A
Anonymous
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The list so far for the one common item on most brit bikes from the late '60s.
Ta.
Ta.
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If we are going to compose a list of all the possible carburettor faults known to mankind,
its going to be a LONG list !
In some off topic thread too....
Warped bodies, warped flanges, unsynched dual carbs, worn jets, bent needles, worn needles, worn fuel seats.
Most of these afflict most brands of carbs, it should be noted.
its going to be a LONG list !
In some off topic thread too....
Warped bodies, warped flanges, unsynched dual carbs, worn jets, bent needles, worn needles, worn fuel seats.
Most of these afflict most brands of carbs, it should be noted.
A
Anonymous
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Further to the above questions...needing said:
6. What are the constraints racers have regarding the use of AMAL Concentric Mark 1s, in which classes, and what carby performance modifications are permissible to each class?
Ta again.
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Rohan said:
Thanks- hotter plugs might hold possibilities.
It's registered as a Norton!
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Anonymous
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Hi Triton Thrasher.
Run-on is throttle shut while engine revs remain high (as driven by the back wheel) and manifold vacuum is high.
Re-opening the throttle gives a dramatic and sudden increase in airflow but the fuel draw through the jets lags behind and creates a lean mixture flat spot. Changing plugs won't help but reducing the fuel draw lag will. Other carbs use accelerator pumps to prevent this while keeping the fuel bowl float level as high as practicable seems to be the method of choice for most AMAL users. This means the fuel is as high up in the needle jet as possible and more/most responsive to airflow draw.
Ta.
Run-on is throttle shut while engine revs remain high (as driven by the back wheel) and manifold vacuum is high.
Re-opening the throttle gives a dramatic and sudden increase in airflow but the fuel draw through the jets lags behind and creates a lean mixture flat spot. Changing plugs won't help but reducing the fuel draw lag will. Other carbs use accelerator pumps to prevent this while keeping the fuel bowl float level as high as practicable seems to be the method of choice for most AMAL users. This means the fuel is as high up in the needle jet as possible and more/most responsive to airflow draw.
Ta.
needing said:
Ta, we haven't seen this engine - if its pulling some oil into the combustion chamber on the overrun, and the present plugs can't readily handle this, then new plugs may well do. Ask yourself too why Commandos don't noticeably suffer this problem. One for the Triumph forum ??
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Anonymous
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Oh contrare rohan.Rohan said:
AMALs are notorious for the flat spot just off fully closed throttle. Noticable during transition from pilot to cutaway pulling away from the lights and also as Triton Thrasher describes above. Any engine, Triumph, BSA, Norton, etc only supply the low manifold pressure to activate the AMAL carby function at each throttle opening.
Ta.
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Anonymous
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Dear rohan.Rohan said:
A1. Yes.
A2. See A1.
Distraction: your monthly limit has been exceeded. Goodbye.
Ta.
A
Anonymous
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They were progressive for their time, perhaps.hobot said:
What horsepower could be expected (measured at the back wheel) of a factory issue Combat engined Commando compared to an ordinary 750?
Ta.
That is a good question.hobot said:
They may not be as metric as it seems -
26mm is VERY close to the old 1",
28mm is ~1 & 1/8 th,
30mm is ~1 & 3/16th
and 32mm is ~5/16th.
They are labelled as mm though, so that was the way the world was going back then.
needing said:
The subject of MANY a thread here. Search, and ye shall find.
5 or 6 hp more, it seems, VERY approx.
With the caveat that the aa functions correctly, the 7000 rpm rev limit is observed,
and that it has been fitted with the so called 'superblends' for some measure of longevity.
Fast Eddie
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What does "5-6bhp more than a stock 750" equate to in numbers? In other words, does anyone know what a stock 750 puts out?
Stock 850s (even with peashooters and date boxes) are quoted on here as producing mid to high 30s. Which I'd say sounds about right, as that is similar to what a good peashooter equipped T140 would put out in real life.
We do, it seems, sadly have to admit that the figures quoted by the factory had very little basis in reality!
