Broken valve

[SteveP]

I thought I'd post some photos before and after.
I think it's finished, for now.
Inaugural run tomorrow, if the sun is shining.
Two years of work. Engine and cycle parts rebuild. Just about all by me. And of course this great site. Thanks to everyone for all the great advice and information.
If anyone is wondering the brown pictures are the before.

 

[jetmechmarty]

Is that stock exhaust with Marshall mufflers?

It’s an attractive motorcycle for sure!

 

[SteveP]

Thanks for that. I'm pleased with it.
The exhaust is a complete system. It's a Marshall deeptone. Sounds really good. I don't think it's made any more.
I got it from a friend for £50. It's a bit rusty in places but I don't think it's ever been on a running bike.

 

[JOHNDADDY]

Pretty! Really like the Green.

 

[SteveP]

Thanks for that.
I'm really pleased with the colour. It was going to be signal red. Until my wife persuaded me otherwise

 

[Jan_P]

British Racing Green ?

 

[SteveP]

It's sort of brg. But I've looked into the history a bit and it turns out that there have been a lot of different British racing greens over the years.
I went to the local autofactors (Halfords) and picked a rattle can that looked about right .

 

[Mailman]

Congratulations! That came out beautifully!

 

[SteveP]

Thank you. I really do appreciate the positive comments

 

[SteveP]

I used two carb rebuild kits- against all the advice on this great site.
Took the bike for it's first run a couple of days ago and it started running rough just past tickover. I thought maybe the pilot jet was the problem.
Stopped to have a look and fuel was pouring out of the carb overflow.
Once home I finally found the problem. One of the float valve needles was jamming in its housing. I don't think float jet assembly was faulty, it was just not suitable for the carb. The geometry was a bit wrong. The float tang was not holding the float jet needle far enough in the housing.
I replaced the float jet assemblies with proper mikuni ones I had in some spare carbs and everything seems fine now.
I should have listened to what the experts on this site said

 

[SteveP]

Bike still running rich. Getting bogged down just of tickover then taking off like a scalded cat.

I'm slowly working through as much information as I can on this site. And getting very good at removing and refitting carburettors. And trying to get the carbs as near spec. as possible.

I'm currently thinking it could be a choke problem so I've ordered a new plunger.

Or maybe an ignition problem?

Since the carbs are be the unlinked BS38's from a 1974 TX650 the float heights should be 24mm. I've tested for float leaks and swapped in a couple of spare floats to try. And tried some spare mikuni needle valves.

My problem is that I've set the floats as per manual measuring front the carb body. When I try the clear tube check the floats seem to be around 3mm lower than they should be. I've attached photo from this site of how the level should be and two photos of my levels. Should I lower my floats by 3mm to 21mm?.

I bought a hydraulic m8x.1 barbed fitting from eBay for £3.35 delivered. Fits great with the threaded section shortened a bit. If anyone is interested in trying this.

Once again thanks for all the help so far.

 

[SteveP]

I've just attempted to adjust my float heights to get the fuel level to lign up with the carb flange joints. I reduced the height of the floats to 32mm.
They are actually touching the carb body. The needle valve probably won't seal and cut off the fuel.
Is it possible that the geometry of the BS38's changed? I've attached two photos. The first is the early 1974 body. The second is a later carb, probably 1976.
Has anyone come across a similar issue?

 

[AUTOMAN]

floats are upside down, mate

cliff

 

[Jim]

floats are upside down, mate

cliff

No they're not.

 

[gggGary]

There are some aftermarket BS38 floats that don't work in the XS650 carbs, for KZ750 twins? dunno.

 

[Jim]

I'm wondering if either the needle or seat (both?) are the correct ones. A too short needle would act as you describe.

Being only 3mm short of the correct level, I might be tempted to put the float frame in a soft jaw vise and see if I could bend the floats down about 4mm or so. Easy does it, the trick is to keep 'em even.

 

[SteveP]

I've got two pairs of floats and three pairs of needle valves (one not mikuni and not fit for pure). I've tried all combinations. What I have noticed is the bodies seem to be deeper in the float area for the later carbs.
I'm wondering if earlier floats were a smaller diameter. I'll be digging into the parts lists tomorrow.
When I stripped the carbs the po had obviously tinkered with them a bit. One float height was 24mm and the other was 30mm.
And thanks for all the replies

 

[SteveP]

Pure - purpose

 

[Slowshed]

Bike still running rich. Getting bogged down just of tickover then taking off like a scalded cat.

I'm slowly working through as much information as I can on this site. And getting very good at removing and refitting carburettors. And trying to get the carbs as near spec. as possible.

I'm currently thinking it could be a choke problem so I've ordered a new plunger.

Or maybe an ignition problem?

Since the carbs are be the unlinked BS38's from a 1974 TX650 the float heights should be 24mm. I've tested for float leaks and swapped in a couple of spare floats to try. And tried some spare mikuni needle valves.

My problem is that I've set the floats as per manual measuring front the carb body. When I try the clear tube check the floats seem to be around 3mm lower than they should be. I've attached photo from this site of how the level should be and two photos of my levels. Should I lower my floats by 3mm to 21mm?.

I bought a hydraulic m8x.1 barbed fitting from eBay for £3.35 delivered. Fits great with the threaded section shortened a bit. If anyone is interested in trying this.

Once again thanks for all the help so far.

I don’t think increasing your fuel level is going to help your rich condition, just the opposite.

If you are running good at idler, then Boggs with the throttle cracked open, then clears up again … I would look at your slide needle positioning.

Is your needle clip in the center position? Are they the stock needles?

If the needle is too low (clip too high) or the needle is fatter than stock you will starve for fuel when you crack the throttle, then as you continue to open the throttle and the needle comes out of the main jet it will clear up because you are starting to add fuel to the air that the slide cut away is letting in.

The same is true in the opposite situation, but you’ll start flooding right off idle because you’re opening up the main and pulling more fuel before the slide cut away is letting in enough air.

Both conditions can feel very similar.

 

[SteveP]

I fitted a rebuild kit. It wasn't right, rich.

So I refitted the original needles and jets, apart from mains, which was one size up. The po had fitted the needles at slot 5.

I kept the correct size (but non mikuni) mains. And used slot 4 as original spec.

No improvement. In fact worse. The air screws aren't having any effect now.

Both plugs are identical after a run. Sooty and black. It seems as though the problem is common to both carburettors. Choke??? I've ordered a new choke plunger.

My attempt at setting the float heights as accurately as possible was just to get the carbs as near original as possible.

Again thanks everyone.