1973 chrysler 70hp 3 cylinder best spark plugs for lots of trolling

[christo555]

hi guys,
my 1973 chrysler 70hp 3cylinder outboard has been running great for 4 years now but i want to use it more as a trolling speed motor than full power running. so my question is: am i harming the motor by running it at just 900 rpm? what kind of spark plugs should i be using to insure easy starting/no fouling?
i and friends enjoy just slowly going around the lake at slow speed. sounds funny to some i'm sure, but we like it.
thanks for any insights/help/comments on what i'm doing to this great motor.

 

[Nordin]

Well a two stroker does not want do run at low rpms for long times. Because it does not burn the fuel well at low rpms.
You will have problems with fooling plugs if you always runing at idle or just a bit above. Therefore you have to hit the throttle and clear up the engine now and then.

You are not making harm to it by runing low rpms but you may build up carbon to the pistonrings earlier and you have to clean the plugs more offen.

If your engine has the MagnaPower I ignition and not converted to regular automotive style with points, capacitor (condenser) and coil, you should use surface gap typ plugs.
Does not matter on brands, NGK, Champion, Bosch or other.
You have to experiment your self and check what heat range will work best.

NGK brand BUX, BUHW for example
Champion brand UL18, L20 for example.

If you do not have MagnaPower I CD ign.system but regular auto typ ign.system then you should use regular plugs with bent electrode.
Brands does not matter, check heat range.
The early Chrysler 75Hp 3 cyl. engine with regular auto typ ign.system (back in 1966-67, the MagnaPower CD was introduced in 1968) used Champion J4J or AC AC-M42K plugs.

BUT remember you always have to clean the plugs on a two stroker and more offen if you run low rpms for longer times.

 

[jerryjerry05]

Use what you have and carry along a second set.
Yours have the gapable plug? They need cleaning more often.
I used to troll in the Chesapeake Bay and the standard UL-18V were good.
Just wipe them off and it's like a new plug.
The problem was the oil builds up and needs to be burned off.

Trolling also produces more carbon and carbon on the rings is a killer.
Use a better oil like Amzoil or a good synthetic.
They say they don't carbon as bad???

I also did a de-carb more often.
I used Mercury's Power Tune or OMC's Engine Tuner.

Some say Seafoam does a good job but the tests I did showed the opposite.

 

[Frank Acampora]

The 50-1 oil ratio is an all-around ratio for general use and wide open throttle use. The engine will have much less demand for oil at low RPM. IF you intend to do nothing but slow speed running then you can reduce the ratio to 75-1 or even 100-1 to reduce plug fouling. UNDERSTAND though that such a lean ratio will not be good for high RPM and certainly will not have enough residual oil inside the engine to prevent corrosion.

If you decide to try this also understand that I never run my engines at slow speed for long periods and have never done this myself--you are taking somewhat of a risk. However, the precedent is there: A number of years ago OMC recommended 100-1 ratio for their engines. For various reasons, primarily the corrosion protection issue, this was changed back to 50-1. Current VRO mixers usually vary oil mix from about 100-1 at idle to 50-1 at WOT.

SO, if you do decide to lean the oil mix I would recommend taking along another tank of 50-1 and use that on the way home, running the engine at enough RPM to get the boat on plane.

 

[christo555]

thanks for the info guys. my boating season just ended here in colorado, but next summer i will try using a 75 to 1 oil ratio. i haven,t had any problems this past summer with plug fouling and hard/no start situation. i did have exhaust smoke for about 30 to 40 seconds on startup after half hour of trolling and then sitting for 15 minutes. but it seems that i'm not harming the motor from what has been said above, except for the carbon buildup on the rings. is this buildup something i can fix by running engine at full throttle for 5 minutes? or some additive?

 

[Frank Acampora]

In my previous reply I thought you were having a plug fouling problem and therefore recommended trying a leaner oil mix.

If you are not having a plug fouling problem then stay with a 50-1 oil mix. You can't go wrong with the tried and true. Generally the new TWC-3 oils do a good job of cleaning the pistons and rings so if you simply run the engine at full throttle on the way home it should avoid any problems.

Additives are, in my opinion, snake oils and not to be used on a regular basis. If the engine has a significant carbon problem (which right now yours does not) A Seafoam treatment MIGHT help but there is no need for it on a regular basis.

 

[S.A. Baker]

Are you fishing somewhere where you actually NEED 70 hp to troll? That would not be my choice for a trolling motor.

 

[christo555]

thanks for the info frank. as usual you came through again. i am using the 2 cycle oil from walmart which i don.t know if it's twc-3 type. i always do the full throttle for 5 minutes back to the beach after trolling for a half hour to an hour. good to know i'm not doing the engine any harm.
well, 7 months of winter coming and making me abstain from boating but then next spring is like new again for me.

 

[Frank Acampora]

Wal Mart Super Tech oil (marine) IS TWC-3. It is in fact a little better than some of the branded oils. I use it all the time. Can't beat it for value.