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Honda BF40A outboard hard to start and only 1 piston is firing.

M

Mark010

Member
Hi, I bought a pontoon with a Honda BF40A outboard last Oct. It started right up and purred like a kitten before I bought it. Now, this spring, after indoor storage, it is hard to start and runs rough when it does start. A former owner said it was a 2010, but the emissions sticker says it was built to 2008 standards.

The previous owner had paperwork from a shop from last August that showed he had replaced the plugs, but complained starting issues continued. The shop cleaned the carbs with repair kit and synched the carbs. The bill for that labor and parts was about $1000. Parts listed were valve set, gasket sets, gaskets, and a jet set.

I have done the following:
-Replaced the tank with fresh gas
-Checked the fuel filter
-Checked the fuel pump
-Checked the plugs (clean and properly gapped)
-Confirmed all plugs are getting a spark

Also, I sprayed carb cleaner in the carbs. This always gets it to start, but sometime it runs only long enough to burn out the carb cleaner, then it dies. Sometimes it will run longer, so I assume it is then burning gas. When I try to start it again without the carb cleaner, sometimes it will start, sometimes not. It does not matter if I try restart it right away or if I wait overnight.

I pulled the spark plug wires off one at a time when it was running on the gas. With plugs 1 and 2, there is no change to the sound when the wires were removed. When I pulled the wire from plug 3 (with 1 and 2 reconnected), the engine kills.

After running it several times with and without the carb cleaner (yes, sometimes it will start right up without the help of the carb cleaner), I checked the plugs again. Plugs 1 and 2 were heavily fouled. Plug 3 was lightly fouled. I also rechecked the gaps. They were in the range listed in the owners manual.

Friendly suggestions would be much appreciated.
 
Hi Mark,

Welcome to the Honda forum.

Sorry this is happening to you.

After reading your post, it is pretty obvious to me that the carbs are, once again, going to need cleaning.

These are particularly sensitive to varnish and minerals carried in most fuel from gas pumps and they don't tolerate being stored with ANY liquid left in the float chambers.

Also, the bad news is that, it often doesn't pay to take them to a shop for "cleaning" as that can be an expensive, losing crapshoot.

Many, many, many shops just don't know how to clean them properly.

The good news is that, if you have any mechanical ability at all and some basic tools, you can do the job yourself for very little money. A new gasket set, a few cans of carb spray and, most importantly, the
HONDA MARINE CARBURETION MANUAL in hand, she will be starting and purring again.

No, not a 20 minute job. More like several hours but....you can do it if you read that manual and it's section covering your specific carburetors.

No need to stress too much over the date of manufacture since the A model hasn't changed much post 2007.

You can order the carb manual at the link below. $43.95 + shipping and tax.

Honda Marine | Shop Manuals Publications | Honda Power Products Support Publications

publications.powerequipment.honda.com publications.powerequipment.honda.com

You might also consider buying the official shop manual from that same site. I recommend having one for any owner doing their own maintenance. I recommend it in this instance because it's a "new to you" outboard and, if the valve clearances have never been checked or adjusted, it is overdue. Yes, the manual is around $100 but that's probably less than a one hour labor charge at most shops these days.

I also recommend getting a Japanese Industrial Standard (JIS) screwdriver set instead of using standard Phillips type that can "booger up" the JIS screw heads. Those were available on Amazon for reasonable money last time I checked.

Any and all questions welcome. If I can't provide an answer there are smart people here that likely can. These posts are monitored by many.

I wish you fair weather and good luck.
 
Hello jgmo,

Thanks for your response! You gave me all the information I needed to move ahead and to believe I could handle the job (I have never cleaned carbs before). I have been puttering away at this project and wanted to let you know I appreciate your advice. Here is an update.

The carbs have all be taken off and cleaned. During the cleaning, I found that the jet set (the little tube coming up from the center of the bowl) was clogged on both carbs 1 and 2 (both associated with the pistons that weren't firing). That jet tapers to a very small opening inside the tube. To clean it out, I cut a bristle off a wire brush. All the other wires I had were too big, or, if they fit the hole, they were not strong enough to push through the clog.

The previous owner just had these carbs cleaned late last summer. I looked up the part numbers from his invoice and found that the shop replaced all the gaskets, all the rubber seals, and the jet sets (the tubes I unclogged).

I have to replace at least 1 gasket that looks a little rough. Do you have recommendations on what other parts to replace while I have it dis-assembled?

Thanks,

Mark010
 
Well, like I said before, I'm very distrusting of most "outboard shops". There are great ones of course but many, many more crooked ones.

