Diagnosing difficulty starting and rough cold running

[ARD]

Hi all,

Looking to spend some time with my new 1969 AS to diagnose the difficulty starting and rough running whilst cold.

What would you check and in what order? The fact it runs well once warm to me rules out the 'basics' but also maybe not - so happy to check everything as then we can properly rule things out.

I've only owned the car a few weeks so have not yet really checked anything. In theory the car was given a tune as part of its pre-sale service, although of course I wasn't there and don't know what it was like before that - but that should rule out basic tuning problems.

History:
- 1969 AS
- Calafornian import to the UK in the 90s
- Car is apparently mechanically original but I have not yet verified this
- Car has hardly been used over last 10 years, probably just the 50mile round trip to the MOT test centre, total ~1,500 miles since 2006. It does seem to have been stored well somewhere dry though as generally condition is good and doesn't look like it was left 'unloved'.
- Had a pre-sale service by the dealer who are well-respected Fiat specialist, included oil change, check/change of cam belt/bearings, tune, new tyres etc. Didn't get a good sense of exactly what was done (my fault for not asking detailed enough questions and needing to pick up on a specific day when the boss wasn't there!)
- We've now done 500 miles since we bought her, probably the most she's done in a month in 15 years! A fair bit of motorway cruising but also some runs in the countryside.

Firstly to rule out more general problems:
- Once warm the engine seems to run perfectly - though of course I have nothing to compare it to other than my previous much smaller 1969 Austin Healey Sprite Mk IV with an A Series engine. Therefore at the moment I am leaving the car to warm up for a good 5 mins before heading off on a journey.
- Throttle response seems good, again little to compare it to
- There's no noticeable smoke
- Oil looks clean but was changed as part of that pre-sale service so has only done ~500miles since
- Car restarts fine once warm, even if it's 'cooled off' since previously running for a few hours. It's just that first time after a couple of days gap.

The symptoms:
- If I don't manage to get it just right first or second time she will not start from cold. As I say, if I luck out with the right choke setting and catch the engine with a touch of throttle at the right moment then she will start from cold. This might mean there is a knack to starting her with I am getting wrong? Have tried to follow the general pump throttle pedal twice, put on manual choke, turn starter and wait to start, if needed a little throttle once half started?
- She will then start with a quick spray of 'easy start' - this is obviously not a long term solution but this is my only proper car so when we plan to take it somewhere we need it! Also, once warm will re-start happily so I don't feel too bad doing this as a temporary measure whilst I fully diagnose the problem.
- The choke doesn't seem to do anything helpful when running. I.e. doesn't increase revs or run smoother, if anything the running is slightly worse with the choke on. This might be how it works - I'm used to an A Series with SU carbs where the choke raises the idle considerably.
- The idle is very rough whilst cold and will gradually lose revs, down to ~500rpm
- The hand throttle has been disconnected so have to sit and manually add 'foot throttle' to keep revs up until warm enough
- Once driving away if still cold (i.e. in a hurry!) then the engine seems to lack power and feels like might stall under acceleration although I don't think it actually does stall - seems to have bigger gaps in torque so need a decent amount of revs to accelerate uphill for example.
- The engine does sound a bit tappety/clackety and there is a slightly high pitched whiring which seems to only come in at slightly raised revs and is quiet enough that it's

So - I want to go and start diagnosing and then fixing the problem. Where would you start and what few things would you check?

[18Fiatsandcounting]

The engine sounds like it's running too lean when it's cold, and the first place I would start is with the choke on the carburetor. With the engine off and the air cleaner top lid removed, verify that the butterfly valves (plates) in the top of both barrels of the carburetor are fully closed when you pull the choke knob all the way out. If they aren't, that could be your problem.

Then start the engine with the choke still pulled all the way out, and these same butterfly choke plates should then open slightly (perhaps one-third of the way from fully closed to fully open) when the engine starts running. This is the "choke unloader" function and acts to make sure the engine doesn't continue to run too rich when it does start. You might need an assistant to watch the choke plates while you start the car.

On my '69 spider, in cold climates, I have to pull the manual choke knob out and give a few pumps to the gas pedal before trying to start. These few pumps shoot a bit of fuel from the accelerator pump into the carburetor venturis, helping it to start. In warmer climates (or above about 50 oF in general), you may not need to do this. It sounds like your accelerator pump is indeed working, and this can be easily checked by looking into the barrel of the carburetor (engine off) and operating the throttle linkage. You should see a stream of fuel shoot from the small jet at the center point of the two barrels and the float bowl reservoir.

Another possibility is that the engine is partially flooded, and it takes a while to clear out the excess fuel before it runs like it should (although it should clear within 10s of seconds and not 5 minutes). To check this, try starting the car with the choke fully disengaged and the gas pedal all the way to the floor and hold it there while you crank the engine. See if it behaves any differently.

EDIT with another thought: Old gas can make an engine hard to start and rough running when cold. I don't know the exact chemistry behind this, but my guess is that the more volatile components of gasoline (the ones that ignite easier) have evaporated away, leaving a gas mixture that is hard to start. The solution here is a new tank of gas.

Try these suggestions and let us know what you find.

-Bryan

[ARD]

Thank you for the suggestions! Unfortunately I went down to the car this weekend and started running through the steps advised and when it got to turning over the engine the battery was dead! Looks like it's at least 5 years old, so I will probably replace. This could also have been making it difficult to start if it wasn't quite giving peak power to the starter motor, but I suspect this is not the main reason, merely exacerbating it.

