604 timing/tuning issue

[ajb]

Hello All

I'll firstly apologise because I'm not a mechanic, so if I phrase any of this in a ridiculous way it's down to my ignorance!

I have a petrol carb model from 1977, and the ignition system has recently been renewed (original parts from the chap in Knottingley, but with Bosch coils).  Shortly after that the fuel pump went, and a new electronic one has been fitted.  This had to be positioned much nearer to the tank to aid feeding it by gravity, but my mechanic is now happy with that aspect.  The route of the fuel lines has not been changed in any way: the pump is simply nearer the tank.

Performance-wise, it is pretty much fine when you get up to 50 mph, but still struggles a little bit when under load - it tends to judder a bit and can occasionally backfire if you don't increase the revs just slightly before letting the clutch up.  I had been running it on 95 Unleaded, but it has improved a little on Super Unleaded (97) plus an additive.  Having stopped it from 'running on' after being switched off my mechanic is of the view that it's most likely to be a timing issue now.

This is where my understanding is a lot less good!  I watched him setting the timing with a strobe-light device: the recommended setting is 10, but he has found that the car runs better on 12, although it tends to run a little warmer.  There's also another issue with setting the gaps (?) in the points (dwell time?): the recommended setting is 72-80, but his device only goes up to 60.

Does anyone have any experience of this issue?  Any advice would be greatly appreciated: you can be as technical as you like, as I'll just print it off and my mechanic will know what you mean!

Thank you in advance for any help you can give.

All the best,

Andrew

[oldpug]

Hi ajb, I`ve had a look at my old Autodata book to remind myself on all the settings for these 604`s.
Firstly unleaded petrol is not suitable for a CARB`604.It needs 98,so add some octain booster or what ever.Not sure what to suggest with setting the dwell(it is 72-80) other than find a different device or adjust each point gap manually to .4 mm(15 thou). As for setting the basic timing you have to do it with the vacuum pipe REMOVED. If the engine has a M79or92 distributor its 10 at 900rpm,if its a M108 distributor its 12 at 900rpm.The M numbers are clearly visible on the dist` body.
All I can say is set it up as per the book and see how she runs.Mind you as its a very old car there could be other issues like air leaks and so on.Also what does the engine sound like,is there any "tappet rattle". The camshaft lobes on these engines can wear a lump out of the rocker arms creating valve clearance problems.

[ajb]

Thanks for this oldpug. I shall print it off and give to my mechanic - it's going to need to go back there as it's becoming very prone to stalling when trying to move off (had to push it off a roundabout earlier this evening!), but as he last set it up with 95 unleaded petrol it maybe that it needs a further tweak. Not only that, but it hadn't been driven a lot whilst he had it, so things are probably settling a bit.

The mechanic who worked on it previously (in Hamburg, Germany) is apparently of the view that it could be converted to electronic ignition using the later electronic system fitted to the 604 (presumably the TI model): I did email him to ask for details but I haven't heard back from him yet. My own thought is that if the current carb system can be set up properly I'd probably stick with that for the time being, but if nothing else it's a thought!

[oldpug]

Your correct,if everything is in reasonable condition and set up correctly the car should run OK. Mind you those "triple" carburetors can cause problems.If I remember its a single carb` for starting,idling and slow speed,then a double choke carb`for driving.(something like that?).Like all carb` engines,if there are blocked jets and so on it will run like a pig.Particularly the acceleration pump,if that`s not squirting fuel you will get a huge flat spot when you put your foot down.