So, you should put little trust in what was done prior.

But, if indeed the gaskets are all new, most can be reused if you're careful removing them. I personally wouldn't do that but you be the judge.

I would hate to "booch" all the work of removing, cleaning, replacing,
and syncing the carbs by reusing a gasket or oring that doesn't seal only to end up with a crap running engine when done.

Good luck.
 
Good point. You mentioned syncing the carbs. Is that required to get this running well when I re-assemble? I thought what I was doing would not affect the syncing. I don't have the tools nor knowledge for syncing. Thoughts?
 
Your question is why I always recommend the carb manual.

Yes, syncing is important to help easy starts and smooth idle. And, although to a lesser "detectable" degree, it does help with wringing out that last 1 or 2 horsepower at top end

It's typically achieved using a manifold with vacuum gauges but it can be done with just one vac gauge. It's just more work that way.

There's also the "lean it out then fatten it up" method using just your ear but that just doesn't work for everyone and is less accurate even for experienced tuners.

Lots of people work on these and don't properly sync them so...
....it's a choice I guess.

I can also say that, without the manual, you're likely missing important areas, like the air jet passages, that need to be cleaned that might bite you when you're done.

If those jet sets clogged after such a short time, that indicates that some VERY DIRTY, contaminated fuel was being run. Those contaminates will be lurking in places you can't see.
Failing to get those carbs TRULY clean when you have them apart just doesn't make sense. But without the manual to guide you it's likely you won't.

Contaminates inside these carbs can be woefully accumulative if not knocked off in a timely manner. That could end up with a carb you just can't get flushed out well and made usable again. Letting that stuff pile up and harden can result in a carb that just refuses to come clean.

If you look at parts availability, you will see the top two carbs are probably not going to be easy to find should you need to locate one either so getting them as clean as possible will make a big impact on how much use. you can get out of this outboard.

Ok, so, having said all that, I will try to help you get them as clean as possible but it will be in fits and starts as I am currently having some issues with my health.

More later...
(if you can stand it ;>)
 
Thank you for that.

First, I hope you are keeping track of which carb came from which cylinder. That's important because I don't think I'm going have you pull the idle mixture screws so as to keep things simple. But, if the carbs get mixed up then the synchronization is likely to be way off. That's assuming it was ok before you opened things up.

Did the outboard ever run well after you bought it?

Also, I hope that you haven't yet refitted the jet set tubes....??

Do you intend to reuse the gaskets, orings and seals?

Make sure that you have a couple of full cans of carb spray on hand with the little straws that should come with them.
 
After reading back over your post, it's apparent that you were happy with the way she ran before storing.

So, I think we should concentrate, for the most part, on what storing it with gas in the carbs may have caused.

While I usually don't like not taking the mixture screws out, I feel reasonably comfortable not doing so in this case (started ok and purred). Always a bit of a risk but I think it's worth taking.

That is, of course, unless it's something you want to tackle.
Those "tamper resistant" idle screws are a real pain and difficult to remove sometimes. I think we can verify idle circuit flow without digging them out of their holes. I leave that decision to you

You have already addressed the jet sets so the main thing that's left is the SE or Service Enrichment system. It's often called the automatic choke or bystarter.
It's controlled by a heated element mounted to carb #1.
See item 18 in the link below


I think that system is likely somewhat plugged and is the cause (along with the plugging you found in the jet set) of the inconsistent cold starting and refusal to run.

Carb #1 (top) is the heart of the cold start system. It has a brass tube that juts down into the fuel bowl and pulls fuel UP to a "SE well" that the thermo valve sits over.
From there it mixes with air, due to jet "suction", in carb 1 and that mix is fed to the other 2 carbs via the external fuel tubes.

That "excess" mixture is fed to the intake manifold from each carb to help cold start and run until the thermo valve heats up and closes off the SE well. 3 minutes or so.

The tube that feeds the SE well is fed fuel from a passage in the bottom of the #1
carb's fuel bowl. I think that passage may be partially plugged. Job one is to make sure that passage is completely clean.

Also, make sure the brass tube is clear and will pass fluid.

Too much info? I know! But knowing how something functions can help you understand why it needs cleaning.

More later.
 
jgmo said:
Also, I hope that you haven't yet refitted the jet set tubes....??
Click to expand...
After spraying every hole I could find on the carb body with carb cleaner and blowing them out, I put the jet tubes back in their holes. But I did not find removing them or putting them back in a difficult process.
 
jgmo said:
While I usually don't like not taking the mixture screws out, I feel reasonably comfortable not doing so in this case (started ok and purred). Always a bit of a risk but I think it's worth taking.

