Adjusting Mixture on Honda BF40A (2003 model)?

[ashfish]

Hi guys,

I hadnt used my boat for a while and took it out the other day.

About 800 yards from the ramp, in a slow speed zone, the engine lost power and then cut out . I recognised the symptoms as water in the fuel as I had suffered this issue before.

I removed the water seperating fuel filter and cleaned it out and replaced it, I removed the filter in the motor and blew it clean and put that back. Then, hanging up side down over the engine I in turn drained every fuel bowl on each of the carbs whilst pumping new fuel through.

Due to my position (hanging upside down in a reasonable swell, I accidentally loosened the mixture screw on the bottom carbie instead of the fuel bowl drain. As soon as I realised there was no fuel flowing from the drain hose into the bottle I realised what I had done. I turned it back to approximately where it was positioned before and then loosened the fuel bowl screw correctly on this carb and pumped fresh fuel through to clean it out.

After flushing all carbs, the engine started and away I went back to the ramp and took the boat out (didnt want to chance another cutout further out to sea).

I took the boat home and completely flushed the tank, replaced all filters an filled it up with fresh fuel to make sure any bad fuel was no longer going to be a problem. I then refueled the tank, put the muffs on the engine and started it. It took a bit to start even once the fuel was pumped up and I left it running for a while to warm up to see if the roughness went away. Unfortunately it didnt. I tried positioning the third mixure screw the same as the others but the problem only got worse.

I dont think I have correctly positioned the mixture screw on that third carby.

Is there anyway to easily adjust the mixture screws on these engines yourself? Can someone please post how to do this.

I dont have the workshop manual for this engine and cant seem to find one here in Australia without having to buy it from overseas and pay nearly three times the price of the manual for the freight.

 

[JUSTINTIME]

Re: Adjusting Mixture on Honda BF40A (2003 model)?

you need the sync tool

 

[ashfish]

Re: Adjusting Mixture on Honda BF40A (2003 model)?

you need the sync tool

Even just to adjust the mixture?

Surely its just a matter of lightly closing off the screw and then opening it up x number of turns?

 

[JUSTINTIME]

Re: Adjusting Mixture on Honda BF40A (2003 model)?

the 3rd lor lower carb is base carb

you adjust idle and number of turns on that carb first, then adjust the rest that way

then you need to sync the carbs

more fuel in one cylinder will draw more pressure

 

[hondon]

Re: Adjusting Mixture on Honda BF40A (2003 model)?

Those are your mixture screws and this is really not that complicated but since you know you have had water contaimination it may become so.Unless the sync screws have been tampered with on your upper carbs it is generally not nesessary to **** with that function.A 2003 engine will have those mixture screws limited by a cap glued to the top of that screw.At least that how it has to be in Cal.If you do'nt have that cap,go to your other carbs and run those screws in while counting the turns.Back them back to where they were and set the problem carb about the same.Tweak away from that point on.

 

[intrepidvoyager]

Re: Adjusting Mixture on Honda BF40A (2003 model)?

+61-2-8213 9373 .......these guys have the manual you need .... also as previously posted ..good idea to get the sync tool ..... find an auto parts store that carries carb synchronizers for multi carb engines .... the ones that work on old su carbs work well. You may have to modify the base of the unit but that's fine ..... I'll see if I can find a pic and post ...

Cheers

 

[intrepidvoyager]

Re: Adjusting Mixture on Honda BF40A (2003 model)?

here we go ....

http://www.jcwhitney.com/jcwhitney/...hopid=100001&pageid=12&TID-100=&redir=k232270

 

[intrepidvoyager]

Re: Adjusting Mixture on Honda BF40A (2003 model)?

Also you might find it easier to use the multi tube synchronizer tool ...don't know your specific engine carbs .... but if you have the vacuum ports on each carb you can ..... any honda motorcycle shop should sell them ...Good luck

 

[intrepidvoyager]

Re: Adjusting Mixture on Honda BF40A (2003 model)?

