Advice about airhead carbs

[bakerlonglegs]

Right-o, I've decided to sort out the carbs on my g/s.

Number of reasons: the fuel consumption ain't great (about 35-40mpg) and looking at the plugs it's running a bit rich; there's a problem trying to balance them (especially just off tick-over) and when it's hot the tickover is very high. So I thought I'd take the carbs to bits to check everything out.

Turns out there's a bit of hotch-potch of bits in them (1981 OE spec in brackets):
Main jet 145 (130)
Needle jet 2.64 (2.66)
Idle jet no. 45 (45)

No idea what the needle numbers are.

What does the collective reckon? I know absolutely jack-all about tuning carbs, I wouldn't know what to change and in what direction. So, my first thought is just to return everything to stock and probably replace the needles while I'm at it.

Any advice appreciated!

 

[Thunder]

Not an expert by any means (they are all tucked up with a frothy mug of Horlicks and a copy of the Peoples Friend ) but I'd get a stock kit of parts and work from there.

 

[fayeslane]

+1 for starting with standard jets.

Unless there have been obvious mods done like hi flow air cleaner or aftermarket exhaust, either of these usually requiring jetting changes to get the best out of them.

 

[Kenny]

Took you long enough to start work on them ( 3 years is it ).. anyway, contact the famous Motorworks ( or your own preference ) and return the carbs to stock with a full standard rebuild kit. Dead easy to do and just do one carb at a time. When that is done, return here and we'll discuss / inform you how to set the mixture screw etc

 

[England-Kev]

Turns out there's a bit of hotch-potch of bits in them (1981 OE spec in brackets):
Main jet 145 (130)
Needle jet 2.64 (2.66)
Idle jet no. 45 (45)

Ok then your fuel consumption does appear to be a bit on the low side, I am getting 50mpg on my ST fully frieghted for camping, even with a svelt person like me cutting the wind up front

So I delved into my official beemer workshop manual, and it differs from your readings....

Main jet 145 (130) ... 150

Needle jet 2.64 (2.66) 2.64

Idle jet no. 45 (45) 40

Needle position. 3

as I remember this is how I have my carbs set, as I also had a mis match of jets, you have to remember that a lot of main jet info is based on the USA being the biggest buyer of the bikes when new, and so they had lower jet sizes for the emission controls there.

 

[Rob Farmer]

There were two sets of jets fitted to the Mono's, they changed in 82 or 83. I've misplaced my Technicians handbook so can't tell you what they were originally. I think the haynes manual has the later sizes in.

 

[bakerlonglegs]

Thanks very much for the advice all

Took you long enough to start work on them ( 3 years is it )

Yes Thing is, the carbs were cleaned up by Scrimingers during the rebuild so they were the one thing I've left alone so far....

Ok then your fuel consumption does appear to be a bit on the low side, I am getting 50mpg on my ST fully frieghted for camping, even with a svelt person like me cutting the wind up front

Yep - I mentioned the fuel consumption to Rob at the Wee-kend, he said it was rather on the high side

So I delved into my official beemer workshop manual, and it differs from your readings....

Main jet 145 (130) ... 150

Needle jet 2.64 (2.66) 2.64

Idle jet no. 45 (45) 40

Needle position. 3

as I remember this is how I have my carbs set, as I also had a mis match of jets, you have to remember that a lot of main jet info is based on the USA being the biggest buyer of the bikes when new, and so they had lower jet sizes for the emission controls there.

I got the 81 figures from my Clymer manual. As Rob says, the numbers changed from 83 - according to Clymer, England-Kev's numbers in red are the 83 onwards numbers. So the settings on my bike don't match the 81 or 83- figures

81 or 83- settings? Both OK I suppose, but which one's best? There's only one way to find out....

FIGHT!

 

[Rob Farmer]

Go for the later ones

 

[bakerlonglegs]

.....just do one carb at a time.

Aaaaaahhh, one at a time OK, note to self...

Go for the later ones

Sounds like a plan, thanks Rob

Cheers all