I'm new and I have a lame question!

[Aerodynamic]

Hey everyone my name is Edward and I'm new to the world of internet forums so bear with me! :frantics:

 

In March I purchased a 74 260z that had been sitting in the back of my auto shop class in high school and was kind of fading away.

I've worked all through the class and all of summer replacing everything many things and now the car is somewhat driveable. Here is the only picture I have:

 

 

 

I do have one question however concerning my triple Weber DCOEs. I have gotten the car running pretty smoothly, not perfectly, but running well when up to speed. For the life of me though, I cannot get it to idle under 1400 RPM while stationary at an intersection or something. The only time I can get it to run at the proper revs is if I physically pull up on the throttle linkage with my hands and hold it there. If I let it go it seems that the carbs begin to leak through again and the idle climbs back up. I barely have to pull on the throttle linkage though; just move it slightly, about 1/8 of an inch.

 

I've gotten the right timing, and the carbs tuned to run smoothly through the revs, but I cannot get the idle down.

 

My question is do I have a leak somewhere, or how can i get the idle back down to normal? I can't really seem to find a straight answer around the internet, so any help would be greatly appreciated. The carbs have been rebuilt so I was wondering if they could be leaking out of the throttle plates, (There is a small gap) but I don't know if that is the problem.

 

Anyway, it'll be great meeting some of you and learning about Z cars in the process!

[Eagle_Adam]

i cant help with your question, BUT

 

Welcome to Ratsun! Great 1st post man!!!!!

[elmerfudpucker]

Hey everyone my name is Edward and I'm new to the world of internet forums so bear with me! :frantics:

 

In March I purchased a 74 260z that had been sitting in the back of my auto shop class in high school and was kind of fading away.

 

Damn it man! could you unfade my truck? Looks good and welcome to Ratsun! give it a few and one of the gang will be in shortly. Post a few good oics (pics) of the carbs to help them help you.

[Wide14u]

get a can of carb cleaner and spray around anything that might have a leak . nice car looks good and welcome to ratsun

[LeviGideon]

Maybe replace the throttle return spring. Could be worn out and not be strong enough to really pull the linkage back to idle position. Either that or it could be a bolt that's too tight and binding up the linkage somewhere. Get pics of the linkage and we can probably help you more.

[SlottedMagz]

If that questions lame then the ones ive asked are down right retarded

[Eagle_Adam]

:rofl: ^^ i know right?? my first few questions on ratsun were....... well........ noobish at best :D

[MicroMachinery]

I second the throttle return spring replacement. If without slight pressure it causes it to go wherever it wants, I'd say it's missing the spring(or the spring is weak/placed incorrectly). That will hold tension against the throttle adjustment screw.

[I'm BLUE]

Pull your spark plugs and see what they are telling you (running rich or lean) ! Apply anti-seize to plug threads on re-insertion.

 

Ideally you want to = Perform a compression check (dry/wet) and write down numbers = my old carb guy said it was best to perform one and have close to even numbers in order to be able to tune properly at all lol.

 

Check for vacuum leaks as stated above ^^^ ... BE VERY careful and have a fire-extinguisher or water near-by (gawd forbid) ... if idle changes or picks up ,,, you have a leak ! check your vacuum hoses and pull them off one by one inspecting the ends visual and physically !!! ( they often are bad and nissan recommend's high replacement intervals which no-one ever performs ).

 

(1) = you need the carter electric fuel pump ... it has the proper range of pressure/volume for tripple dcoe's. = http://www.racetep.c...bfuelspark.html

--- Note: Check your fuel pressure ... anything far-above 5-6psi fuel pressure under load or even at idle ... is probably going cause headache's and leaks period ... it did on mine with a cheap universal pump lol ! (I switched it out fast though ;) ).

 

(2) Check and set your ignition timing ! = this will vary depending on your engine specs/ingition distributor setup ... turn it to 15-degree's-ish and go from there ... IDK

 

(3) I started typing all this out but read this info carefully and perform and if you don't know the parts than look at a diagram or download a pdf file directly from the site ! (it's 2x easier with a friend helping while you adjust if it's a run-ability/idle issue)

= http://www.redlinewe...t_typical_i.htm ... Old Timer told me between carb adjustment's (non-mechanical) you should wait at least 30-seconds-1-minute if not more for then engine to catch up while you are tuning ! Slow small increment's win the race , but it is simpler to turn off a machine and attempt as well lol ( Important = newer dcoe's may have different adjustment's than older dcoe's !? )

 

(4) since they have been "rebuilt" ... you need check and adjust the float height really before tuning !! ... purchase the tool required ! Also make sure that when you cycle the throttle linkage ... some fuel is squirting out of each accelerator pump discharge nozzle ... if not clean/inspect/replace ... they get stuck or gauled (but still working) on some older/well-used models ( like mine did lol )

 

(5) purchase and enjoy the carb synchornizing tool ! Remember you are going to run just a tad richer with air-filters on ...

