'98 Honda BF50AW - Runs at high Idle - Dies at Idle

I'm at a complete loss. I have no idea how you could have matching vacuum readings on all 3 carbs, and come up with different idle speeds for each cylinder some how? They're attached to each other with the crank shaft. How could you possibly do that?

Engine rpm should not wander much. Maybe just a few rpm (less than 50rpm let's say?). An occasional miss, nothing regular, is acceptable, as long as it's not happening frequently.

What happens when the engine is warm, and you put your fingers across 1 of the carbs at a time (blocking any air from entering), while looking/listening for the engine's reaction? If it speeds up, you have something set wrong, or your carb overhaul needs to be reviewed ON THAT CARB. IF everything is normal, working correctly, the engine should slow as you cover each carb, one at a time, to test.

If it needs the choke to start when warm, your idle mixture settings are probably too lean. To be honest, if you aren't able to tell any difference in the way the motor idles from 1 turn, to the 2.5 turns I suggest, that doesn't sound too good. You ARE keeping the mixtures exactly the same, right? When you change one, you change the others to match?

Cold start, first start of the day, you will very likely need to use the choke. It's not REAL unusual for it to stall once or twice, until you get used to hitting the choke when rpms start dropping too far. That messing around shouldn't last more than a minute or 2.

As far as adjusting the choke solenoid, if you can't see the marks from where it was set originally, you just want to confirm it's working correctly, closing the choke plates completely when engaged electrically.

Acid test, when you THINK you have it perfect, throw it in the water and go for a ride. It should idle easily at 900 when not in gear (engine warm), and stay running in gear for hours or when docking/maneuvering in and out of gear. Wide open it should stay smooth but wide open rpm will be dependant on what prop is on it. My target rpm is usually about 5500 or so.

I blame the RPM differences on the digital gauge. It was connected (alligator clip) to each spark plug wire near hard plastic connector to spark plug. When I changed from 1 to 2 to 3 I would get differences mainly from carb #2. These readings would go vary between about 50-100 rpms.

How is it that dash tach has one overall reading of RPM and each spark plug has its own reading?

Is the dash tach accurate? It is Honda OEM.

BTW....what tool do you use to get accurate RPMs, on each cylinder, on these outboards....aside form the dash tach?


Where would I block the air on carbs...remove silencer cover and block manually with hand?


When I adjusted idle mixture screw it was one at a time...not all 3 set at same. I adjusted one and waited to see if there was a change. That is when I did not see much change. Since I did not notice a change, I set back to 1 urn out. At end, I did match all at 1.5 turns out.


It does not need choke to start when warm....only a little throttle at fast idle lever (NOT fully pushing lever back to engage choke).


From 1 turn out...if I close...screw in (lean) it does begin to idle rough. Between 1 and 1.5 it seems to run smooth.

I'm so new to this, it was all just a blur at this point!!!

The fact each piston is connected to a single crankshaft makes it impossible for any difference in rpm from cylinder to cylinder. You can take that to the bank. Do what you want with that digital tach that's telling you otherwise.

I use the boat's tach, or no tach. Been doing this kind of thing most of my life, and these 40's and 50's in particular for a while now. Don't really need a tach.

Idle mixtures should be matched. Start with fully closed and open each of them one turn if you insist (I would go 2.5 turns out). ANY adjustment from there is done exactly the same across all 3 carbs. If you get lost, start over again at fully closed. No guessing....

Yes, block the carb with your hand (I use 3 fingers, my hand won't fit ) I generally install the air box/muffler when I'm done. And it's cheating like hell, but I just use the top bolt to hold it on. Haven't had an issue yet!

Thanks Alan--

I feel better knowing that the RPM would be the same across each cylinder. I trust in your expertise. I would not have been able to get this far without your help. I also appreciate your prompt responses!! Many thanks!!

Although It appears to be running good.....

I will go back and start all over again. I want it as correct as I can get it.

Here's my plan:


1. Remove Silencer cover.

2. Start engine and let it warm up.

3. Use boat's dash tach (RPM is currently to dash tach at about 1000RPM) and set Carb #3 at 950 RPM (+ - 50)

4. Starting from closed, set each carb's idle mix screw at 2.5 turns out.

5. Test each carb by placing hand/fingers over air intake portion of carb and see carbs reaction.

6. Synchronize carbs.

Thought's on plan?

Sounds good from where I'm sitting.

My only concerns are generated with your comments regarding wandering rpm, and no difference in the way it runs from 1 -2.5 turns out. Both seem odd.

The wandering RPM was that digital tach I was using that connected to spark plug cables. Reviews of that tach state that it jumps way too much for accuracy. My dash tach did not ever jump or was erratic.....steady always.

