The K2 carburetter saga goes on

[MickeyMoto]

Joe,

Did you say in an earlier post you do not use vacuum gauges?

It is one thing getting the slides by finger feel, another to set them accurately. I do remember having problems with the cable adjusters on the tops of the carbs. The vacuum gauges will show equal at tickover. When you open the throttle the gauges move the same way at the same rate. If not then the cables need adjusting. I had a flat spot problem until I sorted this. May not be connected, but worth a try? Always worth getting the free play correct and then checking with the tank on... Maybe the BS carbs are more forgiving, not having so many vents etc?

[72degrees]

I'm not happy about changing atomisers without first pulling the slide/needle these days. I discovered the tips of the X1 needles on my old PHBH28s were slightly bent a few years ago. I had done a lot of atomiser changes when they first went on, some of them 'in-situ', but that may have had nothing to do with the kinked needles. Probably me just being ham fisted at some stage putting the slides/needles back in after yet another needle adjustment or slide change.

I find that the idle speed can be inclined to speed up once the engine is good and hot. With the brand new PHBH28s it seems a bit more consistent lately, but I still aim for a happy medium that gives a slightly high idle when hot.

It's a question of preference but I always use my old original mercury filled Morgan Carbtune manometer to balance the carbs. The U tube system seems particularly sensitive to me. Given enough practice you could probably do it by ear, as when the columns start to dip in perfect unison on a slight cracking of the throttle I reckon you can hear how much smoother it is. I think it effects up to 1/4 progression, but I've had plenty of massive flat spots in the usual suspect half throttle/5000-6000 rpm region with carbs that were perfectly balanced in this way before setting out on the test run and still when checked on returning.

Extra air vents might complicate the issue as Mickeymoto suggests. I'd be inclined to bung a pair of BS carbs on and forget originality, to preserve my sanity.

My leaf shifter is really easy to start - if my back is up to wielding the spring-tooth rake

[mad muller]

if it was me i would ask george, no beg him, to sell me his carbs , either that go see a shrink , or buy a honda .

[3potjohn]

Well I could let you have an MGZR with a blown head gasket and a knock on full lock if you like-it will take your mind off the carb problems.....

[mad muller]

thanks for offer , but have enough probs to be getting on with.

[penman]

Thanks for all the replies guys, too many for individual responses, but I'll try to cover all the points here.

Carb balance. In my experience (for what it's worth!) the big issue is getting the slides to rise absolutely in unison for the first mm or so. If they don't rise together, you get hesitation coming off idle and poor response at low revs. I always back the throttle stops right off and balance them by the "finger up the intake" method. Now adjust the idling and finally re-check that the slides are rising off the stops together. I reckon that will be 95% of job done. Vacuum gauges (which I do use) can help you get it spot on, but I think you are only chasing a very small improvement after the initial setup. What they will also tell you is if the carbs are staying in balance as you open the throttle a bit more.

The option of giving up on the HS carbs looks ever more attractive! As someone said, it may even preserve my sanity, though it may be too late! This is a serious option now. If George is interested in selling his carbs, I'd be MORE than interested!

I will take the carbs right off again today and check that swapping atomisers in situ hasn't damaged anything. I must say, they slipped in quite easily though, so I don't think it's likely to be a problem. All the same, something has changed.

And now the really bad news - the leaf blower started immediately, so I was condemned to 2 hours hard labour! And last night's frost has brought another ton of leaves down, so I reckon I'll be out there again about Thursday.

[72degrees]

The advantage of using gauges or a manometer is that any (admittedly very small) differences in cylinder efficiency at low revs is catered for. I've used the finger and eyeball technique on BMW Bing carbs and the dangling rod under the slides method on Morinis, but not until I got the Carbtune did I appreciate how much just a tiny tweak on a stop screw or cable adjuster could make at idling and just off idling speed. I agree, however, that once in to the needle/atomiser determined range and even more so at WFO such fine adjustments make little difference. Then in hill climbs, the latter is the preferred default position

[Ming]

... If George is interested in selling his carbs, I'd be MORE than interested!

I don't recall whether you have tested your 'malfunctioning' carbs on another bike or not - may be the confirmation you need?

