Merc 140-Runs rough, Misses, Bogs?

[doman]

86 Sea Ray with 140 merc and 2bl Mercarb. I will try to explain what kind of issues im haveing and what has already been replaced.

Boat started missing about 2 months ago at higher rpms...figured its been a while since i did a tune up....well i have replaced cap, rotor , plugs, wires , points , condenser and even coil.....Also rebuild the carb....took the boat out everything seemed to be fine ...didnt get better didnt get worse ...sometimes it ould ran perfect sometimes it would just start to miss ....to to point where it would feel like its running on 3 cylinders and wouldnt go past 3500 rpm ..not always...also when i rev it up on the mufs it will sometimes rev up fine sometimes backfire and somtimes idels rough after the rpam have come down ....so i did recheck the timing , points gap , checked compression 125psi on all....put clear fuel lines to so if im getting maybe air bubbles ..No...Fuel water separator clean no water either .....
Well today i took a carb off agin to go trough it again ..just to make sure eveything is nice and clean and i didnt miss anything ..will know tomorrow..however my question is about the resistance wire ....just to eliminate it can i put regular wire from the alternator to the coil and than add a resistor to it or .....just regular wire and coil with internal ballast resistor?. or do i have to stick with original merc resistor wire

The problem is there not all the time just comes and goes regardless of the temp or weather .... Trying to figure out if its either a fuel or ignition related ...if its not a resistor wire .....most of the ignition components are new...also if trim pump is used while engine is idleing sometimes it will actually die and i can see a lot of draw on the volt gauge ....

any input is really appreciated


thanks

 

[dubs283]

Re: Merc 140-Runs rough, Misses, Bogs?

i'm sure making your own wire is fine, just make sure it is to spec

what is the voltage on the (+) side of the coil??

a quick test is to apply 12 volts to the coil during a test run and see if this eliminates your issues, just don't run it long, you will burn up the points fast

is the alternator charging the battery properly - 14.5 volts approx at 1500-2000 rpm??

a fuel pump pressure/vacuum test is always a good idea with runnability issues too

 

[doman]

Re: Merc 140-Runs rough, Misses, Bogs?

Didnt check the coil voltage yet ..will do that tomorrow and also check the alternator voltage as well ..right now i already have the carb apart just want to make sure nothing is plugged up inside ...

I have plenty of fuel reaching the carb ....didnt check the pressure though but i really dont think it runs out of gas if it was happening at cruzing speeds only yeah but even at idle it runs rough at times ...

will a regular wire from alternator work alnog with coil that has internal ballast?

one last question would a bad or clogged power valve casue rough idle?

thanks

 

[dubs283]

Re: Merc 140-Runs rough, Misses, Bogs?

the internally resisted coils are designed to work with electronic ignitions so the specs would probably be different, might work for a while but you run the risk of burning something up - headaches down the road

i'm not much for re-inventing ignition systems, its best to install the parts that are designed for the system

a clogged power port should not affect idle, only the idle circuit in the carb affects idle

it still is a good idea to check fuel pressure/vacuum - then you can rule out systems as part of the problem

 

[fat fanny]

Re: Merc 140-Runs rough, Misses, Bogs?

Yea I would have to agree to rule out the fuel system pressure test and vacum and don't forget that antisiphon valve and vent for cloggage after that I would strongly suggest an electrical short or issue disconnect the wiring harness connector and clean all contacts check and clean all ground connections and it wouldn't hurt a complete continuity test on all electrical leads on both sides of the harness connection the simplest connection can simulate the issues your describing also thise compression readings seem a little low. By the way what type of plugs are you running? I have never had any luck with anything else but A/C mr43lts, Autolite and or anything else has just came up short and didn't last anylonger than a few runs.

 

[doman]

Re: Merc 140-Runs rough, Misses, Bogs?

I have been runing autolite plugs for years never had a problem with them but i do replace them every year regardles ....
As far as compression 140psi is on a new engine ...so 125-130 considering the gauge i have i think its plenty

Anyway cleaned the carb today all the passages ..replaced the check ball ..old one had some gunk on it some it might have been sticking also there was some gunk underneath the power valve ....Even though the carb has been rebuild already couple of months ago there was gunk in there ..i guess ethanol is causing those problems ..I have 3 fuel filters including water separtaor ....anyway fired right up no hesitation no missing no backfireing ....i was really supprised ...carbourator was the last thing i was going to look at since it was rebuild recently. Btw i have 10-11volts at the + on the coil engine running ...my guess is there is no resistance wire alternator puts out 14.5 at around 1200rpm

I was almost ready to go to do a water test but now shift cable sticks engaing the interrupt switch ... so much for boating this weekend...i have to settle for a jet ski tomorrow

 

[fat fanny]

Re: Merc 140-Runs rough, Misses, Bogs?

The only reason I mentioned the compression reading was that before I replaced a blown head gasket I got reading of 150 to 155 on all but one cylinder. I sure hope the after the shift cable issue is solved the debre in your carb solved your problem. Good luck!!!!!!

 

[dubs283]

Re: Merc 140-Runs rough, Misses, Bogs?

..i guess ethanol is causing those problems

i hope you are not using E-85?? (85% ethanol)

in the great state i live in there are different choices for fuel:
-premuim, non-oxy (no ethanol/alcohol) 92 octane gasoline (my choice for boats)

-87,89,92 regular unleaded 10% MINIMUM ethanol blend gasoline (90% gasoline - 10% ethanol)

however, the state laws are funny - they allow up to THREE different companies to add 10% ethanol to the fuel - the fuel maufacturer, the fuel transporter, and the fuel seller

so...it is VERY possible when buying regular unleaded fuel here, you may be getting 70% gasoline and 30% ETHANOL!!!

i'm not sure what the fuels are like where you are, but as they say - buyer beware - do some research about thet types of fuel that are available where you are

as i said - if its available - use premium, non-oxy (no ethanol/alcohol) gasoline

I was almost ready to go to do a water test but now shift cable sticks engaing the interrupt switch

time for a shift cable adjustment, and...

there is a v-spring located in the shift cut-out assy that can be at fault here

there is a new v-spring with yellow paint on the ends that is much stiffer than the old one, cheap and easy fix and may cure your shifting issues

 

[doman]

Re: Merc 140-Runs rough, Misses, Bogs?

yes the spring in fact seems a little weak tripping the switch when going in gear but the cable moves a little stiff as well as specially going in reverse when it has to open up all the way ..what i will do i replace the cable since they are not that expensive and get the spring too this way i wll have piece of mind

As far as fuel goes i guess i will start buying at the marina ..it doesnt have ethanol there

I belive all fuel grades here in Florida have ethanol in them im not sure never really paid much attention until now ....i have been using 89 in the boat for many years never had as many problems as i had in last couple of years ..but if the premium doesnt contain ethanol that will be my choice from now on

 

[kevert]

Re: Merc 140-Runs rough, Misses, Bogs?

I was reading the original problem about the Merc engine and I believe I have something similar, although I know exactly what I did to cause it. Now I just need to know exactly what to do to fix it.

I have never had a problem with my engine, but I decided it would be nice to clean it. So I sprayed some select areas down with degreaser and sprayed it down. Now it is running terribly and bogs down when I hit the throttle. I cannot get it up to full speed and it sounds like this V8 is running on 6. I cut my outting short today as it just is plain not working.

I was suspecting water in the plugs or in the distributer. If there is water in the cylinders, how would I get it out?
Would changing the spark plugs even help without doing some thing more?

From
I should have never tried to fix it if it ain't broke - K