4.3LX Weber 4-bbl Starting Problem-Seems Forever...

[Woody-jh]

1995 4.3LX-Mercruiser, Serial OF421280, Weber 4-bbl
Starts fine, 1st or 2nd crank after winter lay-up.
Then, starts poorly during the season, regardless of the weather...
Have done the following:
-Replaced plugs, rotor and cap (no visual issues)
-Replaced anti-siphon and hose to electric fuel pump. Seemed to help the first few times, started much easier before back to the same old thing.
-Blew out the fuel tank vent line and vent- fumes came back real quick to fill cap. Someone told me spiders like to nest there, just like in propane bbq lines.
-Choke coil found disconnected. Reconnected it and vacuum pull-off set. Functions well, both the choke and pull-off.
Symptoms:
1. Usaully starts, runs for 10 seconds, dies, takes considerable cranking before restart will occur. Need to crank 3-4 times at 15 seconds per time.
2. Oil pressure (gauge) is at 35# after first few seconds of cranking.
3. Does not seem to be any fuel getting into the carb when pumping. Can't smell any, can't see any when breather is pulled. Choke plate is closed.
4. Doesn't even sound like it wants to start, then starts without warning on 3rd or 4th attempt (30-40 seconds) as described above. From that point, it will run OK and start all day, anytime that it is shut off.
Questions:
1. Could my fuel pump be weak, as in unable to pull fuel from the tank to prime itself? Once full, it seems OK.
2. I don't know what the inside of the tank looks like. Is there a hidden filter? Could the suction tube plugged or restricted? How do I check things on the tank side of the anti-siphon valve. Anybody got a photo or schematic?
3. Am I due for a carb rebuild (probably never been done) to get at those nasty internal fuel filters. (Off season job)

Not fun at dockside. I usually start it at home on muffs before heading to the dock to increase my chances of a good start.

I'm focusing on fuel issues, as electrical side seems "OK."

Thanks, Woody-jh

 

[cooter2506]

Re: 4.3LX Weber 4-bbl Starting Problem-Seems Forever...

try running it on an auxillary tank to see if problem goes away. if it does maybe pickup screen in tank is blocked.

 

[Woody-jh]

Re: 4.3LX Weber 4-bbl Starting Problem-Seems Forever...

Disconnected the fuel line at the tank, leaving the anti-siphon ball check on the tank. 1-2 ounces of fuel drained out of the line.
Dropped the fuel line, without the anti-siphon into a two gallon gas can. Boat started after only 3-4 seconds, ran without issue in driveway. It continued to run even when I pulled the hose from the gas can...after 30 seconds I put the hose back in.
So now I am confused. "Seems" like the fuel pump is creating enough vacuum to draw fuel (aux tank was no higher than the permanent tank). The anti-siphon ball check seems to have a stronger spring than I might have thought, but I have already replaced it with a "universal part."
I don't want to spend $300 for a fuel pump (Canadian dealer price), but sure want to have this boat start reliably.
Starting has degraded to the point that I have to dump 1-2 ounces of fuel directly into the carb in order for it to start at all.
Suggestions?

 

[DivrDown]

Re: 4.3LX Weber 4-bbl Starting Problem-Seems Forever...

I have the exact same set up as you. I ended up replaceing the oil pressure switch first, and the replaced the fuel pump. Like night and day. In my case it seems that the fuel pump would work all day once it was warmed up but getting started and running would do the same as you described. I opted for the sierra replacement pump, marine grade but cheaper than Merc.

http://www.wholesalemarine.com/mm5/merchant.mvc?Screen=PROD&Store_Code=1&Product_Code=SIE-18-7326

 

[180shabah]

Re: 4.3LX Weber 4-bbl Starting Problem-Seems Forever...

I have seen several fuel pumps fail in this manner (including one of my own). After sitting, the pump intermittantly does not run when energized(think of an old fan that has a dust contaminated motor - sometimes you got to give it a little spin to get it started, then it is fine). It gets progressively worse.

 

[Woody-jh]

Re: 4.3LX Weber 4-bbl Starting Problem-Seems Forever...

