[70calypsomach]

Well 351C is running pretty good except for initial start up. Have not had it on the road yet (Plates Monday).
Want opinion on weather I need an Electric Choke?
Have a Speed Demon 750 Mech secondaries. Thought I could get away from it being its a summer runner only (Michigan). When I start it up it pretty much fires right up but I have to keep reving it slightly (30 sec) to keep it running. After that it idle just fine (a bit quick, 950 rpm). Is a choke the answer to my problems. Air temp is about 80 deg when firing
Also, When its warmed up and then shut off it will start right up and Idle fine.
Thanks for any help.

 

[sharkmouth]

you didnt state what kind of cam and intake you have.....

in the temps were having this summer, it should fire up and run very smoothly immediately (unless you have a single plane intake and ONE HELL of a cam..... i.e. NET intake duration of 250 degrees or more)

I've always believed a 750 vacuum secondary (much less a double pumper!!) is too much for a 351 unless it is a pure quarter miler......but it should be able to idle; 750 cfm on a small block affects driveability more than idle.

I built a 351C with a cam spec'ed out at 230 net duration....at 900 it idled like a stocker and the power brakes worked great!!!

Take vacuum readings....if the cam is not outrageously big, it should pull at least 14" of vacuum at 900 rpm....if lower, ensure the power valves in the carb are rated a few inches lower than the idle vacuum once the timing and mixture are right.

If not, I'd work with the initial timing and idle mixture adjustment, and if it still idled crappy, I'd do compression tests

BTW, you did pre-oil the engine and follow the initial run-in instructions from your cam manufacturer, and youre sure the cam timing is correct?

(and degreeing the cam when installing it is a good idea)

 

[70calypsomach]

It does Idle Pretty good. Except for cold start up. After 30 -60 seconds its fine.
I have not checked vaccum but power brakes and all vaccum pods work great at idle. I would guess I have 16-17 in h20 vaccum.
It has a roller cam 228/232 I/E @.050 290/294 adv. dur.
High lift .597/.609
High rise dual plane (blue Thunder) (4V engine 11.0:1 compression)
Pre-oiling and break in went fine.

 

[sharkmouth]

At 80 degrees temp that engine with a cam that size should idle right away....chokes arent really needed until the temp gets into the 50's

Assuming your machinist did the valvejob well and the cam (and valvesprings) made it thru break in ok and arent just defective, I'd say timing (including cam timing) and idle mixture need to be refined

That sized cam should idle well at 900rpm

Good luck!!

 

[Teebone]

weather is only one factor..the choke keeps the mixture rich until the engine is ready to settle down(warm)...right now at 80 it is only struggling a bit..when the weather gets cooler it will be a bear to keep running..install the choke and eliminate your problem..