Honda bf75a carbs

Hello to everyone. I am new to the site and I have a bf75a(I think) which I would like to rebuild the carbs but not sure exactly what year it is. My main issue is not easy to start especially when cold and when I pull the choke it does not help at all... even when I get the motor running and pull the choke the motor has no change. The linkages are fine as well. Also I am going through spark plugs. The motor will run great for 2 or 3 times out then she will start running very rough like I have lost a cylinder. I put new plugs in and she runs great for a while. Does anyone have any guesses? Also I am thinking this thing is maybe like 2004-2005... thanks for any help. ERICK

Post the frame serial number and we will check the year.

First check to be sure that the oil level is not too high. It should be approximately 1/4 inch below the full mark. High oil can foul the plugs.

Can you tell which cylinder fails? It you run the engine and pull the spark plug wires off, one at a time with an insulated pliers, each time should reduce the rpms of the engine. If you pull one that does not change the engine speed, then that is the cylinder giving you problems. You then have to figure out if it is compression, spark or fuel.

Check to be sure that the choke butterflies are operating properly on all of the carburetors. Make sure that they open all the way when you are not operating the choke. Keep in mind, that motor also has a manual choke on the front of the engine. If that is pulled out, the choke will always be on.

Before you get into the carburetors, be sure to check compression. It should be around 200 psi....testing with the throttle wide open.

Also....to start that motor, besides choking it, you need to advance the throttle almost all the way to give it plenty of air. Be ready to quickly pull the throttle back once the motor starts so that it does not over rev.

If you have not done much carburetor work....if you find that you need to clean the carbs, I highly recommend purchasing Honda's Marine Carburetor Manual (Available on Amazon) Here is a link to a partial manual that may help http://ww2.justanswer.com/uploads/J...05k.marine_carburetion_manual_-_chapter_7.pdf

Mike

Mike, thanks for the reply. I have checked oil and it is exactly like you say it should be just below the full mark. I'm not sure how to check buftterfies because air box is in the way and you can not pull air box without pulling complete intake assembly with carbs and air box.... even when the motor is warmed up and sitting there idling, if I pull choke it doesn't even effect how the motor runs with I can't understand. Once I figure out how to upload pics I can show a pic of plugs. I am going to try and check compression today. Thanks agian

You can see if the butterflies are moving by disconnecting the connecting linkage and operating each one by hand, one at a time. They should move freely and spring back to open when not held down.

Mike

Ok Mike, I will do that with butterflies and I just bought a compression tester today. After I put new plugs in it seems to run strong but after I would say about maybe 12 hours of run time they need replaced so I'll see what compression is before I do anything else.

Tested compression and was 170-175-175-175 with throttle wide open... had good spark on all 4 plug wires and took linkage off and checked that each carb butterfly choke would move and spring back and they all looked good. I will also add that when starting up I do advance the throttle to get it running just like you say to do.

Tested compression and was 170-175-175-175 with throttle wide open... had good spark on all 4 plug wires and took linkage off and checked that each carb butterfly choke would move and spring back and they all looked good. I will also add that when starting up I do advance the throttle to get it running just like you say to do.

The compression is not bad. It would be good if it were closer to 200, but it should still run ok.Are all plugs fouled when it runs bad? Or just one or two?

Have you checked the timing marks. There is a T with a line on the cam that should align with a similar mark on the top of the engine. There is also a T mark on the starter pulley (some may call it the flywheel, although the actual flywheel is under the powerhead). That T mark should also align with a similar mark on the top of the engine.

Check the temperature of the engine once it is warmed up. The thermostat starts opening at 162 deg F and fully opens at 180 deg F. So that engine should get pretty darn warm. If it is running cold, that could be your problem.


Bad timing could account for both the starting and the running issue. Although, you would think it would run poorly all the time with bad timing. The thermostat issue would not address the starting issue.

Mike

Mike, I checked the thermostat and it was closed. heated water up to 170-180 and she opened right up.... I lined up the timing mark for the cams and the t with the arrow lined right up the the mark for the fly wheel also. So the flywheel and cams are both lined up at the same time. Mike would it be possible to get your cell that way I can send pics or shoot me a text. My cell is 717-360-6239. I can't figure out how to upload pics from my phone to this site. Erick

If you can not post the pictures, upload them to something like Google Photos, Drop Box or similar cloud depository.

Then post the link on the forum.

-A couple of other things to check before getting into the carburetors....
Check the plastic intake silencer on the front of the engine. There should be a metal screen just inside the intake. It could be partially blocked or the screen may be gone. In models up to 2003, the screen had a tendency to break apart and parts of the screen would get lodged inside the carburetors and affect how they operate.....typically affecting the idle.
-Check the crankcase vent hose (which runs from the valve cover to the top of the carburetor silencer.
-Check valve clearances.
-You haven't said, but you are using NGK DR7EA spark plugs, aren't you? You should not use any other plug or brand.
-You also have not said that you have tried to decarbonize the engine. Using a concentrated mixture in a small tank of Sea Foam or Yamaha Ring Free (which I prefer) may help increase the compression if there is an issue with the rings being stuck. That could also allow oil to enter the combustion chamber, fouling the plugs. You might try this first. If you do this several times. ..check the compression again. After a really good decarb, the oil with get contaminated and you should change it before you take the boat out for a hard run.