Managed to at least test a couple of things:
- butterfly valves in the top of both barrels of the carburetor are indeed fully closed with the choke on full
- they seemed to open slightly when the engine first turned over although wasn't able to test properly as the battery was clearly dying - the first time we tried it turned over a few times but very slowly, second time we tried it hardly turned etc
- I think the accelerator pump was working, but slightly hard to judge, I'll have another look next time.

I had also wondered about flooding but as you say would expect this to clear reasonably quickly whereas I have tried leaving a good 5-10 mins between tries and it's not helped.

I don't think it's old fuel as I've now put 2 or 3 tanks of new fuel in since I bought the car. I had wondered about cleaning out the tank and will probably do that when I have time. Also when I say cold, I mean the engine relative to full running temp, the ambient temp is still probably 20C/70F.

Thanks again for your helpful suggestions!

[18Fiatsandcounting]

You're welcome, and I agree it's probably not bad gas at this point. It does sound like your chokes valves are working probably, and you can always experiment later with pushing the choke back in partway, trying to find the point at which is starts the best. I've found that sometimes my engine starts best with the choke only halfway, but of course it all depends on how long it's been since it last ran, what the ambient temperature is, etc. During the summer, I don't need the choke at all, and a few pumps with the accelerator pump usually does the trick.

Fiat engines like a good healthy battery (and thus a good cranking speed) to start the engines, so try a new battery and let's see where that gets you.

-Bryan

[ARD]

Although the new battery definitely turns over the engine a bit more quickly it hasn’t made a difference - and now I can’t get her to start at all

Checked the ignition as well with a spark plug light bulb tester thing and all looks good.

[18Fiatsandcounting]

Well, the good news is that with a new battery, you've eliminated one possibility. The not-so-good news is that there are many possible reasons why the engine isn't starting...

But, let's take a look. If I run across a car that turns over fine but won't start, here is the list of things I check, in rough order of which come first (#1 is first).

1. I make sure the engine isn't flooded by holding the gas pedal to the floor (not pumping, just holding wide open) and turn over the starter motor about 5 or 10 seconds. Let it "rest" for a minute and try again. This helps remove excess gas from the cylinders and intake.
2. I remove the air filter cover and look down the throat of the carburetor with a flashlight, while opening the throttle by hand. Each time you open the throttle, you should see a squirt of fuel from the accelerator pump jet. If you see this squirt, then you have verified that the carburetor has fuel in the float bowl.
3. I remove a sparkplug, maybe two, and verify that they are not wet with fuel (you can tell by the smell) and are not coated with crud, oil, carbon buildup, etc. If motivated, I check all 4 sparkplugs. Check to make sure all plug wires are properly connected while you're on this step.
4. I rotate the engine by hand until the two small holes in the camshaft pulleys are lined up with the raised marks on their respective camshaft housings. When this is the case, I verify that the #1 piston is at TDC by inserting a long screwdriver into the #1 sparkplug hole and resting it on the top of the piston. When you turn the crankshaft (by hand) in either direction, the screwdriver should start to descend. This is almost imperceptible, but you can see it with a good eye. Be careful not to drop anything in the sparkplug hole.
5. With the #1 cylinder at TDC and the camshaft pulleys lined up, the engine should be timed to be firing on the #4 cylinder. So, I note the position of the #4 spark plug wire connector on the distributor cap, remove the distributor cap, and then check that the rotor is pointing towards the #4 spark plug wire if the distributor cap were installed (just try to gauge this as best you can). While you're here, check for anything obvious that is amiss with the rotor or inside of the cap.

If everything above checks out but the engine still won't start, there's more work to do.

-Bryan

[ARD]

Thanks Bryan, really appreciate your comprehensive response - looks a good check list to me! I’ll hopefully have a go through that tomorrow and let you know.
Andrew

[18Fiatsandcounting]

No problem, Andrew. Since it's going to be over 100 where I am for a few days, better to try to "fix" Fiats online in the AC than in my hot and stuffy garage!

-Bryan

[nicks]

Hi ARD,
I was wondering if you managed to solve your starting issues ? Would be interested to know what you reckon the issue was if its sorted.
I have a red 1972 BS1 1608cc with twin Weber 40IDF's and also have start problems. It always needs 5 or 6 attempts but eventually goes, and runs well. This is no different on cold days or warm summer and my current thinking is to check that the choke butterfly valves and the fuel diaphragm pumps are working. I imported mine from Switzerland in 2018 and so still early in my FIAT ownership but absolutely love it. What colour's yours ?

Do you live in the UK by the way , as you mention your car is an import ? I live in Hampshire, and went to the 2018 and 2019 Goodwood Revivals which are always brilliant and an Italian Car meet in Alton in April, may go to the Brooklands Italian car day next year or maybe Brands Hatch. Be good to meet up sometime if you're not too far away.

Best regards
Nick

[SteinOnkel]

From what I know about IDFs, DCOEs etc is that the newer versions don't have a choke mechanism. So they always start like ass. You have to pump the gas to get it to start and then keep it alive with throttle while the engine warms up. If that's not the case and it runs on its own that might seem nice, but it means you are running too rich.

Another reason not to have this outdated technology.

My car (Weber 34ADF) starts hot or cold the first time, every time. It's uncanny, you can't even hear the starter.

Cheers
Steiny