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bf90 carbs

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ryanh0190

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Hello this is my first post. I have a 1999 bf90 I have owned for about 2 years. Now this may just be normal of the carburated motors but not with the ones I have owned in the past. So first off on cold start it usually starts right away with the fast idle in choke position. But then I have to wedge something like a pen to hold the fast idle half way up for about 3-5 min until its its warmed up enough to put in normal position. If taken out of fast idle before warm it will just bog down and die. Once warm its good to go all day and will usually start first turn without choke. Seems to me the motor should have a function that automatically chokes the motor until its warmed. Last night I pulled the carbs and carefully clean all the jets thoroughly.to my surprise they were very clean. When restarting it didn't really seem to make a difference. I had also synced the carbs too. When its at idle it almost sounds like it has bigger cams. I guess I just picture a Honda motor being very quiet and smooth....like how the fuel injected motors run. On a side note, running a factory 17p aluminum prop I'm only maxing at 5200 rpm.
Any help would be greatly appreciated. Thanks

Ryan
 
Also, as i was examining things, it seems as if the diaphragm mounted on the side of the intake manifold would raise throttle based on vacuum? when i disconnect from the little valve? and suck on it the throttle raises. The line goes to a little manifold connected to each carb. Just a guess but if it pulled vacuum to it the throttle would raise during a cold start slowly lowering as it warmed up? This is all just a guess as i am still researching.
 
The 90's do take a little while to warm up and run smooth.

Sounds like you know a fair amount about carburetors, since you sync'd them.

The dashpot that you referred to helps the engine accelerate and decelerate smoothly.

Go to basics, to be sure all is ok....

Once the engine warms up, do a cylinder drop test....pulling the plug wires off the spark plugs one at a time just for a few seconds.
Make sure that the engine looses rpm each time you pull one of the plugs. If not, then you have an issue with that cylinder.

Once they are all working ok, check you idle rpm. It should be 950 plus/minus 50. I prefer to set it close to 1000 if on a hose.

Now, as for the full throttle rpm. Sounds a bit low. Ideally, you should get closer to 6000 rpm at full throttle. Before you start changing propellers, you have to be sure that the motor is running correctly.
What boat do you have it on?

One last thing....if you want to know all there is about these carbs, the Honda Carburetor manual, gets into everything that you are asking about is nauseating detail. There is also extensive info on cleaning and balancing. It is $40, but well worth the money. http://www.helminc.com/helm/product...=&from=result&Style=helm&Sku=TM044&itemtype=N

Mike
 
Thank you for the fast reply. The motor performs strong mechanically. It is on a Hewescraft 199 searunner. It is pretty underpowered for the boat but that is how it came so im dealingwith it. The prop it came with is a honda oem stainless. It would turn at about 55-5600 rpm's wot. Though, i dont know the pitch as its not marked. I would have thought that the aluminum prop being half the weight would be a bit better. The aluminum is still putting out about the same speed at 5000 rpm as the stainless @ 5500 (32-35mph). So as far as the cold start goes, I guess im just a bit frustrated because you would think for a motor retailing at around $7-8k, it would start better. Heck, my honda push mower starts first pull every time regardless how long its sat. And its automatic choke. I was hoping to find Honda had a fix for this issue.

Ryan
 
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