Chevy 305 has rough idle at 8 degrees timing but gets smooth at 16 degrees - 600 RPM.

[Don S]

Re: Chevy 305 has rough idle at 8 degrees timing but gets smooth at 16 degrees - 600

After clean cleaning the distributor the timing advanced at idle by 8 degrees even though the distributor had not moved.

Not sure I follow what you are trying to say here. Did you have it set at 8? then cleaned it and the timing went to 16?????

 

[rs2k]

Re: Chevy 305 has rough idle at 8 degrees timing but gets smooth at 16 degrees - 600

Yes, that is correct. The weights were a bit sticky. I would have though that if would have changed going the other direction though.

 

[Don S]

Re: Chevy 305 has rough idle at 8 degrees timing but gets smooth at 16 degrees - 600

Get everything freed up and working, THEN set the timing and see what happens.

 

[rs2k]

Re: Chevy 305 has rough idle at 8 degrees timing but gets smooth at 16 degrees - 600

I freed everything up and everything seems to be working just fine. It will idle fine at 700 RPM and 8 degrees BTDC. At 600 RPM and 8 degrees BTDC the engine will lope a little and can even die when the prop and exhaust have a load. It idles the smoothest at 14 BTDC (600 RPM). The problem is that idle timing would put it at 42.5 degrees at 3000 RPM which just won't work. Looking at the distributor weights it looks like I can adjust the stops so that it remains at 36.5 degrees BTDC but still idles at 14 degrees BTDC. Does this seem like a reasonable approach?

 

[Don S]

Re: Chevy 305 has rough idle at 8 degrees timing but gets smooth at 16 degrees - 600

The weights in the distributor are NOT adjustable, the timeing needs to be a t 8? BTDC at idle. Adjust the idle mixture on the carb at 700 and it should be fine. Every other SBC engine will run like that, what makes you think you should need something else.

 

[ohiophoto]

Re: Chevy 305 has rough idle at 8 degrees timing but gets smooth at 16 degrees - 600

I freed everything up and everything seems to be working just fine. It will idle fine at 700 RPM and 8 degrees BTDC. At 600 RPM and 8 degrees BTDC the engine will lope a little and can even die when the prop and exhaust have a load. It idles the smoothest at 14 BTDC (600 RPM). The problem is that idle timing would put it at 42.5 degrees at 3000 RPM which just won't work. Looking at the distributor weights it looks like I can adjust the stops so that it remains at 36.5 degrees BTDC but still idles at 14 degrees BTDC. Does this seem like a reasonable approach?

Yes you are correct your total advance is adjustable if you have a distributor like mine, I highly recommend you do not mess with the "Stops" without a timing bench second if you get one loose while on the lake bad things happen in there. Now I just had the same problem you had. Put the boat in the water right after having it serviced at the marina. (1978 228 mercruiser) (Malory/Duel Point)
Now here was my battle, 8 deg would not idle 14-16 deg would idle, if you run it at 14-16 initial it is bad. These are not street motors!! Check to see how much "Play" you have in the timing. Mine was the timing chain! I pulled the tin cover and yup stretched all out (street wise is 10 degrees IMO 5 degrees and its garbage time) 24.99 at advanced auto for steel double roller. Then get some White grease and cover your carb gasket top and bottom with a new gasket. (The white grease is an old gear head trick I learned 20 years ago while messin with the timing piece you will knock the seal off the carb and not know it and it will suck a little air and give you fits! trust me on this one)

Whamo! Good to go! The service manager at the Marina (Friend of mine) said in 20+ years never seen one go bad.

you can pm me I can tell you the rest of the story! or if you need more help