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Honda BF50 WOT only with a little manual choke applied

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I have a 1995 BF50. Cleaned carbs .Twice.Engine idles great.Transitions to 4200 rpm smoothly. BUT will not go above 4200 rpm unless a little choke is applied---then it runs fantastic at WOT. My question: Does Carb synchronization with a motion pro vacuum tool(or similar),have any effect on my leaning out at high rpm,or does carb synching only ensure best idle performance?? Also,I am curious why this engine leans out at higher rpms.... THANKS!!
 
How about some history? Did it run well before and get up in the 5200 rpm range or higher at some time in your ownership? Or is this a recent purchase?

If you bought it and are trying to get it dialed in I would want to know if it has the right jets in in it. Somebody could have been tinkering or may have re-jetted for high altitude.

If it ran ok before, then how did it come to needing the carbs cleaned? Was performance slow in dropping off or did it happen fairly quickly? Was it because it was put away for a while with fuel still in the float chambers?

Syncing is done mostly for obtaining smooth idle and to prevent surging and vibration at intermediate speed. But it can't help but to effect full throttle operation since it has to do with the relationship of the throttle plates of each carb to one another.

Have you checked your valve adjustment? Poorly adjusted valves could have the engine struggling to "breathe".

I know, lots of questions and no answers but if we talk about it, something useful might come up.
 
jgmo said:
How about some history? Did it run well before and get up in the 5200 rpm range or higher at some time in your ownership? Or is this a recent purchase?

If you bought it and are trying to get it dialed in I would want to know if it has the right jets in in it. Somebody could have been tinkering or may have re-jetted for high altitude.

If it ran ok before, then how did it come to needing the carbs cleaned? Was performance slow in dropping off or did it happen fairly quickly? Was it because it was put away for a while with fuel still in the float chambers?

Syncing is done mostly for obtaining smooth idle and to prevent surging and vibration at intermediate speed. But it can't help but to effect full throttle operation since it has to do with the relationship of the throttle plates of each carb to one another.

Have you checked your valve adjustment? Poorly adjusted valves could have the engine struggling to "breathe".

I know, lots of questions and no answers but if we talk about it, something useful might come up.
Click to expand...

It ran well up until last summer---but had a "flat spot" when transitioning from idle to high rpm(,but always had full WOT)....so this summer I decided to do a carb cleaning.
Now it idles and runs really well without the "flat spot" on throttle increase.
I havent checked the valve adjustment.
I am assuming the fuel pump/spark plugs/and main fuel nozzles/jets are all good since the engine runs great at WOT if a little choke is applied.....

THANKS for all your answers!!...and help
 
I wouldn't assume anything yet. When you are "applying a little choke", you are modifying the amount of air that comes in and artificially adjusting for a lean condition. That would say to me that the mains are NOT alright and the carbs are starving at the higher throttle settings.

I'm referring to the parts page in the link below. When you cleaned the carbs, did you use new mounting gaskets? And, did you replace the Oring (item 2) at the top of the jet sets (item 19)?

http://www.boats.net/parts/search/Honda/Outboard Engine/0/BF50A SRJA /CARBURETOR/parts.html
 
jgmo said:
I wouldn't assume anything yet. When you are "applying a little choke", you are modifying the amount of air that comes in and artificially adjusting for a lean condition. That would say to me that the mains are NOT alright and the carbs are starving at the higher throttle settings.

I'm referring to the parts page in the link below. When you cleaned the carbs, did you use new mounting gaskets? And, did you replace the Oring (item 2) at the top of the jet sets (item 19)?

http://www.boats.net/parts/search/Honda/Outboard Engine/0/BF50A SRJA /CARBURETOR/parts.html
Click to expand...

I only replaced one of the carb mounting gaskets,since the other two looked perfect. New silencer gasket.New O-rings for all.
On my second carb cleaning I paid close inspection of the Main jets,thinking that was the problem---but all were spotless.
New fuel line and bulb.Curious if its sucking a bit of air through the tank and/or engine fuel line fittings.

Thanks for the troubleshooting on this one..... any ideas welcome!
 
It has 125, 128 and 130. The 130 is the standard jet under 5000 ft in altitude.

These carbs also have a transition passage....a little group of pin holes in the top of the throat of the carburetors. You wlll have to open your throttle plate to see them.

If your jets are correct for your altitude, then one or more of your carbs' transition passages may be plugged. If you place the straw of brake clean or some solvent up into the hole at the top of throat that the idle jet goes into, you should be able to see a good spray come out of transition holes. If not, then you have to back probe into the holes with a very small wire.

Also, double check that your idle jets are good and clean.

Make sure that you have reconnected all the hoses around your dashpot check valve #40.


Mike
 
Well,I just got back from a good run here at Halfmoon Bay,BC.... perfect start....smooth idle....velvety transition to 4500 rpm..... then bogging down....ugh!! my last bit of maintenance before this was to sync the carbs,and re-check all hose connections as suggested by 'hondadude'.....

I am ready to pull these carbs again and really check those throat transition holes again.I know 100% that the main jets and nozzles are clean,so dont know whats left that is stopping the high-speed circuit from working right.

