Timing Question

[citybreeze]

Hi,  apologies if this is a bit of a silly question, but I've never checked/adjusted the timing before.

On my mk3 Spitfire, I do not have a graduated timing marker as described in the workshop manual.  I have a single point (white tipped piece in image) to work from.  

So is this marking TDC? And I've got to guesstimate the angle of advance from that,  Or is it marking the correct timing setting (8 degrees BTDC I believe) so i just match the markings together?

Also, I tried to check if my vacuum unit was working properly, which it is off the car, but the distributor base plate sticks (does not always move freely back or forth) when tested on the car.  I have added lubrication in the indicated places, but this has not helped. 

Currently the car is running ok, but the top speed seems to be about 60mph.  I wanted to make sure the timing is spot on before moving onto resetting and balancing the carbs (again) and investigating other possible causes of the lack of power.

Any advice greatly recieved!

[Pete Lewis]

its one or triumphs worst markers   there is a small notch  in the rim of the crank pulley  when aligned its TDC

i would set the point gap , and turn the dizzy to get the best running at around 1200rpm  ,  then back of the dizzy to reduce the revs a little   try it if it pinks drop it back till it stops

as for the vac not moving /sticking the   contact  plate have a look at the points and condenser fixing screws if too long they can on many jam the moving against the base 

Pete

[Clive]

Pete has got it in one. Again.

Best bet is those screws in the dizzy locking it up. 

Top speed should be about enough to make the plod really upset. As in 100...

[DanMi]

the original idea with the early cars was to fully retard the Vernier adjuster small wheel on vacuum unit) on the distributer set the timing to TDC when the pointer aligns with the mark and then adjust the Vernier 1 click  = 1degree but modern petrol is different so timing may need to be different from factory settings.

[citybreeze]

I'll check those screws, I fitted a new condenser recently, so could well be that.

So just to check I'm following right;  is it best to set the timing slightly more advanced (say roughly 10 degrees BTDC) and then work it backwards from there to find the point of smooth running, then tweak it back just a little bit more so that it revs around 800rpm-ish?

Also, I don't have that adjuster wheel on my vacuum unit.  I'm not sure if it's something that's missing or if this model isn't meant to have one? The pin moves in and out with vacuum, but there is no adjustment on the vacuum unit itself. 

[Mad4classics]

The handbook describes a method of setting the static timing by adding a spot of paint 6mm to the left of the timing hole in the crankshaft pull ( when viewed from rear ), and aligning this spot with the pointer; which if if mine is anything to go by is pretty blunt.

From this initial point its down to advancing till it pinks then backing off till it doesn't as Pete described. I find I get a small amount of pinking with the standard 6deg advance, so I wouldn't get carried away - but engines are rarely identical.

The original advance unit Delco 7953461 had a vernier adjustment, you seem to have a replacement unit of different design. The number is on the bottom face of the vacuum unit and assuming the distributor is original the number on the body should be 7953460.

From your picture it looks as if the condenser is close enough to rub on the center shaft; you've Got to make sure there is clearance by adjusting the condenser clip. If the condenser catches the shaft it upsets the timing badly.

It's not just the condenser that's poor quality these days, the clips supplied are usually not very good and need fettling  to fit.

I'm going to trying a Delco type Condenser from the Distributor Doctor next, they are supposed to be a lot better.

Rimmer Bros stock the correct length screws if you need any.

David

 

[Pete Lewis]

Yes condensers fouling on the cam is pretty common  awful stuf for sale

The condenser is best as close to the points as posible but it can be located on one of the outside screws and run  the wire In through the coil lead grommet   Ducillier always did it that way.  Lucas and delco always inside   just an option.

Dizzy doctor has good reputation for spares

Pete

[citybreeze]

I have put some small washers in and bent the condenser bracket back, so now everything moves freely.  It would have taken me forever to figure that out! 

I have played with the timing, and it seems to run smoothest at just before TDC, I'm guessing very roughly that its about 4-degrees BTDC.  While it's smooth, I still have the issue of the idle being too fast despite idle screws being all the way out.  So I haven't taken it out on the road yet to see if the lack of top end power has been resolved.

