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Intermittent bogging can the anti syphon valve really cause that?

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vincentmb615

New member
Good day all, picked up a 94 1930 with the Merc 4.3 I bought it with a known bogging issue and I'm trying to hunt it down, it sat for a week and I went to start it on muffs and it was taking forever, so I pulled the fuel line off and there wasn't any fuel in it so I ran power to the fuel pump and got fuel into the carb and it fired right up, but backfired a little and died, is the anti syphon valve supposed to keep fuel in the line or does it allow it to roll back into the tank? I tried to remove it and it snapped off it was corroded so I had to pull the pickup tube out as well, I have a new anti syphon the pickup is on order, isn't it supposed to have a filter on the end of it? And is there a certain length it should be? I could only find the size I needed in 24 inch so It will have to be cut down . Do you think replacing all this will solve the bogging? Its so intermittent it's hard to trace, plugs cap and rotor are new as well as fuel pump and seperator vent is not clogged
 
Some pick up tubes have a screen inside them. Look in with a flashlight.

The anitsipohn could do this for sure. So could a carb that needs a cleaning and rebuild. When you replaced the fuel pump and filter/separator what did the gas look like?

Would be good to rig up a guage and see what the fuel pressure is at the carb when it acts up.

I assume the engine is in decent mechanical shape like compression is ok?
 
Dieter said:
Some pick up tubes have a screen inside them. Look in with a flashlight.

The anitsipohn could do this for sure. So could a carb that needs a cleaning and rebuild. When you replaced the fuel pump and filter/separator what did the gas look like?

Would be good to rig up a guage and see what the fuel pressure is at the carb when it acts up.

I assume the engine is in decent mechanical shape like compression is ok?
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Yes compression test showed good across all 6 cylinders it's so intermittent it'll get up and go and then sometimes it'll bog and choke I have a new pickup coming my old one doesn't have a screen, when the check valve broke I found the spring inside but no ball, I'm hoping it's not rolling in the gas tank, I have a rebuild kit coming it's a Weber 4 barrel 9006s model. Is there a diagram of it or directions on rebuild? Possible accelerator pump issue maybe ? Thanks for your time
 
1. 4.3 liters after sitting can be tough to start. Electric fuel pump has to run to prime carb. You should confirm that the fuel pump works when cranking only. There should be an oil pressure switch (at oil filter location) that gets bypassed when cranking and power should be supplied to fuel pump byway of one of the starter solenoid small terminals.

2. When you say bogging, do you mean under steady state operation like running at 3000 rpm steady all of a sudden the engine looses rpm for no reason?
Or do you mean when you go to accelerate by moving the throttle it bogs down?

Once we understand what you mean by "bogging" we may be able to answer your question better.
 
kghost said:
1. 4.3 liters after sitting can be tough to start. Electric fuel pump has to run to prime carb. You should confirm that the fuel pump works when cranking only. There should be an oil pressure switch (at oil filter location) that gets bypassed when cranking and power should be supplied to fuel pump byway of one of the starter solenoid small terminals.

2. When you say bogging, do you mean under steady state operation like running at 3000 rpm steady all of a sudden the engine looses rpm for no reason?
Or do you mean when you go to accelerate by moving the throttle it bogs down?

Once we understand what you mean by "bogging" we may be able to answer your question better.
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Yes the pump only pumps when cranking, it really makes it take a while to crank, by bogging I mean if you feather the throttle slow it gets up and goes occasionally, other times it stumbles almost like it's starving for fuel and wants to die out
 
1. The electric fuel pump should run when cranking and when the key is in the run position then the IGNITION ON power transfers to the pump as long as oil pressure switch is closed (~5psi of oil pressure closes oil pressure switch). So it sounds like your system is working properly.

When boat sits for a LONG period of time to do a work around for initial starting only, you can pull the wires off the pressure switch and jump the connectors together and just turn the key to the run position for a short time until carb is primed. (this bypasses the oil pressure switch so you wont be CRANKING the engine over for long periods of time) Then reconnect wires to pressure switch and boat should start normally if used somewhat frequently.


