Mid1980's Mercury 2cyl 35hp Spark Plug Question

[3rdMarDiv]

This motor is showing NGK BUHW as the plug to use, however, I'm seeing where the Champion L77JC4 gapped at .30 is commonly used. When I got the motor the L77JC4's were in it. The motor was being used on a pontoon. I now use it on a 16ft fishing boat. I put in the BUHW's and have used them for some time.

It's always ran very rough at idle or slow trolling speed when Walleye fishing.

I recently have seen a number of people saying the BUHW is designed for WOT use and at low or idle causes the motor to run very rough. I'm reading where using the L77JC4 will result in smooth idle and low speed running. Also, that running the motor at faster speeds is fine with the L77JC4 plugs. Biggest advantage I'm seeing to the BUHW is they last much longer and are less prone to fouling.

Anyone have experience in using the L77JC4's and if so what Gap.
.
Any input here is very much appreciated

 

[racerone]

Sparkplugs do not foul on a properly tuned / adjusted motor.

 

[airshot]

My Merc manual calls for the BUHW -2 plugs and that us what I use, never an issue at any speed. Have you done a compression check recently and a spark jump check ?

 

[3rdMarDiv]

No checks in years but I will again...I have a compression gauge and a cheap spark tester I can use. Are you thinking maybe it's running on one cylinder. At WOT it gets up to over 20mph with two people. But I will check it again just to be safe.

I did a lot of work on it a long time ago and I only remember it had over 100psi, if i recall correctly.

Thank you for the recommendations

 

[3rdMarDiv]

My Merc manual calls for the BUHW -2 plugs and that us what I use, never an issue at any speed. Have you done a compression check recently and a spark jump check ?

couple more questions if you don't mind..I did some old notes checking from my original work in 2015 and found my serial number B201516 which looks to be Mfg between the 87 and 88 production year.

Can you recommend where I might obtain a D/L Service Tech Manual covering this time frame?

Is your Merc close to mine in age? Just curious...

I will also check the idle setting and timing again.

It's nice to hear that you run the BUHW plugs with no problems. My recent concerns came from reading about these surface gap plugs being notorious for rough idle and low speed running. What I read was they are cold spark plugs and designed for running at high RPM and not low RPMs.

If your motor is around mines age and runs smooth at idle then likely I have some adjustments and testing to do...

I put any speed to it she runs great, just not so great and slowest speed and idle where its a just a little rough.

Thanks again for sharing some of your time and expertise.

 

[airshot]

couple more questions if you don't mind..I did some old notes checking from my original work in 2015 and found my serial number B201516 which looks to be Mfg between the 87 and 88 production year.

Can you recommend where I might obtain a D/L Service Tech Manual covering this time frame?

Is your Merc close to mine in age? Just curious...

I will also check the idle setting and timing again.

It's nice to hear that you run the BUHW plugs with no problems. My recent concerns came from reading about these surface gap plugs being notorious for rough idle and low speed running. What I read was they are cold spark plugs and designed for running at high RPM and not low RPMs.

If your motor is around mines age and runs smooth at idle then likely I have some adjustments and testing to do...

I put any speed to it she runs great, just not so great and slowest speed and idle where its a just a little rough.

Thanks again for sharing some of your time and expertise.

My engine is a '92 classic 40 hp. Purrs like a kitten at 600 rpm. Found my factory service manual on Ebay, look carefully as they go quick !

 

[3rdMarDiv]

Thanks a bunch..!

 

[3rdMarDiv]

My Merc manual calls for the BUHW -2 plugs and that us what I use, never an issue at any speed. Have you done a compression check recently and a spark jump check ?

I tested both cylinders using a Lisle compression tester and the upper is 145 psi and lower is 142.5 psi.

Plug tester shows both plugs firing very well. My tester has a flashlight bulb inside it that lit up really well.

I did find my service manual, which, was with all my other manuals. (of course lol) This manual my also cover your motor.

Thinking about your saying that your 40hp purred at 600 rpm I wanted to ask..Is that on the water in forward gear? My manual shows neutral idle as calling for between 700-800 rpm and in forward idle between 600-700 rpm. I can check the neutral idle on water muffs, but the forward gear, I believe, was to be done under torque on the water?

As luck would have it my tiny-tach just petered out (10 years) so, I'm ordering another. I can check the neutral idle on muffs with my laser tach, but on the water I need the tiny-tach.

I would also use that to check the WOT at between 5400 and 6000 rpm.

I feel that if your 40 is running smooth, then mine should also without using non OEM plugs.

So, after your post I am staying with the BUHW plugs as per Mfg specs, but I also see there are the ones you use available, the BUHW-2 plugs. I've not seen those called for on my 35, just the BUHW.

Lastly, what gas do you use? I use premium gas, but there are those who will only use Rec fuel.

