Unhappy SC fuelling/timing

R

restojon

New Member
I have been suffering with what I call a "compound problem" on my 71 2000 SC. Just so we're all clear my car has a Pertronix fitted and is on standard carburation and compression. I run with std unleaded fuel with Castrol Valvemaster Plus at the recommended dosage.

Basically I've been chasing my tail trying to get the car to run correctly throughout the rev range, I can get it to idle nice and smooth but it will be flat in power through the revs OR I can get a spluttery lumpy idle which runs nicely through the revs.

From there I tried to play with the timing which with more advance added more go through the revs but pinks under load or if I back it off to stop the pinking it goes flat again in the power.

It also occasionally sounds like it's on 3 and coupled with the horrid power delivery that could very well be the case, richen it up and this seems to go away but then after a while the effects of running rich come into play with misfiring etc.

I've then messed with the timing with the fuelling as described above which helps temporarily but after a time it will either go flat in the power department or will go all lumpy low down.

Prior to all this I also "centralised" the dizzy on 4deg so the timing twiddler had an equal amount of travel each way but strangely prior to this centralising the twiddler had been fully advanced and the dizzy then set to 4deg it ran and accelerated much happier :?: Does the advance curve change with the twiddler?

maybe you can see how I've been going in circles here?

Can anyone throw me a line here please? My sanity and I would be most appreciative :D

thanks
 
That's an excellent description of symptoms there Jon.

It seems pretty clear that there are one of two faults going on. Either the head is very badly coked up - hence the pinking under load with a higher degree of advance. Or there isn't enough advance available from the distributor.

The first is unlikely with unleaded petrol although possible - and it's a lot of work to discover whether it is or not - cylinder head off!

So lets start with investigating the distributor. It has two ways of delivering advance. Vaccum and centrifugal. So start with the vacuum. Take the cap of and disconnect the pipe going to the vacuum unit - the conical object that sticks out of the side of the distributor - at the carn end. Have a good strong suck on the end of the pipe and you should be able to see the baseplate of the distributor, complete with your Pertronix, rotate a little and then return. If not you have a defective vacuum unit. Replace and all will be well.

To check the centrifugal advance retard, grip the rotor arm and see if you can rotate it a little in the distributor. Does it spring back easily to the rest position? If it is seized, it will have seized at fully advanced and you will have compensated by having to set the timing much more retarded than normal. If it is seized then strip the baseplate out of the distributor and clean everything up thereunder. It's just some little bob weights on pivots restrained by springs, so very straightforward.

My best guess? A defective vacuum advance unit.

Chris
 
I agree with Chris that you should check the vacuum advance.

How old is your distributor? Has it ever been rebuilt? How many miles has it done? Over time the springs on the centrifugal advance can lose their tension and their ability to return the weights to the non advance position. Have you oiled the distributor recently? Put a drop of oil under the rotor button. This will help the centrifugal advance work better.

There are timing lights which can be used to measure amount of vacuum advance and centrifugal advance that the distributor has. This could be used to diagnose. Have you considered getting you distributor rebuilt? I had mine done a few years ago by Advanced Distributors in Minnesota.

James.
 
Ok, thanks for the replies people. I will answer to your advice soon but I have a little progress report,

