cold start problem

[gmr714]

I have a 74 260Z with twin hitachi carbs. It will not start after it sits for a few days no matter the temperature. I pump the gas and it turns over but refuses to start unless I spray it with starting fluid. Once it starts it is good for a day or so. I just got it and it will sit for the winter but I want to get it ready for spring. I am not a mechanic but the fuel pumps are good, no leaks. I just cant get ignition when cold without ether. The guy I bought it from said it has always had this problem. Any suggestions would be appreciated. I bought the original 74 service manual by nissan but need a push in the right direction. don't know anyone familiar with these carbuerators. Thanks, MARK

[bahollings]

I have a 260Z with dual webbers with the same exact problem. I had Z Car Source of Arizona work on my car (they do great work by the way) HOWEVER they were unable to fix this problem. I will quote from Jeff from ZSource who told me "The car still has the hard start issue. Part of this is due to the wiring circuit for the electric fuel pump at the fuel tank. The circuit is designed to keep the fuel pump off when starting the car and on when running. This design does not help when trying to deliver fuel to the carbs."

I haven't been able to find a solution for this, my car will start ok after sitting for up to 5 days and then after that I have to give a shot of starter fluid to the carbs.

[Bruce Palmer]

.... working with the flat tops or earlier round top Hitachis?

[bahollings]

I had the flat tops and had dual webbers installed and the same problem is still there.

[bahollings]

what I meant to say is I had the flat tops to start with and thought that was the problem so THEN I had the dual webbers installed, car runs much better but still the same problem if the car sits for more than 5 days.

[Ramses]

Does your manual choke work? I cant get my car to start unless I use my choke. Actually, it would not start without starting fluid until I fixed my choke. I have SUs with a manual fuel pump and the electric fuel pump disconnected.

[Bruce Palmer]

... it more than likely means your carbs are too rich and should be turned lean enough so that you need to pull the choke on however briefly to get it started. This is especially true in cold weather. Carbs that are close to "right on" may start fine in warm weather w/o choke but cold weather starts need that extra "rich" shot to fire and run....

[DaveN]

Mark,

Do you have flat top (original 260) Hitachi's or a round top conversion from an earlier model year? The flat tops have true chokes, the round tops use a movable main jet instead of air flow restriction to get a richer mixture for cold starting.

Flat tops can be made easier to start when cold by fudging the choke butterfly adjustment a little toward fully closed. Conversely, cold starts will be slow (or impossible) if the choke butterflys aren't closing quite far enough. It's a sensitive adjustment, hard to make reproducibly because you do it by bending a wire piece in the linkage. Flat tops also have a special starting jet -- another fuel passage that can become blocked by sludge in the car is stored for months/years with fuel in the carbs.

Round tops have a limited cold start enrichment range. The linkage on the carb should allow 10.5-11mm of nozzle drop from nominal zero (top of nozzle flush with bottom of venturi). 2-3mm of that, depending on carb model & setup, is used for for the hot mixture adjustment; the rest is available for cold start enrichment. The final link to the nozzle, a bent steel strip, can be straightened a little to get about one more mm of max. nozzle drop without binding. The only other adjustments available are to make sure the "choke" cable adjustment is giving max nozzle drop in both carbs in the full choke position and to fudge the float levels upward a little (and run a bit rich all the time). If this isn't enough (it wasn't for my '72 on the coldest mornings in Wilmington, DE) a kettle of boiling water poured slowly over the carbs and manifold just before starting may make the differrence.

Both lack the "accelleration pump" that fixed venturi carbs need, so there's no way to prime a cold engine by stroking the gas pedal before turning it over. That makes them slow to start when cold, you have to prime them by letting them turn over until there's enough fuel in the manifold to get an ignitable mixture into the cylinders. It helps and is easier on the battery to crank in 4-5 second bursts with pauses of several seconds between (to let gas in the manifold evaporate).

Most older carbureted cars become harder to start after sitting for several days because sitting gives the high volatility "cold start" fraction in the gas more time to evaporate from the float bowl. It's especially noticeable in early Z's because you can't compensate by giving the accelleration pump an extra stroke or two.