78' 115

[Dassault]

Hello,
I own a 78 mercury inline 6 115hp. I am having problems trying to solve my "bogging" problem. Last season i chased the problem for months. This season the boat is acting funny again. Every so often, the motor will bog down and struggle to plain, but will take off like a rocket at other times. I rebuilt the carbs last season, replaced plugs, checked spark, compression, water pump, tuned the mixture, checked timing. I can not figure this one out and to make it worse the motor ran great the first day out, no problems what so ever. The motor does seem week even when running properly though. Any ideas, seems like it does much better when i replace plugs, but I eat through them. only getting about 5 trips out of them. I run 93 octane and synthetic quicksilver oil at a 50:1 ratio.

 

[hkeiner]

Re: 78' 115

Squeeze the fuel line primer bulb while the motor is bogging. If this corrects the bogging, then perhaps your fuel pump is the problem.

 

[WillyBWright]

Re: 78' 115

Run regular gas. Ethanol in gasoline artificailly boosts octane and is bad for outboards. Most premium gas is mixed with alcohol which has less power per volume and alcohol does not mix with oil. Try opening the idle needles another 1/8 to 1/4 turn and see what happens. Has the fuel pump ever been rebuilt? The diaphragms get stiff and pump less volume. Alcohol is often the culprit, but age is also.

I was always skeptical about less power in Premium gas until my current vehicle. It gets 37mpg on regular and 34mpg on premium.

 

[Dassault]

Re: 78' 115

Sorry i forgot to mention that i did replace the fuel pump and primer bulb.

 

[Dassault]

Re: 78' 115

Also squeezing the bulb does not correct the problem.

 

[Chris1956]

Re: 78' 115

Dassault, Are you running the gapless plugs? You should be running Champion L76V or NGK BUHW. The never wear out, certainly not in 5 trips. What do your plugs look like? Is it possible you have a hole in the fuel pump diafram? This would allow raw fuel into the crackcase and flood cylinders 5 and 6.

 

[Dassault]

Re: 78' 115

The plugs (gapless) look oily (have oil dropllets on them, i know i am running oil mixture of course) and seem to be fouling out, diaphram is basically new though(replaced last summer in july), with new check valves; runs pretty well half the time, but it seems like it has to be a fuel problem just the way the motor sounds when it is struggling. Last year my floats were sticking, and it did the same thing, but i rebuilt/soaked the carbs and replaced the floats, needle and seats, adjusted the arms, the whole nine yards, leaks very very little fuel when the bulb is squeezed tightly, so the fuel control seems to be working (floats, arms, etc.) Getting a lot of blue smoke when it is having problems though.

 

[jimmbo]

Re: 78' 115

I never changed the plugs on my 1984 115hp during the 14 years I used and abused that motor.
Do a sync and link check/adjustment, that is often the reason of bogging. A switchbox or timing trigger might be working fine when cold but acts up when it gets hot.

 

[Dassault]

Re: 78' 115

thanks jimmbo may try that this weekend, how could i go about checking the electronics?

 

[jimmbo]

Re: 78' 115

It pretty much is a swap with a known good part. Otherwise the service book says "Testing Switchbox and Trigger Assembly. Use Quicksilver Thunderbolt Ignition Analyzer ( C-91-62563A1) follow intructions in the test manual included with the analyzer" Yeah right!!

Sorry

 

[Clams Canino]

Re: 78' 115

thanks jimmbo may try that this weekend, how could i go about checking the electronics?

Most of the electronics are usually pass/fail, so if it's running, it's prolly PASS. Try dropping the distributor cap and cleaning the inside with carb cleaner and Q-tips. (easy) Also replace the little carbon button on a spring inside the cap ($5).

-W

 

[Dassault]

Re: 78' 115

Where do i get the carbon button? local marine store, west marine, if i can say that on iboats, sierra products, or do you have a product #? I did clean the cap out however, but i would like to replace the button now that you mention it.
Thanks clams

 

[Clams Canino]

Re: 78' 115

Any Merc dealer. It's still a good part #.

-W

 

[Dassault]

Re: 78' 115

also could i get the link to clams linc and sync thanks.

 

[Dassault]

Re: 78' 115

I called mercury and they told me that i couldn't buy the button separately from the cap, told me i need a part # ????? And i don't really want to pay that hefty cap price. The button is not really a big deal but if i could find one it would be nice. Thanks

 

[jimmbo]

Re: 78' 115

also could i get the link to clams linc and sync thanks.

http://forums.iboats.com/bbBoard.cgi?a=viewthread;fid=36;gtid=1114512