Fixed - '79 OMC SternDrive 305 GM - No Power over 1,000 RPM

[neilmack]

I have a 79 SeaRay with a OMC Stern Drive 305 GM, 200 HP, Mallory Distributor YL624JV, 2 barrel Rochester carb.<br /><br />Engine starts fine and idles great. Tied up to the dock and in neutral, I can run-up the engine to any rpm, say 3,500, with no problems. Smooth as can be. Never stalls.<br /><br />My shifts from neutral to/from forward/reverse are smooth and easy. No binding.<br /><br />On the lake and in gear, I can cruise along at up to 1,000 rpm with no issues, but as soon as I open up the throttle, all hell breaks loose:<br />- hard to get over 1,500 rpm,<br />- doesn't want to develop power,<br />- at max throttle just barely makes 2,000 rpm (should be 3,300 rpm or more)<br />- runs rough, but not real rough,<br />- might backfire through the carb, might not,<br />- might stall if you try to accelerate to fast,<br />- sounds awful<br /><br />Throttle back to 1,000 rpm, and everything is OK again. Can cruise at 1,000 rpm all day if I had to.<br /><br />Go back to the dock, in neutral, engine will rev up to 3,500 rpm, smoooooooth as silk.<br /><br />I just did a tune-up prior to all these problems developing: points, plugs, condenser, cap, & rotor. Didn't change coil but primary and secondary resistances are OK compared to same new coil.<br /><br />Dwell is 28o (should be 30o) and timing (with timing light) is bang on 7o BTDC. Both with warm engine. Timing advance appear to be OK, timing mark moves towards 12o BTDC as the rpms are increased.<br /><br />Basic fuel checks show gas OK, clean, and lots of it. Been told the timing chain is OK.<br /><br />Any ideas on this one? Help! Thanks in advance. <br /><br />Neilmack

 

[todd5881]

Re: Fixed - '79 OMC SternDrive 305 GM - No Power over 1,000 RPM

Timing!! The timing is off on the engine! Get a timing light and make sure that the timing is to spec-gm 305 should be around 8 degrees, if that checks well then i would give the plugs a look, they may be fouled or something. good luck!

 

[todd5881]

Re: Fixed - '79 OMC SternDrive 305 GM - No Power over 1,000 RPM

check the point gap again it may be off

 

[neilmack]

Re: Fixed - '79 OMC SternDrive 305 GM - No Power over 1,000 RPM

Thanks but after test ride on lake, both point gap (dwell) and timing are OK. My operating manual shows timing as 7o BTDC, and timing light I own shows 7oBTDC. I will check the plugs but they are only 3 hours run-time old.

 

[Don S]

Re: Fixed - '79 OMC SternDrive 305 GM - No Power over 1,000 RPM

You mentioned you changed the points. On some sets there is a second spring you have to install on the new points,it's in the package with the points, just not ON the pointss. It goes around the copper strap. Without that spring (Kind of C shaped) the points will float at around 1500 rpm and cause your problem.<br />Napa points in particular are like this.

 

[Hog Wild]

Re: Fixed - '79 OMC SternDrive 305 GM - No Power over 1,000 RPM

This is certainly still an ignition problem. ESP. after you just changed so many things. One thing to think about is you changed an aweful lot of things at once now you have to figure out which one caused your problems. 1st culprit would be the points as mentioned already. 2nd is still timing what exactly is it when you get up to 2500 rpms out on the water? It should be over 20 btdc at least. I doubt it's the cap, rotor, wires or plugs. Only other thing that comes to mind is you by chance don't have two plug wires swapped around? maybe just trace their paths for a double check that will only show up at full engine load vs. free rev'ing.

 

[CTD]

Re: Fixed - '79 OMC SternDrive 305 GM - No Power over 1,000 RPM

Since it started when you tuned it up I would guess it could be a coil wire (broken on removel) a bad ground strap on the dist plate (broken on removel). Pull one plug wire at the dist cap and see if you have a good strong spark, you should be able to see it jump a 1/4 inch gap and hear it. It is also possible you got bad points or condensor or a fuel problem just started about now.

 

[neilmack]

Re: Fixed - '79 OMC SternDrive 305 GM - No Power over 1,000 RPM

Thanks again, I'll try some of these things on the weekend. Any more ideas? Please post.

 

[butch290]

Re: Fixed - '79 OMC SternDrive 305 GM - No Power over 1,000 RPM

Could the shift disrupter be turning on?<br /> <br /> butch

 

[Bondo]

Re: Fixed - '79 OMC SternDrive 305 GM - No Power over 1,000 RPM

The High-Speed Circuit in your Carb is Plugged/Gummed Up...........<br /><br />Fix the Carb,+ Your Problems will be History............................

 

[neilmack]

Re: Fixed - '79 OMC SternDrive 305 GM - No Power over 1,000 RPM

This weekend the boat would run at 2,000 to 3,000 rpm but not below. No idle. Go figure.<br /><br />Think I found the major problem...I pulled the distributor and found the flyweights in the Mallory distributor were jammed. One of the flyweight pivot posts lifted up and was scrapping on the bottom of the plate that holds the points & condenser. Bowl of the distributor was loaded with metal filings.<br /><br />I was able to re-seat the pivot post with an aluminum foil shim, clean everything, and put it back together. Doesn't appear to be any major damage. Will re-install distributor and try again in the morning.<br /><br />Thanks for all the posts.

 

[tommays]

Re: Fixed - '79 OMC SternDrive 305 GM - No Power over 1,000 RPM

it doesent sound like it would be safe to use the distributor anymore i dont think the shim is going to keep the post in place<br /><br />it seams like it is inviteing a sparking nitemare to happen when it falls out again<br /><br />tommays

 

[neilmack]

Re: Fixed - '79 OMC SternDrive 305 GM - No Power over 1,000 RPM

Agree with "tommays" about sparking nightmare, I'm already shopping on-line for a new distributor. <br /><br />..... Off to the dock in 2 hrs to re-install the distributor.<br /><br />Back....and the repaired distributor fixed everything, <br /><br /><br />works 100% now, <br /><br />thanks for all the ideas in the posts above.