Honda BF50 outboard issues.

Hello new to the forum so bare with me please, also I'm based in the UK.

Right a friend has a Honda BF50 outboard motor, a neighbour had it in his garage for a number of years anyway friend struck a deal to swap the motor for his Mercury 90hp, so he set up the BF50 on his stand and in a barrel of water and began to service the motor.

He stripped the carbs cleaned them, replaced the spark plugs, gave it an oil change and a new timing belt, a new fuel filter, after a period of tweaking it it finally started, but seemed to run uneven, after a bit more tweaking it seemed to run nice and smooth, he was told he would need to have the carbs balanced, so a gentleman at his Boat club offered to do this for him, after swapping the BF50 for his 90hp he launched his boat the motor ticked over on low revs but would missfire when added throttle, he was told it sounds like it has a sticking valve the motors were swapped over and he brought the BF50 home.

We took the valve cover off and turned the motor by hand and all 6 of the valves opened and closed, so we removed the head and found the valves had a coating of carbon and 2 of the exhaust valves were damaged, so the head was put in to a engine reconditioner, the 3 exhaust valves were replaced and all 6 were reseated, also the valve stem oil seals were replaced and the head skimmed, new head gasket fitted.

Got the head back and reinstalled it using the torque settings and tightening sequence I got from one of the threads on here, set all the timing back up and the motor started and ran better than before, so he bought a carb balancer and tried to balance the carbs got them very close but the motor would miss/backfire at low revs and occasionally at high revs, so the carbs were removed again and cleaned out, so tried again and got it really close but no missfire now.

Now this is the issue, while its running if you pull the top plug lead off the engine pitch DOESN'T change, he said he could hear the ticking of the spark jumping to the plug as he pushed the lead back on, now if you pull the second plug lead the motor splutters then cuts out, with number 2 plug disconnected the motor wont start, if you connect plug 2 the motor starts and runs ok and revs nice, the question is what can cause this pull plug 1 and 3 lead and it still runs with no altered pitch or revs.


Sorry for being long winded with the description, hope somebody out there has the answer.

Many Thanks for your help i advance.

Have you checked the cylinder compressions?

Many thanks for your reply, yes the compressions were checked after the head was replaced and they were all excellent, after rechecking everything today it turns out that the butterfly's in carb 1 and 3 weren't opening on idle or throttle, now this has been sorted there is now a noticeable drop in idle pitch when removing plug lead 1 and 3, also the motor still runs with number 2 lead removed.

Thank you to Milgrip for replying and anybody who was thinking of replying.

oberlisc said:

Many thanks for your reply, yes the compressions were checked after the head was replaced and they were all excellent, after rechecking everything today it turns out that the butterfly's in carb 1 and 3 weren't opening on idle or throttle, now this has been sorted there is now a noticeable drop in idle pitch when removing plug lead 1 and 3, also the motor still runs with number 2 lead removed.

Thank you to Milgrip for replying and anybody who was thinking of replying.

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Your problem lies with the carburetor synchronization gauges. Even brand new ones, unless they were VERY expensive, are NOT calibrated.

You will need to get some vacuum tee fittings, and hook all the gauges together into one hose. Then you need to hook that up to a stable vacuum source, which can be one of the carbs on the outboard, a vacuum test pump, or even your car. Just so they all have the same source. Then calibrate the gauges, usually with a screw on the back, but some just have moveable faces, until they all jive. Then do your sync and all should be well.

Thank you for your reply, you can really only sync carb 1 and 2 as carb 3 also adjusts carb 1 & 2 through the linkage, the carbs have been synced and are all balanced, then a Gunsons Colourtune was added to check the fuel mixture, all the adjustment that has been needed has been carb 1, the motor was running perfect in the water butt, it was put back on the boat through the week and was supposedly going back in the water this weekend but I haven't heard how it went, is this a good thing or a bad thing.