1974 260z

[mr mikey]

Hey, this car drove perfectly with no problems yesterday....now that it's morning time it takes lotsa cranking and lightly pumping pedal to get it to bust off. Using choke ofcourse, it will start hitting and finally crank just enough to stay running while my foot is barely touching pedal. After it cranks I move the choke to half and it idles on up a little, but it still has a slight sputter sound to it. It'll rev fine with just easy presses of the pedal....but with a swift 0-75% kick of the pedal and holding at the 75% for a couple seconds, a loud tap sound comes from the 5th or 6th cylinder area. Detonation?

Back to the sputtering, it sounds almost like it's loading up(or not burning all cylinders) and when I'm driving, it poofs black smoke during shits or hilly accelerations. It's got the xr3000 and ran fine the days BEFORE i bought it. The carbs were rebuilt last spring according to receipts....if I didn't have a bunch of other things(projects) on my mind, I'd probably have figured this out already. It won't idle once choke is completely off, and the last time it ran this morning, it wouldn't idle at a steady rpm, it kept going up and down like someone was slowly depressing and releasing the accelerator and each time it would decelerate it would get lower and lower in rpm till it finally just stalled.

Once i get somebody here to actually hold the throttle at a run'able position(and it warms up a few degrees outside brrrr), I'll try to record the sounds it makes and upload them.

Thanks in advance to any help that can be thrown this way.

-Mikey.

Forgot to mention, it has the round top carbs with the spacers and the oil levels are full, so the pistons aren't fluctuating erratically....and it's using the early-style air cleaner. I noticed early this morning the vacuum advance hose wasn't hooked up to the front carb, when I hooked it up, it didn't seem to effect the acceleration much, but it did kill the tap sound when you goose the gas pedal.

Edited November 5, 2010 by mr mikey

[Gary in NJ]

Pumping the throttle while cranking does little with the CV carbs.

Is all of this poor running only happening while the choke is engaged, or is it all of the time? Have you taken a look at the nozzles to confirm that they are moving when the choke is engaged and disengaged? With the choke disengaged, can you move the nozzles further in the "up" direction? You're gonna have to dig a into the carbs to come-up with some more details.

The popping you hear is most likely back-firing through the rear carb.

[mr mikey]

The poor running is during full, half and no choke. When I turn choke off, the levers lift up, but the jets do not retract up to their resting position until it cranks(i can manually push them up and yes, they bottom out). I do know that they don't exactly have an accelerator pump, but it will not hit a lick unless there's a little back and forth movement of the butterfly valve. The "tap" sound(sounds like a ball peen hammer tapping an iron block) upon quick acceleration does go away once the engine has actually increased in rpm, it just makes that tap 2-3times in the first second after hitting the gas. The engine was a crate that was installed 15yrs/35k miles ago....the guy that built the car at that time was a retired race car builder/driver. All I know is he put about 12k miles on it, then passed away and his son used it as a weekend cruiser a few years....it's been sitting garaged since '02.

If anyone wants/needs to know any info, just tell me and I'll see what I can do about getting the info for ya....if I don't understand the terminology of something, I'll quickly say "wait...what?!". That's the queue for you to explain your meaning.

-Mikey.

Edited November 5, 2010 by mr mikey

[mr mikey]

Got the previous owner to come look at it and he got it to bust off, but it was idling so low that anything lower and it would've died. Touching the accelerator during that time would've killed it. Moved choke down to half and it slowly and steadily idled up to maybe 400-500, and when given a little pedal it would respond correctly(except for the loaded-up sound). After it started to warmup good, we eased choke to off position, it would accelerate then, but would backfire out tail pipe with a lil poof of black smoke when you let off the gas. It also seemed that everytime it would backfire that the idle rpm wouldn't be as low as before it backfired. After we got it idling somewhat smooth around 750rpm, it would sometimes have a light "thump" out the front carb when you goosed the pedal. I'd read somewhere on here that a lean condition will cause an SU to backfire, so for a temp test, I lowered the jet on the front carb to about 1/3 choke, and the light backfire problem went away.

Well I went into town and ordered a tuneup kit and some other doo-dads....got back here and couldn't get the car to crank without flooding. Tuneup components won't be here till monday, didn't realize everything except spark plugs was special order.

[mr mikey]

Another oddity I noticed, but it may be because of the electronic ignition....the previous owner had loaned me his boat battery to drive the car home, so after it was running good today, I unplugged it to make sure charging system wasn't at fault. Oddly enough, when I unplugged the battery, it stayed running for about 2-3seconds then just shutdown like you turned the key off. It just donned on me that it was probably the electronic ignition(xr-3000), can anyone confirm this?

Thanks,

Mikey.

