Amal needle tuning, standard 850

I detect a lean condition when accelerating and feel it is occurring between 1/4 and 3/4 throttle.

The carburetors are new Amal Premiers.

I found with California fuel I needed to run a richer, #3 slide instead of a 3 1/2.

The needle is currently in the lowest, or leanest, position, as indicated in the standard settings. That is, the clip is in the top groove.

My question is how much of a change is a single clip from the top groove to the middle groove?

The tune of my engine is factory stock, 14,000 miles, good clean combustion chambers and good (though unmeasured) compression. Stock crossover exhaust and stock air-filter setup with a 1000 miles on the filter.

Ignition is Tri-Spark set to 30 degrees max advance. It idles great and starts easily, hot or cold.

Anyway, the basic question is how much of a change is one clip richer on the needle?

One notch on the needle may be just right. This should not effect you good idle and it's no big deal to reverse if not fully satisfied.

It is my feeling that no 2 Nortons breathe exactly alike. Any factory default setting are basic guide lines and ballpark guesses. Expecting to bolt on a fresh set of carb and having them be on with the tuning is unrealistic, not impossible, just unrealistic.

Tweak away, you have nothing to loose and everything to gain.

Whitworth Ranch said:

My question is how much of a change is a single clip from the top groove to the middle groove?

I found with California fuel I needed to run a richer, #3 slide instead of a 3 1/2.

Click to expand...

I've found that the difference from one notch to the next is quite noticeable. But seeing as how you are starting at the leanest setting possible and you know it's may need something at or on the other side of the middle groove, considering the gas, then you may not notice much. You may be going from way, way lean to way lean moving it one notch.

I just rebuilt my stock Amals and had them sleeved. I don't know what size my new needles and needle jets are, but the counter person at Rabers said they were the same as stock, except that it has three positions for adjustment whereas my stock 850 MK2a needles had only two. Due to perceived leaness in the midrange, I am now running on the bottom, richest needle setting. I am also runnng the stock 230 main jet. The midrange seems fine now, but I am running out of fuel as I go through the gears above 5500 RPM. I have a new main petcock. The old one was half choked off, but I didn't seem to have the starvation problem. Not sure what the problem is, but the beat goes on.

I read somewhere that of your running in the higher rpm range you should have both petcocks on to avoid fuel starvation. A friend of mine holed a piston on his triumph roaring around one afternoon that way.

Play with your needle height ans see what happens, easy enough to do.....

Tim_S

The needles are set in the middle groove and there is a big improvement in pickup. I am pretty happy with the change. I may try another but I am going to test this way for a while.

It was lean enough to cause flat response but not enough to make a true misfire. One groove was good...

Thanks for the help.
Mark

Due to perceived leaness in the midrange, I am now running on the bottom, richest needle setting. I am also runnng the stock 230 main jet. The midrange seems fine now, but I am running out of fuel as I go through the gears above 5500 RPM. I have a new main petcock.

Click to expand...

230 is for the black cap silencers which are restrictive, I run 260 mains on a MK2A with peashooters. You may then find you can drop the needle but maybe not but there is some overlap between the 2.