Honda BF40 Dies at Warm Idle (Help)

Hi. I bought my first boat which is a Boston whaler dauntless with a 1996 Honda BF40. Everything is great, except that the outboard dies at idle after I am cruising around. I attribute this problem to: losing my first trolling fish, and looking like a jackass when coming to the dock.

I'll try to describe all symptoms. All help is appreciated.

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*Boat starts fine while in water or on muffs.

*I noticed that while starting on muffs gets my RPMs in optimal 900rpm zone, in water, RPMs are low, so I have to raise throttle ever to keep from stalling. I increased idle screw, and starting RPM is fine now.

*After startup and short warm up, boat runs fine, and has normal power through all engine speeds. The problem starts when I am cruising, then put boat into neutral. Boat will run fine for a short while (less than 1 min), then start to decrease RPM, then die.

*It is easy to restart if i have throttle lever up, and then put into gear.
*If i start up, then release throttle lever back to idle, then it will die again.

*While flushing the engine with muffs, it starts up ok, and runs ok without the idle dying problem, but after maybe 5 minutes, it will start to race to 2500-3000rpm, then go back to idle for a couple minutes, then repeat.
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When I bought the boat, we took it out for a short run, and there were no problems. The next time i took it out by myself, i experienced the idle problem. No engine alterations were done between then. Seller did mention he added fuel additives. The only thing I can think of is that I filled gas between outings, and did not add additives.

After the problem, I changed all spark plugs (old ones looked fine), changes fuel filters, adjusted idle screw.

Things I suspect, and plan on checking:
Change oil
Change water pump impeller (never changed, but pees ok)
Engine electrical cutoff switch sometimes doesn't make good contact

If anybody has any suggestions on where to start, it would be greatly appreciated.

Thanks
-Eric

Welcome to boating. It sounds like you are starting with a pretty nice package.

First of all the 40A is a very sound engine.

Idle speed should be 950 plus/minus 50. I like to get it close to 1000 rpm when on a hose.

If you have the ability/tool, it would be good to check the compression. With the throttle wide open, it should be around 200 psi.and all cylinders within 10% of each other. Uneven compression, could be the sign of carbon buildup on the rings or valves.

On that vintage, the idle mixture (or pilot screws) part 6...should be approx 2 1/4 turns out from being lightly seated.

One possible cause of the varying idle could be a leak in the intake manifold or one of the base gaskets on one of the carburetors. If you have some brake kleen or starting fluid, while the engine is running spray around where the intake manifold joins the block and around the base gaskets of the carburetors. If you get much of a change in how the engine is running, that would be the place to check. Certainly, at this age, someone has removed the carburetors to clean them. Sometimes, the mechanic is lazy and does not clean the surface of the intake manifold very well and leaves some of the previous gasket on. That can cause air leakage. Likewise, they may have reused a base gasket that was torn or maybe even did not put it on properly....maybe missing one of the bolt holes.

There is also a possibility that one or more of the jet sets in the carburetors have a crack. You have to remove and disassemble the carburetors and check with a magnifying glass. See part #19 http://www.boats.net/parts/search/Honda/Outboard Engine/0/BF40A LRTA/CARBURETOR/parts.htm

The carburators need to be vacuum balanced for proper idle and acceleration. Unfortunately, you need a set of three matching vacuum gauges to connect to the manifold to make the adjustments. Most likely, you do not have that tool, so let us put that aside for now.

Another thing to check is the temperature of the motor at the thermostat. #9 http://www.boats.net/parts/search/Honda/Outboard Engine/0/BF40A LRTA/CYLINDER BLOCK/parts.html It should be around 72 degrees C or 161 degrees F. If you have a lazer temp gun, that will make it easy. if you put your hand on it, it should feel pretty hot. If it feels cool....change the thermostat. The engine has to run at proper operating temperature to idle properly.

I do not think you impeller is causing the idle problem. Changing the oil would be good. Use mineral based oil, not synthetic. Keep the oil level to about 1/4 inch below the full mark. If you think the safety landyard is causing the problem, disconnect one of its leads and take it out of the picture for test purposes (if you can easily get to them).

There are timing marks on the the flywheel and the cam pulley. They should be matched up with the marks on the powerhead. I have not seen time to cause the idle to vary, but you never know.

Those are just a few of the basic things I would check first if it came into the shop. Of course, I do not pull the carburetors off, until I go through everything else.

