Honda BF90 carbs/air silencer

[seastrike18]

My 96 honda recently starting having problems reaching high rpms. not past around 3500 in gear, and very rough but higher out of gear. the idle was not perfect but not bad. i've heard that there are usually a lot of problems with clogged jets of these engines. There is a chance there was water and contaminants in the fuel, i have an external seperator but it might not have have been able to keep up. <br /> I was told to remove the carbs and clean them, but have been stumped trying to remove the air silencer. one of the bolts holding it on is almost completly hidden and imposible for any of the tools i own to get too. has anyone had experience with this engine, and similar problems. i have the maintenance manual and it allocates a single sentence to removal of the air silencer "remove the upper and lower bolts, then carefully remover the silencer from the carburetor mounting plate" needless to say i have not found it quite as simple. thanks for the input

 

[argonaut]

Re: Honda BF90 carbs/air silencer

Hondas are fun, aren't they?<br />Mine makes me long for the simplicity and reliability of a British Seagull I once had go out on me. Stranded after bad fuel left us bobbing around, we found some tools. 25 minutes with a simple tools and we'd stripped and rebuilt it and were on our way home.<br />The Honda's no such animal.<br />OK, I owe Hondon for the assist he gave me last week, so...<br /> <br />Getting the airbox seems to be some sort of test. If you can get it off you're allowed to proceed, if you get frustrated take it to somebody with better tools and more patience.<br /><br />There are 2 bolts. I used a 1/4" drive ratchet, not 3/8", 6" extension, universal joint, and a somewhat thin-walled 10mm socket. Bought a set for $9, handy to have on board and they had thinner walls than my other set. Helped a lot.<br /><br />Top one's easy, the bottom required threading the extension with a universal past all of the stuff underneath. Even with that it's dicey to break it free, and it took my long skinney fingers to get it off, gently tugging the airbox to keep the fastener loose in it's hole.<br />Follow the manual re: choke & throttle, they snap off.<br /><br />Then with the same tool you can remove the 6 carb bolts, leave the plastic silencer plate hanging if you wish, and unfasten the carb vacuum lines and fuel lines & get them clear. Tricky but possible.<br /><br />But listen, having done this last week this on my BF50A (see threads... same carbs) removing the entire intake manifold assembly helps. Then the whole thing -airbox,3 carbs, and the plastic plate on top of the carbs comes off as a unit. I did get mine off the other way, but decided they were easier to reassemble on the manifold then fasten back on as a single unit. If you do it this way use a new intake manifold gasket.<br /><br />Wished I'd just done that to begin with, the manifold's just seven 10mm fasteners, all easy to get to, and it makes disconnecting/reconnecting the fuel & vacuum lines a lot easier.<br /><br />There's an anode in the manifold you can inspect while it's off.<br /><br />There aren't a lot of parts inside the carbs.<br /><br />Cheer up. Rebuilding the carbs is easy!<br />G'luck.

 

[seastrike18]

Re: Honda BF90 carbs/air silencer

Thank you argonaut, I stopped messing with that ridiculous bolt and just took the whole intake manifold off. I now have the whole thing in my house on a clean table ready to be cleaned. I separated each of the 4 carbs and began to disassemble them. I took off the float bowl, took out both jets and took out the fuel tube and idle tube. It was all clean as a whistle in every carb. I’ve never taken apart a carb before so I don’t really know what I’m looking for but I guess I expected something visibly wrong. Does this meen I don’t have a problem with the jets?

 

[argonaut]

Re: Honda BF90 carbs/air silencer

Did you use a magnifying glass? If not get one.<br />Work methodically, number your carbs do one at a time, and replace them in the same order they came off. <br />On the long idle jets there are tiny orifices drilled into the sides, those have to be clean.<br />Either soak them or replace them, should be like $7 each. Look for lengthwise cracks on the end of the inner jets too. Check the tiny holes on the sides of the brass jets, along with the tiny passages inside the venturi. They have to all be cleaned, blown out with comp air & checked.<br />Middle speeds use the long brass jets that were inside the cast tube that extends down through the middle of the float. That's the emulsifier tube. If you've pinched a straw when you sucked a soda you understand how it works to mix fuel and air.<br />I'd just replace the parts inside, and the brass main jets, maybe also the floats and needle valves since you're already in there and your time's relatively cheap. Kidding. Use new rubber gaskets too, those come in a set. Also remember to take out the screws and check & clean them, replace if you're suspicious. When I was done I replaced the intake manifold gasket & used spray hi-tack gasket cement on the carb side.<br /><br />The problem may be the jets themselves, or the galleries that run through the carb bodies, anything that restricts fuel or air causes problems, and since these carbs have such tiny passages it doesn't take much to clog things up.<br /><br />An air compressor helps. Use nitrile gloves to keep the chemicals off your paws.

 

[seastrike18]

Re: Honda BF90 carbs/air silencer

My expensive gaskets got in, and i bolted my newly rejuvenated carbs and intake manifold back onto the engine. started her up and it's running exactly the same. I'm thinking now that maybe the problem is simpler than i thought. maybe a air leak on the quick connect? but would that make it sound so rough, or just starve at at high rpm's? Because it doesn't sound smooth when you give it gas. I guess it could be worse though. After rebuilding the carbs in my living room i'm somewhat content with not worsening the situation.

 

[argonaut]

Re: Honda BF90 carbs/air silencer

Were all jets replaced? The tiny tapered ones should be tossed ...impossible to clean. <br />Normally you'd only consider rebuilding carbs after eliminating bad fuel, spark/timing, the plugs, vacuum problems, and fuel pump/filter.<br />Do all plugs look normal? is mixture too lean or too rich? <br />I'd also use fresh good grade fuel in a known good water-free container for debugging a motor, you can eliminate your tank, it's fuel, the bulb, the lines to the motor, and the fuel filter & go into the fuel pump w/a new bulb & line to a 1 gal can full of fresh. Figure out what it's not.<br />Plugs tell a story and can show whether mixture is too lean or rich and which cylinders are affected.<br />Also see Link to related this thread<br />There's a spray that can help w/vacuum leaks, think I used starter spray. A little bit in suspicious places, when sucked into a leak causes the engine to rev when the octane gets sucked into the leak. Also double check carb plates & rubber carb vacuum lines as they could be cracked or have a poor seal. (between carbs & block) & dashpot.<br />Good huntin'.

 

[seastrike18]

Re: Honda BF90 carbs/air silencer

after bypassing the quick connect ang going right to the in-line fuel filter it still didn't run at higher rpm's. i'm trying to eliminate a fuel supply problem but it sounds kinda surgy at higher rpm's like its trying to go but cant get the gas. this is just in a test tank no load at about 2000 rpms. it also seemed a little smoky. Rings? valves? i think i need to do a compression test and can someone give me more specific information about a leakdown test. <br />-thanks

 

[Nick on the Bad Habit]

Re: Honda BF90 carbs/air silencer

Try running your engine from a different fuel source, such as a portable fuel tank. You may have a fuel system problem. You did not mention that you did a carb syncronizing check after you rebuilt the carb's. It can be done with a single vacumn gauge used on the vacumn port on each intake port.<br />Good luck, Nick

 

[seastrike18]

Re: Honda BF90 carbs/air silencer

I got a compression tester and got good and even compression on each cylinder. i was using a new primer bulb on good gas going straight to the filter. i havn't synched the carbs because i dont have a vacuum gauge but thought that since it was running smoothly at low rpms that they were alright. Is there a chance of one of the fuel pumps not working as well as it should? what is a good way to test them?