Electrical problems on 115hp Johnsons

[1970Thunderbird]

Hello,

I've been looking into some used Johnson outboards, from the mid to late '70s. However, they all seem to have a consistent problem of no spark getting to the plugs. I've even encountered this on 150hp Mercury motors. Some motors have had little work done, so they're pretty stock. But one Mercury had all the electronics replaced with CDI and still wouldn't fire.

My question is, is this a fairly routine issue with outboards that age? It seems all the decently priced outboards are about this age range and I'm interested if these are isolated incidents, or if there is something I should know about motors this old?

Thanks

 

[emdsapmgr]

Re: Electrical problems on 115hp Johnsons

Most of these engines were all solid state by these years, so that is good. When new, all these ignition systems were pretty reliable and relatively problem free. These engines do have their age working against them at this point, so it is not unusual for them to have an ignition problem. Not everyone will work on these older models. The power packs are the most frequent ignition failure item, though at their current age-now the stators and timer bases may be in question. Even the spark plug coils.. You could replace one component, only to have another part fail in 6 months. You can fix an ignition problem, but if the powerhead has bad compression, or scuffed cylinder walls, you are looking at big dollars. Check the lower unit for water in the oil and make sure the trim works. Make your offer based on what it will take to resurrect the engine.

 

[1970Thunderbird]

Re: Electrical problems on 115hp Johnsons

Thanks for the advice. One of my first checks is compression. I've heard 120 is ideal. Is this true? Most of them pull 90-100psi. I've made plenty of offers, but most of the people look at me like I'm crazy when they hear what I'm willing to pay. Yes, your motor may have run great last year, but it won't crank now. I'm not paying $1,500 for a motor that may need that much in repairs.

 

[emdsapmgr]

Re: Electrical problems on 115hp Johnsons

I overhauled my stock 1979 85 hp engine. After boring .030 over and overhauling it, the compression was 125/130. These older models tended to have higher compression than the 1985 and newer. I would say 100 is low. While it will run at 100, you won't make quite the hp as when new-with higher compression. FYI, the early 85 and 100 hp V4 engines used a smaller bore block (92 cubic inches) than the 115, 125 and 135 (99 cubic inches)powerheads.