One last thought.....it is possible that while idling at the low speed, the engine is only running on two cylinders....then the third cylinder kicks in to speed it up....As the engine is idling, using an insulated pliers, pull the spark plug wires off of the spark plugs one at a time. As you pull it off...the engine should reduce in rpm. If the rpm does not go down, that cylinder has a problem. Also hold the wire close to the spark plug as you put it back on and listen for the ticking of the spark. That way you can verify that the troubled cylinder has spark. Then the problem is either in the cylinder or the carburetor associated with that cylinder.

As I ramble on.....one more thing...that you should check first. Drain your carburetors into a glass jar and see what the fuel looks like. You might have water in your fuel. It could be that simple. You will see the water settle to the bottom of the jar.

Also, make sure that you tank vent is working properly ( you can just loosen the fuel cap) and squeeze the fuel bulb when the engine changes speed...to see if that has any effect.


Hope I did not overwelm you...but there are a lot of things to check.

This was pretty disjointed....it is past my bedtime.

So...good luck on your checks and let us know what you find. Then we can go from there.

Mike

Awesome. Thanks Hondadude. That is exactly what i was looking for,very thorough, and easy to follow. I'll start off with the RPM drop test, thermostat and air leak test. Got some hurricanes on their way, so i'll probably have to wait til mid next week. Will post my findings

Update:

I was able to work on the boat today.
I replaced the water pump impeller. The old one apparently was missing 2 vanes.

I tested for the carburetor leak with brake cleaner, and an air compressor. The top carburetor was unaffected by the spray. The bottom carburetor was definitely affected by the break cleaner, and made the engine race. The middle was hard to tell. There was an rpm increase, but it may have been due to fumes making their way to the bottom carb leak. Leak appeard to be in the rear of the carb where it connects to the manifold.

I also did a cylinder drop test. Top two carbs had a drop in engine speed when unplugged. I could hear the electrical arcing. The lower carb was hard to determine. I think there was a small decrease in engine speed when unplugged, and I could hear arcing.

I also pulled and checked the plugs. They have less than 20 hours on them. All 3 were consistent in appearance. They were a dark coffee color. The boat is slightly overpropped. WOT should be @ 5k-6k. Im at about 5000rpm.

While testing, the lower unit was in a water barrel. Would startup, then maintain rpms in 600-900rpm. After maybe 10 min, it would die. I would then have to prime, choke, and start up again (usually me warm engine needs no choke). Engine would last for like 3 minutes, then die again while at idle.

What do you think? Will replacing the gasket solve my stalling problem?

Is it possible that the 3rd cylinder is misfiring at low rpm?

I have a compression gauge in the mail.

Do you still think needle inspection is necessary?

Thanks
-Eric

Want to add that squeezing primer ball does not change engine speed. While sitting, it does get limp, and sounds like it's nearly empty when squeezed. Why is that? I don't understand how air could get into the bulb, unless it's from the carb side, or there is a hose leak (no drips observed)

will check vent during next test
also, the idle screw is more turned a lot more than 2.5 turns. With the engine problems, it runs better like this for now.

when I changed the fuel filters, I drained the large filter and no water was present. Will check carb later

Dry compression test complete. I let engine warm for 5 min at idle. Throttle full open.

top: 179
mid: 180
bottom: 185

I loosened the fuel cap. It seemed to help, but engine still died at idle.

Thermostat housing hot. Probably 130F after a short idle period. Pulled thermostat. It was pretty corroded, and in the open position. Are you supposed to be able to squeeze them closed? It was very stiff

It looks like you have been busy.

First...you said that you have parts of two of the impeller blades missing. Did you find them? If not, they could cause problems in the future. The first place to look is in the water pickup area behind the screens or under or in the water pump base. Hopefully, they are in the pick up area and all you have to do is remove the plastic screens...otherwise, it is back to pulling off the lower unit.

The temperature is actually a little low. If the engine would continue to run, it would probably get higher.....the thermostat is fully open at 162 deg F. So you are probably ok there too.

Here is are two thoughts....

1....since your engine stops after three minutes, it may just be running out of gas. It is possible that your fuel pump is bad. Will the motor keep running if you keep squeezing the fuel bulb? If so, then, either your fuel pump is bad, or there is a blockage in the fuel system.

2....Although, you said that all spark plugs looked the same, the fuel pump may be leaking into the bottom cylinder/crankcase area. The cylinder may be running rich. It does not explain the pickup when you spray the bottom carb gaskets. You can check it by removing the fuel pump, squeezing the fuel bulb until it is hard and see if there is fuel anywhere on the plunger side of the pump.

