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1997 Honda BF50 Bogging down after only 10 hours on carb rebuild

N

Noah4200

Contributing Member
So i did my carbs a few months ago and the boat ran great for 3 outings. It was giving a sputter at trolling speed every minute or so and I turned the fuel screw to 2 turns out and it went away (suspect it was a lean sputter?). Today after trolling around the creeks for a few hours it started the sputter again so i tried to get on plane and it was cutting out badly could not do it. I let the motor cool and switched fuel tanks and didn’t help. Got progressively worse to the point i barely made it back to the dock: The fuel is only 2 weeks old ethanol free with treatment in it. I did notice the middle carb seems to have a slight amount of fuel leaking from the float bowl seam/drain area (weird bc all new gaskets) but it didn’t seem to be coming from the vent (stuck float). Upon bringing it home i lowered the motor to flush and it started and ran great with a higher idle. Revenge slightly did not bog out but of course there was no load. Could be bad fuel (but unlikely) or moisture in filter but l looks like i’m going to have to pull apart the carbs which is crazy after less than 10 hours. Any ideas and would i have to get all new gaskets again? The look nice and new/green still. Btw i let the motor cool down on the water just too rule out an issue with heat (air leak/ignition coil) and it did not help.
 
Hi Noah,

I'm not the resident 50 hp guy here. I've never touched one. That would be Alan Hicks. But he hasn't posted up in a while so I thought I would answer to let you know you're not being ignored.

It sounds to me as if you probably didn't get the idle circuits completely clear or, depending on the level of contamination, there are stubborn contaminants "sluffing off" in there and gummiing up the works....so to speak.

The low speed and high speed air jet circuits are often overlooked by first timers. You didn't say your experience level but no offense intended.
Did you give those a really good hosing out? Compressed air definitely helps along with an adequate amount of cleaner.

Also, I always (well, I used to anyway) prop open the throttle and blast each orifice....idle, transition and high speed....in a "backflushing" routine. I would do that several times alternating from forcing fluid to exit the orifice by charging the circuit to placing the cleaner straw tip directly over each orifice and forcing flow BACK through the circuit. You typically need a spare straw with a 90° bend at the end to hit them all.

That technique works best if the idle mix screw and jet set tube are removed so that you can block each inlet both separately as well as together to increase flow in sections of the circuits. Blocking both together is an effective way of backflowing cleaner through the low speed air jet and take contaminants out via the front of the carb flange.

I use my thumb and fingertips to block while holding my tongue "just so" 🤔

Hopefully your low speed emulsion tubes (jet-sets) are pristine and not cracked. Very hard to clean or even reliably inspect. I have a 50× comparator scope to see them clearly and I finally gave up cleaning them and bought new for my builds.
NOT CHEAP but neither was my time. You must not overtighten the retaining plug for the emulsion tubes or you risk cracking them.

I can't emphasize enough how critical it is to treat that small oring at the top of the jet tube with utmost care. If it doesn't seat, it will haunt you. Use Vaseline when installing.

As far as your float chamber gasket leak, I'm guessing that you will likely find a scrap of old gasket or a minor defect in the flange that didn't allow the new gasket to properly seat.


As far as reusing the gaskets or the orings I wouldn't but many do and get away with it.
If I were going to reuse gaskets I would consider carefully applying some fuel proof sealer that Permatex sells in an effort to ensure I don't need to tear down again.

Here's hoping you get her sorted out and running smoothly again.
 
thanks for your response. I don’t remember the O-ring being that tricky. What in specific is the problem? Also would the vaseline clog the fine holes? Would i need to get new orings again even though they are new? I replaced the emulsion tubes and everything else and really cleaned it thoroughly. I did not replace the floats though. The difficult thing is I cannot test the boat without launching it.
 
If you pinch or stretch/stress the oring putting it in dry, it won't seal. YES! if you slather a big ol' GOB of Vaseline on it that would cause a problem. But you only need a tip of a toothpick amount smeared on for lubrication.

