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Discussion Starter · #1 ·
I own a '72 CB450 and I have made the classic mistake of leaving the petcock on. My oil is now overrun with gasoline and I am scratching my head.
I never saw any gas overflow through from the float bowl overflow tube, so how did it get into the engine?

++Greg
 

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Discussion Starter · #3 ·
I'm starting to think that my float bowl overflow valve is blocked by some residue. I'll take a look when I get home.
 

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Float valves in 450s are brass on brass, unless the seat and needle are perfect they will allow fuel to pass by slowly. As the fuel level rises in the carb bowl it will eventually reach the needle jet tube where it can leak out into the intake via that port or the slow jet port. Yes the overflow should leak some but I believe the angle of the carb facing down negates that somewhat.

I have problems with the fact that I have two Honda's, a 360 and a 450, the biggest operational difference is the the petcocks are on opposite sides of the tanks and for my 450 I tend to turn it to reserve instead of OFF.

So yeah shut the fuel off when you are not using the bike. I even tend to shut the fuel off about a block from the house and let the sucker die in the garage. Call me paranoid but if there is minimal fuel in the bowl there is less chance of gunk forming. The heat from the engine will probably evaporate whats left.
 

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Yup, I shut mine off 4 blocks from home!!
 

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Ive never done this in any of my bikes, I figured that the overflow would take care of it all, but I guess not. Is the issue that the engine wouldnt be lubed enough? Or that your going to explode your engine if somehow the gas in the oil ignites? I feel like with either one you would need a lot of gas in the oil to make a difference. Is there any way to tell if its happening without me having to pull stuff off? I have fresh oil in the thing and dont really want to dump it just to check, and I really really dont want to pop a boot off and see if its got gas in it.
 

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Discussion Starter · #7 ·
Would it make sense to replace the current petcock with one that contains a vacuum-activated valve?
 

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IMO it's one more part that can cause problems. I hate vacuum petcocks though. I'd be more inclined to search for a float needle that is the right dimensions that has a Viton(rubber) tip so it seals better that the stock one.
 

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Discussion Starter · #9 ·
Ive never done this in any of my bikes, I figured that the overflow would take care of it all, but I guess not. Is the issue that the engine wouldnt be lubed enough? Or that your going to explode your engine if somehow the gas in the oil ignites? I feel like with either one you would need a lot of gas in the oil to make a difference. Is there any way to tell if its happening without me having to pull stuff off? I have fresh oil in the thing and dont really want to dump it just to check, and I really really dont want to pop a boot off and see if its got gas in it.
Contaminated oil can cause overheating. I know this firsthand; I ended up breaking the piston rings on both sides because of it.
I've never heard of an engine exploding from contamination.
As for inspection, most folks can tell by the smell of the oil in the crank case. Just unscrew the oil cap and take a whiff.

IMO it's one more part that can cause problems. I hate vacuum petcocks though. I'd be more inclined to search for a float needle that is the right dimensions that has a Viton(rubber) tip so it seals better that the stock one.
Do the make alternative floats for cb450's ?
 

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Is the issue that the engine wouldnt be lubed enough?
Well, yeah, that's the main issue. Gasoline does not make a good lubricant for Honda engines, lol. Among other things, it is way too thin.

Is there any way to tell if its happening without me having to pull stuff off?
Smell your dipstick.

Regards,
 
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Do the make alternative floats for cb450's ?
Technically, no, they are not listed for the CB450, but several years ago I found a set of float needles in the identical size with Viton tips, on eBay. The seller actually showed the dimensions, which is why I took a shot; not much lost if they didn't work.
 
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