4.3L LX Mercruiser 4bbl carburetor issue, PLEASE HELP!

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i_timmers

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Hello,

Yesterday, I took my new(to me) Bayliner Capri 1850SS for a spin on the lake. Problem is, the engine didn't want to spin over 2400rpm. Rolling the throttle over that it acts like it's flooding out the weber carb. This is a vacuum controlled choke system. I did some checking, there seems to be manifold vacuum pressure. In shear despiration, I checked the butterfly valves. They don't seem to be regulating the air flow. I held down(closed) the butterfy valves and the boat started to run smoother. I then throttled up:) and brought it clear up to 4,000+ rpm's and it was running great. The minute I let go of the butterfly valve(open position), she returned to the poor running 2,400 rpm's. All the while, the temps were fine and the oil pressure stayed strong. Any suggestions on this problem? Any and all help would be greatly appreciated.
 
180shabah

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Re: 4.3L LX Mercruiser 4bbl carburetor issue, PLEASE HELP!

i_timmers said:
I checked the butterfly valves. They don't seem to be regulating the air flow. I held down(closed) the butterfy valves and the boat started to run smoother.
Click to expand...

I assume you mean the choke plate, there is almost no way you could do anything with the throttle plates without removing the carb.

I then throttled up:) and brought it clear up to 4,000+ rpm's and it was running great.
Click to expand...

If this was in neutral, it means about nothing, and is bad for the engine. If 4k was under load, then pull the carb and rebuild it.

Bottom line, you are fuel starved, start at the tank vent, and work you way to the carb it's self, until you find the problem/restriction.
 
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i_timmers

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Re: 4.3L LX Mercruiser 4bbl carburetor issue, PLEASE HELP!

The boat was in drive, the misses was steering. When it throttled up, it lifted the bow right outta the water! I did treat the fuel but figured it wouldn't even run if it was the fuel quality. So, start at the tank fittings and through the whole fuel system, eh?
 
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i_timmers

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Re: 4.3L LX Mercruiser 4bbl carburetor issue, PLEASE HELP!

And yes, I did mean the choke plates... I tried to correct it, but it went in as another post, sorry.
 
JustJason

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Re: 4.3L LX Mercruiser 4bbl carburetor issue, PLEASE HELP!

if you physically held the choke closed while the throttle plates where opening up and it ran better... is a sign of the boat running to lean.
closing the choke restricts air... richening the mixture... if it started to run better at this point... do what shabah says....
 
Don S

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Re: 4.3L LX Mercruiser 4bbl carburetor issue, PLEASE HELP!

Have you checked the fuel filter on the engine for water?
What year is this Merc 4.3LX, and what drive?
 
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i_timmers

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Re: 4.3L LX Mercruiser 4bbl carburetor issue, PLEASE HELP!

it's a 1996 with an Alpha 1, generation 2 outdrive.
 
JustJason

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Re: 4.3L LX Mercruiser 4bbl carburetor issue, PLEASE HELP!

start with the "5 basic checks"
1. Spark check
2. compression check
3. fuel sample
4. gear lube check (or lack there off it... or a milkshake)
5. transom and floorboard check...


1-3 will get you pointed in the right direction....
4 and 5 will "help" your decision of how much $$$ you want to put into the boat.
 
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i_timmers

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Re: 4.3L LX Mercruiser 4bbl carburetor issue, PLEASE HELP!

Jason,

#'s 4 and 5 on your checklist are in great shape(I picked this boat up for $4,500 which is a steal for the model, options and year). I checked those numbers through before the boat came home. Everything works and I have a full service history on the boat from day one. It starts and runs smooth on the first crank, there is no oil(which is clean) or other fluid leaking evidence. The facts seem to point to fuel concerns, which i can understand. The boat sat for a year and a half with it being started and idled every couple months. Now that is is being used again, the fuel system is going to have some concerns. I was figuring it was going to at least need a carb rebuild. I am happier going through the fuel system and cleaning that out to see where I'm at.
 
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i_timmers

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Re: 4.3L LX Mercruiser 4bbl carburetor issue, PLEASE HELP!

OK, I pulled the carb off, took off the fuel filter and also pulled the fuel tank sensor. I inspected the fuel, it smells funky and is a deep shade of gold. I plan on having the carb inspected tomorrow to see if the internal filters are clogged since ya can't just check this through the fuel line inlet. Also, I pulled off the anti-syphon fitting. How can I check if this is bad? While checking this whole setup, I noticed no fuel in anything accept the fuel/water filter and some in the carb. Now i just had the boat on the water yesterday(Saturday afternoon). Would the fuel bleed back into the tank that fast? Offer some feedback, Please?
 
