Poor progression & Idle problems with dcnf on Montecarlo

[Guy Croft]

Once warm it Idles smoothly at 1000 rpm and revs freely without any hesitation. But after a while it starts to stumble and die off but if I hold it at 1500 rpm for a few seconds it then goes back to smooth idle for a while again, I suspect the plugs are fouling up? And a bit of a rev cleans them?

On the subject of plugs fouling, especially during stop start traffic, what can be done? Does a different temp plug help? I have BPR6ES in now, would a 5 be better or a 7?

Maybe she's a bit over-rich at idle. Go for Colortune royal blue with hint of orange at outer periphery. Setting up twin carbs is an iteration. Set the balance and idle speed & mixture and check and recheck. Recheck after driving because the manifolding won't warm up properly otherwise. These functions all impact on each other.

Do not go for hotter plugs, the 6 grade are right.

Good compressions and good news about the ignition timing. You had use all worried for a moment!

G

[timinator]

Setting up twin carbs is an iteration. Set the balance and idle speed & mixture and check and recheck. Recheck after driving because the manifolding won't warm up properly otherwise.

This is valuable information. Repeating the wrong procedure will always give bad results. I like to add paint marks to the screw and carb body so there is evidence of where the idle mixture is set. Then you can add a 1/4 turn + or - while you are out on the road driving to respond to real world conditions. Also proof the screw is not moving due to engine vibration. I find it is a better way than trying to remember where I think the screw was set. You can also use an infrared thermometer to read what the exhaust temps are when you are making adjustments. Then by trial and error what temps indicate a good mixture or what balance is between the cylinders. It can give you a way to determine when the engine is to cool to make adjustments.

[davelarcs]

Hi All.

Managed to be home from work early today & the sun has shone long enough to dry the roads, just.

Right, she is running much, much better, a definate improvement, thank you very much for your help so far.

But... While trying to set the Idle mixture, number 2 cyl will only run blue if the air screw is right out (I mean I have had to take it out completely!) & the mixture adjust is right in.

With it like that I have balanced them all the same, and have turned all idle screws (apart from 2 of course) in untill blue, let it settle then turned out slightly to just before orange, and then rechecked the balance.

Took her out on the road, progresses smoothly now, but have only gone around the block, should really tax her before going any further...(does have an mot though). Been a little loathed to spend £100 on tax untill we was getting somewhere :-).

Is the carb u/s? Surely there must be a problem with it. It was like that before, but when I found the throttle plates were passing the progression holes out of sync, I thought I had cured it.

All good fun of course..

Does anyone have a 44 for sale? In case I need one..

Dave.

[Guy Croft]

"While trying to set the Idle mixture, number 2 cyl will only run blue if the air screw is right out (I mean I have had to take it out completely!) & the mixture adjust is right in..."

Air screw on no2 fully out (on cyl 1 it must be fully closed, that is the rule - the barrel sucking more air has the adjuster closed) tends to suggest that the throttle plate on cyl 1 is not closing properly (mis-shapen/worn or not centered properly) thus it is sucking in a lot much air at idle than it should be really.

You need to pull the carb and attend to that. When you do - the mixture screw setting might start to make sense. Nothing I could tell you at this time beyond the above would, sorry! There's no problem BTW with running 60 idle jets where 45s would be adequate, most of the time that is, just means you'd have to screw them in more to lean it out. But there is a limit, according to what the cylinder 'needs' when the airflow thru the carbs is nicely balanced, if they are too big you can end up with no adjustment available to you at all..

If you hold the carb barrel up to the light and examine the fit of both brass throttle plates you might just be lucky and find I am right about this. It can be a real 'job of work' to correct it. I caution folk to strenuously avoid 2nd hand carbs for this reason among a thousand others.

G

[WhizzMan]

You wouldn't be the first to twist a throttle shaft in a double barrel to get the plates to align properly. It takes guts, fine motor control and patience to do it right though. Be careful and check twice if you won't break or bend something else before putting any amount of force on the shaft/mechanism. If the plates or the body itself are damaged, no amount of twisting will cure that. You will have to replace the broken parts for that.

