Mondello Fuel Pump and Return Line

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jpoole

Greasemonkey
Apr 23, 2013
128
4
18
McKinney, TX
Hi Guys, I had a motor installed in my HO, 403 with double roller timing chain. Well my installer told me that the AC delco pump was too close to the timing chain. They talked to Mondello and they sent out a pump that would work. They installed without the return line hooked and Mondello told me that one of the ports was for the return line so I hooked it up.

I drove around a little and it started stumbling under light/medium acceleration. Then it died and wouldn’t restart. It would just turn over and over and occasionally act like it would start. Towed it home with my truck and put the plug back in and it started up. Any thoughts on what might be happening.

Thanks
 

88hurstolds

Royal Smart Person
Jun 24, 2008
1,747
650
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Mondello died a couple years ago, you probably talked to Lynn... he is not a good source for help according to 99% of the Olds community.
What kind of carb are you running?
Is the vent line plugged?
What type of gas cap are you using, is it vented?
What type of timing chain is it?
Lots of people are running a stock pump with a double roller, I am in my 455.
 

mheath717

Master Mechanic
Nov 13, 2008
413
19
18
Florida
I am running an Edelbrock double roller timing set with an Airtex fuel pump with no issues.
 

jpoole

Greasemonkey
Apr 23, 2013
128
4
18
McKinney, TX
Thanks guys, I don't know who made the timing chain it came with the crate motor. I have searched on this and found that the small blocks don't have a problem with interference just some big blocks.

It is a factory CCC quadrajet and the vent is working. It also has a vented cap. Everything was working in the fuel system before the motor swap. When I remove the plug to install the return a lot of fuel came out. This afternoon when I installed the plug back I removed the rubber line to the nipple, nothing came out, then just a small amount when I removed the fitting itself. I am thinking that means the return line is working.

Could the return be allowing too much fuel to exit the pump and causing a fuel starvation problem? It is almost like vapor lock.

I am going on another test drive this morning to see if the problem is actually gone now.
 

88hurstolds

Royal Smart Person
Jun 24, 2008
1,747
650
113
Ive also had a bad EGR valve cause a stalling issue similar to vapor lock.
My Hurst Olds would die like clockwork every 30 miles on my way back from Boston for the last 200 miles.
I would wait a minute and it would fire right back up.
Make sure your EGR solenoid is good and the EGR isn't stuck.

Could be a bad fuel pump too, it's a simple cheap fix.
Easiest way to remove it is from under the car so you don't have to remove the AC.
 

jpoole

Greasemonkey
Apr 23, 2013
128
4
18
McKinney, TX
Thanks will check egr. Can these be installed backwards? Vac port facing forward. 307 faced to back.
 

jpoole

Greasemonkey
Apr 23, 2013
128
4
18
McKinney, TX
took the car for a drive this morning with the plug in the return line fitting on the pump. Everything was fine. Found where I had left my the electrical plug off the carb for the mixture control solenoid. I plugged in and connected up the fuel return and it was the same thing. Stumble on part throttle acceleration.

There was a lot of pressure on the plug when I removed from the pump. Shot off. Also, starting is much better with the return line, without it takes a little while to start and with it it fires right up. (except yesterday when it stranded me).
 

jpoole

Greasemonkey
Apr 23, 2013
128
4
18
McKinney, TX
Took the tank connector off the charcoal canister in the front and blew in it. Very hard to blow in. Tried sucking also and it was moving air from tank , just slow. Same with gas cap on or off.
 
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