BF90 idle mixture screws

[Kent1961]

Well I decided to clean the carbs myself instead of paying the $900+ to have the shop do it. No big deal, all went well until I came to removing the idle mixture screws so I can give the carbs a good soaking. Not knowing then what I know now about how to remove the caps.......I broken them all.
What I ended up doing after I got the screws out was to file a slot across the head so I can adjust with a flat head. What I don't know is what the factory settings are suppose to be.
Can someone help with this?
It's a 2006 90 4-stoke

Thanks

 

[Silvertip]

Re: BF90 idle mixture screws

While this doesn't help you now, it may help others BEFORE they try this. BEFORE you remove an idle mixture screw from any carb prior to a rebuild, turn it in until lightly seated while counting the turns. THEN remove it. When you reassemble the carb turn the screw in until lightly seated and back it out the number turns noted prior to removal. The original setting was correct so after cleaning there is no reason that same setting wouldn't right except for a very slight tweak of 1/4 turn or so. There is no exact setting for these screws -- only an initial setting and then a fine setting once the boat is in the water. Start at 1-1/2 out from lightly seated. One at a time, turn the screw in until the engine gags then back it out the other way until the engine gags again. Happiness is somewhere between those two points and you should have a very smooth idle, especially with a four stroke. Repeat for the others.

 

[Kent1961]

Re: BF90 idle mixture screws

Silvertip
I appreciate your reply. Knowing the settings prior to removing them is always a good thing. The reason I didn't know what the factory setting was is because once the tips break there's no way to screw the needle. At that point you have to drill a small hole and use an easy out to remove the needle. Once you put a drill to it, the needle will turn and the drill is faster than my eyes.

I've rebuilt many carbs in my time so I know about trying to find the happy medium for this but what I don't know is the setting sequence of the carbs. Meaning, I have four carbs, I believe at idle one or two of the carbs control the way it idles. So from what I recall you have to set the carbs in sequence starting with the idle carb(s) and work out from there.

On my bikes, depending on what set-up I'm running (pipes, manifold, etc) the setting for the air mixture is recommended at "X" amount of turns out and then you find the happy medium from that point. Since I have four carbs, one or two of them are more involved in performance at idle than the others I would suspect that the settings for all four would not be the same and/or as much as a half turn different from each other. So there has to be a starting point for each carb. Are you saying the starting point for all four is 1 1/2 out?


Thanks

 

[skawtay]

Re: BF90 idle mixture screws

Hello Kent1961

Sorry to intrude upon your problems but can you tell me how to safely remove the wonky idle jet assembly? I also have a 2006 BF90 that has at least one low speed jet gummed up (works OK at open throttle). I have the carb bank off and stopped disassembling when I realized the idle jet screw has some strange tab on top and won't just screw out. Any idea what the numbers (that are stamped on the swivel tab) mean?

My idea (likely a dream only) was to remove the low speed jets, spray them a few times and maybe save myself the complete disassemby, therefore the expense of replacing all the gaskets and trying to realign the damper etc.

I wonder if all Honda BF90s suffer from easily clogged low speed jets? I used fuel stabilizer etc.

skawtay

 

[Kent1961]

Re: BF90 idle mixture screws

skawtay

From what I've read, the caps are glued on, if you use a soldering iron to melt the glue the caps can be removed.
Once you get the caps off, please let me know what each of your screws were set at by counting the turns in.

