345 surging

[grnbinder]

Howdy all. Posted about a surge on my 71 1110 a while back and Allan E. sent me a reply about a possible va. advance problem which I also thought of after I had posted. Well I checked it and it is not the problem. It does the same thing whether the vac. advance is connected or not so I am still at a loss and looking for answers. any and all ideas are welcome. Thanks, Jim.

[Bill Bennett]

Which engine and carb?

[sgyearsley]

I had surging and hesitancy with change of seasons. I have to tweak my timing and adjust the carb mix every freakin' season. Looking at the old posts I see a lot of potential areas to check. It's a head scratcher when nothing seems to work.

Does anyone have the spec timing numbers (baseline with rpm, advance with rpm)? I searched the sight and the timing and the accel diaphragm seem to be the main culprits for this kind of thing. I found 5 at top dead as the most commen suggestion. I am at 6 and 32 right now and she mostly likes it, but a little knock with really heavy acceleration. (77 Scout, 345 with a petronix and standard 2 barrel).

(sorry, not to hijack the post, but I think these answers might help since everyone refers to spec without actually saying the numbers).

I guess it's time to buy a service manual.

[grnbinder]

Which engine and carb?

Hi Bill. It's a 345 and was told by mike mayben it was the good holley, think the number is 2210. Jim.

[Bill Bennett]

Have you tried plugging 'all' the vacuum lines? Maybe the power brake booster is leaking or the smog equipment that needs vacuum to operate has a broken plastic connection or split rubber hose? It seems someone mentioned about a possible vacuum leak through a casting plug on the underside of the intake manifold. A vacuum leak can create a 'lean' surge as the air/fuel ratio will change with the extra 'air'. A engine surge can also happen if the air/fuel mix is too 'rich'. If you had the Holley 2300 carb, I would suggest checking for a blown power valve, fuel level too high in the float bowl due to incorrect setting, a bad fuel needle and seat or a warped main body where it meets the throttle body. Have you tried adjusting the carb 'idle jet' settings? Is the choke flap fully open when the engine is at full operating temperature? Have you checked the gasket between the base of the carb and the intake manifold? Is there a vacuum port on the base of the carb with a rubber 'cap'? They can crack and leak vacuum with age. If the carb is 'really' old, it could be the throttle shaft is worn enough to allow air leakage through the hole in the base of the carb.
Bill Bennett 68 Travelall 304A 350cfm 2300