1985 e150tlcos compression/misfire

[thomascorr]

Hello, I have a 1985 E150tlcos engine that has an even reading of 80 psi on all 6 cyls. I am worried that is too low. any comments? The engine seems to idle OK, and at WOT it feels OK, but in the RPM range from 1200 to 2200 the engine developes a significant misfire. I have over the last 6 months rebuilt the carbs 4 times, replaced both power pacs, replaced all six coils, changed the stator & trigger base - the same mid RPM range misfire persists. When I got the engine the VRO was dismantled & I premix at 50:1. The engine also drains black oily exhaust looking discharge from under the bottom basket that runs down towards the lower unit on both sides. It is like an oily gas carbon mixture that comes from the bottom of the powerhead (i think) grossly discoloring both sides of the mid section & on to the lower gears housing. Any ideas about that? I have changed the plugs & plug wires - spark checks out OK. Last carb cleaning (1 month ago) I went through the reed valves, too, replacing 3. Any thought/comments/ideas would be very very much appreciated . thanks for any input!

 

[oldcatamount]

Re: 1985 e150tlcos compression/misfire

The compression is low but it still should run ok. Take a timing light (and a Buddy) for a boat ride. Hook up the light on each of the cylinders as you run the motor. That'll show you if you are having any ignition breakdown. I'd doubt the problem is carb related (unless they aren't synchronized correctly). When you cleaned the carbs, did you totally dismantle them (including the welch plug(s) and did you replace the carb to intake gaskets?

 

[Capt Ken]

Re: 1985 e150tlcos compression/misfire

First I would throw that compression guage away and get a correct one. A cylinder will not fire with less than 90 psi. So if the engine starts and runs, the guage has to be bad. If the timing light trick doesn't show a misfire, then you may have a problem with some of your reeds. I still wouldn't discount a problem with the carbs. Those floats have to be indentical in height and competely clean or they will flow differently.

 

[emdsapmgr]

Re: 1985 e150tlcos compression/misfire

Possible your powerhead base gasket is shot. That permits the exhaust gas to escape at the powerhead base, instead of going down the midsection. It's a common problem with older crossflows with high hours. While a messy problem, it is not usually indicative of an impending failure. Unfortunately when the base gasket goes (the black tarry substance is the telltale here) there is a secondary problem. Exhaust gas will also leak from that gasket area, into the cowling. As it gets worse, it will leak more exhaust into the cowling. When running, the exhaust gets sucked back into the airbox and into the engine internals and the combustion process. That's probably the most important reason to remove the powerhead and put on a new base gasket. It is possible an exhaust leak could affect engine running/performance. That year's engines did have low compression heads. OMC went to them when the no lead fuels came out. Some of them ran 85-90 lbs when new. As long as yours are all within 10% of each other, you are probably ok.

 

[thomascorr]

Re: 1985 e150tlcos compression/misfire

The compression is low but it still should run ok. Take a timing light (and a Buddy) for a boat ride. Hook up the light on each of the cylinders as you run the motor. That'll show you if you are having any ignition breakdown. I'd doubt the problem is carb related (unless they aren't synchronized correctly). When you cleaned the carbs, did you totally dismantle them (including the welch plug(s) and did you replace the carb to intake gaskets?

thanks for the reply & info/suggestions. When the carbs were cleaned they were completely dismantled each time, soaked in carb cleaner, all parts in the carb kit were used including the intake gaskets. I am, however, unsure as to the synchronization.

As to the compression gauge, I used two different gauges of the screw in type that were both recently purchased for about $35 & $75 respectively. Both gauges showed virtually the same readings of 80 - 82 psi on all 6 cyls. I did the last test after running the engine for 5 min or so & with all plugs removed. I will repeat the compression test again today.

I will take a ride today with a timing light and see if I can find a spark irregularity.

I am unsure of the wisdom to rebuild this 1985 engine. Shall I take off the powerhead to change the bottom gasket (solving the oily discharge issue) without putting in rings & bearings?

thank you all for your time & expertise. I will let you know what I discover in the near term. Thanks very much

 

[emdsapmgr]

Re: 1985 e150tlcos compression/misfire

If you do the labor yourself, you are looking at 2-3 hours to pull the powerhead and do the base gasket. You will need a 3-legged wheel puller, mounted on the top of the flywheel to lift the engine. It sounds like a bigger deal than it is. If you are planning other work, this might be a good time to consider it-when things are more accessible. Misfires can be carb related. Have you done a sync and link? That syncs the carb openings with the spark advance. If that adjustment gets out of whack, you can wind up with odd running problems that you noted. It is easy for that special adjustment to get altered if the carbs have been off numerous times. You'll need a factory manual to use as a reference. See: outboardbooks.com You don't have much at risk with these proejcts: these tasks are mostly labor-related and don't involve much $ outlay. Good winter projects. If you later get into a large $ outlay, you should then decide if you want to make the repairs/rebuild or get another engine.