Checking each Cylinder? Pulled Plug and RPM Drop?

[enginesilo]

I went to check out a boat and I did the spark test where you remove one wire at a time while the engine is running to see if the RPM's drop down.

I tested this with all 4 and one of the cylinders seemed to drop a tiny bit, but not as much as the others. The cylinder that did this was the top right side cylinder if you were sitting in the boat driving.

The boat was idling around 1100 to 1200 rpm's or so and when I removed the 3 others it would drop about 100 to 200 rpm's. When I pulled this top right cylinder spark wire it would drop maybe 100 or so. You could hear it change, but didn't change as much as the other 3.

I put the spark plug cap close to the spark plug with a pair of pliers and you could hear the strong spark jumping hard and making the link between the cylinders and the engine would then pep up a bit and rev a little higher, but again it wasn't as noticeable as the other 3.

The engine is a 1999 or a 2000 (Still confirming) Johnson 115HP model # J115PLSSB, which I think is a carbureted model. I opened the cover and it was immaculate, looked almost brand new inside and ran great overall. This was the first time it ran after being winterized all season. It took a good few times to get it cranking, then once it fired up it ran like a dream. It idled perfect and started without any throttle, just a little choke if any.

Think I might have an issue here? If I buy I will probably have it surveyed, but before I get to that point and tips you guys can share will be helpful.

 

[guy74]

Re: Checking each Cylinder? Pulled Plug and RPM Drop?

Thats a 2000 model engine. Could be that the carb for the cylinder that doesn't make as big of diference has a partially plug idle jet (not producing it's 1/4 of the total power at idle.)

 

[F_R]

Re: Checking each Cylinder? Pulled Plug and RPM Drop?

I just don't think you have a real issue based on that test alone. I'd back it up with a compression test and if the cylinders are about equal, consider it OK.

 

[enginesilo]

Re: Checking each Cylinder? Pulled Plug and RPM Drop?

Thanks for the replies guys.

I checked the compression and it was a perfect 120 across all cylinders. This engine literally looked brand new when I opened it up. All the wires were nice and clean, the block was nice and painted, and it looked almost new. The owner told me that he maybe used it 30 or 40 hours if he had to estimate.

I was thinking that also about a possible carb jet being clogged or something like that. Think something like SeaFoam would clear it out?

 

[iwombat]

Re: Checking each Cylinder? Pulled Plug and RPM Drop?

It's possible that a heavy dose of seafoam, the kind you'd use for a decarb, might clear it out. I wouldn't count on it though.

Any time you're buying a used motor, count on a waterpump replacement and carb rebuild as part of the cost of taking ownership.

 

[enginesilo]

Re: Checking each Cylinder? Pulled Plug and RPM Drop?

It's possible that a heavy dose of seafoam, the kind you'd use for a decarb, might clear it out. I wouldn't count on it though.

Any time you're buying a used motor, count on a waterpump replacement and carb rebuild as part of the cost of taking ownership.

That definitely isn't the way I want to start it off, but I understand your reasoning. What does it typically cost to rebuild carbs on an engine like this?(A guesstimate is fine, the mechanics charge $100 per hour around here I think)

By the way, are there 2 carbs total, or 4?

Is the water pump the mini impeller that cools the engine? If so I changed one in the past, are they fairly easy to do?

 

[iwombat]

Re: Checking each Cylinder? Pulled Plug and RPM Drop?

Carb rebuild kits are about $35 each - give or take. If you can change an impeller you can certainly rebuild a carb.

Water pump kit (including new impeller) is going to run you around $40.

Both jobs are good "intro to maintaining your own outboard" kinds of procedures.

 

[enginesilo]

Re: Checking each Cylinder? Pulled Plug and RPM Drop?

Carb rebuild kits are about $35 each - give or take. If you can change an impeller you can certainly rebuild a carb.

Water pump kit (including new impeller) is going to run you around $40.

Both jobs are good "intro to maintaining your own outboard" kinds of procedures.

Wow, the rebuild kit price is cheaper than I thought it would be. How many carbs does this engine have? 2 or 4?

How difficult is it to rebuild a carb? Does it require a pop off pressure tester, and then hard core tuning of high and low speed screws? I am talking from Seadoo jet ski engine experience so this may not pertain. What is entailed in a rebuild?

 

[iwombat]

Re: Checking each Cylinder? Pulled Plug and RPM Drop?

Again, I'm not familiar with your year/model, but I'll assume 2 carbs. I could be wrong.

Rebuilding involves removal, soaking, and blowing out with compressed air. It also involves removal and cleaning of the fixed jets, replacement of the float valve and float. The only remotely tricky part is removing the core plug and cleaning the idle jets as well as making your own jet removal tool. All the jets are fixed and there's no adjustments to be made.

As far as carbs go, it couldn't be easier. This isn't a Rochester Quadrajet.

 

[enginesilo]

Re: Checking each Cylinder? Pulled Plug and RPM Drop?

