Flat spot - a simple solution at last

[HFStuart]

For the last 18 months I've been chasing a huge flat spot on my 1978 Beta Spyder. It's a 2 litre and is running a 34 DMTR with electronic ignition. The car hasn't been on the road all that time as it's needed some TLC.

Anyway I'd checked everything, the carb came apart, a spare was put on and taken back off again. The distributor was checked for mechanical advance and to make sure the vacuum diaphragm was working. Anything that might give me an air leak was disabled / plugged and then refitted when it had no effect.

Nothing made a difference, until yesterday when I noticed that every time I cracked the throttle open the vacuum tube at the carb sucked itself flat. A new piece of tubing and the car drives as it always should have.

I spent yesterday evening with a beer wondering how could I have missed something so obvious ? Obviously I failed to follow a systematic sequence and convinced myself something major had gone wrong.

The reason I post this up just as a reminder to look for the obvious solution first. I would have saved me hours on this if I had.

Stuart

(Edit due to typos)

[RedLexus]

I see the same here in work , everyone assumes a major breakage! A friend couldn't get his Talbot Avenger rallycar to run right , played with jets , distributor etc... then I reached in underneath the carbs and reminded him he's forgotten to put in the lower mounting bolts in the carbs , to the manifold.... Got a laugh out of that.

[Guy Croft]

If one of the secondary choke retaining screws comes loose on sidedrafts, the choke rotates. So quite randomly the power comes in and the engine runs great. Then it runs on 3 cylinders again.

That one had me 'foxed' for a while on a 2 liter Pinto RS2000 many years ago. I even had to get it on a rolling road to find out the cause.

After that I tended to lockwire them.

G