Carbs on a65 FIREBIRD

[bill shortall]

 My firebird  does not want to tickover  when i stop at lights.  it backfires when i try to start  it  it has electronic ignition  which is correct i have put different slides in  and have cleaned out the jets
It ticksover high when the adjustment screws are  backed off
any info greatly appreciated

[Bess]

Hi,
    Which year is it?

Best wishes...

[LightningAndStarfire]

Which electronic ignition do you have? Have you checked with strobe light that it advance the ignition point correctly from low revs up to 3500 rpm?

[bill shortall]

its  a 69 and the timing is spot on and its a Boyer  dual  coil

[Allan G]

If it's back firing then the carbs are too lean.

Remove the idle screw, remove the carb top with slide.

Have a #78 drill bit glued into a WD40 straw or a 0.016" guitar wire and use it via the Air screw Hole to clean out the idle jet.

Then... get some carb cleaner and spray via the air screw hole and you should see 2 streams of carb cleaner squirting out of the carb from the 2 little holes in the body. One hole (these are jets of a pre determined size) would be under the slide if it was fitted, the other is the engine side of the slide.

When the slides are down the front little jet feeds the slow running circuit, as the slide opens the second jet comes into play enrichening the mixture until the slide and needle
Jets come into play. If these are blocked you'll get the symptoms your receiving.

When your done clean the tips of the air screws with some
Carb cleaner and a lint free cloth, screw back in and back them out 1 1/2 full turns. You may need to adjust the mixture a little either way once the bikes heat soaked (ie done at least 10 miles on a sunny day)

Always adjust the air screw (horizontal) until it gives you the fastest running speed, then start to screw it back in until the revs are just about to drop slightly. Then adjust the slide screw to set the RPMs.

By adjusting the air screw to as the above your setting the optimum fuel air ratio for slow running.

If you find your finding that opening the throttle causes the revs to faulter then you need to change the slide, richer if the bike tries or does cut out.

Leaner (so higher number) if the engine bogs a bit (ie doesn't rise cleanly) but continues to run.

Never ever adjust the idle mixture screw to fix this issue 

[bill shortall]

Thats great many thanks for your time

[Bess]

Hi,
    Further to the other posts.

The 1969 model, maybe worth checking the carbs are 930/25 and 930/24. Recommended settings, slides should be 2.5 and your needle position should be 3, which is different to the other years.

Worth having a look at this, some help setting up both carbs equally:

http://amalcarb.co.uk/downloadfiles/amal/Mk1_Hints_and_Tips.pdf

Best wishes...

[Allan G]

Not sure where you got your jetting from Bess, if it was the parts manual it's likely to be the 68 jetting given. In many cases what the bikes were sent out with is not only different from the parts book but also the WSM. It's worthwhile taking note that what the bikes rolled out of the factory with is what Amal jetted them up with. With any changes along the way.

http://amalcarb.co.uk/carbspec/carburettor/spares/id/6598/

In 68 the (what is now known as) 4 stroke carb didn't exist, only the (what later became the) 2 stroke carb. The jetting was found to be too rich and whilst this was fine for the 2 stroke adaptations were made (spray tube, jet holder and a different needle jet), in 69 they also introduced the jet bush pilot jet, this was carried over to all carbs to prevent the engine dying when the throttle was shut down due to starvation in the idle circuit.

Strangely the Amal website doesn't list a 68 firebird carb, I would have to consult my jetting manual with the specs. 

The lightning and firebird are good examples of this, for 69-72 on the firebird there was no other changes(excluding frame) all bikes had air filters and same exhaust. Same for the 69-70 Lightning's. all the jetting is the same. Yet if you jet a 68 Lightning the same as a 69/70 for example it will run at its optimum. For that exhaust and air intake setup. The 68 firebird is different here because the exhausts changed from 1 1/2" to 1 3/8" as did the exhaust layout.

[Bess]

Hi Allan,
             I have carb specifications for all A50 and A65 models and years, cross checked from various sources.

For the Firebird it gives different Amal numbers for all 4 years, Amal are generalising, quoting the original specification for 1970.

Best wishes...

[Allan G]

Amal would have on file and use the last spec used for a certain year (being on their retailer dealer list I know this) so if you ask for carbs for a 68 Lightning you would get a 2 stroke carb with 190 main jet, 2.5 slide. (By way of example)

As microfiche were expensive to make BSA only made new changes when a new production year began. Amal would have already started shipping the later jetting spec to BSA but as the microfiche for 69 were made in 68, BSA didn't alter the microfiche until end of summer 69 for the 70 models. The 70 jetting is what your best looking at as (as previously mentioned) there were no other changes which would affect jetting. The carb number change would also equate to: changes in carb top, chokes fitted or not and type of banjo fitted.

[Bess]

Hi Allan,
             So you recommend changing the internals of the 1968 carbs 930/25 and 930/24 to the internals specified for the 1970 carbs 930/35 and 930/34?

Best wishes...

[Allan G]

68 carbs have 2 stroke jets which will run rich. You would have to change spray tube, jet holder, needle jet, needle for a start.

You would likely have to go one slide leaner and lower the needle one position also (but this is with the new 4 stroke needle) and one main jet smaller....if your running a 68 bike (with 68 style exhaust)  your best way is to set the bike up as per the tuning guide unless you know someone who has already done this. The above is a guide relative to the other carbs that changed.

[johnjag]

Hi - also check for any air leaks via the attachment to the head. JJ.