Engine missing - Making popping sound ?

[gnrboyd]

I have a 1993 50 Hsp Evinrude. I pulled it out of the garage today and fired it up in the driveway. While idling, it will occasionally make a popping sound. The sound sort of has a muffled pop noise that kind of like a dud firecracker. I'm not sure if that is officially called "missing" or not. ?? Once in a while it will die when it pops. When it does pop, tach usually drops 300-400 and then gently rises back up. The idle was up around 1300 but I turned down the idle screw one complete revolution and the idle is now around 900. (What is the standard rpm setting at idle while on muffs? As I recall, you should set it higher on muffs as it will drop when in water.)

Last year, I had a problem with it dying once in a while as I was idling at the dock. I didn't get a chance to use it much last year so I didn't deal with it. Anyway, I think it is probably related to the above as I do recall it doing that last year as well.

Does this sound like a common problem? Any ideas would be appreciated.

Thanks

 

[SparkieBoat]

Re: Engine missing - Making popping sound ?

RPM around 1100 in the drive way on muffs, should be around 900 in the water. you need fresh fuel, clean carbs, new champion plugs, check coils with spark gap tester, also replace any old dry rotten fuel lines.

 

[gnrboyd]

Re: Engine missing - Making popping sound ?

Ok, I will turn the idle back up a hair. I have fresh fuel, the carbs had carb kits put in 2 years ago, plugs were new last spring and I only used the boat 5 days on water, the fuel lines are in good shape.

Looks like I need to get a spark tester. The coils "appear" to be in good shape. (no cracks..and they look pretty new.) I do have one spark plug boot that has a small tear in the rubber near the end of the boot but isn't near the connection. I taped it with black tape so I don't think that has anything to do with it.

One other thing... it takes a minute or two after starting cold before the missing starts. Not sure if that helps the diagnosis or not.

Thanks for your input.

 

[tx1961whaler]

Re: Engine missing - Making popping sound ?

The mild popping while on muffs can be normal for some engines. There is no back pressure and they pop sometimes. If it does not happen on the water, then I really wouldn't worry about it. The idle should be adjusted on the water.

 

[SparkieBoat]

Re: Engine missing - Making popping sound ?

your carbs can become gunked up just by letting fuel sit in them for a few weeks, especially if the fuel is not treated with something like sea foam or stabil. the fuel drys out leaving the oil to dry into a gunky mess. I would take a look at the plugs also...2 stroke motors are rough on them, even with low hours they can get fouled out. if you notice one plug noticeably blackened, I would replace them all, and check that coil to see if it is working properly.

 

[gnrboyd]

Re: Engine missing - Making popping sound ?

I had fuel stabilizer in the gas when I used last used it. (last year) I will buy a spark tester and start with that. If it's ok, I will run over to the lake and test on the water before I do much more. Maybe tx1961whaler's point of this being normal on muffs is all that's going on. (With my luck, it's something more...)

Thanks everyone... I will update this post when I find out more. (Feel free to add any comments though.)

 

[tal]

Re: Engine missing - Making popping sound ?

I'll share my recent experience I had with my 85 120hp and same issues. First, the smaller engines I've owned in the past do not appear to be affected by back pressure or idling on the muffs as much as the larger engines. I've never had a 50hp idle up high like the bigger motors do. That being said, you should still set the idle in the water as the manual says.

I had the same "pop" or "huff" out the exhaust. I was sure it was an electrical issue since I redid my carbs 3 times, all new fuel line, etc. I borrowed my friends CDI adapter to check voltage on the power pack. Everything checked out fine. I started diagnosing more by unplugging the cylinders one at a time. I noticed one of the cylinders, when unplugged, would completely smooth out the engine. I found I had a bad plug wire on that cylinder by using a timing light to inspect spark. I was sure I found my problem but with the bad wire replaced, and perfect spark, I still had the miss/pop sound.

I ended up pulling the carb for that cylinder off one more time. I went through it and it was completely clean. I had an extra carb bowl gasket laying around so I replaced that gasket, nothing else changed. I installed the carb and started the motor to find the miss/pop/huff was gone. Long story short, it was the carb after all. It took me a few months messing with it every other weekend and towing it to the lake for test runs. Other than it smoking a little at startup and idling a little high (have it set up for it trolls at low speed better) my old motor runs good now. Long story short, do not overlook your carbs no matter how many times you think you cleaned or rebuilt them.

