OVERHEATING PART 2

[Deleted]

I finished putting the top end back together again with the re-cored rad, up-rated water pump etc., and crossed my fingers !!
I also fitted new contact points etc., and then found I needed a 'dwell meter' ?
That aside the engine sputtered in to life whilst it dealt with the oil I had put down a bore whilst testing the compression. It eventually settled down and I let it run for a while on a fast tick-over.
I had to reset the mixture control etc., and I've got a 'flat spot' which I can't seem to get rid of ?
When I open the throttle it hesitates as if its starved of fuel. I checked the mixture as per the manual by lifting the pin, and an adjustment on one side was all that was needed. However, the flat spot remains ?
The important thing was that I ran the engine for nearly an hour on and off in a stationery position, and the temp control stuck rigidly in the middle of the dial. I was very pleased at that. Tomorrow I'll give it a road run -
and hopefully the 'flat spot' won't be too troublesome.
Incidentally it's running on Sainsburys premium grade fuel.
I'll also do the dwell setting and put the strobe light on it.
Mike

[Phil Nottingham]

Have got (correct) oil in your dashpots?

[Deleted]

Good point Phil - I went straight out and checked them. There doesn't seem to be any resistance at all
when I lift them ?? Is it special oil ? or normal engine oil ?
Mike

[Phil Nottingham]

It should be a light SAE 20 but if worn then engine oil can be used or ATF

[glennr]

I kept this info from somebody's post but i can't rememember who, but it may be of use......


If you've checked the carb and the dashpot is topped up with SAE20 oil, the problem is likely to be on the ignition side. Have you replaced the condenser?
Did the old plugs not give any clues as to which cylinder(s) were misfiring?
Have you run a compression test?
How old are the HT leads & are connections sound?
Are connections to the coil sound?

Misfires like this are annoying and it is just a question of methodically plodding through the possibilities until it runs well. I ended up refurbishing the distributor through JRW; expensive but transformed the car (1966 MkIII).

(A word of warning in case you are not familiar with these engines. Take care not to crossthread or overtighten the plugs in the aluminium head or you will end up having to put in helical coils as I have.)

Question:
What type of oil should I put in the top of my suction chamber and how much should I fill it up?

Answer:
We sell two different types of oil for this purpose which are still made to the original SU factory specifications.
The first is SU Damper Oil, which is a straight 20 grade and comes in a handy 125ml bottle. This oil is for use where the carburetter is fitted with a damper inside the piston and can be used on all SU, Zenith and CD carburetters.
The second type is SU Dashpot Oil, which is for use in earlier, pre-war, SU carburetters where no damper is used.

In the case of carburetters fitted with dampers the oil should be filled to a level just below the top of the hollow piston rod, so that when the damper is fitted it does not displace the oil any higher than the top of the piston.

SU Damper Oil (125ml), Part No: BDR125S, Price:£3.50
SU Dashpot Oil (125ml), Part No: BDP125S, Price:£3.71 SU carburetter cleaner, Part No: BCC500S, Price: £6.70

[RichardF]

My experience of identical symtoms (after setting the carburation) are:
1. Timing/dwell way out caused the flat spot. I set the dwell and timing - cured the problem.
2. HT king lead was found to be breaking down (process of elimination). New HT king lead cured the problem.

Good luck

Richard
Southampton

[harvey]

richardf said:

My experience of identical symtoms (after setting the carburation) are:
1. Timing/dwell way out caused the flat spot. I set the dwell and timing - cured the problem.
2. HT king lead was found to be breaking down (process of elimination). New HT king lead cured the problem.

Good luck

Richard
Southampton

You should always check and set the dwell, then the timing Before making any adjustments to the carbs.

[Deleted]

WOW !! Thanks guys. Brilliant and useful info from everyone. I acted as suggested and bingo.
Dwell and points set, timing set, carbs set and away she went . Sweet as apple pie !!
Took her for a 20 mile run and she reacted like a brand new car !! Temp spot on - tickover spot on - acceleration amazing etc etc.., I'm a very happy man !!
thanks to all,
Mike