Idle drops randomly

[ScottMk]

Hi there I have a MKIV Spitfire with a problem I cant seem to diagnose. 

When I'm out driving around and pull up at a junction or roundabout every now and again the idle will drop to around 500rpm, next junction or roundabout and the idle is fine at 850rpm. 

At 1st i thought it was a old coil as it was very warm to touch but changing that has made no difference, also as part of its yearly service i have changed the HT leads, plugs, rotor arm, dizzy cap and fuel filter. 

Has anyone else every come across this?

[Andy Moss]

I had this problem for ages. Rebuilt the whole ignition and carbs. Only thing that solved it - had carbs professionally rebuilt. I’d rebushed the spindles and everything. I can give you a number that is reasonable if you like. 

[Pete Lewis]

make sure the idle screw are set correctly and the fast idle cam for the choke  has a small gap so its not holding the idle. 

have some free play in the accelerator cable as heat can affect  its length and vary the idle 

worth a nip up of the manifold bolts

so give the basics a look at  before you dive into carb refurbs but spindle wear will cause this 

always the simple and basics before opening the wallet 

Pete

[ScottMk]

I found a gap between the air filter housing and the carb intake. Do you thank that could of cause the drop in idle when warm? I have fixed it in the picture. The filter housing was bent in a touch. 

[Pete Lewis]

well try it 

i wouldnt expect it to make any major change

the twin throttle springs do apply a lot of load and wear the spindles not the best set up by triumph

 

[ScottMk]

I have also found what sounds like to be an air leak from the exhaust manifold when cold, all the securing nuts are to the right torque so I know it’s not that. Just tried to see the cost of a new one but it seems they are very rare. 

[Pete Lewis]

https://www.jamespaddock.co.uk/manifold-gasket-1360-4

Pete