 

I would make damn sure you have a good HOT SPARK ignition system with FAT 8mm plug wires ...

My bro has a mallory uni-lite dizzy with his Tripple 40DCOE's/L28 ... it's a fawking cooler than shit old school tech Ignition system !

If you have a knarly camshaft grind ,,, and port-work/bigger valves ... of course these "general settings" you are reading are going to be of not a lot of use to you lol ... BUT the methodology should be followed closely and performed in tiny increment's ! I honestly don't know you

 

 

 

Once you get these baby's dialed in ... I guarantee you won't look back ... they are easy to adjust ... roller bearing throttle-shaft's mmmmmmm ... they're fun period ! :lol: :cool:

 

Generally when it comes to carbs .. everyone has their own little quirks/methods :)

 

 

 

( credit to "redlineweber.com" )

 

It is most important to verify all linkage and levers are installed without binding and the linkage opens to full throttle and is allowed to close to the Idle Speed Screw. This is the number one and two reasons for tuning errors, improper linkage installations and over tightened linkage nut, causing binding in the linkage assembly.

The Individual Runner carbs, DCOE, have individual Idle jets and mixture screws for each barrel. They also have an additional air bleed screws and lock nuts. This is not used for idle adjustment or idle quality. The settings for these screws should be closed.

 

Standard DCOE Settings:

 

Speed screw ¼ to ½ turn in after contact with lever maximum.

Mixture Screw 1 turn out from lightly seated.

 

“Lean Best Idle” Procedures

After confirming the linkage allows the throttle lever to seat against the Idle Speed Screw. Back off the Idle Speed Screw, then turn the screw in until it contacts the throttle lever and turn it in ½ turn. Turn in the Mixture Screw in until it “LIGHTLY” seats, then back it out 1 full turn. Loosen the 8mm wrench size nuts on the “air bleed” screws, turn in the air screws until it seats then tighten the nut.

a. Start the engine, it will run slow and like a tractor. As long as it will stay running, the idle speed is not important at this point.

b. First, turn in the mixture screw until the engine runs worse, then back out the screw ¼ turn at a time. The engine should start to smooth out. Continue to back the screw out ¼ turn at a time until the screw does nothing or runs worse. Then turn it back in to the point where it ran best. You want to tune the engine by sound. Adjust each mixture screw to the best, fastest and smoothest running point. Do this procedure with each mixture screw.

c. Now you may adjust the Idle Speed Screw. It should be sensitive and only require ¼ turn in or out to achieve the idle speed you like.

d. These carbs are commonly used in pairs, this makes the synchronization important, be sure to bring the high flowing carb down to the low flow carb. Then bring them both up to “proper” Idle speed. The Idle Speed Screws are not opened more than ½ turn in.

e. After synchronizing multiple carbs, reconfirm steps b. c. & d.

 

“Simple Rules for Calibration”

 

If your mixture screw is out more than one turn like 11/2 turns then your idle jet is too lean, go up one half size on the Idle jet.

If you mixture screw is not out one full turn, something like only 1/2 turn out from seated then your Idle jet is too rich, go down one half size on the idle jet. This is all based on the important fact that your speed screws are not open more than ½ turn if they are then that is also an indication that you have a lean Idle circuit. You are cheating by opening the throttle plates and exposing additional progression holes in the transition.

Pump By-pass Valve: The pump by-pass valve is designed to allow fuel into the pump circuit and when depressed, by-pass a percentage (hole on the side of the valve) of the fuel delivered to the accelerator pump nozzle/jets. We have included the zero by-pass valve in our jet kit. This will deliver all of the available fuel to the engine and not by-pass fuel back to the fuel bowl. This will increase the duration and volume of the pump shot with the original pump jets. To decrease the duration and increase the fuel volume we have included in our jet kit the larger 55 pump nozzle/jets. This is for maximum fuel delivery from the accelerator pump circuit. The accelerator pump by-pass valve is located in the bottom of the fuel bowl, one is required per carburetor.

 

DCOE Adjustment controls Tuning & Adjustment

 

 

 

 

 

 

 

1. Critical! Be sure for initial carburetor set up all air by-pass screws should be in closed position. These are not commonly used in standard carburetor adjustment.

2. Set the idle speed screw at ¼ to ½ turn in after contact with throttle lever. When doing multiple carburetors all linkage should be disconnected. All carbs should be bench adjusted to same setting.

