Irratic timming

[wire knot]

After adding a rebuilt carb, setting the dwell.
The timming is jumping, maybe 2 deg., from
the setting mark.
Where is the most likley problem?
The chain cover does not have a timming
mark that sticks out, it is just a slash molded into the cover. Anyone familiar w/these.

The motor is a OMC '75 -350/4bbl

Thanks
WK

 

[Silvertip]

Re: Irratic timming

Worn upper distributor shaft bushing or stretched timing chain. My guess is distributor shaft bushing. Hook up a dwell meter and watch the needle while blipping the throttle. If dwell jumps around, its the distributor. I've also seen brand new points that have a loose contact. The engine runs fine at idle but the contact bounces at higher rpm again causing dwell and timing to jump around.

 

[wire knot]

Re: Irratic timming

Thanks silvertip,
The dwell does not move, at all.
through all RPM's, ......no load , anyway.

 

[Coors]

Re: Irratic timming

hook a vacuum gauge up, and check that; if vacuum is good, may be chain

 

[bruceb58]

Re: Irratic timming

Coors,

How is vacuum going to affect timing?

 

[Don S]

Re: Irratic timming

The chain cover does not have a timming
mark that sticks out, it is just a slash molded into the cover. Anyone familiar w/these.

What year is your engine. The older ones did not have a way to have a "Molded in" timing marked. They were stamped sheet metal with a welded on timing mark.

As far as your timing jumping, they are never 100% solid. A little crossfire or arching between the distributor cap and rotor will cause that. How long since the cap and rotor were replaced?

 

[wire knot]

Re: Irratic timming

Thanks for the replies,

A vacuum test is in the works.

Don, according to the block # , its about right.
I do think the chain cover was replaced.
All the ig parts are new.

This engine runs great up to 4200 rpms,
then when I get into the 4 bbl, it starts to kick out.
It seems like an ignition problem.
I was thinking of replacing the whole distributor.

thanks men, any more ideas?

WK

 

[Bondo]

Re: Irratic timming

This engine runs great up to 4200 rpms,
then when I get into the 4 bbl, it starts to kick out.

Please Explain,..... "it starts to kick out."

If it's breaking down,+ running Rough,.......
I'd be looking at the Fuel Delivery thru the 2ndaries.......

Sounds like it might be going Lean to me..................

 

[wire knot]

Re: Irratic timming

bond-o,
breaking down may be a better description.
Just won,t take full throttle.

She isn't runnig rough,except at wot.

 

[Bondo]

Re: Irratic timming

Sounds like it might be going Lean to me..................

 

[180shabah]

Re: Irratic timming

Ditto - I would be looking at the fuel side of the equation here.