I will note the change in the carbs behaviors as I move from 1 to 2.5 turns out

Update #3

Completed steps 1-6 from post #64.

Findings:

2: The engine started this morning (with choke applied) on first try. Used high idle lever (no choke) for a little throttle, for about one minute or less, then motor idled to about 980RPM.

3: RPM per dash tach set at approx. 980RPM

4: Set idle mixture screws at 2.5 out from closed. I closed screws and noticed engine wanting to stall. Unscrewed to 2.5 turns out. This was performed on ALL 3 carbs. Let it run like this for several minutes. To verify that there was a difference between 1 and 2.5 turns out, I turned ALL screws back in to 1 turn out and engine idle a little slower; perhaps not quite as smooth as 2.5 turns out. Closed screws completely and returned to 2.5 turns out and idle increased slightly (vs when they were at 1 turn out)....to approx. 1000RPM. Engine is running very smooth at this setting.

5. When I covered air intake at each carb, one at a time, engine wanted to stall. This happened on all three carbs.

6. Synchronization was still pretty accurate from update #2. Fine tuned them a little more to within approx. 18mm of each other. Carbs 1 and 2 were adjusted to match carb #3.


NOTE:

The engine is running excellent! Starts quickly, idles smooth, place in gear and increase RPM to about 2500-3000, and return lever immediately into neutral, engine returns to idle with no hesitation. Very, very smooth running engine!!! I am VERY HAPPY!!!

Sounds like you may have it!

Next: water test....

Fingers crossed all goes well....

First....I need to thank you Alan...THANK YOU!! If it were not for your tips, advice, answering all of my beginner carb 101 questions, having patience with me, etc......I would never have had the confidence to do this.

Your support has been priceless.

I have experienced 99% success the first time thanks to you! Fingers crossed for the water test (last 1%)....coming soon!

I also want to THANK jgmo for his assistance throughout this carb rebuilding process. He hasn't been here recently, but I'm sure he has his reasons. I hope that he is also able to read this post soon and see that I have had success with my first rebuild.

Again, I can't thank you enough for your assistance!

THANK YOU!!!!


After water test.......

On to other Honda outboard maintenance items! More Honda outboard 101 questions coming soon to a Honda outboard repair forum near you!

You are most welcome. It's not like I didn't have any questions when I got into this....

Standing on the shoulders of those before you.... while saving yourself a 6-800 dollars repair bill in the process!

Hopefully you can share some of your experience one day, with the next hot dog that comes along wanting to get his hands dirty and try his hand at a carb rebuild.... -Al

SoCalAngler,

Oh, I've been lurking but I've seen enough of Alan's posts that I knew he would take good care of you. He knows way more about the multi-carbed outboards than I ever will.

So glad it's going great for you and I will still be watching to see how the other 1% goes. I really can't imagine that it would be anything but great too!

Giving you a big pat on the back for hanging in there and gettin'erdone!

Not everyone is as tenacious!

THANK YOU jgmo!!! Like I said, with the two of you providing assistancce I would not hav been able to do this job.

Thanks again!

BTW....hope you are feeling much better/stronger these days!

Yup. I should have mentioned that. Seeing a project like this through to the end takes a certain amount of "grit". Good job....

Update #4....

Took to lake today. Approx. 15mph winds and choppy. Temps about 50F.

Choke applied and fired up immediately. Idled at dock. Idle was low at 500RPM. I used high speed lever to keep idle up to about 900-1000RPM.

Let warm up for approx. 10 mins. Motored out to lake. After 10-15 mins cruising at 5-10mph, I opened her up gradually to about 4400RPM at 21mph. This was directly into wind/chop. Ran to other side of lake thinking I would run downwind on the way back to launch ramp. Ran great for 5 miles at 4400RPM at approx. 20-21mp, non stop. After 5 miles I reach the other side of lake. I reduce speed and cruise around at approx. 10mph. Did this for about 10-15 mins. I increased speed again, as less chop on that side of lake. Get her to 5900 RPM and 27MPH. As I reduced speed from 27 mph, there was backsplash into boat's splash well, splashing upper part of motor.

Point downwind and run for 5 mins at approx. 5-10 mph. Sat there with engine idling for about 15-20 mins while I fiddled with new Lowrance fish finder. Idle was still low at around 600RPM. NOTE: At home, after carb rebuild, idle was set to 1000RPM. I thought idle would increase as motor warmed up, but it did not.

I then decided to run downwind. I increase speed gradually and motor is running rough...sputtering as I increase speed/rpm. Did this for about 2-3 mins. I thought it way be water in engine compartment as there was splashing of water all around splash well of boat and hood of motor did take a few splashes. I reduced speed back to idle. Sat there for 3-5 mins idling holding high speed lever at 1000RM. Increased speed gradually and opened her up to 5900 RPM and 27-28mph. She ran great!!! Ran another 4-5 miles downwind without another sputter. I ran a few more miles at 5000RPM and not a sputter. I slowed speed down to idle. No issues, other than still a low idle now at about 600-700RPM.

