is my 1098 over-carbed???

[moggymaniac]

Hi guys,
I've just put a lead free head on my 1098cc engine which is otherwise standard. The car is running on a 3 branch tubular exhaust manifold by Jeff Howell and stainless larger bore exhaust by pipecraft exhaust systems. The inlet is standard alloy mini manifold and HIF44 Carb. I bought the car like this minus stainless exhaust system. The car runs well and ticks over at a good idle speed and revs well but the idle has never been as smooth as it could be and cruising in lower revs creates occasional misfire but nothing to write home about. I'm just wondering if I'd be better off running an HIF38 1" 1/2 as maybe the current 1" 3/4 as perhaps on a bog standard head the extra fuel provided by this Carb is wasted? Any input much appreciated!
Jamie

[philthehill]

Straight answer - 1 3/4" is too big for a near standard engine. 1 1/2" would be much better.

[bmcecosse]

Although the SU is a very flexible carb - due to the variable choke design - you will indeed be better with an HIF 38. Try an AAA needle.

[moggymaniac]

Thanks a lot! Was going to get a rebuild kit for the 44 but I'll just get a 38 for it instead with an AAA needle and report back

[moggymaniac]

Can I use the same inlet manifold for a hif38?

[bmcecosse]

Yes!

[bmcecosse]

Meantime -what needle is in the 44 ? And try EP90 in the dashpot damper...it may make all the difference you need.

[moggymaniac]

Great! I'm not sure as one Nevern had the 44 apart but I believe the previous owner installed it straight from an early er standard 1275 metro if that's at all helpful? Will do! Is that slightly more viscous than than the usual oil for the dash pot then?
Thanks, J

[philthehill]

The EP90 is a thicker oil and will stop the damper rising as quick and should help to eliminate any flat spot or miss fire when you put your foot down.
I still say that a 1 3/4" SU is too big for your near standard engine and that the 1 1/2" SU would suit your engine better.
The only reason that bigger throated carbs are fitted is to allow larger amounts of air to pass through them into the head/combustion chambers. As you describe your head/engine is near standard you will not reap the benefits of the 1 3/4" carb and yes your engine is over carburetted.

[moggymaniac]

Thanks very much! I'll get to it then . And try some EP90 in the meantime. J