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Advice for an Amateur refitting SU carbs

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Steve, I've got two pairs I eventually want to freshen up as well.  So if you find any info, sources for parts etc. post up and let us know. 

 

One pair were fitted to an L28, anyone know how I identify the needles in it?

Mike

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Hey guys,

 

I was wondering if anyone in Brisbane would be able to give me a hand one weekend installing my new SUs and tuning them. I just spoke to the guys at Carb and Gas and they said I would be looking at about 400-500 to get them installed and tuned (assuming everything went perfectly) and 150-200 if I just wanted to tune them. It is at this point that everyone telling me to do it myself starts to make sense.

 

It won't be until March that I'm back in Brisbane to do it, but I'm sure there would be a carton in it for any good samaritans  :)

 

-Steve

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Steve,

I live too far away to help unfortunately, however I hope this info helps.

When I first got my 240z it was running way too rich. I talked to so called Carburetor experts who told me to chuck the 240z Hitachi carbs as they are no good and will always run rich etc, their suggested cure was to buy British su's @ $800.00 for the pair with additional costs for fitting.

I was a little taken back at this and started reading the Haynes workshop manual and all articles on the internet as I was going to sort this out myself. I played around with it but was too scared to get too serious. luckilly a friend of my wife's came up to Darwin to visit with her husband who had a fair bit of experience on British su's. He helped me set my carbs up so it ran much leaner and the car pulled stronger, even though he couldn't get it quite right as it had a bent needle in the front carb - even better he taught me how to tune them myself.

Since then I have replaced the needle in the front carb and re tuned the carbs by myself. I was very happy with the results and when I moved back to Townsville I got the same friend to check my work, he only made a very slight adjustment to the mixture on the front carb. He was impressed with my work and I have to say it really isn't that hard. I say read up on it and have a go yourself. Make sure you have all the linkages etc and they operate properly and check the float levels on both carbs and reset if necessary- the Haynes manual will show you how to do this. Also ensure both pistons move freely when you lift them with your finger and they drop properly with a definite click noise. If they don't you will need to ensure the needles are centred properly. When you fit them have a go at tuning them yourself. The only fancy tool we used was a "su tuning hose" ( a metre long length of plastic tubing, cut off a roll I think was left over from when we had a water bed) We used this hose to listen to each carb and adjust the balance with the throttle adjusting screws until the sucking sound was the same in each carb. Simple but it works.

Anyway I am no expert but some of the people in these links I have attached obviously are there is some very good advice in these articles. Seeing as you are not going to do the job until March you could pick some info out of these before you start.

I hope this helps, I don't know much about the science of carburettors but it all seems quite simple providing you are patient and set them up carefully. Let me know if you want me to explain how we adjusted the mixture etc.

 

Regards Peter

 

http://www.sonic.net/~kyle/su.html

http://www.ztherapy.com/

http://www.teglerizer.com/sucarbs/techtip6.htm

http://www.teglerizer.com/sucarbs/techtip6.htm

http://dimequarterly.tierranet.com/tech/SUTech/sutech.html

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I had a lot of trouble with my flat-top SU's. I honestly thought they were worn out so I removed them and cleaned them up a bit including replacing the gaskets in the power valves with home made ones.

However, I never got a decent result from them until I put the K&N oval filters back on (not shown in the photo) and ran the air/mix breather and vacuum hose in to each of them. The design of the flat tops means you have another air inlet at the front carb which is supposed to balance air / fule mixture between both carbs rather than adjusting the needles. It's all good in theory but it's just another point of breakdown when these things start to wear out.

It's a pitty there doesn't seem to be any useful information on the flat tops or mods you can do to improve them and overcome their shortcommings.

Flat tops actually have some marked improvements over the older dome tops but at the cost of complication.

 

Looking at this photo now, I had it all wrong. The next step will be to reduce intake turbulence with some sort of Ram tube rather than the K&N filters

DSC_0826-1.jpg

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Doctor Z,

It is good that you can sort out the carb issues yourself.  I think we all have to learn ourselves as there seems a shortage of competent people to do it for us.

I know nothing about the flat top carbs myself as mine are the old round tops.

 

Zedback,

The needles in the round tops have the numbers stamped into them on the shoulder at the top of the needle (where they locate into the slide) Mine are stamped N54 which I think is the standard needle for an L24.

 

I'm sorry I didn't answer this earlier.

Regards

Peter

 

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Car started this morning as per usual, then stalled and the would not start again due to a flooded engine. Had to wait 30 minutes for flooded engine to subside, hook up an additional battery (mine was dying) and finally it started.

 

I really need to sort out the carb problem however I know I wont be able to find the time with uni. It's idling really rough currently.

 

I'm tempted to just spend the $600 and get Carb and Gas to fit and tune those 240Z carbys I bought.

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Steve

 

If you can find a stock 240z air filter housing - install it!

