1974 Evinrude 135 fouling plugs at idle?... About ready to give up...HELP!

[a_kraker99]

Some of you might know me and my brother on here by now with our Evinrude 135. For those of you who don't here is a little history.

1974 135 Evinrude has been fouling plugs like crazy. We idle a lot for fishing which I know isn't the best use of a motor this big, but in the past it seemed to do it just fine with a trolling plate on the back. The last couple years it will not idle good after only 1 or 2 trips on new plugs. Even with the new plugs it is not very good. It was never like that before. Lately we have been using the QL77JC4 because of a recommendation on here. Otherwise I think it is supposed to have the UL77V's. Maybe that is part of the problem?

I might be missing some of the things we have done to it but here is what I remember right now. New coils, powerpack, stator, plug wires. Carbs have been rebuilt. Compression is good.

We are running 75:1 mix while idling. (fuel with 10% ethanol)

So after idling around 1100 RPM for a while in a no wake zone it just starts dying like it is loading up on fuel. I am not sure if this is because there is too much fuel being delivered or because it isn't all being burned off. When it is idling, it doesn't like to be tilted up very far or it will quit. We can't even use a trolling plate because the engine will stall out.

On our last trip after running full throttle (running great) for about 3 minutes we got into a no wake zone and idled for about a minute before the boat just slowly and completely died. It sounded like the engine was blown or something. Got towed in and started it on the hose back at home and it ran fine again....

I am at a complete loss..... I am hoping someone will have the magic fix. Please!

 

[w2much]

Re: 1974 Evinrude 135 fouling plugs at idle?... About ready to give up...HELP!

You may try the QL78 YC plug. See my post on this. Also you may lean out your low speed mixture.

 

[a_kraker99]

Re: 1974 Evinrude 135 fouling plugs at idle?... About ready to give up...HELP!

You may try the QL78 YC plug. See my post on this. Also you may lean out your low speed mixture.

It is fixed jet. Is there another way to lean it out?

 

[w2much]

Re: 1974 Evinrude 135 fouling plugs at idle?... About ready to give up...HELP!

Perhaps check the needle and seat in the float chamber.

 

[FAC]

Re: 1974 Evinrude 135 fouling plugs at idle?... About ready to give up...HELP!

I have a '76 135 Johnson and basically deal with the exact same thing! I think it might have something to do with the parts required to make 135hp on the same 99 cube block as the smaller 80, 90 hp models. (maybe even the 75 i cant remember) the higher compression and "bubbleback" exhaust might make it a little more finicky.

If I remember correctly I am also running QL77JC4's.

My engine would start fine Hot and cold but idle way to low and stall when put into gear. My engine would also "sneeze" out the exhaust relieves a lot. If i "cleared it out" by revving the engine out of gear it would usually help. once it was running good or after cruising it would usually idle okay and not stall, but if I shut it down, even for less than 60 seconds it would act up again.

What I ended up doing (after lots of troubleshooting-question asking-head scratching-fixes) was increasing the timing above spec. I was apprehensive about advancing the timing,(as i would be about leaning the mixture) the last thing I wanted to do was meltdown my powerhead. Basically I followed the link and sync procedure until adjusting the length of the rod the connects to the stator. The setting I ended up with there was essentially full possible advancement by that adjustment. It now runs much better! I have one full season on it like this with zero further changes. I still feel like I may be covering up some other issue or issues compounding into this problem, but I am satisfied with how it is performing.

Except I took the boat to the mammoth area this past summer and launched at Crowley lake 6800'' and twin lakes 7100'. At these higher elevations I was having essentially the same problem all over again, but adding a loss of power to the list of symptoms. This seems to support that we were running too rich at low elevations aswell. I didnt try to fix it during that trip and returning to sea level It ran normally.

Things I did to try and fix it that didnt work:
Carb rebuild
link and sync
changing plugs
fuel pump (not because I thought it would solve the problem, but the diaphragm tore)

If I were you I would start with a proper link and sync and make sure you are getting a good strong spark. Then water test it and if it is acting the same try advancing spark beyond spec. If it works great, if it doesnt make sure to redo the link and sync so its back to the proper timing!

I was also considering going to normal side electrode plug so I could play with the gap, but i never got that far. Hopefully some of this gets you going in the right direction! haha Maybe somebody can chime in with lots of knowledge on these old omc's and set us both straight. please let us know how it turns out though, Its nice to have an ending.

 

[seahorse5]

Re: 1974 Evinrude 135 fouling plugs at idle?... About ready to give up...HELP!

Have you tested the temperature of both cylinder heads? If not warming up to around 140?, you will not get good combustion at idle and can foul plugs. You may need a new thermostat.

Use the QL77JC4 plugs gapped to .030" for best results. The QL78YC plugs have an extended nose and could possibly be hit by the piston while running.

Check the strength of your ignition system, that was a weak point in those motors. The spark should jump 7/16" gap at cranking speed with the sparkplugs installed. If it doesn't, then weak ignition is also part of your problem. The engine has to crank over about 350 rpm to generate enough ignition power.

 

[a_kraker99]

Re: 1974 Evinrude 135 fouling plugs at idle?... About ready to give up...HELP!

Thanks for the tips.

I haven't checked the temps yet. Will do that next time.

Why do some people recommend gapping at .030 and some say .040?

Weak spark has been a problem in the past which is why we got a new powerpack, coils, stator, plugs and wires. I haven't checked the spark since the new stator. Probably because I feel like I am at the end of the line if it isn't strong now! It would jump a 7/16 gap but looked pretty weak and was intermittent during cranking.

 

[a_kraker99]

Re: 1974 Evinrude 135 fouling plugs at idle?... About ready to give up...HELP!

Just another quick bit of info. in case it is relevant. Last time we were out the gauges in the boat kept going in and out. Not sure what is causing that. I feel like the only electrical part that we haven't changed is the rectifier. Any thoughts on if that issue could be related?

Basically it either seems like we are getting too much fuel, not a good enough spark or both. Doesn't seem like you could get too much fuel with a fixed jet though.