OK ...after carefully rereading your post ...it is possible that you have some crud lodged in the idle circuit of one of your carbs and just pushing fuel thru is not clearing it out .....if you can't get a smooth idle after syncing ... pull the idle screws and get a can of carb cleaner with the little red tube ..... open the drains and blast carb cleaner into the idle mixture screw ports. Use a bit of wadding or rubber disc with tube hole in it
to stop the cleaner from shooting back at you ...the idea is to get the cleaner blasting thru the idle circuit.

use vasoline on the idle screw o rings when reinstalling and make sure the o rings are not getting hung up .

if that does not work follow the carb cleaning instruction posts. Good luck !!

 

[ashfish]

Re: Adjusting Mixture on Honda BF40A (2003 model)?

Those are your mixture screws and this is really not that complicated but since you know you have had water contaimination it may become so.Unless the sync screws have been tampered with on your upper carbs it is generally not nesessary to **** with that function.A 2003 engine will have those mixture screws limited by a cap glued to the top of that screw.At least that how it has to be in Cal.If you do'nt have that cap,go to your other carbs and run those screws in while counting the turns.Back them back to where they were and set the problem carb about the same.Tweak away from that point on.

Unfortunately there are no caps on those screws, thats how I was able to accidentally unscrewed one instead of the drain screw when hanging upside down over the engine trying to drain the water from the carb.

I'll have another go at adjusting it today after I run it with the muffs and get it up to normal operating temperature. I think that was my problem last time (trying to sync them too shortly after a cold start).

Plan of action is:
1. Let engine reach normal operating temperature and then turn off.
2. carefully tighten carb 2 counting the turns until first contact and writing down the result.
3. put carb 2 back the way it was.
4. adjust carb 3 to the same setting as carb 1
5. restart engine and see if any better.
6. if still not running smooth, make minor adjustments to carb 3 and see if it improves.
7. if no improvement, try the carbie cleaner trick on carb 3 and repeat process.
8. if no improvement, take it to the stealer and part with copious quantities of money to get it done properly.

 

[jayceebaik]

Re: Adjusting Mixture on Honda BF40A (2003 model)?

I got this specs from my Honda manual.
But this is ONLY starting point. Not an exact spec.

It depends on Main jet size.
If you have 102 main jet.. 2-1/8 turns out.
92 main jet.. 2-1/4 turns out( engine serial 2000001 -
2007399)
105 main jet ... 3-1/2 turn out
125 main jet .. 2-1/8 turns out
130 main jet ... 1 turn out
135 main jet.. 2-1/8 turns out.
--------------------------------------------------------------------
when you adjust mixture screw, if engine rpm doen't fluctuate.
your carb maybe clogged up..
if possible use your tachometer.. adjust you mixture screw until it gets
highest rpm..try not to use ear muff. you need some kind of back pressure
, put your engine ;s lower unit in big bucket with full of water..
i hope it helps..
thanks

 

[JUSTINTIME]

Re: Adjusting Mixture on Honda BF40A (2003 model)?

what manual is that?

cuz, one is 2-1/8 other is 3-1/2?
on a bigger jet, LOL

sounds like selco

 

[intrepidvoyager]

Re: Adjusting Mixture on Honda BF40A (2003 model)?

Hey cjay ....this is a very imp point from fish

when you adjust mixture screw, if engine rpm doen't fluctuate.
your carb maybe clogged up..

I would add ...... 90% is clogged.

you can try a quick fix by squirting lots of carb cleaner in the idle mix screw port ....open the bowel drain first ...use the red tube that comes with most carb cleaners... this maywork ...but if you have ethenol mix where you live .... you may have to pull and clean the offending carb/s

good luck

 

[jayceebaik]

Re: Adjusting Mixture on Honda BF40A (2003 model)?

i got this spec from 2010 honda spec book.

 

[intrepidvoyager]

Re: Adjusting Mixture on Honda BF40A (2003 model)?

hey ashfish ....don't know if mentioned but make sure your throttle plates open at the same rate ..... Not that they just all close ... once had an issue on a multi carb merc where one of the throttle plates only started to open after the other 2 were open a 1/16 th. or so ....

i found on older engines it can be difficult to sync without a sync tool. If your engine has vac ports a motorcycle shop can sell you a vac tube sync tool

if not get one of these ...fits most carbs and makes the job a snap.

http://www.jcwhitney.com/jcwhitney/...hopid=100001&pageid=12&TID-100=&redir=k232270