[69vettester]

Heres the situation..
I put a SA670 carburetor on my new engine build. The carb was new but had been sitting on my shelf for 4yrs. The initial start up went well, I got it idleing smooth and nice throttle response. Did a 30min. 2000RPM break in(HYD.Roller).
Took it out to a country road to go through the gears. It was running super , real steady full power through the gears, didnt have it over 3500rpms. after 10miles, I got on it a little to open the secondaries, and it crapped out, Started surging and chugging I think some backfire in the exhaust...I nursed it home and havent been able to get it running right since(2days working on it). I pulled the carb and cleaned it, blew it out, replaced the power valve(theres only one).
Now it seems to idle perfect, and good standing throttle response , But starts crapping out as soon as I get in gear and load some power. It Bucks and surges and wont steady out. Ive been moving the dist. a little to the advance and next time a little to the retard, doesnt seem to make a difference.

Ive got a Demon 750 on the Way, but Via Lars, I should be able to easily get the engine timed and tuned with this one.

Does anyone Have a diagnosis, The major symptoms are, The bucking off Idle under load, it pulls but not steady , its stuttering as it tries to accelerate, Its popping in the exhaust until it FULLY warms Up. The Colder it is The louder The Popping out the headers..
:huh:
Should I check the dist. Gear?? It ran great for a few miles, so I dont think Im off a tooth?
Anyone had a similar situation? What resolved the problem?

Thanks, any help is appreciated..
Tom

 

[ArtsVette73]

The 670 is plenty enough carb. I have it on my 73 383 and have had no issues. Matter of fact I jetted it down.

 

[DJ Dep]

Maybe a fuel pump going bad? Just guessing here.

 

[rjent]

Man, I have read your post multiple times ... kinda stumped. backfire in the exhaust is usually too rich. I think the secondairies starting the symptoms is paramount to your problem and a major clue. Do you have another carb? A Q-jet, anything you could bolt on to test to see if your symptoms change?

I suspect a carb problem, but with such limited info it is hard to tell ... :thumbsup:

 

[69vettester]

Ok I found the problems..
Turned out, The Dist. was ballpark Ok.
It was that Carb., Like I said I took it apart and blew out the Metering blocks. But as I looked closer this afternoon, every rubber Gasket was leaking, The vacuum secondary diaphram was slightly torn in two perimeter places, Used a little RTV(no access to fuel flow from there). The secondary float's needle and seat wasnt working . Blew it out with fuel sys. cleaner and immediatly saw it seat a tiny bit Higher. It had been hanging open a hair and the bowl was filling up.
Its running very Nice, Idle perfect, pulling strong in all gears. Still breaking it in so no 3500rpms + , and no WOT. Ill Time it Tomorrow, I know its close already.
The SA670 Had sat too Long and surprise, it had deteriorated...But its Good to go...until the speed Demon gets here.
Thanks all
Tom

 

[69vettester]

Man, I have read your post multiple times ... kinda stumped. backfire in the exhaust is usually too rich. I think the secondairies starting the symptoms is paramount to your problem and a major clue. Do you have another carb? A Q-jet, anything you could bolt on to test to see if your symptoms change?

I suspect a carb problem, but with such limited info it is hard to tell ... :thumbsup:

rjent..I Just saw your reply..you nailed it..:thumbsup:

Tom

 

[rjent]

rjent..I Just saw your reply..you nailed it..:thumbsup:

Tom

I get lucky sometimes :laughing: