i think my carb is way out of tune.

i have a holley 750 DP on a mildly built 350

the car starts awesome, but after it runs a while, it has a really bad starting problem. it smells like its running really rich, and when it finally starts a huge black cloud of smoke comes out of the exhaust.

the car also seems to bog for a very split second just off from idle.

i dont think the jets in the carb are stock, as i got the carb used...and it was on a very well built 383.

how should i start tuning it?

i've never even owned a holley DP, let alone try to tune one for performance


do these symtoms seem like tuning issues, or should i start looking for something else to make it start better when warmed up?

could a bad coil make the car hard to start like this?

 

after trying various combinations with my 750 dp on my 350 and many dyno pulls i figured out that it was just too much for carb for my 350.. i got it to run decent but only got 300 hp out of it.. a friend offered me his 650 in trade for my 750 if it worked out better for me.. after tuning it a little and tryin a few diff jet combos i was able to get it to run near perfect and make 50 extra hp.. just food for thought..

 

Many, Many Many Many did I mention many? carb problems are actually ignition problems. Before you blame the carb be sure the
whole ignition system is up to snuff.

Irreguardless your plugs are probabily fouled now and finished.
Get new ones.

That being said. Your 750 double pumper should have 70 primary and 80 sec jets.

Flip the carb over and look at the throttles plates at idle.
The idle transfer slot should just barely be exposed under the throttle plate. if its exposed more than .030"
+/- readjust it and adjust the secondary throttle stop for this also.
Choose a power valve with a opening point that will allow it to remain closed at idle in gear. eg if manifold vacuum is 5.0" in gear, get a
4.5" rated power valve.
Reinstall the carb. Be sure to use a PCV . if the cam is much bigger than stock you'll need more intial advance timing to get the idle speed right. The carb throttle opening (idle speed adjustment) should be near right on now, once the car warms up.
Adjust the idle mixture screws for best idle speed and vacuum.
readjust the idle speed screw.

Remember give the car all the initial timing it wants to achieve the desired idle speed when the throttle blades are pre set up
as discribed above. Or real close to it. If the throttle blades are set open too much at idle it will run rich and stumble just off idle.
The bigger the cam the more initial timing it will need.
When set up properly it will idle rock steady at 750 rpm even with a rough idle race cam. And not be rich or burn your eyes out while idleing.

 

www.mortec.com has a section on tuning the Holley. Check it out!