Engine backfire question...

[tolly28]

Another engine question here. We seem to have a new miss/ backfire from the port side engine that developed and worsened over the weekend. The story is long, so I’ll keep it short. You guys are a great source of info, so I thoought I would check with you all!

My engines are Chrysler 318s. Both have recently new caps, rotors, plugs, plug wires, and coils. Both engines had the points eliminated with Ignitor ignition modules before we purchased the boat. Carbs are Carter AFB. I have fuel filter/ water seperators before the fuel pumps and in line filters before the carbs.

When we were leaving Anacortes. On Thursday, the port engine backfired a few times and did not want to rev up. I backed out of it, opened the hatch and gave then engine a once-over. Fired it back up, flogged the rowers and she jumped up on plane without a problem. Both engines ran great for entire trip that day. The next morning we ran out to do a little fishing. Again, as I initially applied throttle, the port engine backfired and did not want to rev. Backed out of it, and after a couple of tries to get on plane, both engines ran fine for the day. The next morning when we left for our next destination, same thing. Once on plane ran fine with the exception of a couple backfires during the trip. And then the story gets interesting…

As we pulled into fisherman’s bay in a 20 knot or so wind, while turning into a slip, the STARBOARD engine suddenly without notice died. Dead. Would crank, but would not fire. It was quite the ordeal as we were unable to turn due to the wind which was taking us away from the dock. Fortunately we were able to fend off of some pilings and a dingy dock, otherwise we could have beached… Eventually I was able to get the engine running and we were able to get into a slip. Initially, I was thinking bad fuel, given the backfiring of the other engine. After a trip to the parts house, new fuel filters were in place. The engine started and ran for a few minutes, then died and would not start. I now decided to look at ignition, discovering that there was no spark coming from the coil. After putting a volt meter on the coil, I discovered that there was only .25 volts to the coil. If I disconnected the coil, I had 12 volts, but the second I connected it, voltage would drop. After some looking around I realized my ignition switch had given up. I could wiggle the switch and wires and the engine would die. To get us home I ended up “hot wiring” the coil. Now when trying to get on plane this engine would die apparently starving for fuel. Alleviated that problem by reinstalling a fuel filter which I think was not quite seated properly and sucking air. After that, the starboard engine ran great, as usual. I’m hoping a new ignition switch and maybe rewiring that circuit will do the trick.

Back to the PORT engine which now will not rev under load at all without backfiring and would not clear up like before. The engine purrs at an idle, hold good oil pressure and does not smoke.

When all this craziness started with both engines, I replaced both dist caps and fuel filters.

I’m thinking some sort of fuel problem and wanted some input from you guys. Any ideas?

Sorry for the long post…

THANK YOU!

[bradvo]

Steve, I am no motor head but when I read this it sounded like it started when you replaced the Distributer caps? Was there moisture there? I would have maybe given a call to the fuel dock also as , but you came out of a fuel dock that does have high turnover of fuel. I also remember a post that Talman put out about a bad fuel supply that was mainly up north from the union 76 supplier? maybe a long shot but I do not know where you have been filling? hope you get it worked out.
Brad

[SomeSailor]

Might be a silly one... but on the motor that was backfiring and stumbling:

- plugs aren't all fouled up?
- timing hasn't been messed with?
- have a centrifugal distributor? (spring broke?)

Backfiring sounds liek electrical or spark related usually. Timing of the spark at the wrong place... maybe a pre-mature spark (carbon on a plug) or corrosion on a rotor bug somewhere?

Sounds like you have a couple of things bitin' at your ankles there.

How was the trip?

[Salmon Troller]

If it will start, run, & idle, then my guess is like Somesailors, the distributor has a problem. We have Chrysler 360's. The prior owner advised that he had replaced both distributors as the advance mechanisms had taken a "set" and would not permit the engine to go more than 2800. No clue of this was the advance springs, corrosion, or whatever.

[heymagic]

New parts aren't any real guarantee of reliability....bad side of the engine parts world. The backfire could be anything from a bad cap to electronic ignition crapping out. Could also be going lean as you throttle up. Did you examine the contents of the old filters for water? Even a bad electric tach can cause problems. What brand of spark plugs ? If Champion then immediately go buy 16 NGK or Autolites and change them out. Look in the dist caps for signs of moisture or a sooty, flat black line between contacts. Also watch the coil towers for arcing under load as ytou are running. Gene

[Seapuppy]

might as well add my two braincells here.....
check the torque on the carbs too...but it sounds electrical to me..not being there to listen and get my hands dirty...I would also look at the coil.........
it's really hard to come up with a real answer since I'm not able to feel, see and listen.....I think I'd go and get all new plugs..distr. cap..rotor...wires and then also check the advance and timing ....if your still getting this...then I'd seriously look at the coil, spark module and resister(if they are there) and then work up to the switch..but you changed that...so then it's gotta be wiring or worse timing jumped....which leaves timing chain...but that's really a rare case...so then my 2 braincells fire off to bad gas.....stick some of that heat stuff aka water scavanger stuff into the tank.......
I think that would be my process to narrow it down.....only thing left would be burnt valves...but it's too intermittent for that .....so gotta be either electrical in nature or gas related.......