Thanks

 

[Frank Martin]

Re: BF90 idle mixture screws

We Start The Adjustment 3 Turns Off The Seat
To Remove The Caps You Must Use A Large Soldering Iron The Caps Are Hot Glued On And Need To Be Prety Darn Hot To Liquify The Glue Then The Caps Come Off With Hardly Any Effort And A Needle Nose Pliars
Do Not Soak Honda Carbs Use A Ultrasonic Cleaner Or A Mild Carb Cleaning Spray Soaking Will Remove A Teflon Sealer Used On The Raw Aluminum
Final Adjustments Must Be Made With Vacume Meters On All Carbs To Have Them Run Right When Its All Done
You Can Remove Brass Jets And Soak But Not The Carb Bodies Best To Replace The Idle Screws That Have The Ends Broke Off Makes The Whole Job Easyer

 

[Flakeys]

Re: BF90 idle mixture screws

I have a Honda carburetion manual and also a pair of 90HP engines which I've done all this on last year. The mixture screw setting is 2-1/4 turns out. As someone also stated, you need to synchronize all four carbs with each other using a vacuum manifold set. This will ensure that no one cylinder is working harder or less than the others during the range of speed and load setting. Use the base carb (#4) to set initial rpm around 900 and then going down from 1,2,3 you want to adjust the adjusting screw (not the mixture screw) to attain the least amount of vacuum difference in each cylinder. After complete, recheck idle rpm and adjust with the base #4 adjusting screw as needed to get 950 +/- 50 rpm. Hope this help you out.

 

[Kent1961]

Re: BF90 idle mixture screws

Frank / Flakeys

Great info! Thanks for the help.
I guess I need to find vac meter somewhere now. If anyone knows where I can find one please let me know.

Thanks again!!

Kent

 

[JUSTINTIME]

Re: BF90 idle mixture screws

you can make one or buy it from honda

 

[Kent1961]

Re: BF90 idle mixture screws

Flakeys

Just back in town from a long work trip and was reading all this again.
So I understand what your saying, the mixture screws for all four carbs are set at 2-1/4 turns out. From there I won't have to adjust them to "fine tune"?
Then I hook up the vac meter, the only adjustment will be to the idle speed adjusting screw to set each carb.

Is that right?

Thanks!
Kent

 

[Kent1961]

Re: BF90 idle mixture screws

Justintime,

Never built one, heck never used one but want to learn. Can you you give me some details on what all I need and how to make the vac meter. Also, where on the carb to I hook it up?

Thanks
Kent

 

[JUSTINTIME]

Re: BF90 idle mixture screws

you will need 4 vacuuma gauges
some rubber hose and need to buy the inserts that crew in

 

[Kent1961]

Re: BF90 idle mixture screws

JUSTINTIME

The inserts screw into the guages or where??

Sorry for the ignorance but I've never done this. I appreciate your help.

Kent

 

[JUSTINTIME]

Re: BF90 idle mixture screws

engine
do u have the factory manual?

 

[Kent1961]

Re: BF90 idle mixture screws

I don't have the manual. Can you send me the info I might need to my email?

 

[JustJason]

Re: BF90 idle mixture screws

hmmmm... if you haven't been through the service procedure on this one... or ever balanced 2 or more carbs per engine (talking 4 stroke, not 2)..... ya may want to pay a shop for a snyc and link.... It's pretty easy to screw up if you don't know how to do it. And you really really need the manual on your motor. Depending on the make/model/year.... the carbs may call for an even vacuum or stepped vacuum.
a carb balancer alone is a couple hundred bucks for the tool.

 

[Skinnywater]

Re: BF90 idle mixture screws

Justintime,

Never built one, heck never used one but want to learn. Can you you give me some details on what all I need and how to make the vac meter. Also, where on the carb to I hook it up?

Thanks
Kent

Check online for a motorcycle parts supply company. They will sell a manometer for well under $100 bucks. Get the one that would be used for a Honda 750 four and it will have the screw in adapters to connect to your carbs.

OR

If it's not improper and alright with ADMIN, I have one that uses mercury (slack tube) manometer that is for a 4 cylinder with Honda adapters.
It's only been used once and I'll never need it again.
Less then what I paid for it, plus shippin'....

 

[JUSTINTIME]

Re: BF90 idle mixture screws

there you go, u can use that

 

[drew0982]

Re: BF90 idle mixture screws

thanx for the tips guys... here's the service manual for the honda bf90... get it quick before they delete it:

http://www.mediafire.com/?j00zh0byjoa

cheers!
andrew