Any ideas before I pull carbs?... THANKS to all!!
 
As I review your posts...it ran at full throttle before you cleaned the carbs. That logically would be the first place to look.

However...to eliminate other coincidental potential sources of problems....

Did you take compression? I cannot believe that I did not ask that yet. It should have been the first test. You are looking for around 200 psi.
Did you change the fuel filter?
Have you tried using another tank and hose? That will remove any doubt about the fuel system on the boat.
Does it still get to full throttle with a little choke?
Does the runability improve if you squeeze the fuel bulb?

If you have tried all that, take a timing light and take the boat out and move it from plug wire to plug wire and make it fail each time. Watch the timing light and compare the flashing of each cylinder. They should all look about the same. If not, then if could be electrical.

Mike
 
Thanks Mike-- Havent taken compression test . Changed fuel filter first. Changed fuel tank line and primer bulb. Havent tried different tank. Havent changed the hose connectors yet.
It runs to full power without a miss,when just a little manual choke is applied. Squeezing the fuel bulb makes no difference.

It ran to WOT no problem last year--- but had a little annoying flat spot when transitioning through mid-range.....so I cleaned the carbs(found a little dirt inside),and that eliminated the flat spot problem...only to have the bogging down at WOT....

My biggest clue on this so far is the obvious leaning out at full-throttle,as demonstrated by the choke application..... I am starting to think these carbs are extremely difficult to get entirely clean....
 
NEW CLUES FOR HONDA BF50 !!

So I am thinkin' this through again----Fuel-Spark-Air---- how hard could it be,right?? So again I pull the sparkplug leads while running in idle: bottom carb drops rpm ok,middle carb drops rpm ok.top carb -makes no difference...hmmm how could this engine run so smooth if only firing on the bottom two carbs?? I swap plugs since I must have a dead plug(after only a year use? maybe.)
Nope,all plugs work---top carb still does nothing when lead is pulled in idle or higher rpm....So I must not be getting anything from the lead then,right? Nope===nice big fat spark for top carb lead... Is the carb bowl dry,maybe?? Nope,fuel drains as usual.

So,next clue: When I screw in mixture idle pilot,on bttm carb---engines wants to die---so back to one turn out and all is good again.Ditto for middle carb. Top carb?? screwing idle pilot screw all in doesnt affect engine running at all...hmmmmm.. so I have been running on just two carbs then??? explains why I cant get to WOT...

So now what?!! .... :confused:
 
Well, it's not firing on that cylinder so it doesn't surprise me that messing with the idle screw makes no difference. I work on the small twins a lot and it always amazes me how smoothly they run when one cylinder isn't firing. So I'm not surprised the triple does the same.

What I would want to know is if the carb is delivering ANY fuel. If it is, the plug should be wet if you pull the plug wire and let it run on the other two cylinders for a minute or two. That would answer your question. Either that or artificial enrichment using propane or carb spray...DON'T USE ETHER! That stuff damages pistons.

If you determine that it is lacking in fuel delivery,you may have a poor seal in #1 carb where the jet set tube pushes up into the top of the carb throat main passage. That O ring can be tricky to get "popped" in there without rolling it sometimes and creating an air leak.

Other than that, your equation for combustion is missing one important piece....Compression. It should read;
fuel (in sufficient volume) air (in sufficient volume) spark (at the right time) and compression. The other three can be present but with poor compression she still won't fire because the fuel won't vaporize.
 
I DO remember on one of those carbs---maybe that top one--- that I didnt get that "pop" as I pushed in the fuel nozzle.... But still,I am surprised that that carb isnt letting that cylinder fire at all...!! ....
 
It is probably firing at full throttle, once you choke it a little. The choking is acting like the idle and transition passage.

Sounds like you need to pull the carb and make sure the idle and intermediate passages are clear. If you did not seat the idle jet, that could also be a problem.

At least you only need to redo the one carburator.

Mike
 
hondadude said:
It is probably firing at full throttle, once you choke it a little. The choking is acting like the idle and transition passage.

Sounds like you need to pull the carb and make sure the idle and intermediate passages are clear. If you did not seat the idle jet, that could also be a problem.

At least you only need to redo the one carburator.

Mike
Click to expand...

Thanks"Hondadude" Mike... you are right in saying that at least I only have one carb to re-do... Pulling the carb tonight--I have 2 of those little nozzle o-rings left.. :cool:
 
Make sure that the idle jet is clear. Also, before you put it back together, shoot some brake clean or similar solvent through its straw up through the hole at the top of the carburator. Make sure that there is a good spray out of all of the pin holes at the inside roof of the front of the carburator. You will have to open the throttle plate to see them.

Do not put the carb back on until you see a good spray.

Also, lubricate the o ring on the idle jet and it should pop right in.

Mike
 
hondadude said:
Make sure that the idle jet is clear. Also, before you put it back together, shoot some brake clean or similar solvent through its straw up through the hole at the top of the carburator. Make sure that there is a good spray out of all of the pin holes at the inside roof of the front of the carburator. You will have to open the throttle plate to see them.

Do not put the carb back on until you see a good spray.

Also, lubricate the o ring on the idle jet and it should pop right in.

Mike
Click to expand...

Thanks.... I was curious to know if the orientation of the idle jet side-holes is important .. for instance do they need to be aligned parallel with the choke plate or some other configuration.... or just pop it in with a fresh o-ring...??
 
hondadude said:
Just pop it in. Orientation of the holes does not matter.

Mike
Click to expand...
Pulled that jet(skinny nozzle) out last night... It looks like there MIGHT be a split on the side of the tube at the end opposite to the o-ring end... even under a magnifying glass it is really hard to tell for sure if it is a split or a scratch....

Assuming that it is a split: what symptoms would occur because of it??? I would have thought that the top cylinder with this carb would fire at least a little... :confused:

(I ordered some replacement idle jet nozzles, but I really dont like just changing out parts as a method of troubleshooting.... )
 
I generally change them out anyway, especially on older models. A split can cause what you are experiencing and the vacuum balance would be difficult to sync up and keep sync'd.

Mike
 
I change them out "just because".....

Just because they are a pain to get clean...if you can ever get them completely clean.

Just because they trap stuff up inside that you can't see unless you do have a good "scope". I have a GREAT scope and can see the particles easily and still can't get that crap out of there half the time.

Just because they fatigue and crack and "leak" internally.

Just because they are cheap and easy to replace.

Just because I don't like miss-diagnosing a bad one and am forced to tear the carb down again.

Just because time is money and I don't have time to "putz" around with these little darlings.

Many many many times, I just replace the carb bowl and the jet set and get on down the river.

Just because life's too short.

Hope that does it for you.
 
Now that summer is just about over,I have my Honda 50 running at WOT......
I would like to update this thread since alot of interesting postings just seem to end,leaving everyone wondering what the outcome/solution was.
So anyway,after just replacing the main jets/nozzles with new ones and cleaning the carbs a third time,re-syncing again etc..... my anticipation was high as I set out on a boat run,fully confident that I had solved the bogging-down at full throttle. Imagine my dismay when the engine did the same bogging down at about 4000 rpm.Seemed even a little worse than before. UGH!!:mad:!
I pulled off the engine cover to have a look,although by now I was out of ideas on what to check next. However I noticed that the choke solenoid adjusment screw was loose and had backed out.I tried to screw it back in a little,and realized that the screw was a little corroded,and the plastic piece it threads into was stripped.I tried a slightly oversized machine screw as a replacement,so it would thread itself into the plastic piece(the piece that touches the choke solenoid actuator arm). I fired up the engine thinking this wouldnt have any effect except for cold starting,but with throttle advancement the engine would hardly run....hmmmm methinks this adjustment screw must actually do something even though I cant find it in the shop manual or Seloc manual. Sooo.I backed the screw out until it was just slightly threaded in.Started up the engine again,and this time it took throttle advancement well....1550 rpm....2000 rpm....2500....35....40...45....5000....5600 !!! Smooth running....excellent transition between rpms and no hesitation....

Okay : whats goin' on here??:confused: I thought that choke solenoid actuator was ONLY for helping with cold starts?? THANKS!!!
 
Well, First off, let me say congratulations for finding your problem and thank you for letting the group know what took place.

You are correct that the solenoid actuator is ONLY for HELPING with COLD STARTS. But, as you found out, it is clear that if not adjusted correctly, it can HURT with "runability". Which is going to be true for any choking or "cold start enrichment" system should it malfunction in a particular way. To put it in basic, good old boy terminology, the engine don't want no choke after it's warmed up.

I suspect that your choke was hanging up slightly in the "enrich" position and, after warm up, was keeping the desired air/fuel ratio from reaching the approximate 14:1 "metric" that we all try to achieve when burning gasoline.

The only thing wrong with the above stated theory is that, when you began this thread, you said that you had to "give it a little choke" to get it to run right at higher rpms. So, we all, or at least me, thought you were lean. So, I don't know. But, again, I'm glad you got it sorted out. And, even if you missed much of this season, you should be ready for the next and that's a comforting thought when sipping a hot cup-o-joe on a cold winter's morn.
 
Thanks for the reply,jgmo ! Yup,it it sure nice to be able to run "full-out" again.... . Perplexing choke set-up for sure,especially since I could only get WOT when choking it a little. Since it was running perfect last summer,I never even looked at that choke adjusting screw....still cant fin it mentioned in the manuals either.... thought the manual would say something like"screw in a quarter inch" etc....
 
I never paid attention to this adjustment before. I looked it up in the official Honda manual and there is a full page describing the adjustment. It adjusts the throw of the choke caused by the manual choke knob (the one you pull out on the engine).

Just a thought...is it possible that you did not completely seat the manual choke rod into in the groove on the plastic manual choke knob when you put the carbs back on? If you did not, then the choke butterflies would most likely be held slightly closed. It could be like pulling out the manual choke about 1/4 to 1/2 inch, depending on how far you put it in.

If that is the case (and even if it is not), you probably still had issues inside your carbs that you fixed during your cleaning. So all was not in vain, but most likely frustrating.

I also congratulate you for your perseverance.

Mike
 
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