Our Dyno tests on both my old 240z Sc race car and standard 260z road car have proven that the stock 240z filter housings (with inbuilt ram tubes) improve performance of up to 10% over ram tubes and socks or those lousy uni filters........so if you keep on eye out on ebay and see a see a filter housing ...grab it!

 

If you Zed is flooding then check your float height and ensure they have not holed and sunk....from memory it was around 3.5 turns out on each mixture knob would get it running with SM needles

For Hitachi gasket kits try the various Zed car shops in the US (Arizona Z car etc).....if in fact they are NLA thru Nissan

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Hey Alan,

 

Cheers for the advice. I'm currently running the stock 260z air box - I didn't end up getting the alternative ones.

 

I've got a pair of 240z carbys ready to throw on so I just can't justify spending extra money on the old flat tops I'm currently using. To be honest I don't even know where the mixture knob is  :-[

 

Once my current round of assignments is over I'll get the manual out on a weekend and see what I can achieve.

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We should make our own video on the 240Z carbs and stick it on youtube so everyone has access to it. Just basic tuning; where to start and how to adjust...

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We should make our own video on the 240Z carbs and stick it on youtube so everyone has access to it. Just basic tuning; where to start and how to adjust...

 

Hell yeah, that would be fantastic.

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We should make our own video on the 240Z carbs and stick it on youtube so everyone has access to it. Just basic tuning; where to start and how to adjust...

 

Thats a fantastic idea :)

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Well, next meeting on the 12th we shall see what we can come up with..put all the "brains" together! hahaha

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I just got hold of a repair kit for $50 from:

 

http://cgi.ebay.com/ebaymotors/Datsun-240Z-Carburetor-Repair-Kit-1969-8-71-39-5063_W0QQcmdZViewItemQQcategoryZ6763QQihZ009QQitemZ190300207064

 

The needles are N47 and M49, it suite the 71 240z round top carbs. I have never pulled an SU apart but started to on sunday and found they where very easy to dismantle, clean, change out parts and reassemble. I completed one on sunday and am part way through the second.

 

i found in one of the float chambers that someone had replaced the float locking pin with a nail ???

Your flooding problem will almost certainly be due to an incorrect float level.

 

The video idea is great. I will try and get some footage while I have the second one apart.

post-1064-144023519936_thumb.jpg

post-1064-144023519943_thumb.jpg

post-1064-14402351995_thumb.jpg

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Well Jospef's (josef's) dad has agreed to help me swap the carbys over on saturday week (23rd).

 

I've had a look at the condition of the carby's and everything seems to be A-OK. No need to buy a repair kit or replace any of the parts except one of the fuel hoses and one of the screws for the vacuum cover.

 

I was just thinking, since we are going to be doing the swap on a Saturday at his place, I should try and get together as many bits as possible beforehand.

 

It's a pretty straightforward swap from what I understand, but I've got a lot of hoses that will need to be blanked off and will probably be looking at removing the carbon canister thingy.

 

My question is for people who have done this swap before:

 

Were there any parts/bits that you had to pick up that weren't obvious in order to swap over 260z carbs to 240z carbs?

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This might help you guys with tuning the round top carbs.

It's a bit like watching Al from Home Improvement on their "tooltime" segment but the dude knows what he's talking about.

 

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Pushed back carby swap til the 6th.

 

Has anyone ever heard of/used colortune? Here is an example of how it works on a bike:

 

When the flame is 'bunsen blue' the mixture is correct.

 

I found a thread discussing them too:

 

"Re: Gunson Colortune

That old thing was great for carbs like SUs or Strombergs, where basically, if you set the mixture at tickover, it was correct for the rest of the range."

 

Quote stolen from http://www.cobraclub.com/forum/general-cobra-discussion/15744-gunson-colortune.html

 

I'm seriously considering buying one for when I do my carby swap.

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Steve I replaced my flat tops (that were running fine) with 240Z SU's and manifold I also left the carbon cannister in place and used the standard 260z, 3 line fuel rail, although I had a 240Z spare fuel rail just in case I also used the standard power brake hose to the carbie manifold, if you need any pics let me know?

The other thing is if you are removing studs holding the carbie manifold put plenty of penetrine on them a couple of days before dismantling so you don't break the studs and use proper good quality spanner and sockets so to try and avoid breaking 30 Y.O studs, if this happens they will have to be drilled out which I left for the professionals. Does your car have extractors? I also purchased new fuel rubber hose lengths and cut to fit I also used the original heat shield foil around the fuel hoses to help stop fuel evaporation when engine hot. I have also used a 240Z air box. The job is just doing it carefully and don't be in a hurry I was able to do it, so I am sure you can too!! Lynton 8)

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Well I watched the educational videos that we got from the states and they are very helpful. I am 90% confident that I'll be able to do the conversion to 240z carbs on sat.