2. Your LEAN bog when accelerating is most likely due to a worn accelerator pump in carb. This will be solved by a good rebuild.

See image of accelerator pump

shopping.png
 
vincentmb615 said:
So should I dump the EBay kit I ordered and get one from Mike? I'd rather not waste my time trying to do it twice but I reckon I will replace the pickup tube the anti syphon and rebuild the carb all in one shot
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Depends on who you bought it from. Had one guy who paid $13 for a complete carb kit wonder why it didnt work well...
 
Dieter said:
Depends on who you bought it from. Had one guy who paid $13 for a complete carb kit wonder why it didnt work well...
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This one was about $29 it wasn't the cheapest one but it wasn't the most expensive either, I was poking around at West Marine the other day what if I get a fuel line with the primer bulb and put the bulb right in front of the fuel pump to aid and starting when it's been sitting I only can take it out every other weekend due to my work schedule I really don't like those long crank time trying to get fuel up there but I also don't want to keep priming the fuel pump and burn it out either will a primer bulb work in the situation or will the pressure from The pump just caused it to collapse?
 
Dieter said:
Yeah hes not going to win an oscar but he has supplied me with good parts for many carbs- mercarbs , old carter AFBs, Edelbrock’s Rochester two jets...
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Definitely help me understand where the floats and the accelerator pump are Marine carburetors are completely backwards in lawn mowers and motorcycles or ATVs I feel confident I can rebuild it myself after watching that I'm just worried about the whole adjustment part of it shows the accelerator pump has three adjustments and if you are a bogging to put it on a different level and try it there but I don't want to keep rebuilding the car taking it on and off on and off so I'm thinking I'll just rebuild it the way it is see what happens when I change the plugs they were black going to rich condition I believe
 
Take pictures of your set up before disassembly.
put all linkages back in the same holes/locations as they were.

No voodoo stuff going on just a lot of pieces to keep track of.

Make sure you have compressed air to blow all passages out and good carb cleaner to clean parts. Take your time and stop if unsure and ask first before making a mistake
 
kghost said:
Take pictures of your set up before disassembly.
put all linkages back in the same holes/locations as they were.

No voodoo stuff going on just a lot of pieces to keep track of.

Make sure you have compressed air to blow all passages out and good carb cleaner to clean parts. Take your time and stop if unsure and ask first before making a mistake
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I was calling shops locally to see if I could just have it rebuilt professionally I found two that do do it but one other shop said he has a Weber that's pretty much the same as mine but it has an electric choke instead of a manifold choke so I decided to go this route and order this one are there any more steps involved to hooking it up correctly or does it just need power and ground
 
kghost said:
Power comes from Ignition on, Purple wire. NOT battery power
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I just noticed you're from Mass my father lived in Roxbury I grew up on the cape most of my life I broke down and yanked the carburetor off and dropped it off at the repair shop said they get it back to me by Friday 295 for a whole rebuilding jets floats etc judging how I had to pry it off the block I'm starting it hasn't been off in a long time hopefully I'll have it back Friday that's when my pick up too should be here as well I will keep you guys updated I'm probably running on the muffs on Sunday morning if all seems well driving over to the lake
 
vincentmb615 said:
I just noticed you're from Mass my father lived in Roxbury I grew up on the cape most of my life I broke down and yanked the carburetor off and dropped it off at the repair shop said they get it back to me by Friday 295 for a whole rebuilding jets floats etc judging how I had to pry it off the block I'm starting it hasn't been off in a long time hopefully I'll have it back Friday that's when my pick up too should be here as well I will keep you guys updated I'm probably running on the muffs on Sunday morning if all seems well driving over to the lake
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Boat ran good today for about an hour and the fuel pump started shorting out I had to tap it with pliers to get it back to the ramp. Also when I went to fill it up it was spewing gas out the vent hole and the pump clicked like it was full, would that be a clogged vent somewhere? Also is the electric fuel pump high or low pressure?
 
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