The Stovebolt Site Forums The Shop Area Engine Shop Fuel Pump Too Much Pressure

Matt, I just measured my throttle plate mounting holes. They are 11/16" center to center and the throttle shaft length matches your 2nd pic measurement. I think it will work. Since you are able to remove the throttle plate screws yourself (per you pics), send me a PM and we can figure out how to get this throttle plate assembly to you.

I will check the fuel pressure tomorrow if I can locate a fuel pressure test gauge to borrow from our local auto store. How exactly do I test the pressure? Do I just hook up the tester to the fuel line past the pump and then turn the engine over a few times and then check the reading?

They sell combination pressure / vacuum gauges at any auto parts store for about $20. Buy one.

Disconnect the fuel line at the carburetor and put the hose over the steel line. Crank the engine and read the gauge.

You can use a T connection to test the pump pressure while the engine is running. Same results either way.

I personally prefer to put in a Tee and test it while the engine is running, but if you are looking for overpressure either way will work.

Thanks Otto!

I deadhead the fuel line into the gauge, and idle the engine for half a minute on the fuel in the float bowl. If you can't idle that long on the gas in the carb, fix the carburetor. A fuel pump test has three steps- - - -volume, pressure, and vacuum. 30 seconds at idle should pump at least a pint of gas into a catch container. Idle pressure should be 3-4 PSI, and the pressure should stay there for at least a few seconds after shutdown (tests the output check valve). Check the vacuum on the input side- - - -it should be at least 12-15 inches of mercury, and it should also stay there after shutdown. (tests the inlet check valve). Failing any or all of these tests means you need a rebuild or a replacement pump. Passing the pressure and vacuum tests with low volume means there's a restriction or an air leak between the pump and the gas tank. The flex line between the engine and the frame should also be vacuum checked- - - - -some of them are prone to get pin hole air leaks.
Jerry

I checked the fuel pressure. It's reading 4 psi.

Ok guys... Here is an update and I'm left more puzzled now than ever!

I called up a local guy who runs his now business of restoring classic carburetors. He just happened to be driving near me so he stopped by and spent 2 hours looking everything over with me. His conclusion was that the Rochester B carburetor I have is good and working as it should.

Here's the problem.... We could not get it to start. After trying for a few minutes, I showed him the fuel sitting in a pool down in the intake by opening the throttle and looking through the carburetor. We pulled some plugs and the plugs are dry. Shouldn't they be soaked in gas after filling the intake with gas???

At this point we checked the ignition and initial timing all of which checked out ok. Pugs are firing. Compression checks out to be good on all six cylinder. Valves have clearance at the rockers.

We put a vacuum gauge on the port of the intake and were getting NO VACUUM reading at all while turning the engine over!!!! The only way we could get any vacuum when turning the engine over was to cover the top of the carburetor by hand. It seems like the engine is not sucking the fuel in at ALL. The guy put his thumb over one of the plug holes while i turned it over and said it was blowing out but never did it try to suck in.

Could the problem be somewhere between the intake/exhaust OR between the intake and the engine???? When he left, he assured me that the carburetor is not my problem right now! But he left confused and said he would be thinking about this all day!

Should I pull the intake/exhaust manifolds off and check for any issues there????

Has anyone else ever experienced an issue like this?

*Reminder: the engine is a 235 with the 848 head.

How confident are you in this guy? You shouldn't be drawing air through the plug hole on the downstroke, you draw through the valvetrain.

If covering the carb gives you vacuum, it sounds like you were trying to measure ported vacuum, not full.

Also, if you get vacuum when you cover the carb, then it is drawing air from the intake like it should.

It sounds like you need to find a different "expert". Send me a PM and I'll respond with a phone number. I have an idea what's going on, but a 2-way conversation about doing "cranks but no start" diagnosis is always better than trying to do it by text. It's virtually impossible to get a vacuum gauge reading at cranking speed, regardless of where you connect the gauge, and anyone with enough experience to try to advise you should know that.
Jerry

***Update***

Let me give a BIG shoutout to Jerry (Hotrod Lincoln)! He called me yesterday evening and helped walk me through troubleshooting this. Had me take valve cover off and rotate engine until the #6 cylinder valves started to rock. Once the exhaust valve rocker went up and then back down and the intake just started to move, I looked at the distributor rotor. It was pointed at the #1 plug but a little bit past it. Once I rotated the distributor back a bit (counterclockwise), and tried to start it, it coughed a sputtered a bit. Jerry encouraged me to check to make sure I had it set so that the points were just beginning to open when the rotor points to #1. After another minor adjustment to the distributor, Jerry encouraged me to heat up my spark plugs with a blow torch to burn off the carbon deposits and fuel built up from where I had been flooding it. After I did that and let them cool for a half hour, I put them back in and it fired right up!!!!

