mercruiser 4.3 LX GEN+ bogging out past 3/4 throttle

[kpiazzisi]

I am totally fustrated I have owned his boat for two weeks. It bogs down past 3/4 throttle. So far I have changed fuel, fuel filter, spark plugs (gapped them), plug wires, distributor cap and still have the same problem. If I am attempting to pull my wife and daughter out of the water on a tube, I can't get the boat to plane. The more I bury the throttle the more it bogs and losses power. Here is something really wierd, if I open up the engine cover I get the slight increase in power and eventually the boat will plane. Without towing a skiier the boat is fine at cruise as long as I accelerate to cruise very gradually, but as soon as I go over that the boat bogs again. Today I listened by the engine and it sounds like the bog sound is comming from the carb. I had the carb off as well and partially apart (float bowl exposed). I showed it to the guy at Advanced auto and he said it looked amazingly clean as if someone had just rebuilt it. I am assuming the problem is the carberator? Maybe the mixture, jets? My engine serial number is 0F821555. please help

 

[John_S]

Re: mercruiser 4.3 LX GEN+ bogging out past 3/4 throttle

I am totally fustrated I have owned his boat for two weeks. It bogs down past 3/4 throttle. So far I have changed fuel, fuel filter, spark plugs (gapped them), plug wires, distributor cap and still have the same problem. If I am attempting to pull my wife and daughter out of the water on a tube, I can't get the boat to plane. The more I bury the throttle the more it bogs and losses power. Here is something really wierd, if I open up the engine cover I get the slight increase in power and eventually the boat will plane. Without towing a skiier the boat is fine at cruise as long as I accelerate to cruise very gradually, but as soon as I go over that the boat bogs again. Today I listened by the engine and it sounds like the bog sound is comming from the carb. I had the carb off as well and partially apart (float bowl exposed). I showed it to the guy at Advanced auto and he said it looked amazingly clean as if someone had just rebuilt it. I am assuming the problem is the carberator? Maybe the mixture, jets? My engine serial number is 0F821555. please help

Did you put it in base mode and set the timing? Should also adjust mixture and idle speed while in base mode, but not causing your 3/4 throttle problem. Clean flame arrestor. Weber carb, correct? Check to see if the weighted air valve over 2ndaries are not sticking.

 

[kpiazzisi]

Re: mercruiser 4.3 LX GEN+ bogging out past 3/4 throttle

John,

Mine is a two barrel. I think the weber is a four barrel? I agree with you, I don't think the problem is the timing. I did not set the timming. I actually have a question about how to set the timming, so I am glad you brought it up. I believe I have the thunderbolt IV and not the thunderbolt V. I heard the thunderbolt IV does not require to be set to base mode, but the thunderbolt V does. I only see one mark on my timing cover and one mark on my pully. From a post that I read on here, lining the two up with a timming light will put in at 0 degrees. The Merc manual says it should be at 10 degrees BTDC, so how do I found that without a mark on the cover that says 10 degrees?

I am going to have to review my anatomy of the carburetor, because I don't know what a weighted air valve is or were it is located. You could have said the Flux Capacitor was sticking and it would have meant to same thing. I will try to educate myself tomorrow and give it a shot. Do I need to pull the carb off to do this?

 

[John_S]

Re: mercruiser 4.3 LX GEN+ bogging out past 3/4 throttle

John,

Mine is a two barrel. I think the weber is a four barrel? I agree with you, I don't think the problem is the timing. I did not set the timming. I actually have a question about how to set the timming, so I am glad you brought it up. I believe I have the thunderbolt IV and not the thunderbolt V. I heard the thunderbolt IV does not require to be set to base mode, but the thunderbolt V does. I only see one mark on my timing cover and one mark on my pully. From a post that I read on here, lining the two up with a timming light will put in at 0 degrees. The Merc manual says it should be at 10 degrees BTDC, so how do I found that without a mark on the cover that says 10 degrees?

I am going to have to review my anatomy of the carburetor, because I don't know what a weighted air valve is or were it is located. You could have said the Flux Capacitor was sticking and it would have meant to same thing. I will try to educate myself tomorrow and give it a shot. Do I need to pull the carb off to do this?

Well, I looked at your serial number range on MercruiserParts and showed a '96 or '97 which should be T5. I believe all gen+ engines would have been T5, too. Why do you think you have T4? Is there a purple/white wire with a plug on it laying on the intake? I assumed a LX was a 4brl model. The air valve is only in the 4brl, so on your engine it is right next to the flux capacitor.

I said the idle mixture/speed adjustment is not causing the issue. Timing could. All three should be check/adjust as part of yearly maintenance. After the timing is complete, and out of base mode, make sure it is advancing when you rev the throttle.

Have you cleaned the flame arrestor as part of yearly maintenance? Have you made sure the choke plate is opening fully when warm? Otherwise, if carb problem, the recent rebuild may be in question.

