SU Carburetor tune

[nahurry]

Anyone in or around upstate SC know of a good mechanic that can tune my new z therapy carbs on my 240Z?

[w3wilkes]

My experience with new Z Therapy carbs is I put them on the car and they ran just fine out of the box. Didn't touch them. I live at almost 5,000 ft and think they might be a little rich because I bet Z therapy probably sets them up for lower altitudes.

[Patcon]

You could call L japan auto services

232-1533

I don't know if he works on anything that old

[nahurry]

I found a guy in Anderson. 

[Jeff G 78]

With a Unisyn and a few youtube videos, you can tune them yourself with great results.  I once swapped a set of SU's mid-race and tuned them in the pits.  The whole job including removing the carbs from a red-hot engine, installing a new pair, tuning/synchronizing them, and buttoning up the choke cables and airbox took under 30 minutes.  The problem ended up not being the carbs at all, but it ruled them out.  The actual tuning took less than five minutes.

For videos, search University Motors John Twist SU.  He has a great series of British SU rebuild and tuning videos.  The Hitachi SU's are similar enough that the tuning is the same.

[AK260]

My experience with new Z Therapy carbs is I put them on the car and they ran just fine out of the box. Didn't touch them. I live at almost 5,000 ft and think they might be a little rich because I bet Z therapy probably sets them up for lower altitudes.

I think you are right - when I was new to Zs and bought my ZT carbs I just bolted them up and they were great. The MOT man said they were a tad rich but that’s the SM needles for you, so we dialled them back 1/6 of a turn to pass.

But you always need to balance them as a minimum.

I agree with Jeff above - they are so simple to set up when you understand what the screws do and have an airflow synch tool.

This is the one many of us use.

https://www.ebay.co.uk/itm/294818904813?

At OP ….

Is your engine totally stock? If yes ignore the rest.


If not, you may find that you are setting up perfect tune on the driveway for idle and fast idle but at WOT it may be too lean - in that scenario with a modified engine you need different or custom needles. But in general if stock cam etc (or mildly modified with headers etc), the needle profiles will be appropriate for the variation in the demands of the engine when set up for idle and fast idle.

FYI - The stock 240Zs carbs use slightly different (usually N27 or N54) needle profiles to the SM needles which come with ZT carbs - so some people complain about SM being too rich on their engines.

[Jeff G 78]

The carbs that I threw on mid-race were fresh ZT carbs and I still had to tune and sync them.  My carbs as well as the ZT carbs had SM needles and once tuned, both ran equally well after I fixed the underlying fuel delivery issue.  SU's are extremely simple and with just a basic understanding, you can get them very close.  A wideband O2 along with a spark plug check will help you check them under load.

[AK260]

The carbs that I threw on mid-race were fresh ZT carbs and I still had to tune and sync them.  My carbs as well as the ZT carbs had SM needles and once tuned, both ran equally well after I fixed the underlying fuel delivery issue.  SU's are extremely simple and with just a basic understanding, you can get them very close.  A wideband O2 along with a spark plug check will help you check them under load.

That’s a good point, my widenand sensor transformed my life! In fact I now need to get a life [emoji1787]