No, you don't have to do ANYTHING that I suggested. If you don't think the carbs are your issue then don't let me convince you otherwise. I am OFTEN WRONG from 2,000 miles away.

As matter of fact, after rereading your post, it is odd that it started and ran good in a barrel after you got it home. That might indicate that you have a cylinder dropping out after extended low speed operation. That could very well be an intermittent ignition system problem. I don't know.

Good luck with it.
 
jgmo said:
If you pinch or stretch/stress the oring putting it in dry, it won't seal. YES! if you slather a big ol' GOB of Vaseline on it that would cause a problem. But you only need a tip of a toothpick amount smeared on for lubrication.

No, you don't have to do ANYTHING that I suggested. If you don't think the carbs are your issue then don't let me convince you otherwise. I am OFTEN WRONG from 2,000 miles away.

As matter of fact, after rereading your post, it is odd that it started and ran good in a barrel after you got it home. That might indicate that you have a cylinder dropping out after extended low speed operation. That could very well be an intermittent ignition system problem. I don't know.

Good luck with it.
Click to expand...
No i totally agree with you and thank you! I doubt i would have developed a serious ignition problem from one trip to the next. It has a brand new flywheel and the coils look pretty good. Does testing the coils with a multimeter even show a heat problem? Anyway, in hindsight i didn’t keep up well with fuel treatment. Also the times i drained the bowls the pressure of the fuel tank expansion due to hot and cold temps forced fuel back into them i think? One time i added treatment then didn’t even run the motor to get into the carbs lol. So lesson learned. I feels just like my lawnmower or dirt bikes when they have carb issues. I’m going to follow your advice and really do a stellar job this time so i can at least rule this out. Then be religious with storage and treatment. These carbs seem very sensitive to fuel varnish. I backed out one of the leaking float bowl drain screws and the smooth tip had brown corrosion all over it so i’m sure they are somewhat varnished. I will wait to order parts until i have them apart. Also and this is a big one my fuel lines look terrible!! Dry rotted and gummy. I’m getting all new lines as well (this could be definitely it). I squeezed the bulb and fuel got on my hand so they are in bad shape. My dad will be here in 10 days for a fishing trip so i have to get this right.. I will get parts ordered ASAP. I’ve done it once already so should be much easier no ancient gunk to clean off surfaces. So should i get some more of those orings? What about new floats? Thank you!
 
I've probably cleaned over 200 of the BG carbs with the accelerator pumps (mid 2000 and newer) and replacing that oring sort of became a religion with me because I feel that it burned me so many times when it wouldn't seal.

I rebuilt car carbs for nearly 40 years and, yes, these little Keihin Honda carbs are the most finicky little things I've ever encountered. Such small passages make them super sensitive to contamination. Ate my damn lunch until I figured them out. BTW...the much beloved Mike Boyd (hondadude) that helped so many people here over the years, talked me into buying the Honda Marine Carburetion Manual and I'm glad he did. He used it so it was great for me as a resource.

Very good call, in my opinion, to replace those fuel lines. Anything sluffing off inside of them will sabotage all your efforts.

No, I don't think ohm testing the coils will flag a bad one that is breaking down. Only an oscilloscope will do that. But Honda coils are pretty reliable and typically fire or they don't. Hard to say though.

I have learned to be distrustful of spark plugs. New ones included.

On an engine this old, I would want to know valve lash, compression and leak down rates if I'm having issues. It's just the basic assessment creed of mechanics.

I would also do a decarbon treatment as there's likely some build up. It can really kill combustion at lower speeds and idle.

Water works just as good as most cleaners to break carbon up but I've got nothing against Sea Foam or Techron ll in the tank or Berrymans or BG 44 spritz either. Just depends on how much you want to spend.

If you haven't sealed the plug boots with dielectric grease, you should. That's good protection but also makes doing a basic cylinder cut-out test very easy.

