Carbed 4.3 timing adjustment sanity check

[Blorton]

Hey Guys,

Recently picked up some dieseling, so wanted to make sure the timing was right.

Am I missing something on setting the timing on this guy? The factory manual came in and was unclear as to the actual timing marks. I followed the grounding purple wire, checking rpm and had a valid flash from the 1 spark plug. All I’m seeing is a kind of bracketed notch off the flywheel. My boat seemed set a bit advanced and easing that back down near the mark seemed to help. She shuts off cleanly most of the time now.

Any advice?

 

[dubs283]

Should be using an advance timing light that you can adjust to desired idle timing. Line up the marks at the proper setting. Otherwise use a conventional light with timing tape on the balancer

 

[Blorton]

Thank you! I was using a static light. I’ll get an advance one.

Also - what’s the friggen size on that hold down bolt? I was able to wedge a 14mm in there but it wasn’t pretty. Gonna order the correct offset ones.

 

[dubs283]

9/16" you can get a special wrench for it. Hooked box end 12 pt, works quite well

 

[Blorton]

Tyvm. Big river should have those to me this weekend.

 

[Rick Stephens]

Other cause for dieseling is overly rich. Deposits in the cylinder and on the piston stay hot and lit up.

 

[achris]

9/16" is 14.29mm, so a 14mm ring spanner will be a tad tight... (Not sure what this 'wrench' thing is though. )

Chris.

 

[Blorton]

Other cause for dieseling is overly rich. Deposits in the cylinder and on the piston stay hot and lit up.

Aye - I have already done a bit of de-carboning as a step one. And there is techron in the tank currently. If none of this clears it up, I’ll “clean” that 2bbl carb right into a 4bbl.

 

[Blorton]

Wouldn’t an “italian tune up” also help? I’ve certainly been doing that when conditions permit.

 

[Rick Stephens]

A carb rebuild with attention to float height is what fixes rich, or lean, running.

 

[achris]

Wouldn’t an “italian tune up” also help? I’ve certainly been doing that when conditions permit.

You could try the old rally driver trick...

You get the engine warm, then running at around 2000rpm start very slowly, VERY slowly, pouring about 1/2 litre of distilled water into the carb... Effectively steam cleans the combustion chambers...

Another effective option is a Merc product called 'Power Tune'. That does work well. Just follow the directions on the can. (Yes, you have to read instructions. )

Changing to a 4bbl carb won't clean the combustion chambers...

Chris...

 

[Blorton]

Yes Sir. Have a fleet of old carbed vehicles around and an ultrasonic cleaner that just croaked.

The water trickle trick is exactly what I did last week. Have done that in the past on other vehicles with success. Though I always thought using something like a garden spray mister in spurts would be safer/better

The 4bbl comment was a joke about how I’d rather put in an upgrade than clean the current part.

 

[Blorton]

Can you guys recommend an online place to order mercruiser parts from?

 

[achris]

Can you guys recommend an online place to order mercruiser parts from?

Which parts? Sometimes it's better to go directly to the manufacturer than Merc.

Like this....
Base engine parts - GM
Gaskets - Felpro
Trim pump - Parker-Hannafin
Most drive bearings - Timken
Some electrical parts - Bosch or Delphi
Spark plugs - NGK

 

[Blorton]

Ty Sir! I need to order the parts to convert to dry joint exhaust manifolds and I was thinkjng ahead to doing the distributor replacement with plugs and wires, impeller, etc.

 

[achris]

Manifolds and elbows - Merc, Barrs or HGE (google search is your friend)
Why are you needing to replace the distributor?
Spark plugs - NGK at any auto shop, same with plug wires. Get 8mm Silicone, check you get the right ends!
Impeller - Merc.

The best Merc genuine parts online shop I know is 'Mercruiserparts dot com'

Chris......

 

[Blorton]

Thanks! On the dizzy, I figure since this engine is coming up on 25 years of age, might as well make sure the sparky bits are fresh.

 

[jimmbo]

If the timing has retarded, the throttle plates may have been opened to regain the Idle Speed, that by itself is major cause of Dieseling. I will assume it has Electronic Ignition, so no Points to wear, but the timing will retard as the Timing Chain wears and stretches.

 

[achris]

Thanks! On the dizzy, I figure since this engine is coming up on 25 years of age, might as well make sure the sparky bits are fresh.

If it's got any (lateral) movement in the shaft, just re-bush it.

 

[Blorton]

An update:

The innova 5568 timing light I ordered off big river came in. I opted for that one since it includes an rpm readout, with voltage and dwell as bonuses. (Nice to have confirmation the alternator is working correctly.)

Anyway, I got the engine timed correctly and did find that the idle rpm was a little high so I adjusted that as well. I put the light back to zero advance to guesstimate if it was wrong beforehand when I tried setting it with my non-advance light and it looks like it was off a few degrees. So that was a nice find.

The engine shut off cleanly when I was all done, so that’s encouraging.