Wits end with damn carbs

[paulbaker1954]

Nearly at screaming point now!!!!!!!

Carbs off for overflowing carb, new float valve from DS, new spring from Gerben all cleaned and back together. Bench tested for levels all fine no overflows etc etc. Bench checked at least 3 times.

Then put carbs back on bike and no overflow, started and ran but did notice an intermittent backfire from left hand side (? could an intermittent backfire be caused by an overflowing carb???)

Now the nightmare .....turned fuel, on this morning ready to sync carbs and guess what carb bloody overflowing again!!!!!!!!!!!!!!!!!

I must be missing something obvious here but no idea what. Only thing I haven’t changed is the float valve itself but as I said it seems fine

What the hell am I missing here I am running out of options

[Johnwebley]

Tap the offending carb with plastic hammer. Or plastic screwdriver grip.should cure sticky float.
Take bike for run and enjoy.
The vibration will cure sticky floats.

Also put some Redex red cleaner in tank to clean fuel lines.

Works for me.

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[Nurse Julie]

I had exactly the same problem Paul on my CB550/4. Did everything that you did and still pissed fuel. A new set of float valves and seats and hey presto....all sorted and have been perfect ever since.

[K2-K6]

Agree with previous posts about temperamental valves. 

To the question of backfire, yes it will do that.  Popping on overrun is usually air bleeding in,  but proper backfire is normally excess fuel entering the exhaust and partially building there until it gets ignited by hot gas and explodes.

Seems to confirm your initial diagnosis of source neat fuel getting through motor to pipe.

Left field view,  you could try a mix of about 70 to 1 two stroke oil in fuel. It may just about give better movement of valve to seal it. It's not a cure but will allow possibly assessment and time to review if it makes that valve work more consistently.


Edit,  if you drain all fuel then make a mix with 5ltrs plus the oil you can make sure it's properly mixed prior to using in tank.  It'll have no real consequence for combustion at that ratio,  and may even help with internal corrosion in the pipes too 

[paulbaker1954]

Thanks John
Took drain screw out and let carb go dry so float would fully drop, tapped a few times and that seemed to cure the overflow problem

Went for a short run and seems to be running well

still bit of a backfire at idle but hoping will just settle with a bit of use

[Trigger]

I have had these problem on two sets of carbs. One was back firing through the air box and the other just would not stop overflowing.
If you take the float valves out and inspect with a magnifying glass, you should find that the brass is pitted. A new set of these worked both times >>> https://www.ebay.co.uk/itm/Honda-CB-550-Four-F-F2-K3-Vergaser-Schwimmerkammer-Ventile-Carburetor-Float-Kit/401500262334?hash=item5d7b47cfbe:g:atwAAOSwwKhcq3pI

[hairygit]

Surprised to hear you say that Trig, most people who use keyster kits say the jets are okay but the float valves give problems so they buy genuine ones.

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[paulbaker1954]

I have had these problem on two sets of carbs. One was back firing through the air box and the other just would not stop overflowing.
If you take the float valves out and inspect with a magnifying glass, you should find that the brass is pitted. A new set of these worked both times >>> https://www.ebay.co.uk/itm/Honda-CB-550-Four-F-F2-K3-Vergaser-Schwimmerkammer-Ventile-Carburetor-Float-Kit/401500262334?hash=item5d7b47cfbe:g:atwAAOSwwKhcq3pI

Trig
these have all been replaced with Cruzinimage float valve only a few months ago and no 2 that was overflowing I just swapped for a DSS ONE

I have a theory that sometimes when I put carbs back on the floats get dry and the pushing and pullin etc when  fitting the carbs maybe causes the actual float valve or float to get sticky. This is supported by the fact that I drained the carbs to force the floats to the lowest position tapped the carb and then it seemed ok

This is just my crazy theory though

Am going when I have some time to check the float levels again and see if they have changed

[Trigger]

Surprised to hear you say that Trig, most people who use keyster kits say the jets are okay but the float valves give problems so they buy genuine ones.

Sent from my X6pro using Tapatalk

I have never had a problem with Keyster float valves on SOHC's, i always replace the o rings with Viton. Julie kept taking he carbs off and resetting the float height and they still leaked. I popped a new set of Keyster valves in and so far 300 miles without any problems 

[royhall]

I have had these problem on two sets of carbs. One was back firing through the air box and the other just would not stop overflowing.
If you take the float valves out and inspect with a magnifying glass, you should find that the brass is pitted. A new set of these worked both times >>> https://www.ebay.co.uk/itm/Honda-CB-550-Four-F-F2-K3-Vergaser-Schwimmerkammer-Ventile-Carburetor-Float-Kit/401500262334?hash=item5d7b47cfbe:g:atwAAOSwwKhcq3pI

That is a good eBay site to save for future use, not spotted them before. Cheers.