 

:o :o I just realised that I don't have a gasket to replace the intake manifold gasket that is currently on the car! Is this something I can pop down to Repco and buy? The old one is looking pretty wrecked!

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Well I watched the educational videos that we got from the states and they are very helpful. I am 90% confident that I'll be able to do the conversion to 240z carbs on sat.

 

:o :o I just realised that I don't have a gasket to replace the intake manifold gasket that is currently on the car! Is this something I can pop down to Repco and buy? The old one is looking pretty wrecked!

 

Should be able to get 1 fairly easily. I'm fairly certain the same gasket is used for exhaust and intake from memory. So you'll need to unbold the exhaust manifold also.

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Cheers Gav, if you hadn't said they were the same they would have had no idea what I meant on the phone! I called a supercheap and repco to no avail, but Lawnton Autobarn said they didn't have it in stock but could get it by this afternoon! :)

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Well I'm just about good to go. The only question I have is whether to use the 240 or 260 inlet manifold. The Z therapy video Shaun bought states that the 260 has markedly improved airflow, but it looks uglier with all the emissions crap sticking out of it. Hmmm...

 

The work I did on the carbs tonight included:

 

Setting both the mixture and idle screws to their correct settings before adjusting after fitment.

Shortened one needle to be the same length as the other.

Adjusted both floats to be the 5mm distance from top. (they were really far out)

Adjusted both choke linkage to open both butterfly valves the same tiny amount. (the butterfly valves weren't opening at all)

 

Two days ago I would have read the above list and had no idea what any of it meant. These Ztherapy videos are pretty bloody good. I'm tempted to make a couple of my own during the fitment and tuning process.

 

Oh and no I don't have extractors Lynton :P

 

I'll let you guys know how everything goes tomorrow :)

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Well I'm just about good to go. The only question I have is whether to use the 240 or 260 inlet manifold. The Z therapy video Shaun bought states that the 260 has markedly improved airflow, but it looks uglier with all the emissions crap sticking out of it. Hmmm...

 

The work I did on the carbs tonight included:

 

Setting both the mixture and idle screws to their correct settings before adjusting after fitment.

Shortened one needle to be the same length as the other.

Adjusted both floats to be the 5mm distance from top. (they were really far out)

Adjusted both choke linkage to open both butterfly valves the same tiny amount. (the butterfly valves weren't opening at all)

 

Two days ago I would have read the above list and had no idea what any of it meant. These Ztherapy videos are pretty bloody good. I'm tempted to make a couple of my own during the fitment and tuning process.

 

Oh and no I don't have extractors Lynton :P

 

I'll let you guys know how everything goes tomorrow :)

 

I'd stick with the 240z intake manifold. What's important is port matching more than the manifold. I can't see any major difference between the 240z / 260z intake manifolds other than the number N63 / E88 from memory.

 

They might have slightly wider diammeter. Measure the openings on both ends and see how big they are? If the 260z manifold is larger it 'should' flow better, but the only way to know for certain (Dyno!).

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Well it went quite well, the job is 99% complete and I drove the car home this afternoon. Josef's dad Paul was a great help, but since he had a sprained wrist I did 100% of the work myself under his direction - and you guys know that I am not a mechanically experienced person. it just goes to show that these engines are really easy to work on. :)

 

I do need to get a set of choke bits though, as the little plates I rigged up from the 260 manifold aren't exactly ideal. I'm going to PM greg for them.

 

As mentioned previously I set the carbs up before the install as specified in the video and they didn't need too much work to get running nicely. The mixture was really rich for both carbs initially, but it is running great.

 

Probably the biggest plus for me is the improvement it has made on the braking. I have the hilux front calipers, stock rear drums and a reconditioned stock master cylinder, and there was quite a bit of travel in the pedal when I had 260 carbs. I never found the floor but when you compare it to what I have now it was not ideal. I think the brakes are better because the 240z manifold has a much better vacuum seal (doesn't have like 100 emissions hoses running off it using the vacuum), and therefore it is ensuring much more vacuum is located at the MC. The pedal feels firm and the car stops very quickly.

 

Driving the car is beautiful, with the carbs opening up really nicely. They pull in low revs quite well and can rev highly without a problem. The only things I still need to do are:

 

Replace fabricated choke mechanism with original one off another manifold.

Perfect tune (front carby is still running a little rich according to colortune spark plug)

Tighten throttle return springs (the springs I had to add to the throttle to close the butterfly valves when I release accelerator are a little loose, this is an easy fix)

Source another wingnut for the airbox :) I only have one

 

I have a bunch of photos/videos but I can't find the camera cable just yet, so when I'm ready to procrastinate study some more I'll throw them all up so you can see the procedure.

 

 

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Good stuff, can wait to see the pics and video. My colortune arrive on Friday so I'll be tuning mine latter today with it.

 

What needles did you end up using?

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