'73 240z - Project Build

[demo243]

Cleaned up the heat shield - not as fancy as my original design, but seems to work quite well; can actually touch carbs 3 and 4 now. Made a few other small tweaks with out much change.

 

Did notice something interesting this evening. When cold it will fire up and idle @ 900. Fires nearly instantly! Way easier then my old SUs. But as soon as I rev it, it gets hung at about 1200 rpm (LED charge light doesn't provide enough draw; so I need a rev to ~3500 to awaken the alt which is needed to get the AFR gauge working). Then as I was driving it around I was having trouble with I'll call it rev hang - getting caught around 2000rpm. My first thought was slides getting stuck, but that doesn't seem to be the case since the shaft rotates fully closed which would force the slides down. 

 

Then I noticed that it seems to be more apparent during light throttle applications - think backing out of the driveway, parking lot speeds, neighborhood cruising. But if you give it a good romp and let of quickly it will drop right back down to ~1200. 

Could be a vacuum leak maybe? AFRs are looking decent but it is definitely popping out the exhaust at idle a bit- I figured this was do to its high idle. 

Pilots seem to be good - although a very small change (think 8th of a turn) makes a big change in AFRs. Then add the filters on and it richens up (expected... UNI filters are restricting). Ive been basing my tuning on AFRs for the moment since it "easier" but maybe time to try the high/low idle method.

[demo243]

Played around a little more the other night. Dropped the needle clip a couple notches raising the needle- making it richer- and it definitely helped partial throttle. Cruise was really rich though- 11-12. Pulled the clip up one notch and seems to give a real stumble when getting on the throttle during highway cruise. Raised the idle up to 14.5 with the filters on, which seemed to help cruise a bit but still in the 12s.

 

I need to check a few thing before I order any brass.

- vacuum leak

- definitely have an exhaust leak, possibly before the o2 which would be screwing everything…

 

Then I’m going to drop the needles back down. Really need to pull the carbs and pull the idle adjusters, but want to wait till I decide what jets I’m going to try so I can do it one less time.
 

Based on my plug check my idle is good- afr shows 14.5…- but I’m not sure I believe it… still smells rich… but the pilot is 7/8 of a turn out which is on the rich end of the jet - meaning I might need a richer pilot? But that doesn’t make sense… and leaner would likely help lean out cruise, but not sure it will work since I’m less then a turn out on my current 22.5s….

 

 

 

Im thinking I may bump to a richer main 145 from my current 142,5 as I could use a touch richer at wide open ie on ramp pulls. With that I may try a leaner needle jet paired with the richer setting on my current needle. But need to do some more reading. 
 

Trying to figure out my idle/rev hang… seems some people say a lean condition… but car smells rich… and afrs so mostly rich too. 

 

I’ll tag @datzenmike maybe you’ve got some thoughts? I think you’ve messed with some slide carbs before?

 

Still happy overall- pulls hard on highway on ramp runs. Feels faster in the butt dyno but stiffer suspension I’m sure plays into that too…

 

 

Back to reading ….and researching…

 

Busy weekend so probably won’t get anything done till after the holiday. 

Edited May 22 by demo243

[demo243]

Still have my fuel issue….

 

Same as before. Went for a run on the highway after making some small tweaks as I try to decide what additional brass to order… and sure enough went super lean and lost power. Managed to limp it off the next exit. Shut it down, fired it back up and was fine.

 

Must be something in the tank intermittently blocking the pick up. I still find it surprising that the car will still run… Only thing left in the fuel system is the tank and the hard lines. All vent lines were replaced and the vapor tank is currently vented to the atmosphere so I don’t think it’s a pressure thing.

