How to tell a weak fuel pump- test?

[Fourspeedwagon]

I've been troubleshooting various systems and now I'm at the fuel pump..

First off, background. Car starts, idles and runs low rpm just fine. However, the tach is showing somewhere around 2000 as the highest it'll rev and any quick blip of the throttle causes it to stumble and almost die. I've drained the fuel tank, cleaned the filter/petcock, cleaned the plugs, set the points/timing, and tried a different coil.

Is there a standard test to check the output of the pump? Am I barking up the wrong tree looking at the pump as suspect? Any other place I should look at before or instead of the pump?
Thanks again fellas- Greg

[jstenner]

Could be float level...to low...or fuel circuit in carb gummed up/stuck or otherwise constricted.

[roy mawbey]

I presume you have also checked the main and idle jets under the square jet cover if you have Zenith 32 NDIX carbs? Have you tried taking the air cleaners off and then when looking down the throat and the venturi's and then pushing down to the stop the throttle levers several times to see if the accelerator pumps are squirting fuel down the venturi's?

You could also take off the connection from the fuel pump to the L/H carb and AFTER removing the coil lead so the engine will not fire place the end of the delivery pipe into a correct receptable and get someone to turn the motor over so you can see the delivery. It should be enough to fill a bowl quite quickly. A full bowl will enable anyway full revs for sure for a short time. If its just a small dribble maybe the flexible diaphragm is damaged in the pump?

The stuttering does sound like not enough fuel getting past the jets.

Roy



Are the float needle valves possibly sticky these control the flow of fuel as the float rises in the bowl.

[Fourspeedwagon]

I haven't opened the carbs at all, but I did check the squirters. The drivers side seemed weaker than the passenger side.

Is a solvent type "carb cleaner" or similar the answer to gummed up insides or is that worthless in this case?

I'm a bit trepidatious to take the carbs apart to far.. But I suppose I need to learn at some point.
Thanks for your patience and helpfulness- Greg

[jstenner]

Caveat: my only experience is with my old Solexs. If I wait too long between drives, the bowls dry out and the float/needle tends to stick either fully or partially closed giving symptoms similar to what you describe. A light tap or two on the bowl and I'm back in business. Since this is inside the bowl, no amount of carb cleaner down the throat will make a difference. If your car has been sitting a long time, it might be that you need to disassemble the carbs to clean/free things up.....

HTH

[roy mawbey]

Greg,

If your car runs with the Zenith 32NDIX and as you mention you have not had the carbs apart, buy a rebuild kit ( or 2 ) from www.stoddard.com as directly you remove the jet covers etc, its best to replace old gaskets. The manifold gaskets as well will need to be new if you remove them.

If you look on the ' registry ' or just google 'Zenith 32 NDIX' you will find info on how to get those carbs running okay. You might try first just removing the square jet covers ( 10mm spanner ) and after removing the 4 brass jets ( 2 idle and 2 main don't mix up! ) check to see if they are blocked.

The 2 brass mixture screws with the knurled edges ( approx 14mm dia) should not been fully tightened in. They control the carbs mixture and balance but the starting point is usually about one and half turns out from closed. ( its a fiddle with the carbs in place but is possible)

Trouble is if you don't know the carb history someone could have really messed about with the mixture screws which can affect things.

The float needle valves can be changed easily if the top cover of the carb is removed and you will see the float valve inside the bowl behind the fuel inlet.

Of course all this depends if they are Zenith and not Solex

Roy

[roy mawbey]

Greg,

I should have put 'its a fiddle to unscrew the 2 brass idle jets( top ones in the chamber) and the the 2 bottom main jets in the chamber with the carbs still attached. Best to remove each idle jet one by one clean it and replace then you won't mix them up. Also the idle jet delivery hole is very small. No air compressor then use a stiff bristle form a brush to clean not wire.

The 14mm mixture screws are quite easy to get at.

Roy

[roy mawbey]

Greg,

Me again! Your question about fuel pump pressure is answered on here as well as giving you some good info on the small pump
http://www.type356a.com/

Roy

[Fourspeedwagon]

I'm pretty sure they are zeniths. I don't see a name on them but from a pic I found on google image they look right. I had them rebuilt 15 years or so ago.. Hopefully in the next day or two ill have a chance to find an assistant and check the pump


Is a rebuild an "expert" job or could a person without experience pull it off successfully?

[roy mawbey]

Greg,

You do have Zenith carbs. Before you strip the fuel pump check the delivery it well might be okay. If you have to renew the parts in it that is possible but apart form the diapragm there are small valves in the body as well. The stroke of the pump is governed by a rod that pushes onto a cam on the distributor drive and that moves the diapragm to provide the pressure. You have to get that movement distance correct and many use a special gauge to do that.

I do have instruction somewhere to detail the procedure. If you find your delivery is very weak then you can ask me and I will find it.

Roy