My own 850 had been incorrectly fitted with a base gasket when I bought it, so the CR was only 7.6:1. Add that to the single carb that was fitted and I was probably in the low 30s at the wheel. This is only an estimate though and I do kick myself repeatedly for not putting it on the Dyno before I stripped it down!
Stock 850s (even with peashooters and date boxes) are quoted on here as producing mid to high 30s. Which I'd say sounds about right, as that is similar to what a good peashooter equipped T140 would put out in real life.
We do, it seems, sadly have to admit that the figures quoted by the factory had very little basis in reality!
My own 850 had been incorrectly fitted with a base gasket when I bought it, so the CR was only 7.6:1. Add that to the single carb that was fitted and I was probably in the low 30s at the wheel. This is only an estimate though and I do kick myself repeatedly for not putting it on the Dyno before I stripped it down!
Fast Eddie
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needing said:
Fitting velocity stacks that by-pass the pilot holes and line up smoothly with the choke diameter is a common mod that is claimed at adding 2-3bhp by some. These were initially developed by Jack Shemans and are sometimes referred to as 'Shemozzles'.
In Stan Shentons Triumph tuning book, he advised smoothing the inlet to use the stock short plastic Amal things (in production racing).
I personally never managed to get any of my own bikes running as good as I wanted on the Shemozzles and instead used the Stan Shenton idea for a while and later on went to a much shorter version of Shemozzles with much larger inlet size (ie short n fat) which seemed to work best on 8 valve Nourish engines.
Fast Eddie said:
The threads here previously discussing this have quoted approx 42 or 43 rear wheel horsepowers at the rear wheel,
with some dyno charts to back this up.
And the Combats have been quoted as 48 or 49 hp, and I think one mention of 52 horsepower.
This may be the best of the best - but the stock bikes were claimed as 60 marketing dept hp, and the Combat as 65 hp.
HOWEVER, no-one has yet been able to produce a pair of dyno charts, showing a balanced and non-balanced exhaust system comparison,
say for an 850 that came stock with the balanced system.
Heck, hobots brochure for the Drouin supercharged Commando claims 100 hp, I seem to recall.
Amazing what a bit of puff can do - never mind the reliability (?!?).
A
Anonymous
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Re: Needing Air through the rev range
Thanks for the feedback re horsepower.
The last dyno run with 200 main jets and long needles pushed 42 hp at the rear wheel.
The next series of dyno runs is scheduled for next Wednesday and has the full suite of Phase 1 carby mods on board. These are the lower end throttle opening and transition mods but I will be using 106 needle jets, short needles and 220 main jets. This time the throttle shut-off will be at 7000rpm. Analysis to follow but should be flatline AFR 13/13.5:1 and maybe push 47/48 hp based on your feedback.
I gather the 58 hp for standard Commando and 65 for Combat is for engine output, not rear wheel (about 80% is left).
Ta.
Thanks for the feedback re horsepower.
The last dyno run with 200 main jets and long needles pushed 42 hp at the rear wheel.
The next series of dyno runs is scheduled for next Wednesday and has the full suite of Phase 1 carby mods on board. These are the lower end throttle opening and transition mods but I will be using 106 needle jets, short needles and 220 main jets. This time the throttle shut-off will be at 7000rpm. Analysis to follow but should be flatline AFR 13/13.5:1 and maybe push 47/48 hp based on your feedback.
I gather the 58 hp for standard Commando and 65 for Combat is for engine output, not rear wheel (about 80% is left).
Ta.
Have you LOOKED at the spray tubes in the Amals for an 850 ?!!
There is a reason for that.
And why they are different to the 2 stroke versions.
Who was the ex-factory gent on one of these forums, that used to rabbit on about "cutting the spray tubes to increase the signal across the jet "
There is a reason for that.
And why they are different to the 2 stroke versions.
Who was the ex-factory gent on one of these forums, that used to rabbit on about "cutting the spray tubes to increase the signal across the jet "
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