So the backfire/popping is back

First weekend with the boat. Some may recall here when we did the sea trial on the boat, one of the engines was popping/backfiring around 2/3 throttle and up. The surveyor thought it was the port engine, wrote it up as so. Also noted starboard engine tech was erratic/optimistic..seemed to read higher than actual engine RPM. After a while it would calm down.

We asked for it to be taken care of prior to closing on the boat. The yard replaced the distributor cap, rotor, (said they found an issue there) and plugs (they replaced because 2 were fouled a bit likely from the issue with the disti cap), compression check (all reasonable), they said they took it out for a test run..WOT..zero issues. It was put on the sellers tab. if the compression check came back poor I would have backed out of the purchase.

So we close on the boat Friday, stay on board the night, before lunch the next day I took her out for a run..started up fine, headed out fine, started pushing on her...the popping/backfires were still there. Grrrr!

Today, took it out again, this time paying more attention...started up fine, headed out, started pushing throttles forward...she started popping earlier than 3200rpm. I think it started before 3k. This time my ear seemed to think "wait..is that the starboard engine?" So I pulled back on the port engine, and pushed the starboard engine forward. Popping. Pulled back on starboard engine, pushed port forward. Smooth, no probs (only briefly ran to 3800 or so). Pulled back on port..pushed starboard..popping around 3k again.

By now I'm red with anger. based on surveyors expertise and report...we battled for the yard to address the issue with the "reported" port engine. Now it ends up being the starboard engine, what are the chances of having the yard do the same for that one? Now I'm worried starboard engine!

I'm kicking myself for not really digging into it more when we did the sea trials, asking the hired captain to do each engine one at a time to 100% determine which engine was at fault.

On the way back today from the short run...I verrrry slowly pushed the throttles forward, she did get up towards 3600rpm before doing some backfiring. So I pulled back. I'm fearing the backfiring will cause some damage back there somewhere..crack an exhaust or something.

Who owns the boat ?

scoflaw said:

Who owns the boat ?

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We closed 3 days ago, Friday...so me 'n wife.

Well you are where you are no point dwelling on past mistakes.

it sounds like the port engine could've used a tune up so perhaps start simple and there on the starboard. Cap, rotors and plugs aren't that difficult if you're handy. At the very least pull the plugs and check the conditions. If you're not talk to the yard about it. Sometimes we think the worst when it's a simple problem.

I would replace the dist. cap / rotor / plugs on the STB engine also. Arching or moisture in dist cap can definitely be the cause of what you are describing. If you can't tell that they have been changed, I would also replace the spark plug wires. This will also get you a good maintenance baseline on both engines. As far as the tach, there is a knob on the back of it that you dial to the the # of cylinders (4, 6, 8). The contacts get corroded sometimes and cause the tach to act erratically. Find the knob and turn it through the settings once or twice, then leave it set on 8.

Don't stress about it, you have a nice boat, but it's 21yrs old, bound to be a few things to work out, does not sound like anything that is not easily fixable.

I had similar backfiring/popping when i advance my throttle beyond 2700 rpms. Based on the conditions of my plugs it pointed to a fuel issue. I swapped my port and star fuel pumps and that was exactly what it was. I had a bad low pressure fuel pump. Not sure if it applies in your case as i have the CF3 modules but worth a mention.

Cap, rotor, and plugs. Cheap and easy. At least both engines will be in the same state of tune.
Then check each engine, one at a time. Backfiring and popping could be loads of things, so let's start easy.
Like Bill K says, you got a nice 21 year old boat. It's gonna need "stuff". Don't sweat it, it's part of boat ownership. Plus you are on one of, if not THE, best forums to get help. There are lot's of people on here who can help.

I had similar issues with an engine, boat had twin Crusader 454s. Spent weeks and lots of $$ on new parts until finally giving up and dumping some Sea Foam in the fuel. That fixed it right away (after 20 min running), was a fuel issue. From then on, I start there first. Later, genset issue turned out to be bad fuel line, ran fine off a 1 gal. jug. Same thing, start with the fuel.

Happy to report, had the yard give the starboard engine a tune-up, new cap, rotor, plugs, wires...took her out for a 2 hour cruise yesterday ran like a champ! Backfire/popping..non existent!

Congrats. Must be huge relief....

YeOldeStonecat said:

Happy to report, had the yard give the starboard engine a tune-up, new cap, rotor, plugs, wires...took her out for a 2 hour cruise yesterday ran like a champ! Backfire/popping..non existent!

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It's possible the port engine backfire was covering up the starboard engine backfire so that effort wasn't really wasted. Now you have two engines with maintenance baselines for the price of one. Good deal in my book!
Glad you didn't get stuck with an albatross!

surveyor should have put in new plugs when he took out old ones for compression test. he sounds alittle inexperienced IMO

aquaholic said:

surveyor should have put in new plugs when he took out old ones for compression test. he sounds alittle inexperienced IMO

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Our surveyor wasn't an engine surveyor, he was boat only and they do basic engine lookover. We used Chris Nebel which we got his name from a search of both these forums and another boating forum.

The yard head mechanic did the compression test.

Could be that both engines were back firing a bit and back then only the port one was ID'd as the culprit.