1981 OMC 3.8L V6 timing marks?

[rav38]

I've searched these threads high and low, got close but no cigar. My 1981 170hp V6 3.8L (model number J170STMRC1F) has bogging problems at higher rpm. Rebuilt carb, new fuel filter, coil, distributor cap, points, condenser. All plugs are the same, not fouled. Adjusted air/fuel to best rpm allowed better take off plane, but still loses rpm and bogs almost like a governor is attached after warming up a little. Get about 3000rpm at 32mph, i know i can do better. It used to run fine, then had this problem and they replaced the coil and it worked. Now I'm guessing the timing is out of whack. I looked at the timing marks but they are rusted out. Attached picture, mebbe someone knows what they are.Sorry for crappy picture.

 

[rav38]

Re: 1981 OMC 3.8L V6 timing marks?

Never mind, got me some naval jelly and sandpaper. Marks are now visible, with 12 visible at the bottom of pic, 8 degrees above it, etc. The lower angled in the middle is 0 degrees, or TDC. Numbers below the 0 are BTDC, the ones above are ATDC. So peaks are 4 degrees, valleys as well.

Still got bog issues, but now I know its drive related. Took out the boat, tied it to the dock, disconnected the shifter from the carb, ran the motor up to 4000 rpm, no problem. Checking prop for correct size, anode, rudder, etc...

 

[Howard Sterndrive]

Re: 1981 OMC 3.8L V6 timing marks?

Still got bog issues, but now I know its drive related. Took out the boat, tied it to the dock, disconnected the shifter from the carb, ran the motor up to 4000 rpm, no problem. Checking prop for correct size, anode, rudder, etc...

your problem is not likely drive related

check the anti-siphon valve
or, go for a run using a 5 gal outboard can hooked to the fuel pump

your symptom sounds like a fuel delivery problem
ever clean the flame arrester screen?

Adjusted air/fuel to best rpm allowed better take off plane,

unless you changed jets and metering rods in the carb, I don't see how you accomplished any adjustments to "air/fuel" - the only screws on your carb are idle mixture screws

 

[rav38]

Re: 1981 OMC 3.8L V6 timing marks?

Sorry, misstated air/fuel adjustment needles (for idle and low speed operations). Have cleaned flame arrester screen as well. Will research anti-siphon valve, let you know what develops. Thanks for the direction

 

[bruceb58]

Re: 1981 OMC 3.8L V6 timing marks?

disconnected the shifter from the carb, ran the motor up to 4000 rpm, no problem....

You do realize that your control at the helm allows you to increase throttle without shifting right? No need to disconnect anything at the engine.

 

[rav38]

Re: 1981 OMC 3.8L V6 timing marks?

Huh? If I move the control, it engages the shifter no matter what. The ONLY way I could rev the engine without moving is to disconnect from control (one cotter pin, very easy).

 

[bruceb58]

Re: 1981 OMC 3.8L V6 timing marks?

There is either a button you push or move the lever in or out from the mount to allow throttle without shifting.

Every remote ever made has this feature.

Post a picture of your control if you can't figure out how to do it.

 

[rav38]

Re: 1981 OMC 3.8L V6 timing marks?

Yes it has a button on the right side under the throttle handle. I don't think I can even move the lever without holding it in. If not, then I am actually dumber than a doorknob
Gonna try out the external gas tank this week after I fix rudder trim tab, had a busted off bolt in it.

Thanks, guys. I'm more of a noob than I knew All help is greatly appreciated.

 

[rav38]

Re: 1981 OMC 3.8L V6 timing marks?

The only anything on my throttle is the clutch and the trim button. It doesn't move without that pressed in, except to reverse. Also, the anti-siphon was not the problem. Ran it without and the problem remained. Gave up the ghost and let a mechanic look it over. Will post what they find. Thanks everyone for your help.

 

[bruceb58]

Re: 1981 OMC 3.8L V6 timing marks?

Hopefully thay show you how the control works. If not, post a close up picture of it.

 

[rav38]

Re: 1981 OMC 3.8L V6 timing marks?

Will do. The guys who will look this over have a great reputation in town. I just got this sneaking suspicion that it will be something I did wrong with the carb. Was very careful rebuilding it, especially the accelerator pump. We will see.

Thanks again, gentlemen.

 

[rav38]

Re: 1981 OMC 3.8L V6 timing marks?



Here's a pic of the control.

 

[rav38]

Re: 1981 OMC 3.8L V6 timing marks?



Here's two more. Button on left is trim. Button on right is what I call clutch.

 

[bruceb58]

Re: 1981 OMC 3.8L V6 timing marks?

Grab the handle and pull it away from the side of the boat. Once you do that, you can advance the throttle without it going into gear. That's what the name "Neutral" with the arrow pointing to the left means.

 

[rav38]

Re: 1981 OMC 3.8L V6 timing marks?

Will try that next time I head up there. Thanks again!

 

[rav38]

Re: 1981 OMC 3.8L V6 timing marks?

Ok, the throttle pulls from the swivel at the bottom, which allows it to rev up without the drive engaged. I was trying to pull it from the top of the handle Thank you, Bruce, for cluing me in! The original mechanic bailed cause my stringer drive is so old Got another one to check it out once we get temps over the 50s (prolly Friday).

Thanks again, Bruce!