Ongoing PD46 carburettor woes (possibly)

[keithtraffic]

Sorry - quite a long post!!

As per earlier posts, following major fuel seepages from around the carb bowls and (as it turned out) the fuel tubes between the carbs and also sporadically from the overflow tubes, I undertook to rebuild them.

With help from comments on this forum and Brainj who miraculously managed to supply me with four springs used on the throttle slider link arms, which had been lost during cleaning, the carbs have now all been re-assembled, bench balanced and refitted to the bike - re-fitting them was a nightmare!

During the rebuild the carbs have been vapour blasted and cleaned in an ultrasonic cleaner as well as having all the replaceable jets etc have been replaced along with the seals and O-rings etc. Taking note from others comments I have tried very carefully to make sure that all the internal passage ways were clear and clean.

The good news is that they look good and all of the fuel leakages have been cured.

To complete the exercise I have just finished carefully making sure the timing is spot on (at least statically), the points are good and the tappets are all correctly set up. (Both the timing and some of the tappets clearances were a little bit off).

The bad news is that the bike will not run smoothly at all!

Actually no-1 cylinder is hardly firing - its exhaust  pipe is still cool after a couple of minutes whilst the other three cylinders are all hot. just to be sure this wasn't anything to do with the plus I have swapped 1 & 4 plugs over but to no avail.

To explore a bit further I did remove the screw where you would attach a vacuum gauge and spray some carb cleaner in and immediately the revs picked and No1 cylinder fired up, perhaps suggesting an issue with the fuel delivery to that cylinder. I have also checked that there is fuel in the cab (by opening the drain screw) and confirmed there is a regular flow of fuel.

Its worth saying at this point that No1 cylinder has always been a bit of a problem in this regard, causing the engine to 'chug' at tickover until the engine has warmed up which makes me wonder if there is possible a more deep seated problem?

I am loathed to remove the carbs again and have another go at clearing them as there seems to be no clear way of knowing if the clearing is successful.

Does anyone have any suggestions - is there anything else which could cause this type of symptom other than the carbs? If I do take them off again what can I do to make 100% sure that all the passageways are clear and there is nothing else causing the problem? Any guidance would be appreciated!

[K2-K6]

Thorough diagnosis so far keithtraffic 

Initial thoughts would be idle circuit on #1 carb as presumably it chimes in if you lift the throttles,  and shows it's running when getting fuel via it's main jet?

Worth turning the idle mixture screw all the way in and slowly back it out towards 3 full turns while ticking over to judge the response.  This to double check the flow of that circuit.

If no/ little response,  try blowing air in via the idle mix port with screw removed ( engine not running) then reassemble to try again.

[Bryanj]

Suggests that push in pilot jet or the pathways to/from same.
Last time i had one to do got it running great then it sat 8 weeks and i had to pull the pilots again----i hate pd's and once my box of bits is gone i dont want to see any more

[OZZYSBIKES]

I agree with Bryanj

My K3 has them on, I've done very little mileage on it and had the carbs in bits three times, it still doesn't run perfectly at all throttle openings, I am about to start looking for the 550F carbs

[SPR]

I agree with Bryanj

My K3 has them on, I've done very little mileage on it and had the carbs in bits three times, it still doesn't run perfectly at all throttle openings, I am about to start looking for the 550F carbs

Let us all know how you get on

[deltarider]

... just to be sure this wasn't anything to do with the plus I have swapped 1 & 4 plugs over but to no avail.

How about the plugcaps? Have you tested their resistance? Do caps 1 and 4 show more or less the same resistance? Do you run 'R' plugs by any chance?
Are you sure the idle RPM shown on your tacho are a true 1100?
Also verify the carbs vent. If necessary cut one or two inches of the vent tube(s).
For the moment, this is all I can think of. If I owned a K3, I'd add a small dose of fuel system stuff (or kerosene or lamp oil for that matter) each time you fill the tank.

[K2-K6]

To extend the addative theme above, running and looking after very small carburation systems appear to  benefit from using two stroke oil with less of that "crystalline" debris accumulation that blocks small jets.

Consider something like a 90 to 1 mix ratio and assses if it reduces the incidence of blockages in these pd systems.