Check the dampner very closely for timing marks. Should be there if there is only a single mark for timing tab.

 

[kpiazzisi]

Re: mercruiser 4.3 LX GEN+ bogging out past 3/4 throttle

Maybe I do have the T5. I assumed I had the T4 because on mine the Knock Control Module is not piggybacked onto the ignition control module the way they show it on the T5. I do have a loose wire laying on the intake manifold, but not sure if it is (Pur/White), I will check tomorrow when I am home.

I believe the choke is opening all the way. I recently I had my wife drive the boat while I removed the air filter and I saw a steady flow of fuel pouring down the barrels of the carb. Of course this was done after the boat was already planing. I may have to check this again during acceleration.

I have not cleaned the flame arrester yet, but will do so and post the results soon.

Timming- I only see one mark on the damper and one notch on the timing cover. Linning them up give me 0 degrees...correct? I read somewhere that there is also an "A" on the Dampner? I will take another look. So what you are saying is that I should have more then one mark on the Dampner?

Carb - I am thinking the problem is the Carb. I thought about buying a new one but they are 500 + dollars and on back order. There is a guy selling new 4 barrel on ebay, but then I also have to find a 4 barrel intake manifold. Do you know where I can get a good 2 barrel carb? I could rebuild the one thats one there, but I am novice at it and not sure if I trust a rebuild considering a poor rebuild job may be the cause of my problems now.

 

[John_S]

Re: mercruiser 4.3 LX GEN+ bogging out past 3/4 throttle

Most of the V6's are like some of the 5.0L/5.7L/alphas, don't have a knock module or sensor.

I looked in the V6 service manual. The gen II 4.3 has a timing tab (with marks) on cover. The gen + looks like it went to composite timing cover with single pointer. For that style, there should be multiple marks on damper. If you have looked very carefully and there is none, I would assume the two marks lined up would be TDC. Measure the diameter of your damper, and see if there is a timing tape available. Or maybe someone here with same diameter can give you the measurement for 10 degrees BTDC.

You can check choke sitting at the dock. After the engine is fully warm, choke should be fully open.

When you say "pouring" into the carb, do you mean heavy mist coming from venturi, or literaly pouring in? What does it look like at idle?

 

[kpiazzisi]

Re: mercruiser 4.3 LX GEN+ bogging out past 3/4 throttle

It is all starting to make since now.

T5 - thankyou for clarifing that I have the T5


Timming - I will set the timing tomorrow by grounding the Pur/Whit wire on the manifold and then lining the pointer with the correct mark on the Dampner. I probably have more then one mark on the dampner, I just need to look harder. I imagine if I measure the circumference of the dampner and divide by 360, that will give me the linear measure of what one degree would be..correct? I could then just times that by ten and make the appropiate mark to the left of the 0 TDC mark?

Carburator- I found a guy in St Pete florida (one hour from where I live) that sells remanufactured 2 brl carb for less then 300 bucks. The beauty of it is that I can drive there and bring him mine avoiding the core and shipping charge. He said to test my Fuel Pump first. He said to disconect the line at the carb and in 15 seconds the pump should fill up at least one pint. He said I could also check the PSI which should be b/t 4 -6 PSI. The only problem is that the fuel pressure guage I have does not have the correct adapter to connect to the fuel line. Do you know where I can find one of the adapters to go from the autozone Fuel Preasure guage to the Mercury Fuel line

 

[kpiazzisi]

Re: mercruiser 4.3 LX GEN+ bogging out past 3/4 throttle

I forgot to clarify the question about weather fuel was "heavy misting" or "pouring" into the carb. It was definetly a controlled symetrical heavy mist.

 

[kpiazzisi]

Re: mercruiser 4.3 LX GEN+ bogging out past 3/4 throttle

update-

Timing - I found the marks on the engine pulley and adjusted the timing. I do have the t5 with the pur/wht wire laying on the manifold. I grounded the wire and adjusted the timing. It was set at approx 6 degrees. I set it at 10 degrees.

Chock - The chock was in the fully open position after running for only a couple of minutes on the muffs. A little off topic - I accidentally ran the boat for less then 2 minutes with the water turned off. Is that long enough to cause damage?

Fuel pump - at one point today the boat would not start. It was not getting fuel to the carb. I checked voltage and it was getting 12 volts to the pump during engine cranking. I tapped on the fuel pump with a wrench and it turned on. I then checked fuel output and got 24 oz in 30 seconds. If I did the math right thats only 22 GPH which I think is lower then the accepted amount?

To isolate the fuel pump I bought an inline low volume electric generic fuel pump from Advanced auto and rigged it to work using a couple of different brass fittings. It actually looks pretty good and fits into the stock location well. The pump has a 4-7 Lb shut off and is designed for carburetor applications. It only cost me $49.00 and another $10 for fittings. If it solves the problem I will break down and buy a merc pump for approx $200, otherwise the original pump goes back on and I move onto replacing the carburetor. I did notice a few particles in the fuel while doing the fuel volume test, but the screen in the carb was fairly clean.


