Major engine hunts when cold

[David Lewis]

1954 Major runs well, but the engine revs up and down when it is cold, and then evens out when warmed up. Feels like air is getting in somewhere, so went through the system last year and found no leaks. Did the diaphragm test and it seems OK. So what can I try now?
 

[tiresntracks]

It sounds like the damping valve in the vacuum governor may be broken.
 

[David Lewis]

Interesting. Guess I can look that up in my parts book and then go take a look and see. Thanks for your help.
 

[mick richman]

Had the same problem. Ended up partly dismantling the fuel pump and found the diaphragm was split. Not too hard to get out except for the fourth bolt.
 

[David Lewis]

That makes sense, because it stops hunting at very low idle, i.e. is getting enough diesel when it only needs a little. Will check it out. Thanks.
 

[richard bartlett]

just another thought, mine's a 1955 FMD and had similar problem, the diaphram was split so replaced it but I also discovered one of the two pipes that run from the top of the diaphram housing to the manifold had been rubbing on the engine block and had a hole worn in it.
 

[David Lewis]

Thanks for the idea. I thought cracked pipes might be the prolem last year, so I tested them and they are OK. So I suspect it's vacuum pump diaphragm or fuel pump diaphragm - both easy fixes (if I get lucky).