That is where I would concentrate before you pull the carbs off. Also, the pickup when spraying the gaskets, might be misleading if some of the fumes are being sucking into the intake. If so, then you may have idle passage problems in one or more carburetors.

Mike

I found 1 vane of the impeller in the housing. Will need to hunt for the second.
I'll go and replace the thermostat. I'm sure its long overdue.

I WAS able to keep the motor running while continuously pumping and maintaining a firm primer bulb. However, after about 10 minutes, i experienced the rpm racing to a sustained 2500rpm for a few minuted before i shut off.

I am unable to remove the fuel pump right now. I dont have sockets or wrenches in that size. too tight in there.

I sprayed the brake cleaner around carbs again without compressed air. Still has rpm jump.


I noticed that the engine appears to every now and then sneeze (is that a backfire?)

Possible it is a compound problem of fuel pump and gaskets?

The sneeze is telling you it is running lean. They will do that sometimes, even if all is ok, until they are fully warmed up. It could also tell you that the idle mixture is out of adjustment or one of the carbs have an issue.

And....yes....it could be a compound problem....but do not jump ahead of yourself. It sounds like you are on the right track to one of your problems....which may be the only one.

I have no definite explanation for the racing. It could be any number of things. Assuming the fuel pump is bad, fix that then see what happens.

Mike

Thanks for the quick follow up.

Ok, i got excited, and I managed to get the fuel pump off. I had to jury rig a 1/4" drive 8mm socket to a ground down allen wrench.

I'm not familiar with the fuel pump, but i assume the plunger is the cylinder which protrudes into the engine. I unbolted the fuel pump, and with the fuel hoses attached, i primed the ball til it was firm. There was no obvious fuel leaking out the plunger.

It still could be the fuel pump. If you have a small hose, remove the hose going from the fuel pump to the bottom carburetor, and connect the small hose to the nipple on the fuel pump. Run the hose to a container. Pull your safety landyard off, to cut the spark....then crank the engine and see if the pump is pumping. If it only dribbles, then the pump is bad.

Mike

One other thing to do to verify that the pump is not pumping. Squeeze the fuel bulb and see if you can drain any fuel out of the top carburetor. I would think you can.

Than run the motor until it stops and see if you can drain any fuel out of the top carburetor again. There will probably be no fuel.

Mike

Got to do some tests today.

First, I disconnected the line from the fuel pump going to the bottom carb. There was white buildup on the nipple where the fuel hose was clamped to. I attachd a small hose section, pumped the ball, and took some fuel samples. For the first (2) 4oz samples, there was a reddish brown liquid that settled to the bottom. Only a small quantity, like half the size of a m&m. After I kept priming the ball and draining through the hose, no sediment was found.

I hooked the hose up to a cup, and cranked the engine w/o the killswitch plugged in. Little squirts of fuel was spitting out intermittently (not a full stream). It was not a dribble. For 5 seconds of cranking, I collected 1/4oz of fuel.


Next, I reattached the fuel hose going to the carb, and primed til firm. I then drained the top carb I would guess 1/2 oz to 3/4 oz was drained. The fuel was clean. I then started engine, and let it run. It stalled about 6-10 minutes later. I drained the top carb, and it was empty. The middle carb was empty. The bottom carb had less than 1/4oz in the bowl.

What do you think?
Thanks again

And in case you were wondering why i never started with the easiest test first... I never knew draining the carburetors was so easy. I thought you would need to remove them or disassemble the bowl.

I can not explain the colored liquid. Have you taken a fuel sample to be sure it is not coming from the tank? I have seen a lot of strange buildup in older tanks. If previous owner's have used Stabil, sometimes that, over time, turns to gel.

If you have a small extra fuel tank, it would be good to do all further testing with that...so you know you have known good fuel.

With the fresh fuel, flush the motor again....by opening the drains to the carburetors one at a time and watching the fuel coming out. If there is any discoloration at the start, keep flushing until it clears out. Do the same from each carburetor, one by one.

There may be just junk in the system. I am leaning towards the problem being a bad fuel pump, but I tend to do a lot of testing before spending $100 for a new pump. It does seem that, if you had everything primed and the other two carbs full of fuel, the pump should have put out more than 1/4 oz.

Try your running test again and do your cylinder drop test again. If you think the flow is good by watching it come out of the fuel pump when you squeeze the bulb, then it is probably the pump.

If you change the pump, be sure to get an new o ring.

