'58 FH carburetters

[david.birkett]

My Huntmaster is running very rich. It has a 376 carb, the Draganfly catalogue indicates it should have a 240 main jet and a 25 pilot but the main jet is 280 and the pilot is 30. Can't identify the needle jet. The needle is on the top notch.
Is this a recognised config. for a FH or a carb from some other model that a previous owner found handy to bolt on?
Advice and comments please!

[john.nash]

Dave,

Has this just happened or did you just buy the bike ?

If it's just happened, then it's something like float levels or air filter blocked etc

If it's the latter.
Are you sporting the recommended air filter ??
Taking off the airfilter, and running a bellmouth, which many of us do let's in more air which requires higher jetting.

Re-jetting either an art or a science.
It's a science if you take your bike to a company with a dyno.
It's an art, if you do it yourself with a fistful of jets

In either case, having the needle on the top notch (so the needle is further down into the jet) doesn't sound good.

cheers

[david.birkett]

Thanks John.
Bought the bike a few months ago, sorting out the carb. came further down the list than sorting out the oiled up left plug (rebore cured that) and gearbox (new selector pegs mean it stays in top now) and oil gushing out of the primary chain case. Cured most of the leaks but need a brave pill before having another look at the final drive shaft length.
Back with the carb,there is no air filter. Won't bringing the needle up to the recommended third notch make it run even richer?
Dave.

[john.nash]

Back with the carb,there is no air filter. Won't bringing the needle up to the recommended third notch make it run even richer?
Dave.

Unless someone else has some settings of theirs to go by, for a setup without an air-filter, then you'll be doing yours by trial and error.
Even then all bikes are a it different, but someone else's settings will get you close.

Can you get a faster/slower idle, by playing with the mixture screw. If so, then you're about right with the idle jet.
If you cannot get an idle, or only an erratic one, then there is maybe something else going on (worn slide, leaky joint etc).

I usually do the main jet by tanking along the road at WOT, closing the air slide, to see whether the bike bogs or not. I'd put the needle in the middle position for this.
stop. change jets. go again. repeat until happier.
Once you're in the ballpark, then it's a case of pulling the plug out and checking the colour after running it flat out (you'll want to kill the engine at speed and coast in)
You'll maybe get it close enough like this, but always best to be a bit richer than leaner ...

Or, as I said before, book it for a dyno run ( at £50+/- ) and make sure you have all the jets to hand to avoid going back.

[nevhunter]

Another possibility is the size of the cut out at the front of the slide, is wrong. If the slide has been replaced and the cut out is less than original it will run rich EXCEPT at full throttle where the main jet controls the mixture. ( as John says). This is when the slide is fully open and out of the way.
Amals ( and any other similar design carb) are pretty easy to tune once you know the basics of how they work. If you obtain a copy of the many publications showing the basic tuning sequence and have a play you will understand your machine just that bit better. A lot of the problems are from mixing parts from different models amd altered and poor fitting parts. The carb has to be the right size for the engine. If the engine's performance has been enhanced, ( cams, compression up ports flowed, overbore etc ) it may need a slightly bigger carb to run properly especially at the full throttle position.
If the engine is basically STANDARD and in good condition, I find the factory recommended jets ,settings etc are a good start and don't have to be departed from very much . This depends on the availability of original spec needles /jets floats. The needle jet is a wearing part and wears to a richer state. The needle which runs through it can wear also but this happens at the lower range of throttle (the top portion of the needle), mostly .Nev

[adrie.degraaff]

Your carb. slide move is devided in 4 stages,

first 1/4; idel and air screw.

2/4; angle of the slide.

3/4; needle.

4/4; mainjet.

If you have this right, go back to the first and do it again until your happy.

But in most cases the slide and needle are to worn to do this good, so send it to your lokal carb. restore man, or to one of the best (cheap) in the Netherlands.

[john.nash]

Here is my favourite amal tuning document:

http://www.hitchcocksmotorcycles.com/pi ... tters_.pdf

Yes, it's for concentrics (main jets on monoblocs and concentrics are the same ) but the approach is the same.

Personally, I'd go back to :

• standard idle jet, standard slide cut out and standard needle jet size
• I'd put the needle clip back in the middle
• If you reckon that 240 main is standard, with an air filter, then I'd maybe go to a 250/260 (without) to start with.

In my experience, messing with air filters or exhausts mostly affects the main jet, the needle height and sometimes the slide. Only occasionally, have I had to change the idle or needle jet. You can often sort out the idle with the mixture screw.

The wrong slide size is most easily detected when coming off or dropping back onto idle.
spitting back through the carb, when moving off, is usually too lean a slide for example. If your bike, conversely, doesn't go back onto idle cleanly (stalls or bogs) then it's either too rich/too lean

Of course, all this trial and error is going to cost you money in parts to try.
Where do you live ? I have a box of main jets and some slides that we could try with ...

I'd repeat that if your idle is all over the place and varies (one time faster, then stalling) when you drop back at a road junction,for example, then your carburettor maybe worn. There are other symptoms, like the mixture screw having no effect.
I think that every brit bike I have had, that had an old amal with it, has needed a new carburettor body

[david.birkett]

Thankyou John, Nev, Adrie.

I have had the carb. apart, washed it clean and blown through all its orifices with an airline and the mixture screw makes no difference no matter where it is. Yes, the idle is inconsistent when the throttle is closed and yes, it occasionally barks. Putting your comments and suggestions together with the performance I am getting from this carb. seems to indicate the best solution is to stash away enough beer chits to swap for a new carb. and stop worrying about worn slides, worn bores, doctored cutouts and all the other unknowns.

David.

[john.nash]

I know it's not exactly original kit, but consider just buying a concentric. Cheaper and as good.
I have concentrics on my '47 and '54.

They fit straight on and surrey cycles:

http://forum.arielownersmcc.com/viewt ... ?f=23&t=50

supplied mine ready jetted, for your bike. He will also removed the idle "bush" and put in a proper jet.
Just tell him that you're running without the O/E filter (ask him for a gauze or something) and would need higher main jetting (probably .. )