Last night in bed I had an epiphany moment, I wondered if the timing twiddler had an effect on max advance dependent on where you set it rather than just an overall effect.
I cleaned and lubed the dizzy then started the car this morning at the previous settings. I made a visual note of the advance at idle (off the advance scale on pulley) and at approx 2000rpm (without Vac). I then stopped it, loosened the dizzy clamp and then twiddled the twiddler almost to max advance, started the car and then reset the timing by turning the dizzy to previous visual settings. At idle and bringing up the revs the advance behaved as before but when I revved to 2000rpm the max advance had reduced by quite an amount. I set it to 4deg BTDC and idle didn't sound as smooth at the exhaust end but I thought it was a good place to start from, I experimented with 2 deg BTDC which was very rough and then sent it to 6deg BTDC which it seemed to like but when revved the advance seemed to be going a bit on the far side so I settled for 4deg BTDC. I locked it off and went for a drive.
Now things got interesting at this point, I live in a very rural area with single track lanes for miles around which are a favourite with local dogwalkers amongst others. I was driving up one of these single lanes passing two of the aforementioned dogwalkers when my little 2000 Herbie'd and let out the most enormous backfire accompanied by a cloud of brown soot which filled my rear window and covered the dogwalkers in carbon-y soot. I was absolutely mortified :oops: The engine stopped dead and on further inspection had blown off the damper cap from the carb and blown off the intake trumpet into the air filter housing. These dog walkers were less than impressed as you can imagine and questioned the roadworthiness of the vehicle using swear words a Royal Navy stoker would've blushed at.

I did some running repairs on the blown off bits and drove the car to the nearest turning point and came home, on the way home the car behaved so much better, virtually no pinking unless I really lugged it, quite reasonable spread of power across the revs only going a smidge flat up the top end of the range, a smooth-ish idle but still very spluttery at the exhaust with a bit of vibration in the cabin and occasional episodes of going onto 3 pots. In relation to the 3 potting I richened it up a half flat which seemed to help.

I removed the air filter which has seen better days if I'm honest and this has cleaned up the top end rev range but I decided not to go any further without an air filter. Once I have a new one I will get going again on the diagnosis but I think we're going in the right direction. I have printed out a small degree disc which I will try to attach to the pulley with a fabbed up pointer to get an idea of exact advance figures and so on as I would like to pursue this theory of the max advance being affected by the positioning of the twiddler. I may be wrong but it seems to do what I think it's doing.

Lastly, in answer to the above suggestions I checked the mechanical advance and it was working, I checked the vacuum by holding the timing light on the pulley and sucking on the tube and it did advance. As I mentioned I did give it a clean up and some lube so in that sense it works ok but the story will continue when I have an airfilter.
 
All the vernier does is allow you to fine tune the timing exactly. It doesn't have any effect on the amount of advance. It gets round the problem that can happen of the timing altering as the pinch bolt on the distributor is tightened. It should be set to the middle of travel before setting the timing on the clamp, and then altering the vernier if necessary to get it spot on again.
 
I always thought the "twiddler" on the dizzy was just a micro-adjuster for advance/retard rather than a means of controlling the amount or rate of advance increase as rpm is increased. TBH, I have always just set my timing by turning the dizzy as this is what I was used to doing on other cars. Next time I'm under the bonnet I'll take a closer look at it.

As for your unintended smoke victims, maybe explaining that a classic car is actually greener than a Toyota Pious would have helped :) .
 
Thanks for your replies, obviously my findings are "provisional" in the sense that I was not able to accurately measure advance figures but it does point to the fact that something is not right with my dizzy. :idea: The advance certainly appeared to change and certain characteristics as I described appeared to change in relation to my adjustments, it could be a case of coincidence with the carbon explosion and everything sorting itself out though.

One thing though, the advance weight springs do look really flimsy.

Also another thing, what should the advance mech be stamped with? Mine says 13.
 
:LOL: :LOL: :LOL: :LOL: :LOL: :LOL:

I'm afraid I have very little sympathy with the luddite "countryside set", so I really enjoyed your little incident!

So it sounds like your distributor is now working as intended. I'd put money on your attentions having lubricated and/or freed up various aspects of the mechanism, so it could conceivably have been at the root of the problem all along.

The other aspects of the incident seem to demonstrate a need for a full scale good old fashioned service. I'd simply do the lot, starting with the ignition system and working right the way through.

So that's new points (keep the existing condensor unless you know it to be faulty - there are too many duff new one's around out there. If you have got a back in the day old fashioned Lucas one lurking at the bottom of a tool box, fit that instead), new rotor arm, new distributor cap, new leads and new plugs. I recommend buying all bar the plugs from SimonBBC. DON'T use your local motor factor! They tend to stock Chinese imitations.

