350 Mag Still Bogging Down

[Don S]

Re: 350 Mag Still Bogging Down

Post a picture of YOUR fitting where the antisiphon valve attaches, Then I can show you exactly what I mean.

 

[Reel Poor]

Re: 350 Mag Still Bogging Down

The boat runs great at 3200RPM's, as soon as I try to go higher it seems to bog down. I ran at a steady 3200 for about 20 min with no problems....it's gotta be something between the tank and carb.... if the seperate tank doesn't work I will have to check the fuel pump pressure (will need to buy a gauge).

Tony<br />Check with a local parts/tool suplier for a <br />vaccum/low pressure combination guage. <br /><br />With this single guage, you can check fuel pressure between the carb and the fuel pump.<br />Low pressure...Bad Pump<br /><br />It will also check fuel pump suction pressure between the tank and fuel pump.<br />Insufficient suction...Bad Pump<br />Excessive suction...restricted between lowest point of pick-up tube and fuel pump

 

[FreeBeeTony]

Re: 350 Mag Still Bogging Down

I am going to try the seperate tank tonight....<br /><br />Could the fuel pump be bad and not leak?

 

[Reel Poor]

Re: 350 Mag Still Bogging Down

Yes <br /><br />It has valves in it that will go bad a limit pumping capability.

 

[bobafett]

Re: 350 Mag Still Bogging Down

Can somebody help me with my post on bogging in a merc 140 ?

 

[FreeBeeTony]

Re: 350 Mag Still Bogging Down

OK....tried seperate tank and did not help.<br />I ran a seperate line from the input of the water seperator to a 5-gal jug. Got to about 3300-3400 before it bogged down. Removed seperate tank and connected main tank......same results.<br /><br />Guess this rules out the following:<br />1) fuel tank obstruction<br />2) bad gas<br /><br />Guess next step would be to check the fuel pump pressure. Going to look for a gauge tonight.<br /><br />It almost sounded like it wanted to "clear-out" tonight. Maybe it's just my imagination, I don't know.<br /><br />Since I started troubleshooting this I have replaced the water seperator twice.<br /><br />What is the procedure to check the fuel pump pressure? Install a "t" before the carb and install the gauge? What about the fittings?<br />I have the Merc manual to get the specs.<br /><br />Ant other suggestions?

 

[FreeBeeTony]

Re: 350 Mag Still Bogging Down

Went to 3 stores......can't find a fuel pressure gauge.<br /><br />Can I test the capability of the pump by putting the fuel line into a container and crank the engine for a certain length of time and measuring the output?

 

[Limited-Time]

Re: 350 Mag Still Bogging Down

FBT<br />Try a hi-preformance speed shop. They carry fuel pressure gages...there not the poartable type but it will tell ya what ya want to know.

 

[Reel Poor]

Re: 350 Mag Still Bogging Down

Tony a "T" is the proper way.<br /><br />Can you hook your extra tank directly to the fuel pump inlet fitting? If so this will completely eliminate the fuel supply rout.<br /><br />I have seen the housing for fuel seperator clog with debris under the fittings. By running thru the filter, it, and the feed hose COULD still be suspect.<br /><br />

Can I test the capability of the pump by putting the fuel line into a container and crank the engine for a certain length of time and measuring the output?

Thats an OK check, but not definitive. You can have volume without sufficient pressure.

 

[FreeBeeTony]

Re: 350 Mag Still Bogging Down

RP,I thought of bypassing the seperator......it's not that easy to get to......but I will probably try it next.

 

[Reel Poor]

Re: 350 Mag Still Bogging Down

I thought of bypassing the<br />seperator......

Also the origonal pump supply hose.<br /><br />Use a new piece of hose from your aux tank to fuel pump.<br /><br />

Limited-Time <br />Member # 55136 posted June 20, 2005 07:58 PM<br />--------------------------------------------------------------------------------<br /> FBT<br />Try a hi-preformance speed shop.