 

I almost picked up a used tank a couple weeks ago and kicking myself now… Looking at the S30.World and Vintage Tank Solutions tanks now. I like the poly and simplicity of the VTS one… but also complicated as you need to source a pick up and sender unit… S30.World is more reasonable and basically just a bolt in replacement… I don’t have the time or patience to deal with cleaning and repairing the current tank…

[benzo]

@demo243 Hope you get it sorted and your thoughts lead to the solution. This last post reminds me of my situation where I think I have corrosion in my tank and may have sucked up or blocked the pick up making my engine run messed up then another time plug # 4 was getting fouled. Cleaned the jets and changed fuel filter and adjusted the idle mixture for #4 cylinder on the carb to lean it out slightly and the car to date has been ok. I too am looking at dropping the tank and cleaning out and resealing/coating it as I have to replace my sending unit as well.

[datsunfreak]

22 hours ago, demo243 said:

 Looking at the S30.World and Vintage Tank Solutions tanks now. I like the poly and simplicity of the VTS one… but also complicated as you need to source a pick up and sender unit… S30.World is more reasonable and basically just a bolt in replacement… I don’t have the time or patience to deal with cleaning and repairing the current tank…

 

I am a big fan of fuel cells in the spare tire well. 😁

[demo243]

7 hours ago, benzo said:

@demo243 Hope you get it sorted and your thoughts lead to the solution. This last post reminds me of my situation where I think I have corrosion in my tank and may have sucked up or blocked the pick up making my engine run messed up then another time plug # 4 was getting fouled. Cleaned the jets and changed fuel filter and adjusted the idle mixture for #4 cylinder on the carb to lean it out slightly and the car to date has been ok. I too am looking at dropping the tank and cleaning out and resealing/coating it as I have to replace my sending unit as well.

It’s definitely a frustrating problem. Hard to recreate and tough to diagnose on the side of the road when it randomly happens. But everything else checks out and the tank is pretty much the only thing left… the filter confirms that it’s nasty🤮 

 

12 minutes ago, datsunfreak said:

 

I am a big fan of fuel cells in the spare tire well. 😁

I’m considering that as well. The radium is sweet! But $$$. The ATL one is interesting but a bit small I think.

 

The biggest thing is I don’t really want to have cell hanging out back there… and want to keep the stock fuel door fill. If I could hide a cell there - even slightly smaller I’d be down! I’d even consider cutting the spare tire well out. But really just after a simple easy solution right now, and since I already re did all the fuel tank lines I’m leaning toward the s30world tank

[demo243]

I did work on and drive the car a little bit today. I had an exhaust leak before the o2 sensor so tried to fix that. The gaskets I ordered weren’t right so didn’t fit… but I had an extra from the header so I used that. Had to double up on the header to pipe gasket as neither flange looks straight…. Again my displeasure with MSA…. Should just pony up for a Zstory exhaust… I just want a nice stainless header!!!!

 

Didnt notice any real change from that…

 

Had a wierd very lean idle at initial start up, but that quickly dropped down with a blip of the throttle or 2 and the idle coming up.

 

I dropped the needle clips all the way down (rich) the other day and now part throttle (and cruise) are VERY rich- part throttle in the 10s! So need to raise that clip back up and test again. Still trying to wrap my head around how the needle jet and needle work together- it seems the jet and needle diameter should influence 1/8-1/4-1/2 throttle most and the needle clip does 1/2+ mostly. Needles are much easier to change… but if I’m opening em all up then the jet can be changed at that time too- but not much info on the jet…

 

WOT is in the 13 dropping to 12.5 range which seems pretty solid. I might try one richer main to see if it doesn’t go to rich. 

Still thinking about going leaner on the pilot- mostly to help with “idle”/“no” throttle cruise … but everything says the opposite…. At ~14 I am 1/2 to 5/8 turn out from full rich which indicates I should go to a richer pilot jet- but no one is running that rich of pilot jet on their twin carb set ups- and im

afraid of that making it richer at low rpm cruise… on top of that pilot are a pain to remove since I need to pull the carbs and bowls…

 

I really need a weekend where I can just tune it all weekend but unlikely to happen so I’ll just have to keeping hitting it in sections and pieces…

 

Still - all things said the car drives pretty well. Has its quirks… but still fun to drive! I would argue it drives better with these carbs in this state then it did with the SUs.