I did some testing today. Electric fuel pump (Mercruiser OEM).
1. I disconnected the fuel line at the carb, it was dry. Cranked the engine until fuel appeared.
2. Pressure tested using a compound gauge. 8 psi. at inlet to carb. Mercruiser Spec is 3-7 PSI so passes.
3.Reconnected coil wire, engine started and ran fine.

Questions:
1. Is there an internal check valve inside the fuel pump that is letting the fuel drain back, creating "vapor lock" overnight?
2. Can a fuel pump that puts out 8 psi have trouble pulling vacuum?
3. I have changed the anti-siphon check valve at the tank. Do they all have the same spring setting? Not a lot of clearance for fuel to get through. If the spring was too weak, th ball would get sucked into the outlet port, if the spring were too strong, the pump would have trouble getting the ball off the seat.

Getting tired of heavy cranking to git er goin!

 

[futz]

Re: 4.3LX Weber 4-bbl Starting Problem-Seems Forever...

how do you start the boat?

 

[Woody-jh]

Re: 4.3LX Weber 4-bbl Starting Problem-Seems Forever...

I've tried a few ways, and I think that you ask a very good question.

1. Owner's manual says to pump the a couple times, then set the throttle at 1/3 full range. Starting time has been deteriorating badly lately, but it was never good. Probably 5 cranks at 15 seconds each, no attempt at starting, then instantly it starts. Never seems to be any fuel in the carb until it starts.

2. Lately I have been moving the throttle to 1/4 full range, turning the key for 5 seconds, then cranking..thinking that the electric fuel pump might need some time to get fuel flowing. Sometimes a bit more successful than 1st way.

3. On a bad day, I pour 1-2 ounces of fuel directly into the carb (2-bbl side), blower and flame arrestor on, and that gets it going after a couple of quick cranks.

Starting at home on muff or in water doesn't seem to make much difference.

To my understanding, fuel pressure must be satisfied before the pump gets 12V power. I am seeing 30 PSI on my dash gauge wehn cranking, 50 PSi when running. Voltage should be close to 12V, because I run 2 batteries when the blower is on. Blower seems to drop voltage a bit. Are there any other "interlocks" besides oil pressure?

 

[jtybt]

Re: 4.3LX Weber 4-bbl Starting Problem-Seems Forever...

Could be you have an air leak allowing both some drain back an rather pulling gas, will pull air. I've had a couple encounters with everything from bad fuel tank fitting to actual holes in the pick-up tube in the tank.

There is also the possible junk in the bottom of the tank. Some tanks allow the removal of the pick-up tube. check it out.

 

[DivrDown]

Re: 4.3LX Weber 4-bbl Starting Problem-Seems Forever...

These fuels pumps are a sealed electrical unit there is nothing that we can do to repair them. I messed with this issue for almost a season starting with rebuilding the carb last year , then and engine failure not related, this year when I replaced the pump and not one problem with starting now.

 

[Wet Wonder]

Re: 4.3LX Weber 4-bbl Starting Problem-Seems Forever...

When I had a similar problem , I followed the "fuel system tests" in the sticky section in this forum. Did the air in the line test, vacuum tests, pressure test, and found that I had a lead in the line. Whatever is the cause of your problem, I would suggest spending an hour or two doing the complete fuel system test in the sticky. It's a rational way to find or rule out causes from the tank up to the carb. I'd definitely do that before buying any parts.

 

[Woody-jh]

Re: 4.3LX Weber 4-bbl Starting Problem-Seems Forever...

Good advice. I have been doing the simpler tests using a compound gauge, but I do not have it tubed in as shown in Don/Jason's guidelines. I have disconnected and taken spot readings, whereas the guideline lets you observe things live. (i.e. air)

I will do these tests then report back. One question that nobody has answered yet, are anti-siphon valves specific or custom to an engine? I only had a choice of one at my local supplier, it looked like the one I changed out, but who says that one was correct?

And another, I have checked the anti-siphon several times, but have not touched the tank fitting that it threads into. It looks like a factory joint into a fibreglass tank, so have been concerned that I might really mess something up. But to get to the pick-up tube, I guess that I will have to. Can anyone share an adventure, hopefully a good one with pick up tubes?

Thanks,
woody-jh

 

[jtybt]

Re: 4.3LX Weber 4-bbl Starting Problem-Seems Forever...

At one time, fiberglass tanks were notorious for leaving tons of crap inside.

