Stock 240z (SU) carb rebuild

[s30zgt]

Hello. after re-evaluating my first repair option ( was gonna take care of the surface rust but was advised to take care of the carb in my other thread if i wasnt going to strip her down to bare metal) i decided to fix that instead. My friend, from whom i bought it from, told me that one of the carbs was running rich but having no prior experience with carbs i took her to a professional.

 

Tony from http://www.lacarb.com/ ( they offered a free troubleshooting and minor tune up) took a look at my carbs and verified that they were indeed running quite rich. He told me that my SU's were still in good shape and with a rebuild could be back to factory spec. He quoted me $625 for the rebuild and tune.

 

My questions are

1: Is this a fair price for a rebuild or highway robbery? I personally dont like having mechanics work on my car but having no experience on carbs i though a free diagnostic wouldnt hurt. This also leads into my next question.

 

2: Would it be cheaper to do it myself with a rebuild kit? Sure total of all the parts i need may be cheaper but i know the knowledge and experience is really what i am paying for by going to a professional.

 

Just list of the few problems i am experiencing with the carbs to help with this evaluation.

Running rich

Romping on gas backfires at higher RPM

Stickey throttle(although i have read that could be the throttle linkage and could be cleared up with some lithium grease)

high idle rpm around 1000-1500

 

thank you for your time and insight.

Edited February 24, 2011 by s30zgt

[cockerstar]

For that price, I'd be looking at a set of Ztherapy carbs. They come with a DVD that walks you through tuning and the install. If you're having a rough time with it I've heard they have great tech support.

http://ztherapy.com/

[s30zgt]

I guess for that price the Ztherapy Carbs do make sense but seeing as these carbs have lasted this long on her, i would like to stick with the original equipment and see if i can bring them back to spec. Throwing out relatively good carbs seems like a waste.

[30 ounce]

Don't "throw them out"!! Just send them to ZTherapy for roller bearing throttle shaft install and rebuild. Or exchange them. There isn't any reson to keep the original carbs just because they are original. The replacements will be exactly the same (with some very important improvements that are not visible (internal)). $625 is just enough to make ZTherapy a more desireable option. Of course you could rebuild them yourself for around $200.

[Tony D]

I guess for that price the Ztherapy Carbs do make sense but seeing as these carbs have lasted this long on her, i would like to stick with the original equipment and see if i can bring them back to spec. Throwing out relatively good carbs seems like a waste.

Did you even look into the suggestion he gave you before you came up with that dismissive comment?

 

There is nothing you will do to 'rebuild' the SU carb running rich that costs $625.

 

I'd go into it, but you need to go to the Z-Therapy site and read on what their service entails. When these carbs run out of life, they run LEAN under partial load, and you richen the hell out of them to keep them running properly at partial throttle.

 

I do not know "Tony at LA Carb" and before I went to him, I'd consider Tony at AltZ in Huntington Beach, or any of the guys at Vincent Foreign Car Service...hell even Art at Sunrize Z Service....all of them are Z-Specialists and know about your car, your carbs, and hell they may even give you a 'free diagnosis' that comes with a pricetag that will send their kids to college too. But I doubt it, they will at least explain to you what is going on rather than throw you a line...

 

 

Oh, and the way you 'bring them back to spec' is you replace the bodies with new ones, because they wear out the bushing area in the body. Short of NEW NISSAN SU's (at the last I saw, over $2200 a set, if you could find them!) the practical alternative is Z Therapy and their bearing/rebushing service.

 

As a guy who doesn't know about carbs, I might suggest you don't argue the finer points in what it will take to 'restore yours to spec' with guys who DO know carbs...

[SHO-Z]

You might want to look at this http://forums.hybridz.org/index.php/topic/97153-mchh-carb-swap/

 

I would contact this member and see how it is working

[s30zgt]

@ Tony D

 

Wasnt being dismissive. His suggestion is very much something i would be considering. As for LA Carb, I was referred to him by some hot rod and Porsche owners who had their carbs worked on (and it doesnt hurt that his shop is only a few blocks from my work). Having never been to any of these Z specialists and knowing no one personally who has worked with them, i went with the advice of the people i know and trust. Wouldnt you?

