Lancia Montecarlo Tuning Issue

Road-race engines and ancillaries - general discussion
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LanciaNut69
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Joined: June 22nd, 2011, 10:45 am
Location: Newbury, UK

Lancia Montecarlo Tuning Issue

Post by LanciaNut69 »

Chaps and chappesses,

I hope someone out there can help or at least give me some other options to pursue. The patient is a Series 2 Montecarlo. 2 Litre 8 valve engine, on standard 34 DATR carb and manifold. Exhaust manifold is standard, as is the exhaust system with the exception of the rear box. Cams are standard. Jetting in carb is as per the tech manual.
Compression test when engine to full temp 1 - 4 as follows - 157, 153, 155, 154 PSI
Tappet clearances all within tolerance
Valve timing correct
Ignition timing timed off No.4 @ 10 BTDC

Plugs - NGK BPR6ES - New - 0.8mm Gaps
Leads - new
distributor cap - new
Hall sensor - new
Ignition Amplifier - new
Coil - original, but appears to be ok.
Fuel pump (mechanical) - new
Fuel supply and return hoses - with inline filter - new

Vacuum port on inlet manifold for heater controls temporarily plugged as hose is showing signs of age

Car was delivered to me with all of the above in place - with the exception of new fuel lines and filter, and ignition timing - as a non-runner. After checking and resetting timing, the car started but ran extremely roughly and lots of smoke from the exhaust (rich) No adjustment to the idle mixture, cleaning and blowing jets and emulsion tubes made any difference, and tickover was not less than 1100 rpm.

Noted that fuel was running into the chokes, so needle valve was checked, along with float level and all appeared ok. A fuel pressure regulator was fitted, which solved the problem of excess fuel, and cleaned jets allowed some adjustment to be made, but tickover remained high, albeit at a slightly lower level of 1000 rpm.

Revs are gradually increasing and falling over a period of 10 - 20 seconds. Gaskets between manifold and spacer, and spacer and carb have been renewed. Spray of carb cleaner around joints has no immediate effect of increasing revs, but I think there must be a leak somewhere.

A pair of colourtunes in No 1 and No 3 showed a proper mixture and yet the plugs were sooty on removal.

Does anyone have any ideas or pointers? Any help gratefully received!

Darren
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Urbancamo
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Re: Lancia Montecarlo Tuning Issue

Post by Urbancamo »

Hi Darren

First off all very clear explanation, leaves very little room for questions. All "what is wrong in the engine"-topics should be made just like this.

Usually erratic idle like you described is caused either by vacuum leak or excess fuel. So we must narrow down the fault, and sooty plugs will tell me that excess fuel is going in to engine. If engine had major vacuum leak somewhere, it usually would run roughly, but would not run rich as these are not fuel injected engines.
I once fixed a fuel injected car wich had 5 cracks in the inlet manifold gasket and it ran like it had only 3 cylinders. At the same time computer was dumping extra fuel in the engine as best it could because lambda sensor obviously saw that engine is running really lean. New gasket and it ran like new again.

So my questions and suggestions are following:

- I bet if you try to adjust idle mixture screw, nothing really happens? What happens if you try to close that completely...does the engine still run or not? If it runs somehow with screw closed, it will draw fuel somewhere else than from idle circuit. It should shut off when idle mixture screw is closed.

- Even the needle valve looks good, it still might not capable of doing what is supposed to do. It is a precision made component wich will wear out upon time. New fresh fuel pump even with pressure regulator might be too much for used needle valve.
You can try remove the fuel line from the carb, track it down to some container and start a car. Does nothing really change? It should run 15-30 seconds just fine without fuel supply so this might be enough to see if nothing really changes.

- Does the carburettor have plastic or brass float? If it's brass, it might have tiny leak somewhere, usually in the soldered joint where it attaches in to carburettor cover and fullcrum pin.
If the float weighs more than it should be no matter what the material is, it doesn't close the needle valve like it should be. Even 1 gram or even less excess weight might cause this.

- Check that float is moves freely without any sticking and it's straight, not twisted. It also shouldn't have excess play in the fullcrum pin area. Some carburettors have so narrow float bowls that slight misalignments might cause float to stick.