[penman]

The advantage of using gauges or a manometer is that any (admittedly very small) differences in cylinder efficiency at low revs is catered for. I've used the finger and eyeball technique on BMW Bing carbs and the dangling rod under the slides method on Morinis, but not until I got the Carbtune did I appreciate how much just a tiny tweak on a stop screw or cable adjuster could make at idling and just off idling speed. I agree, however, that once in to the needle/atomiser determined range and even more so at WFO such fine adjustments make little difference. Then in hill climbs, the latter is the preferred default position

I agree with everything you say. I like the dangling rod approach for Amals, especially when you have three to contend with on the Trident. For me, it doesn't seem to work so well on the Dellortos, which I put down to the flat slide - but it's also more or less impossible to watch both rods simultaneously due to the layout of the carbs.

As you suggest, I'll try riding on full throttle only, that should work, and is likely to be highly entertaining!

Ming: No, I haven't tried the "dodgy" carbs on another bike. It would need to be a "known good" K2 I suppose to really tell me much. I think I'm more interested in swapping the HS for BS and just accept the fact that they work. Assuming they do!

[EVguru]

I think at this stage I'd want to try changing one carb at a time and perform ABA testing. That is test with one arrangement, change one factor and test and then revert to the first arrangement to confirm that the results revert.

I often remove atomisers for cleaning (after a layup) with the carbs in situ, but it's easy to damage the needle tip. I have a piece of metal with a slot cut in it that goes behind the throttle cable ferrules where they enter the grip. This raises the slides and needles out of harms way. This is also good practice for a long layup as it prevents condensation collecting between the needle at the atomiser, which is what causes corrosion damage between them.

Just as a sanity check, make sure you've got adequate fuel flow from the tank.

[72degrees]

I often remove atomisers for cleaning (after a layup) with the carbs in situ, but it's easy to damage the needle tip. I have a piece of metal with a slot cut in it that goes behind the throttle cable ferrules where they enter the grip. This raises the slides and needles out of harms way. This is also good practice for a long layup as it prevents condensation collecting between the needle at the atomiser, which is what causes corrosion damage between them.

That's a cunning dodge. <Makes note>

[penman]

I think at this stage I'd want to try changing one carb at a time and perform ABA testing. That is test with one arrangement, change one factor and test and then revert to the first arrangement to confirm that the results revert.

I often remove atomisers for cleaning (after a layup) with the carbs in situ, but it's easy to damage the needle tip. I have a piece of metal with a slot cut in it that goes behind the throttle cable ferrules where they enter the grip. This raises the slides and needles out of harms way. This is also good practice for a long layup as it prevents condensation collecting between the needle at the atomiser, which is what causes corrosion damage between them.

Just as a sanity check, make sure you've got adequate fuel flow from the tank.

Paul's posting got me thinking a bit more logically again, thanks!

Checked the fuel flow, fine, but it definitely needed checking. Also took the carbs off and checked the needles for any damage, all OK thankfully.

Now I've put the borrowed "BS" carbs back on with the "diy" CM atomisers and the bike goes really well. This is probably the best setup to date. Blipping the throttle is instant, no flat spots anywhere in the range and I think it has even improved low revs torque slightly. I don't expect an awful lot of grunt from an engine like this, but it definitely seems to be improved and it's not quite so easy to stall it. So I think this is my benchmark performance, certainly I'd be happy, no, DELIGHTED with it going like this. Now do I start a complicated business of swapping one carb at a time in the hope that that will reveal something, or do I just take the "HS" carbs back to NLM and see if they'll swap them for a pair of "BS". I've not yet decided. And there's no guarantee that another pair of BS will work.....

Eurocarb have confirmed that the D and CM atomisers are no longer available from them. They also can't tell me the difference between HS and BS. To be fair, this is a well and truly obsolete carb as far as they are concerned!

I think the work I've done has shown that swapping atomisers can make significant but small differences - you can cause or cure an annoying flat spot for example. I don't think it changes a perfectly running bike into a complete dog however. There is something else going on and I don't know what it is though it is certainly carb related. I had another go at comparing the HS and BS on the bench today and this time I checked the bore of the atomiser air feed - it's 1.5mm on both. I can easily slide a 1.0mm copper wire through all those passages and a thinner wire through each of the pilot orifices. Everything is clean. What the heck is different, they are identical but one works and the other doesn't. And it's repeatable.

Regards,
Joe (feeling better after riding a bike which works!)