johnson…if you find a solution for this problem please post your solution to me directly or to this web site and I will do the same. Just like you I have replaced fuel pump, line, and changed over to a 12 gallon portable tank and still have the same problem. I have not noticed the bubbles but will be on the lookout.
quote:...if you find a solution for this problem please post your solution to me directly or to this web site and I will do the same
Will do.
FYI:
Someone mentioned once the problem could be temp. related. Yesterday while running the motor on muffs I used a pyrometer on the heads. After about 15 mintues the left head checked 79 degs. and the right was @ 115 degs. I pulled the t-stats to check them in a pan of water. The left t-stat had a sand pebble stuck in it…it was holding the t-stat open about .075" all the time. Removed the pebble - tested the t-stats - they checked good. They’re 133 deg. t-stats.
Re-installed the t-stats. After 15 minutes of run time the left side was 84 degs and the right side was 91 degs. - that’s exceptable. I don’t know if the t-stat would have ever opened with the pebble stuck in it. Maybe that also was part of my problem… How long had it been it there is anyone’ guess.
What’s the chances of a rock getting stuck in the t-stat to hold it open. I need to play the lottery more often.