5.0 backfiring thru carb

[cooter2506]

5.0 Mercruiser 1988. I haev backfiring thru carb. Timing is close. Use the thumb over the #1 cylinder method. New cap, rotor, plugs and wires. It has Thunderbolt 5 Ignition system. Not sure what it could be. Rotor is at #1 cylinder when at tdc so im confused. Any suggestions?

 

[Don S]

Re: 5.0 backfiring thru carb

You don't set timing by putting your thumb over the Spark plug hole, you only find if that piston is coming up on comperssion stroke or not. That doesn't tell you anything about the timing.
Does this thing run?
TB5 Ignition? 88's didn't have it!

So you aren't the only one confused.

 

[Bondo]

Re: 5.0 backfiring thru carb

Ayuh,........

And Backfiring thru the Carb is Usually a Fuel Delivery Issue..........

 

[Coors]

Re: 5.0 backfiring thru carb

thumb? Buy the tools.

 

[Don S]

Re: 5.0 backfiring thru carb

Do you have the plug wires in the proper location. #1TDC for the compression stroke and then going from that point in the proper rotation and sequence all the way around?

 

[cooter2506]

Re: 5.0 backfiring thru carb

Yes I have the correct order of fire on the Distributor. I used the thumb test just to make sure the #1 piston is comming to tdc as the rotor is hitting #1 on the cap. And you are correct 88 had a Thunderbolt 4 system mine is actually a 1998 with thunderbolt 5. Sorry for the confusion.

 

[cooter2506]

Re: 5.0 backfiring thru carb

Sorry it doesnt run when it backfires I stop cranking. So I cant even set the timing properly

 

[bruceb58]

Re: 5.0 backfiring thru carb

You really need to double check your spark plug wire routing.

 

[cooter2506]

Re: 5.0 backfiring thru carb

I have doen that many times but in mass confusion I will check again by pulling all wires of and placing them on the correct plug. Thanks

 

[bruceb58]

Re: 5.0 backfiring thru carb

Was the engine running before you made all these changes? Why did you need to readjust the timing? Did you pull the distributor?

 

[cooter2506]

Re: 5.0 backfiring thru carb

Did bot pull Distributor. Only cap. Set cap in proper location. ENgine ran before. This is an engine swap out. Mine was shot swapped it with a rebuilt one. When I was hoisting from my truck I cracked the distributor cap so i installed a new one.

 

[Don S]

Re: 5.0 backfiring thru carb

Did you replace the rotor also?

 

[cooter2506]

Re: 5.0 backfiring thru carb

New rotor, cap, plugs and wires

 

[SuperNova]

Re: 5.0 backfiring thru carb

1-8-4-3-6-5-7-2 clockwise. Start with the terminal the rotor is pointing at when #1 is on TDC compression. It sounds like you are one terminal too advanced.

 

[cooter2506]

Re: 5.0 backfiring thru carb

Removed all wires and redid plug wiring according to clockwise rotation and the intakemanifold numbers. Still backfiring. Sorry for being a pain but getting very frustrated and hate to take it to a marina for service.

 

[SuperNova]

Re: 5.0 backfiring thru carb

If it ran before and all you did was replace the distributor cap and related components and now it doesn't run....that kinda points you in the direction you need to look. You are overlooking something. I suggest you bring #1 up to tdc on compression, remove the dist cap and see exactly where the rotor is pointing. If you use the thumb method you will feel air twice from the cylinder--once on overlap and once on compression --the compression pulse is a lot stronger. Then line up the timing marks on the crankshaft balancer and the timing cover- then look at where the rotor is pointing. I really think you're just a little off with your timing. Or you damaged the distributor more than you think you did.

 

[Don S]

Re: 5.0 backfiring thru carb

Look at your rotor. Count the number of openings in the metal ring. Should be 8, bet you money you have 6.