SU Carb Technical Articles
Various articles and how-to's.
59 topics in this forum
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- 4 followers
- 103 replies
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Hello, I recently got a Datsun and I’ve been trying to tune the carbs so I can finally drive it. Unfortunately the carbs have been extremely weird. I’ve been following this page https://zcarguide.com/tuning-adjusting-datsun-240z-su-carburetors/ on how to tune the carbs. After I follow all the steps to step 10 where it says “start engine” the car shoots to 2000rpm then slowly dies. I’ve checked for vacuum leaks on the balance tube, distributor, and gasket but I’ve closed everything. I don’t know if this has anything to do with this but when I use my choke I’m at 2000-2500rpm but it does keep an idle. Now quite sure what I’m missing. I’ve checked out my Hayne…
Last reply by Patcon, -
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- 2 followers
- 26 replies
- 6.1k views
I've been battling with my 71 240 recently to get it running right. I spent about 4 years working on the car and the engine, and this is the first time I got it to run somewhat right. Here's what I have: freshly rebuilt L28 Flat top engine with E31 head CB performance programmable box triggering a MSD unit 230/460 cam (IIRC) "Rebello modified" carbs that I purchased from a form member a while ago. I think they are bored out to be bigger and I matched all intake ports. Zstory street header to 2.5" pipes to Zstory muffler in the back Now, here's the problem: I have installed a O2 sensor after the final merge in the header. The carbs …
Last reply by dutchzcarguy, -
- 8 replies
- 5.7k views
Note: This is a Microsoft Excel (XLS) Tool Click on this link or the screen shot below to download the file: Hitachi Jet Depth Calculator
Last reply by 240260280, -
- 1 follower
- 34 replies
- 4.8k views
I bought this pair of SUs for my 260z and I think I’ve finally gotten to the actual step of putting them on the car but I’m noticing a couple inconsistencies with the two. One carb doesn’t have a piece of linkage that the other carb does, and one carb moves the Cylindrical thing at the bottom of the carb (that I assume is fuel related) and the other doesn’t. There could be nothing wrong and they’re both acting as they should as far as I know, this is my first time with the SUs so if someone can tell me what is or isn’t wrong here that would be appreciated. The picture highlights the present and missing linkage, and the thing at the bottom that moves…
Last reply by Cooper260z, -
- 1 reply
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Working with a friend on a stock 71/72 240Z. It currently has both an aftermarket electric fuel pump and a mechanical pump. Both appear to work. Can the manual pump work if the electric is turned off and or the other way around.
Last reply by Captain Obvious, -
- 0 replies
- 2k views
I brought on my float chamber lids upstairs for a picture to show a member where I measured 23mm down. I found this little flat circle on my kitchen floor last night. I can't imagine where else it would've come from? Thanks for any ideas.
Last reply by siteunseen, -
- 12 followers
- 39 replies
- 6.8k views
I've recently been through the wringer on mechanical fuel pumps. I LOVE the stock mechanical pumps and dearly wish to be able to use them more. Silent, plenty of volume to run triples etc up to 250 hp (my educated guess). Stock new pumps put out a CRAP load of volume even at cranking speeds. The cheap "offshore" GMB and Spectra fuel pumps that are out there that look like the stock Nikki/Ampco/Kyosan Densi pumps have been reported here and elsewhere are a ticket to very early failure. I can further attest to this experience. Had a fresh GMB make it about 10 km before leaving a customer/friend stranded. So after much investigation of the issue, I have good news…
Last reply by 240dkw, -
- 0 replies
- 1.8k views
I am in the middle of a fuel tank refresh. Tank is out to Rad shop for cleaning and coating. Meantime I am checking my sending unit and gauge reading. Do these pictures of the gauge reading look right at max float and min float levels travel with the sending unit? what else should I do? Hoses are 4 years old. Ran a can of carb cleaner through the supply and blew it out. How many gallons does your tank hold?
Last reply by 7tooZ, -
- 1 follower
- 8 replies
- 4.2k views
You can tell I’ve been drinking and thinking again... If the SU needles have richness “stations” (Progressive diameter changes) every 1/8th of an inch, why does moving the richness adjusting knob by as little as 1/4 turn make a significant and measurable change in AFR? The thread Pitch on that adjuster is 1.0 mm, so it should take 3.5 turns to make a one station shift..... Just saying, what the heck is going REALLY going on that no one wants to talk about... Is there more to the amount of fuel that is allowed to leave the jet tube than the simple needle OD/tube ID difference right at the top of the bridge or top of the jet below the bridge? Or a complex fun…
Last reply by Captain Obvious, -
- 1 follower
- 5 replies
- 2k views
Reassembling a pair of 3-screw round tops for my 72 240z. Trying to get the jet nozzles to go fully in smoothly, until they touch the mixture screw. With the piston-jet needle installed, the jet nozzle binds with several millimeters to go. When I manually retract the piston-jet needle, the jet nozzle smoothly slides in fully without binding. I've rolled the needles on a flat plate and they're not bent. Is this an issue or am I over thinking this? Searched the forums prior to posting, didn't find anything. Regards
Last reply by kenward1000, -
- 1 follower
- 28 replies
- 3.9k views
Just recently purchased "rebuilt carbs" and slapped them on got everything hooked up besides the gas pedal, everytime I start my car it rocketed upto 4000+ rpms and I shut it off... i made sure the butterflys were completely closed and it still does it, if I starve the carbs of air I can get it to idle pretty low but cant seem to change the idle otherwise using the mixing screws or idle adjuster screws... any ideas what maybe causing this?
Last reply by Datonedatsun, -
- 3 followers
- 50 replies
- 5.8k views
I have a decent little collection of the long wing bolts and the mating long “nuts” they thread into, but the one part of this assembly that I am lacking in is the little cup washer with the rubber grommet underneath. Been hunting for a replacement in the generic hardware world and have come up virtually empty handed. About the only thing close is from RedLine Performance in Auzzie land. Many of you may have touched these over the years if you’ve done side draft carb installations. Redline 52-110K Those cup washers lower right are perfect, well, they are 3/4” diameter while the real ones are 7/8”. There is one in the first picture top right. I co…
Last reply by Captain Obvious,
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