I still have some fine-tuning to do I believe but it ran strong for about a half hour and revved up without stumbling or anything!

I also want to give a big shout out to Dan (Gdads51). He had the right throttle body for a Carter YF I bought with the wrong throttle body. He sent that to me and it arrived in the mail yesterday! I have not put it on yet but I am going to in the near future and see what I get with the Carter YF running on the truck!

This forum has been a BIG help to me (a NEWBIE).

THANKS!

CONGRATULATIONS!!!!!!!!!!!!!!!!!!!!!!!!!

Glad you have it running!

Jon

"I love it when a plan comes together!" Good on ya for being persistent enough to keep plugging away (and following my suggestions!) I've found repeatedly that a few minutes in a 2-way phone conversation beats hours on a keyboard, just about every time. There's a lot less chance of misunderstanding what's being suggested and wasting a lot of time and effort.
Jerry

And *that* is why we're here!

Thanks for the motivational boost -- you brought me back in from the ledge. Then again, Stovebolt HQ is in a single story building ...

So with all the help, I did get it running again but it’s running very sluggish on acceleration. I managed to drive it about 10 minutes but it was running so sluggish that I pulled back in and parked it. When I pulled the plugs this is what I found. Am I only firing in 2 cylinders? The plugs are starting from left #1 through #6 on the right. It looks like only #3 and #4 firing right. Any thoughts?

Is that oil fouling or carbon fouling?

Pull one of the wires from a dirty plug and see if it's getting spark. Use a spark plug tester which is a little light bulb with leads on each end to connect between the wire and the plug. If that wire is firing, it will light up.

Or put a screw driver bit in the end of the wire and hold it above a metal part under the hood and see if a spark jumps.

Otto,

I've checked all of them with a spark plug tester. All of them are lighting up. It is definitely carbon fouling, not oil fouling.

For some reason, the carburetor is running WAY rich. That can be caused by a too-high float level, a stuck power valve, or a warped top housing that creates a vacuum leak that causes the power piston to stay in the full rich position. There are some very well written instructions on how to diagnose and repair a warped top cover on the forum.
Jerry

Thanks Jerry! I’ll have to check out the carb. I know the float is not too high. I set it a little low actually trying to compensate. The only thing I can think of is that it might be a slightly warped housing. However, I did notice that the holes in the housing for the screws requires me to thread them through the housing before screwing into the bowl. I wonder if that is a problem causing it to push the top housing up a bit when it screws down. I’m not getting any leaks in between though. Just a little weeping but not really leaking.

What would make plugs 3 and 4 so different though? I ran it and when I pulled back in, I shut it off immediately before pulling the plugs to keep it from idling any at the end.

Matt, I've completely lost track of what carburetor you are using.

Is this a Carter YF that has been rebuilt to proper specs according to carbking?

Going back to the title of the thread, have you verified that the fuel pressure at the carburetor inlet is between 2 and 4psi?

My truck's pump runs at 2.5 psi for 8000+ miles.

My fuel pump is putting out 2.5 psi. I’m still running the Rochester carb I rebuilt. I have what I need to get the Carter YF on it with the exception of the accelerator pump/plunger. I discovered that it is cracked and causing the Cater YF to leak. I need to order one online so I can try out the Carter.

Matt, those screws that secure the bowl cover to bowl should not bind or need to be threaded through the top holes. That issue could be preventing your top from properly sealing to the bowl and create vacuum leaks. Sounds like someone may have used oversized screws at some point. The quick fix for that is to carefully drill out those top cover holes so the screws pass through without having to be threaded in to the cover.

The screws may be the correct size but after decades of overtightening them, the soft cover holes have been mushroomed, a careful gentle drilling should solve that issue.

" I’m still running the Rochester carb I rebuilt."-- - - - -I believe that is a big part of your problem. A brand new, never run Rochester makes a good paperweight. Once somebody puts gasoline into it, it becomes a stinky paperweight. A 70-something year old Rochester that's been worn out and "rebuilt" a few times is a good candidate for the recycle bin. The only reason Rochester B's exist is Chevy got tired of buying Carter carbs and decided to make their own units that were designed to barely survive the warranty period on a new vehicle in the 1950s. Chevy had no idea (and didn't care) that hobbyists would be trying to make these old rigs keep running 70 years after they rolled off the assembly line. Carter's sales slogan was "The ABCs of carburetion are 'Always Buy Carter!" They built an aftermarket direct replacement carb for the Rochester B that sold well over a million units. When the one-millionth carb came off the assembly line, the CEO of Carter had it gold plated and presented it to the CEO of General Motors.
Jerry