New topic - Carburettors

[(RIP) maverick]

Recently stripped my carburettors and replaced the o-rings, diaphragms, gaskets and generally clean out all the dirt. Asked around for information how to reset the carbs and get it to start easier. The general feedback was set the butterflies/throttle control so that you can see exactly the same amount of light when holding them up filtering through? Turn the air/idling screws out about 1 1/2 to 1 3/4 turns. Once they are fitted back on the bike adjust the idling by turning the air/idling roughly the same amount in or out until it idles. Use vacuum gauges or carbtune to balance the carbs?

Now once the gauges or whatever I will use to balance them is on which screws do you turn to balance the carbs? The throttle control screws or the air screws? I have not touch the throttle screws since resetting them and only adjusted the air screws to get the bike to idle but will get around the balancing during the week once I have more information regarding the setting of the carbs. It runs fine at the moment and not stalling or backfiring so think it is pretty close to what it should be however it still does not start easily in the morning and the moment I touch the throttle it takes longer so my guess is it might be getting too much fuel and flooding?

Any comments, ideas and suggestions as always very welcome.

Thanks

 

[cookie]

check valve clearence. won't make any difference unless they're way out, but all the books tell you to do it, so i will.

set air screws to whatever bmw say. you can alter them slightly at tickover to see if engine smooths out any.

make sure there is free play in throttle cables.

then: set throttle screws using a vacumn balancer of some sort. morgan carbtune is cheap & reliable.

then: ensure equal play in throttle cables by revving the bike. hold at 2/3000 rpm* watch guages to see that (guage )indicators start together & are level at steady throttle. they will vary a bit. they always do. adjust with cable adjusters as necessary.

job done. time: 15 mins. go down pub.

don't piss about balancing carbs by ear, or by looking down the veturii's, it's not worth the effort. only way to 1/2 accurately do it without guages is to do one pot at a time then turn down throttle stops by an equal ammount. don't do this on a bmw by disconnecting spark plugs. coils don't like it! you could try removing relavant float bowl & crimping the fuel supply to pot you want to shut off, but life's too short really.

*don't do this too long. 'specially on a hot day.

 

[PeterNicholson]

Carburettors?

'Ere - wot's one of them, then??














(oilheader)

 

[cookie]

Oi! mr smug.....

don't come crying round here when your noncy, namby pamby, new fangled fuel injection goes tits up, oh no

 

[judge]

Re: Carburettors?

'Ere - wot's one of them, then??
(oilheader)

Its what you fit to namby-pamby Oilheads if you're going to do anything serious with 'em, see Ernie's bike @ www.overlandsolutions.com

 

[Spanish Bob]

Re: Carburettors?

'Ere - wot's one of them, then??


...well, well Mr GS jockey have a look then at the r900 gsrr (?) that HPN built (www.hpn.de). carbs, can´t miss them, they are they mushroom shaped things behind the sticky out things on the side of the bike.











(oilheader)

 

[Howard Millichap]

Re: Carburettors?

'Ere - wot's one of them, then??
(oilheader)

One. ONE!
I'll have you know, we've got TWO carburettors. So there.

 

[Howard Millichap]

On my twin plugged engine Cookies' method does not work. I do it this way:-
1/ Plug on your vacuum guages.
2/ warm engine.
3/ set throttle at 1500rpm(ish) using the twist grip. [helps if you have a friction screw]
4/ adjust cable adjusters to give balance on the gauges. I think this is most important because this will give you a balanced engine when you're riding along.
5/close throttle.
6/adjust tick over by ear and feel. I do not use the gauges for this. I set it so that I get a good BMW "dance" at around 750rpm. A nice even beat.
The test is that the revs pick up cleanly without a hiccup from tickover when the throttle is openned. If it hiccups, there is something out because one cylinder picks up before the other. They should open together, obviously.

 

[cookie]

howard, as a matter of interest why does my method not work on your engine?

can't see any probs (or benefits) adjusting cables before throttle screws.

my experience tells me that i can adjust carbs by ear (did it for 20 years) bike sounds great. put guages on and adjust to them: better.

i'm sure you have much greater experience than me with these particular engines & i'm curious.

 

[(RIP) maverick]

Thanks Cookie and Howard for the info and hope all other's know what carburettors is now. Cookie's explanation makes the Haynes manual description more understandable now and will give that a bash. Howard if that does not work will give your way a go too as I have nothing too lose except different ways to set a carb.

Cookie why would the valve clearances be so important when setting the carbs? My one head(besides the one on my body) does rattle a bit louder than the other and will have a look at the clearances. I have given some though in replacing the rockers etc as it could be that they have been worn out over the last 13 odd years but for time being trying to ride more than work!


My main problem is to get the bike started within the 3rd or 4th turn if not the 1st as I continuesly worry that the battery will run out before the bike starts in the cold. Since cleaning the carbs the choke works again and that is a bonus but still a bitch to start on cold days.

