Spitfire Kangeroo Problem

[rolyberkin]

I am not that mechanically minded with engines so bear with me.

My Mk3 spitfire is a bit of a pain to drive, to pull away if you press the accelerator very slowly it will pull away slowly, if you put your foot down it semi kangeroos down the road.

My diagnosis was to start with the carbs and look at balancing and tuning but could it be anything else, it has been like this since I have had it!?

 

 

[poppyman]

Sounds more electrical to me, cap/ rotor /points wire arcing on coil. I would check ignition system first.

Tony.

[Clive]

Oil in dashpots?

[thescrapman]

Mechanical throttle linkage.

try new engine andgearbox mounts then convert to a mk4 pedal and cable setup.

[Clive]

15 minutes ago, thescrapman said:

Mechanical throttle linkage.

try new engine andgearbox mounts then convert to a mk4 pedal and cable setup.

Good spot, forgot about the "quirky" linkage.

[Pete Lewis]

Amd have a look at the angles on the carb levers , they can be set such that engine movements due to torque affects  the throttles 

Hence the idea of engine mounts and update to a cable set up

Pete

 

[DanMi]

Also on the MK2 there is a spring that goes from the nearly horizontal arm to the chassis. If this is missing or weak the pedal is simply to light and then as you accelerate your foot comes up then as you slow it drops causing a kangaroo effect. So make sure all throttle return springs are good. Or as others have suggested change to cable if not worried about originality

 

[Colin Lindsay]

3 hours ago, DanMi said:

Also on the MK2 there is a spring that goes from the nearly horizontal arm to the chassis.

Same as the MK1 GT6 and mine is far too light, so the pedal is much too sensitive. There's an 'S'-shaped metal sort-of-extension piece between the spring and the chassis which I'm hoping is still there on mine - too lazy to run out and check - but as the originals are unavailable if anyone has a suggestion for a good replacement spring, I'd love to source one.

[Blitz]

Mine did it until I fitted the spring. Much better now 

[Mad4classics]

2 hours ago, Colin Lindsay said:

Same as the MK1 GT6 and mine is far too light, so the pedal is much too sensitive. There's an 'S'-shaped metal sort-of-extension piece between the spring and the chassis which I'm hoping is still there on mine - too lazy to run out and check - but as the originals are unavailable if anyone has a suggestion for a good replacement spring, I'd love to source one.

Canley Classics have stock of the extension wire link 136979, but list the spring as NLA; Rimmer Bros have stock of the spring136835 but list the wire link as NLA. Assuming it's the same parts as a Spitfire MK3.

With these correct parts fitted I personally like the feel of the accelerator.

 

David

[Badwolf]

Mine did exactly the same. Cause was over-rich mixture mainly due to choke linkage not releasing but also carbs did need leaning off a bit. Plugs were black and sooty on 3 & 4 whicb was the give a way as the choke linkage to 1 & 2 was not connected at the time.

[daverclasper]

Iv'e also had that (though more like hunting/less extreme) with jets set too rich on Vitesse.

Edited September 17, 2019 by daverclasper

[Colin Lindsay]

3 hours ago, Mad4classics said:

Canley Classics have stock of the extension wire link 136979, but list the spring as NLA; Rimmer Bros have stock of the spring136835 but list the wire link as NLA. Assuming it's the same parts as a Spitfire MK3.

GT6 is 137482; NLA from both. I wonder how it differs from the Spitfire version?

[Mad4classics]

On 17/09/2019 at 20:56, Colin Lindsay said:

GT6 is 137482; NLA from both. I wonder how it differs from the Spitfire version?

So the link 143747 is available; assume different length? Spitfire MK3 measures 18swg ( looks like piano wire?) 7 3/4" long. I don't know how the spring differs; odd must be some reason the parts are not common, but the length from the chassis hook point to throttle arm is probably different.

David

Edit: The spring 137482 with link 143747 were fitted to USA spec cars after FDU75001 according to the parts list; these are the same parts listed for the GT6 (perhaps a different spring rate to give a heavier feel with the later spring???), so I suspect the earlier parts for the Spitfire would fit the GT6 and these are still available.

[rolyberkin]

14 hours ago, thescrapman said:

Mechanical throttle linkage.

try new engine andgearbox mounts then convert to a mk4 pedal and cable setup.

Plan to check the carbs and timing etc at the weekend, It has new engine mounts but will check gearbox mounts, silly question, is the linkage to cable an easy conversion and does it require new parts or sourcing second-hand ones, is there a list of components or how to guide anywhere or anyone have any photos?

[Clive]

You should be able to find a parts diagram of the late spitfire setup. That will give you a parts list.

Accelerator pedals are an easy swap and should be available easily enough s/h. Then s cable, the trickiest part will be the carb linkage end, but you will need the bits from a mkIV Spit (1500 may well work too)

There is a good reason everybody uses cable linkages, even herald. Goodness knows why they used that lever arm system.

[rolyberkin]

A quick update on this one, took my car into my local garage to have the carbs balanced and timing set etc etc. He found a few issues and it now runs fairly well but is still a pig to drive, so now going to look for a later pedal assembly! 😞 

[Herald948]

On 17/09/2019 at 17:00, Mad4classics said:

So the link 143747 is available; assume different length? Spitfire MK3 measures 18swg ( looks like piano wire?) 7 3/4" long. I don't know how the spring differs; odd must be some reason the parts are not common, but the length from the chassis hook point to throttle arm is probably different.

David

Edit: The spring 137482 with link 143747 were fitted to USA spec cars after FDU75001 according to the parts list; these are the same parts listed for the GT6 (perhaps a different spring rate to give a heavier feel with the later spring???), so I suspect the earlier parts for the Spitfire would fit the GT6 and these are still available.

I don't know what, if anything, this relates to, but FDU75001 and later US-spec. Spitfires had the mechanical linkage attached to the single Stromberg rather than the dual SUs.