4.2l engine knocking

mbalbritton said:
And the Saga continues...

I had another carb thread going, but I'm going to continue this entire story in this thread. Started having a flooding issue, and rebuilt the carb. This did not fix the flooding issue, so I bought another carb figuring the old one was just flat worn out.

Got that installed this morning and no fuel dumping all over the place outside of the carb, but seems to be still flooding. just down into the venturis. While installing the carb I did notice that there was coolant seepage around the bypass hose on both ends when there hasn't ever been before. I continued working and tried firing the jeep up. it started to run and stumbled, then wouldn't fire. Looking for fuyel leaks, I notice more wetness around the bypass hose. I pulled the relief valve on the radiator and it was pressurised..... Noooooo, no no no no...

Pulled the cap off and cranked the engine again. coolant starts rising and coming out the radiator. FAWK!!!

Started pulling plug. These are brand new plugs, maybe just a few minutes of run time on them. 1,2,3 slight bit of soot and wet, I assume with gas. 4,5,6 look brand new, but wet. Unfortunately after Covid, my sniffer is AFU and I can't tell from the smell.

Seeing as I've been suspect of #5, I'm wondering about a blown head gasket.

So many different things going on here, Non start, flooding/carb issues, pressurised cold coolant system, knocking...

I was already planning to pull the head and open it up to swap the #5 piston out in an attempt to get a little more life out of it while I source and determine what exactly I want to do for an engine swap. Just a bit discouraged right now.
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Jeep Life.
 
Ok, so. Crank all you want, I can’t get a single fire of any kind. Nothing. Pull a plug wire and check for spark. Good there. Pulled the carb back off and looked down into the intake. Absolutely saturated with fuel. I pinched off the fuel line and turned the key without the carb or anything on it. It fires immediately with what little fuel and vapor were in the intake and cylinders.

Go check the float needle on the brand new carb and it’s functioning fine. No debris.

Either I’m getting too much fuel pressure, or the carb is dumping too much fuel down the intake.

Could I have a return line issue?

Typing as I’m working here. I just put compressed air to the fuel return line coming off the filter. I would imagine I should be able to blow compressed air back to the tank. I can’t. Not with 100 psi. Could this be causing the fuel dumping into carb issue? Could it be enough pressure to over power the needle?
 
to verify. take a jug of gas and gravity feed the carb. if it runs ok, then go down the fuel pressure road.
 
Jeff B said:
to verify. take a jug of gas and gravity feed the carb. if it runs ok, then go down the fuel pressure road.
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or run your return line from the filter to a jug using a piece of tube and see how that does

Edit: FWIW when I got my Jeep it had that small holley 4bbl and an offy intake on it with no return line and seemed to run fine
 
Thinking about the 2100 swap.

The adapter plate is a Mr Gasket part. No problem. Then there’s the throttle linkage. Mc2100 pulls back to the firewall, while the BBD pulls down. Need to sort that.

There’s also the heat rise tube on the 2100. Does that really matter? I feel like I plugged mine off on an old AMCv8 I had.

Anything else to think about?
 
It’s a pretty easy swap. I made a little bracket for the pull down cable and blocked off everything else.

FWIW I’ve been daily driving on one of those Amazon 2150s for about a year now without a hitch. Only thing I did (and would recommend) is to jet it for your needs and put a decent power valve in it.
 
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It was back in 2001 I swapped a 2100 on my 87 YJ. So I may be a little off here. But I swear I used a throttle cable off a early 80s Ford van with a carb. It was really long and fit the YJ gas pedal too.
May wanna look into.that.
 
@orange150 In this picture:
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Is that plug in the manifold below the carb where you brake booster was sourcing vacuum? Mine is there and interferes with the throttle linkage. I’m guessing you moved the brake booster to the big port on the back of the base of the carb?

Edit: that won’t be low enough for brake booster. I need manifold vacuum, and off the carb would be ported.
 
I'll take a Pic tomorrow where my booster vacuum is pulled from. It works with my weber and to my recollection, comes nowhere the carb linkage.
 
EFI and done.
 
mbalbritton said:
@orange150 In this picture:
View attachment 415259

Is that plug in the manifold below the carb where you brake booster was sourcing vacuum? Mine is there and interferes with the throttle linkage. I’m guessing you moved the brake booster to the big port on the back of the base of the carb?

Edit: that won’t be low enough for brake booster. I need manifold vacuum, and off the carb would be ported.
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That is where my brake booster was hooked up. This picture is old so the setup is a little different.
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Alright, I'm getting pissed.

