1974 260Z carb problem

[glennyboy]

Hi all

I just went through the work of rebuilding these twin carbs, these have the floats in the bottom, and the power valves on the sides..... Still runs rich, so i reversed the rubber gasket on the power valve, lowered the needle valve all the way down. Runs better but needs plenty of choke when cold. No black smoke like before, i have since read that these carbs were crap and recomended using the previous years carbs. Anyone had the same problem.

[=Enigma=]

I think you will find that there are very few cars that still have these "flat-top" carbs on them. Most have long ago been converted to the earlier SU "round top" carbs. The flat-tops were introduced due to more stringent emission regulations being implemented in the US starting in 1973 I believe, and are generally not considered good performers.

If you're going for strict originality, it may be possible to get them working but finding replacement parts may be difficult at best. It would be much easier to replace them with the earlier round-tops.

Here's a good place to start researching these carbs:

http://www.jetlink.net/~okayfine/SU/tunacan.html

[Bruce Palmer]

.... back when those cars with the flat tops were new, I knew guys that went looking for the earlier round tops when the cars were brand spanking new. The dealers even got ropped into doing the swaps as a means of keeping customers happy.

But as I talk to all the inquiring customers at ZTherapy, its amazing how many have fought these bad boys for all these years and are just now getting around to doing something about it. Maybe it's just now that they can do something about it.

[Exdamyankee]

If you don't plan on having the car judged in the "Stock" class (the ONLY reason I would ever consider keeping them on a driver), do yourself a favor and get rid of the flat-tops.

Buy a set of used round-tops and be done with it. Or, if you really want to do the job right buy a set of used round-tops and send them off to Z-Therapy for a first class rebuild. Then you're set for good.

Good Luck,

Fred

Tampa, FL

'74 260Z 2+2

[VIN #3242]

The flat top carbs have, in my humble opinion, but one purpose in this day and age.

Attach a chain to them, after throughly cleaning them, of course, and attach the other end of the chain to your favorite small boat--instant boat anchor!!!

You will really cannot go wrong with a set of carbs from ZTherapy. They are, or at least should be, the standard by which all other SU rebuilders are judged.

Just my 2% of what ever currency you favor...........

Jim

[sleepyzzz]

.... back when those cars with the flat tops were new, I knew guys that went looking for the earlier round tops when the cars were brand spanking new. The dealers even got ropped into doing the swaps as a means of keeping customers happy.

But as I talk to all the inquiring customers at ZTherapy, its amazing how many have fought these bad boys for all these years and are just now getting around to doing something about it. Maybe it's just now that they can do something about it.

Bruce,

my package showed up and we will be working on rebuilding my carbs this week:)

thanks for the great service.

butch

[Murderz]

Hey everyone

i have a 74’ 260z and it’s having a strange running issue and I’m not sure what exactly it is, fuel delivery is working properly lines and everything seems ok, replaced distributor cap and rotor and spark plug and wires are fine so no firing problems. When the car is running and driving it’s going with no issues until I shift into 4th gear, the car starts to hiccup and just stop running and die. I’m not sure what the problem is so I came here hoping someone has a similar problem and maybe people can give me ideas. Thanks.

[siteunseen]

Sounds like you are running out of fuel?  Does it have the flat top carbs?

We have some flat top guys on here, @Captain Obvious @Zup

[Zed Head]

I can't find it in the FSM but maybe a 260Z owner can, if it exists.  Some cars have a "top gear" switch that opens a solenoid valve to let the vacuum advance of the distributor work.  I know that my 76 280Z had one.  It's an emissions device, retarding timing in the low gears to give cleaner exhaust, and adding advance in high gear for fuel efficiency.  So, any engine that has emissions devices might have it.

Find the hose to the vacuum advance and follow it back to its source.  Not even sure why that would cause the engine to die unless moving the breaker plater causes ignition problems, which does happen.

You should give more info about your car, like how long you've had it, and whether it ever ran right.

[Murderz]

It has round top carbs, and I’ve had it for a few years now. It ran perfectly for a long time and then this issue came up and we’ve been stuck. We thought that maybe it wasn’t getting enough spark so we checked the spark plugs and wires and they’re fine, but we did replace to distributor cap and rotor and it seemed to be working perfectly until today when I drove it it gave me this problem.

[Zed Head]

2 hours ago, Murderz said:

It has round top carbs, and I’ve had it for a few years now. It ran perfectly for a long time and then this issue came up and we’ve been stuck. We thought that maybe it wasn’t getting enough spark so we checked the spark plugs and wires and they’re fine, but we did replace to distributor cap and rotor and it seemed to be working perfectly until today when I drove it it gave me this problem.

You kind of mixed up the before and after.  You said it ran perfectly until this problem came up.  But then you said the problem came up today after you replaced parts to fix the problem.  Did you fix one problem and new one came up?  Or did you replace those parts and it din't fix the problem?

Anyway, is the problem reproducible?  It happens every time you shift in to 4th gear?  Or did it happen once and you haven't tested it since then?  If you can determine what conditions cause the problem it will be easier to solve.

[Murderz]

It ran perfect for a long time and the problem came up and we couldn’t figure out what it was, we thought that maybe it was an issue with the distributor so we replaced some parts on it and it seemed like it was ok. When I drove it today we noticed that the problem is still happening. We don’t know what is causing it. Sorry for the confusion.