That is, of course, unless it's something you want to tackle.
Those "tamper resistant" idle screws are a real pain and difficult to remove sometimes. I think we can verify idle circuit flow without digging them out of their holes.
Click to expand...
Is mixture screw and idle screw the same thing? I am guessing it is the screw with the small head that sits partially recessed in the carb. The head is very small, it has a spring, and the tip is a very small, short shaft (as opposed to a tapered end like the other screws).
 
If that is the screw you are referring to, I counted the turns until tight before removing it. Then I cleaned it and put it back in tight and counted turns back out to get it back to its original position. I have not touched any of the external, spring-loaded screws related to the throttle.
 
jgmo said:
You have already addressed the jet sets so the main thing that's left is the SE or Service Enrichment system.
Click to expand...
It is now cleaned. The "needle" inside was gummed up a bit. It is clean now, as well as the rest of the aperatus. That probably explains why I noticed no difference when it was running, and I pushed the key in to initiate the choke.
 
Well, that last sentence has me fairly confused.

You say you have to push the key in to initiate the choke??

That should not be if this outboard is a post 2007 model OR if it has the bystarter fuel enrichment system.

But maybe it's an older pontoon with a newer outboard installed and that "push to choke" has been disconnected?
 
Yes, removing or installing the jet set isn't difficult but it could be hard on that little oring. The oring sealing properly is so critical I never like reusing one.
 
Blocking the passage where the jet set installs is part of the cleaning process.

Sorry for all the rapid fire but I wanted to catch you before you left for the dealer.
 
jgmo said:
You say you have to push the key in to initiate the choke??
Click to expand...
Above the keyhole, it says "push to choke." I could investigate the wiring to see if it is disconnected. If it is, does that mean the choke is self-initiating? The pontoon is a 2006. I found the owner previous to the one I bought it from. He was not the original owner, but he said he put this motor on. I think he said it was a 2010. I have been unable to find anything to indicate if that is accurate.
 
To help me with my confusion, could you compare items 15 and 18 in the link below with your #1 carb?
Also,. item 5 is the mixture screw. It has a sharp point on the end.
 
When handling the jet set oring it is important to take care not to stretch it more than is just necessary to put it on the tube.

It is also good to use a tiny bit of lube....like Vasaline...on the oring prior to pushing the tube into the passage so as not to nick or roll it.
 
I will instruct you on sealing the passage. You simply use your finger. The when is more important than the how. I hope your skin isn't sensitive to the carb cleaner.
 
Yes, 15 and 18 in the link look like my carb and choke.

I wear rubber gloves when working with the chemicals, so plugging the hole won't be a problem. Which hole do I plug, and then what?
 
Ok, here we go...
Look at the FRONT mount flange of the carb body. There are two holes about 3/16" in diameter. One just above and slightly to the side of the other.
Those are the slow and main air jet passages.
The top one is the main air jet and the lower or inside one is the slow air jet passage.

You may have already sprayed them but we're going to "backflush" them.

Look at the engine mounting of the carb and locate the tiny orifice at the top of the carb throat. That's the idle port.

Now open the throttle all the way and locate all the other orifices that can't be seen when the throttle plate is fully closed. There should be about 7 tiny holes. The ones that are closest to the end are the transition ports and the 2 or 3 farthest inside are the main or high speed ports.

Find a way to prop the throttle linkage wide open. I use a pocket screwdriver but anything that works will do.

You can now see and access all of those little holes.

I want you to put the carb spray straw in the nozzle and then use the end of the strae to cover each one of those holes, one at a time, and give each a shot of fluid. Try to note where fluid comes out each time for your own reference. It's messy so outside is the best place to do this.

Are you with me so far?
 
Next, put the straw in the slow air jet hole (lower one) and plug the jet set tube hole with your finger. While observing the idle orifice....the tiny hole closest to the engine....give it a good spray and ensure a good amount of fluid sprays from the idle orifice. That indicates the passage is clear. But I then like to cover the orifice with the straw tip, plug the jetset tube hole and backflush again. You want to see fluid coming from the low speed air jet passage when doing that. If so, the passage is completely clean.

Now put the straw in the main air jet passage, plug the jet set hole and spray in there.
You should now see fluid coming from pretty much every one of those tiny holes at the rear of the carb throat....including the idle orifice.
If so, the passages are likely clean but I like to cover each orifice with the straw tip and give them one more shot to be sure.
 
After you're done with that, I have just a couple of questions and you can probably start reassembly.
 
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