[5thhorsemann]

Electronic ignition systems usually don't get sick, they just drop dead. Look to see that the components are installed corectly. Also, when I swapped out the flat tops on my 73 for 72 SU's I found that I couldn't run the vent tubes from the carb bowles to the K&N filters, as the vents SHOULD BE outside the air filter AND THEREBY ISOLATED FROM MANIFOLD VACCUME. I had no manual to go by and wasn't thinking when I put the thing together. but it will pull the fuel back through the jet at speed causing a lean condition, mine sounded similar to what yours is doing, worth a peak.

[Gary in NJ]

To confirm the condition of the battery and charging system you'll need to get a volt meter on the battery and check its static state (12.5VDC +/- .3) and the current to the battery when the car is running (14VDC +/- .3).

It sounds like you may have several issues going with your car. Attack one at a time.

You mentioned that you ordered a "tune-up" kit, but it sounds like you'll need to address the setting on the carbs as well. You'll need a Unisync for that job. I assume you have a timing strobe light for the tune-up itself.

Edited November 6, 2010 by Gary in NJ

[Travel'n Man]

I would have to agree with Gary - you have several different things going on.

You said the carbs were rebuilt - did a qualified shop rebuild them?

How long did the car run perfectly until it began these challanges - how long have you owned the car - did you just buy it?

If it has been sitting since '02 you need to start at the gas tank and work your way to the carbs - I'm sure it is all gunk'd up in there - was this the first time the car was ran since '02?

Don't do anything until you can use this site to search, read, and learn about your particular car and type of carbs and dizzy on your car -if the car has been sitting for 8 years don't even put in a new plug until you have cleaned out your gas tank and the float bowls, nozzles - checking the fuel line from the bowls to the carb - this is a very special piece of fuel line - do not go cheap replacing it - use the correct item once you replace it. While you have all the gas out of the tank you will want to inspect all the fuel lines though-out the car (I'm sure you will be surprised with what you find)

I would begin with a fresh tune up - make sure all your setting are correct with timing - dizzy - plugs - valves / then once all that is refreshed and correct do some research on your carbs - I've been reading on mine for several years now so don't expect to learn it all overnight - you very well could have different issues going on with float level - nozzles - a bad rebuild - incorrect idle adjustment - crap in your bowls -old set up fuel - and old lines that could be cracked letting in air.......the list can go on.

Once you have read up and studied you will need to reset your carbs to the basic setting and then fine tune from there................once completed your carbs will be fantastic!

Keep us posted with your findings.

[mr mikey]

Wow, ok, thanks guys....now I got lotsa excellent tips to keep me busy for a while. 5thhorsemann, I actually did replace the vaccuum lines and ran them to the air cleaner. Could that be what's making it not wanna start? I have to spin the motor over atleast 10sec before I even get a response sounding anything like it wants to crank, and this is with jets lowered to full choke position. I know that spinning the motor extended periods is bad on starting system, hence why I'm wanting to get this starting issue straightened out first.

On another note, I noticed I keep losing clutch fluid somewhere when it sits. I parked it on the concrete, filled up reservoir, and let it sit overnight. This morning the reservoir was empty(even the part below level of tank, so it's not just the tank-to-cylinder seal), there was no fluid, not even a stain, on the floor(so i guess it's not siphoning down like i'd thought). Anyone else had a similar problem? Only other thing i can think of is maybe it's leaking past the rear seal. As far as i know, it's the original clutch master....clutch slave was replaced when carbs were rebuilt. And from what i'm told, it was a local datsun specialist that did the carbs; I think he's retired now, but maybe I can have him take a look at them for me.

I pulled carpet and now realize why i got such a good deal -.-

All metal between firewall and front of spare-tire area will have to be replaced. Good thing is the previous owner felt bad enuff after seeing it, that he's going to provide all metal needed.

[mr mikey]

Well I undid the hoses from fuel bowl lids and it fired right up(had to hold gas to floor with choke on and jump off gas soon as it hit)....but it fired right up with no real hesitation. Or so i thought....i walked around to adjust choke a tad while running(choke cables are seized up, so i leave the holders on carbs a lil loose to move cable housing up and down to adjust choke), soon as it idles up and is sounding really smooth it starts to cough and sputter and then starts falling in rpm and goes dead....i smell something weird, and look down to see white smoke pouring out of where the 6wires go in/out of the xr3000 box. Now, this may not even apply here, but my old ford with an msd6 burned it's box once also....and what did it was the coil had failed(either the coil burnt the box or the box burnt the coil, not sure.)

I'm having such shitty luck, this is truely laughable

and yes, the crane box IS wired correctly....everything grounded well. *sigh*

Edited November 7, 2010 by mr mikey

[mr mikey]

Well, I ordered a Pertronix unit/coil combo to replace the Crane assembly. My dad's opel gt still has it's pertronix in it, and it's going on 20 next year.

[jaltman]

Perhaps this once again proves the old adage that 90% of all carburettor problems are electrical in nature.