 

More ramblings in the future.

[benzo]

@demo243 totally understand what you are saying. After reading your updates i too would rather have a stock tank and either replace or cleaned out since the filter is showing debris. Remembered watching a vid of someone who was cleaning out their Z tank and they used some bike brake cable to snake out the pickup tube as there was debris inside. 

[demo243]

7 hours ago, benzo said:

@demo243 totally understand what you are saying. After reading your updates i too would rather have a stock tank and either replace or cleaned out since the filter is showing debris. Remembered watching a vid of someone who was cleaning out their Z tank and they used some bike brake cable to snake out the pickup tube as there was debris inside. 

 

I really like the idea of the poly VTS tank, but needing to buy a sending unit and pickup - then deal with drilling and installing them... along with the overall cost of it is putting me off. But... I new sending unit and simple pick up/return/vent on top sounds pretty nice... I have already dealt with a leaking sending unit o ring and am not stoked on the old sending unit anyway...

 

 S30world is so much simpler since it is "plug and play"  but the big question remains- do I keep the vapor tank or delete it...? I had originally planned on deleting it but with no good way of plugging the vents on the tank I ended up replacing all the lines. Now I can order a tank with out the extra two vents... Im torn... I already did the hard work of replacing the lines, but don't really want to do it again. VTS would delete it... so I lean toward deleting it with the S30world too.

Hmmmmm

[benzo]

@demo243 I am more of the plug and play type so I would lean toward the S30world unit. I am reading some folks deleted the vapor tank. From my understanding it is there for overflow when filling so you don't smell the vapors and the gas goes back down into the tank but seems you can loop it back into the tank if you delete it but seeing they make one with the vapor tank delete that sounds like it'll work out.  I did get a poly tank for my truck and I do feel confident now as I never worry about corrosion but that tank was a plug and play setup .

 

Edited May 31 by benzo

[demo243]

Carbs are back off the car- 

 

 

Working on a few things --- 

 

Plugging the idle adjustment screws

Main/Pilot Jet Swap

Hopefully solve what is I believe to be a vacuum leak...

On the vacuum leak front - it is likely from the manifold- when I pulled the manifold I found a couple things. For starters the intake flange is about 1mm thinner then the exhaust. Ive got some stepped washers coming, but will need to file/grind them down since they are a 2mm step... Also there is quite the interference between the oversized washer I was using (came with the MSA stud/hardware kit) and both the header and intake... That combined with the offset seems to have bent a couple of the shared studs... 

 

There is so little room next to the weld... guess Im going to have to file the washer down

 

Same on the intake - can see it was connecting on all runners... but I'm guessing not tight enough to prevent a leak

 

I picked up some new functioning digital calipers - but this give an idea of the thickness difference.  MSA header and TWM manifold.

 

Also - upon opening up the float bowls to drain the remaining fuel for the jet replacements I confirmed that I definitely need a new tank and lines. I found rust sediment in all of the bowls. Will probably pull the trigger tonight, but I am leaning toward the VTS poly tank for long term rust prevention and simplicity of less places for a future leak out of the tank - pick up and sending unit both mount to the top so much simpler. Will order up lines to replace the feed and return lines as well - planning on Nickel Copper 5/16 for feed and 1/4" for return. 

[demo243]

Well this would definitely be my problem….

 

 

The inside of this tank is NASTY!!!! 

[mainer311]

The inside of my roadster tank looked like that. I can't imagine the truck is any better. I bought a big piece of chain from HD and dropped it inside, capped the holes, and then tumbled it around the yard for a while. I ended up using a KBS Coatings motorcycle tank restoration kit on it (only 10 gallons cap.) and it's been great ever since.

