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1999 Honda BF50AX 2 cylinders only

trooker

New member
Beleaguered but not defeated I carry on, trying to solve why #2 cylinder is not performing.
I have done as follows, including the reading on many related forums, thank you all for the insights.
Immersion cleaned carbs several times, verified visible tiny thru holes in body were clear,set float, replaced all jets, pilots ,seals and gaskets
Set valve lash, only notable was #2 Intake that was at .003 instead of .006 nominal
New Thermostat
New fuel lines and racor filter
New spark plugs
Synchronized carbs using Carb Tune device
swapped coils
Compression check hot and cold with throttle plates open = 90-100 psi
Engine performance is erratic. An Engine load test on stern of boat strapped on trailer, showed good pretty good burn on all cylinders.
However the sea trial did not go well it made 5000 plus rpm seemingly all firing, but 2500 rpm and down was very rough.
Even after the carb synch at home, the engine ran pretty well in the barrel but pulling # 2 wire made no difference in rpm.
#2 plug is wet the other two run a bit rich.
Wondering if the compression is too low for lower speed operation, but still don't understand #2 cylinder.
I am wondering if the top and mid carb can be interchanged to determine if problem is carb.
Any ideas or related experiences would be welcome
 
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Yes, the compression is what I would consider marginal at best. You probably need to perform a leakdown test to determine what should be done next. I'm guessing worn rings because all three are the same. You could try doing a wet compression test to see if it comes up significantly. That's something you can do if you don't have a leakdown tester. But Harbor Freight sells an adequate one for not a lot of cash.

I don't know if you can swap middle/upper carbs. I don't think so but maybe I'm wrong.

Hopefully, somebody here will have better suggestions for you.

Good luck.
 
I agree with Jimmy....the compression is really low. It should be closer to 200 psi.

The top two carbs can be interchanged....but before you do that, check the timing marks.
If the belt is off one notch, that could make the difference in all of the cylinders.

Mike

One thing you did not say is..if you checked the spark.
 
Thanks for your interest, I did check spark from the standpoint of swapping coils and the #2 problem persisted. I also rechecked
the timing this morning, all good.
The good news (maybe) is that, I was able to swap carburetors and the problem ( pull the plug wire with no affect on running) followed the #2 carb to the #1 cylinder
Since I have rebuilt the carb with all new components and detail cleaned it several times it seems a replacement is needed.
At $250 a piece, hoping there is nothing run with this logic.
 
Ok, before you spend the money on a new carb, would you be willing to try cleaning it again? There's really no reason, that U know of, that the carburetor would have changed to make a replacement necessary.

If you didn't blast the %&$# out of the main jet air mix passage from the front of the carb (small drilled tunnel just above carb "throat") with a straw on a brake kleen can, and "back~N~forth" flush the idle-transition-and high speed orifices via main air mix passage using same straw carefully positioned over each orifice ......then I would try that before popping for a new unit.

Use a finger, thumb or other tool to block off fluid flow from the usual two paths of exit to only one. To do this properly, the jet set and emulsion tubes should be removed as well as the idle mixture valve. For example:
If you plug idle mix screw cavity while spraying with straw inserted into jet set recepticle, the spray will exit the idle orifice at a much higher velocity. This helps dislodge stubborn deposits. Then, keeping idle mix screw cavity plugged, position straw tip over idle orifice and reverse flush. You will need to prop the throttle plate open to access the transition and high speed circuit orifices and give them the same sort of treatment.

Note where fluid exits and block what you can to direct the force of spray to a single path. I use my thumb and fingers to accomplish this. Reverse flush each passage and spray into the main air mix, the jet set recepticle, the orifices and the idle mix screw seat.

It is my opinion that if you didn't clean all the carbs using this method then you probably just got lucky getting the other two carbs clean enough to feed the cylinders. I recommend that you re-treat the other two carbs in the same manner to ensure COMPLETE cleanliness.

If this works for you, you will have saved $250 and with that, you could actually rebuild the lower end with new rings and bearings!. Relap the valves, install new springs and VOILA!
You got yourself a FRESH 50 horse!

Good luck.
 
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Just to confirm, you replaced the "jet set" with new parts right? That's the jet that you remove the top screw, outer tube (main jet) slides off and the inner tube (jet set) is held in place with an o-ring (friction). There can be a couple problems with the jet set and replacement is the easy solution. A bad jet set would cause the problems you describe.

I have always called this jet the pilot jet or idle jet. Honda calls it a jet set I guess...

I'll probably screw up the description of this process, but with the jet set removed and the mixture screw removed, hold the butterfly open and shoot carb clean into the mixture screw hole. You should see a good stream (maybe it was two?) into the throat.

edit - JGMO beat me to it. I was trying to remember the procedure he told me about ;);)
 
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Just a thought....when you changed the thermostat, was the old one stuck open? As well....when you first checked the oil level, when you bought the motor, was it too high?

If the answer to either one is yes, then it may be possible that your rings are carboned up. The engine could have been running too cold or it could have been burning the excess oil. A good heavy decarb might be in order. After which, you should changed the engine oil and recheck the valve clearances.

The leakdown that Jimmy recommended or adding some oil to the cylinders and if compression increases could point in that direction.

Mike
 
Just a thought....when you changed the thermostat, was the old one stuck open? As well....when you first checked the oil level, when you bought the motor, was it too high?

If the answer to either one is yes, then it may be possible that your rings are carboned up. The engine could have been running too cold or it could have been burning the excess oil. A good heavy decarb might be in order. After which, you should changed the engine oil and recheck the valve clearances.

The leakdown that Jimmy recommended or adding some oil to the cylinders and if compression increases could point in that direction.

Mike

I don't want to hijack this thread, but the BF45 I'm working on had a thermostat stuck open. Do you have a recommendation for a de-carb procedure?

Thanks,
Matt
 
Re cleaned carbs in great detail according to suggestions, One carb working better but number two did not.
Replaced with new carb and engine is running better. Plugs show rich burn, most likely expected considering low compression.
But for now we take it and start saving for an upgrade. Thank you to all for the participation and interest it was a big help.
 
I agree with the Sea Foam idea. Or maybe some Ring Free or both. Many have had some pretty dramatic compression improvements happen after doing de-carbonizing.
Good luck!
 
Mix 1 part Sea Foam to 4 parts fresh fuel in a small tank. A gallon should be more than enough. Hook up fuel feed to tank and run the engine. When it starts smoking, sputtering and knocking, turn off the engine and let it set for 30 minutes to an hour. Change over fuel feed to pure gas. Start engine. You should see a lot of smoke & crap coming out of the exhaust. Repeat. If you still get a lot of smoke and crap out of the exhaust the second time, do it again. Besides decarboning the rings and valves, this will also further clean the carbs.
 
Back to square one! how frustrating is this...
Engine ran pretty nicely synced carbs and ready for sea trial.
Just started engine up in yard ran well for 3 minutes and went down hill to 1-2 cylinders.
Plugs are wet. wondering if the ignition controller is causing this. Don't know how to test that.
 
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