OMC fuel flow problems

CJL · 04 June 2003, 16:18

HI there,
Just wondering if you can help me out with some pointers.

I`ve got a OMC (Johnson) 140hp O/B which is connected to a primer bulb then a diesel/water seperator to bayonet connector and then on to a 75 gal poly prop deck tank. The pipes are all USGC approved and appeared to be in good condition as too are the bayonet connectors.

When the boat has been warmed up at tick over and then used at over 3/4 throttle it dies back after a few mins as if its suffering from fuel starvation. Once when this happened I spotted the primer bulb deflated. The engine restarts immediately without priming.

As I was out for the day, I swapped to a normal 25L deck tank, removed the seperator and the primer bulb. It then worked, not missing a beat for the rest of the day.

Is it likely to just be the primer bulb valves gone (Although it looks in good condition and works when blown through the wrong way) or is it some kind of air lock?

Has anyone got any suggestions?

Chris.

dgpw · 04 June 2003, 16:33

Where the pipe is attached to the primer the tank or the fuel separator It could have rucked up inside. Ie the rubber is part covering the pipe inside. This would be intermittent and would only effect fuel flow at high revs when the whole pipe is needed.

That is right isn’t it h2o Happened on the 7.4

CJL · 04 June 2003, 16:36

I suppose.

I`ll try cutting the hoses back an inch or so on all the connectors
Its either that, the bulb or the tank - agreed?

Chris

PS Why aint you working??

dgpw · 04 June 2003, 16:38

I am in a meeting on, on the phone to the US and the East. Not concentrating prop though. Will be in work at 1am tomor though

Why are you not working

CJL · 04 June 2003, 16:43

My boss is away so that makes me the boss for today.

Didn't you know, if your the boss you do F**k all, all day!

dgpw · 04 June 2003, 16:48

Are you amking you low life workers make you tea.

CJL · 10 June 2003, 13:00

Tried cutting the pipe back and checked all the one way flow valves. All seem to be working and I did find a section where the inner pipe had collapsed from the outer rubber tube. Will give it a try next weekend.
I`m pondering replacing the diesel/water seperator anybody know of some good brands?
Barnet Marine fit a rarther swanky number to their tornados but its £50+

Dave, Still up for the Contender worlds? I`ve emailed you the dates.

Chris

whitingiom · 10 June 2003, 14:09

I've got an old Johnson VRO, and twice recently whilst charging along at WOT in pretty flat water, it has died completely.

Restarted immediately on turning the key and has carried on running perfectly.

Could this be a problem with the bulb/ fuel line?

I've actually got a brand new one still in packet, so I could put it on if you think that would cure it?

Thanks

stuart hedges · 10 June 2003, 14:38

There are a number of things it could be but at least you have tested the engine with another tank so you know it's nothing that end.

Has the fuel system been running ok or has it been changed.

It could be a seal gone in the filter making it draw in air, which side of the filter is the primer bulb, in or out.

Alan · 10 June 2003, 15:07

Quote:

Originally posted by whitingiom
I've got an old Johnson VRO,

I used to have a 150 GT VRO and the fuel flow problem was that it burned around 15gph at WOT!!

CJL · 10 June 2003, 16:24

Stewart,

The fuel system is set up as follows
Engine
Pipe
Primer bulb
Pipe
Diesel/water seperator
Pipe
Bayonet Connector
Pipe
Tank
Obviously I change the tanks as i go.

The collapsed section of the bulb restricted the pipe bore to about 1/3 of the usual bore.
Do you think thats it or should I keep hunting?
I may replace the bulb regardless for peace of mind.

Chris

Charles · 10 June 2003, 16:56

Quote:

Originally posted by Alan

fuel flow problem was that it burned around 15gph at WOT!!

Hey Alan, that's worse than me:
50 liter = 10.9984624 gallon [UK] per hour per engine, that's doing about 38knts....4200revs

Alan · 10 June 2003, 17:07

The engine was a Gulf import '87 model Johnson 150GT VRO which were legendary for their ability to consume petrol. An engine designed from an era and land of cheap petrol! Its ultimate demise and replacement with a 150 Opti was the cause of great celebration!

Cookee · 10 June 2003, 19:05

One of the things I would check is the breather on the tank - if the bulb is collapsing then the fuel pump is sucking ok, but if the breather isn't ok then it's trying to create a vacuum!

DM · 10 June 2003, 20:03

Quote:

Originally posted by Cookee
if the bulb is collapsing then the fuel pump is sucking ok, but if the breather isn't ok then it's trying to create a vacuum!

Nail, Hit, Head, If the bulb is deflating there is a blockage tank side of bulb. As Cookee says, either breather, collapsed fuel pipe or maybe a cloggage in the separator/filter. As it sounds very knackered, I'd sell the engine and boat off cheap. I may know a buyer.

DM

stuart hedges · 10 June 2003, 22:45

If the collapsed bulb is reducing it by that much I would imagine it is definatly that, as others have said, if the bulb is compressed it has some kind of blockage or breathing problem.

Powerboat · 10 June 2003, 23:09

Sounds like a fuel air vent partial blockage problem ! Should be easy to solve.

Best wishes,

Stuart

CJL · 11 June 2003, 10:37

The breather on the tank is OK. I ran it last night with no problems for an hour up the Thames at full chat.
The fuel line blokage seemed to be the problem.

I pity David Manning if he sells his boats every time he has a minor problem!

Chris

DM · 11 June 2003, 10:58

Quote:

Originally posted by CJL
I pity David Manning if he sells his boats every time he has a minor problem

Sorry, I didn't know you were supposed to mend them yourself. You could have told me before as I'm just about to buy my 987th boat

DM