MikDee

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Re: 4.3L LX Mercruiser 4bbl carburetor issue, PLEASE HELP!

Check to see if there's any clogged filter in the tank, inline, before the antisiphon valve. The antisiphon valve is a one way valve, Try blowing through it from the tank side, it should react like a coach's whistle, a vibrating burst of air should come through in that direction, and nothing should pass through in the other direction. Then you'll know if it's working right.
 
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i_timmers

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Re: 4.3L LX Mercruiser 4bbl carburetor issue, PLEASE HELP!

Mik,

It seems to take alot of pressure to push past the check ball from the flow direction, is this normal? It is vibrating very fast when I do blow through it but I'm close to feeling my ears pop. I just wouldn't think it would require so much pressure. I have read it doesn't take much more than 3-5 psi of fuel to idle this boat. I have a poly tank and cannot seem to get the fitting off the top of the tank in order to remove the pickup tube. I am draining the fuel tank today thru the fuel level sensor access, this is right next to the pickup tube. This way I can inspect it throughly before I go breaking the tank or something stupid. If necessary, I will apply air in reverse to blow out the pickup tube and clean up the residue.

Thanks,

Tim
 
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180shabah

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Re: 4.3L LX Mercruiser 4bbl carburetor issue, PLEASE HELP!

This is bringing back some memories, I recently went through all of this on a rescued '96 4.3LX.

Replace the antisiphon valve.

You already have the carb removed, get the rebuild kit and rebuild it. you will have it half apart to get to the filter anyway.
 
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i_timmers

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Re: 4.3L LX Mercruiser 4bbl carburetor issue, PLEASE HELP!

Same engine as mine! I will replace the antisyphon and bringing the carb in right now. Along with that, I will be replacing the fuel filter, fuel and blowing out the pickup tube. Hopefully this will fix the ailing performance. If you can think of anything else, lemme know!


Thanks!
 
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i_timmers

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Re: 4.3L LX Mercruiser 4bbl carburetor issue, PLEASE HELP!

Bump!

Any hints/tips on removing the pickup tube from the fuel tank? Mine is not behaving and I DO NOT want to crack or break the tank. Is there a chemical I can spray on it to help loosen up that fitting?
 
Bondo

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Re: 4.3L LX Mercruiser 4bbl carburetor issue, PLEASE HELP!

Why don't you run it on an auxiliary tank,..... Just to Test it.......

Diagnosing a Problem 1st,.....
Is Easier than Breaking everything finding out your in the Wrong Place...........
 
MikDee

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Re: 4.3L LX Mercruiser 4bbl carburetor issue, PLEASE HELP!

i_timmers said:
Bump!

Any hints/tips on removing the pickup tube from the fuel tank? Mine is not behaving and I DO NOT want to crack or break the tank. Is there a chemical I can spray on it to help loosen up that fitting?
Click to expand...

It's not a left hand thread, is it? although I doubt it?

By the way, it shouldn't be that hard to blow thru the antisiphon valve, I would replace it myself being as you have it off, and it's questionable.
 
MikDee

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Re: 4.3L LX Mercruiser 4bbl carburetor issue, PLEASE HELP!

I had 2- 18' Wellcraft airslots, 1 with a 165hp Mercruiser straight 6, and 1 with a 302/188hp V8 Mercruiser, both had a tank on each side of the boat, just ahead of the driver, and after much heartache I took the hoses off them, unscrewed the antisiphon valve, and found a stainless screen filter about the size, and shape of 1/3rd of a lead pencil, about 3/8ths" around, inside the aluminum fuel line, that was full of sand, seaweed, and debri?! from the previous owners, I decided that I had a spin on filter seperator at the motor, so I removed them permanently, put the valves back, and never had a problem again!
 
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i_timmers

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Re: 4.3L LX Mercruiser 4bbl carburetor issue, PLEASE HELP!

Well, after inspecting the carb, it's never been serviced(rebuilt). All the bolts have been tamper free from the factory. This can't hurt. That lead me to the fuel/water filter being changed along with the anti-siphon fitting. This is now become more like a service than a repair in my eyes. The fuel being drained is just because it looks and smells not right. I will pump it out(most of it) and run this in the cars little by little till it's gone. I would like to just blow out the pickup tube(with the strainer on the bottom) in the tank. Again, as a preemptive strike for good flow to the rebuilt carb since I can't seem to remove it. This really only leaves the fuel filter as the last straw in the "lack of fuel"
 
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