- Check that secondary choke flap is not stuck slightly open. If the secondary flows a bit more than it needs in idle, it starts to draw fuel from secondary auxiliary venturi and end result is terrible, uneven idle. I've seen this in the past. Car ran even you closed the idle mixture swrew completely.

And oh, my own mistake in the past; I had customers car in my shop wich had a new Weber DGV carb and I forgot to tighten up the primary idle jet holder. It was slightly open.
Guess how many hours I spent trying to find a fault? It didn't make any sense why car had really bad idle after slight re-jetting!!
Well we have a phrase in my country wich says "If you don't do anything, nothing will ever happen"

T
Last edited by Urbancamo on May 21st, 2013, 1:25 am, edited 1 time in total.
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Guy Croft
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Re: Lancia Montecarlo Tuning Issue

Post by Guy Croft »

Good report!

The compressions are pretty low.

If the mixture's right but the plugs are sooting up - the bore/ring combo is worn out - she's oiling up. And yes, that would give a very unstable idle.

Ger her properly hot by driving (if at all possible) and redo the comp test dry and then after squirting a few tsp of oil into each bore in turn and report please.

G
Guy Croft, owner
LanciaNut69
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Joined: June 22nd, 2011, 10:45 am
Location: Newbury, UK

Re: Lancia Montecarlo Tuning Issue

Post by LanciaNut69 »

Hi Urbancamo,

Thank you very much for coming back to me and giving me some pointers. Apologies for the delay - I spent the weekend at Mallory Park for the PPC in the Park event.

To come back to you on the points you raised

The idle mixture screw does not currently do much. Screwing it (carefully) to the stop does not result in the engine stalling. It should be a new one as part of the overhaul kit. Do you mean removing the fuel supply line while the car is running? I could do that by clamping the fuel hose. I'll give it a try and report.

Carb has a plastic float - again new I believe - I will recheck everything again though.

I will also check the secondary choke - thanks for that! I did check and both jets and emulsion tubes were properly fitted - I have made that mistake in the past!

I'll report back as soon as I have some results.

Thanks

Darren
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LanciaNut69
Posts: 61
Joined: June 22nd, 2011, 10:45 am
Location: Newbury, UK

Re: Lancia Montecarlo Tuning Issue

Post by LanciaNut69 »

Guy Croft wrote:Good report!

The compressions are pretty low.

If the mixture's right but the plugs are sooting up - the bore/ring combo is worn out - she's oiling up. And yes, that would give a very unstable idle.

Ger her properly hot by driving (if at all possible) and redo the comp test dry and then after squirting a few tsp of oil into each bore in turn and report please.

G
Hi Guy,

Thank you for that. I thought more info was better than less. I will certainly do as you say and report back the findings as soon as I have them.

thank you

Darren
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LanciaNut69
Posts: 61
Joined: June 22nd, 2011, 10:45 am
Location: Newbury, UK

Re: Lancia Montecarlo Tuning Issue

Post by LanciaNut69 »

Next update - slightly delayed, but better late than never.

Compression test redone at full temps, plugs black and sooty, black smoke evident on revving.

Dry test

1 - 162
2 - 164
3 - 171
4 - 169

Wet Test - 2 tsp oil in bore prior to test

1 - 205
2 - 197
3 - 202
4 - 199

I think this confirms the given diagnosis of worn rings then.

Urbancamo, carb checked over again and everything as it should be.

Look forward to any comments.

Darren
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Guy Croft
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Re: Lancia Montecarlo Tuning Issue

Post by Guy Croft »

only 3 causes I can think of really for an engine 'hunting' - speed going up and down erratically:

1. Distributor or other ignition fault
2. Flooding
3. plugs wetting up due to worn rings - as discussed


G
Guy Croft, owner
LanciaNut69
Posts: 61
Joined: June 22nd, 2011, 10:45 am
Location: Newbury, UK

Re: Lancia Montecarlo Tuning Issue

Post by LanciaNut69 »

Thanks again Guy,

Engine is now out and tomorrow another will be fitted. It will be stripped and rebuilt at some point, but for now it will go to the back of the workshop,

Darren
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