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2000 Honda BF50AY Timing/Carb Issue?

N

newboater67

Contributing Member
I recently installed a new tach and charging coil. I ran the motor for about an hour just fine. Coming back in it started sounding like it was missing and sputtering or coughing at low rpms. It idles high, around 1100-1300 rpm which I verified with an inductive timing light on all 3 cylinders. It coughs thru carb #3. I pulled the plugs and it's fouling plug 3. Looks black but feels more like gas than oil. I checked the timing marks and they are right on, but when I look into the cylinder bore with a fiber optic inspection camera and bring cylinder 1 to its absolute highest point, I'm 3 teeth past the timing mark on the flywheel. Am I being too critical since I can actually see the piston? I'm thinking the timing is right. The flywheel is pinned so there is no way to move the flywheel 3 teeth. TDC for cylinder 1 will always be at the same point on the flywheel. I checked the compression and got 184-184-186. The Honda service manual calls for a minimum of 199 but I'm hoping 184 is good for a 13 year old 4-stroke. Leak down results were 2.5%, 5% and 5% at TDC with an OTC leak tester. Carb sync looked balanced but I didn't right down the numbers. I haven't messed with any carb adjustments yet. I've had the boat a year and also recently switched from E10 to REC90 non-ethanol gas. I drained the tank down, and changed all the gas lines, filters and plugs when I switched gas. I did not change the fuel line/primer bulb. I removed the muffler and feel gum buildup on the bottom near carb 3. Should I leave the timing alone and tear down and clean the carbs before doing anything else?
 
First. You have put together a very complete list of data.

As long as the cam timing mark and the flywheel timing mark both align in the proper spot, the timing is probably fine.

I am not sure how you took compression, but if the carburetors are not completely to full throttle, the compression will be off some. So the compression is probably ok. The leakdown looks good.

You did not say if you checked the spark or if you performed a cylinder drop test. Since you have a timing light, put it on each spark plug wire and watch the light. Make sure each cylinder blinks about the same rate. If one blinks twice the rate as the others, then you could have a CDI problem.

If you have not changed the spark plugs, have you at least moved them to different cylinders to see if the problem follows any pattern? It could just be a bad spark plug.

If all the above checks, yes it could be the carbs. I assume that you have drained the carburetors into a glass jar to check for water or debris. If not, that should be done.

Since you have pulled the muffler off of the front of the carbs already, check the air jets in the front of the carburetor. The sneezing sounds like it running lean, the spark plug indicates it is running rich...not consistant.....so it is anybody's guess.

I just had one today, that was very similar to yours....dark spark plug on #3 and everything else checked out. We did the carbs about a year ago and the customer faithfully uses PRI-G fuel treatment and uses his boat a lot...so I was pretty sure that it was not the normal carb goo problem. If I turned the idle mixture screw out about 2 turns farther than it should be, the cylinder kicked in.

We removed the screw and shot some brake clean and compressed air into the hole and debris came out of the front of the carburetor and was flushed out through the drain in the muffler. The engine smoothed out and saved a good customer a complete carb job. He picked up some debris that blocked the air jet and caused it to run rich in that cylinder.

Maybe you will get that lucky.

In other words, I like to eliminate every other possibility before removing the carbs.

Mike
 
Thanks Mike.

I'm hoping I'll have time to run the checks tomorrow or I may be doing them in the dark anyway.

I put in new plugs just before the test run. I pulled them, rechecked the gap and moved them to different cylinders. Still fouls cylinder 3.

Will double check the firing. I didn't drain the carbs. Will go through your list step by step.

I'm new to this, so everything I've done so far is from reading the Honda manual or lots of time on the computer reviewing posts, compiling info, buying test equipment and running the tests.
 
Well, at least as far as I am concerned, you are approaching it the right way. Sounds like you are very methodical. I am sure you will fix the problem in short order.

Mike
 
Thanks, it's part of the service mentality. You also have to take some credit for it though. I've spent a considerable amount of time reading your posts and searching the net to find out what the tests do. I've been repairing medical imaging equipment for 40 years. Funny thing is I didn't want to be a mechanic and didn't have money for college so I went into the military to learn electronics. Turns out it's still 60-70% mechanical.

Thanks Again,
Bob
 
That's interesting! I went into the Air Force with an Associate Degree in Electronic Engineering Technology, maxed the tests, and was slated for a cool Electronics job.....until I got to basic. They made me a Vietnamese Linguist.

Once out, I finished my degree and did the Engineering thing and several related jobs until I retired. I was hired a few years ago to mechanize the business's inventory. Once I did that, I gradually started helping out when they had electrical issues (which are more than you think in a boat). Things just evolved from there.

I used to tell the "real" techs at work, that I would handle the electrical and related items until I get to the grease, then the rest is up to them. That did not last very long.

I bet the medical imaging has made some major changes over those 40 years. The electrical side must have been pretty basic then, compared to the electronics and software driven devices of today.

Mike
 
Too Funny!! I'm retired Air Force. Did my first 6 as an inertial navigation and radar tech and my last 14 in biomedical maintenance. We covered every piece of equipment from one end of the hospital to the other and anything you could find in between, from ICU and surgery to bed pan washers. Went straight into medical imaging when I got out and have been doing it for another 21.

It's weird how things come back around, gave up the grease and washing with gas, for 120 degree ramp temperatures and planes too hot to touch in the middle of no where. Went into medical and steam sterilizer burns, and hear I am wishing I had learned a lot more about engines and carburetors.

The medical imaging is all digital detectors and black boxes now. They still have circuit boards but the chips or solder connections are so small you couldn't replace them if you wanted to. Oddly enough though, I still have some of my parts from the IC and transistor days when we used to troubleshoot to the component level. When we have to break out the schematics it's not good. There is one board in the CT scanners I work on that has 32 pages of 11x17 schematics, but you can usually figure it out with block diagrams. I might actually have to break out a scope a couple times a year. I think it's been calibrated more times than I've use it in the past 5 years.

I'm sure you've seen the same changes in the electrical ignitions and everything else that goes on and is monitored in the motors since NMEA started. I had to laugh one day when I was picking up some parts at a Honda dealer in Port Charlotte and he was checking out a very big Evinrude with a laptop and a trained ear. I'm pretty sure he was just confirming what he thought he had already heard though. At this point I know enough to be dangerous, but hope to learn quickly. I really didn't know squat when I bought this boat used a year ago, or I would of opted for a newer motor with NMEA output. Can buses can cause some weird stuff too though.

I haven't had a chance to check the motor yet and it may have to wait until Sunday now. Having neighbors for dinner Saturday and the wife has a new honey-do list. It's killing me. I want to play with the motor. Thanks for your help. I'll definitely let you know what I find out. I'll probably be asking for more advice.

Take Care

Bob
 
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