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HONDA 9.9 FITS!

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weasel68

New member
Help please...I have a 2020 Honda 9.9 four-stroke BF9.9D that is giving me fits. I can only cold start it by using starting fluid and goosing the throttle and when it warms up all is well....I can then stop the motor and one button push restart it no problems at all. When it cools...will not start unless I use starting fluid....what voltage should I be seeing to the bystarter? As I crank the engine and I have a dc voltage meter connected to the wires I do not see much voltage at all.....fresh fuel, removed and cleaned the carb and jet, new plugs....really got me scratching my head...last season was the first season I owned this motor and every single time I hit the button and it fired right up. BABJ-1814591
Thanks for any advice!!!
 
Hi,

Sorry you're having problems.

Finding little to no voltage to the bystarter while cranking is normal. The bystarter is in "enrichment mode" by default and only requires voltage to "turn off" and lean out the mixture after the engine has started.

In other words, no voltage to the bystarter should cause easy starting followed by an over rich condition and stalling after the engine warms up. About 2.5 to 3 minutes. So, low volts to the bystarter is not the problem here.

My first guess is that there is a blockage in the passage at the bottom of the float chamber that feeds the bystarter "well".

Or, the bystart dip tube that pulls fuel from that well is plugged.

But, first, unplug. remove and test the bystarter to make certain that the bystarter needle valve has not gotten stuck in the extended (no enrichment) position. It's rare for that to occur but it does happen.

If that checks ok then I recommend removing and thoroughly cleaning the carburetor paying particular attention to the feed passages at the bottom of the float chamber and the bystarter feed dip tube.

I also would urge you to STOP using starter fluid (ether) as it will cause damage to the engine's combustion chamber components.

One screw holds the "slide clamp" to secure the bystarter so removal is easy.

Test by applying 12 volts dc from a battery to the brown/white wire and connecting the black/green wire to the battery ground for 3 to 4 minutes. Watch the needle valve to to see if it extends about 1/8" or so during that time. If it extends then the bystarter is ok.
!BE CAREFUL! as the bystarter valve becomes very hot when powered up.

I say clean the ENTIRE carburetor because, if the bystart passages are dirty, then it is a CERTAINTY that the carb has been contaminated and other circuits are also dirty and just waiting to cause problems.

Hope you get it sorted and

Good luck.
 
Listen to JGMO he really knows his smaller Honda motors and without him I would still be having issues. My issue was similar but it also only started then warm and struggles when cold. My problem was the primary jet tube! If you remove the float chamber (4 screws) and look at the underside you will see two coppery coloured tubes going up thru the carb. The one goes directly up to under the bystarter goes in and I used a fine sewing needle to make sure it was clear ... mine was.. however the other tube is the primary jet tube and was blocked solid and nothing would clear it at all so I ended up with getting a new carb!! I used carb cleaner to clean ALL the orifices in the carb .. I actually did mine 6 times!!!! If you have a dealership near you it's worth getting the carb ultrasonically cleaned if you can. Obviously you have fresh fuel in the tank and the float chamber is clean and you have washed out the fuel feed chamber that slides over the dipstick tube ..they get water in them and that causes huge issues!!
 
Oops . I just been corrected by our expert JGMO that the 9.9 carb is different to my 20D carb as it has no primary jet but still take all the other valuable advice!!
 
jgmo....I may owe you a beer!...
"If that checks ok then I recommend removing and thoroughly cleaning the carburetor paying particular attention to the feed passages at the bottom of the float chamber and the bystarter feed dip tube"

It was plugged between bystarter well and the carb bowl....bench test for the bystarter passed...letting some parts soak some and then will reassemble!
 
Before you put it back together, test the accelerator pump delivery nozzle output. It's VERY important to the way this carburetor performs overall.

If you spray cleaner into the tube feed while the throttle plate is wide open, it should shoot a stream 8 feet out the rear of the carb throat. If it doesn't, you should backflush the nozzle a few times until it does.

Good luck.
 
Before you put it back together, test the accelerator pump delivery nozzle output. It's VERY important to the way this carburetor performs overall.

If you spray cleaner into the tube feed while the throttle plate is wide open, it should shoot a stream 8 feet out the rear of the carb throat. If it doesn't, you should backflush the nozzle a few times until it does.
SPOT ON! also very dirty....I also disassembled the metal piston underneath the accelerator rod and lots of gunk in there...for the learnings of others...there is a small metal bearing under the piston and spring . Luckily I saw it fall!
 
Very good news! Nice going getting it done.

But....
Now you know that you have to be vigilant about the quality of your fuel. Check your tank and clean it if necessary.

These carbs are EXTREMELY sensitive to ANY fuel contamination and heartache with breakdowns are in the future if you don't keep up with that.

Try to source your gas from the cleanest pumps you can. Most marina and recreational area pumping stations are selling crap on a cracker.

They don't do frequent filter changes and I have found many to be holding water at the bottom of the tanks.

High volume, name brand stations usually keep up with the filters....I like Costco for that...but....
...you should ALWAYS spot check quality no matter where you buy. A few minutes letting a sample sit in a clear container can save you hours on the water or in the garage.

And please, please, please, ONLY use ether starting fluid in an emergency. NOT for testing.

Now....soap back in the box... ...and...

....Here's hoping you have a GREAT boating season!
 
Run sea foam in the gas regularly and especially during storage for any long periods, cleans varnish in the carb and valves and deals with ethanol or water in the fuel.
 
Here's some comments about the accelerator pump and the "small metal bearing" that the OP saw fall out.

I've written about this several times before and it's no big deal but just FYI for anyone interested.

The accelerator pumps on these Keihin BJ and BG carburetors are totally useless junk.

To repair the pump you have to replace the carb bowl and piston but you will get nothing in return for the effort.

That little "small metal bearing" is the pump supply charge check ball. It comes with a new float chamber captured in it's seat with a crimp. So, if it is rolling around loose, it has failed and all the pump will do when stroked is push fuel back into the main chamber. I can't remember ever finding one still captured in it's seat on any carb I have disassembled. It cannot be repaired to my knowledge.

No matter though because the pump piston and bore will be found to be worn out anyway. Trying to "shine" them up won't work and new parts is the only "repair" possible. But, like I said before....no return on investment. You won't notice a lick-O-difference after doing so.

Well, Ok...if you HAMMER the throttle....IMMEDIATELY after putting in a new one you MIGHT see a wee bit of difference. But...that will only last for a very short time since I don't think it's an exaggeration to say this piece of crud pump assembly starts falling apart almost instantly after first use.

I have actually removed the piston and spring in them for customers on several outboards and no one can tell the difference in performance.

And THAT'S JUST WIERD too!

Because....
....if the accelerator pump nozzle gets even a little bit plugged up...
...there can be ALL sorts of problem symptoms!

From hard start, stalling and low power!
WHY?
I am not really sure!

It's as if this carb can't BREATHE correctly if that pump nozzle isn't fully open.

To sum up...
Keep the dust bellows boot fresh to keep out dirt.

If you find a worn piston or bore, don't worry too much about it UNLESS it's cocking so badly in the bore it's seizing and not letting the linkage travel freely.
(Even then, no big deal...the linkage is spring loaded and will still work)

And, if you find that little ball rolling around loose or it falls out and goes down a crack, just shrug and move on.

But KEEP THAT NOZZLE CLEAR!

These things should have never been added to these otherwise pretty great little carburetors.
 
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