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Carb questions
Posted by: Gratzie ()
Date: June 22, 2022 07:58PM


I posted this question on FB and it was recommended I post it here for more in depth help. My wife's dad left her a 66 Monza 110 and we have been working on it after it sat in his barn and garages for many years. I recently took apart the carbs to find that the left carb had a 50 main jet and a small chrome ball sitting in the bottom of the accelerator pump cavity. The Right side carb has a 49 main jet and did not have the ball in the accelerator cavity. The car was running well but was pinging or detonating on the highway. Today I Deflashed the heads as best I could, set the float levels and modified the distributor to limit the centrifugal advance a bit. What would you folks recommend for main jets in the carbs and is that small ball supposed to be in both carbs or no ball at all? Thanks in advance for the help. I'll also add a post of the info on the car itself.

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Re: Carb questions
Posted by: Frank DuVal ()
Date: June 22, 2022 08:50PM

I'd use 50 depending on your altitude. Can go as high as 52. Others will chime in.

No chrome balls loose in the accelerator pump cylinders. The check is the brass piece next to the cylinder, and the check ball in the accelerator pump body.

Never had to limit advance before.

Frank DuVal

Fredericksburg, VA

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Re: Carb questions
Posted by: RobertC ()
Date: June 23, 2022 12:17AM


Based on jets, you have two different vintage (year) carbs.

You need to determine which carbs you have - and if they match.

There is a book by Bob Helt on Corvair Rochester Carbs - available from Clark's Corvair and possibly other vendors.

65 - 66 primary carbs have a power enrichment valve (PEV) indicated by the plug in the attached pic. There is a PEV valve under the venturi cluster - or should be - on PEV carbs.

Other LM carbs have "air bleed" circuit to support "smog".

You do not indicate that your 66 engine is a 66 CA smog engine. Of course, smog equipment may have been removed - vast majority have been removed by now.

As stated, you do not state where you live (elevation) as far as jetting. Some people go richer given the condition of current gasoline. 50 is ok with the PEV valve. I would use 52 jet if the carbs do not have a PEV valve. Others will have other recommendations.

As stated, the only thing in the accelerator pump well is the accelerator pump. You probably want to check that the accelerator pump discharge holes (two) in the upper side of the venturi are not plugged.


You need to determine the distributor that is on your engine. There is a stamped number on the side of the housing. Assume yours is still original, but there is no guarantee at this point in time. And, determine that the internals are correct.

A list of distributor specs is in the FAQs on this site. You need to scroll down to find all the info - springs, weights, and cams.

There is also a stamped number on the weight plate of the distributor shaft.

There is a stamped number on the arm of the vacuum advance. The vacuum advance may have been replaced, so the number on the arm may not match the specs. The "generic" replacement vacuum advance is 217 (memory?).


Personally, I do not agree with your limiting the centrifugal advance. Too early? You do not state the initial timing and do not state if your car is a manual or PG. Based on my 110/PG, "they" can be sensitive to timing. But, I have neve experienced pinging at steady highway speed.

Good luck.

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Re: Carb questions
Posted by: Gratzie ()
Date: June 23, 2022 10:50AM

Thanks everyone for the replies. The Monza (Gratzie) belonged to my wife's dad before he passed away and we have been slowly bringing it back after sitting for many years; to the tune of 1200 miles since 1977 and 59k total. Around town, the car drives and runs fantastically with the exception of some heat soak hard starts. We have driven it back and forth between Northern Ky and Indiana a few times to visit her mom which is when I am chasing the ping or detonation. To answer some of the questions, I watched a good Corsa video from a guy who REALLY seems to know Corvairs. Anyways, he had ALL the years of carbs on a bench and took the time to educate on each one. What is sad is that just prior to passing away, my wife's dad told me that he had purchased a "rebuilt" carb from someone who was a GM tech years ago yada yada. The left carb is very clean and has a red and white remanufactured sticker on it but I think he was a victim of a swap out. That left carb is now actually a 60 or 61 with no power enrichment, a manual choke cable boss in the top, the 5 star venturi dog leg and no heat vent of course. The right carb has all of these features as a 66 should and looked pretty original. In any event, I will be searching for a 66 carb or at least a correct year core for a Clark's carb purchase with a decent core value. The car is a 110 powerglide. The distributor number is 1110319. When driving on the highway between 60-70 mph we found that trying to give her any amount of throttle would invoke a slight ping, any climbing or more throttle would result in a significant ping, which I did not allow it to do by letting up on the throttle and allowing speed to drop. We have a smaller tire on the corvair (185/70//13) and I would suspect we are in the mid 3000 rpm range when this occurs. If we take an off ramp or slow down, the pinging is almost instantly gone, even when over 1/2 throttle or under load. When I took the distributor out, it does have remanufactured stamped on the housing so perhaps that was replaced at some point also. With the distributor modification I am at 12 before for base timing at 660-680 rpm (in drive-vac advance plugged) and 21 or 22 before total at 3500 or so rpm (vac advance still unplugged.) I know this is long, but I appreciate the help a bunch. If I can get it straightened out in time, we have another trip scheduled to go up in mid July.

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Re: Carb questions
Posted by: RobertC ()
Date: June 23, 2022 11:36AM

Remanufactured distributor:

I would take the distributor apart and check all the pieces against the link I provided - including the distributor shaft / weight plate. Then, you will know what you have versus what is in a stock 319 distributor.

Also, check the number on the vacuum advance.

Remanufacturers know nothing about Corvair distributors. They assemble a bunch of parts and put it on a distributor machine and "approximate" (my opinion) a Corvair distributor curve.

Depending on what you find, you might be better off finding a good 319 distributor.

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