Wrong needle?

[JOWETTJAVELIN]

Would the wrong carb needle cause a car to run too rich at idle, but then at high speed too weak?

I just can't get the balance right; it's either too rich and idling roughly or idling smoothly but missing at high speed, which disappears when the choke is used.

When I rebuilt the carb they sent me an AAT needle but the one which came out was, I think, AAB.

Could this be the problem?

[Alec]

Hello Jowett Javelin,

it sounds like the wrong needle. Did it run OK with the first needle, if so I would refit it? Why did they send you an AAT?

If you list what modifications you have done possibly someone could suggest a suitable needle to try?

Alec

[bmcecosse]

What carb is this for ? The AAT is a very weak needle, much weaker (at revs) than the AAB which is actually a richer needle than even the AAA which is the generally recommended 'starting point' for 1.5" carb on a reasonably well modified A series.

[JOWETTJAVELIN]

HS4, 1275cc.

Many thanks for the info, think I'll order an AAB then to replace what came out; best to err on the side of rich.

[bmcecosse]

Better with the AAA - if you find it weak (I doubt it!) you can always give it a rub with a fine file to richen it up. You could of course file the AAT that you have - in stages - till it works well. It's pretty much useless at the moment, so nothing to lose......

[JOWETTJAVELIN]

OK I'll give it a go. The exhausts on these cars (Marina engine) were always stinkers if I remember correctly. Now I know why!

[JOWETTJAVELIN]

Fitted the new needle today (AAA) as suggested and things have been much better. No more coughing and spluttering at high speed which I expect was down to mostly air being burnt with the AAT. Power has gone up aswell. Will check plugs and fine tune after I've done a few miles.

I went to look at the old needle in the garage and it was actually an ABB fitted originally. Any idea how that would have behaved?

Thank-you for the help.

[bmcecosse]

Easy check on 'mintylamb'........ but ABB is quite a bit weaker than the AAA.