 

As for the "bringing them back to spec", your comment on how they wear out the bushing areas on the body and that toward the end of life they run lean and you have to richen them to run right is exactly what i was looking for. Knowing what is the cause of the problem and how to go about fixing them is more helpful than to just go and swap it out for new parts. That and saying that i would like to see if the stock ones are fixable is hardly "arguing the finer points".

 

Your comment has however helped me realize that i do know someone that has had work done at one of these specialty z shops on his 300zx. I have to ask him which one though.

 

@SHO-Z

Thanks man. I will definitely take a look at that post.

[Tony D]

My point was you made a comment, obviously without investigating what he suggested. (This is where I was going with the "dismissive.")

 

Had you gone to the site he gave you, my post would not have been necessary (they go over what goes wrong, and how they address the failures so it doesn't happen again.)

 

These are an OEM carb, and they were originally designed to be throwaway when necessary. When the bodies wore, you replaced the unit.

 

The only viable alternative now is rebushing them (there are places back east who do Triumph and other English carbs, this repair/restoration is not new) Z-Therapy is the #1 Z-Car Carb source. Their prices are much more inline with 'our' marketplace than the markeplace you got the recommendation from... which was why I mentioned 'giving you a line'---he quoted based on what you would 'expect' from that shop. Personally I think it's far higher than required when Z Therapy will do a premier job (on your carbs, if you wish) and leave you plenty of $$$ for a specialist like Tony at AltZ, any of the Guys at Vincent Foreign, or Sunrize Z to dial them in like new. But as mentioned, Z Therapy gives you a nice video to show you how to do it yourself. It goes along the lines of 'teach a man to fish...' the more you know about it, the less chance you will be taken for a ride.

 

Many times I've seen 'carb specialists' not get our Z stuff right. There are things (covered in the video) that point it out. When YOU know how to do it, even if you never do it yourself, you will KNOW if your stuff was done right.

 

And finally, by 'aruging the finer points' it was relating back to voicing a desire to 'keep what you have'--had the site been read, you would know YOUR carbs can be sent in and returned to you...keeping them as you desired. That does seem to be a fine point to argue over---'wanting mine back'---when precisely that service was offered! That's where I was coming from. That you voice interest in the MCHH gives mixed signals, do you want the stock ones there, or not?

 

I have seen regional/marque disparity in pricing before. I was made acutely aware when I started out and was privy to internal part coding at GM dealerships. It was there I found a $39 alternator for a Nova was the same one as one for a Caddy that was $249. Just a different box. The pricing you got IMO was 'for the box' and I think you came to the right place to ask if it was appropriate. I think you can see the consensus is, compared to what you will get from ZT, it's probably out of line for the market. Especially the L.A. market.

 

If you were in the local Z Club they might be able to steer you to more local sources. "Los Angeles" in your location is a big area, so not knowing what precisely is your location it's difficult to give any more specific or closer 'installation specialists'...

 

Good Luck.

Edited February 28, 2011 by Tony D

[rjstcroix]

s30zgt,

 

Messed up carbs? Time, effort, $$$, parts, refinishing/restoring, consider all these things. Do it what ever which ever way you prefer. Either way you'll come to the same conclusion: Z Therapy reman'd SU's are the best solution to correcting worn out SU's for the Z car.

 

Regards,

 

RSC

[s30zgt]

@tony D

 

I had researched and gone to Ztherapy's site many times before i posted this. That was one of the first places that google comes up when you search "240Z carb rebuild". While i do believe they would make a fantastic carb with improvements on the original design I was just making sure if there were any other avenues that were possible that a carb newbie wouldnt know about.Didnt know about keeping the originals, thought it was a straight exchange with their listing for a core charge.

 

The response i meant for SHO-Z link was really to show thanks and appreciation for his suggestion on possible useful information. I do want to stick with the SU's but learning about a different way doesnt hurt. I should have made that more clear in my response.

 

I am glad you pointed out that the pricing was a bit too high for the quote i got. Yes i do believe i asked the right people by coming here. On the Ztherapy carbs, I really can tell the faith you guys put in their work and the fact that they go through and tell you how the carbs work and what goes wrong is a big plus. They are still at the top of my list for carb suggestions.