 

[Bondo]

Re: 4.3LX Weber 4-bbl Starting Problem-Seems Forever...

but have not touched the tank fitting that it threads into. It looks like a factory joint into a fibreglass tank, so have been concerned that I might really mess something up. But to get to the pick-up tube, I guess that I will have to. Can anyone share an adventure, hopefully a good one with pick up tubes?

Ayuh,... What you Should have is,...
A threaded flange made into the tank, in which a brass elbow fitting is screwed into...
The Elbow will have the anti-siphon valve screwed onto the out-bound side,...
On the In-bound side, there should be a copper tube soldered into the Elbow fitting, or a plastic tube pushed into the fitting...


Btw,.... You're fighting an Issue that's plagued these carb/ fuelpump combo's since they came out...
Many have tried to Nail down the Cause,..... I've yet to hear of a Definitive Answer...
Many, Myself included, have built a By-pass for the Oil pressure switch to prime the carb before starting.....

If you really Find the answer,..... I can't wait to hear it.....

 

[Woody-jh]

Re: 4.3LX Weber 4-bbl Starting Problem-Seems Forever...

Bondo, excellent response, your insight is most appreciated.
I didn't realize so many people had installed fuel pump bypasses.
Sounds like playing with the tank fitting and pickup tube could be "not fun," or would you recommend that I get the pickup tube out and check it out. I'm concerned about causing a leak point at the tank flange. Will the pick up tube come out with the tank fitting easily, provided it is still joined? Or, is the pickup tube a "factory sealed" assembly.

I'm begining to think that my manual method of pouring gas in the carb, even though it might be the lazy guy's method is automated when you install a fuel bypass.
Where has Mercruiser been all these years- there's so many 4.3's out there?
Thanks
woody-jh

 

[Wet Wonder]

Re: 4.3LX Weber 4-bbl Starting Problem-Seems Forever...

Bondo, excellent response, your insight is most appreciated.
I didn't realize so many people had installed fuel pump bypasses.
Sounds like playing with the tank fitting and pickup tube could be "not fun," or would you recommend that I get the pickup tube out and check it out. I'm concerned about causing a leak point at the tank flange. Will the pick up tube come out with the tank fitting easily, provided it is still joined? Or, is the pickup tube a "factory sealed" assembly.

I was able to get the tube out easily. I removed the compression fitting in front of the elbow that sends the tube down into the tanks, and then just unthreaded the elbow from the tank flange and pulled the tbe up.

 

[Woody-jh]

Re: 4.3LX Weber 4-bbl Starting Problem-Seems Forever...

What shape was the pickup tube in? was there a screen on the end? Did you have to clean out your tank?
Thanks, Woody-jh

 

[Wet Wonder]

Re: 4.3LX Weber 4-bbl Starting Problem-Seems Forever...

There wasn't any screen on the picup tube and it was perfectly clear. I then took apart all the fittings up to the water separating filter and resealed and connected them with pipe dope to close any air leaks.

 

[Woody-jh]

Re: 4.3LX Weber 4-bbl Starting Problem-Seems Forever...

The saga continues...poor starting that is.
One thing I have noticed is that every time I unthread the anti-siphon valve from the tank fitting, there is usually very little fuel in the hose, in spite of repeated cranking. The anti-siphon always seats tight one way, is free flowing the other when I blow into it. Then I reassemble the fittiing and hose from anti-siphon to water separator, and the engine starts WITHIN 3-5 seconds of cranking- even though I have just filled everything with air by breaking the fittings/ hose.
I just don't get it- how does the fuel get from the tank to the carb and start every time I take the anti-siphon apart, but it is forever to start unless I do this.
PS: Only one more run left this year, and I intend to rebuild carb over the winter, but looking for any ideas. Also, I will install the fuel pump "cheater switch" which some of you have said is the way to go.

Thanks, Woody-jh

 

[mariahmx20]

Re: 4.3LX Weber 4-bbl Starting Problem-Seems Forever...

Bondo, thanks for the insight into the oil pressure bypass issue. I own a 1992 Mariah and have had this starting problem since new. I would have thought if you need to prove oil pressure to run the fuel pump that some type of bypass would be built into the starting circuit. If this is not the case how do you build the bypass. Thanks, Steve.