Progress - She runs at last! (75 CB400F)

[Chris400F]

I need to get a 4mm helicoil kit now ....

Someone else had this problem recently too, this thread should help: http://www.sohc.co.uk/index.php/topic,11339.0.html

[ManicGTI]

Thought i'd drop this simple little Carb Float explanation here for prosperity, although it's light on actual technical explanation: https://www.fix.com/blog/motorcycle-carburetor-float-height-adjustment/.

I've had another thought regarding my richness.  At the moment I have the Fuel tank sat off to one side on top of my garage shelf's, (ie >1m higher than the bike itself), running a temp long fuel hose down to the carbs so I can work on it with the tank off.  Would the additional head from this setup cause me issues?

All being well I should get a chance to pull the carbs and reBench Sync / Float Check tonight

[K2-K6]

I like that one Oddjob.

Manic, you should have no effect on jetting as the mixture is influenced by the float height which sets a equal pressure into the jets because it interrupts the fuel coming into the carb. You may struggle to get the floats to shut off the fuel if you had any effect at all.

Sounds like you've got too much air to get the revs down though in order to make any sensible judgment of it.
As already posted, check to see if the slides are going fully down, the only thing lifting any throttle slide when left alone is the tickover / throttle stop screw on any system,  the operating mechanism (cables twistgrip etc) should all finish their influence when you let go of it.

[Nurse Julie]

Carbs are like life, you can't get enough head 

[ManicGTI]

Carbs are like life, you can't get enough head 

Hey, it's cold and lonely out there in the garage.  I'll take what I can get.

[Laverda Dave]

Bryan, The float valves are from the Keyster (?) kits I bought and do not have a viton sealing rubber on the tips as the old ones did. I'll give it another go maybe over the weekend when I get the helicoil kits (thanks for the tip Chris, the kit is on order). I will test the floats to see if any are punctured.
Its only the carbs that are stopping progress and the MOT 

[petermigreen]

Thought i'd drop this simple little Carb Float explanation here for prosperity, although it's light on actual technical explanation: https://www.fix.com/blog/motorcycle-carburetor-float-height-adjustment/.

I've had another thought regarding my richness.  At the moment I have the Fuel tank sat off to one side on top of my garage shelf's, (ie >1m higher than the bike itself), running a temp long fuel hose down to the carbs so I can work on it with the tank off.  Would the additional head from this setup cause me issues?

All being well I should get a chance to pull the carbs and reBench Sync / Float Check tonight

I read in classic motorcycle mechanics magazine recently that you should not mount your tank/fuel source to high for this very reason.

[tom400f]

I've got an old two stroke oil tank you can use of you want Dave. You can make a list of the stuff off mine you have 

[ManicGTI]

With a bench sync it is easy to get the slides so they dont close

first back off the idle screw till it falls out, then un adjust the carb slide adjusters so all slides hit the bottom pick one(on the 550 k3 its easy as one has no adjuster) and adjust the slide adjuster till it nearly moves, refit the idle screw and adjust it till the one you picked lets your prefered drill bit fit, 3mm is too big you need 1.5 if poss, then adjust all the others to the same. Finally undo the idle screw again and make sure all slides hit the bottom.

Run engine till hot ad ajust with gaudes AFTER you haveset tappets, cam chain and ignition timing

Ok, I just tried it this method and hit on an isssue straight away.  Essentially the idle screw bottoms out just at it touches the casting, so i'm getting nothing out of the idle screw.  Hmm, an adjustment i've missed?

[K2-K6]

I think the motorcycle mechanics need to sit down with a nice cup of tea and a biscuit to give themselves time to think about that.

 It's exactly what a float chamber is for,  to break the head pressure ( no sniggering at the back there,  oddjob and Julie) and provide a reasonably constant fuel weight for the carb's vacuum to work on, which in turn gives you a chance of linear jetting response.

If it didn't do this then as the fuel tank volume varied then so would the jetting and the float height would be absolutely meaningless.

[ManicGTI]

I believe we are taking about the same screw,  yeah the casting is to far away from the tip of the idle screw.

I had the carbs completely in pieces, only the chokes were left on. Idle screws all completely removed,  so yes it does look like I may have assembly incorrectly. Bugger.  I'm not sure what could even be wrong!

Sent from my ONEPLUS A3003 using Tapatalk

[mike the bike]

Take a few photos,  we may be able tp spot the problem.

[Bryanj]

If the tickover screw when screwed all the way in still has a gap to the lever it adjustes you definately have the slides not right

[Nurse Julie]

"Snigger, Snigger"

Sorry couldn't help myself. 

I'll write out "I shouldn't snigger in class" 50 times as a punishment.

I will stand in the corner for 10 mins, sorry Sir 

[ManicGTI]

So, 5 minutes after posting my 10PM message last night I took a long swig from the beer bottle sat on my workbench.  It was a big mouthful.

Sadly however, it turned out that the cool, refreshing (and undrunk!) Hop House 13 was in fact at the other end of the bench.  The bottle I had taken a swig from contained the petrol I had drained from the carb bowls.

Yuck. Luckily I don't 'think' I actually swallowed any, but I've gone through many litres of water to dilute and flush it through.  I can still taste petrol now.

At that point, my interest in continuing to work in the cold diminished rapidly.  So the only picture I have is this one:

If the tickover screw when screwed all the way in still has a gap to the lever it adjustes you definately have the slides not right

The lever does touch the idle screw when fully screwed in, but only just.  This is with the slides all bottomed out (ie the individual slide adjusters all screwed in as far as they will go), there's about 6mm gap.