 

I know the LA location is a bit vague. I reside in downtown El Segundo. If this were the 70's i could stroll down a few blocks and have Pete Brock and his crew at BRE do any work i needed. When I spoke to John Morton at JCCS last year he told me the shop used to be on Oregon st. Still wish that shop was here. He also told me that his favorite car was the Scarab and not the 510 that he is always pictured with. (useless trivia =P)

 

 

 

Thanks again to everyone for all their helpful advice. I really appreciate it.

Edited February 28, 2011 by s30zgt

[Tony D]

Alt Z is in Huntington Beach near Warner and Gothard.

 

I didn't mention a direct response to your question #2---an 'overhaul' on these carbs are generally soft parts, gaskets, etc.

 

They don't address the throttle shaft leaks, so generally if there is high mileage, the throttle shaft leaks. An 'overhaul kit' likely won't do anything for you. Likely (I would hope to gawd) the LA Carb "Overhaul" for that price would be the Z Therapy Carb set, and labor to install/tune them! If it was a soft parts kit (about $40) and then tweaking to make it run smoother (my biggest fear for a new guy going to a shop not knowing) then in response directly to #1 "Yeah it's highway robbery." Depends on what exactly you are getting!

 

IMO for all intents and purposes, the Z Therapy carbs ARE 'the originals'... The improvements they do are something you should do while undergoing such a significant major work on the carbs. There are plenty of places as I said that do straight 'bushing replacements'---they center the shafts and put oilite bronze bshings back in there giving you exactly (for all intents and purposes) the same design. This is poor eeconomy (they rebush for maybe $175 a pair...if you're good with a drill press or Bridgeport, you can do this yourself...) as bushings tend to wear, and eventually you will need to replace them as well. A removable ball bearing is like a weber carb, a design improvement. For their increased costs you also get a cleaned carb body and proper finish, etc... I mean, you already know I guess. If you are cleaning everything up in the engine bay, then that cleaning works well.

 

Just so you know, there isn't any identifying carb stamps on these things, there are no 'matching numbers' carb sets like Rochesters with their little aluminum tags. A three screw in general is a three screw. Any carb is as good as another coming back. That is the key difference between 'overhaul' and 'remanufacturing'---recall above that the original remedy for this situation was to replace the carburettors with new Nissan/Datsun Hitachi units. This is, in effect what ZT is doing, more than a mere 'overhaul' they are dimensionally checking and 'remanufacturing the carbs to act as new---just like what you would do with the cars back in the 80's and early 90's when these carbs were still available new from Nissan Dealers. My NEW set was $1200 in 1991, they have 6 months of driving on them and 4 Smog Checks...I might entertain selling them for $2000... I got plenty of cores to send to ZT for that price!

 

DO this: take a small spray bottle of water and while the car is warm and at idle, spray a stream of water at the throttle shafts. If the car stumbles, you're leaking at the shafts and you are looking for either a new body, rebushed body, or ZT Remanufacturing.

 

This is the same process we went through on Corvairs years ago. I rebushed my own carbs, and installed seals that were an aftermarket improvement. Then I found some NOS carbs...for more than I had paid, so I snagged them and put them on the shelf. They're still there with the right tags and all for my car to be 'correct'...

 

But Hitachi SU's? No worries, as long as you have the right screw configuration you're set. Nobody will be able to tell they weren't the originals.

 

Cheers.

[s30zgt]

@ Tony D

Thank you for all the great info. You have really helped me understand my carbs better. As soon as i get some free time i will break out my FSM and exploded view model for the carbs and try the method you suggested. I will update with the results.

 

I did notice that ZT carbs were much more than a simple rebuild and why they commanded a higher price than the carbs i found else where. I will have to clean up the engine bay if i go with those ZT's. It will look very out of place in there amongst the grimy parts.

 

My reasoning for sticking with the SU's is because of their ease of tuning, info is well documented, and soild performance...at least that is what i have read. Originally i had planned not to invest any money into the L24, thinking that it would be costly to repair, low ROI, and my money would be better saved for a engine swap (L28et,SR,or RB) but if it needs just a couple hundred bucks (knock on wood) to get the car back to stock running performance, thats a bargain. Plus it would be nice to have a cleaner running car in the mean time while i save up for rust repair, paint, and maybe an engine upgrade

[Tony D]

Realistically, the SU's on the car will support an N/A build to close to 200HP which is a very potent street Z.

