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Hard to start when cold


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Here's my problem: My stock 1972 240z runs great. It has plenty of power, idles very smooth, takes the gas well and overall performs great.

However, if it sits for a couple of days, it is very hard to start. The choke works fine, it has a recent tune-up and everything seems to be working well.

But after a couple of days sitting, it has to crank and crank for a long time before it will start, (several seconds, maybe a minute). It seems almost like it's not getting gas. Once it starts, it runs perfectly.

As soon as it runs long enugh to let the chock off,...you can turn it off and it fires up on first turn for the rest of the day.

Any ideas?

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I had read somewhere that the early Z's car's had two fuel pumps,...one mechanical in the engine bay and a second electrical one located near the fuel tank in the rear.

My car does not seem to have the electrical pump in the rear. Could this be the problem?

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The mechanical pump will take a little cranking to get your fuel lines and the fuel bowels filled after being parked for a while the eclectic pump was added to help against vapor lock. But should help this problem since it pumps right away vs having to crank the motor over and over to get fuel up to the carbs

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after a couple of days sitting, it has to crank and crank for a long time before it will start, (several seconds, maybe a minute).

Before you get all wrapped up in fuel pumps trying to fix this issue, I will point out that it should not be that difficult to start the car after sitting for just a few days.

I can let my 260Z sit for two weeks and it will start within the first ten seconds. Later that same day once the engine has been "freshly started", it will fire off within the first two seconds, so I do see a reduction in cranking. But having to crank for a minute or so? Come on!

Requiring 60 seconds of cranking to get the car to start after sitting for two or three days? That's a problem. And not the kind of problem that a fuel pump should be used to fix. The only problem a fuel pump "could" fix is if your float bowls are going dry over a couple days of sitting... And if that's the problem, then you better spend some time trying to figure why your float bowls are going dry after sitting just a couple of days.

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I agree with the captain. As I was reading this, it didn't sound like fuel to me. It sounds like an ignition problem. My 73 Z has an annoying problem much like it. I've figured out different ways to get around it, but my car does it too (not starting seemingly with endless cranking). I've tracked it down to the ignition key switch, not the mechanical one where the actual key goes in and turns, but the electrical switch mechanism behind it which contains the plug leading to the wiring harness. Change that part. You can use the switch out of other early Z's, they are all the same--but like everything else with cars, it could be symptomatic of some other problem as well. Changing out the switch hasn't fully solved the issue in my car yet, but it helped.

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This sounds like many other 240s that I know of, running SUs, including mine. I have an electric pump at the rear, and no mechanical pump. If I hav'nt used the car for a few days or even a month, the pump will click for 15 seconds, then it will take another 10 or 15 seconds of cranking for the engine to fire. This can SEEM longer. My car starts first time when it has been recently going. (the same day) and it has had the same symptoms for the last 12 years. No better, no worse.

The mechanical pump alone has to drag the fuel all the way from the tank with the engine cranking, and then fill the bowls, so it seems logical that it will seem take a little longer than an electric pump that is pushing the fuel with no cranking.

When cranking it can seem like a long time, when in reality it may not be long at all.

He states that his car starts perfectly after it has been running. If the problem was ignition, would it not show the same hard start symptoms at any old time? Half day. one day. one week.?

When I first got my 240 twelve years ago, I thought it unusual that it took longer to start than a modern car, but now it is quite normal for it.

Just my observation.

Edited by olzed
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Air, fuel, spark. I think we can rule out air, since the engine runs once you do get it started. That leaves fuel & spark. Both easy to check. Before doing so, have you verified that the choke is indeed working properly?

With the choke lever pulled all the way back, the fuel nozzle at the bottom of each carby should be pulled about 1/4" down from the bottom of the carby. Have a helper pull the choke lever while you watch/feel the fuel nozzles to make sure they move. Your hard start issue could simply be that one or both nozzles are stuck. If the choke is indeed working properly, then check for spark & fuel.

Pull a plug wire and put it about 1/4" from a good ground (not touching). The strut mounting nuts at the top of the strut tower work well for this. Crank the engine and look for a spark. You may need a helper to crank the engine for you. You should see a nice, healthy spark. If not, you need to dig into the ignition system. Check the cap, rotor & points and all the associated wiring. Could be a sketchy connection at the ballast resistor or at the coil.