[demo243]

12 minutes ago, mainer311 said:

The inside of my roadster tank looked like that. I can't imagine the truck is any better. I bought a big piece of chain from HD and dropped it inside, capped the holes, and then tumbled it around the yard for a while. I ended up using a KBS Coatings motorcycle tank restoration kit on it (only 10 gallons cap.) and it's been great ever since.

I’ve already grabbed a VTS poly tank. Lucky for the Z cars there are a few options out there.

 

 

sending unit and pick up mount on top. Never have to worry about rust again!

 

Just need some time to try and pull the fuel lines. Not looking forward to that job… but if I’m doing the tank I might as well do the lines too so the whole system is fresh

Edited June 14 by demo243

[demo243]

Committed now!

 

 

Already regretting it… but it will be for the better.

 

Going to switch things up a bit to make it a little easier to run the lines. Going to swap the connections on the fuel rail and have the fuel enter from the firewall side. Then will mount the regulator to the firewall and it will pick up the fuel line right from the tunnel. Saves a couple tricky bends, and also cleans up the front of the engine bay.

 

Trying to think of something to replace the isolators without spending $100 on a whole set when I only need a few… also probably going to have to zip tie a couple clips since the screws snapped off and I can’t get in there to get em out

[demo243]

Car is back on the ground and on the road! For the moment….

 

Busy few morning last week during the heat. Lots of 4 letter words were said but new fuel and return lines were run. There was no way I was going to be able to match the originals without taking a whole lot off the car… I ended up terminating them at the firewall and just before the rear diff mount. Moved the regulator to the firewall and flipped the fuel rail fittings around. Also changed up the fuel rail mounting- moving it from the manifold to the back of the carbs hoping to isolate it from heat more- should also allow me to pull the carbs and make changes without removing all the fuel lines. Fuel routing isn’t my favorite but it will do.

 

Got the new Vintage tank solutions tank prepped and ready to go. It seems to be slightly larger than the stock tank but pretty close. Working with poly was nice- super easy. Pick up and sender unit mounted up easily and plumbed cleanly. I ditched the vapor tank since there is only one vent on the pick up set up and tank. It now runs though a roll over valve.

 

Then I got to work on the manifold. With a fresh set of calipers I measured the two flanges which are close but not… the TWM manifold is actually fairly disappointing… some parts of the flange were a perfect match others were off by almost 1mm… the 2mm offset washers were far too big of a difference so I ditched those. Ended up spending a bunch of time filing the “stock” fat washers to get them to sit nicely. They contact both manifolds but won’t rule them out as a possible vacuum leak issue…

 

I mounted up the manifold with out the carbs which definitely was easier. Carbs mounted up pretty easily as well. 
 

Testes the fuel system and everything held tight- then fired her up! No fuss firing it up. 
 

As for the smaller pilot and larger main jet- smaller pilot seems ok at idle, still only 3/4 turn out from full rich. Larger main is definitely to big at WOT as in 10-11 afr. Going to bump back to the 142.5 mains. As for the pilots- it’s a tough call.. 20 seems good or better… but it’s still very rich at low/no throttle cruise- I’ve been told it could actually be better with a richer pilot and leaner air screw setting… considering bumping to 25. Seems counterintuitive but I’m told the air screw makes a big difference especially at low throttle cruise.

 

Lots to think about… back on the road briefly but carbs to come off to make some jet changes. Still have a slight rev hang issue-although better- that points to a possible vacuum leak issue too.

 

Heres the photo dump-! 
 

 

 

 

 

 

 

 

Edited June 24 by demo243

[demo243]

Swapped back to my “baseline” settings- 142.5 main and 22.5 pilot. Car is better all over - so leaner pilot and a richer main were the wrong way.  I mentioned the leaner pilot being better before- atleast by smell- but the 22.5 is more reactive off the line. Less the 1 turn out says to go richer so going to try that way. And hope that more turns out (leaner) is better. Still have the rev hang issue so need to keep hunting for a vacuum leak. Might try some nicer clamps for the flange adapters.
 