Decided to head back to dock and call it a day. At dock idle was 600-700RPM. Checked engine compartment in parking lot and there were only a few drops of water at lower portions of case. I dried them.

I was very happy with the way she ran, Except.....the sputtering. Even though it was a short time, I did not like it.

What can that sputtering have been?
Why was idle down so low even though I set it at 1000RPM at home? I did set idle when temp was approx. 68F-70F.

Next steps?

Thanks!

No clue on the sputtering, but that low idle would be no big surprise here. The increased back pressure on the exhaust, which is now 2' underwater, along with the cold lake water, could both cause that. Just use the idle set screw on the bottom carb to increase the rpm's a bit. I shoot for about 850 rpm (+-50 or so). Too high makes it difficult to shift, so I usually favor a little low, ans long as it's not stalling.

Then go run the hell out of it!

Sputtering, as long as your fuel supply isn't contaminated, should clear itself up.

Thanks Alan! Is the brief sputtering something to be concerned about? Potential carb contamination or not fully cleaned? Fuel is fresh and does have the Honda OEM branded Stabil added.

I'll check idle again next time out and adjust at lake as necessary.

With my described running results, do you believe carb rebuilding was a success? I'm just concerned about the brief sputtering....perhaps a bit paranoid!!

BTW.....I agree....I do want to run the hell out of it!!!!

Go run it like you stole it. If the sputtering if it doesn't clear up after running it for a day, THEN address it. No clue what it might be.


Assuming that clears up, it sounds like your carb job WAS successful! -Al

I agree...she needs to be run!!! It was pretty windy and choppy yesterday. Felt like I was in the ocean back in my sailing days!

I'll take her out again later during the week.

Update #5:

On the lake again....02-19-21. Smooth surface, wind free conditions. Beautiful!

She's running great! Increased idle ever so slightly, on lake, after she was warmed up (now at 950 RPM). Ran her all over lake. Fast, slow, idle, etc. Not a one hiccup!

Prop appears right on the money......27mph at 5900-6000rpm. This is with two adults aboard and 3/4 full fuel tank. I have Doel fins and they get her up on plane at about 14mph.

I removed seats to replace pedestals, so unable to run her until special order pedestals and seats arrive.

Questions:

Since tank is about 1/2 to 3/4 full and I DID add Honda OEM Stabil additive.....

1. How long can gas sit before there are issues?
2. I plan on running her again in approx. 3 weeks That will be 4 weeks between use. Is that too long for gas to sit?
3. If necessary....I can install old pedestals/seats to run her again next weekend.
4. Should I run her in tank at home, or drain tank and put gas in my truck (I assume it is safe in my truck), or drain carb bowls, or ?

Bottom line.....I do NOT want to take any chances on bad gas leading to carb issues!!

Thanks!

That all sounds great to me! Congratulations!

In my opinion, since you added a quality fuel stabilizer, letting it sit for a month, with treated fuel on board, is perfectly acceptable as long as the vent can't take in any rain water.

The only caveat to that is that "life happens" and sometimes a month can suddenly turn into 6 or 8 or ???....depending on whatever unpredictable circumstances overtake us. (just ask me)

As long as you keep that in perspective, it's going to be just fine.

I take it you're running her out on Diamond Valley....
Very nice impoundment when the wind isn't up.

Have FUN!

The Doel fin, and other similar whale tale devices, WILL crack that plate they are mounted too. A good 30% of the 40-50hp Honda's I get have been welded or are cracked/missing pieces of that plate. A suitably sized 4 blade prop will work similarly, without long term breakage issues.

If you added the recommended amount of Stabil, and have run the engine long enough to have some of that mix in the carbs, you SHOULD be good to go. If there's ANY doubt, rather than guess, draining the carbs. It only takes a minute...

Great!

The doel fin issue is a concern. I hadn't heard of such issues.

I did not compare speed required to get on plane, with/without, the new 4 blade prop I recently added. Perhaps that is a test I should do next time I take her out. If not much difference, then I'll ditch the doel fin.

If you decide to keep the fin. at least pull it on occasion to check the cavitation plate for cracks.

Alan, I'll check that out each time I return from an outing. More than likely, I will remove it, especially if the 4 blade prop gets her on planer close to same MPH as with doel fin.

Maybe eyeball it frequently, and pull it a couple times a season? Cracks start out small, and they're easily fixed by a good welder at that point....

I wonder if the potential for damage (cracks, welding, broken off pieces, etc.), are even worth the return?

Not in my book, but it's your boat!