1985 GT150 smoking like a banshee

[omcforever]

I have followed behind people that have used the Joe Reeves method and it almost always is not right. Too many variable in modern solid state electronics. The tech bulletin Jerry posted is a good way to get it close until a shop can test on a dyno or test wheel and tank. 34 BTDC,,,yikes,,,,,,,Like Jerry stated, I usually set mine at 28 degrees BTDC. Safe and never tell the difference vs 30 BTDC...…….especially if you have the GT/XP higher compression heads.

[NoZero]

If you don't figure it out swing by Riverside Marine in Old Hickory,

Hahaha... was just up in Madison picking up the L77JC4 spark plugs and drove by - forgot that they are closed on Sundays. I usually buy my oil from them... as a matter of purpose to keep good people doing what they do.

[NoZero]

ok all.

1) I found out the Vacuum Switch was leaking tonight. I will clamp it off for testing, but a new old stock switch has been ordered.

2) I am ready to dive into timing - My air intake cover really says 34 BTDC on it. This is a GT150 - so is it likely that this is a franken-motor... that has parts cobbled from a non gt-150... thus the super advanced timing number?


3) I plan to check it for reference - and if it appears to be set according to the 34BTDC spec, I will set it at 28 per your comments.


4) OMC repair manual will be here Saturday -between now and then, where the heck is the adjustment to sync the carbs? Link on them is good. ... wanting to make sure they are sync'd and I can't find any blinking mixture screw. ?? (or where to put my vacuum leads)

5) I also think that I have gaskets leaking everywhere. - don't think the guy last year used everything (anything?) from the OMC carb kits I took in. In addition, it looks like the cylinder head gaskets and the bypass cover gaskets are leaking - cylinder head leak is not as obvious - the bypass cover gasket appears very leaky. I'm guessing the cylinder head gasket leak could account for overall low compression.


Haha... man. Rabbit hole of outboard repair. This thing is in crappy shape! I really thought the mechanic last year would've seen some of this and let me know. He's off the list. haha..

I don't care if she's not perfect, and I know she will eventually give up the ghost, but I just want to get her "nominal" for her last few years (hopefully).

[NoZero]

bypassed the vacuum switch with new fuel
line, and put in the L77JC4s, and she runs like a new motor! - climbs to 5500rpm with ease!

thanks for walking with me through my ignorance, fellas.

[omcforever]

I would try and re-torque the head gaskets and by pass covers if you think they are leaking and replace if it doesn't stop. If your bypass gaskets where leaking as much as you say, wouldn't be running good at all/if at all. There are no mixture screws on that motor. Idle controlled by fixed factory idle orifices/proper link and sync. (when you say bypass cover gaskets/you are referring to the 3 on each side of the block,,,correct? item 14 and 32 of exploded view attached)
If so, only gas-air mixture/crankcase pressure are held back by the gasket's.

https://www.boats.net/catalog/johnso...-amp-crankcase

[316jughead]

bypassed the vacuum switch with new fuel
line, and put in the L77JC4s, and she runs like a new motor! - climbs to 5500rpm with ease!

thanks for walking with me through my ignorance, fellas.

Isn't it great what good spark plugs can do. On your idle pick up timing, I always set it at 8 to 10 degrees BTDC, that will help on any hesitation on take off.

[NoZero]

OMC - Thanks - I'll take a look at the specs and torque all the bolts accordingly. ...and yes, those are the gaskets. They are just wet and "fuel-ly", but it does run great now. I'll have to look at Timing at some point - Now that the air/fuel leak is gone, idle speed is low, and if I try to adjust idle speed to 700rpm in gear, it will die out when I give it throttle to accelerate from idle. - just more ignorance that I need to learn away.

[316jughead]

Read your service manual on setting the idle pick up timing, this is critical.

[NoZero]

Here is some help on your max timing. This is for an earlier model but you have the exact same ignition system.Attachment 364126 omcforever recommends less than 30 degrees BTDC. I know you will not notice any difference in top end at 28 Degrees BTDC.

Attachment 364126



Sorry about the double thing.

Jughead - if you are still around, I'm reviving this thread for a question on Max timing. Same outboard as my OP.


I have installed: new trigger base, new stator, new rectifier, and (1 - port side) power pack.


Link - sync has been done, and pick-up timing has been set at 8deg.


I'll be attempting to set MAX timing tomorrow, and I have questions about having rpms at 2,600-3,000 and the timer base fully against the stop screw. Am I disconnecting the timer base from the arm?


thanks all-

[omcforever]

No matter what method you use, be sure to verify with a test wheel at 5000 rpm. The OMC alternate is just to get you close until then. I dont use the OMC alternate way. Seen some big variations. Jerry dosent post much anymore.

[NoZero]

Thanks -

I am currently looking for an OMC 387388 test wheel in the nashville area. Can't find one to save my life.

[omcforever]

Set max timing at 28 degrees. You will thank me later.

[omcforever]

I would loan you mine but just a tad too far away,,,,

[NoZero]

Thanks -

I am currently looking for an OMC 387388 test wheel in the nashville area. Can't find one to save my life.

hahahaha.... thank you. Wife has family up in Celina/Rockford, and you are right... you are a bit of a drive away.

[ChampioNman]

Is riverside marine still open? They'll have one for sure.