Ordered up some 25 pilots and 140 mains but probably won’t be till after the holiday that I get to try them. 
 

Worth mentioning the change in rail mount seems to be good. Cooler temps, and allows me to remove the carbs for jet changes without dealing with the fuel lines. Clunkier on the car then on the bench but definitely doable.

 

zip tie for safety 

 

 

Edited June 25 by demo243

[demo243]

Few minor updates-

 

Ditched the 5 panel wink mirror- it works really well in the 510- but in the Z it ends up to low and too close to the driver, and really only 1 or 2 of the mirrors work. So trying something different- channeling my inner golfer with this convex golf cart mirror- so much more visibility, we’ll see what it’s like on the road.

 

 

Then I picked up some new rubber carb mounts- in doing some digging around for tuning advice I realized there are two versions - the new version is an ovalized port and an old version with a round port. Going to try the old style round port since it matches the manifold better. Of course nothing is simple… went to pull them off and the spacer was stuck to it… so I just ordered another set of spacers. On hold for mounts till those show up.

 

Of course when ever I take something apart I find another issue…. Really disliking this header and manifold…. Looks like there is contact between the number 1 port and almost at the number 5 port… so the manifold will have to come off again … 

 

 

 

And just for good measure at least they still look awesome! 
 

 

[demo243]

Progress!

 

Bumped the needle clips up to the mid spot with out much change…

 

Went back and bumped em up one more - slightly leaner. Big change! 
 

Highway cruise is now a solid 14. Mid throttle is solid 13 and WOT down in the 12s.  Town cruise is still a little rich but no big deal… could probably tune em a bit more - but not quite ready to throw money at jets and needles just for the sake of trying…
 

Also golf cart mirror definitely works! Still would like to see a bit more behind me- but that due to the Sparco seats sitting slightly higher and I don’t want to drop the mirror lower.  Wide angle is great! Can see the blind spots though the quarter windows.

[demo243]

Finally swapped the sticky rubber back on and took her for a cruise this morning before it got too hot. Thought about a couple of the local cars and coffees but decided to just drive it. Sticky rubber is a 45 series instead of a 50 so the car dropped 1/2” and definitely scraped the exhaust again. 
 

Obligatory 7Eleven shot

 

 

Edited July 14 by demo243

[demo243]

Updates!

 

The biggest being I figured out what is causing my Rev/Idle Hang issue! Long story short - it is mechanical. Ive been chasing a vacuum leak that wasn't there - not a bad thing, since I cleaned up some other things dealing with that. It seems that with little/no throttle I am not engaging the return spring enough to close the slide - this could be due to a few things...  Friction on the throttle shaft from a mis alignment; either due to the rubber mounts or the support brace I am using- or could be a miss measurement on my part of the spacing between the slide mount and the return spring/accel pump offset.  Im going to try lubing the needle bearing that the shaft rotates on first and see if that helps. 

 

Click below for the video of the rev hang issue.

 

I also swapped rubber mounts, I initially missed that there is a new style and old style. The new style has an oval outlet to the manifold, vs the old style with a round outlet. The old style round outlet better matches the manifold so I went with that. Still need to port match the manifold at some point... but Im not chasing those minute gains at this moment. 

 

Finally- I swapped to a 27.5 pilot, up from the 25. This had minor effect, but also a big change. At idle it bought me about an 1/8th turn on the airscrew. Its worth mentioning now that the air screw on these carbs makes a BIG difference! Essentially you can run practically what ever pilot you want and fix it with the air screw! Car has run great on 20, 22.5, 25, and now 27.5! But the air screw really effects your low/no throttle cruise and it seems the leaner you get turns out the leaner your cruise is. For example with the 22.5 pilot I was 1 turn out for and idle AFR of 14.5ish... but at low/no throttle cruise around town I was around 12 AFR! With the 27.5 at 1 1/8 - 1 1/4 turn out I am at 14.5-15 at idle and 13-14 around town cruise. Back on track - this bump to the 27.5 also seems to make a BIG difference on the highway "roll-on" ie 5th gear cruise to accelerate - much less of a stumble or super lean condition. With all that said I think I'm going to jump from 27.5 to 32.5 to see how that changes things. 

