Mercruiser 4.3 Vortec Backfire and no start

[nola mike]

Yes you need to put it in base mode to set the timing.

Only if it's a TBV... Thought we were working on a TB-IV

 

[Superjetjim]

Yes you need to put it in base mode to set the timing. As others have said the compression is good enough that the engine should run. It does seem to cough and with no backfire clearly timing should be closer. Agree with NOLA timing or firing order must still be off…
can you post a video of cranking it while turning the distributor? If yiu dump a little gas out down the carb first it should couh and run momentarily unless maybe there is a vacuum leak making it very lean.
did you have the heads intake or carb off it?

Thanks for the reply.

I had the carb off rebuilt it (I’m familiar with rebuilding carbs have done several before)

I poured fuel using a squirty bottle down the carb a couple of times. It fired momentarily as in the video. But nothing more.

I also tried manipulating the distributor cap about an eighth of a turn in either direction to 0 and it didn’t help - one thing I did notice though is that when it was anything other than zero it didn’t even attempt to fire..?

What I still don’t understand is why the same unburnt fuel vapour is coming out of the crank case breather on the rocker cover as the exhaust?

 

[nola mike]

Thanks for the reply.

I had the carb off rebuilt it (I’m familiar with rebuilding carbs have done several before)

I poured fuel using a squirty bottle down the carb a couple of times. It fired momentarily as in the video. But nothing more.

I also tried manipulating the distributor cap about an eighth of a turn in either direction to 0 and it didn’t help - one thing I did notice though is that when it was anything other than zero it didn’t even attempt to fire..?

What I still don’t understand is why the same unburnt fuel vapour is coming out of the crank case breather on the rocker cover as the exhaust?

You might have a stuck valve, bad guides, rings... See earlier comments about leak down testing

 

[Superjetjim]

Only if it's a TBV... Thought we were working on a TB-IV

How do you tell which type I have?

 

[MichaelBC]

How do you tell which type I have?

An easy way would be to read what is written on your control unit.

 

[Scott06]

How do you tell which type I have?

Yes you have a TB V shown in your photos attached to exhaust elbow

 

[Superjetjim]

I have it booked in at a Mercruiser dealers tomorrow, lets see if they can adjust the timing and get it running. Will report back.

 

[Superjetjim]

Yes!!!! Result!! She’s a runner. Thanks SO MUCH to you guys on here for your help and persistence. All it needed was the timing mode and light and away she went. The Mercruiser mechanic had it up and running in 30 mins. Short clip attached.

I’ll connect it up to the hose and run it for half an hour at the weekend - if it’s all good I’ll drop it back in the boat.

 

[Lou C]

Great glad to hear it. Now just get yourself a timing light and next time do it yourself! My old 4.3 still has the ancient (but reliable) Prestolite points distributor so I check dwell, timing & idle speed every spring. Points get replaced when they are pitted or it starts running rough. 63 on the meter is actuall 630 rpm...

 

[nola mike]

Great glad to hear it. Now just get yourself a timing light and next time do it yourself! My old 4.3 still has the ancient (but reliable) Prestolite points distributor so I check dwell, timing & idle speed every spring. Points get replaced when they are pitted or it starts running rough. 63 on the meter is actuall 630 rpm...
View attachment 356976

I had that same timing light for 30 years before it finally died

 

[Bondo]

I had that same timing light for 30 years before it finally died

Ayuh,.... I too, had one like that, that finally died,.....

I used that excuse to run out, 'n buy an Inova, which is not only a light, but digital dwell, rpms, etc,.....
Good thing too, as somebody had borrowed my ole analog tach/ dwell meter, 'n not returned it,.....

 

[Lou C]

OK did either one of you ever get fooled setting timing with that thing when the dial got turned off of zero (and you didn't notice lol). I'm looking at it and what the heck changed the timing while it sat over the winter....happened to me twice! Now I remember to make sure the dang pointer is on ZERO!

 

[todhunter]

OK did either one of you ever get fooled setting timing with that thing when the dial got turned off of zero (and you didn't notice lol). I'm looking at it and what the heck changed the timing while it sat over the winter....happened to me twice! Now I remember to make sure the dang pointer is on ZERO!

I've still got this same light I use, and yes, the dial has bit me before. I'm praying for it to die so I can go buy an Innova, lol.

 

[Scott06]

I had that same timing light for 30 years before it finally died

Same here still have it… still works. Did upgrade to a Digital tach/ignition analyzer. Can see how many kV the ignition is putting out. Very helpfull if you get a baseline on your engines when they are running good.