Set up the ignition as per the book. No experimentation until after you've sorted the carb and valve gaps.

Then, as you say, the new air filter. Have you got an HS carb or a HIF? If the latter I'd recommend buying a full overhaul set and changing all the O rings of which there are legion.

Check the valve clearances and see if any are tight. That is known to affect the slow running and is a good plan anyway.

Now with a good ignition system, set the carb up. It's easy peasy on an SC, you just need a colourtune and it should take no more than five minutes.

At that point we can now think about acquiring a new set of symptoms to talk about! But hopefully your engine should be transformed :wink:

Chris
 
Thanks again for the helpful replies, if I'm honest I very nearly giggled at the minstrel-like soot covered dog walkers :twisted:

I think the dizzy has improved, however normally I would try to root out the problem and fix it but in this case I am just going to go at this full tilt and replace everything. I did the leads today as I had some on the shelf and it has marginally improved matters, I am going to replace the fuel pump diaphragm etc, it's just had new plugs so they should be ok with a clean but there was two things I wanted to mention hence the reason for this post.

Firstly, I have heard some hissing from various areas in the engine bay. Managed to locate one possibly two of them but there are more, they come and go. One is the take off for the servo from the manifold, Jubilee clip has fubar'd itself so when it gets warm it starts to leak. Carb flange has started to leak too and there is a leak into the float bowl (HS carb) where the lid goes on. The one(s) I can't find seem to come from near either the reserve tap or near oil filter area.

I believe the reason for this is I have just fitted a new thermostat and it is now running much warmer than it has done previously it's now around the 88/90deg mark and the underbonnet temps are much higher causing things to expand quite nicely.

Now the next thing I stumbled upon, elsewhere in another post of yours Chris York you mentioned colour tune.
Setting up with a colourtune is extremely easy - and skyblue is indeed rather weak - and it will get weaker with a little more engine temperature. With the colourtune in, set the engine revs to about 1,000 - a fast tickover - and then get fiddling with the mixture screw. Start with it at the rich end - orange - and then turn it until the colour goes sky blue. Then come back the other way until you can just see the first flecks of orange in the sky blue. Should take no more than 5 minutes.]
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Thing is I originally come from the motorcycle trade and have used colour tune for bikes and presumed it was the same procedure for cars but it appears not, on bikes you aim for a dark bunsen blue flame. I have based all of my settings on this :roll: :roll: :roll: So it's back to the drawing board when parts are with me, armed with this new knowledge I intend to beat this problem and get the old lady running lovely again.

Once again thanks to everyone for their advice, I always appreciate it. :mrgreen:
 
Another little tip here - if you suspect you have an air leak on the engine side of the carb - ie air being sucked into the engine - a good way to detect this is to spray a puddle of WD40 or similar around the area in question and watch it being sucked into the leak (or not). Certainly sounds like it would be a good idea to renew the servo vacuum hose and have the carb off and re-seal the phenolic resin spacer to the inlet manifold. If there are leaks in these places, they will have a dramatic effect on slow running and you won't be able to set the mixture at all.

Chris
 
Just a quick update, I've fitted the air filter, HT leads, dizzy cap and arm, sorted the air leaks (best as I can hear) and made sure the choke is coming off fully and given the carb a good check over. I have not fitted the fuel pump rebuild kit yet.
I got a rev counter, strobe and colourtune and set to it.

Idling at 800-850 (lumpy running lower than that) I set the ignition to 4deg btdc and did the colourtuning to show the first flecks of orange. Got the idle back to 800-850 and kept at it until it settled down. I kept giving it a clear out every minute or two also.