Cheers

 

[PeterNicholson]

(ducks to avoid hail of abuse)

I remember now - I had one on my KMX, one on the Rat, four on the GPZ and two disgustingly gummed-up ones on the Guzzi, still sitting in the garage waiting to be cleaned out.

Glad to see Howard has the up-rated SOH unit fitted and working




And yes, I have seen the R900GSRRrrrrrrrrrrrrrrrrrr.








With carbs.

 

[cookie]

Cookie why would the valve clearances be so important when setting the carbs? My one head(besides the one on my body) does rattle a bit louder than the other and will have a look at the clearances. I have given some though in replacing the rockers etc as it could be that they have been worn out over the last 13 odd years but for time being trying to ride more than work!


the principle is that carbs are the last thing done 'cos they're affected by all the other stuff like valve clearances, air filters etc. TBH i think clearances are only important if they're too tight, first symptom being t6hat bike won't tick over when hot.

wouldn't worry about the valvegear rattling. means they're not too tight and besides which: they all do that sir. usually easily audible over the piston slap bmw rockers are on needle rollers & i doubt they ever wear out (someone's BOUND to prove me wrong on that, in fact i remember a friends all fell out into the rocker cover once) anyway you'd know if that happened.

one pot on my r100gs is louder than the other but it's slap from those big pistons i reckon, though others have suggested valve guide wear.

not got to the bottom of the starting problem yet. i expect ALL engines to start first crank within a couple of revolutions. my beemer does, then stops. repeat 2/3 times & off i go. rubbish CV carbs would be my guess. doesn't happen on my le mans or the r90s i have at the mo, both equipped with big dellorto pumper carbs. if i solve it, i'll let you know.

 

[mikyh]

The problem with old rockers is different

usually easily audible over the piston slap bmw rockers are on needle rollers & i doubt they ever wear out (someone's BOUND to prove me wrong on that, in fact i remember a friends all fell out into the rocker cover once) anyway you'd know if that happened.


The problem is that the smooth faces which ride the valve stems become scored. They are originaly surface hardend, but if the scoring is too deep, you grind past the hardened surface and it becomes scored again real quick.
The needle bearings are indestructable indeed.

Miky

 

[cookie]

ah yes. you prolly right about that.

 

[Mick Fagan]

I'm on my 14th BMW now and all of them had one rocker making more noise than the others.

I always used a longhish screwdriver as a stethoscope and listened and invariably it was the R/H exhaust rocker that was the loudest.

I have found that hard starting is often because one has the valve clearance too tight. This can be for a number of reasons. Firstly there could be wear and the valve gear is getting tired and closes up.

Secondly you could be running very close valve clearance so you can rev higher for racing purposes. I did this on a 90s in the mid seventies and was able to drop down a gear for a certain corner close to 8,000 RPM and then come out faster as I didn't have to down shift after the corner like the other BMW in the race. Before I closed the valves up I got valve float starting at about 7,600 RPM and I would have destroyed the heads otherwise. Interestingly, the redline for the R90s is 7,300 so only a little more and it's off.

A downside to this, was that it really became hard to start with tight tolerance. To ride it back home after the races I changed the clearance back to normal and it started easily once again.

Mick.

 

[Howard Millichap]

howard, as a matter of interest why does my method not work on your engine?

can't see any probs (or benefits) adjusting cables before throttle screws.

Well I'm assuming that when you say "throttle screws" you mean the ones that adjust the tickover. If so, thats all they do.
You do need to balance the engine when you've got the throttle open. Because that is how you ride the bike. i.e. when under way the tickover setting makes no difference.
So what I'm saying is that the most important setting is the balance on the cables. Which is why I recommended setting the RPM at 1500ish using the twist grip.

 

[nobby]

colour tune

hi maverick
I have always used colour tune when setting the mixtures seams to work for me if you want to use it give us a call

cheers nobby th courier

 

[(RIP) maverick]

What about compression?

Thanks Nobby,

Will give you a call in the week but pondering about this at the moment...........

Had a word with my Dad last night and he reckons I should do a compression test and see if the rings has not worn to the extend where it loses valuable pressure. Alternatively it could be a valve not seating properly and loses compression when the bike starts up. The more I thought of it the more it seems to make sense as the bike tends to start after turning for a while which indicates it builds up pressure until it is enough to combust and start? So will check it in the week the moment I get my hands on a compression tester. The bike idles and pulls very smooth at the moment and reckon the carbs is balanced and set near efficient as it possibly could be. But yet the little bugger does not like firing up in the cold. The saga continues and the oximiser tickle charge the battery overnight to keep max load for those extra turns at night..........

Cheers


ps. Mick sure is the right hand side head on mine that's making the extra noise!