Doing that carb passage "backflush" I explained before can really make a difference and possibly teach you things about how the fuel flows that you might not yet know.
 
jgmo said:
I've probably cleaned over 200 of the BG carbs with the accelerator pumps (mid 2000 and newer) and replacing that oring sort of became a religion with me because I feel that it burned me so many times when it wouldn't seal.

I rebuilt car carbs for nearly 40 years and, yes, these little Keihin Honda carbs are the most finicky little things I've ever encountered. Such small passages make them super sensitive to contamination. Ate my damn lunch until I figured them out. BTW...the much beloved Mike Boyd (hondadude) that helped so many people here over the years, talked me into buying the Honda Marine Carburetion Manual and I'm glad he did. He used it so it was great for me as a resource.

Very good call, in my opinion, to replace those fuel lines. Anything sluffing off inside of them will sabotage all your efforts.

No, I don't think ohm testing the coils will flag a bad one that is breaking down. Only an oscilloscope will do that. But Honda coils are pretty reliable and typically fire or they don't. Hard to say though.

I have learned to be distrustful of spark plugs. New ones included.

On an engine this old, I would want to know valve lash, compression and leak down rates if I'm having issues. It's just the basic assessment creed of mechanics.

I would also do a decarbon treatment as there's likely some build up. It can really kill combustion at lower speeds and idle.

Water works just as good as most cleaners to break carbon up but I've got nothing against Sea Foam or Techron ll in the tank or Berrymans or BG 44 spritz either. Just depends on how much you want to spend.

If you haven't sealed the plug boots with dielectric grease, you should. That's good protection but also makes doing a basic cylinder cut-out test very easy.

Doing that carb passage "backflush" I explained before can really make a difference and possibly teach you things about how the fuel flows that you might not yet know.
Click to expand...
You are helping me so much man! It always seems to act up before my dad comes. The engine only has like 1000 hours but is old. I did new flywheel ( magnet delamination) timing belt and tensioner and valve adjustment and compression was like 194 +-2 i think. No leak down tho. So these little rings what are the symptoms you had when they were not seated exactly? Also what is the best decarb method you prefer? I presume getting a fuel hose without the fitting and sticking it in a bottle of some cleaner while underway…stopping letting soak then run it hard or something? I will NEVER let plain fuel sit in these carbs more than a few days again!
 
jgmo said:
I've probably cleaned over 200 of the BG carbs with the accelerator pumps (mid 2000 and newer) and replacing that oring sort of became a religion with me because I feel that it burned me so many times when it wouldn't seal.

I rebuilt car carbs for nearly 40 years and, yes, these little Keihin Honda carbs are the most finicky little things I've ever encountered. Such small passages make them super sensitive to contamination. Ate my damn lunch until I figured them out. BTW...the much beloved Mike Boyd (hondadude) that helped so many people here over the years, talked me into buying the Honda Marine Carburetion Manual and I'm glad he did. He used it so it was great for me as a resource.

Very good call, in my opinion, to replace those fuel lines. Anything sluffing off inside of them will sabotage all your efforts.

No, I don't think ohm testing the coils will flag a bad one that is breaking down. Only an oscilloscope will do that. But Honda coils are pretty reliable and typically fire or they don't. Hard to say though.

I have learned to be distrustful of spark plugs. New ones included.

On an engine this old, I would want to know valve lash, compression and leak down rates if I'm having issues. It's just the basic assessment creed of mechanics.

I would also do a decarbon treatment as there's likely some build up. It can really kill combustion at lower speeds and idle.

Water works just as good as most cleaners to break carbon up but I've got nothing against Sea Foam or Techron ll in the tank or Berrymans or BG 44 spritz either. Just depends on how much you want to spend.

If you haven't sealed the plug boots with dielectric grease, you should. That's good protection but also makes doing a basic cylinder cut-out test very easy.

