merc 4.3 alpha one bogging under load

[jlynngt]

hi there, we have a merc 4.3 alpha one that boggs down and cuts out when we go full throttle.. at a 1/4 throttle it seems to run fine.
we have replaced the coil, both fuel filters, the ignition assembly sensor, checked the breather line and did a fuel pressure test. it seemed to run a little better when had a 1/2 tank of gas rather than full. any new ideas as to what it could be would be greatly appreciated. thank you

 

[fuzzybob]

Re: merc 4.3 alpha one bogging under load

jlynngt, welcome. You will get help on this forum but you need to post a little more info..... the yr and or the ser# of the engine, is it carbed etc.

 

[jlynngt]

Re: merc 4.3 alpha one bogging under load

u can tell i'm new to this ey? its a 91 and yes its carbed

 

[jlynngt]

Re: merc 4.3 alpha one bogging under load

serial # 0D429481

 

[mkast]

Re: merc 4.3 alpha one bogging under load

When was the last time the engine was tuned up?

 

[jlynngt]

Re: merc 4.3 alpha one bogging under load

not sure, we just bought it a few months ago. we know that it had been winterized at a local boat mechanic who told us that the guy had always taken care of it. we are fairly new to boating and trying to keep our expenses down by doing fixes ourself...if it were the plugs or wires in your opinion, wouldnt we notice it at lower rpms as well as wot?

 

[jlynngt]

Re: merc 4.3 alpha one bogging under load

not sure, we did the fuel pressure test at the dock not on the water...had good pressure then.... should we do it differently?

 

[scipper77]

Re: merc 4.3 alpha one bogging under load

It's worth your while to get a timing light and dwell meter. You can pick one up for next to nothing on craigslist if you can find one. So many people have these things left over from 20 years for there cars. I don't know if this is your problem but it's easier to pin down a problem if you eliminate the easy variables first. Plus it feel good to open up the throttle after you tune up the motor and get pulled back into your seat because things are running so well!

 

[fuzzybob]

Re: merc 4.3 alpha one bogging under load

You could try looking down the throat of the carb while a helper pumps the throttle and see if you get a couple streams of gas coming out. Like scipper 77 says look at the easy stuff first.

 

[jlynngt]

Re: merc 4.3 alpha one bogging under load

ok we looked down the carb when opening it up...we have enough fuel going in...cleaned another filter...put a bottle of carb cleaner in the tank...took it out and it ran great for about 5 minutes...we were able to plane off and then all of a sudden we bogged again....now seems to be getting worse...before it was running ok in between 1/4 & 1/2 thrttl now not so much...bogging off at lower rpms as well as higher...any new ideas?

 

[maxxman04]

Re: merc 4.3 alpha one bogging under load

how old is the gas, and how many different additives and such are in tank? also, looking down carb will tell you if there is in fact gas, but is it actually the right amount? suggest FULL tuneup, new filters, timing check, fuel pressure check. gas may be flowing, but needs to be the right amount, right pressure.

 

[jlynngt]

Re: merc 4.3 alpha one bogging under load

thank you all for your help

 

[buggiedad_67]

Re: merc 4.3 alpha one bogging under load

you might try looking at your tank vent it might be vacum locking

 

[scipper77]

Re: merc 4.3 alpha one bogging under load

what do the plugs look like?? are you running rich and fouling them? poor timing and weak spark could cause incomplete combustion. Why do you think that the carb is the problem? I personally wouldn't mess with the carb until I checked the timing and dwell if you have a points system (which I'm guessing you don't on a '91).