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bf90 smoke. idle/acceleration/deceleration issues

J

jakepitsville

Member
Hey to All.

Having few troubles with my Honda Bf90 1998/99 1400hrs. I noticed the engine was sluggish on acceleration and had stopped idling properly -by this I mean it took 10 to30 and would slowly lower from 2000rpm.

so I overhauled the fuel system. The fuel filters were a bit dirty so they were replaced and fuel lines were flushed. The carbs were drained and were clean. The carbs were then pulled off and cleaned with spray carbie cleaner ( I could not get the jets out - they were stuck in there - Is there some trick removing these). The choke was reset/cleaned Everything was reassembled, The pilot screws were reset to 2and 1/4 turns and the outboard took abit to start but started ok. Idle was reset to 1000rpm. On snapping the carbs acceleration was better but the engine would not return to idle as. It was also noted that the diaphragm was not moving - I removed the dashpot valve and it was also noted there was no vacuum or air movement what so ever coming from the acceleration pipe. This pipe was cleaned and is no blocked

Help.

Also was noted some smoke from prop exhaust on deceleration after hard acceleration. In a car this would most likely mean valve stem seals - is this the case here???


any help would be greatly appreciated
 
spend another few hours on the outboard today. on rechecking - the bottom cylinder (think its no4 - the lowest one) seems to not be working well at idle. IE by pulling off the lowest spark plug lead the engine does not change although the plug is sparking fine! Any one of the other 3 leads causes the RMP to die and the engine to cut out. I pulled down the bottom carb again and still no change.
 
The first thing i`d suggest is that you get the carbs stripped off again and then get all the jets and emulsion tubes removed and cleaned as without doing this then you`ll keep banging your head against a brick wall.

I`ve worked on motorbikes for 30 odd years and outboards for the last 6 and dirty carbs seems to be the biggest problem outboards have due to modern fuel and carbs not being drained off properly after use.

If i come across jets that are stuck in place within a carb then i use one of the wee kitchen blow torches to lightly heat the metal that the jet is screwed into to release them. You`ll need to replace the small rubber "O" rings on the emulsion tubes but that should be done anyway. If you have a search on the forum then you`ll find loads of threads in regards to carb cleaning as it`s such a common problem. Once the emulsion tubes are cleaned then check them very carefully with a magnifying glass for hairline cracks as if they are then they have to be replaced.

In regards to your bottom cylinder not seeming to be working then start your engine and then spray a wee bit of something like wd40 or easy start around the manifold between the carb and engine block. If your revs increase then you have an air leak which will cause a cylinder not to work properly. I found 2 of the black plastic spacers on my BF50 had hairline cracks on them that you couldn`t even see when not under any pressure. Also all gaskets should be replaced each time the carbs are removed as if they`re not then your leaving yourself open to problems.

Once the carbs have been cleaned properly and refitted and then checked for air leaks then you may need to check the carb balance.
 
Thanks for the reply Matt. Will do in regards to the Carbs - will do a full overhaul on them. Of note I have hooked up a vac gauge to each intake manifold and the problem one is running much less vac. would that to be expected ?
 
so just pulled down the offending carb and there was some grit inside the middle jet and reduced flow - cleaned it all up. put it all back together and no change. - I changed out spark plug leads to double check and used a different set of plugs but that didn't change anything although so minor oily residue on offending cylinder plug. Pulled off the rocker cover and all the valves were moving and looked ok.

Tomorrow I will do a compression test. I am unsure how I am suppose to do a leak down test????

thanks
 
You need a leak down tester that you screw into the spark plug hole on each cylinder in turn to see how long they hold pressure.

When you tried the engine then did you give the manifold a spray around with either wd40 or easy start while it was running to check for air leaks?
 
I have a service n repair manual. Everything is off now was easy to get head off. Just try to figure out how to remove everything from head. Oil pump is pretty stuck
 
ok updates. head is all apart and was not to hard once I had read the manual a few times to get a good picture of what needed to happen. I have 3 burnt exhaust valves that have not been seating well at all. all the intake valves are seating super!

just trying to source some valves here in New Zealand.

Does anyone know why my valves would have become burnt and not seat well??
 
The most likely causes for the valves burning out is that the clearances were set incorrectly or were skipped when being serviced. Another cause could be the mixture being too weak or possibly the engine having overheated at some point.

An awful lot of home mechanics seem to be scared of removing the rocker cover so the valve clearances simply don`t get checked.
 
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