Kurt in S.A. wrote: ↑Sat Jan 08, 2022 11:19 am
Does the main and the washer sit within the small detent in the bottom of the bowl? Been a while since I looked at the bottom of the bowl but thought there was a ringed area in the bottom. Could the jet and this bowl area work together in some way?
Kurt in S.A.
I've always understood that the washer and the ringed area were intended to work together to keep the main jet submerged when fuel is sloshing around in the bowl. Whether that function is needed or not is another thing.
All very interesting, as for the washer I am beginning to think that the it is there as the carbs were developed for aircraft use, as no other motorcycle I have ever had used it. As for my problem, I have discovered a slight error my rebuild. I had been a little too timid in tightening up the main jet assembly stopping a turn too soon leaving it loose . I put it back in today with a little oil and was able to put a couple of extra turns on it . Haven't been out as its been frosty all day but will have a go just as soon as the weather picks up a bit. Thanks for all the advice .
mkj wrote: ↑Sun Jan 09, 2022 11:28 am
All very interesting, as for the washer I am beginning to think that the it is there as the carbs were developed for aircraft use, as no other motorcycle I have ever had used it. As for my problem, I have discovered a slight error my rebuild. I had been a little too timid in tightening up the main jet assembly stopping a turn too soon leaving it loose . I put it back in today with a little oil and was able to put a couple of extra turns on it . Haven't been out as its been frosty all day but will have a go just as soon as the weather picks up a bit. Thanks for all the advice .
Bings have been commonly used on light aircraft but I don't know whether they were developed for that in mind.
The main jet assembly should be sealed by the O ring so being a little loose may not have made any practical difference. On neglected carbs the main jet assembly can seize in place and be difficult to remove so it's as well not to over tighten them on installation. A lubricant helps. Having done battle with one that had seized I always use silicon grease on assembly.
I had tightened the main jet up to the new o ring which left the upper section loose so that the atomiser was loose in the carb body and I this assume effects its ability to lift the fuel, I hope so anyway for it has to be something and this was defiantly wrong, will find out for sure as soon as I give it a try, no frost today but who needs to go out in the dark and wet when they don't have too.
Talk about seized jets, the idle jet had been superglued in place, I ground it out with a dremmel but it left only 1 thread to hold it in place but it still worked for many years, I bought a second hand carb just this year to replace it, it was not in very good condition but all the threads are good and it this carb I am having trouble with.
Today tried again as the weather was not too bad but sadly tightening up the main jet assembly made no difference. Went to get some fuel then tried balancing the carbs with home made manometer but it would not cooperate. Noticed I had trapped the right hand diaphragm reassembling it but still no difference, both slides are lifting and fuel is coming out of the jets. Tried a plug chop, right hand side seemed a little, rich so just because nothing else has the slightest effect I deliberately miss fitted the right hand diaphragm so the slide would not lift and would you believe it and instant improvement. From this I conclude the right main jet has some how enlarged itself whilst sitting in my garage doing nothing . I may of course be wrong but I think I am now getting somewhere.
mkj wrote: ↑Sun Jan 16, 2022 10:02 am
Today tried again as the weather was not too bad but sadly tightening up the main jet assembly made no difference. Went to get some fuel then tried balancing the carbs with home made manometer but it would not cooperate.
I don't see how the main jet can have any impact at all on a manometer balance at idle or at the usual figure of 2000 RPM to check throttle cable synch. The engine needs to be under load and at a minimum of 3000 rpm before main jet size has much impact and even then it has to be several sizes out. There is no point in attempting a cable sync balance if it won't balanced at idle as the fuel flowing through the idle circuit is still additive to the main circuit. It might be there are two problems but it sounds like there is one in the idle circuit.
Impact of pilot system.png (8.68 KiB) Viewed 1021 times
I have kind of given up on my manometer and will order a set of vacuum gauges, a set of three so I can use them on my k75 as well. I will look again at the Idle circuit as it has to be some thing but that was why I replaced the right carb as there was no thread left for the idle jet. Expected blackened plugs from the right side but it just stops firing on the when the throttle is opened, however I get some power if I put the auxiliary carbs on under throttle but the best response is using only the left diaphragm. I even tried squirting wd 40 into the carb with the throttle open with no effect, I use wd40 in place of aero start as it seems much less brutal, unconventional I know but I have started many motors with it. One day I will discover what is wrong.
I think you're totally missing the point and purpose of vacuum gauges and manometers.
Their purpose is to allow fine balancing (synchronizing) of the carbs in relation to each other on an engine that IS running properly on all its cylinders. The fact that you "even tried squirting wd 40 into the carb with the throttle open with no effect" is puzzling. That would normally indicate no compression or no spark.
Have you actually done a compression test?
Treat this engine as two separate engines. Get the 'good' side running properly; it should idle steadily, it should stall when turning the mixture screw all the way in, and it should rev up when pulling the throttle cable just as any single cylinder thumper should. Then, and only then, move on to the other side.
Mechanic from Hell "I remember every raging second of it...
My bike was on fire, the road was on fire, and I was on fire.
It was the best ride ever!"
I wouldn't give up on using a manometer when you getting the engine running something like right. Vacuum gauges may help in that they will show just how far out one cylinder is and perhaps lead you to a resolution of the problem or at least indicate when the problem has been resolved, but ultimately they are not as good as a manometer for doing a final balance for the simple reason that they are an order of magnitude less sensitive.
Last edited by barryh on Mon Jan 17, 2022 7:36 am, edited 1 time in total.
Thanks for the advice , I do understand about balancing and synchronisation, the manometer works fine as long as the both cylinders are close but if the difference is larger one cylinder swallows the oil in seconds. As for compression last time I tested it it was fine since then its had a Siebenrock Big bore kit which has improved compression if any thing. It was a pre existing problem which is why I checked the compression to start with. I plan to balance the idle circuit with the diaphragms disabled when the vacuum gauges arrive, see what that says. Oneday sombody will read and say either what an idiot or corr thats whats happening to my bike.