To check the fuel, pull the coil wire and remove the dizzy cap and secure it out of the way so that it doesn't get hit by the the fan or something. The idea here is to prevent a spark, as the next step involves working with raw fuel. Next remove the fuel delivery hose from one of the carby bowls. Wrap a rag around the hose as you pull it off to catch any fuel that spills out. Hold the hose in an empty soup can (or similar container) and have a helper crank the engine. Fuel should flow from the hose within a few seconds. If no fuel flows or it takes a while for the fuel to flow, then check the fuel filter, fuel pump and fuel lines. Could be a clogged filter, defective pump or cracked fuel hoses that allow air to get sucked into the lines. Also check that one of the carbies doesn't have a stuck needle/seat in the float bowl. There should be enough fuel left in the float bowls to start the engine after sitting a couple of days. My car can sit undriven for weeks, yet the engine will start on the first turn of the key.

Hope this helps. Keep us posted on what you find.

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The mechanical fuel pump is the fault. weak when cranking, takes forever to pull fuel from the tank. This is likely made made worse by a weak check valve in the pump that lets the fuel drain back. The pump works adequately when the rpms are up.

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The mechanical fuel pump is the fault. weak when cranking, takes forever to pull fuel from the tank. This is likely made made worse by a weak check valve in the pump that lets the fuel drain back. The pump works adequately when the rpms are up.

It's not the fuel pumps fault. You guys are missing my point...

When you shut the car off, the carb bowls are full to the proper level. When you go to restart the car a couple days later, the bowls should still be full to the proper level. You don't need ANY fuel pump when you first start the car because the bowls are already full! You should not HAVE to pull fuel from the tank.

And it's not like that fuel in the bowls gets sucked in all that quickly. How do I know this? Because there has been occasion where I want to pull the carbs off my car and I want them to be as empty as possible before I pull them. Just less mess, that's all. So I disconnect and plug the fuel input lines to the carbs and then start the engine. It will idle for a good minute or so before it starts to sputter from fuel starvation.

In other words, when you first start your car, you should have about a minutes worth of fuel already in the carbs. It should be able to run for quite a while with NO fuel pump before it runs dry.

So, if your bowl levels are already low, or if you're percolating the fuel out of the bowls on hot shut-off, or if you've got very low compression, or a weak spark, or your carbs aren't functioning properly, or, or, or... The point is that the underlying problem is not the fuel pump.

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This sounds like many other 240s that I know of, running SUs, including mine.

Now that you mention it, I don't usually actually time my cranking time. I was guessing with my ten second estimate. So out of curiosity, I timed it this afternoon. Today was the first start in about two weeks:

First cold start - about four seconds.

Warm restarts - Less than one second.

Granted, I'm running the flat top SU's which supposedly aren't as good as the round tops, but I'm content. Even thirty seconds of straight cranking without so much as a "pop" would seem like an eternity to me. I'd be looking for a problem!

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He can easily check this by spraying some gas into the carb mouths, and then crank it over. I'm thinking it will fire right up.

We seem to be 50-50 on this.

It will be interesting to see his result.

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I've also got an advantage with the flat tops in that I've got the float bowl sight glass on the side of the carbs. I checked the bowl level yesterday before I tried to start the car and it was down a little bit. Evaporation over the past two weeks I assume. Not a whole bunch.. A WAG would be 10% down?

If I shut it off while full hot in the middle of Death Valley one summer afternoon and then came back two weeks later and tried to start it, I could believe that my bowls could be completely dry. But parked (in a garage), even in the middle of summer, in the Philadelphia area that was not the case.

I don't think it's simply the flat tops either. I also ran round tops for a few weeks last summer, and had about the same starting performance. Only time I ever really had to crank the car even remotely as long as 30 seconds was when I just put the carbs on and the bowls were bone dry.

He can easily check this by spraying some gas into the carb mouths, and then crank it over. I'm thinking it will fire right up.