 

[bigdaddyofhouse]

Re: 350 Mag Still Bogging Down

Did you ever check your alternator?My boat started great but wouldnt get over 2800 rpm's.It turned out to be my alternator.<br />see if you have 13 volts on battery.Its a easy thing to check.<br />Just throwing out anouther place to check.

 

[FreeBeeTony]

Re: 350 Mag Still Bogging Down

Now, I'm stumped.........I bypassed the fuel seperator with the seperate tank and same problem.<br /><br />Any I barking up the wrong tree here? Maybe the carb is no good?<br /><br />I am going to try and check the fual pump pressure tomorrow......a friend has a gauge. Any hints on installing it? I want to check it at the input to the carb but that is a hard line...how can I break in there?

 

[Mahoney]

Re: 350 Mag Still Bogging Down

sounds to me that its your secondary circuit in your carb. If you hear it getting "throaty" with no backfire through carb, it tends to indicate your secondaries are engaging and letting in too much fuel. Have you had someone drive while you were looking into the carb?<br /><br />I had same issue when I was working through a bad carb, you could literally see fuel being almost splashed around the secondaries when they engaged. A safer and easier check is to shut down after you get the bogging and then check the inside of the secondary carb barrels. If they are soaked with fuel, that could definitely be the issue.

 

[FreeBeeTony]

Re: 350 Mag Still Bogging Down

That sounds like the exact problem Mahoney! See my previous post .<br />What is the fix? Are you saying that the secondaries are opening too early? I thought maybe they weren't opening early enough.

 

[Mahoney]

Re: 350 Mag Still Bogging Down

Missed what type af carb it was, but for a Rochester there are a couple fixes. I can't speak to the adjustments on other carbs, but a few things could cause this. Either the secondary needles are riding to high in the jets, letting to much fuel pass too soon, or the air valve tension is too loose. On a Rochester Carb manifold vaccum will dictate when the secondary air valves open letting in air past the fuel needles and beginning the fuel flow. If the tension is too loose, the air valves tend to open early and completely(before the engine is ready for the mixture, leading to a bog.<br /><br />If youy have a Rochester I can probably guide you through some easy tunings to at least isolate the problem, if it is something else, you should wait for someone more farmiliar with that carb. Or do a quick search on secondaries, and/or bogging down

 

[Mahoney]

Re: 350 Mag Still Bogging Down

Just glanced at your other post. if you did a rebuild and used the same secondary rods and made sure not to bend the hanger, I would go back and check the Step-Up Spring."i glanced quick at Don's post on the mercruiser carb link". I believe this is the thing in those carbs that dictates, based on manifold vacuum, when the secondary rods start to move and allow fuel flow. Maybe you mis-seated this, or forgot it all together?

 

[FreeBeeTony]

Re: 350 Mag Still Bogging Down

It's a Weber/Carter. So it sounds like I am getting too much fuel too soon? There are springs I can change to make the "secondary" ckt start later.......I am going to try this tomorrow. Thanks Mahoney.........

 

[Mahoney]

Re: 350 Mag Still Bogging Down

are you getting any backfire when running on the lake or when snapping the throttle open all the way to the secondary circuit if on muffs? If not, I highly doubt your bog is from a lack of fuel, but rather too much. It should pop through the carb right away if it leans out that much from not having fuel flowing when the secondaries are engaged.<br /><br />You mentioned that you had someone driving and could change the performance a little when monkeying with the carb secondary operation. Being very careful(head and face out of the way) you could try and hold the secondary airvalves closed when the driver throttles up enough to hit the secondary circuit and see if you can manipulate the bog at all, better or worse, if so, you have most likely isolated the area at least.

 

[FreeBeeTony]

Re: 350 Mag Still Bogging Down

It doesn't backfire at all! I am going to change the springs on the metering rods to weaker ones, this will keep them closed longer. I bought a "kit" of springs and installed the strongest ones thinking I needed more fuel sooner.<br /><br />This is the most promising news yet!<br /><br />I can't wait until tomorrow!