Logo
FULL SITE MENU

87 60hp 3cyl. Merc. bogs down when giving throttle while in gear.

3

3keepers

New member
I have a 1987 60hp Mercury. It is bogging down when I try to accelerate in gear. I have had the carbs rebuilt. We have checked the stator, trigger, power pack (switch) by replacing them with new parts to just check one at a time for improvement and no improvement. The stator, switch and coils are all less then one year old. It is getting spark to the plugs but if you pull the plug wire off the #3 spark plug it does not affect the running of the engine. (you can see the spark jumping brightly when you hold the plug wire close to the spark plug but not connected. When you pull the plug it has fuel on it but it is not firing. IT seems like it is flooding with fuel on the #3 however if you pump the bulb no fuel is leaking out of the carbs. My mechanic and I are totally stumped. Do you have any ideas what to check. If I left out anything you need to know let me know and I will try to see explain better. I first took it in to get the carbs adjusted because it was not idleing good but I had no problem with acceleration. He could not get it to adjust and said there was debris in the carbs from deteorating fuel lines so recomended all new fuel lines, filter and carb overhaul. After that it idles perfect but now it bogs down when you try to accelerate in gear.
Thanks for any help!:confused:
 
If that's the OLD triple with two carbs, setting the idle right is very tricky! I use a temp gun on the plugs to get the mixture right--it's that hard to do.

In your case, try opening the lower idle jet screw one 1/4 of a turn at a time (counter clockwise) and see if that helps.

Jeff
 
What is a temp gun? is that something my mechanic should know. We did mess with them for about 20 min yesterday. We would close the bottom off completely and very slowly open it. So you think it may still be in the carb settings? We have discussed the possibility of it being a problem with the reeds but that is major on this engine just to look. It is the one with the 2 carbs for 3 cylinders. We can go back to the settings again but we have messed with them so long that we thought we had possibly eliminated that. THe mechanic was going to try to rig up something to bypass and see if we could swap the top and bottom carbs to see if it somehow is a problem with the bottom carb.
Thank you
jeffrey
 
In this set-up the carbs are jetted differently. Is there any chance that they got switched around when they were re-installed - that could explain alot...
 
we are trying to check and verify if the two carbs were jetted differently. Good idea. THe mechanic thought they were the same but he is going to try and check online to verify.
 
There was two different Walbro carbs used on the 1986/87 models.

If it has the WM-13A's on it then they used the same jetting for top and bottom.

By mid-87 they had scrapped those and switched to WM-16A carbs that ran different jets (the main carb body was identical, as was the vent jets) but the top carb used a .074" main and the bottom a .072".

Although I never saw a bulletin (but haven't sifted through the hundreds I have on file either) I kinda assume they went to the different carb body with different jets to clear up a chronic deficiency - Merc doesn't usually change carb models unless there is a problem, they tend to tweak the same carb body for multiple generations if it's working ok...
 
We are pulling the carbs to check the jets today. I will let you know what we find. I found my manual and it did show two different jets but it was .076 and .070 if I remember right for our elevation. I left the manual with the mechanic. He told me he thought they were the same number and was pretty sure he replaced them with both .076 jets. He said one was really hard to read and it could have been .070 instead of a 6 so he was checking and hoping it was just his mistake. Do you think just the jet difference would account for that #3 cylinder flooding out? and causing it to bog down when I accelerate?
 
Got curious - here's Service Bulletin 88-8 - directly to point...
 

Attachments

  • 60 Merc 3 cylinder carb jets.jpg
    60 Merc 3 cylinder carb jets.jpg
    85.2 KB · Views: 423
I'm digging but there was probably an earlier bulletin dealing with the 13A model carbs which were originally fitted with .785" jets top and bottom.

Have to assume, based on this, that an earlier recommendation to change the bottom jet to .072" is out there and this one goes on to change the top jet to .074.

That was the jet configuration in the 16A models which replaced the original carbs...
 