The normal way to check to see if there is a ring problem is by a leak down test....but I am assuming that you do not have the equipment to do that....so a good decarb won't hurt anyway.

I am trying to think of something common to all cylinders, that could cause the problem.

At this time, I am out of ideas. Something else may come to mind or even better....someone else will just in with the magic solution.

Mike

Hi,
Just a couple of questions and a comment.

The plugs.....what plugs are you using? And, when you pull them to replace them, what do they look like? Are the electrodes burned down? Has the gap widened? Has the gap gotten smaller? Or, are you having to replace them because they are badly soothed up (black)? Are any of them wet with oil? Gasoline?

My comment is that when you pull the choke and no change takes place is that the change should actually be quite huge. I mean, if the engine is warm....not even fully up to temp....just warm, pulling the chokes out should almost, if not actually doing so, kill the engine. Since that's not happening, it indicates to me that the choke mechanism probably isn't working.

The other possibility is that the choke may be "on" all the time and not opening. This would have the engine running rich all the time and could be why you are fouling plugs so often.

I know that you have considered this already but I thought it would be worthwhile to state it again. Solve your choke mystery before considering anything else.

Jgmo, I am using NGK DR7EA plugs.... as far as the plugs go, to me they look a little sooted up. I wish I could figure out how to upload pics from my phone cause I have pics of the plugs. I pulled the linkage rod off that connects all the the choke butterflies and they all spring back so I appears to me that they are ok. There was a time I was running up the river and the motor was running well the it started losing power and I went from 32 mph down to about 22mph. I reached back and started squeezing the primer bulb and the power came back and running back at 32 again. Then if I let off the primer bulb it would go back to losing power and I did that a couple times and then finally the power just stayed normal and that was after several times of squeezing the primer bulb and then letting off of it. It actually kind of slipped my mind that I have had this happen to me several times this year while out on the river, so I don't know if I'm sucking air in someplace in the fuel line or if it could possibly be something going on with a fuel pump. Also I am not sure what the year of the motor is but the number on the motor is BBAL 4600772 if someone knows how to match the number to get the year. Thanks!!!

Have you tried to put the pics in a storage folder and then to the forum from there as hondadude suggested? I know people do have problems loading photos on this site but I don't know why.

I just can't get past the chokes not making any difference. From much of what you've said, it sounds as if she's pig rich but with what you just wrote about having to pump the bulb, that sounds like a lean condition. Confusing.

Are you pulling your fuel from a permanent tank in the hull or from a portable? Have you tried taking a fuel sample from the bottom of the tank? Contaminated fuel can cause strange runability issues.

You may have a good idea about the possibility of a fuel hose sucking air. That would surely have you pumping the bulb if it's happening.

I am running a portable tank and I am pretty anal about the gas. After every trip out I always use a battery powered siphon and siphon all the gas out. Then when I'm getting ready for another trip out I put fresh gas in. I know it's overkill but that way gas should never be an ossue.... plus I have a fuel/water separater on as well. One thing I should add is I have been disconnecting the quick connect fitting at the gas tank and running the motor till it completely runs out of gas... maybe I should not be doing that.

Oh no! Continue running the engine out of fuel! But don't stop there. Drain the carb bowls. #1 way to prevent carb issues!

Anality about gas is a good thing! Especially with outboards.

The water separator, on the other hand, can be a source of many problems. If poorly or incorrectly serviced and maintained. It is my opinion that they are typically drained too infrequently and properly serviced even less. I have come to the conclusion that many boats, with a certain type of owner, would be better off without one.

Also, if you decide to get into the carburetor, get the Honda Marine Carburetion manual that hondadude recomended. I've been successfully rebuilding carbs for years but I took his advice and got the manual. I learned things about how to clean and repair the carbs I thought I knew all about. I use it often as a reference and I can't overstate it's value to someone "going in" for the 1st or 50th time.
Money well spent and you will NOT regret the purchase.

Yes I opened up the link that hondadude attached and printed off all the pages for the carb manual... there is a pretty good YouTube video as well on cleaning carbs for a bf90a which looks to be almost identical to my bf75a. Thanks for the advice.

Hmmmm. One thought. I don't know a thing about this engine, but it's possible that the fuel line disconnect may not be sealing well allowing air to get into the fuel and causing the erratic running. Those things do wear out. As a test, you may want to bypass it and see what happens.

EXCELLENT suggestion chawk! Yes! Those do wear out and I had one drive me crazy once.

Also, Seaark, pay particular attention to those main jet feed passages that run parallel to the carb throat if you do a cleaning. Compressed air or canned cleaner through the drillings from the inlet side is often overlooked.

Good luck.

Thanks guys for the suggestions. Chawk, I got me a brand new fuel line with primer bulb and a barb fitting for the tank also. My plan is to do away with the quick connector and go straight from the tank to the motor eliminating as many connections as possible and see what happens.

JGMO, I do want to clean the carbs here this winter. I just to come up with the money for the gaskets... Looks like about $150 at least with the gaskets and o-ring kits to do all 4 carbs.