Sounds like it might be easier with a manual. Any publisher's that put out good manual's for the Johnson engine's? Definitely haven't ever made my own tool to do a job so that may be out of my league if I am sort of new to these engine's and mechanic's as a whole? I've pulled jet ski engine's, removed and reinstalled carbs, intricate exhausts, but never got nitty gritty on the insides.

I probably wouldn't rebuild the carbs right away if I wasn't concerned and honestly and hoping I don't have too somehow. I haven't bought the boat just yet so I will be taking this into consideration, but again I would rather not have to do this right off the bat. Maybe i'll do a water test and do this test again beforehand, and see if it seems to clear up. I may also have it professionally checked by a mechanic so they could tell me immediately. Just hate to have to pay out right away.

Keep the feedback and comments coming

 

[iwombat]

Re: Checking each Cylinder? Pulled Plug and RPM Drop?

Well see, here's the thing . . .

Both are vital systems to the overall health of the engine and, personally, I like to know everything is up to snuff.

Waterpump (and thermostats) keep the engine cool.

Carbs keep the engine lubricated (aha! two-stroke, remember?)


Running an outboard without either in proper working order can mean serious problems ahead.


Making the tool requires an old screwdriver and a file (or bench grinder makes it quicker)

 

[enginesilo]

Re: Checking each Cylinder? Pulled Plug and RPM Drop?

Where can I get a good OEM Manual that would also cover rebuilding if I had too?

About how long do you think it would take a mechanic to rebuild if I didn't have the time and just paid to have it done?

 

[iwombat]

Re: Checking each Cylinder? Pulled Plug and RPM Drop?

You can get OEM manuals here (should be link at the top of the forum). Don't know if they'll have 2000 though. Might be new enough that you need to get one at a dealer.

 

[tashasdaddy]

Re: Checking each Cylinder? Pulled Plug and RPM Drop?

your manual will be a Dealer Item, your carb kit OEM #438996 aat $22.79 or sierra kit
http://www.iboats.com/Sierra_18_724..._row.73--**********.831819548--view_id.174129

from what i can decipher you need a kit for each carb. total 2. for starboard, and port carb.

http://shop2.evinrude.com/ext/index.aspx?s1=bf6ad09c53cead335fcfd8a6471c0f7f

 

[ottertail]

Re: Checking each Cylinder? Pulled Plug and RPM Drop?

It is not uncommon for cylinders to effect the engine rpms differently. If the engine runs good and has good compression don't worry about it. Some times boat owners create more headaches and worry than the engine does!

How many people on this site are actual certified technicians?

I see a lot of people offeriing help in this forum but some of it is running the owner in circles.

 

[enginesilo]

Re: Checking each Cylinder? Pulled Plug and RPM Drop?

Thanks for the replies guys. I guess i've heard both sides of the story. I am hoping I don't have to do the carb rebuild this season, but if it has to be done it has to be done.

I am going to plan to do the test again, and try to rev the engine once the boat is in the water to see if it clears it up. I am also going to get some new plugs since it was coming out of a fresh winterization and might just be all fogged out.

The local mechanic said it would cost about $200 with parts to rebuild the carbs if I needed it done so that doesn't sound like a bad deal.

I think I am going to head back up, water test it, maybe have it surveyed (or might skip this since I already did the tests and if it needs the carbs done I have a guy locally that will rebuild for the cost of the survey), and bring it home.

 

[iwombat]

Re: Checking each Cylinder? Pulled Plug and RPM Drop?

"It is not uncommon for cylinders to effect the engine rpms differently. If the engine runs good and has good compression don't worry about it."

think this comment is right on and it encouraged me to go back and look at the posts. After going back and looking at the original posts again, this nonsense about carb rebuilds all started from "will seafoam clean out a gunked up carb". Well, looking at your tests and observations a little more closely, I don't think you have a gunked up carb. Those leading questions can get you into trouble

If you're comfortable doing carb rebuilds then I'd say it was worth the time, effort and cost to do it yourself for peace of mind. Given what you observed in the tests, I don't think it's worth paying someone else to do it. Honestly, I don't think you really have a problem. I just operate on the better safe than sorry principle if it's financially reasonable to do so.

 

[guy74]

Re: Checking each Cylinder? Pulled Plug and RPM Drop?

I agree that you probably don't really have a problem, and that all cylinder won't produce the same drop in rpm when the spark is disconected. As said above, proably not worth the $ to have the carbs rebuilt. I always go though the carbs and waterpump on any motor thay is new to me just for the piece of mind, doesn't cost much if you do it yourself. I always look at it as protecting my investment. I'm not a "certified technician", but I've had to fix their "certified" messes more than once.

 

[enginesilo]

Re: Checking each Cylinder? Pulled Plug and RPM Drop?

Thanks for the replies guys.

Thinking this isn't a problem and am going to try to run it. Since it doesn't seem too expensive or problematic I am going to buy the boat.

Now I am trying to figure out the best way to test the Lower Unit in my other thread.

Thanks guys, I will keep you posted!

 

[tashasdaddy]

Re: Checking each Cylinder? Pulled Plug and RPM Drop?

there again we are getting the cart before the horse. the only way to tell is get it in the water, and a test run.