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PR: Proprietary Items GP advice & suggestions


vibrac

Well Known and Active Website User
VOC Member
I have been lucky enough to source 2 off 1-1/4" GP2 carbs for our twin racer (No longer available new) Its a size I feel is ideal for a twin short circuit racer in UK, the motor is not overtuned at the moment and will run on I-3/4 pipes with the least restrictive silencer we can get away with, which I guess may get to 110 Db max (105Db is scrutineer bay level) I wonder what slides to start with? at the moment what we bought have has No 4 fitted and advice from racers is welcome. I have alway been a TT man untill now but as we are not restricted by the BHR 1948 barrier anymore and the Amal GP started around 1950.......
 

greg brillus

Well Known and Active Website User
VOC Member
Not sure what help I can give on account of the methanol fuels we run down here in our burning climate...........Anyway, the slide numbers on the racing carb's are generally in 32 th's of an inch so just check that the slide does in fact have a cut away 1/4" in height. On petrol type fuels I would think a cut away 1/4 or slightly more would be a good start. We had genuine 32 mm TT's on the racer which is 1 1/4" and that bike ran very well, good power and torque. On my current 500 racer the Amal Mk 2 smoothbore carb was set up too rich, and the engine would not come back on power cleanly out of corners. I modified the slide as per normal, opening up the cut away (cant remember exactly how much) perhaps a mm or so, and after a test ride around the block, the engine pulled cleanly out of any corner. It is actually better than i had the twin racer set up........Unfortunately I never got the chance to get the twin spot on as i don't have it anymore. But a slightly larger cut away on both carb's would have cleaned it up that bit more. I will most likely be running an 1 1/2" GP Amal on the racer with the new Comet engine that is being installed/ built as we speak. The beauty of these carb's is they are ideal for Methanol fuels due to the large 302 amal float bowls they run......Other more modern carb's are great but their fuel bowls struggle to deliver enough fuel to the main jets. Good luck with it all.........
 

Mike 40M

Well Known and Active Website User
VOC Member
My 350 Manx was fitted with an 1 3/8 GP2, a #5 slide 330 Main jet 109 needle jet, in very bad condition when I bought it. It got an 35mm Gardner now and runs very well. I tried a new Burlen Amal Matchbox on it. Didn't supply enough petrol. Replaced it with a Gardner float bowl, no problem with that. When at Goodwood last year, I noticed that the Manxes used SU or Gardner float bowls.
 

vibrac

Well Known and Active Website User
VOC Member
Interesting about fuel supply with matchbox float I am hoping that it will be ok with 1-1/4 as there is little room for a bigger chamber on the front which is very updraught. I never got on with the gardener carb on the comet I had an Amal float chamber lash up I don't think I would recognise a Gardner float chamber any pictures?
 

Mike 40M

Well Known and Active Website User
VOC Member
Main problem with my Matchbox was that it come with totally incorrect fuel level. But according to my KTT racing friend who tested it compared to a couple of his, flow rate was less than his old real AMAL ones.
The Gardner chamber is approx. as wide as it's long. As Mr Gardner now is quite old, Dick Linton is now supplying them. Had good help from him getting my carb working.
Gardner float.jpg
 

Bill Thomas

Well Known and Active Website User
VOC Member
I ran my Gardners without a float, So no flow problems !.
It was a little weaker with an almost empty tank, As different from a full tank, But not a problem.
Glad to know Ron Gardner is still with us, I went to his house and had a few off him over the years.
Nice Bloke. Cheers Bill.
 

greg brillus

Well Known and Active Website User
VOC Member
Does anyone know what is the largest one made in the Gardner range, I need something at least 1 1/2" or 38 mm up to 40 mm would be ok.
 

Comet Rider

Well Known and Active Website User
VOC Member
Tim,
Give me a call sometime.
In my dad's box of bits I have a selection of SU and large AMAL floatbowls that might work from his sprinting days.

Neil
 

davidd

Well Known and Active Website User
VOC Member
Its interesting that the Amal 510 delivers more fuel than any other Amal float bowl. Maurice Candy commented on this as his 500 Manx used one also. His engine produced 64 BHP. The Flash at 40 BHP got 37 MPG at Daytona, so fuel flow did not seem to be of great concern. I did check the maximum flow, which was about 3/4 of a gallon in a minute. I raced at Daytona several times and there was no cheating because my fuel tank was a little more than a gallon, which would do 10 laps while our race was 5 laps with a warm up lap.