Scott B. ran the dyno to 192 at the MSA event last April on an overbored L28, with headwork from Slover's in L.A. and a cam from Ron at Isky in Gardena. The SU's will support that kind of power without much effort, Scotts were not opened up, did not have a polished bridge, cut suction piston, or being bored out to 50mm or whatever. A good remanufactured carb with the proper Needle and Jet pair will do the job just fine, with good vacuum and drivability.

 

That is what you get with the SU's: very good street manners, and very little sacrifice in overall performance. Lots of midrange torque.

 

Thing is, a set of ZT Carbs if you keep them clean and maintained will command a far higher price than any of the 'core carbs' you see on e-bay! And they go from anywhere from 150-400$! ROI should be pretty good if you choose to go a different route. They are 'desirable parts' to sell off in the future. Keep your invoices and receipts for proof of provenance.

 

A good set of carbs and ignition system, will give you a nice performing car. They're a hoot to drive even bone stock. They are a very well balanced car.

[s30zgt]

@ Tony D

 

I finally got the time to try out the water bottle test you mentioned. I took the car out for a quick drive to get her to temp and when she was good and warm i took the water bottle and sprayed the throttle shafts. spraying either carb with water yielded the same result, no stumbling. Just to be sure i let the carbs dry and tried again but again no stumbling. While i know this is not the most thorough test, would this imply still good throttle bushings on the carbs and what would you suggest as the next course of action?

 

Having had a talk with the previous owner i learned that the engine was rebuilt about 2 years ago. Not sure if the carbs were included in that rebuild but surely if they were rebuilding the engine they would have taken a look at the carbs as well.

[Tony D]

If youre not getting stumbling there with water, you can check again with carb cleaner to see if a more volative (thinner) solvent goes in there. That would be expected, but it doesn't sound like you have shaft leakage, and in that case $650 is highway robbery.

 

Group Z the local Z Club is having a 'Show and Shine' at 1200 on Saturday at Fuddruckers in Buena Park (91 at Beach Blvd, near the 91 5 interchange) you might want to mosey over to see if you can get some local direction there for a shop that can assist with basic carb setup. Either Alt Z or Sunrise Z should be able to accomplish this for you at a much more reasonable cost. The Z Therapy Video may be all you need...

 

Seriously may be nothing more than a couple of quick twists of the mixture screws under the carbs and you're on your way.

 

Remember the downfall of the SU is it's needle taper. If you aren't willing to alter the taper to match your engine's needs (and just grab stock needle profiles) then all you can do is richen or lean out the mixture through the entire RPM range. If you retaper the needle, then you can have a lean idle, and rich power section... but with stock needles you're stuck. Most guys adjust them way rich anyway. It makes for smoother driving, but not the best fuel economy, fume production, etc...

 

It's why the Dreaded and Despised Flat Tops used on the 73 and 74 cars had a separate adjustable idle circuit for emissions compliance (and why people rape them for the needles, which have a richer taper on them than earlier carbs...)

Edited March 10, 2011 by Tony D

[s30zgt]

@ Tony D

 

Thanks for the tip. I will definitely try to swing by that meet. I am also gonna pick up the ztherapy video just to see if i can get the carbs running smoothly myself. From what i have read all i need is a unisyn and colortune right? I know im still new to carbs but after seeing video tear downs and the exploded model of the SU's, it doesnt seem that difficult to tune. Or am I way over my head?

 

While i am not adverse to the idea of a custom tapered needle, it does sounds like an advance procedure and not something to go at ham-fisted. I am guessing if i were to go this route one of the specialty Z shops should be able to do it.

 

Really dodged a bullet by coming here first. Thanks again to everyone.

[Tony D]

I don't know many that retaper needles. I know how to do it because I had to learn back in the late 70's when Single SU fed Turbochargers were 'state of the art' for a relatively infamous Air Cooled Turbocharged Flat Six Rear-Engined car...

 

It's not that difficult if you know what the positions and etc are...

 

But there is a REASON I jumped to EFI when it became 'cheaply affordable'... Anybody that says 'carbs are easy' hasn't really gotten into tuning one for a foreign application where you have to map everything!

 

A gasket set and readjustment isn't hard at all. Setting of the float and getting it right between front and back is likely the trickiest part if you dont remove the needle from the piston.

 

Try it, you might like it!