1987 4.2L Fuel Supply Question - Pirate4x4.Com : 4x4 and Off-Road Forum

79'cj-5 · 11-06-2011, 09:18 AM

I have a 87' YJ w/ the 4.2L in it. I'm also running a Webber carb.

It doesn't seem to be getting enough fuel (have a fuel pressure gauge at the carb - at best it reads 2 psi). If I clamp off the fuel return line, I get more than enough fuel pressure. I have a fuel pressure regulator, so I can dial it to what the Webber carb wants (3 - 3.5 psi).

So, my question is, do I need the fuel return line?? What benefit does it serve?? Am I going to run into issues in the future if I just block it off and run a regular inline fuel filter??

daryl · 11-06-2011, 05:09 PM

My CJ's 4.2 with an mc2100 has an inline filter and no return line. Works just fine.

79'cj-5 · 11-06-2011, 05:33 PM

Sounds good ... looks like I'll be messing with the fuel lines this week ... Never ending project!

CJim7 · 11-06-2011, 05:38 PM

I never ran a fuel return line when i had a Weber on the old 4.2, Regulator at 3psi and it ran great.

11-06-2011, 09:18 AM	#1 (permalink)
79'cj-5 Newbie Join Date: Jun 2005 Member # 48753 Location: Brownsboro, AL Posts: 54	1987 4.2L Fuel Supply Question I have a 87' YJ w/ the 4.2L in it. I'm also running a Webber carb. It doesn't seem to be getting enough fuel (have a fuel pressure gauge at the carb - at best it reads 2 psi). If I clamp off the fuel return line, I get more than enough fuel pressure. I have a fuel pressure regulator, so I can dial it to what the Webber carb wants (3 - 3.5 psi). So, my question is, do I need the fuel return line?? What benefit does it serve?? Am I going to run into issues in the future if I just block it off and run a regular inline fuel filter?? __________________ ---------------------- BUILT not bought!! 87' YJ 4.2L w/ 4.0L head swap, Ford T18A, Mopar Performance Dana 44 axles and 36x13.5 Irok's 79' CJ-5 - waiting its turn in the garage

11-06-2011, 05:33 PM	#3 (permalink)
79'cj-5 Newbie Join Date: Jun 2005 Member # 48753 Location: Brownsboro, AL Posts: 54	Sounds good ... looks like I'll be messing with the fuel lines this week ... Never ending project! __________________ ---------------------- BUILT not bought!! 87' YJ 4.2L w/ 4.0L head swap, Ford T18A, Mopar Performance Dana 44 axles and 36x13.5 Irok's 79' CJ-5 - waiting its turn in the garage

11-06-2011, 05:38 PM	#4 (permalink)
CJim7 Registered User Join Date: May 2006 Member # 72257 Location: IdaHo Posts: 1,325	I never ran a fuel return line when i had a Weber on the old 4.2, Regulator at 3psi and it ran great. __________________ I drive the fastest barbecue on 4 wheels...

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11-06-2011, 05:09 PM	#2 (permalink)
daryl Registered User Join Date: Jan 2009 Member # 128286 Location: Southwest Florida Posts: 261	My CJ's 4.2 with an mc2100 has an inline filter and no return line. Works just fine.