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Old 20 August 2019, 09:32   #1
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BF50 running on 1 cylinder? Help!

I have two 2007 Honda BF50's that I bought a year ago to convert my hurricane 530 back to twin engines (from a single 75 4s merc). Engines are carbureted 3 cyl remote control type. The previous owner ran the engines for me before I bought them and they ran pretty well. Both engines were in remarkable physical condition, bought as a pair(sequential serial numbers), fresh water use only and no sign of use at all really aside from some heavy sand abrasion on skegs/propellers(sandy river use). from the props up they look like they just rolled off the show room floor.

Before mounting the engines, I wanted to do a full service on them and make sure they were in good running order while they are still on the stands.

Trouble set in on the first engine I started.

I bought a new fuel tank, hose and fittings, put a new in-line fuel filter in the engine, and filled the tank with fresh fuel. connected a brand new set of controls. When I turned the key the engine started instantly but it ran like crap, bouncing around on the stand. Pulling the plug wires one at a time revealed that it was firing on the top cylinder only (pulling top wire shut the engine off, pulling wires 2/3 had no effect).

Next I opened the drain screw on the carb bowls, lots of clean fuel present in all 3 bowls, no dirt or debris visible.

I then pulled each spark plug one at a time, grounded it against the block and turned the engine over with fuel disconnected. Good spark on all three plugs, plugs dry, no sign of excess fuel in the cylinders 2/3.

Decided to run a compression test at this point just for piece of mind. 185psi on all 3 cylinders for a luke warm engine block. Just about perfect, major relief!!!

Re-installed the plugs, reconnected fuel line, primed the bulb and started the engine again. Engine now ran perfectly smooth on all 3 cylinders for about 2 minutes!!! I goosed the throttle a few times and raised the rpm for about 30 seconds. When RPM's settled to idle speed it started running like crap again Pulled the plug wires one at a time again and found only firing on cylinders 1 & 2 this time. No sign of life from cyl 3. Shut engine off and restarted, only running on cyl 1 again now.

Drained all three carb bowls again, lots of fuel in all bowls.

So what should I do now ribnet experts? Tear the carbs apart and give them a cleaning? Ordered new gaskets today just in case. Seems like I might have intermittent clogging of jets on cyl 2 & 3 carbs? I don't think the floats are sticking because the bowls are always full of fuel. I started this project later then I wanted, did not mean to let fuel sit in carbs for a year but life gets in the way. Previous owner said fuel was stabilized but who knows.
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Old 20 August 2019, 13:52   #2
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Swap the plugs with the running one and try it again. (make sure you mark them ) Sometimes they break down under load.
It's an easy check to do before you start pulling things apart.

Use fresh fuel.
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Old 20 August 2019, 14:07   #3
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Good theory, thanks!

I have a fresh set of plugs to go in but did not want to soil them if it was running rich or lean. Old plugs looked fine but you never know. New ones going in now!

I did use fresh fuel , straight from the pump.

Stand by...
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Old 20 August 2019, 15:45   #4
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Next thing to check could be HT leads. Stu makes this stuff look easy.


A carb strip down could be on the cards, but rule out electrical issues first.
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Old 20 August 2019, 15:56   #5
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Good call HT leads
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Old 20 August 2019, 17:50   #6
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Spent an hour trying to get it to start at all. Had pulled safety lanyard out by accident.

Finally Swapped in fresh Honda plugs. No joy. Still firing on two cylinders. 2 cylinders sounds slot better then one!
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Old 21 August 2019, 02:27   #7
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Those carb hondas are a pain if left with old fuel in. My money would be on the carbs, a full strip down with every jet removed then a couple of cycles in an ultrasonic bath & a squirt through wit carb cleaner & a blow with an air line would be my next move. If you dont have a bath then a soak in thinners while stripped for a day & then a good squirt through with carb cleaner & a blow out with an air line.
There are several tiny drillings in those carbs which easily get blocked as fuel evaporates and leaves a residue.
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Old 21 August 2019, 04:51   #8
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I'd be leaning towards ultrasonic cleaning the carbs too, but the plugs was worth a try.

If you want to check the HT leads, try firing it up with the cowl off in the dark.

Sometimes it's visible if you have a dodgy lead.
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Old 21 August 2019, 06:33   #9
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Well carbs it is I guess. I do have access to an ultrasonic bath. Might as well do all 6 carbs while I'm at it.
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Old 21 August 2019, 09:33   #10
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Is it better to disamble clean/soak in carb cleaner then do ultrasonic cyle or the reverse? I'm thinking carb cleaner first, ultrasonic second, then blast with air so I know that all the carb cleaner is fluched out before re-assembly. Never cleaned a carb before.

I have the Honda carburation manual, anyone know where to get a BF50 service manual .pdf?
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Old 21 August 2019, 13:01   #11
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Try this for the service manual:
Boatinfo - Honda Service Manual for BF35A, BF40A, BF45A and BF50A


Whatever you do, Just make sure the carbs are thoroughly cleaned and balanced.
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Old 21 August 2019, 18:44   #12
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Thanks. Boatinfo worked! Great site.

All set to go now.
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Old 25 August 2019, 10:19   #13
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Well think I found the culprit. Just popped the cover screw of carb #3 (the one that never fires). See pictue. Jet seems to be totally blocked with some sort of christals around the emulsion tube.
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Old 25 August 2019, 10:30   #14
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Totally blocked
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Old 25 August 2019, 10:34   #15
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Wow, but it's good to find something positive, I bet you feel better already!
Now the thorough clean up.
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Old 25 August 2019, 10:53   #16
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Yes I was starting to doubt myself as until I pulled the jets out the carbs looked so clean it looks like is never been used! Like taking apart a brand new engine. I expected to see the bowls full of gunk, but nope, perfectly clean.

I guess the bowls were drained but fuel stayed sitting in the jet tube
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Old 02 September 2019, 15:04   #17
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Well this is a head scratcher.

Took the carbs all appart, soaked them in ultrasonic cleaner, cleaned the jets out extra with carb cleaner and blew everything out with compressed air. Reassembled with new gaskets.

Same result!!!!!!! Still only firing on top two cylinders! Drained carb bowls again, All full of nice clean fuel.

So I have perfect compression, thoroughly cleaned carbs, new plugs, new fuel- But no bang in bottom cylinder.

Pulled all plugs again, grounded plugs and turned engine over to confirmed I have spark on all three cylinders. All good!

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Old 02 September 2019, 15:43   #18
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I've done exactly the same in the past and had to do it all again but eventually cleared it. That solidified fuel or whatever it is can take a lot of breaking down.
Just a thought can you substitute one carb for another to see if the fault switches with the carb
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Old 02 September 2019, 16:02   #19
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I agree with beamishken, you have to be persistent for efficient cleaning of the tiny drillings in the carbs it doesn't always work first time and yes swap the suspect carb and see if the problem transfers to another cylinder,
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Old 02 September 2019, 16:15   #20
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Agree with above... you don't always get a carb sorted 100% on the first clean even if visually perfect.

Other thing... did you just soak the carbs in the ultrasonic fluid or using an ultrasonic machine? If the former you may need to get them done in the proper machine.
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