I will check the serial number on my motor. I am just not sure if that alone would accound for the fact the #3 cylinder is not firing even though it has spark. It just completely bogs down when you give it the throttle and will often die. That seems like more then just blubbering as it is saying in the bulletin. Hopefully the mechanic will finish pulling the carbs today and checking them. Thank you for your input. You seem to really know these motors.
Jeff
 
This is just one of the models you tend to remember because it was such an idiotic design.

Whoever came up with the idea that incorporating the reeds and the center main crank bearing into a single unit which had to supply the 3 cylinders from two carbs hopefully didn't stay employed very long.

The follow-on model added a plate to the intake and went with 3 petal style reeds and three carbs - the way God intended a 3 cylinder to be fed :)
 
We checked the jets and they were in fact correct. I think he has ordered a crankcase gasket ( I hope I have the right name). He said mine was cracked and it could be pulling in air. He has exhausted all he knows to do with the carbs and we are getting no improvement.
 
The top seal is easy--remove the flywheel and trigger coil. drill a tiny hole in it, screw in a sheet metal screw, and remove it. (Did one on the ramp at my marina.)

The bottom one requires major work to change.

Jeff
 
great thanks.. will have a look - changed fuel filter today to a paper one - had suspicions the glass tube one was letting thru some particles.. pulled carbs to check if i had varying jet sizes but couldnt get jets out so just dbl checked them (cleaned last week) and put them back - they were real clean.

Im having intermittent issues - like cyl 3 is giving trouble - 1 and 2 seems to be running the best - i thought maybe a loose coil wire on 3.. at sea it kind of started varying between power and reduced power - like a blocked jet kind of thing - but carbs were perfectly clean..

Past few days shes been running quite well - ive replaced fuel lines, setup timing.. 1 1/2 turns out on mix screw - not quite sure where to go.. Dont have torque wrench here for flywheel removal unfortunately..

Im thinking maybe my tank is sucking air somewhere - but it also worked well before..

Maybe the cheap paper filter is too restrictive or something? although i doubt it - will put old one back and see..


fyi - motor starts and idles perfectly - just no power on WOT although it worked fine day before.. today just no power after filter change and tank swap..
 
Last edited:
Sounds like you might be loosing spark on # 3. Do a full throttle run, then shut her down fast as you can--NO idling allowed! Pull plugs and compare colors.

Jeff

PS: Seen several of those coils go bad over the years.
 
hi jeff - verified today.. while idling and timing light hooked up - cyl 1 and 2 fire perfect, but 3 skips a beat every second and its exactly in time with the sound dropping..

I will try change the signal wires and plug wires between 3 and 1 to make sure its the coil - if 3 is STILL skipping a beat could it be the control box thing? coil is $37, box is about $160!!

Also - after a little bit of a run - the motor just bogged and almost died (same happened yesterday for the 1st time)! briefly pumped bulb, but no luck - will try more squeezing 2moro with friend.. man it was running so well past 2 weeks - :( just got the darn thing.. and def no parts around close.. ill check the fuel lines for any sign of an air leak -


Heard of some pwners having cyl 3 issues because of crank seal - im afraid to take anything apart on this thing - bolts stripping etc not fun!

is it possible to test the coil pri/sec side with it disconnected using a multimeter? I could compare to the other 2 that appear to be working..

Not sure what caused the bog - ill test the fuel pump 2moro into a bottle and see if it pumps well..

also - is a idle timing of around 6-7 degrees good? I can either time it more and close butterflies or the other way round - whats a good idle advance?

thanks again! doing fishing and having a machine running not 100% is a bit unnerving in the water!
 
Swap the coils and see if the problem follows.

Warning! Make a wiring diagram FIRST or you could go nuts getting it right.

Jeff
 
Fuel pump pulse come from #3? Disconnect fuel line let it run out of gas, see if #3 picks up before it dies out. If so fuel pump diaphragm is dumping fuel in to # 3.
 
Hi - I FINALLY diagnosed a faulty trigger - but the issue only showed up much higher than the merc AND cdi troubleshooting rpms! Around 2500 one cyl just dropped dead which kept me thinking the stator high speed was faulty!!

Tip: Rev the bastard past 2k when testing EVERYTHING! Replaced mine for $35 and shes running tops. That only took me a few months to finally figure out :0
 
Back
Top