Funny, if you look at dotted line on the manual it says to cut along this line and attach to the spline...LOL I had looked at all the manuals splines only.

 

[3rdMarDiv]

Sparkplugs do not foul on a properly tuned / adjusted motor.

So true...Except for some who use a 40:1 oil mix saying...I'd rather foul out plugs and better lube my cylinders...or...Plugs are cheap, motors ain't..LOL I stay at specs 50:1

 

[airshot]

Forget the last guy bulb tester, you need one that can adjust the gap the spark will jump and that should be around 3/8" as a minimum...600 rpm in gear in the water underway ! Adjusting in a barrel or on muffs is just a rough adjustment. While underway in the water for all final adjustments ! I have used E10 fuels since they came out, never an issue, just follow instructions for E10 fuel usage and maintenence. I always use a stabilizer and my engine calls for 87 octane E10, using premium only empties your wallet faster and makes your engine less effiencient unless the mfgr calls for premium grade. Use whatever the mfgr calls for to get best performance!

 

[3rdMarDiv]

Forget the last guy bulb tester, you need one that can adjust the gap the spark will jump and that should be around 3/8" as a minimum...600 rpm in gear in the water underway ! Adjusting in a barrel or on muffs is just a rough adjustment. While underway in the water for all final adjustments ! I have used E10 fuels since they came out, never an issue, just follow instructions for E10 fuel usage and maintenence. I always use a stabilizer and my engine calls for 87 octane E10, using premium only empties your wallet faster and makes your engine less effiencient unless the mfgr calls for premium grade. Use whatever the mfgr calls for to get best performance!

Actually, E10 sounds good to me and yes, I use Seafoam 1 oz per Gal.

Q: How did the compression test look to you?

I'm thinking since it's over 100 and within 10 psi of each other so, good to go there?

Ordered a Lisle 20700 Spark Jump Tester and it will be in tomorrow...Thanks a bunch as I never knew such a thing existed. Much better than the light bulb tester. I'll set it at 3/8" to start.

Q: Do you test with the engine running by connecting to the plug or off plug and connect to a ground. I'd prefer to a ground if that will do the job.

If that test looks good then I will take her out and check the rpm on the water. I'm thinking that will smooth things out...

 

[airshot]

For general use your ounce per gallon on Sea Foam is rich....., at the end of the season then your good. If your running rich on your oil mix you might need the extra Sea Foam....personally, my luck has not been good with Champion plugs in Mercury motors, in the older OMC engines they were great but never Mercs.

 

[3rdMarDiv]

For general use your ounce per gallon on Sea Foam is rich....., at the end of the season then your good. If your running rich on your oil mix you might need the extra Sea Foam....personally, my luck has not been good with Champion plugs in Mercury motors, in the older OMC engines they were great but never Mercs.

Nice to know I'm mixing rich. If can use less that's fine. getting too pricey.

What do you use per gallon..

If you don't mind me asking.

 

[jimmbo]

There are Much Better Snake Oils than SeaFoam for cleaning the Rings, Merc's Engine Tuner, and BRP's Engine Cleaner, as two. CTC makes a decent one too.

Oil should be a Good TCW-3 and mixed at 50:1. Any more is wasting Money, cause if a Bearing is running Smoothly with 50:1, more Oil isn't going to make it run Smoother.

 

[3rdMarDiv]

There are Much Better Snake Oils than SeaFoam for cleaning the Rings, Merc's Engine Tuner, and BRP's Engine Cleaner, as two. CTC makes a decent one too.

Oil should be a Good TCW-3 and mixed at 50:1. Any more is wasting Money, cause if a Bearing is running Smoothly with 50:1, more Oil isn't going to make it run Smoother.

Thank You Much for the information...Copied the info and will check into them. I'm using Pennzoil 2 Stroke XLF.

Found the MERC and BRP on Amazon. Thanks and I'll start with the MERC. I noticed Quicksilver has a matching product. For some reason I was thinking Quicksilver was the same as Mercury?

Lots of good reviews...Thanks

 

[jimmbo]

It is. Mercury was sold in Merc Dealerships, while Quicksilver was available to Non Dealers, but these Days, all bets are off on that

 

[racerone]

I think " Quicksilver " is the brand name for Mercury accessories.------Such as oil , props and repair kits.

 

[jimmbo]

 

[racerone]

Just marketing 101 in my opinion-----Plus the legal aspects of dealerships and aftermarket parts marketing,-------Sort of like GM and AC-Delco

 

[3rdMarDiv]

View attachment 402170 View attachment 402172View attachment 402171

Definitely pick up as my next gallon. I see it it is about twice the price of the Penzoil, but you do get what you pay for don't you. Also assuming I will want the 2 stroke version..Thanks