BF50 running on 1 cylinder? Help!

[johnrambo]

Ok good to know this had happened to somone else!

All three carbs are slightly different unfortunately! Can't switch them.

I do have my second twin engine I could pull one off, but that one has not been cleaned yet and will probably exhibit the same symptoms.

[johnrambo]

I let them soak in ultrasonic degreaser in a heated medical grade ultrasonic machine for 45 minutes each. Dirt stopped floating out of the orifice's after about 20 mins.

[Fenlander]

>>>let them soak in ultrasonic degreaser in a heated medical grade ultrasonic machine for 45 minutes each

Sorry to query that... wasn't sure if you had access to the machine or just the fluid.

[Milgrip]

Diagnosing engine problems is a process of elimination. I would try switching that suspect carb with the other engine to see if it makes a difference.
(you know how quick and easy it is to get the carbs off by now)

[Fenlander]

>>>I would try switching that suspect carb with the other engine to see if it makes a difference.

Agree.

Having access to that second carb set on the other OB I'd have to use them to assist this diagnosis. You could run that engine up first and check... even if not perfect... that it runs on all cyls then swap the carbs over and see if the engine with the problem is then OK.

In fact you could do the double swap and put the carb set you have been working on over to the other engine and see if the same cyl fails to fire. Then you really would have pinned it down to that carb.

Only on a 10hp single carb OB but earlier this year I had a very similar deposit around the long jet as you show in post #14 but after a devil of a job getting it to run right following what I thought was a good clean found deposits also in the blind passages of the carb. It was a mixture of hard crystals and soft gunge which resisted solvents and compressed air finally needing poking through with soft wire praying it wouldn't break off in an inaccessible place and scrap the carb.

It actually took three separate strip downs and cleans with unsatisfactory running in between before it was clear. I didn't have access to an ultrasonic bath but having seen the nature of the deposits I cleared out not sure it would have helped much.

I know when those deposits got in the fuel system and it was only left for a month before they dried/hardened to give me all that hassle.

[johnrambo]

Thanks guys, some good ideas. New plan: I will try and get engine 2 going. If that runs well, I will try switching the carbs, if that works I will re-clean carb #3. I suspect carb #3 on engine 2 is just as bad as the one on the first engine, they have lived the same life.

First I think I will try switching the coil packs over from engine 2 to 1, that is a pretty easy switch to make and should rule out bad coil problems.

Swapping the carbs is actually quite involved, have to unbolt the intake runners from the head, have to pull the whole intake/carbs/air filter assembly off as one unit. $60 in intake/carb gaskets and an afternoons work every time it comes on and off.

One thing I did not remove when I cleaned the carbs was the fuel mixture screw. These engines are "ultra low emission" variants which I have come discover means that there is a special cap "glued" to the top of the fuel mixture screws which prevents them from being turned counter clockwise. According to the Honda shop manual you have to break the tops off the screws, extract them and replace them with new ones, re-adjust them, and then glue another cap on if you want to remove or adjust them Was hoping this passage would not need to be cleaned as it is just an air passage, should never have been fuel in there. Perhaps this was an invalid assumtion. if I go through this procedure the "ultra low emissions caps" will not be going back on!

[Fenlander]

Yep to get every air and fuel passageway clear I drilled out the cap... brass on mine... to access the screw. Just a case of counting the turns and putting the screw back the same. No need to replace the cap.

[johnrambo]

Been doing some research on what jet does what at what RPM. The mixture screw orifice size controls idle low rpm mixture, the mixture screw orifice + the needle jet orifice control mid range rpm mixture, and the mixture screw orifice + needle jet orifice + main jet orifice control high speed mixture.

I am having trouble at idle and low rpm so the mixture screw/mixture screw orifice is where I should have started . I had not clued into the fact that mixture screw hole actually was the low speed jet. I thought it was just allowing air thru a passage get to the other jets. Is does seem to run a lot smoother if I increase the RPM's. Makes sense now.

I cannot drill out my mixture screw cap as it is actually bonded to the head of the screw, its not a brass cap pressed in to cover the screw over like many carbs. Drilling would turn the screw and break the head off. they actually designed a necked down section into the screw head so that it would break off easily. The google has revealed that many before me have made this mistake and the easy mode is to put a soldering iron on the cap until the glue burns off, then it can be removed with pliers. All hail the google!

I'm betting if I remove the mixture screw and spray some carb cleaner/compressed air through it will run.

[beamishken]

Originally Posted by johnrambo

Been doing some research on what jet does what at what RPM. The mixture screw orifice size controls idle low rpm mixture, the mixture screw orifice + the needle jet orifice control mid range rpm mixture, and the mixture screw orifice + needle jet orifice + main jet orifice control high speed mixture.

I am having trouble at idle and low rpm so the mixture screw/mixture screw orifice is where I should have started . I had not clued into the fact that mixture screw hole actually was the low speed jet. I thought it was just allowing air thru a passage get to the other jets. Is does seem to run a lot smoother if I increase the RPM's. Makes sense now.

I cannot drill out my mixture screw cap as it is actually bonded to the head of the screw, its not a brass cap pressed in to cover the screw over like many carbs. Drilling would turn the screw and break the head off. they actually designed a necked down section into the screw head so that it would break off easily. The google has revealed that many before me have made this mistake and the easy mode is to put a soldering iron on the cap until the glue burns off, then it can be removed with pliers. All hail the google!

I'm betting if I remove the mixture screw and spray some carb cleaner/compressed air through it will run.

I was going to suggest a heat gun or one of those soldering irons that run on butane that have a tiny heat torch fitting
But I see you have found the soldering iron trick

Cordless Butane Gas Powered Soldering Iron Pen Shaped Tool - Blue https://www.amazon.co.uk/dp/B008F17R..._D.OBDbXW71EP9

[johnrambo]

Well, some success to report! I decided to try and clean the carb jet in place. Getting the cap of the carb pilot jet screw was "fun".

Heating with my soldering iron did not work. Got a bigger soldering iron from work, with a tip as big as a shovel, that did not work either. could not get enough heat into it. I then drained all the fuel hoses/bowls, and put a tiny butane torch on cap. Applying an open flame to a screw buried deep in a rats nest of wires and rubber fuel hoses was a bit dicey to say the least. At last, with the sizzle of liquefied retaining compound, the cap yielded to my will and popped off.

Removed the jet, gave the orifice a few blasts of carb cleaner, followed by compressed air and a rinse of fuel. Re-installed jet in its original position (1+3/4 turns), fired up the motor and we are running on three cylinders again!

Idle is still a bit rough, but its progress. I tried to adjust the carb mixture to smooth things out, dialed the jet in until the revs dropped (1 turn), then dialed the jet out and the revs kept increasing until the jet was un-screwed all the way. The revs should have dropped on the way out at some point so I could find the "midpoint" number of turns. Strange. I guess the passage must still be restricted.

Now on to engine #2! This one should go faster. Going to burn the caps off the idle jets while all the carbs are apart so I can give them all a full cleaning. Might go back and disassemble engine #1 carbs when I regenerate the patience.

[JamesF]

This has been an interesting thread. We've got a BF50 behaving oddly, also suspect the carbs, and I wonder if your description of the low/mid/high rev mixture control explains some of the symptoms...


Anyway, I know next to nothing, but good luck getting it all working!