Hi folks,

When setting up a M4 timing is the maximum advance still the same 32deg from the static point as for a M28? I understand that the static point is 12deg(M4) rather than 8deg(M28) but does this alter the way of marking up the flywheel as per Ken's Flickr picture? Or do I just mark it up the same?

https://flic.kr/p/7zco2j

Many thanks for any help.

Ian

Isn’t it one mark at TDC and one at 12deg? Or am I missing something?

Ian,
the specified centrifugal advance for an M4 engine, according to Citroen, is 12 to 16 degrees on top of the 12 degree static setting.

That would mean having the 'full advance' mark on the flywheel just 5 teeth round from the 'peg in hole' position.

However, 28 degrees total advance seems rather conservative to me, considering the low compression ratio used in M4 engines, so it's probably worth using the 'old school' method of optimising the timing.

I'd try one more tooth on the flywheel and if there was any hint of detonation/pinking with that setting, revert to the original...

Be carefull with this. Good M4 engine won,t pink, because they are that low compression, they only run hot when giving them way to much advance. My advice is they run very well on 28 degree of max advance.
Giving them too much advance they are only fuell to heat converters.

Don,t rev them either, these are torque engines (well in proportion) not rpm engines.. A good M4 gives you (almost) the same amount of torque till 3500rpm then a 2cv6 engine.

Thank you both for your replies.

I have a new problem for me to solve today now. On the way to work in my other M28 Dyane it suddenly lost the ability to idle. The idle screw/jet appears to be in place so I'm thinking I'll have to look for a blockage before I try and set off home later...!

A common issue for sudden poor idle, is the choke pull off diaphragm has perished and let's false air in.

The widget sits on the left of the carb looking at the engine from the front. Its held on by two screws. A test is to take it off and put a bit of tape over the hole, then screw it back on.

It may be something else of course.

blocked idle jet...?

Hey Ian, how ya doin?

Hi there folks,
It was indeed just the suggested blockage of the idle jet.

I don't have the choke pull off device I have the older(?) 21/24 version of the carb.

That's good then

That older carb, how does that perform, as I have one on the shelf and was thinking of trying it.