I went to the exhaust and it still sounded spluttery although not as bad, I experimented with timing and more advance settles the exhaust sound down to a nice 4 cylinder purr. Bringing it back to 2-3 deg btdc made it more spluttery. I reset it to 4 deg btdc and drove it up the road. idle to 1/4 throttle is still fluffy and doesn't settle onto 4 until you bring the revs up. Uphill is the same but if you are not loading the engine up for instance accelerating on a slight downward incline it's happy to go on 4 pots from idle onwards. It has stopped pinking under load though unless you really lug it.

I decided to do a compression test, I got 150psi on number 1 and 155psi on all the others, I had noticed it's breathing heavily into the crankcase so thought it worth a look.

I am going to fit the fuel pump kit tomorrow and see how we go with that, one thing though what plug gaps are people using with NGK plugs?

If this doesn't cure it I intend to get some points and a condensor and fit a degree disc and pointer to the pulley and compare advance figures and characteristics between my Pertronix and good old fashioned points and condensor. It just seems to me the ignition system advances a hell of a lot so you either are timing it for idle and 1/3rd throttle but losing the top end or, timing it for 2/3rds onwards throttle and having awful idling.

So there we are, progress so far. Is anything I'm saying screaming something at the more experienced P6 owners?

All suggestions welcomed as ever, thanks.
 
Time to check the valve clearances me-thinks. It's only when you have to adjust them it gets really difficult.

Chris
 
Thanks for the reply. I'll do that early next week Chris, I do know one clearance is slightly baggy on 4 exhaust. I did a head and valves change late last year, the head gasket I used was 0.5mm thicker than std (no I haven't worked out the altered C.R). I still have my distance pieces that I machined up for doing the cam removal for the clearances. I've also been given a small selection of shims so hopefully I can sort that out.

I'm going to do the fuel pump today and recheck the plug gaps and possibly experiment with different gaps as in my bike experience I've found NGK's like a bigger gap than some other plugs. Who knows it may work it may not but for a few minutes work it's worth a go.

I'm going to try to find my old points and condensor and see if they still work enough to do this test on max advance figures too in the coming days, the Pertronix has it's own built in advance but I do not know exact figures as yet.

Thanks to everyone for their help. My hairline salutes you :mrgreen:
 
DaveHerns said:
Wide valve clearances won't be the problem. Tight ones will
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That's what I was thinking too. My vlave gaps were all way below spec and this contributed to poor idling and less than smooth power delivery when accelerating. Going from what I've learned on the forum, it's usually exhaust clearances being below spec. that causes problems.

Like Chris said, I would carefully check valve clearances (with engine stone cold) before doing anything else. It's very easy and quick to check them.
 
The valve clearances will be checked early next week. I've got a lot on in the next few days so it has to wait a bit however there has been some progress today though.

I opened up the gaps in the plugs to .028" and it has made a miracle sized difference to it. The book says .025" which actually comes out at 0.63mm, not the 0.7mm stated in the Rover manual. 0.7 comes up just shy of .028"

Are you still with me :?:

The car is idling better although still not completely right, the three cylinder thing has all but disappeared (at the moment). I cleaned the plugs which were a grey colour on the electrode and insulator and sooty black around the outer part of the plug. If I remember correctly that indicates rich at idle and roughly correct mixture at higher revs (???)

Still not right but it's getting closer, thanks for the help friends. :mrgreen: :mrgreen: :mrgreen:
 
Another progress report.

I've been doing bits and pieces as time and weather allows. I stripped the fuel pump and found the diaphragm was resembling a Belgian waffle in places. I replaced it and did the non return valves whilst I was in there. When refitted the fun started, I found the extra pressure generated by the new fuel pump parts showed up a leak into the float bowl where the press fitted brass union into the lid is fitted, this must have been sucking in air but not showing as a fuel leak due to the lack of fuel pressure. I sealed this up and re colourtuned it and checked the timing. Car was noticeably happier and whilst on test behaved much much better than before. I still intend to do the clearances as I can tell it is slightly heavy and uneven on the pick up but it's 9/10ths of the way there now.
 
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