I have sprayed carb cleaner around the manifold gasket and carb/heat-shield/manifold area and cannot identify any air leaks.

My next job will be to check the throttle plates are closing correctly, then it'll be back to trying to trying to set the carbs up, again! 

Other than an air leak, is there much else which could cause the fast idle? 

[NonMember]

Not really. The power you get from a petrol engine is primarily controlled by the air flow. Fuel must be matched to that and the power falls off either side of optimal. Ignition being out can lose you power but can't gain it. So if your idle is too high it's because there's too much air getting in, somewhere.

You said you'd set the idle screws fully out. Did you also adjust the fast idle screws? It's possible to still have them acting with the choke off, if they're a long way out. For that matter, does the choke actually go fully off? What about the lost motion links on the throttle shaft? Is the pedal returning fully and actually releasing the throttles?

[citybreeze]

 

4 minutes ago, NonMember said:

You said you'd set the idle screws fully out. Did you also adjust the fast idle screws? It's possible to still have them acting with the choke off, if they're a long way out. For that matter, does the choke actually go fully off? What about the lost motion links on the throttle shaft? Is the pedal returning fully and actually releasing the throttles?

I've tried fast idle screws in and out, choke cable connected and disconnected, doesn't seem to make a difference to base idle, unless I pull the choke out of course. 

The pedal not returning fully was not something I had considered, I'll check that tonight.  I put new throttle return springs on yesterday as these looked tired, but hasn't made a difference though. 

I think I'll dismantle, clean and re-fit all the linkages to make sure there isn't something stuck too. 

[yorkshire_spam]

On the outside at 1,000,000 to 1. IF the throttle plates don't close properly, but you can't see anything on the carb that's stopping them. Are they fitted correctly? On SUs at any rate it's possible to get the throttle screwed onto the spindle in such a way that they jam before they close... resulting in fast idle that you can't get rid of.

[Ben Caswell]

On 6/27/2018 at 10:16 PM, DanMi said:

the original idea with the early cars was to fully retard the Vernier adjuster small wheel on vacuum unit) on the distributer set the timing to TDC when the pointer aligns with the mark and then adjust the Vernier 1 click  = 1degree but modern petrol is different so timing may need to be different from factory settings.

I thought the markings were 4 deg apart on the vernier and it takes about 50 clicks between each mark

that would make it about 11 0r 12 clicks per degree.

[Pete Lewis]

i would agree with Ben about the vernier clicks

fast idle  ..have you checked the choke fast idle screw is not holding the idle open , there must be a small gap between the  choke cam screw and the cam,  when the choke is IN .

pete

 

[Mad4classics]

The click adjust on different models is not the same.

The original Delco spitfire distributor is one degree per click. Always seems a bit course to me for a vernier!

Having said that the pictures first posted show a version without a vernier - so no click adjust...??

 

 

You should have 15thou clearance between the throttle lever to pin when the peddle is at rest.

If you temporarily disconnect the throttle rod, which is sping loaded, it will rule out a peddle adjustment problem.

The throttle spindle itself can get so badly worn it lets in air. SU do give a limit in the service manual. Disconnect the return spring temporarily and see if it rattles about in the main body.

It could be just down to adjustment there's a lot of levers and linkages to play with.

David

 

 

[citybreeze]

Success! I think!

As a few of my parts orders arrived today, I did a few jobs this afternoon;  Replaced the jets, fitted new gaskets to top of float chambers, fitted new vacuum hose, slackened off and readjusted all choke and throttle spindle connections.

After that, the car wouldn't start, so I reset the carbs to factory settings and voila! 

It now runs reasonably smoothly at about 900rpm, with the idle screws engaged about a turn in.  I think it still needs a bit more adjustment to the mixture to be its best, but at least it's within the realms of normal running it last.

I'm going to take it out for a run later and see if the lack of top end power issue has been fixed too, now that the vacuum advance isn't sticking. 

Not sure exactly which of the changes fixed the problem, but I'm very happy that it's done!

Many thanks to everyone for all your advice and suggestions. 

[Anglefire]

Thats a result - as for what fixed it - who knows! Probably a combination of all of them.