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Syncing of BF50X carbs

M

matt.speedtriple

Regular Contributor
Hi folks,

Just a quick question in regards to syncing carbs. I finally got my boat in the water today after a 2yr full refurb right back to the fibreglass skin which was all that was good.

Anyway, when i fired up the engine then i needed to adjust the tickover as the water was cooler but i started getting the engine struggling and coughing. When it coughed then all of a sudden then the revs would pickup to 3000rpm but then fall back to around 800rpm.

I tried adjusting the mixture screws, put in new plugs and fitted new ht caps but still the same. I also replaced the fuel pump as i had one handy. The carbs have been fully stripped, put through my ultrasonic cleaner 3 times and then blown through with compressed air and then carb cleaner and everything way ok. After fitting the carbs (all gaskets replaced) then i balanced them but i`m now wondering if i should`ve removed the link bar between all 3 carbs before syncing them?

Further up the rev range then it seems to be fine running at 5500rpm wot and reaching 18 knots with 3 large people aboard.

If anyone has any ideas and also if the link bar (number 16 on the link below) should be in place when syncing the carbs then i`d be very grateful.

http://www.lingshondaparts.com/pe/h...ock_01=17ZV50E1&block_02=E 14&block_03=32051

Cheers, Matt.
 
Leave the linkage connected.

I do not understand what you mean when you said "adjust the tickover". What is that?

If you have a BG31B carbs, then the idle mixture screws should be turned out 1 turn.

if you have BG31BG carbs, then the idle mixutre screws should be turned out 2 1/8 turns

Make sure that your jet sets (the long skinny tubes) do not have any cracks in them.

Make sure that your gasket surfaces were clean, especially the intake manifold.

Make sure the timing marks are lined up properly.

Go back to basics and check compression and spark.

Mike
 
Cheers for the reply Mike.

Tickover is idle speed. I was a motorbike mechanic for years so everything was fitted and cleaned as it should be. Compression readings are all coming out around 170psi but considering the outboard was used on a fish farm and has been sitting idle for a few years then i`m not surprised and this should increase as the engine frees itself off again.

As the boat is now moored on a swing mooring then i`ll do what i can to check things but not easy while hanging over the back of the boat.

I`ll try taking up a spare coil with me and see if that helps plus try the carb sync again as with the linkage between the carbs removed and trying to bring the revs up on each carb then number 2 is much slower to respond than the other carbs.

Cheers, Matt
 
So, you DID remove all the jet sets and REPLACED the small Orings at their tips for the main passages? Same for idle mix screws? You VERIFIED idle, transition (intermediate) and high speed ports at throttle plates open and flowing petrol (carb spray) before reassembly?

If so, then I would say you have an intake leak or leaks. Just use whatever method you normally use for finding them.

If you didn't answer the above in the affirmative, then I would say go back and perform those tasks.
 
jgmo, ALL the above points were carried out and ALL gaskets and "0"rings were replaced. ALL ports were verified with both first 6 bar of compressed air and then DOUBLE checked with carb cleaner. Jets sets were tested under pressure to verify there weren`t any hairline cracks in them. There was also a new manifold to intake gasket fitted on reassembly of carbs to engine.

If it was something straight forward then i would`ve had it sorted out and been away out fishing on my boat i`ve worked so long and hard to complete.

I`ve another set of carbs that i`m going to go through and then try at the weekend and see if that makes any difference.
 
I would do a decarbination on it before going through another set of carbs. Although it is most likely impossible to do on a mooring, check/adjust valve clearances. Then recheck compression.

Also check for critters in any of the hoses, like the crankcase vent, etc. If it was sitting, there was time for the critters to find their way in and get comfortable.

Mike
 
Well just spent the last few hours fault finding and it turned out to be one of the black plastic spacers between the top carb and manifold had a hairline crack in it. Changed it and rebalanced the carbs and everything is running sweet.

Cheers to all for your help and first fishing trip tomorrow afternoon is now on the cards.

Matt.
 
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