Carb question

I have a 770 Oliver that runs good except when you open the throttle too fast it dies or spits and sputters. Runs great at full throttle and runs good if you open the throttle slowly. Is this a carb issue? If so, any ideas on what to do about it? Thanks in advance for any advice, and I apologize for my ignorance.

Depending on the type of carb you could have a partially blocked passage
somewhere. The other thing is not quite enough main screw fuel adjustment. The
guys on here are going to tell you a bunch of things to look for. Trouble is
that there is nothing like standing there with a screwdriver in hand.

like jeffcat said most likely carb, its going lean as the load increases , a blocked passage or just a mixture adjustment , the other thing is lack of advancement in ignition timing in the dist.

INHO on this is ya need to do a major tune up , start off with a valve adjustment as they are over looked by the younger set thee days . Old engines used solid lifer/ cam followers and require adjustment when used . When they were the prom pony power a major tune up was usually done once a year . Next make sure your manifold bolts/ nuts are tight . Next on the list is the usual plugs and points and check the dist shaft for side to side movement . Then put a timing light on it and set the timing as per MFG spec.'s . Now comes the fine art of adjust the carb . Ya start off with a base line set then you fine tune the ideal for best slow speed and set the curb ideal then ya set the main jet and setting that for best throttle response , max power with out over fueling . It also may require a carb rebuild and i dopn't mean taking it apart and usen a can of spray carb cleaner and a quick spray and blow dry either . When i rebuild a carb it gets taken apart and takes a bath in real cab cleaner usually over night then it is washed out in HOT soapy water then rinsed the blowen and rodded out with number drill bit and blowen out again and each passage is checked for flow . Floats are checked and hand leaned and polished to take off any tarnish as that adds weight and it may or may not change the wet set but this is how i have done it for way over fifty years and it works for me . I do a lot of carb rebuilds from old cars and trucks to lawn mowers garden tractors play toy carbs and tractor carbs .

Tractor carbs do not have an accelerator pump like car carbs had so when you open it up due to that is running lean it can do what your seeing. Open up the min jet say 1/2 turn at a time and try till you find the sweet spot

Check the point gap, the centrifugal advance, and distributor shaft for side play. If the plugs haven't been changed lately, they may be part of the problem. Check the spark quality at the plug end of each wire. It should jump 1/4" to ground.

If it has a main jet adjustment screw, back it out about 1/4 turn.

When properly adjusted it should take sudden throttle without hesitating. A common adjustment needed when the air temperature drops.

If there is no main adjustment, could be the main jet is partially clogged. It will need to come out and be carefully cleaned with a small drill bit or torch tip cleaner. Dried ethanol residue tends to stick in the jet, it has to be scraped out. Flushing and blowing will not remove it.

(quoted from post at 10:59:06 11/22/19) I have a 770 Oliver that runs good except when you open the throttle too fast it dies or spits and sputters. Runs great at full throttle and runs good if you open the throttle slowly. Is this a carb issue? If so, any ideas on what to do about it? Thanks in advance for any advice, and I apologize for my ignorance.

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Many tractor engine carburetors have an accelerator pump that is operated by a drop in engine vacuum when the throttle opens. In some, vacuum acts on a little piston, in others, a diaphragm is used.

I don't know whether your specific machine does has an accelerator pump, or not, but I'd consult a manual to find out.

Old, yes some do. I don't know about that Oliver but my Blue Fords, 65 Ford 4000, 68 Ford 4000 and 65 Ford 5000 did have that pump. The local Ford tractor dealer did not know enough to know anything about a carb. Took it to a place the owner-mechanic was a former owner of a Ford tractor dealership. When he got into the carb from the 5000 that pump was stuck so bad he had to send it farther to a better machine shop than he had to get that aclerator pump removed and the bore cleaned up and new pump installed. So yes the newer tractors than yours do have that pump and that Oliver would be same age as these Fords were.

Along with the reply's I would also make sure thermostat is bringing eng up to operating temp.

The updraft carbs used on Olivers have an enrichment circuit that is supposed to help prevent a lean condition when accelerating
the engine. It is a very small passage in the carb that works with vacuum drop when the throttle is opened. They can be plugged
and not be obvious when doing a carb rebuild. If you search online you can probably find a writeup that explains how the carb with
the enrichment circuit works. A 770 probably has a Zenith carb, but the circuit exists in other carbs as well.

Before you dig in do as OLD said open jet up a
tad. Its got a zenith or marvel schiebler and set
too lean will stumble as you described

(quoted from post at 08:59:06 11/22/19) I have a 770 Oliver that runs good except when you open the throttle too fast it dies or spits and sputters. Runs great at full throttle and runs good if you open the throttle slowly. Is this a carb issue? If so, any ideas on what to do about it? Thanks in advance for any advice, and I apologize for my ignorance.

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Old and rwb are both referring to the MAIN jet. There are two, the main and the low speed. low speed is usually very close to the top of the updraft carb while the main is usually a larger screw on or near the bottom. The low speed could be the problem too but understand that it is an AIR adjustment so you will want to try closing it slightly to try correcting a lean at low speed problem.