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Thread Like Summary
Allan G, Blown Income, BrizzoBrit, Gary E, Gordon Gray, Hillbilly bike, Hugh Jörgen, JER.Hill, Jon W. Whitley, Mark Parker, pushrod tom, RobJP, royaloilfield, semprini, Shane in Oz, Vincent Esposito, wadeschields
Total Likes: 26
Original Post (Thread Starter)
#879985 05/08/2022 8:58 PM
by wadeschields
I am so excited !! I have been looking for GP carbs for my 1966 BSA Spitfire at a reasonable price for over a decade.. Shockingly this pair was on Ebay and promoted on facebook Spitfire group page so I was sure they would go for the normal price or more but I won the auction at half price so now my search is complete.

Aren't they pretty.

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Liked Replies
by NickL
Originally Posted by Shane in Oz
Spitfire GPs are like hens' teeth. You did well there.

In practice, of course, 932s work better, with the GPs kept for special occasions.

Now to spend the next 10 years getting the bike to start easily and run well with them fitted eh?
Some blokes like a load of hassle................
2 members like this
by Lannis
Originally Posted by pushrod tom
Or.........It could have been the marketing dept. Sure they would not try to sell less hp. Kind of like the Hot Rod Mag test of a new Lightning Rocket where they did something like 132 with an out of the box machine!

Whoo! On stock gearing, what was that then....10,000 RPM?

Oh, the good old days when Bob Green and Floyd Clymer were holding the stopwatches .....

2 members like this
by edunham
After sitting for 6 months, I charged up the battery in my ‘66 Spitfire and it started on the third kick. Let it warm up for a few minutes and it idled at 8-900 rpm on the GPS.
2 members like this
by Spitfire Ken
Spitfire Ken
1 member likes this
by Gary E
Gary E
Originally Posted by wadeschields
I already had the float and I have the bracket to hang it... The guy I got the carbs from offered to clean the float to match and it came out great. I need to look at the bracket I have to see if the parts that connect are all there. I think the bolt on top of my float looks different then the pictures I have seen of others, so I might have to source that if it doesnt work.

Great info everyone thanks !!!

If the float eye bolt can't be sourced, which is very likely, you can make one like what I did here.

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1 member likes this
by TripleTown
Congrats on the find, they look beautiful! Personally, i'd prefer to have them on display rather than on the road, but hey...
1 member likes this
by edunham
Good for you Wade! Spitfire Ken is right about the cables. Basically it is a cable with the regular ferule at the carb end and a second ferule a few inches above that. It comes with a hollow threaded tube with a split in it and a seat for the ferule at the top. The tube is threaded into the top of the carb where the cable normally enters. You thread it up or down to raise the slide. You then use the regular cable adjuster to adjust for free play in the cable. I have them on my Spitfire. It starts easy and idles like an old Triumph with slightly worn carbs (pretty good but not perfect). As for the flat spot that DWR talks about. I had that when I originally set my carbs up with a ColorTune. Eventually, I put the ColorTune back on the shelf and adjusted the mixture by ear until I no longer had a flat spot when opening the throttle. Its a little rich and can load up in very heavy traffic with lots of idling, but runs fine normally.

Ed from NJ
1 member likes this
by NickL
What's a smooth bore 32mm look like Nick? If they made them there is a reason.

Amal didn't make them, various blokes did them , Mick Hemmings supplied the pair
i had they were actually 33 bores once machined. A lot of blokes who raced nortons used
them, hence the Mick Hemmings connection. They were very good carbs and were
eligible under the pre 72 racing rules.
1 member likes this
by NickL
Whats the difference in them? were they just "finished"?

They were fitted with the trumpets then the assembly was bored and polished
as an item. There was no step or joint and the taper was of course just a
continuation of the trumpet. The trumpets were not removable.
Snag with them was, one of mine had the progression hole blocked by the
machined material and it was a bitch to clear, doesn't really matter on a race bike
but without those holes you know what amals are like, no idle etc.
Blimey Allen that was 30+years ago now.............. I used them for a couple of seasons
then went to the weber carb.
1 member likes this
by pushrod tom
pushrod tom
Yeah, The early LR's had a 42 tooth sprocket as part of the brake drum. I have that with a 22 front on my Speed bike which recorded a best of 166+. A bit overgeared for street use :}
1 member likes this
by NickL
Originally Posted by Mark Parker
It needs that because the trumpet otherwise doesn't do much. Where the slide sides are might be thinner but isn't helping. Pwk are not smooth either nor VM nor TM but better, Lectron are very good, but old school GP2 no needle in the way. Not Big but on a 654 they could kick butt. If the quirks are under control.

It's not the 32 concentics on the MKIV so much that are the key to it's equal hp with the lower 9-1 compression, it's the altered port, as using that port on a Firebird with 30mm gave a similar increase at Umberslades on their dynos in 1970. 32s would help but not on their own. That head with GP2s and 10-1 would have been nice.

That engine had +0.060 10.5- 1 Venolia pistons in it and a reasonable head, it had been worked/flowed and
had srm inlet valves. We were clocked on it at 108mph at one circuit, about 15mph too slow but for a 650 it
wasn't bad. We both weighed about 180lb and the old outfit was no lightweight. I put it together to learn to ride
the old crate again in 1991 after a 15 year lay-off. It rekindled my dormant lunacy.
1 member likes this
by Richard Phillips
Richard Phillips
Congrats Wade, you now enter a unique cadre of enthusiastic GP carb owners. I love to run these carbs once set up they make beautiful power range that just keeps on pulling.
Setting them up according to your instructions is pertinent: The float perfect and the cables to set up the slides are the big hitter. Yes they will idle and that is all in the cables. Keep an eye on that cable adjustment because they will change and make sure they are lubed. You might have trouble finding the correct cables.
I’m planing a 64 Spitfire Hornet replica using the GP carbs and original ET ignition with 6CA points plate. Have to finish my West Coast Hornet first.
Good luck,
1 member likes this
by Gary E
Gary E
Originally Posted by NickL
Originally Posted by edunham
After sitting for 6 months, I charged up the battery in my ‘66 Spitfire and it started on the third kick. Let it warm up for a few minutes and it idled at 8-900 rpm on the GPS.

Can't be a fast one then..........
Doesn't matter. Idle is important for normal riding.
1 member likes this
by edunham
It runs pretty fast. The idling comes from the cable kit described earlier in this thread. I also have the mixture a tad rich to get rid of the flat spot when the throttle is opened from idle. I have all stock settings and jets, except the needle clip is in the next higher position. When I was originally putting the bike together, I got the BSA shop manual, the owner's manual, and the parts book. They all listed different jets! I don't remember which stock setting I have, but it is one of them! A further complication was that I had a bad cam from the factory. The intake on the primary opened late and closed early, which I didn't discover till after the bike was together and I was trying to find out why it had no pep. I then put in a new Megacycle cam (don't remember the number, but its the one that is just slightly hotter than stock), which transformed the bike. That wasn't the end of it, though. With the cam and stock jetting, it was still lean in the mid-range. That was when I discovered that the previous owner, presumably in an attempt to deal with the cam issue, had put in the lean GP needles. Changed to the proper needles and now it runs like a top. Although after 20 years of no aircleaners, it is now starting to smoke a bit (although not constantly).

Ed from NJ
1 member likes this
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