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Jul 21st, 2025 | | | | Joined: Aug 2018 Posts: 46 Wrench Fetcher | | Wrench Fetcher Joined: Aug 2018 Posts: 46 | So, the carb needed a cleaning and a rebuild. I did that, put the carb on and have it purring like a kitten at idle it is running super smooth I did have to back the mixture screw out 2 turns from seated. This is the zenith 228 carb.
When I put it into gear and try to drive the engine dies unless it is getting a lot of gas.
My only guess is a timing or vacuum issue.
Any suggestions or ideas would be appreciated.
1950 GMC 1/2 Ton Long Box
228-Zenith carb- SM420-bendix brakes
| | | | | Joined: Sep 2001 Posts: 29,262 Bubba - Curmudgeon | | Bubba - Curmudgeon Joined: Sep 2001 Posts: 29,262 | How did you adjust the timing? | | | | | Joined: Aug 2018 Posts: 46 Wrench Fetcher | | Wrench Fetcher Joined: Aug 2018 Posts: 46 | I have not yet,. I have to look it up as it is not like setting it on a small block.
1950 GMC 1/2 Ton Long Box
228-Zenith carb- SM420-bendix brakes
| | | | | Joined: Feb 2000 Posts: 4,886 'Bolter | | 'Bolter Joined: Feb 2000 Posts: 4,886 | Was it running before the carb work? | | | | | Joined: Nov 2002 Posts: 2,715 Carburetion specialist | | Carburetion specialist Joined: Nov 2002 Posts: 2,715 | Needing to have the idle mixture screw out two turns on a Zenith type 228 carb screams:
(1) Full race camshaft
(2) Massive vacuum leak
(3) Horrible compression
(4) Major timing or other ignition issues
Jon
Good carburetion is fuelish hot airThe most expensive carburetor is the wrong one you attempt to modify. If you truly believe "one size fits all," try walking a mile in your spouse's shoes!The Carburetor Shop | | | | | Joined: Aug 2018 Posts: 46 Wrench Fetcher | | Wrench Fetcher Joined: Aug 2018 Posts: 46 | Well, I timed it to vacuum today and am making between 17 and 18 pounds at idle. With the carb open it drops to 5 but then climbs back up to around 15. I tuned most of the vacuum bounce from 16 to 18 pounds out with the mixture screw. It is probably closer to 1.5 turns out now. And the vacuum vibrates between 17 and 18 pounds with a drop to 16 once in a while, but it is not a rhythmic drop to 16 it seems random. I will do a compression test when I get back home this weekend. The vacuum advance seems to be working on the carb,. Under acceleration the rod pulls in and the distributor rotates.
Also changed plugs and wires today, that seemed to help as well. The plugs that came in it were fairly new,. But when I pulled one, it was black and sooty with carbon.
Last edited by Drtheo; 08/24/2018 3:10 AM.
1950 GMC 1/2 Ton Long Box
228-Zenith carb- SM420-bendix brakes
| | | | | Joined: Aug 2018 Posts: 46 Wrench Fetcher | | Wrench Fetcher Joined: Aug 2018 Posts: 46 | Carbking Jon,
2 things I noticed when rebuilding my carb:
Someone removed the spring from under the mixture screw an replaced the mixture screw with one from a 28 model carb
The second thing is that the carb drawing g shows a main nozzle under the main jet in the angled passage way under the bowl, mine did not have that nozzle piece.
Does the 228 use the nozzle or is that only in the 28?
1950 GMC 1/2 Ton Long Box
228-Zenith carb- SM420-bendix brakes
| | | | | Joined: Nov 2002 Posts: 2,715 Carburetion specialist | | Carburetion specialist Joined: Nov 2002 Posts: 2,715 | What is the carburetor tag number?
Jon.
Good carburetion is fuelish hot airThe most expensive carburetor is the wrong one you attempt to modify. If you truly believe "one size fits all," try walking a mile in your spouse's shoes!The Carburetor Shop | | | | | Joined: Aug 2018 Posts: 46 Wrench Fetcher | | Wrench Fetcher Joined: Aug 2018 Posts: 46 | I will check when I get home today
1950 GMC 1/2 Ton Long Box
228-Zenith carb- SM420-bendix brakes
| | | | | Joined: Aug 2018 Posts: 46 Wrench Fetcher | | Wrench Fetcher Joined: Aug 2018 Posts: 46 | The plate reads 21. Then 10920
1950 GMC 1/2 Ton Long Box
228-Zenith carb- SM420-bendix brakes
| | | | | Joined: Aug 2018 Posts: 46 Wrench Fetcher | | Wrench Fetcher Joined: Aug 2018 Posts: 46 | Turns out I had a vacuum leak in my wiper motor, so with that plugged it runs well with one turn out on the mixture screw.
Last edited by Drtheo; 08/26/2018 12:45 AM.
1950 GMC 1/2 Ton Long Box
228-Zenith carb- SM420-bendix brakes
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