[davelarcs]

I caution folk to strenuously avoid 2nd hand carbs for this reason among a thousand others.

Mmmmm. Indeed, but are DCNF's available new, if so what sort of prices am I looking at?

[Brit01]

pm sent to you Dave. Just to give you an idea. Appear to be difficult to find new.

[Guy Croft]

"if so what sort of prices am I looking at?"

..absolutely no idea tho I can tell you only 40s are aval and if you give up your linkage (balance quadrant assy at carb) you'll never get another.

Look at it this way:
1. U_overhaul - what does it cost you?
2. ..but - do you actually have the expertise to get & do everything?
3. If I overhaul them it could take me a day and half - think what that costs.
4. If the answer to (2) is 'not sure' you buy new even if it costs £700 inc vat - or more.

I mean to overhaul carbs, apart from anything else you have to have an expert working knowledge of every single bit. Every jet, gallery, orifice etc etc. I rarely engage in carb overhauls unless the carbs are historic Italian-made Webers and the client is completely sanguine about costs. I have a pair of 40DCOE overhauled (haha) by some big-name here right now and what a balls-up they have made of the job. There are so many 'sharks' esp via internet offering 'good second-hand' carbs or 'overhauls'. I see this junk from time to time. Much of that seems to come from Germany for some curious reason. My 3 year old could do a better job.

Now - where is Gemma?

GC

[davelarcs]

Hi All & Guy.

Have taxed the Monte on Friday, took her for a good 2hr drive today, still a little 'spitty' but after about 10 miles things started to change and after a little while she started to run more & more smoothly.

Now running great, better than ever, I guess a good run has done the engine & carbs a world of good. And also was reasonable on MPG. Win Win.

Once again a very big thanks to Guy & others who helped me with this.

[WhizzMan]

Good to hear you have your car on the road again and are enjoying it.

Did you put new fuel in? Modern fuels aren't mixed primarily for carburetor use and tend to go "stale" rather quick. The combination will make it hard for carbed engines to run proper on older fuel. I've seen examples of cars that ran like a bag of nails, wouldn't allow themselves to be properly ignition timed and after putting new fuel in, were purring like a kitten and gave no trouble whatsoever.

[davelarcs]

Thanks Whizzman, the fuel was "fresh" but from a supermarket station, before I went for a run, I took it to a "proper" petrol station to fill up, that probably helped things.

[WhizzMan]

I have no idea what differences supermarket station fuels have where you live. In the Netherlands, there are just too few distribution points and refineries at a competitive distance to the filling stations to have a business case for making "cheap" fuel. We have the major brands holding a very significant part of the market here and in general, the automated unattended 24h stations are cheapest but just "labels" owned by major brands. This gives the "supermarket stations" not a lot of choice where to get their fuels and they tend to have the same fuel from the same refineries, just not with brand labels on them. They do tend to buy from whoever offers them fuel the cheapest, but individual differences between the major brands are negligible here. Most of what you can get here is "euro 95" which is unleaded 95RON with up to 8 (or is it 10?) percent bio fuel (ethanol usually) percent mixed in. The premium brand stations sometimes carry "plus" fuel that is usually 97 or 98RON and promises cleaner engines, less fuel consumption and has a lot of happy people in their advertisements. My daily drive is converted to run on liquid injected LPG and has the ECU remapped for RON98. Because the original fuel system needs to function properly for startup and cold running, I put in RON98 so the ECU doesn't get confused and retards ignition advance during those circumstances. My non daily cars are either mapped for 98RON or just get 95RON put in them. Quality is good everywhere and there are not a lot of differences.

Supermarket fuel gets a lot of bad publicity, but often is the exact same fuel you buy at the main brand stations. This may be different where you live, but often supermarkets use the fuel as an incentive to get shoppers inside their supermarket and they actually make nothing or very little on the fuel. A lot of the quality actually depends on how old or stale the fuel is you are buying and how clean the tanks and pumps are kept. If you really want to know what quality fuel you are getting, it may be worth finding out what company delivers the fuel, what compartment in the truck they pump from and what other stations get fuel from the same compartment. You'd be surprised how many stations of different brands sometimes get the exact same fuel delivered, depending on where you live.