Hard to start and weird to drive 240z

[Reverend]

Ok i dont know is this a carb problem or what but feel free to move it in right section.

It doesn't matter is it cold or warm weather but my 72 240z is hard to start. By hard i mean it takes time from 2-5 minutes and after it starts it barely stays alive until engine starts to warm up. And yes i use choke.

Starter is sounds to be ok but is this problem fuel or ignition related?

Also when engine is warmed properly it still has some issues with throttle. I drove few days ago around the block and when i give a little push it stalled but when i hit pedal to the metal it works like it should.

Also sometimes while clutch engaged the rpms are quite high. for example if i drive 30mph 1500rpm and i change to 3rd gear rpms rise to 2000 while clutch engaged. This doesn't happen all the time but sometimes.

Thank you already.

[Zs-ondabrain]

Sounds like it's time to rebuild your Carbs or invest in some New ZTherapy ZT carbs. You can't go wrong and it sounds like the carbs, not the ignition.

Can you say "Spring Cleaning"?

Dave

[Reverend]

Hi Dave

Well atm i got no funds to do that..is there any other methods than total rebuild? Yesterday i tried to adjust floats but it idled even rougher than before..

[Gary in NJ]

Have you checked the throttle plate shafts? A can of Gumout could be a small investment to determine the problem.

[Zs-ondabrain]

sounds like you got a couple of issues. Check for vacuum leaks around the throttle shaft ( spray carb cleaner around the shaft, if the idle drops, you gotta leak, as carb cleaner doesn't ignite like fuel)

Pull the Dome and clean out the backfire suet off the inner dome and off the pistons outer rings. this will allow a little easier movement. When you put the dome back on, pay attension to the piston. make sure it's free to move up and down as you tighten each screw. alignment is the key.

With the engine at a higher RPM (around 2500 to 3000) spray the inside clean with some carb cleaner. This'll free up some crap.

Might also be time to pull the fuel hose on the floats and clean them out and clean out the floatbowls. These carbs don't need Constant attension but minor cleaning and adjustments shouldn't be ignored. Keep it clean, lubed where needed, check your oil level in the top pot. Look real close at the dipstick, it'll have 2 small lines that the oil level should sit between. I use a 50/50 mix of household oil and 20 weight motor oil. Some use 5 weight, tranny fluid and other concoctions to achieve a smooth lift and drop of the piston.

Make sure your linkage balls are cleaned and relubed using some Silglide or similar lube. Make sure your return springs are good and holding the throttle shafts closed when you're not giving it gas.

That's all I got for fixing on a budget. Just woke up and got a large order to fill.

Dave

[JimmyZ]

I'll echo a lot of what Dave said and add a little. If it were me I'd do it in a certain order.

As far as the throttle sticking the linkage has a few places it can stick. If you remove the linkage from the carbs do the throttle plates move freely? Isolate the linkage or the carbs as the culprit.

Rule out the ignition completely before tinkering much with the carbs. Verify that the plugs are clean and the points are new and set to the right gap. Use a dwell meter as a final check of your points setting. A dwell check can also show how much slop there is in the distributor bushings. When checking dwell verify that the rpms are correct otherwise the reading will be different from specs. Be sure the condenser is new as well. Doesn't hurt to have a new cap and rotor either.

Supposing that the ignition system is good...

If you DON'T have round top SU's ignore the rest of this post. I'm assuimg that since it's a 72 it does have what came with it. (Round T's) Flat tops are a different creature.

With a proper ignition hard starting either warm or cold indicates inadequate fuel supply. (This gets deep sorry) After installing a new fuel filter do your normal SU carb maintenance. Clean the domes and pistons and verify free travel once all the screws are tightened. For the float bowls verify that the bowls are clean and that the needles/nozzles are clean and move freely. Do a search here for setting float height. There have been some really neat tricks and specs posted. One thing that caught my attention was a 70's dealer update to the factory specs of float height regarding differing heights of front and rear floats. (I think geezer posted that one)

Here is one site with a different method for setting up carbs than I've been taught. Might be worth a try... http://datsunzgarage.com/engine/index.htm

After the carbs have been cleaned and inspected and the floats set, do the usual mixture adjustment outlined in haynes and other manuals. If the hard starting still occurs then your fuel rail could be suspect. Don't enlarge the restrictive orifice at the discharge end when cleaning. It maintains your fuel pressure. Remove the rail from the car fill the rail with laquer thinner and blow with compressed air. Pay special attention to what comes out of the discharge end. If anything comes out at all clean the crap out of it. If the rail won't pass fuel then no amount of tinkering with the carbs will solve anything.

Edited June 5, 2010 by JimmyZ

[Reverend]

I've adjusted the floats (front carb was totally wrong) and now its gets gasoline much better. Also i've check the pistons etc. Now when driving it wants to go ahead and rpms rise but it just wont go. For example: I was driving 20mph 2gear and tried to accelerate rapidly. Rpms rise to 3k but engine seems to stall..rpms didn't drop but it felt like accelerating and pushing brake at the same time. Is it running too lean or something?

[Gary in NJ]

How did you adjust and verify the float height? Perhaps you've got them better, but not right?

As JimmyZ mentioned above, don't forget to check your ignition system for problems too.

[Reverend]

Well i checked that there is 23mm from fuel surface to float top. Then i adjusted the float itself. Rear is about 12mm and front is about 15mm. I also sprayed carb cleaner to carbs while running and idle rise up a little and then it returned back to normal.

Driving it after adjustment was strange as i said before. I could rev the living h**l out of it while idling on parking lot but when driving it was not possible. Carbs popped and banged few times also while driving. is it now getting too much fuel?

[Zs-ondabrain]

popping and banging out the rear is too much fuel and back firing out the carbs is typical of too lean.

if there is no power after 3KPRM, it could be a few things. Lack of fuel or air will allow it to idle and rev while parked but lag under a load (while driving)

Also, a bad coil will do the same thing. Won't run under a load but will idle and free-rev just fine.

[gogriz91]

Sounds trivial but I wonder if the fuel filter needs to be replaced?

[Reverend]

Fuel filter is brand new. Not the original style though. One of my colleagues suggested that it could be vacuum advance..?