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2001 Honda BF90 4 stroke carb air box removal

J

jimr

New member
Anyone have an answer on how to remove one of the partially hidden 10 mm bolts holding the airbox to the block to get to the carbs on this engine? It is on the right side about half way up the inboard side of the engine. Must be a trick to it.

Thanks in advance

Jimr
 
There are two pieces to the airbox/muffler. The one on the front of the engine should come off easily by removing a couple of bolts. The one on the front of the carburetors should be left on until the entire assembly is removed.

The easiest and recommended way by Honda is to take off the entire assembly at the intake manifold.

You have to remove the throttle cable, loosen or remove the front muffler assy, and loosen the top cover, and remove the four fuel lines from the fuel pumps. It all comes off together and then it is easy to disassemble.

Others may jump in and have ideas how to shortcut it, but the hard part would be putting the hoses behind the carburetors back on correctly, if you do not take the entire assembly off.

Good luck

Mike
 
Thanks Mike
Was wanting to Seafoam the carbs from the front and didn't want to break the gasket seals at the manifold.
Maybe drill some holes in the airbox and plug them might be the better option. I may just add some seafoam to the fresh fuel and see what happens after running that through. I had water in the fuel and drained the tank. Seems to run ok but has a slight intermittent miss.
Jim
 
I assume you are trying to decarb the engine.....

If so, you can remove the phillips screws on the rear of intake manifold....one for each cylinder. Take out one at a time, while the engine is running and spray the cleaner into the hold. Do that on each cylinder.

If you are thinking spraying into the front of the carb will clean the carb....it will not. It just passes through into the intake. Putting it into your fuel will we more successful for trying to fix the miss...unless it is a carbon buildup in cylinders.

Mike

ps I assume that, if you had water in the fuel, that you already drained each carburetor and flushed the engine fuel system.
 
Fuel system flushed and new filters and plugs. Good tip on the manifold screws as that was my intent to decarb thru the carb intakes.
I'll give it a try to try and correct the intermittent miss....Great info.

Thanks again Mike
I'll update after doing this. This is a friends boat that sat for two years as he fought a bad illness. Now it's time to go fishing!
 
Engine now idles good and will rev running on trailer. Engine will die out in gear and accelerating under load when in the water.
Where do I go from here. Fuel does not seem to be the issue.
 
A couple things are in order.

Do a cylinder drop test. I know you said the engine is idling good, but I have had many say that to me only to find that one of the cylinders are not firing. With the engine idling on a hose, use an insulated pliers to pull the spark plug wires off....one at a time. If the cylinder is firing, the engine rpm will decrease....then it will increase to the previous speed when you put it back on the spark plug.

Check the compression of your cylinders. If you do not have a compression gauge, you can borrow one from Autozone.

If you have a separate switch for the choke, take the boat to the water and with the boat backed into the water....still on the trailer...start the motor....let it warm up.....then put it in gear and as you are accelerating, momentarily activate the choke. See if that helps the engine keep running while you are trying to accelerate. If it does, then you need to remove the carbs, disassemble and clean them.

If you get to that point, I highly recommend the Honda Carburetor Manual. It has a great step by step for the 90 and how to be sure all the passages are cleaned properly. If you do not know what to look for, it is easy to miss one of the intermediate paths. https://www.amazon.com/Honda-Marine-Carburetion-Service-Repair/dp/B00D2Z1AFO

It is well worth the $40.

Mike
 
Success finally!! After running 2 cans of seafoam directly thru the carbs and letting the bowls sit 4 days with seafoam in them the engine would finally rev while choking.
I knew it was fuel related then. As a last ditch effort before a carb overhaul I ran a can of BG induction cleaner full strength followed by a can of BG carb treatment full
strength thru the engine and it finally came around high speed and at idle. The plugs didn't like that second can as it was just finishing the last can. Had to coax the engine with some stating fluid sparingly and it came around and restarted. Runs like a new one now. Sure beats overhauling those carburetors! I did get that Honda Manual and was ready to dig in. Highly recommend the BG product. Most car dealerships have it in stock.
 
Would recommend an immediate oil change. Some of that stuff very likely got into your oil, dirtied it up, and diluted it.
 
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