Carb jets

[Graeme77]

Sorry, more questions from the newbie

Decided to take my carbs apart. They have obviously been apart before, and i suspected they were all over the place.

I was right  

Cleaned everything out and no blockages. One float valve was a little sticky, but i had a new spare.

The top grommet seals in the top caps weret seated right which im sure was slightly effecting the way they shut. All sorted now though.
Float levels were all over the place, but all correct now.

The last thing, and the thing im asking about, is the needle jets.

The actual needle jets were located on the 5th? setting, holding the needle up highest. Ive put them onto the middle ring, as standard, but im not sure if the 5th ring placement was intentional.
I have 132.5 jets in it.
These will richen it up right, and lifting the needles as i have will richen it more wont it.
Any thoughts?


((((EDIT to say, by moving the needle to the middle setting ive actualy lowered the needle, that'l lean it a little wont it, not richen it.))))

Secondly, the jets themselves. 132.5, as i say, apart from one, which is 152.5!!!

I have a spare set of incomplete carbs. These have a set of 116 jets in. Should i use these, get another 132.5, or something else?

The bike has pod filters (i have the origional air box though) and an aftermarket 4-1.

The last thing is the jet holders, the tubes with all the little holes..The ones on the bike, with the 132.5 jets, have very small holes for the first 2, the other 3 are slightly larger. On the holders with the 116 jets, these first 2 holes are pretty much the same size as the other 3.
Whats the difference with these?

Oh, i forgot, one other thing too.
There are little tubes linking the carbs together (not the fuel tubes). Carbs 1/2 are joined and carbs 3/4 are joined. However, where the throttle return spring is the pipes are open. Should these also have a loop of tube joining them?

Thanks, ill get this think purring eventualy

[Graeme77]

I fitted the tubes with the bigger holes and the 116 jets, synced them on the bench, ill see how it runs now.

It was rich before, and idled rough (no wonder with 1 huge jet!).

Not ridden it yet though, so untill i get some vac gauges and can take it for a spin there's not much else i can do.

[Graeme77]

It runs better now. Picks up real quick when you blip the throttle. Sounds better but isnt too smooth idling at 1000rpm.

Primary chain rattle was a bit better too.
Re-fitted the stock air box and got a big improvement. Idle at 1200 and any revs above that and the primary rattle is all but gone. Trying to let it idle at 1000rpm and its lumpy. The primary chain rattles on every lump as the crank tugs on the chain.

So, heading in the right direction, not a bad result i guess for a bench sync.

Time for some gauges, maybe ill flog a few spares on ebay to fund them.

Bike seems to be slowly going back to stock LOL.

[K2-K6]

Ha, no wonder it was chuntering it's chains with carb set-up like that. Seems you're getting it to how it should  be though now.

Mostly it's hard to get a really even tickover below about 1100rpm, perhaps when brand new maybe a little lower but I percieve it to be kinder to the generla health of the chains to be smooth at that rather than chase a lowered figure without any good reason.

As you've found you can get the sync pretty close by eye when on the bench but you can also do them with an improvised "feeler gauge" under the slide to get a really good physical match and I'd be willing to bet they'd be very close when checked with vac gauges.

[Graeme77]

I set them using a piece of mig wire as a feeler gauge, from the head side of the carbs.

I guess i now know why the exhausts all blued at a different rate!

Going to look at ignition again tomorrow, i timed it static, then checked with a ligth, but it was bouncing around at idle. Ill see if i cant settle it down a little.

If not ill just let it idle high.

My old 125, with a micron, made no power untill 3500rpm so i set the idle at 3250rpm

Only for a day of so, screaming at the lights got tiresome.

[Spitfire]

I don't know if you have seen this but it may be handy,
http://www.motorcycleproject.com/motorcycle/text/specs.html

Cheers

Den

[K2-K6]

Den, that's a really useful collection of information and helpful to quite a lot of the people on here.

Greame, that could be arguably the best way to set them (using a gauge) intially as it is physically correct and will not take into account of any other irregularaties so assuming the carbs are near enough correct it then allows a good platform to work through any other stuff.

The slight increase in idle can have another benefit whch is often overlooked with these bikes which you'll feel when you ride it more. When you close the throttles completely i.e. slowing into a corner, with the carb slides right down at the bottom and engine revs up then the vacuum in the carbs makes it quite difficult to smoothly roll the throttle back on. The effect you get is it feels unduly resistant then, as you put more effort into it suddenly you snap to more opening, it's not dangerous but a bit difficult to get it smooth. If the idle is slightly higher it minimises this feel and allows a smoother operation just not enough to feel it's pushing you when closed, at a guess 1100/1200 for low speeds maybe 1300 if you used it faster for a longer period. It has a much cruder action than some modern CV carbs which natuarally damp this feeling for you.

[Graeme77]

Good point about the idle speed.

I have another pair of carbs of a slightly different design. I believe they may be later F2 carbs. Not sure if there 100% complete, might be missing jets. I have 3 brand new genuine floats for these too. My other set are earlier. Ill get the numbers off the carb bodies later and check.

I suppose what im getting at is, are the later design carbs any better?

[K2-K6]

The F2 carbs step to a different strategy for running the motor at varying speed and load.

They are set to run as lean as possible in a steady state constant speed (probably this era saw the first real steps on bikes to clean up emissions) and are supplemented by an accelerator pump that operates as you move the throttle open more. It just pumps more fuel in to accept the load you are trying to put out so instead of going lean as the slides come up a spray gets it temporarily rich to facilitate the acceleration phase.

They also have a cable operated choke that gives rich run to start but pushed in half way will run the motor at about 2000rpm with mixture backed off to avoid making the bores too wet (you can see the change in intent from the old set-up and overlaps what we were saying about contaminating the engine oil) and also helps to get the engine hotter faster, Has benefits to the exhaust too as it runs dryer like this and gives less chance to help rot the pipes from the inside.

The F2 motor has bigger valves, wilder cam and higher redline so the spec jetting for the F2 carbs may not be entirely accurate for previous engines, guess you'd have to run a set-up to correct if not ideal.

Probably not much different from a rider point of view, maybe marginally snappier if you wack it open quickly.

[Graeme77]

Thanks, ill no doubt see if there complete when i get a chance, whether ill ever try them or not i dont know.

Maybe one day, out of curiosity

I also have perverse thoughts about fuel injection though

All a way off though, first things first, get it running and ride it for a good while. Got to get it reliable as we've just booked our IOMTT 2012 and the cb will be our transport.