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4.2 with Weber Carb. Need help!

16K views 15 replies 11 participants last post by  Got it at last 
#1 ·
So my buddy has a 4.2 with a brand new Weber carb and a new motor he had a "friend" install. So now he has a ton of issues and asking me to help. I consider myself pretty mechanically inclined but have very little experience with the 4.2 and Weber carbs.

So far my research has shown I should remove the FPR (aftermarket) and add a stock fuel filter as the return isn't attached to anything. The PCV is on the far end of the valve cover and not attached to anything. Some guidance would be greatly appreciated.

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#2 ·
You cant remove the FPR if it has an aftermarket electric fuel pump. The electric pump generates too much pressure for a carb system. An inline filter is a good idea between the FPR and the carb. There should be a second port on the FPR to hook the return line to.

The PCV should be hooked to a vacuum source at the bottom of the carb, perhaps on the riser plate, look for an Allen head plug or similar that you will need to install a nipple into. The normal PCV line is 3/8".
 
#3 ·
You cant remove the FPR if it has an aftermarket electric fuel pump. The electric pump generates too much pressure for a carb system. An inline filter is a good idea between the FPR and the carb. There should be a second port on the FPR to hook the return line to.

The PCV should be hooked to a vacuum source at the bottom of the carb, perhaps on the riser plate, look for an Allen head plug or similar that you will need to install a nipple into. The normal PCV line is 3/8".
I've read a few posts on other forms that said as long as the electric pump is only 4-8 psi, it should be fine. His looks to have a small shitty Mr Gasket pump on the frame rail.
 
#4 ·
That's true...4-8psi pump would work perfect. The carb you are working with works well with 6psi.

Just because it looks like a cheap Mr. Gasket pump doesn't mean that it is actually only producing that small of a psi. Most electric pumps are more in the 30-60 psi range to be able to work with a fuel injected motor. The only way to tell for sure is to hook the line coming from the pump to a fuel pressure gauge. Besides, if it was actually an electric pump rated for a carb, then why did the previous owner install the pressure regulator in the 1st place?
 
#5 ·
That's true...4-8psi pump would work perfect. The carb you are working with works well with 6psi.

Just because it looks like a cheap Mr. Gasket pump doesn't mean that it is actually only producing that small of a psi. Most electric pumps are more in the 30-60 psi range to be able to work with a fuel injected motor. The only way to tell for sure is to hook the line coming from the pump to a fuel pressure gauge. Besides, if it was actually an electric pump rated for a carb, then why did the previous owner install the pressure regulator in the 1st place?
The pump looks just like this one. I'll try to get the actual part number next time I'm under there.
Mr. Gasket 12S Micro Electric Fuel Pump https://www.amazon.com/dp/B000BWCERY/ref=cm_sw_r_awd_8b1KvbSB8HVP9


The best way I can describe the Jeep's owner is he listens to every guy who claims to be a mechanic (including the douche that installed the motor) and he blindly spend money with out a plan (hence the plethora of shiny bits under the hood).

Great guy but doesn't do enough research and just throws money at his Jeep. Problem is now he's about $9k deep in this 87 and he's frustrated. It leaks oil badly (pretty sure it's just the valve cover and oil pan gasket). There's a slight leak at the fuel pump. Fuel gauge doesn't work (he put all new custom gauges in). The carb is an obvious issue. He claims it idles at like 3k and he said it wreaks of fuel.

I'm no mechanic but I have done quite a bit in my 39 years and consider myself mechanically inclined, I honestly just have very little experience with carbs. My Jeep is a 91 with the 4.0.
 
#6 ·
Well, if he listens to what everyone says, tell him to get rid of that carb if it's a 32/36 and get a 38/38 instead. The 32/36 simply isn't enough carb for a 4.2L. I found that out the hard way on my '90 YJ.
 
#7 ·
Carb issues

I run my weber at 3.5 psi and changed the main fuel to a 70 from the 60 that came with it-runs much better, but still work to be done. These can be tricky, but there are good write ups out there to walk someone through it on this site. I also saw that you mentioned oil leaks-I struggled with aftermarket gaskets & finally went OEM-especially on the pan-problem solved! If you drop the pan, check rear main while you're there!
 
#8 ·
I have an '87 with a 4.2, I run a Weber 32/36 along with a Holley fuel pressure regulator set at 3 psi, my Jeep is running great. But I also use the stock mechanical fuel pump and fuel filter. I'm not sure what the advantage of having an electric fuel pump is. I have read the Weber 32/36 works best at 3-3.5 psi, and I'm pretty sure most electric fuel pumps push more than that without the use of any kind of regulator.
 
#9 ·
I have a stock 4.2, DUI distributor, NO sensors or computer. Weber 23/36 with a STOCK mechanical pump and the STOCK fuel filter/ regulator. I had a separate FPR but it caused a lean condition and overheating at 70+ MPH so I removed it Fuel pressure at the carb is 4.8 psi with a certified gauge. Bowl vent to charcoal canister, front PCV valve to fitting on the adapter plate, rear valve cover vent to the hole on the left front corner of the air filter. No jet changes yet. It does run slightly rich but will spin 35" tires on dry pavement with the stock gears.
 
#13 ·
I have an '87 with a 4.2, I run a Weber 32/36 along with a Holley fuel pressure regulator set at 3 psi, my Jeep is running great. But I also use the stock mechanical fuel pump and fuel filter. I'm not sure what the advantage of having an electric fuel pump is. I have read the Weber 32/36 works best at 3-3.5 psi, and I'm pretty sure most electric fuel pumps push more than that without the use of any kind of regulator.
You use an electric with the stock FP? what is the order from tank to carb for all. EFP, SFP, Pressure Reg and filter. Thanks! AC
 
#14 ·
You use an electric with the stock FP? what is the order from tank to carb for all. EFP, SFP, Pressure Reg and filter. Thanks! AC
Welcome to the Forum!
 
#16 ·
Welcome to the forum @alan.colpitts
This thread was put to bed back in 2015.

If you have a question about this scenario your best bet is to start a thread of your own here in the YJ tech section so we can focus on you.
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
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