Swapped out to an MC2100. Modified the throttle linkage, got everything fitted up, fired it up and success... for about a minute. then she starts loading up again. WTF! Shut it off look down the venturis and fuel is pouring down the intake with the engine off. There is NO WAY, NO FUCKING WAY that I have 3 carbs that have stuck float or dirty needle issues and the same problem.

This issue popped up seemingly out of the blue. I'll rewind and walk through everything I can think of.

driving along fine, only issue was that damn knocking. we were idling through a parking lot and I felt two surges. The wife was driving and I asked is she did that, she hadn't done anything. then it stumbles and dies. Clearly a flooded engine, I get it started, and nurse it home. Since then New Fuel Pump, new hoses, new Filter. Rebuild original carb that failed, I figured it was just worn out and still dumping fuel. Bought new BBD carb that didn't fix the issue, and figured cheap china issue, still dumping fuel. I wanted an MC2100 on it if I'm going to continue to fawk with this thing. In the mean time I found that the return line seemed to be plugged. I had a hard time pushing compressed air through the line. eventually I got it to where I could hear air flowing in the fuel tank. Again, still dumping fuel.

So, there's too much fuel pressure is what is seems like. Why all of a sudden? I don't have a fuel pressure gauge to check it, but what could be causing excessive pressure if that's the issue?

I haven't run the return line to a separate gas tank yet, so that's next, just to see what's happening. But I've run without a return line before. surely that can't be the issue...
 
mbalbritton said:
Alright, I'm getting pissed.

Swapped out to an MC2100. Modified the throttle linkage, got everything fitted up, fired it up and success... for about a minute. then she starts loading up again. WTF! Shut it off look down the venturis and fuel is pouring down the intake with the engine off. There is NO WAY, NO FUCKING WAY that I have 3 carbs that have stuck float or dirty needle issues and the same problem.

This issue popped up seemingly out of the blue. I'll rewind and walk through everything I can think of.

driving along fine, only issue was that damn knocking. we were idling through a parking lot and I felt two surges. The wife was driving and I asked is she did that, she hadn't done anything. then it stumbles and dies. Clearly a flooded engine, I get it started, and nurse it home. Since then New Fuel Pump, new hoses, new Filter. Rebuild original carb that failed, I figured it was just worn out and still dumping fuel. Bought new BBD carb that didn't fix the issue, and figured cheap china issue, still dumping fuel. I wanted an MC2100 on it if I'm going to continue to fawk with this thing. In the mean time I found that the return line seemed to be plugged. I had a hard time pushing compressed air through the line. eventually I got it to where I could hear air flowing in the fuel tank. Again, still dumping fuel.

So, there's too much fuel pressure is what is seems like. Why all of a sudden? I don't have a fuel pressure gauge to check it, but what could be causing excessive pressure if that's the issue?

I haven't run the return line to a separate gas tank yet, so that's next, just to see what's happening. But I've run without a return line before. surely that can't be the issue...
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Some sort of goober in the return line or tank that wiggles around and sometimes blocks the return? Do the return to a can test then you'll know if you need to drop the tank?
 
I wouldn't think a blocked return line would cause fuel to push past the needle in the 2100.

It does just have the mechanical fuel pump on it, right?
 
orange150 said:
I wouldn't think a blocked return line would cause fuel to push past the needle in the 2100.

It does just have the mechanical fuel pump on it, right?
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Yep, mechanical pump.

Just pulled the return line and ran it right off of the filter. Gotta say, sure seems like an excessive amount of fuel being returned. About a gallon a minute if I had to guess. I had a gallon jug, and in about 20 seconds of run (nice idle) it filled about a third of the jug.

A regulator would help, but it still doesn’t answer why. Why all of a sudden is it an issue?
 
mbalbritton said:
Yep, mechanical pump.

Just pulled the return line and ran it right off of the filter. Gotta say, sure seems like an excessive amount of fuel being returned. About a gallon a minute if I had to guess. I had a gallon jug, and in about 20 seconds of run (nice idle) it filled about a third of the jug.

A regulator would help, but it still doesn’t answer why. Why all of a sudden is it an issue?
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Maybe the return line was clear before, but now it’s not for whatever reason?
I’d rig the return line to a larger container so that you can run the engine for longer and see if that alleviates the problem. If it doesn’t, then you know the return line is not the issue.
 
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I still think there's too much pressure in the lines. I noticed a bit of weapage around the hardline coming off the fuel pump. I might drop the tank and make sure I don't have a crushed line or something going on. Visual inspection of the entire line determines nothing. But she is running. Love the way she starts too.

And no, I haven't adjusted the carb yet. this is straight out of the box.
 
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