Carb conversions

[Fairlady5150]

Fairly new Roadster owner, and very new to SU's. I've decided I just don't like them, and I want to go another route. Anybody have any thoughts on a carb conversion for a 1600? I'd love to hear your feedback and experience on selection, installation, etc.

[notoptoy]

The "natural" upgrade from SU's is to go to factory style Solex or Dellorto's or Mikuni's. But I would add that the SU's are really simple once you figure them out. They also hold a tune well. There are plenty of people on here who can talk you through the pains of SU's so don't give up without trying first.
Downdrafts are basically out of the question due to clearance issues, though they have been done. I have not seen a well executed downdraft set-up with most looking downright ugly.

[Gregs672000]

Get a Cannon intake and a set of 40 Webers, 40 Delllortos, or 40 Mikini. Run 30-32mm main venturi, invest in a wideband O2 set up and some carb jets. Be prepared to tune and learn (we'll help if asked), and be rewarded with more tune ability and a great sound/look.

[Pjackb]

Fairly new Roadster owner, and very new to SU's. I've decided I just don't like them, and I want to go another route. Anybody have any thoughts on a carb conversion for a 1600? I'd love to hear your feedback and experience on selection, installation, etc.

Could you elaborate on why? understanding what you don't like would help the very knowledgeable people around here steer you in the right direction,

One thing everyone will tell you about SUs is that they're very reliable and simple to live with once you understand them

[Fairlady5150]

The issue I had is they were running very rich. So I started by checking for high fuel pressure and inspecting the float assemblies. The fuel pressure wasn't high, and the floats were good, and so were the float / needle valves. But I decided to swap those just in case. This helped but the car was still running rich. So I inspected the brass needles, and found that one was slightly bent and the other was worn, so I replaced those. Now I can't get the car started. The only thing left is to replace the jets / nozzles. But if the car ran previously, and all I did was swap the needles, I can't figure out why I've got nothing now. Those piston and needle assemblies are so simple, I'm not sure what I could have done wrong.

Unfortunately ZTherapy has a 6 month lead-time, and I can't find a local SU expert. Well, there's one, but he's a Brit snob who told me the Datsun Roadsters were junk, so screw him.

[Linda]

You can try a pin guage to see if the nozzles are worn
Bent needles, worn nozzles or an incorrectly torqued down dome can cause problems. The ADQ needles correct rich idle also
https://www.amazon.com/HHIP-4103-0092-R ... B01BHHHILS
Linda

[DCooke]

There’s a roadster owner here in Chicago that just swapped out his SU’s for Mikuni HSR42 Harley carbs. He said it was easy and the kit even came with the linkage and mounting adapters. He said is was about $300 per carb. Apparently this is done occasionally on British sports cars.

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[Fairlady5150]

DCooke That looks pretty sharp. I'm interested in looking at that. Looks like that's a 2.0, I wonder if there would be any issues doing this on a 1.6 liter. Are you aware of any horsepower loss or gain? Any chance you could get me in touch with him?

[Fairlady5150]

Linda
What is the correct torque for the domes?

[Linda]

It’s not a torque value. It is just that the domes need to be tightened down evenly while checking with the piston pin on the side, that the piston can raise up and drop smoothly. If you tighten the right side first, let’s say, then the left side the piston and/or needle can bind. Then if you don’t check the action you miss that the piston is hung up and the car runs bad.
Also if you get the pin guage, which Keith has offered to lend out, you can see if the nozzles are so egged out that the carbs will not work correctly either. The correct size is .092 for the 1600 I believe , per the Tech Wiki by Keith, the carb guru.
Another issue is if the nozzles are not centered in the carb, but I have never had that happen but it can exist.
I like the “magic number” method for setting the nozzles because it is more precise.
All of this is in the Tech Wiki write ups, and the archive posts. Just takes some time to dig it all up.
Linda

[Fairlady5150]

Linda thanks, I'll take a look at that.

[Ted928]

If you have spark and fuel you should get fire which it sounds like you don't have.
I would spray some starter fluid to see if you get it to fire.
Does the choke mechanism lower the nozzles as they should? Remove domes and actuate the choke, do you see fuel at the top of the nozzle?
Where do you have the fueling adjustment knobs (how many turns out from full up are they? Two turns out is a good starting point.
The wiki has some great info.

[brn2rde]

I will try to remember to snap some pictures later, but we built an intake and added a 2 barrel weber knockoff downdraft carb when rebuilding the 1600 in my daughters car. Runs absoutely perfect, starts like a new car.
So sure, it is possible. Not even that difficult really. I wanted something that would run and start with no fuss and that is what we got. Can't say if it makes more or less power, but that was not really the goal.

[brn2rde]

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[notoptoy]

That's the best looking conversion I have seen. Nice custom manifold.