Measuring the flow of fuel is critical. Measure the first time 1 gallon flowing out the petcock with the gas cap removed. Then measure flow with the fuel cap on. This will tell you if you have a vent slowing the fuel flow. Then do the test through the float with the cap on. If you get 8 ounces or more per minute it should be OK. If you are at the low end you should be checking to see what the obstacle is. I used a large 3/8" tap called "the Guzzler" made by Pingel. It also had a lever/cable operated remote "off" mechanism, which could be operated from the handlebar. This is required by some racing orgs. It is quite expensive, but it works very well for all different fuels.


You may be missing fuel because it is squirting out the vent hole of the float. I noticed this on the dyno. On overrun the fuel would squirt out the vent the entire time the throttle was closed due to a frequency vibration that was not noticeable to the rider. Depending on which way the vent hole points, you will not be able to notice this. The fuel shoots out and evaporates prior to discovery. Tightening the float mount a bit cured the problem.

David
 

Bill Thomas

Well Known and Active Website User
VOC Member
The late Dave Houghton, Sprint raced a Velo with a GP and remote float, " Road Class ",
He had that petrol coming out the top of the float chamber, Every now and again over many years,
His cure was to renew the float vale and seat, Worked every time. Cheers Bill.
 

vibrac

Well Known and Active Website User
VOC Member
What I have learnt:
The GP2 has the float level at the bottom of the O on the carb plug it also departs from the TT and earlier GP in the pilot adjustment by metering the air and not the fuel so it is in line with road carbs ie: in for rich.
Thanks for the offer Neil we will see how it all fits together and runs on the dyno
I hopefully await any other slide size recommendations....
(which is where I came in ;) before the flow (pun) altered)
 

Phil Davies

Well Known and Active Website User
Non-VOC Member
Does anyone know what is the largest one made in the Gardner range, I need something at least 1 1/2" or 38 mm up to 40 mm would be ok.
Ron does carbs up to 44mm, 40 and 42 are common sizes to him, I think the 44 is only available in 'tube connect' form, but I am not 100% as none of mine are bolt on.
 

Phil Davies

Well Known and Active Website User
Non-VOC Member
What I have learnt:
The GP2 has the float level at the bottom of the O on the carb plug it also departs from the TT and earlier GP in the pilot adjustment by metering the air and not the fuel so it is in line with road carbs ie: in for rich.
Thanks for the offer Neil we will see how it all fits together and runs on the dyno
I hopefully await any other slide size recommendations....
(which is where I came in ;) before the flow (pun) altered)
The reason the fuel is metered is specifically so high downdraft angles can be used, unlike with air metering.
What I can tell you is that there is a known 'low air flow' fuel pick up problem on GP's - precisely because of the fuel delivery method and route (and there is a fix!).
What I can also tell you is that 100% you will see a performance increase from Gardners over GPs, precisely because of better fuel metering and delivery and its consequent atomisation into the choke. One important item that lots of peeps with Gardners forget is that they do not automatically enthalpy compensate like GP's (because of the fuel delivery method), that is one reason why they are so easily adjustable - because they have to be each time!
What I also also know is that Ron's float chambers do not froth, unlike the amal's (despite what amal used to say to the contrary).
 

greg brillus

Well Known and Active Website User
VOC Member
Great Info Phil, can you advise as to the approximate cost of the Gardner carb's and the float bowls to suit. this will be to run on a 665 cc Comet race engine. Cheers.......Greg.
 

vibrac

Well Known and Active Website User
VOC Member
The reason the fuel is metered is specifically so high downdraft angles can be used, unlike with air metering.
What I can tell you is that there is a known 'low air flow' fuel pick up problem on GP's - precisely because of the fuel delivery method and route (and there is a fix!).
Phil as I have MK2. GP and a steep down draft I would be most interested in the 'fix' for the front carb
 

highbury731

Well Known and Active Website User
VOC Member
Does anyone know what is the largest one made in the Gardner range, I need something at least 1 1/2" or 38 mm up to 40 mm would be ok.
I read somewhere that Gardner would make his carburetors any size. Someone asked for a 2 1/4" carb to fit to a Harley, so he made it
Paul
 

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