3. Set the idle mixture screw to one turn out form lightly seated. When checking the seated position to make only light contact with seat, aggressive seating will damage needle and seat of carburetor,

4. Start engine as long as engine starts and runs do not set up idle speed first. First adjustment if possible should be to find smoothest idle with each mixture screw on all carburetors. Some prefer to do one barrel of each carburetor then come back and do the second barrel

5. After preliminary lean best setting of idle. Check carburetors for synchronization. Commonly done by checking lead or front barrel of each carburetor.

6. You will always want to bring high flow carburetor down to match the low flow carburetor. If this cannot be done you will need to recheck bench assembly for binding throttle in high flow carb. Once you have matched both carburetors you will need to set the idle to the desired idle speed setting. This will be done by adjusting both carbs up or down the same amount and re checking for synchronization.

7. Make one last check of lean best (smoothest running position) idle on all mixture screws one last time.

8. Best idle should end up with the mixture screws at or near one turn off seat. Check rule of thumb for idle jet selection in Weber basic idle adjustment instruction.

[SlottedMagz]

I second the throttle return spring replacement. If without slight pressure it causes it to go wherever it wants, I'd say it's missing the spring(or the spring is weak/place incorrectly). That will hold tension against the throttle adjustment screw.

 

is that the soring connected to the the choke cable im guesing there the same just different names cause my 240 has the same issue (did its all apart right now)

 

there SU's not DCOE's though that probably doesnt matter much in this case

Edited September 12, 2012 by SlottedMagz

[I'm BLUE]

*Fuel Pressure ... check it ! = you need the carter electric fuel pump if everything is leaking everywhere after ... if you have new/newer gaskets and the bolts are not over-tightened.

*Linkage = light to medium return springs on linkage ... the heavier the tension means the more stress endured on the throttle-shafts.

*Make sure your air-bleeds arn't turned way out of adjustment .. ( your sounds exactly what mine did the very first time I simply "installed" and started my dcoe's because I was excited lol )

*Idle adjusment screws/bolts = make sure they are not bent/flared on the bottom edges ... info says 1/4-1/2 turn ? in after "contact" with the lever ! Sometimes these can be just so everly slightly different on the bottom edges after years of wear/abuse/

 

If it feels like it is binding anywhere ... stop driving the car if possible and figure that out :)

 

If it simply feels like the throttle is climbing for no-real reason = I would re-adjust/re-tune everything as it could only get worse.

 

It was a long post above by myself ... but good info ( I hope !? lol )

 

Best thing ever in tuning Tripples .. A Sun Diagnostics Machine !!!

 

[Aerodynamic]

Hey guys thanks a lot for the replies! Looks like I've got some work to do this weekend haha.

 

I have tried tensioning the throttle return spring in the past and it left me with a stuck throttle! But I agree my spring probably needs replacing.

 

As for the vacuum leak, I may have one at the manifold; gotta check back on this.

 

I found an old picture of the engine bay. The fuel lines are set up differently now. I have a consistent 3.9 psi at the carbs.

 

 

That black hose in the back going into the manifold is to do with the vacuum correct? I haven't really touched that thing since I started working because tbh I don't really know what it is.

[Aerodynamic]

Also @DTP,

 

Just read a lot of your information and much of it I have not thought to do/check. Thanks alot!

[datzenmike]

The black hose goes to a one way valve and then to the power brake booster. If you have an automatic ther will also be a very small hose to the transmission.

 

Can't tell from the picture but is your vacuum advance to the carb connected?

 

From your description I don't see the idle as a vacuum leak. Have someone pull up on the peddle while you watch what's moving on the carbs. I see that your fuel return line is not hooked up. It will run better with it than without.

 

 

before I forget... NICE car!!! and nice zx? rims, always liked them

[]2eDeYe]

Great tech posts DTP!!! :thumbup:

 

 

 

 

Edit: Nice Z car too :lol:

[72240z]

Its not a lame question. Triples are a challenge for mechanics let alone kids with shop classes under their belt, the fact your where you are with them is pretty impressive. There are a million things that could cause the issues your having. Start with DTP's suggestion, pretty good advice.

 

Today I found that the throttle shaft was twisted on 1 of mine with a misaligned butterfly on another causing a situation where its been impossible to sync them. Which of course caused other issues like popping, hanging idle etc... Who thinks to check that though? lol I think us DCOE guys are gluttons for punishment.

 

On a side note My friend and I have discovered a way to bench flow them. Take a shop vac and hold it to the back side then the sync tool to the front. Very effective way to bench match your dcoes :-).

 

DTP I was talking to an old timer at the NJZCC show last sat who was swearing by that machine lol.

[I'm BLUE]

Also @DTP,

 

Just read a lot of your information and much of it I have not thought to do/check. Thanks alot!