Mike

I flushed out some fuel samples from the gas tank at the hose which connects to the onboard fuel filter. There was some sediment and some small amounts of water. I then unscrewed each drain plug and flushed out fuel til it was clear. Each carb had traces of water, and small amounts of very fine black sediment. Does the inside of the primer bulb disintegrate? It looks to be in good physical condition on the exterior.

I ran the engine, and did the cylinder drop test. The firing became rough when I unplugged each wire. I could hear arching when held close to the plug.

The engine ran fine at idle while intermittently pumping ball. After idling for like 10 minutes, it started to pick up rpm on its own, and went up to like 2500 til i shut it off.

I'm planning on ordering pump, oring, thermostat, and gaskets for when/if i need to clean carbs (due to water and sediment in bowl samples). Boats.net apparently thinks Hawaii is a foreign country, so i pay almost double normal shipping rates (they said they need to pay export taxes which is totally false). I figure I should order the parts just in case I need them because s/h is a killer. Are there any more parts I would definitely need for a carb servicing?

What do you think of the plan?
Would carb inspection be the next step if replacement fuel pump doesnt solve all problems?
If so, would I need to get vacuum gauges to sync carbs after servicing?

I forgot to mention, that while the engine runs smoothly at 1100 rpm, and purrs as some would say. At 900rpm, it sounds a little rough, and has a small jerking motion to the overall engine vibration (maybe not warmed up?). This is my first outboard engine, so I dont have much to compare to. Thats why after also finding all the crap in the fuel samples, i suspect I may end up doing carbs for piece of mind.
Thanks

It sounds like you are making progress.....it seems to be running longer and your cylinder drop test seems to indicate the all cylinders are firing good. The idle should be set at 950 plus/minus 50. I usually set it close to 1000 rpm when setting it on a hose.

Idle smoothness is also effected by the carb vacuum balance. If you can find a set to borrow, it might be worth the time to balance them before you pull them apart....it might fix a lot of problems. Sometimes I get lucky and that fixes all the problems.

Also, check those idle mixture screws.....initial setting should be 2 1/4 turns.

I am still not sure about the huge increase in rpm....perhaps cracks in the jet sets but I have never seen that much of an increase. ....or could be the gasket issue we discussed before.

If you are going to do the carbs...these are the parts I would replace...

#34, 22, 19, 2, 3 and 37 Those should cover just about anything you will need in the carbs. http://www.boats.net/parts/search/Honda/Outboard Engine/0/BF40A LRTA/CARBURETOR/parts.html

Yes the squeeze bulb and hose can deteriorate from inside. I have seen many that have linings inside the hose where the lining came loose and blocked the fuel flow. The diaphragms in the pump can also deteriorate

One other thing to check.....part #40. It is a check valve. It has an arrow on it. Make sure that the arrow is pointing toward the carburetors. Pull it off and make sure that it will pass air only one way. Be sure to put it back on correctly.

Mike

Will order parts now, and report findings later this week.

When you mentioned the idle mixture screws, i thought you were referring to what i now know is the idle stop screw. Will check the idle mix screws after parts come in. My original thermostat is frozen, so i'll probably stop the running tests til parts arrive.

Check valve in correct orientation. Will verify proper functioning.
Thanks.

Sounds like you have a plan.

Good luck! Let us know how it works out.

Mike

Got some work done today.
First, I flushed the fuel system. At first, there was more of that red blob crap and minor sediment. It ran clear after about a half pint was flushed. I dont understand where its coming from. The main tank is clean. The main fuel filter is new, and the onboard fuel filter is new too. I am taking samples after the onboard filter. I would think that the main filter would filter fine particulates, so the crap must be in the fuel hoses in the outboard?

I changed fuel pump, and thermostat.
Started up.
Noticed the water pee stream seemed fuller. After about 5 minutes, the thermostat housing felt hot. I'm sure the old one wasnt working at all. It was seized in the open position. Good buy

Engine then stalled after about 5 minutes. Checked the fuel in the carb bowls, and they were full of fuel (unlike before)

I then reset the idle pilot mixture screws 2 1/8 turns out. I tried to tune it by ear from there, but it was difficult, so i just left them at 2 1/8 turns out.

I hooked up a carb sync vac gauge to do the idle speed timing screws. The top cylinder was pulling a higher vacuum than the other 2, so i tuned #1 down.

The engine IMO seemed to run much smoother at idle, but it still had the rpm hunting problem, and i think i recall that it still stalled. I also remember that one time it started hunting after putting the engine cover on (i think). After removing the cover, it seemed to stop the hunting. However, it has that problem regardless of the cover being on or off. Just removing the cover stopped it that time.