Doing that carb passage "backflush" I explained before can really make a difference and possibly teach you things about how the fuel flows that you might not yet know.
Click to expand...
I want to also add that i synced the carbs also. But always felt like the motor shakes a lot at idle. I want to say it didn’t shake as bad before my overhaul but maybe i’m mistaken
 
Well, 194 compression is, at least I think it is....very close to NEW spec? I don't have the SI so I can't be positive. But with compression that high, leak down is not going to be an issue.

A damaged oring or clogged jet tube can create no start, hard start and very poor idle for the most part. But keep in mind that, at transition and wide open throttle, each circuit, including the idle circuit, contributes fuel. So, to achieve full power, you don't want even a very tiny leak from a stretched oring. That's why I don't like reusing them. I have reused them before and it works....sometimes. But since I had a parts room, I kept them in stock so I wouldn't have to.

Doing a decarb on a multi cylinder carbed outboard doesn't lend itself to doing it the way I like to which is spritzing water or Berrymans into the intake at 2500 rpm. So, that leaves doing something like a high dose of Sea Foam or BG or Marvel Mystery Oil in the tank. If I were going to do that, I would look at some YouTube videos for ideas because I don't have experience doing it or dosage quantities written down.

I think you might benefit by doing a cylinder cut out test. It might reveal some useful information.
 
So my worst nightmare has happened..Boats.net has not shipped my parts it’s been a week and they have been saying their system is down since friday and not responding. My dad will be here wednesday so i am going to have to clean these carbs without new gaskets or rings. If i find a part that’s in bad shape i might possibly find it at a place in JAX an hour away. I rebuild them recently so the gaskets are all new i can jest be careful and use permatex if needed. I’m most worried about the little orings. You guys think this is doable? if i lived in the amazon or something this would be life!
 
See if you can find an industrial oring shop nearby, take your old one with you. It’s likely metric. We have a place in a small town nearby, may also find them at a hydraulics shop.

I don’t like RTV in a carb, you tend to have small bits break off and travel somewhere bad unless you are very careful. You almost new gaskets may be reusable if you are careful when taking them apart.
 
ok i blocked the passages and cleaned everything. Going to use a tiny bit of silicone grease on the o rings. So when i seat them is there any trick and how tight do i want the caps..they were pretty tight before. i don’t want the cap to come loose. Also the fuel screw and float drain look to be same size oring is this correct?
 
Ok everything is back together…new fuel lines and going to get new REC 90 gas. What is the best fuel treatment? There def was some gunk in the float bowls
 
I really like sea foam, been using it 20 years in all my carbs. Go heavy on it where you’ve have issues, it won’t hurt. Use double what’s recommended and give it a good high rpm run under load, if all goes well.
 
So i’m out here and it’s still bogging when trying to plane. it’s running really smooth and quiet down low though. i stupidly didn’t check the plugs but i’m wondering if one or more is just gunked up. we had been extended idling for multiple trips without much WOT and i turned the fuel screws to 2 1/2 turns to try to combat the trolling sputter. turned them back to 1 turn now but the plugs may already be fouled. i’m almost certain it can’t be fuel or carburetor at this point. we are just anchored up fishing
 
So after thinking for awhile…the boat ran worse and worse the longer we ran it. At first it was just planing but the warmer it got it started sputtering even at idle to the point i was worried we would get home. For brief moments rpm’s would raise and it would sound ok for seconds. So i’m thinking electrical…
 
Running the sea foam tank now and it was already running bad as soon as i started at the dock. So whatever is wrong its just getting worse no matter what. I’m almost thinking pull the carbs off again tonight and go through them again. We are on our 3rd seafoam soak now and came very close to getting it to plane. It seems to bog around 3500. Pulling individual plug wires just makes it run worse. Worse part about this is that i cannot test it in the driveway.
 
Ok did another plug drop and #2 made no difference. Tested with a plug and NO spark. Swapped coils and still nothing. So does this mean i need a new CDI?!?
 
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