[tolly28]

The coil and cap are new. When this all started getting crazy I changed the cap. I didn't change the rotor, though. The resister is bypassed for the igniter modules.

The cap I pulled off looks fine, without any moisture or signs of tracking.

The wires are pretty much new within the past few months.

I was just at the boat, and at the dock it runs great. Out of gear it revs right up, smoothly without missing a lick.

One thing that I noticed when coming in the other day was that my ancient lighted engine synchronizer was only reading the port engine (the starboard one was the one that died suddenly on me). I cleaned up all of the connections to the synchro, and still does not read stbd engine. So, I'm guessing it has gone out. I'm wondering if this might be a component to the issue????

I've talked to a few guys that think the backfire is fuel starvation related. I'm looking at both. I will get bak down there and check the plugs and timing.

I have the next week off from work due to a sprained ankle...line of duty injury....Doctors orders! Not too bad that I can't hobble down the ramp to the boat, though!

I really appreciate the feedback and will keep you all posted!

[tolly28]

also, to answer a question, we had topped off our tanks at Cap Sante (about half on each tank) just before leaving. Last fuel before that was Edmonds when we were coming home from opening day. I'm pretty sure Cap Sante's fuel comes from the refinery next door.

[heymagic]

It's not the rotor, nor timing chain. Could be an issue with the synchronizer, most likely a failing plug or fuel related- going lean under a load. One thing to try, needs two people, is to remove the spark arrestor and close the choke plate as someone else accelrates the boat. Don't slam it closed but start at about 1/2 closed. That will pull more fuel into the carb and if that stops the backfire then the most reasonable place to start would be carb. It doesn't take much fuel or spark to rev an engine without a load on it.

[tolly28]

Made my way back to the boat and checked a few things. Plugs look good, timing is good. I reinstalled the canister filter to make sure it was sealed up and cracked the fitting on the inline filter and had fuel- no noticeable air. Checked out the distributor- mechanical advance looks ok, springs intact. Timing advances on marks with rpms, too.

I'm going to eliminate the synchronizer to rule that out.

I hope to get out and run it soon to see if anything has changed.

Thanks for the help!!

[Prizzo667]

If you have eliminated the plugs and fuel supply, and know that your timing is advancing with engine rpm, you need to look into the secondary ignition. When you change a distributor cap, the wires need to be removed. Any chance that the connectors were damaged on removal? Sounds like an easy job but we are talking about what is possible here. I have inadvertantly done things like this and chased my tail for hours because I did not start from scratch with the basics. A fine mist of water from a squirt bottle will give the plug wires an easy path to ground that would normally only become apparent under load. Watching the lightning show is pretty cool too.
Weak coils will also behave this way. Switch the coil from one engine to the other to find out if it is ok without buying any parts. An ohm meter will also tell you if the secondary winding of the coil is an open circut. I have seen engines run well at idle and have an internal open circut in the coil.
Good luck tinkering.
Paul 8)

[tolly28]

Here's an update:

Trying to narrow down what was going on I did the following:

1. Reinstalled fuel filters
2. Checked inlet screen at carb: clear
3. Checked timing: good
4. Pulled a few plugs and checked: looked good, small amount of carbon
5. Checked mechanical advance mechanism: moved freely
6. Cleaned rotor: small amount of carbon on outer tip
7. Eliminated ancient Judson Engine Snchronizer, which suddenly stopped reading starboard engine.

Saturday at Fisherman's Bay I added some fuel conditioner that Island Marine Center reccommended (called 2+2). Both fuel tanks are at about 1/4 right now.

SO, this morning I took the boat for a run, and she ran fine. When I applied throttle, she jumped up on plane like a ski boat. I ran around in the bay, doing several starts and stops without any problems whatsoever. So maybe one of the above did the trick. I'll try again in a few days and see if anything changes.

[Salmon Troller]

I'm glad you solved it (hopefully). These deals drive me nuts when I can't actually confirm the cause. I feel so much better when I have the broken part in my hand or at least find where I installed something backwards. Best of success!