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Carb float level issue - or? (XS 400 SE)


oscar_m
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Folks,

I preffered to start another topic rather than put everything in one post, so that those topics stay clearer. To the point.

I had my carbs being cleaned and regulated during March this year, as I had really problems getting the bike to start up last year. After I got the bike I was nicely surpised by it's response, nice power, and somehow - more speed achievable - COOOOOOL! :D:D:D:D:D

Yep - but - I also noticed increased fuel consumption (fine with that though) and recently I also some kind of fuel leakage which seems like..hmm..overflowing of the carburator. I did some reading about how to set up float levels, but wanted to get a second opinion before starting doing all that messy stuff.

1) I left my bike with fuel tap on "reserve" and after some time it started to drip fuel through air filter box

2) It did not happen on the "normal" position of the tap, although I have noticed that my bike likes to smoke black after start-up, which suggests fuel in the combustion chamber

3) I noticed that even though I have pretty much fuel in the tank, I have to switch to reserve (didn't happen that much before) since the bike has some significant "drop" of response at low RPM's (when I try to run at traffic lights it's like it had a cough before really jumping ahead). So either it is fuel starvation or the oposite - it is flushed with fuel or something

4) I also think that my oil isn't "oily" anymore but starts to smell with fuel aaaaaaaaaaand this would lead to the same conclusion

Thanks for any hints/additional things to check/how-to's etc.

regards

Oscar

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Hi Oscar, i would recheck the float levels and also make sure they move freely and are not sticking either up or down, also check the carb overflow isnt blocked

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I'd be looking at the vacuum petrol tap, sounds clogged up too and not stopping the flow overnight when parked up!

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from what I read in the past Carb floats are RARELY upset.. that is to say they never need adjustment once set.

I would look elsewhere like Drewpy said

1) I left my bike with fuel tap on "reserve" and after some time it started to drip fuel through air filter box

mmm, so petrol dripping through into the air filter box is nothing to do with the floats

its the floats that stop petrol entering the carb

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1) I left my bike with fuel tap on "reserve" and after some time it started to drip fuel through air filter box

mmm, so petrol dripping through into the air filter box is nothing to do with the floats

its the floats that stop petrol entering the carb

no floats set the fuel level in the carbs. the petrol tap shuts off the fuel, that's why we have them.

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no its the float valve that does this, crap in the float valve or even wear can be the culprit even if the float height is correct

very true, i could have worded it better i suppose, at least someone knows what they are talking about :rolleyes:

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Thanks guys for your suggestions. First I'll check the petrol tap and fuel filter for any sediments or wear, then I'd probably check the carb valve as you mentioned. I'll let you know my "outcome".

regards

Oscar

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Thanks guys for your suggestions. First I'll check the petrol tap and fuel filter for any sediments or wear, then I'd probably check the carb valve as you mentioned. I'll let you know my "outcome".

regards

Oscar

I have checked my fuel tank + fuel tap, previous to getting carbs dismantled.

The fuel tank had some sediments, but the fuel filter was ok. The fuel tap works like this (when the bike is not running):

1) NORMAL: fuel is stopped

2) RES: fuel is flowing constantly

3) PRI: fuel is stopped

Can you tell that is the normal operation? I don't get it why RES is working differently than PRI. I thought PRIming is used to flood empty carbs and it allows free fuel run. RES I would say is OK, as it allows fuel to flow when the underpressure is too small to "suck" the fuel out of the tank. Am I wrong? If the RES is working this way, then the carb float valve should stop the fuel from overflowing - and looks like it didnt...

BEsides - I had a look on the sparks. DAMN! They were black like hell, I had no problem saying the mixture is too rich. I had recently problems with the bike dying at small revs - now I know why...

regards

Oscar

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I have checked my fuel tank + fuel tap, previous to getting carbs dismantled.

The fuel tank had some sediments, but the fuel filter was ok. The fuel tap works like this (when the bike is not running):

1) NORMAL: fuel is stopped

2) RES: fuel is flowing constantly

3) PRI: fuel is stopped

Can you tell that is the normal operation? I don't get it why RES is working differently than PRI. I thought PRIming is used to flood empty carbs and it allows free fuel run. RES I would say is OK, as it allows fuel to flow when the underpressure is too small to "suck" the fuel out of the tank. Am I wrong? If the RES is working this way, then the carb float valve should stop the fuel from overflowing - and looks like it didnt...

BEsides - I had a look on the sparks. DAMN! They were black like hell, I had no problem saying the mixture is too rich. I had recently problems with the bike dying at small revs - now I know why...

regards

Oscar

The tap is working incorrectly, it should operate thus

normal fuel stopped

res fuel stopped

Prime fuel flows

This would be correct for a vacuum operated tap without any vacuum applied (engine stopped)

so it looks as though someone had built the tap incorrectly?

Carb overflow is down to a valve passing as has been said.

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The tap is working incorrectly, it should operate thus

normal fuel stopped

res fuel stopped

Prime fuel flows

This would be correct for a vacuum operated tap without any vacuum applied (engine stopped)

so it looks as though someone had built the tap incorrectly?

Carb overflow is down to a valve passing as has been said.

Well... it looks like everything is ok here and it's just me being confused... It's all about the petcock design. In some bikes (e.g. Honda CB 250 which I can compare) the petcock has an arm and an ARROW pointing the current setting. In this bike it is the ARM that shows the current position (while actually hidding it under the arm), which made me confused. I had a look if the tap can be assembled another way, but it seems impossible, as the words "PRI ON RES" would be upsidedown...

Nevertheless - it shouldn't happen that the carb overflows even when the tap is on "pri", so this is still to check.

best regards

Oscar

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  • 1 year later...
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try and check you put it on right, (gaskets etc) and move the main rubber thing around.

also check the alloy for trueness

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