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1967 Spitfire Jetting specs. #780644 08/05/19 9:28 pm
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PFribley Offline OP
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Purchased a basket case 67 spitfire 3 years ago. Got it all back together seems to run ok but it is way too rich on the bottom. When you start it, it billows black smoke out the exhaust and 8 cycles. Found some jetting specs in a manual from the day. Here is what it calls for jetting in the 32 Concentrics and that is whats in there now. Not even close. They are new bodies, slide, needle, needle jet, pilot jet. Even installed the stay up floats .080 from the top of the bowl. Need help!!! Thanks.

#3 slide ( brass chrome)
2 ring needle (in leanest position)
107 needle jet
20 pilot

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Re: 1967 Spitfire Jetting specs. [Re: PFribley] #780645 08/05/19 9:35 pm
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triton thrasher Offline
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Well, try 106 needle jets first, seeing as they’re cheaper than 3.5 slides.

With the smaller needle jets try the needles in the middle slot at first.


Amateur Loctite enthusiast.
Re: 1967 Spitfire Jetting specs. [Re: PFribley] #780650 08/05/19 11:13 pm
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gavin eisler Offline
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Might be the float valve needles are passing, what sort are they?
What are your pilot mix screws set at, somewhere between 1 and 1 and a 1/2 turns is in the ballpark. These are used to set the idle mix where your problem is.

Last edited by gavin eisler; 08/05/19 11:15 pm.

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Re: 1967 Spitfire Jetting specs. [Re: PFribley] #780693 08/06/19 6:46 am
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Allan Gill Offline
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Where did you buy them from and do they have 2 stroke or 4 stroke jets fitted?

In 67-68 all Concentrics were fitted with 2 stroke jets (by 69 4 stroke jets were introduced and new jetting values for the carbs)

4 stroke jetting changes includes....

Pilot jet moved from being a jet in the float bowl area (2t) to being a press fit bush closer to the welch plug (all carbs from 69)

Change of spray tube from slanted towards the head (2t) to flat topped (4t)

Change of needle jet from being thick all the way through (best way of describing it, but the whole jet is metered for flow) (2t) to only being sized at the bottom, the upper wall of the jet is thinned out and does not meter the fuel (4t) 4t needle having a 0.35 hole drilled across the carb to allow leaning of the mixture on transition to needle jet position.

Needle having 1 ring for 600 series and 3 rings on 900 series (2t) to having 2 rings above the clip positions on all carbs (4t)

The jet holder, holds the main jet and needle jet on one fitting being more bolt shaped on 2t and being fluted on 4t pushing the main jet further into the float bowl.

Once you establish those then it’ll be easier to sort the problem. The original 2t jetting was rich... but not plume everywhere with smoke rich, so I’m thinking that you have 4 stroke jets in there. This will give a lot richer condition especially at needle jet.


beerchug
Re: 1967 Spitfire Jetting specs. [Re: PFribley] #780694 08/06/19 6:52 am
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Allan Gill Offline
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Just a note that AMAL haven’t supplied chromed brass slides for probably about 8 years now, I bought some of the last ones they had but even at this point anodised slides were well in the market by then.

The chrome brass slides are also quite heavy, there were some others on the market which were the standard mazak slides but chromed.

So either your carbs had been sat on someone’s shelf for a very long time.... or they aren’t what they seem and someone has made a carb up to suit.


beerchug
Re: 1967 Spitfire Jetting specs. [Re: PFribley] #780706 08/06/19 2:23 pm
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PFribley Offline OP
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Its all late AMAL parts. Purchased everything separately according to the above specs. Did try a 15 pilot jet. Air screw went from 2.5 to 3 turns out to about 1/8 of a turn out to get the bike to start and idle nice. Have some 106 needle jets and 3.5 slides. Going to take a big swing at it and see what happens!!!

Last edited by PFribley; 08/06/19 2:24 pm.
Re: 1967 Spitfire Jetting specs. [Re: PFribley] #780726 08/06/19 6:10 pm
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Allan Gill Offline
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The reason I mention is because no spitfires were ever jetted with 4 stroke jets.

I would jet it as per a 69/70 lightning and go from there.

#3 slide
106 needle jet
Try needle in it’s lowest position but be prepared to raise it.
180 main jet.

When tuning the idle mixture. Tune it for idle, that’s the leanest that it will go giving the maximum revs when at tick over. Ifit fluffs when taking throttle it’s the slide that needs changing. Not the idle Mixture.

Also if the carb is setup as per a 4 stroke then it won’t have any pilot jet in there least the screw in type. As previously mentioned it will be the bush type. If you haven’t done so I would seriously recommend taking the carb apart and comparing the examples as my previous email.

Last edited by Allan Gill; 08/06/19 6:12 pm.

beerchug
Re: 1967 Spitfire Jetting specs. [Re: PFribley] #780727 08/06/19 6:17 pm
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gavin eisler Offline
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new premier bodies with replacable pilot jets? or are you screwing pilot jets into the roof of the float chamber in the 2 stroke position?


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Re: 1967 Spitfire Jetting specs. [Re: gavin eisler] #780734 08/06/19 6:36 pm
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Allan Gill Offline
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Originally Posted by gavin eisler
new premier bodies with replacable pilot jets? or are you screwing pilot jets into the roof of the float chamber in the 2 stroke position?


Good point! I’m taking the liberty of assuming that if these carbs are new premiers then they wouldn’t have been supplied with the chromed slides from Burlen.


beerchug
Re: 1967 Spitfire Jetting specs. [Re: PFribley] #780756 08/06/19 9:38 pm
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PFribley Offline OP
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These carbs aren't preimers. and the pilots are in bottom of the body of the carb.The big swing was too lean. Wouldn't start. I have 2 Commandos and 2 tridents so I have a nice collection of AMAL parts. Took the 3.5 slide out and moved the needle clip to the richest setting. Put the 3.0 slide back in. Squirted some starting fluid in the carbs for effect. Gave it a kick. Fired right up!!! Finally sounded like a proper BSA even though it didn't run very long on the prime.Still have some more tuning on the air screws but I can work with this. I parked this bike for 3 years cus I couldn't get the carbs right and it really bumed me out.I assumed the book I had with the original post jetting had to right. And something else was wrong. I will ride it for a while do some plug reading and see if any more tuning is in order. Still has the 20 pilot jet in it.May have to do some tuning on it. Without much running the air screws are 3/4 to 1 turn out. I like thus bike and hope finally ride it more!!! The 107 needle jet most likely was the culprit all along. Thank you all for the advice,


Sincerely yours,

Pat Fribley


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