 

All other jets - needle, needle jet, and main seem to be good.

On a more annoying note I seem to have developed a squeal in the rear end somewhere - likely due to the coil overs being so low. It seems to be only on acceleration - so I am thinking a u joint in one of the half shafts or maybe drive shaft.... tbd

 

 

Edited July 27 by demo243

[benzo]

@demo243 Good on you for sorting this out and sharing. I have been keeping up with the updates as carb related issues or tuning is always interesting. Was curious about the idle hanging issues as I had something similar but mine was a vacuum leak and not mechanical like your situation.

 

The pilot system is or plays a huge roll for idle and drivability issues. My issues was I had suspected something ( rusty tank) got into my pilot jets and caused issues but after cleaning out and syncing the carbs and then adjusting the pilot screws for each cylinder I was able to make the engine run good at idle and cruising. For my situation # 4 plug fouled so for most times people say turn the idle mixture screw out 1 1/2 turns out and should be good but for me cylinders #1-3 1 1/2 turns was ok but #4 I did 1 1/4 turns and that kept # 4 plug from fouling resulting in a good idle and drivability. I don't have a AFR guage so just doing it by reading plugs and listening and feeling but I should get a guage as that would make it easier for tuning. That Mikuni Manual also is a good read and lot if info for troubleshooting.

[demo243]

@benzo thanks! It’s been a fun albeit frustrating process!

 

Ive been lucky with my carb dealings in the past- first time Todd from Wolf Creek had my PHH 44s dial from the rebuild for my L20b; literally didn’t change anything other then set the pilot screws. Second time I snagged the jetting info from @Duke for the same Mikunis on my KA.  For these I got an idea of where I should be from MikuniOZ and one of the Triumph Moto guys- and luckily they got me close! I think I’m only 1 or 2 pilot changes from being done- and honestly could just run it as it is!

 

AFR gauge really makes it easy to see what the carbs are doing. I’m using that mostly, but I am using plug checks for the pilot air screw balance. I have played with them a little to even out the carbs. 

[demo243]

Played around a little bit more this evening. I have a very minimal amount of adjust at the slide mount- so played with that and the idle adjuster. Tried to lube the needle bearings, but really no access to them… I can try by putting the front end up and hoping the lube drips down. 
 

Still thinking of ideas… but ultimately thinking I may eventually need to make another throttle shaft with a couple extra degrees offset between the slide mount and return spring hole angles.  I could potentially try to add an additional return spring… but that seems over kill and I don’t have much room either…

 

Just gonna keep driving it for now.

 

Still trying to decide if it try 30 or 32.5 pilots… should probably try both… thinking I might go 32.5s first though if they are better with no issues then I can skip the 30s and save myself $30. TBD

[demo243]

Quick and dirty- but proof of concept is there. Here is my initial bandaid fix to the rev hang issue-

 

 

I want to move it further back - between 4 and 5 I think - and want to clean it up. But overall it helped. There is still a slight occasional hang between 1,500 and 2,000 rpm but much better and easier to drive when it hangs. Downfall is the pedal is definitely stiffer.

 

After some more reading it does sound like many Moto guys use a push /pull dual cable set up. And V performance does mention the potential need for an external return spring. This was just what I had on hand and could grab quick from Orielly. I have another split clamp lever coming and will play around some more.

 

Car felt really good today- makes me even question about playing with the pilots - but I still think a slightly richer pilot with more turns out on the air screw will help… just need to decide if I want to try 30s or 32.5s….