I think a more objective test would be to pull the tube between the bowl and the nozzle before he tries to start it and measures the amount of fuel that comes out. If the volume of fuel that comes out is close to what should be in there, then the problem is somewhere else. Spraying a bunch of fuel into the carb intake before you try to start it can mask a whole bunch of other potential root causes. Checking the bowl level would rule out just the bowl level.

So what I'm going to do is count my lucky stars on just how easily and readily my car starts. Maybe I'm the anomaly?

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Hmm. I have brand new fuel pump and all the other accesories. But still my z takes time to start. And i have no-points dizzy too.. + my starter engine runs twice faster than the original. Only thing that i havent renew is the plug wires. But when warm, it starts faster than lightning, which is nice.

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At first I was thinking the ballast resistor might be keeping the spark too low at startup, but on reviewing the wiring diagram, like many cars, the ballast resistor is out of the circuit during startup. Measure voltage at the + on the coil. It should be 6 volts with the key in the on position and 12 volts with the key in start. If its not, I'd look at the ignition switch.

If the startup voltage at the coil is too low, it'll be hard to start when cold, but ok when the car is warm, since 6 volts is the normal running voltage anyway.

Edit: 2 other thoughts, if startup voltage is weak (<12 volts), jumper 12 volts to it from the battery, but dont leave it there too long after the car starts. See what happens. Thought 2, got a spare coil? An old weak coil might produce the same symptom.

Edited by jaltman
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dtalfa---when you start the car from cold, turn it off again immediately so the engine is still cold. Then try to start it again. Does it fire straight away.??

If it starts straight away then your slow starting is a fuel issue.. If it is STILL hard to start then some other issue.

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dtalfa---when you start the car from cold, turn it off again immediately so the engine is still cold. Then try to start it again. Does it fire straight away.??

If it starts straight away then your slow starting is a fuel issue.. If it is STILL hard to start then some other issue.

Yes,..the very second it starts,..you can turn it off and it will start right up.

Naturally,..it needs the choke for a couple of minute but once it starts, it starts the rest of the day within 2 seconds of turning the key.

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Time the cold start up with a real watch. I think the 'couple of minute' is a slight exaggeration. My 73 with new carbs takes a while to fire after sitting 2 weeks or so, haven't really timed it because I know it is a carbed engine. It just seems to take a lot longer because I'm so used to the fuel injected Saturn, split second ignition.

Bonzi Lon

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Yes,..the very second it starts,..you can turn it off and it will start right up.

Naturally,..it needs the choke for a couple of minute but once it starts, it starts the rest of the day within 2 seconds of turning the key.

Problem solved.--- No Problem. ---Lack of fuel in the lines or carbs from sitting.

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Time the cold start up with a real watch. I think the 'couple of minute' is a slight exaggeration. My 73 with new carbs takes a while to fire after sitting 2 weeks or so, haven't really timed it because I know it is a carbed engine. It just seems to take a lot longer because I'm so used to the fuel injected Saturn, split second ignition.

Bonzi Lon

Please read my original post, I never said "a couple of minutes". I said it takes several seconds, maybe close to a minute.

I have owned, driven and restored antique cars since 1978. I'm very familiar with older "non FI" cars. This one takes much longer than normal. I currently have a 1958 MGA with dual SU carbs. It starts within 5 seconds after a long time sitting.

I just went down to the garage to time my start. It's been sitting for 5days since last start. It took 32 seconds of cranking before it started.

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I just went down to the garage to time my start. It's been sitting for 5days since last start. It took 32 seconds of cranking before it started.

Yeah, I consider that excessive. Maybe I'm just blessed with a fast starting car, but that's definitely too long where I come from. Your MGA sounds more like my Z.

So have you checked your float bowl levels yet?

I'm assuming your garage hasn't reeked like gasoline for the past five days...

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  • 5 weeks later...

OK,...here's an update. I have checked most everything on the car, so today I decided to pull the top off the float resevior prior to starting. The float bowl was dry as a bone!!!

I placed the open fuel line inside a cola bottle and turn the ignition over. It took almost 20 seconds of turning before I had fuel squirting into the bottle.

Where did the gas in the bowls go?

There are no signs of leakage under the car.

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