I tested for the vacuum leak again with brake cleaner. I think there was a vacuum leak, and that the fumes were not making their way into the intake.l

I removed all carbs, cleaned, and replaced needle jet, and seals and gaskets. Carbs were surprisingly clean. I have been reading how other people experience problems with the cracked needle, or leaking float, so i think this was a good investment.

Carb cleaning was actually not too bad. The worst parts were scrapping the gaskets, and reassembling the choke solenoid linkage. Gotta double check that tomorrow.

I had to do some unexpected errands during the day, so the engine was reassembled at about 8pm tonight. I did not get a chance to test yet.

Hopefully will have a chance tomorrow morning before i gotta go work.

Btw.. there are 2 small clear hoses going to drain holes on the bottom of the engine compartment. One is connected to the bottom carb, and the other to the air box. What are they? Both had blockages.

They are both called drain tubes. One, I think is for the bottom carburetor bowl drain. The other allows built up water vapor that condenses to drain from the muffler cover.

While you were in the carbs, did you check the jet set (long skinny tube going up the center of the carburetor for small cracks?

Hope all that effort works for you.

As for the red stuff. Use a different tank for your testing. If you have a built in tank, it could be from that, even though you have filters. If you keep finding it, you may have to remove the fuel sender and take a peek.

Mike

Everything looks good!

So in the morning before work, I was anxious, and started the engine for 10 minutes. Idled very nicely, and i was so relieved. Shut off, and went to work.

In the evening, I started up, and idled nicely, then did the rpm hunting thing, and eventually sputtered and died along with a little bit of myself. Drained the Carbs. I recall about 3/8 f an ounce in each carb.

The next day I disassembled the fuel hoses from the tank, blew out, and reconnected. Also blew out quick disconnect fitting to tank. I also checked the check valve of the ball. I noticed that there was no suction on the input end unless it was held at a 45 degree or more angle. I read about not keeping the ball flat, but I didnt realize that it needed such a slope to close the check valve. I reassembled the fuel hose assembly with ball in a more vertical orientation.

I started engine up, and it idled very nice, and had no hunting or stalling issues. I ran it for about 20 minutes, and everything looks good so far.

I replaced the carb needles, so I saved the old ones and plan on doing an inspection of them soon.

I'm thinking that:

1. Vacuum leak caused bad idle/hunting
2. Primer ball orientation/loose quick disconnect fitting caused bad fuel flow at idle causing stalling.

What do you think??

I plan on going for a test run on thursday, and ill keep you updated.

BTW... would SAE30r7 fuel hose be sufficient, or should I use r9?
With the effort to clean the carb, I feel obligated to keep fuel system clean.

The check balls in the squeeze bulb can be pretty stubborn at times. Depending on the age of your bulb, it might be wise to buy another before next season. Do not get the cheap ones. Get one made by EVinrude/Johnson, if you can...they are the best.

I am not used to seeing those hose ratings. I guess I have not looked that close. I just look to be sure that it for Marine use, for outboards. There is also different hoses for under deck and inboard/outboards.

Googling the ratings, the r9 would be an overkill....it looks like it is rated for fuel injection pressure. You only have to deal with less than 10 psi...and that is caused by the squeeze bulb.

Mike

Good luck on your test....it looks like all your work is paying off!

Had a nice day out on the water last week. Everything appeared to be running excellent. No stalling issue, and very smooth idle! The harbor I went to had a tricky current/wave environment, so i was relieved that the motor performed very well.

After reading my previous post, it doesn't make sense that the hunting was caused by the vacuum leak, since it still persisted after the carb servicing. Maybe a fuel delivery problem?
Anyway, I'm gonna replace the fuel hoses, and buy some stabil for good measure. The reason I asked about the SAE30r9 hose was not just the pressure rating, but because the fuel hose i picked up was r7 and only approved for EEC and fuel vapor use. My napa doesnt carry carb hose. I found some online.

I also rechecked the idle pilot screws. Rpm was highest at 3/4 turns past the 2 1/4 turn position. I adjusted all 3 carbs to the same position. As a side note to anybody reading.. get a carb sync gauge set.. the liquid one i got sucks. Needs to be calibrated all the time, and sucks liquid into engine.

Thanks mike for your help. I would have been shipwrecked by now without your expertise!

Congratulations for sticking it out. Success is good!

Mike