Choke Issues

[bbodie52]

With regard to the fuel pump, both fuel pump pressure and volume must be considered. The Corvair shop manual specifications state an expected fuel volume of 1 pint in 40 seconds or less (from the mechanical pump at cranking speed), and a pump pressure of 4-5 pounds (at 500-1000 rpm). If the pump produces normal pressure but a low volume, a leak on the suction side, or a partially blocked feed line or clogged fuel inlet filter might be the cause, and this could potentially cause a fuel starvation problem when the engine is running at a high consumption rate.

See page 6M-26 for fuel pump testing procedures. Most vacuum gauges also provide for fuel pressure testing.


Usually available from $11.00 - $25.00 on Amazon.com, at Sears or local auto parts stores...

http://www.amazon.com/s/ref=nb_sb_ss_c_ ... Caps%2C252

[mgkoret]

Thanks to Larry, I do have a functional fuel pump to try now.
I will pick up a vacuum gauge tomorrow and test the old one. I needed to pick one up for carb balancing anyway

[larry202br]

Hope it works for ya! Keep us posted.

[mgkoret]

Well two things found out.
1) there was an air leak in the vacuum hose by the ignition coil and distributor. I got that hose replaced and it actually doesn't die as easily.
2) I still think the fuel pump needs replaced and I will do so, when I can get the lock bolt out of it. It is stuck and isnt budging. Been hitting it with blaster, but no luck so far (it snapped my wrench if that tells you anything...)

Having a couple other issues that just arose and will post those in a new thread. Thanks for everyone's help in getting this figured out. Its running, which is more than I can say a week ago!

[bbodie52]

...I still think the fuel pump needs replaced and I will do so, when I can get the lock bolt out of it. It is stuck and isnt budging. Been hitting it with blaster, but no luck so far (it snapped my wrench if that tells you anything...)

Did you loosen the jamb nut on the fuel pump bolt? The bolt itself is seldom more than finger-tight, but the jamb nut holds it in place by applying pressure against the bolt threads and the aluminum housing. If the bolt itself were over-tightened aganst the side of the fuel pump, either the aluminum threads in the oil filter adapter would strip or the bolt might crack or damage the side of the fuel pump.

Loosen the jamb nut locking set screw in place and remove set screw (Fig. 59)
TO INSTALL THE PUMP...

Install the pump into the accessory housing, outlet connection to front. Carefully feel pump position with set screw, being sure set screw pilots into locking hole. Tighten set screw 9 to 15 ft. lbs. Then tighten locknut 9 to 15 lbs.

[mgkoret]

There was so much grime built up right there, I couldnt even see the nut! Back outside I go!

[mgkoret]

Fuel pump = Done
Thanks for that, had no idea about that nut being there. Came right off!

Quick question: While finding out the flooding issue, when I cover the carb opening, the left carb sends the RPM through the roof, but the right carb covered chokes the engine out. Is this normal? everyone says to do this test, but no one says the results or if the left and right are different. Thanks!

[bbodie52]

...when I cover the carb opening, the left carb sends the RPM through the roof, but the right carb covered chokes the engine out. Is this normal?

I'm assuming that you are talking about an engine that is idling and fully warmed up to operating temperature, with the chokes wide open and disengaged.

It sounds like your engine is idling on the right carburetor only, with little or no fuel mixing through the left carburetor. In other words, only air is being drawn into the left three cylinders at idle, but a fuel/air mix is properly feeding the right side and the idle speed screw on the right side has been opened excessively to compensate for the starvation on the left side.

I'm guessing that there is a blockage in a fuel circuit in the left carburetor that is preventing fuel from mixing with the air intake. When you cover the carburetor intake, the vacuum in the carburetor throat increases tremendously, forcing fuel to be drawn in from the float bowl, which in-effect suddenly brings the left three cylinders on-line and causes the idle speed to rapidly increase as the left cylinders suddenly receive air mixed with gasoline.

Conversely, covering the throat intake of the right carburetor only (the only carburetor that is working properly at idle) starves the right three cylinders for air. Since no fuel/air mix is feeding the left bank, blocking te air intake on the right side kills the combustion on the right side and the engine dies.

Check the idle mixture screw setting on the left carburetor. It should be backed out at least 1 1/2 turns from being screwed in fully. If changing the idle mixture screw setting makes no difference, the idle fuel circuit passage may be blocked. You may need to disassemble the left carburetor, chemically clean it in carburetor parts dip, and blow out all the passages with compressed air. This will hopefully correct the fault and then you can properly sync the idle speed setting of the two carburetors.

[mgkoret]

I had already dipped them both and blew them out, but maybe something else got jammed in there. I thought motorcycle carbs were touchy! I will do it again and see how it goes.

[bbodie52]

Hopefully your left wing carb will respond well to a fresh enema. Both carbs should respond the same and should be capable of being balanced for equal performance at idle and at an open throttle.

[mgkoret]

Well, I got the carb off, cleaned, and re installed.
At first, the engine fired up as it should. Then it went back to the "normal" issue. Im not sure cleaning it again is going to fix it. This time, when i covered the carb, the result was different. It would fire up as i covered it, then go back down and "pop" and gas would actually hit my hand. I now have a pressure gauge so i can do some tests with that for vacuum leaks. Not sure what I can do to get this thing going.

[bbodie52]

I don't know if this will help you, but the attached Rochester carburetor manual does a good job of describing the various functions and circuits within the Rochester carburetor. Perhaps if you read this material and study the diagrams you might be able to determine just where things are not functioning properly in the problematic carburetor.

[mgkoret]

I have the same materials and have gone over them.
I think I have it narowed down to a vacuum leak or clogged float vapor releases. It just boggles me because I just blew them out.
Is it possible to do a vacuum, test with a compression gauge? I have one of those hah
I will do the old carb cleaner spray trick to try to narrow it down if it is a leak. Just with the way it is suctioning, it sounds like it is pulling in air from somewhere else. The line from the choke pull off to the carb looks good, and the pull offs are new. The gaskets at the base of the carb connection to the intake look ok from the eye, but I have no taken them off to look at them. Could be cracked. Lots of great info of the forum, just trying to track down the real cause. The manual and rochester guide give alot of good information as well, I am just more of a hands on learner or a show me learner. Show it to me or explain it directly and I got it and can repeat it. Sometimes just words on the page doesnt get me anywhere.

Why or why doesnt Branson have a club! haha