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bf75a hesitates upon throttle have replaced the whole intake system

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Porterhouse

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I have been working on a Bf70a an to start with it had been setting for a year or 2 so attempted to rebuild carbs an couldnt ever seen to get a couple passages cleaned so I just ordered a whole new intake. By the way leak down is less than 5 percent an compression is good. The engine still wants to lean cough upon acceleration. You can close the choke an the engine will stop hesitating but not die out like it should. Have sync an linked carbs with vaccummate an still no luck but what I have noticed is on #1 cylinder I noticed when pulling sparkplug wire it wasnt running as strong on it as the others so thinking problem is around there somewhere. Pilot screws have been adjusted anywhere from 1 to 3 turns with no luck. Engine is also in time thanks any ideas or experience would be greatly appreciated thanks
 
From what you said, I have to assume that the carbs are clean and the fuel lines have been flushed....

Initial setting for pilot screws is 1 7/8 turns.

Not knowing what year it is (although, it probably does not matter), part #2 http://www.boats.net/parts/search/Honda/Outboard%20Engine/2003/BF90A3%20LHTA%20VIN%23%20BBBL-4500001%20TO%20BBBL-4599999/THROTTLE%20CAM/parts.html may not be adjusted properly. It aids in acceleration and deceleration.

Also, check to be sure that the motor is coming to temperature. If it is not, it will not run correctly.

As for #4 not running strong, could be idle mixture or could fuel could be leaking into it from one of the fuel pumps...pull the pumps and squeeze the fuel bulb to see if any fuel comes out around the plunger.



Mike
 
Thanks Mike Ill try that this morning but i noticed the valves are really carboned up bad while intake is off. Number one being really bad so I may go ahead an pull head an have valves done.
 
Before you pull the head, you may want to try decarbonizing using a small tank and a heavy dose of SeaFoam. Follow the directions on the can.

I have gotten lucky of couple of times by shooting engine tuner into the holes that you connect the vacuummate to while the engine is running.
You may need someone to start and run the motor for you while you hold your finger over the hole, as you shoot tuner in, cover the hole, shoot tuner, cover the hole, etc.

I think you get the picture.

Mike
 
well I pulled head an had it checked it was warped alittle an had the valves all checked. Installed head an problem is still there. While on vacuum mate you can see one #1 cylinder is lean coughin. So today im switching number one carb with number two an see what happens
 
Make sure the engine is getting to temperature. The BF75A and BF90A's sneeze a lot until they are warmed up.

Only balance the carbs when it is warmed up. If you do not have a temp gun, grab the oil filter....if it is pretty warm, the engine is probably close to temperature.

Most likely, one or more of the pin size holes at the top of the carburator or part of the idle passage is still plugged up.

Mike
 
hondadude said:
Make sure the engine is getting to temperature. The BF75A and BF90A's sneeze a lot until they are warmed up.

Only balance the carbs when it is warmed up. If you do not have a temp gun, grab the oil filter....if it is pretty warm, the engine is probably close to temperature.

Most likely, one or more of the pin size holes at the top of the carburator or part of the idle passage is still plugged up.

Mike
Click to expand...
I checked engine with temp gun an its getting up to around 170 an I balanced carbs with it being warmed up but im swapping carbs around an ill let u know what that does. THis thing is beating me pretty good
 
well switched carbs an still no luck so I left the air intake of the intake system so I could watch carbs. The problem is not actually a lean cough it is more of a back fire. I notice flames coming out of the carbs. I must have a timing issue but the marks on the cam an flywheel line up. Guess im going to pull flywheel of an check flywheel key an see if its sheared. Any Ideas?
 
Running the motor without the air intake will cause a lean condition. I do not know if it would cause backfiring.

If you did a leak down test, the cylinders should have been at top dead center with all the marks aligned, otherwise, the flywheel would have moved. So I am not sure you will find a sheared key. But, you never know.

As a recap...new carbs...head worked on....good leak down....good temperature....

You are going to double check correct timing. Hope you find something there.

Valve clearances?
Carb base gaskets?
Small hoses on rear of carburators....cracks?
Spark plugs?
New good fuel?

I am running out of ideas.

Maybe someone else on the forum has some thoughts.

Mike
 
Tell me about it me to I have tried everything I can think of. Have been doing this for 12 years an this one has been the hardest for me to fix by far. An its probably something simple but dang I sure have overlooked is somewhere. leak down was less that 5 %. New Carb base and Intake gaskets. checked all hoses on carbs with air pressure.Replaced spark plugs a few times. Running on shop tank with new fuel. Head was warped a little had it shaved an cleaned an pressure checked. If you dont mind I could send you a video via email if you got time just to let you get an Idea.
 
Just wondering if you have resolved this problem with your motor? I've got a Honda 90 with what seems like the same issue. I just took the carburetors off to get them ultrasonically cleaned in hopes that it will fix the hesitation / cough from low rpm? I notice that carb 3 has the most vacuum flucuation when I syncronized them. When the motor "coughs" #3 carburetor vacuum dips on the sycn gauge.
 
Porterhouse,
Have you ever done a running compression check? Sometimes a running compression check will identify problems a cranking check doesn't uncover.

Your problem sounds like it could be, given all that you've been through already, that you might have a weak valve spring or two. How closely did you inspect the valve seats and faces when you had it off? Or did the machine shop clean those up for you? Have you looked very closely at the intake cam lobes?
Just some more ideas to throw at you.
 
Here's a thought. The igniter for the electronic ignition can be a real bear as it begins to fail. You'd think that an electronic component would be either on or off, but I've experienced otherwise. I had this happen on a Honda car after it warmed up. Replaced the igniter and all was well. But, these are expensive. I was fortunate in that I had an accord with the same part - swapped and problem disappeared, so I ordered a replacement. On a Honda motorcycle, I had the 'pulser' fail as well. It's what picks up from the crankshaft when to fire the plugs. But that was a 4 cylinder motorcycle - and therefore had two pulsers; each affects 2 cylinders - so not exactly your problem. Then again, I don't have a Honda 4 cylinder outboard (mine is 3 cyl), so perhaps your arrangement might explain.

Have you checked your spark plug leads? I'd be learning towards and ignition problem at this point. Can you swap those components between cylinders? Chuck
 
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Hi all

Did you manage to get the problem sorted I have the same problem on twin honda BF75's both on the same boat with exactly the same problem. On the water the will get up to full throttle but one engine is using about 25% more fuel. They both back fire at tickover and they cut out if you decerate hard. any ideas.

Many thanks
Jon
 
Hi Porterhouse, did you ever resolve your problem with this motor? I potentially have the same issue to solve. Thanks Joe
 
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