I am taking the boat out tomorrow to see if the new fuel pump does the trick.

 

[180shabah]

Re: mercruiser 4.3 LX GEN+ bogging out past 3/4 throttle

If you had to tap the pump to get it started - you need a new pump.

 

[kpiazzisi]

Re: mercruiser 4.3 LX GEN+ bogging out past 3/4 throttle

Maybe a pump and a carb. I took the boat out this AM and it is still doing the same thing. The Advanced Auto Fuel pump worked fine. I can only conclude that the carburetor is the problem. This is after new plugs, fuel filter, new wires, adjusting timing, new rotor and button. I will bite the bullet and dump another $300.00 for the re manufactured carb. I will post results after that in a few days.

 

[John_S]

Re: mercruiser 4.3 LX GEN+ bogging out past 3/4 throttle

update-

A little off topic - I accidentally ran the boat for less then 2 minutes with the water turned off. Is that long enough to cause damage?

I hope you are good with the impeller.Keep a clse eye on the temps.

Even though it wasn't the problem, 4 degrees off is significant.

Maybe you forgot to mention it, but was the flame arrestor filthy?

 

[xltier]

Re: mercruiser 4.3 LX GEN+ bogging out past 3/4 throttle

had a volvo tuesday that wouldnt go on plane and it was a partially restricted check valve in the tank pickup tube.

 

[kpiazzisi]

Re: mercruiser 4.3 LX GEN+ bogging out past 3/4 throttle

Maybe I will take a look at the check valve. I ran it without the flame arrestor and had the same problem. I got 24 oz of fuel in 30 seconds when doing a fuel volume test , so I do not think fuel delivery is the problem either. I noticed the last time I took it out real early with no extra weight and really calm water that I can accelerate past the point where it bogs out by burring the throttle all the way down.

I think it's got to be the Carburetor at this point ...right? Can anyone tell me what carb to use? I found a number on my Carburetor 08082A-1, (at least that's what I think it says) and I can not find that number anywhere on the internet. The outfit I was going to use in Largo Florida now seems shady. He is now saying he has none on the shelf and told me he could "rebuild mine". I immediately asked him to clarify rebuild or remanufactured. He said remanufactured. I have talked to other people who are telling me that they have had bad experience with remanufactured carbs and I am better off keeping the one I have. One person recommended a new edelbrock 1409, but I would have to go to a spread bore manifold. What is your opinion on remanufactured carbs? I could try to rebuild the carb, but growing up back in the carburetor days I remember people always tinkering with them and never getting them right.

 

[180shabah]

Re: mercruiser 4.3 LX GEN+ bogging out past 3/4 throttle

1409 = squarebore

 

[dsmmace]

Re: mercruiser 4.3 LX GEN+ bogging out past 3/4 throttle

Do you have a 4 barrell carb already?

I fixed my issue which was the same as yours just by taking my one year old carb off and cleaning and spraying the hell out of it with carb cleaner until I saw no more yellowy gum left. I don't think the boat mechanic put fuel stabilizer in it like they me they did.

 

[John_S]

Re: mercruiser 4.3 LX GEN+ bogging out past 3/4 throttle

While this doesn't have info on 3/4 throttle bog, it may be of some use: http://www.boatfix.com/merc/Bullet/97/97_08.pdf

 

[kpiazzisi]

Re: mercruiser 4.3 LX GEN+ bogging out past 3/4 throttle

thanks for the link. I like keeping things simple. For $250.00 I rule out the carb with a Rochester (better then Mercarb from what I have heard). Although a card is less complex then fuel injection, there are still way to many passages and moving parts. To me it's just not worth it. With all the ethenol now in the gas and the likely hood of this thing setting with that shi**** gas in it, I might as well go for cleaning out the whole fuel system including the carb. Should have it real soon. I will keep everyone posted.

 

[dsmmace]

Re: mercruiser 4.3 LX GEN+ bogging out past 3/4 throttle

Mine cost nothing to repair as I had a can of Carb Cleaner in my shed and 25 minutes to remove, dissassemble the carb and clean it.

 

[kpiazzisi]

Re: mercruiser 4.3 LX GEN+ bogging out past 3/4 throttle

The new carburetor did the trick. My boat no longer bogs out at full throttle. Could I have fixed the old carburetor.....who knows. I would have been into it for the cost of a rebuild kit, carburetor cleaner and my time. To me $250.00 was not a bad deal and now I have a completely re manufactured carb. The only issue that remains is that the boat will hesitate if I jump on the throttle. It did this before with the old carburetor. I contacted the person I bought the carb from and he said it is probably not the carb and advised me to check the timing which I have done several times. This is more of a minor annoyance since I don't normally jam the throttle all the way down at once and usual do a gradual steady acceleration. If anyone has any thoughts, please respond.