Slightly Lean Or Slightly Rich Which Is Best

[davdeborg]

hi

just put all new jets and needle in my amal carb and its a massive difference on my 151 350cc

with the old needle and jets air screw mix was about 1 1/4 turns out .

with new needle and jets I can only get it 3/4 of a turn out to run smooth.

if I turn it past 3/4 the engine starts to die so 3/4 is about right and bike starts and rides ok.

I thought only being 3/4 turn out would be a bit rich ive fitted it with the same jets and needle as I took out as standard.

so guess the answer I want is it better to have it a tad on the rich side rather than a little lean?

I know bikes run hot if there running lean are they likely to run a bit hot if running a bit rich ?

thanks guys a novice on this lean rich kind of stuff

appreciate any replys

[nzralphy]

Bikes slightly rich will; resist stalling slightly better, and will have better pickup when you open the throttle quickly. BUT will tend to oil a plug - especially true if you use cheep oil - so use a platinum plug.

My 2c worth.

[davdeborg]

these are the jets

Main jet- 150

Needle jet - 2 stroke-size 106

Pilot jet - 20cc

Needle on position 2

and v groove needle all supplied by amal

[davdeborg]

Bikes slightly rich will; resist stalling slightly better, and will have better pickup when you open the throttle quickly. BUT will tend to oil a plug - especially true if you use cheep oil - so use a platinum plug.

My 2c worth.

yes mate using platinum plug and fully synthetic oil

cheers

[bondy]

dave sorry mate i sold mu Amal ages ago thought you had bought a new Amal?

[davdeborg]

no I had it checked and its fine replaced all jets needle etc its just e bowl surface where it fits carb body seems bit warped.

think it been over tightened ill take it to local engineer he will skim it take few thou off it im just being picky

[davdeborg]

now the bike bogs a bit at first surely cant make it any richer ?

air screw only 3/4 turn out now after 5 mins its ok its just when been started for few mins ok as long as you don't open throttle.

open throttle after couple mins its ok .

[bondy]

i had the same problem with an Amal kept oiling the plug tyred new jets needel still was the same so i bought a new bing ran sweet

[davdeborg]

just been doing some research etc and just ordered a new rubber manifold flange from inmotion

as the carb face which fits to flange on inlet manifold is smooth do you use a o ring as shown in manual as there is

no cut out in flange on carb for o ring to fit in ?

or does carb just butt up against the rubber flange ?

help appreciated

[stevem75]

Not surprising the air screw has to be turned in (richened) after replacing the old worn out jets. As the jets wear they allow more fuel to pass, thus richening the mixture. The subsequent adjustment to make up for the rich running is to back out the air screw (leaning) the mix. Now that the new jets are installed and the proper amount (less fuel) is being metered through the carb the air mix needs to be richened to compensate. As far as being too rich or too lean, once these carbs are set to factory specs and maintained that way you really don't need to worry too much about it. 3/4 to a full turn on the air mix in or out won't harm the engine in any way shape or form other than make it run a little uneven until the ultimate setting is found. Bultacos run really well if proper ignition timing, no air leaks , and a properly functioning carb are used.

Steve