Sputtering

[My260Rocks]

While driving in heavy traffic my 260 starts sputtering. At first i thought maybe it was a cooling problem, but my gauges all read cool. This only happens at idle or near idle in usually warmer weather. I have 71' SUs. Any suggestions? Thanx

[Cliff. Elford]

Please define sputtering. My 71 sputtered at idle when the mixture was too lean or a plug was bad or the timing was off. Low octane gasoline at times caused that also, I feel. How about the points? For that matter how about a tune up? In any event have fun! cliff.

[My260Rocks]

well at idle you cant tell there is a problem, but when I try to accelerate my engine starts to sputter, but once i get moving it stops sputtering and if i make a short stop (like at a stop light) I have no problem. Only in heavy stop and go traffic do i have problems.

[AxtellZ]

i would check the condtion/balance of the carbs. How long since a tune-up? Try pulling the plugs to check for fouling, and the balance/rich vs leaness of the carbs. At least you can begin to rule out stuff. Good luck, Jeremiah

[2ManyZs]

Do you still have water running to the carbs? It is possible that while sitting still it is trying to vapor lock, sometimes the water control valve will keep water going to the carbs after the engine is up to temp and will overheat the intake. If you still have the crossover line hooked up to the intake try blocking it off and see what it does. If you put the early carbs on the original intake you probably still have it hooked up.

I'd also check your fuel pump and filter while you are under the hood along with what everyone else has said.

[My260Rocks]

Vapor lock sounds like a pretty good suggestion. If I plug up that connecting pipe how will that effect the car? I mean it may solve one problem, but will it cause something else to go wrong or not work like it was supposed to?

[2ManyZs]

I had mine plugged off for as long as I owned my 73, the only thing was I had to run with the chokes on a little longer in cold weather.

One of the "big" things now days is cold air intakes right? Well it makes sense not to heat the intake with warm or hot water, it just heats the air going to the engine too. Z cars were notoriously cold blooded and only got worse with the added smog equipment so this is one of the main reasons it is there. Try blocking it off and see what happens. It can't hurt, but it may help.

[AxtellZ]

May i ask, what was done with the coolant lines when the carbs were swapped? My 260 had 3 lines from the thermostat vicinity, 1 through the original carbs, 1 through manifold, 1 through balance tube, if i recall. I just put a 4 inch piece of heater hose & plugged the ends with a bolt of appropriate size. (for the carb line, the other 2 i let be) [outlet-hose-bolt].

Recently i've developed a leak in one of the other 2 lines- thought the head gasket went at first, but i just found it with a mirror & light! I may just go ahead and block off all three now.

As has been said before, the only downside may be the "coldbloodedness", by eliminating the warm radiator fluid through the intake manifolds. good luck, Jeremiah

[Cliff. Elford]

After giving it more thought I remember solving that very problem on my 71 by increasing the mixture screw on each carb by one half turn. It stopped sputtering and the shifting in heavy traffic improved mightely. The car was running too lean to properly "take off" from a dead stop, especialy if it was stop and go traffic. cliff

[Sonic]

i have a 73 240z with the smog removed, 71 su carbs, and just tuned up and syncronized. i have the same problem, most often when going uphill. it seems runs fine when not under a load.

sounds like i'm no getting enough gas to one of the carbs; like its running on three cylinders. and there is air bubbles going out of the new nissan fuel filter when i pull over to check the engine.

what should i do?

[2ManyZs]

Sonic,

If you have air bubbles in the fuel filter you may have a problem with your electric fuel pump, of course I'm assuming since yours is a 73 that you do have one. All the 73's were recalled to have one installed so yours should have one. Have someone check the output pressure on it with a fuel pressure gauge to start with. I don't remember exactly but I think it should be around 8 pounds. I don't have a service manual here for a 73 so I can't be sure, maybe someone else has one and they can post it for sure. You might also do a visual inspection of the fuel lines to see if the are crimped anywhere, the metal line under car may have been hit at one time or another.

As far as the sputtering under load, is your timing set correctly and is your vacuum advance working right? These would be two of the places I would look first. Of course there are quite a few other things that could be causing it but if these don't help cure the problem then you can at least rule out two things, by then there should be quite a few more postings with more things to check.

[My260Rocks]

I use to have THAT problem, at first it was because I had a short to the fuel pump, which i wired around. Then the pump whent out half way between Dallas and Houston! I changed it to a high volume pump that knocks and burrs like crazy, but NOW i have some major fuel pressure. My problem isnt related to fuel delivery. I'd like some more in depth description on how to stop the flow of radiator fluid through my carbs though. Everything else checks out, it must be vapor lock.