 

[gnrboyd]

Re: Engine missing - Making popping sound ?

tal.. Point noted about carb.... I appreciate your input.

I'm not much of a mechanic but thought if the spark checks out ok (after I buy a spark checker) then I will try running some engine tuner through the carbs before I start taking things apart. Thanks for the input.

 

[SparkieBoat]

Re: Engine missing - Making popping sound ?

what fuel stabilizer did you use? I would take it to the water and run it with a separate fuel tank, get a 6 gallon tank and put about 2 gallons of premixed gas in it, then add a can of sea foam and run it for a little while, that stuff really dissolves residue well.

 

[gnrboyd]

Re: Engine missing - Making popping sound ?

I had Seafoam in the tanks last year but nothing near the ratio of 1 can to two gallons.

More to the story... I bought the boat in the fall of 07. The sellers had previously had a major problem with the vro pump that required the head be rebuilt. (Yes.. I am aware of the debate on disconnecting the VRO.) The only reason I bought the boat is because I got a really good deal on it. The compression checked out so I figured even if the motor didn't hold, I could still sell the boat/trailer and get all of my money out of it. It was a calculated risk that has paid off for the most part.

The marine shop repair ticket indicated that double oil should be ran for first 3 tanks (18 gallons) during the break in period. I did that but noticed it didn't really like to idle very well with that double oil. I didn't run it much at all in 07 since it was late in the year when I got it. It took the 08 season for me to run the full 18 gallons of the double oil. Last year, I only ran it 5 days on the water which was about 10 gallons. I had Seafoam in the tanks trying to help clean out the double oil. (I don't recall the ratio but perhaps I didn't run it heavy enough.) It did idle better with regular ratio oil (using VRO) but it would still stall/sputter and occasionally die when idling. Other than that, it ran fine.

Anyway, the reason I mention this is that I wonder if all that double oil is still causing problems. I will get some engine tuner and some more Seafoam and see if that helps.

 

[SparkieBoat]

Re: Engine missing - Making popping sound ?

I only suggested a concentrated amount of sea foam to clean the carbs...running the extra oil could have fouled the plugs..only thing I could think that could be hurt from too much oil. You need to just troubleshoot the list of things eliminating ignition and compression...and if it will run out good run it some...but make sure that you do not have any cylinders running lean this can damage your piston/cylinder.

 

[99yam40]

Re: Engine missing - Making popping sound ?

What is being described is a lean sneeze. Go through the carbs or pay some one to do it. Lean running will eat pistons.
You need to run these motors often and keep the fuel fresh.

 

[gnrboyd]

Re: Engine missing - Making popping sound ?

Update: I bought a spark checker and that seemed to check out ok. The plugs look ok. I put about a 1/4 can of seafoam in a gallon or so of gas and ran it in the driveway but it didn't seem to help. (That probably wasn't enough for a deep clean...but that was all the Seafoam I had on hand at the time.)

At first, it didn't sputter/miss. After about 10-15 minutes, it started doing it again. It seems kind of random. It will idle fairly well and then all of a sudden will start sputtering.

I then took it to the lake and ran it. I was able to adjust the idle down a little (1200 driveway/1000 lake) but anything below that and it would die. The motor seems to run fine other than at idle.

Sparkieboat mentioned to make sure non of the carbs are running lean. How can I tell? Is this just by sound? Is there a lean adjustment screw on the carb? I don't have a manual (yet) so I am not sure where it would be.

I think I will replace the fuel line also and see if that helps any. It isn't hard or cracked but I suppose that could have something to do with it as it is several years old.

I also probably need to do a deeper clean of the carbs than just running a little seafoam through it. By the way, can you use regular carb cleaner or is that harmful to an outboard?

Thanks

 

[SparkieBoat]

Re: Engine missing - Making popping sound ?

you will need to remove and clean the carbs to make sure they are working ok, you can do a visual inspection while running and look for and even spray pattern on all carbs. I also think it would be a good idea to do a compression test on the cylinders.