The Stovebolt Site Forums The Shop Area Engine Shop Zenith 228 uphill battle

All,
I have a Zenith 228 on my 57 235. It runs great on flat ground, open road or city. But when I go uphill it starts to loose power. A meter has been placed on it and shows it needs more fuel. The jet has been adjusted all the way out to allow for max fuel. Any thoughts on what may be causing this?

What condition is your fuel pump?

I am not really sure. I purchased the truck from someone and do not know the exact condition of it. It looks like a standard one, like a plate was placed over where the glass bowl would go. I can try to look for a number. If I did not answer your question please let me know......and thanks!

Sounds like the fuel filter needs to be changed.

Pete

what meter has been placed on it to determine that it needs more fuel unless you have an adjustable jet other than a fixed jet there are no adjustments to a zenith other than idle. if you do have an adjustable jet it will have plenty of gas if turned all the way out.

i see a lot of gmc's with chevy carbs on them which work. not too often a gmc carb on a chevy

we used a innovate l2 fuel sensor ......it went up the tail pipe.....I'll change the fuel filter. Think i may even buy a electric fuel pump. Any thougts on what manufacture and model of fuel pump would work well? Thanks again......

6v or 12v?

You still haven't answered which jet are you talking about? Is it the idle adjustment or do you have an adjustable main metering jet? The idle the jet has nothing to do with driving and like Ashton says, if you do have an adjustable main metering jet, you will be getting plenty of gas. A bad fuel pump will usually cause hesitation instead of low power. Have you ever driven a 235 before? You may be expecting too much out of your little 6 banger. I'm not really sure about the validity of your meter check. If you are actually experiencing a lean mixture, it could be the power valve in the Zenith is not functioning. I would invest in having an experienced person rebuild your Zenith before I would think about an electric fuel pump. I like electric fuel pumps, but I don't think that is your real problem at hand. It could also be something simple like a too low float setting.

The system is 12v.
The carb is NOS from eBay. It has an adjustable main jet. Tag# 11280C.
The gentleman that is doing the work is well known in my area. He did say it could be the float and something else that is in the carb. Maybe it is the power valve; I will pass it on. We are going to try the one I purchased new from Carbsonly (this weekend I hope). I do wish it was lack of experience regarding the 235 but, I have had my other 52 chevy with a 235 in it sense 1991. I had a Rochester on it and it would hold the hill, if the grade was not to steep :-).
Thanks again for everyone’s input....
..

I agree with crenwelge, no need for a electric fuel pump. Recheck the float level and set a tad high if its correct now. The high setting will richen the mixture a bit. The idle screw is just that, for idle only. It has no effect once the throttle is opened. Set it using your air to fuel ratio gauge in the tail pipe, look for a high 12:1 to mid 13:1 ratio at idle. I would expect to see 14.5:1 AF ratio when driving, or higher even. It sounds like the power circuit is not working. It should apply more fuel as the vacuum drops, such as climbing a hill. If your gauge does not drop when climbing hills or working hard, then its internal. You could also have to lean of a jet since this carb was not designed for this engine.

Electric pumps have the place, its just not here. If you do decide you want one, be sure to wire it through a oil pressure safety switch. You sure don't want it running if the engine isn't!

Joe

Lots of possibilities here, and really insufficient information to know what to suggest.

First, as others have suggested, if the adjustment being made is the idle control screw (a pointed screw held in place by a spring screwing into the throttle body [lower casting]) then it makes no change in the mixture at any engine RPM above idle. If the adjustment is a "T-handle" which screws into the bottom of the center section (bowl) at approximately a 45 degree angle, then this effects the mixture at higher RPM's. MOST type 228 carbs do NOT have this adjustment.

Issues could include ignition, fuel delivery, or as simple as the incorrect type 228 carburetor. If the carburetor was designed for a much larger engine (type 228 carbs were used on engines as large as 321 CID) the venturi would be too large, thus flooding the engine with air and a meter would show needing more fuel. The only solution to this issue would be a proper sized carb.

A fuel tank vent was was stopped up could cause the issue. If the tank cannot vent, fuel might trickle out, but in insufficient volume to run at load (up the hill).

A weak fuel pump, or a worn camshaft lobe could not supply sufficient fuel to the carb.

Suggestions:

(1) verify that the carb is the proper size for the engine, else replace the carb. If the carb is the wrong size, nothing is going to help other than the right size carb.

(2) test the fuel pump output (see your shop manual)

(3) replace the fuel filter

(4) try a test run without the fuel tank cap (will test the tank vent)

One other thing: do a compression test to determine the condition of the engine. A badly worn engine WILL lose power on a grade!

Jon.

Funny, there was supposed to be a post here! The carb has an adjustable main jet. I do have another 52 with the same 235 so have drove them sense 91. I absolutely love the trucks! I will pass on the information to my mechanic. He did say something about the float but did not want to tare open a new carb until he looked at a few other things. I have no idea what those would be, I can replace a starter, brakes and the like but stay away from carbs and rebuilding motors.

Thanks again you guys for all your input, you have been great!

Thanks Jon for the ideas. I will pass this along and see what we can determine.
The data I have shows it will work for 1954-61 (respectively) GMC 248 or 270 w replacement zenith number of 11280. I took this info and purchased a 228 NOS from ebay # 11280C.
I put it on as a temp because I was waiting for carbsonly to return the one I purchased from them late last year ( # to be edited).

Take care

Zenith suggests this unit for engines of a minimum of 300 CID. This carb is the largest of the 228's. It will work well on engines as large as 325 CID. When you open the throttle, vacuum is going to approach zero, venturi velocity is going to be too small, and the engine will run lean to very lean.

Since you have another carb coming, in the meantime when going up a hill, experiment with increasing the throttle only slightly, rather than wide-open. MAYBE with a smaller throttle angle, you won't totally kill the air velocity through the venturi, and the engine will run better than at WOT.

Jon.

Will do Jon. Thanks again for the help with my issue, it is greatly appreciated!

So if the # 11280C is to large for the 235, can it be downsized? Or still used for parts?

I have had to put the carb on hold. When my mechanic started work on fixing my broken parking brake he also found oil in both rear wheels. They are covered! and the brakes are all but gone. So once that is done the Zenith issue can proceed.....

Thanks again everyone for the help. In the future, what type of informatin should I have provided to support my question?