The Stovebolt Site Forums The Shop Area Engine Shop Zenith 228 on a 261 Fuel Starvation?

(1949 3600, 261 Engine and SM 420)

My Rochester B crapped out (signs of disintegration in the accelerator pump) after a 3 y.o. rebuild. Rather than wait around for parts I decided to throw on a spare Carter YF2101S, yeah I know it's not perfect for the 261 but I got work to do! Anyway, the Carter ran great but even with the throttle closed wouldn't slow below 2500 RPM. Must be leaking vacuum somewhere but I couldn't see where.

So I put on a shiny, never been used since it's rebuild in 1970, Zenith 228 that I bought once in case I wanted to go back to a manual choke. The Zenith starts easy and idles super smooth and then dies after about 20 seconds. If I choke it it will run longer, still smooth, but will idle at 1,000 RPM for about 15 seconds, then slowly decline to 500 RPM for 15 seconds or so, then back up to 1,000 RPM, but at some point will suddenly die like it's run out of gas.

I pulled the fuel line off and put it in a bottle and its pumping gas alright (don't know what the amount should be though). Played with the idle mixture to no avail. Took the top off the carb and the bowl was about 1/2 full. The float and needle were fine and moved freely. The accelerator pump worked fine.

Tomorrow I'm getting a new fuel pump and will take the carb apart to check that the galleries are clear in the idle circuit. Any other ideas of what I should be looking for?

A carburetor rebuilt in 1970 isn't going to last long on today's fuel regardless of ethanol content. You'll be rebuilding it sooner rather than later. Gaskets are probably dried out and brittle as is the accelerator pump.

The erratic idle is likely due to fuel leaking down the carb throat. Look down the throat while the engine idles and see if there is fuel dribbling on the throttle plate. When it conks out, see if there is a puddle of fuel sitting down on the intake manifold.

Test the accelerator pump by goosing the throttle with the engine off and looking down the throat. You should see squirts of fuel.

Your fuel pressure should be a 2-4 psi. Your current fuel pump may be too high pressure but I'd test it first.

Don't put too much faith in a new fuel pump unless it's an original pump that's been rebuilt. The new ones all come from China and are pretty much junk right off the shelf. (see some recent threads about multiple faulty new fuel pumps).

The accelerator pump is working fine. If I turn over the engine without the key on, and then look down the throat of the carburetor and manually pump the throttle I get nice neat jets of gas down the throat. If I do the same thing immediately after the engine dies it's half gas half air or nothing at all. No leaks or dribbles on the carb. It seems to fail more like starvation rather than flooding, but I'll check the inside of the manifold when I pull it tomorrow.

I don't have a gauge for testing the fuel pressure psi. The flow into a bottle seemed ok, definitely not too high, if anything it's a bit modest on the output. The current fuel pump is 3 years old, made in China, which is why I'm suspicious of it. Replacement parts these days have no durability.

You have good reason to be suspicious of the pump. I had one fail after a few hundred miles and its replacement failed to pump a single drop straight from the box. Anothe r person on this forum posted a nearly similar experience last week. I installed the rebuilt original pump and the trouble ceased.

Re: accelerator pump: When the engine is stopped, the accelerator pump should pump the same amount of fuel as it does when the engine is running. If it isn't, it's either faulty or there is no fuel in the fuel bowl.

That fuel has either leaked out, or there wasn't any to begin with. Either the fuel pump didn't fill it, or the needle is stuck in the seat, float is stuck , the accelerator pump isn't working, etc.

Fuel filter?

Fuel tank vent?

Jon

Some of those carbs had a little screen right by the needle & seat that can become clogged.

George

The pre filter in the 228 Just ahead of the needle and seat is clean, and fuel flow from the tank appears unrestricted.

I pulled the 3 year old pump off and it was very soft in its action. Took maybe a pound of force to actuate it. It still had spring, and at its last 1/4 stroke it produced vacuum and pressure if you held your finger over the intake/output.

Got a new Precision fuel pump (made in Korea), which is spec’d for the 261. It takes something 30lbs of force to operate and kicks out considerably more vacuum and pressure. Seems like a lot of muscle required to move this thing. Makes me worried for the cam!

Oh, and the old pump had a 3 piece riveted lever riding on the cam. I thought that kind of lever was only for rod actuated pumps? The new Precision pump has the typical one piece, formed, lever.

Have to bend some lines now and we’ll see if this makes a difference.

So the new fuel pump hasn’t changed anything. Truck still starts, runs, and dies after 20 seconds or so. Likely a plug somewhere in the idle circuit?

The new pump does pump 4 times as much gas though, so I’m leaving it on.

Next step is disassembly of the carb and blowing out all the channels. This is the first time it’s ever run so even though it’s been sitting on the shelf for years it seems unlikely that there’d be clogged galleries anywhere

Color me Stoooopid.

The adjustable main jet on the Zenith was set to fully closed! 🙄

Set it to 4 1/2 turns open and she runs super smooth now. Will have to rebuild it with ethanol proof parts at some point, since this Zenith was overhauled in 1970. Still, it’s good fun to pull something off the shelf after decades and have it work so well. Just remember to check the factory settings!

You'd be surprised; spiders, dirt, dust, etc, find their way into cracks , crevices , and orifices especially after 50 years. Even if it's in a box, it's true.

Glad you found it!

4 1/2 sounds like a lot. You might try dialing it back a little at a time to see how it runs. Factory initial setting is 2 1/2 turns, with a range of 0 to 5 turns.

Jon

Was following a settings guide I found on the internet for the 4 1/2 turns. I don’t have it in front of me right now but will report back tomorrow. It did say that 4 1/2 was just a start and that, once warmed up and idling at mid power that you fine tune it lean back to rough and then richen to smooth.

Was using the initial Zenith 28/228 settings from carburetor-blog.com. Worked out well.