 

No problem man ! Hope it helps ( somewhere in that black-hole of mumbling goodness of mine and hope it's correct lol )

 

2eDeYe' timestamp='1347580226' post='756769']

Great tech posts DTP!!! :thumbup:

 

 

 

 

Edit: Nice Z car too :lol:

 

Thanks J2eDeyE !

 

I feel "whole" now that all the mods have acknowledged my existence on ratsun....

 

:lol:

 

Its not a lame question. Triples are a challenge for mechanics let alone kids with shop classes under their belt, the fact your where you are with them is pretty impressive. There are a million things that could cause the issues your having. Start with DTP's suggestion, pretty good advice.

 

Today I found that the throttle shaft was twisted on 1 of mine with a misaligned butterfly on another causing a situation where its been impossible to sync them. Which of course caused other issues like popping, hanging idle etc... Who thinks to check that though? lol I think us DCOE guys are gluttons for punishment.

 

On a side note My friend and I have discovered a way to bench flow them. Take a shop vac and hold it to the back side then the sync tool to the front. Very effective way to bench match your dcoes :-).

 

DTP I was talking to an old timer at the NJZCC show last sat who was swearing by that machine lol.

 

Yeah definetly not a lame question and absolutely can be a challenge for everyone ! Tripple's are an experience of their own :lol: ( love/hate right ? lol ) :cool:

A million things that this problem could be on this setup is right :lol: (seriously yeah!)

 

Good catch/point on the throttle shafts/buttefly contacting bore(s) !!! and Ouch on the twisted throttle shaft !! DCOE guy's being glutton's for punishment is about right :rofl: bahaha

Best luck on the replacement dude and hope it works for ya :)

 

That's way interesting !! I will have to try your's and your friends method !!! very cool !!! :cool: ( I didn't even think about that :unsure: !!!!! nice work 72240z )

 

 

:lol: no shit !! that's awesome on the chat with the old timer about Sun Machines ! Sun Machines ... they just ,,, just ... KICK ASS :lol:

I think my brother first introduced me to them (at his shop) ... I about shit bricks and my world as I knew it changed that day.. :blink: :lol:

My buddy has one as well , but he moved out of state not long ago damn it lol.

Brother now has one as of recently :devil:

[Aerodynamic]

@ Datzenmike I do have a return line set up now, though it seems in that picture that a lot of the stuff isn't connected. I'll hopefully be able to upload a current picture of how the engine looks but I have work in a little while and its 103 degrees outside so I'll wait for now.

 

Does anyone know the general tension for the return spring? Mine doesn't feel too tight now that I've checked.

[72240z]

I wanted to mention that spring in my post but forgot. It doesnt look nearly close to strong enough. Most set ups using a spring to the valve cover use two springs and usually at least 7lb each. I am using a single 12lb cut shorter so It's prob more like 15+lb. You can get various rates at home depot and see what works for you. They need to be held closed tightly though.

[Aerodynamic]

Definitely going to buy a new spring tomorrow then.

 

Ignition was actually something I was going to look into next as I feel I am not getting as strong a spark as I should be. I'm getting there slowly!

[datzenmike]

I think all 280z with L28s had EI remote igniter distributor. 280zx ('79 through'81) had the more desirable matchbox EI distributor. Both us a breakerless transistorized ignition and high output coil.

[Busta Nut]

Nice Z!!!

 

.....I agree....stronger spring dude. I'd make sure the butterflies are closing all teh way also. It was an adjustment issue on mine. Right at the end of the steel rod.

 

Welcome!

[Mr.Woof's72z]

Ignition was actually something I was going to look into next as I feel I am not getting as strong a spark as I should be.

Pick up an E12-80 out of a '79-'81 280ZX. http://datsunzgarage.com/engine/ has wiring diagrams for the E12-80 into the 240/260. I run an MSD Blaster II into an E12-80 out of an '81 ZX, so far it seems to be the best combo between price and performance. That datsunzgarage website has lots of useful info as well, and welcome to the Z side of Ratsun!

[banzai510(hainz)]

I would adjust the valves.

ck the return spring.

synce the carb close as possible.

ck the jet blocks

Adjust the timming/distributor

 

after that find a triple carb guy and get it going perfect.

 

Then lower it with soem nice rims!!!!!!!!

[72240z]

Pick up an E12-80 out of a '79-'81 280ZX. http://datsunzgarage.com/engine/ has wiring diagrams for the E12-80 into the 240/260. I run an MSD Blaster II into an E12-80 out of an '81 ZX, so far it seems to be the best combo between price and performance. That datsunzgarage website has lots of useful info as well, and welcome to the Z side of Ratsun!

 

I run the E12-80 with a Crane coil and I agree for the price you really cant beat it. Though at like 5k I get a rpm hesitation till maybe 6k then it skyrockets. Its tough to diagnose a problem when you have to be run to 7k flat out to see it. Well in greater NYC anyway lol.