Re: Backfired .....
 

I'm still thinking lean too. Maybe the fuel in the carb bowls is getting low at wot, maybe fuel filter restricting too much at high speed?

Re: Backfired .....
 

Thanks guys ... plug on right is the new motor. Plug on left backfiring motor(port) . The new motor (starboard) is definitely lean .. Port motor is ok (not lean) ...antway putting in new fuel filters and might go ahead and check compression ....As much as it pains me to pull all the plugs but guess I should .

Re: Backfired .....
 

Mike, you running the stock Merc fuel/water seperator filters????? If so, consider swapping them out to the Racorp units with the drain plug. They filter down much farther than the stock Merc units do.

I swear on my screen it looks like the plug on the left is carboned up badly.

Re: Backfired .....
 

Here it is lightened up a lot. Pic doesn't look pretty but you can see color on the tips better.

I noticed they are different plugs too. Maybe NGK on the left and Champion on the right??

Re: Backfired .....
 

Could the fuel lines on the suction side be old and soft, and collapsing at wot?

Re: Backfired .....
 

Scares the hell outa me to think the fuel line could be collapsing :eek: But I'll check em .... Using Formula31's link ...
http://dragstuff.com/techarticles/h...read-plugs.html

The plugs aren't that bad per that website ....

Re: Backfired .....
 

Mine are Stock ... use these ? http://www.marinefilters.com/product...ber=W320RRAC01

Has 3 ports ... one in two out ? 90 GPM ..guess you could use just one ?

Re: Backfired .....
 

No mine are not "see thru". I'll get up in the boat today and post the model # here.

I had several racers and "big boys" recommend these. They also recommended draining them after every run, or every other run, unless you have a problem. You can also buy the filters only which just replace the originals in the cannister. Everyone swears by them.

Also, be aware if you are running mechanical fuel pumps they won't fit in the stock location, as the Racorps are taller. I had SS couplings made up which bolted up to the posts that the stock bracket bolts up to. Then I just bolted the bracket to the end of the couplings. Worked great, but the spacers cost me two bills.

Cheesh, I forgot that picture was before I cleaned up the engine compartment and repainted the pulleys. Looks bad. But you can clearly see the spacers I'm talking about.

Re: Backfired .....
 

Mike, the Racorp units I'm using are: S 322 OUL Russ

Re: Backfired .....
 

Do those screw onto the existing fuel filter mounts? ( with the offsets of course)

Re: Backfired .....
 

Thank ya sir .. will look into them

Re: Backfired .....
 

Yes....

Re: Backfired .....
 

Have you removed your anti siphon valves? They can stick and restrict fuel flow. Are your fuel pumps original? If so you might want to replace the one on the backfire side. However IMHO you probably have crap in your fuel system. Are your fuel bowl levels set correctly? Have you cleaned the fuel filter screen in your carb? Just food for thought. Joe Murray

Re: Backfired .....
 

Lot of times it's the simplest things.

Re: Backfired .....
 

The best way to check Champion spark plugs is to throw them in the water. If they float then use them...

Re: Backfired .....
 

Boy if THAT'S not the truth I don't know what is.....I wouldn't use one in my lawn mower, that doesn't run anyway.....

Re: Backfired .....
 

I wouldn't put them in my mother-in-law's car.

Re: Backfired .....
 

I would....:D :D

Re: Backfired .....
 

A few years ago, I had a cruiser. I was running it to the marina I was going to kee it at for the Labor Day weekend. On the way there, I heard a big pop/bang in the engine compartment. I figured I blew the engine, called Seatow and got towed in. Ruined my whole planned out holiday. When I finally got around to finding out what was wrong, I found one of my Champion sparkplugs had the entire center electrode blown out of it. It was even still connected to the plug wire.

Re: Backfired .....
 

Here's my Champion story:

In the late 1960s I had a 1967 427/390hp Corvette. It used the AC 43N spark plugs.

When the plugs had about 4,000 miles on them I would get a breaking up approaching the red line. Nothing I could do would stop it except put in a new set of 43Ns. I was good again until 4,000 miles and the same problem.

I worked for an auto parts chain back then and I told the AC reps about what was happening. They sent a set of my plugs to the lab and the results came back that there was nothing wrong with them. (They looked perfect.)

I tried a comparable set of Champions and they did it in a weeks usage. I never got around to trying Autolites.

Re: Backfired .....
 

I got All the plugs our ...DAMN ..its hell being old .....fat too ... :rolleyes: anyway .. #4 and #8 look a little wet ...and more carbon ...like they have not been firing consistantly ? I am going to run compression check today and go from there ....by the way this motor had NGKs BR6FS the starboard motor had Champions RV8C .. keep ya posted

Re: Backfired .....
 

Good news .....
8 170 7 170

6 168 5 168

4 168 3 165

2 168 1 168

So I will get new plugs ...... I installed new fuel filter .... Shop gave me some fuel additive by Mercruiser ....try it ? or go ahead and put new cap and rotor ?

Re: Backfired .....
 

Seeing there were/are different types of plugs in there now, that's the first thing I'd do.

Re: Backfired .....
 

How old are the plug wires? If stock, you might consider changing them too. A good (scary) way to check them is at night, very dark, no nearby lights, and a spray bottle of water (old fastastic bottle or something like that). While running, mist a little water around the wires and watch for lightning.

Re: Backfired .....
 

got it all back together but didn't fire it off ....I cant remember if we put wires on the port motor last time we had it out ....I think we did ...june ...but I know even new set could have a bad wire ...Wires are better than old days and also ignition voltages are higher .....could be though ...I am happy about the compression though ....had enough valve issues in 04 .....

Re: Backfired .....
 

Be sure to run the blower first! :eek: :D

Re: Backfired .....
 

Now THAT would be a good idea. :D

Re: Backfired .....
 

went out about an hour late today .....did one WOT for about 1-2 mins ...no backfire .....maybe we got it ...maybe we didint .... :drink:

Re: Backfired .....
 

Think positively "Grasshopper", for postive thinking yields positive results.

(sheesh, I'm starting to sound like Cuda) :D :D

Re: Backfired .....
 

That's what I call a hell of a woman :rolleyes:

Before you get too involved, check the fuel filter water separators. A few drops of water will cause a stumble or backfire at WOT.

Good luck

Re: Backfired .....
 

new plugs ..fuel Filters ...Fuel additive ....and 1/2 quart og Marvel mystery oil ....I'll need to really get it hot and make serval runs .. but so far is ok .....I was stoked about compression being ok .... If I pull those motors one more time I'm putting "wing nuts" on em .....

Re: Backfired .....
 

My dad used to refer to it as having a zipper on them. :p

Re: Backfired .....
 

It's the Marvel Mystery Oil that did it. I don't know whats in that stuff, but it will do anything but grow hair on a bald head. :evilb:

Re: Backfired .....
 

Okay, this may sound strange but my 454 Mag had the same problem and the only thing that fixed it was a new coil. I know it sounds weird but it worked. Just ask Gordo.

Re: Backfired .....
 

Coil cap and rotor were next ....member messaged me about reving the motor up to 3000 rpm and then throw a rag over the carb ....let it almost choke out then remove the rag ....let it clear up then do it a cpl more times ....sez it unclogs everything ......

Re: Backfired .....
 

I think sometimes changing the coil fixes a problem, because they are actually fixing a bad connection, or coil wire.