[Johnny4428]

I have experienced a bit of these woes, as many of the people on here have. I have had my carbs off three times and have found the easiest way for me is to remove air filter box and drop air box collector with intake rubbers attached loosen off 8 m6 nuts from intake manifold pull back and slide out. This is probably not much help but I have juggled between poor or faulty plugs “ngk” and blocked pilots and this was even after an initial complete strip and rebuild of carbs. I remember prior to a complete restoration of my bike I took the carbs off and they were ultrasonically cleaned, made no difference whatsoever probably pilots blocked. Also all four had blocked vents. I now have a bike that runs and ticks over very nicely, in fact I have never had the bike running like this in the 33 years I have owned it. You will get there, (hope it doesn’t take 33 years)! Good luck!.

[matthewmosse]

My k3 was always ok in the time I ran it - at least carburettion wise, and the first 6 months of that it sat idle while I passed my test. I liked the extra mpg, not that big on shorter trips but stick the bike on a motorway and the economy was great. A roads it matched my mates superdream  to the penny on fuel stops, motorway work I could get away with 50% fewer fuel stops. I did find some of the springs on the central cable area and choke return broken when I wanted to put them on my sidecar bike. Not had to resort to redex in the  fuel on a k3 but on my wifes 250 nighthawk I saved myself hours of messing around by spraying carb cleaner on the air cleaner and running with redex in the fuel. Took a few weeks commuting before it ran right but I developed a hatred of removing carbs and airbox over the years. Same trick worked with the cb500 sidecar with overflowing carbs.

[deltarider]

When was this ^? Petrol has changed. Even with todays petrol K3s will run fine, provided they ride regularly. Why K3 slowjets are more prone to (partially) blocking then those in the oldstyle carbs? No idea.

[keithtraffic]

Thanks everyone for the feedback.

Have been 'playing' a bit today to see what happens. I adjusted the idle screw all the way in and then unscrewed it (as suggested by K2-K6). All the way in and No 1 cylinder pretty much stalled but it did pick up as I unwound it (which I think is as expected). I did find that unwinding it too far also seemed to cause the cylinder to get very erratic. I am not sure if I expected that to happen - is that how its supposed to work? Anyway I returned it to 1.5 turns out.

However things do seem to have 'calmed down a bit and I can get the engine to run with all cylinders seeming to be working - at least they are all getting hot! The tick-over is a bit high - 1800 rmp and the engine still doesn't seem particularly happy at a lower tick-over.

I am inclined to take it out for a run and see how things go.

What are the options for changing the carbs to non PD types - is that a viable option?

[K2-K6]

That's exactly how it should work if the idle circuit is clean and operating correctly.

You should be able to take it from too rich to run well all the way to too lean to again prevent good running. Tentatively, that appears to show the carb as ok.

Unless you've already tested it,  I'd test and record compression for each cylinder next.

Reality check also for carb sync,  have you set them with a bench method otherwise referenced on the site?

[keithtraffic]

I don't have a compression tester (yet!).

Is there a good one that comes 'recommended' Having watched a couple of videos on this it seems that the 'best ones' have their pressure valve close to the cylinder?

The actron cp7828 which was recommended in the video I saw seems pretty expensive from Amazon - nearly £80!

[K2-K6]

This one should work ok,  but you'd ordinarily need to hold it in the centre cylinders while someone else turns it over for you as it's contorted to do both together.

https://www.mandp.co.uk/products/compression-tester-push-in-type-594478

Usually they have a schrader valve in the end that you push to release, also you don't have to screw anything into the plug threads as some of the kits don't have the correct thread pitch!

[keithtraffic]

Hi All,

Will need to think about the compression tester, but took the bike out yesterday to see how it performed.

Despite previously reporting that things had settled down and I could achieve a smooth tick over, albeit a bit fast, went out to the bike and started it up and again No1 cylinder was not really firing. Nevertheless decided to give it a run to see if things improved.

The throttle response was initially was pretty sluggish until about 3000 to 3500 revs and then things picked up and the bike really accelerated - like a bat out of hell - actually much better than I remember it (which could be the result of the carb rebuild and also getting the timing correct?).

After a good blast it did seem that No1 cylinder was running OK but then I stopped for a while and when restarted No1 cylinder was again not really running properly.

I am getting the feeling that this is still something to do with carburation but as mentioned before I really don't want to take the carbs off again if I can avoid it. So apart from compression is there anything else I can do as a diagnostic before committing to removing the carbs again?