Odd Running Problem

Odd Running Problem
J

jafo

Old Time Jeeper
Posts
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Location
Blue Springs, Missouri
Vehicle(s)
1979 CJ7. 304 V8 3 speed.
It's sunny and mix 70's here. I just got home and the jeep ran fine. So I needed to take one more trip tonight. So I take off, everything is fine. I get to the turn lane and go around the corner. I feel the jeep lean as I get around the corner and straighten out the wheel and as soon as I straighten out it looses power and dies. So I coast into a lot, park and turn the engine over and it starts. But something's not right. It idles fine but as soon as you crack the throttle it wants to act like it's running out of gas but them let off the throttle and it idles again. So I just let it idle for a few minutes. I drop the hood, get in and press the throttle and now it revs up fine. Was this a vapor lock? I've not had this happen before on anything I've ever drove. Fuel pump, carb, sending unit and fuel filter have all been replaced recently.
 
I would suggest you check the fuel tank vent system. Too much vacuum in the tank can cause the engine to stall. This can be checked by removing the gas cap, listening for air rushing in after a drive and burning off a few gallons. There might even be a problem with a rich fuel mixture, so check the spark plug burn deposits to be sure.
 
Torxhead said:
I would suggest you check the fuel tank vent system. Too much vacuum in the tank can cause the engine to stall. This can be checked by removing the gas cap, listening for air rushing in after a drive and burning off a few gallons. There might even be a problem with a rich fuel mixture, so check the spark plug burn deposits to be sure.
Click to expand...

I forgot to add that I checked the gas tank cap for vacuum and it was neutral, no vacuum or pressure. I did this while the engine was idling.

I'll look at the rich mixture but it just seem like all the fuel drained out of the carb. I notice if I go somewhere and park for maybe 20 or 30 minutes, it can be a little hard to start like the fuel has been drained out of the carb. If you let it sit shorter periods it starts right up.
 
Vapor lock can be caused by the fuel getting too hot in the carb float bowl. A isolator between the carb and manifold can help here. Jeep did develop a fuel filter in the later CJs to help prevent this but it did use a 1/4" return line, not sure if you have one. Fuel can leak out thru bad gaskets and evaporate thru vent tubes on aftermarket carbs.
 
Are you sure that your fuel filter has the correct orientation? The return line should be in the 12:00 position directly above the supply line to the carb.
 
mriplaybass said:
Are you sure that your fuel filter has the correct orientation? The return line should be in the 12:00 position directly above the supply line to the carb.
Click to expand...

Mine is not like that. My filter screws direcrly into the carb bowl. I have a supply line running to the pump, from the pump up to the filter that is on the carb. I don"t rwmember seeing a return line. I'd have to look.
 
There was originally a return line on the right side that went into the top of the gas tank sending unit.
 
If you don't have the correct inline filter you don't have a return line. This can cause stalling. The inline filter is in addition to the carb filter.
Last year a friend complained about his engine stalling at stops. I check into it for him and found he had the wrong inline filter and no return line. I dropped the tank and installed a return line and the correct filter. Cleared the stalling issue he had.
 
Please post up some pictures of the f'filter setup you have.
AMC went to the return system to help with the v'lock issues.
LG
 
Ok. I'll try and get some up this week. It's only done this one time. Only going around the corner only fast enough to make the jeep lean. Then it really never stalled it just acted like it was running out of fuel. Like it needed to catch up. But it's only done it once and I've been around the same turn hundreds of times in this jeep. It's just really wierd.
 
Could be a float setting issue too.
One other thing-Do you still have that Horseshoe connector, on your coil? They are a source for many 'cut-out' issues, like you speak of.
LG
 
Ck your float level.
If it was 'bad-gas', it would run crappy all the time.
LG
 
Along with checking that carb float level, which can change due to vibration, The fuel pump could be shot and not putting out enough fuel to the carb. This issue could also be from a bad fuel filter or even issues going all the way back to the fuel tank.
 
This is a reman. carb. I also just put a new fuel pump on about a month ago. I"ve been driving daily and it hasn't reaccured. It hasn't been as warm as that day in a while either. That's why I was thinking bad gas, meaning possible water in the gas. I did buy gas from a station I normally don't before that. So that's why my thouhht process is at bad gas. I've been through probably 6 or 7 tanks of gad since with no problem. I'll just drive it and if it does it again, I'll start digging into the float idea.
 
Ok finally got some time to tinker. Being the previous owner left a brand new stock fuel filter in the glove box, decided to run and get some fuel hose and install the correct filter. It is now installed and running fine.

So this got me to thinking about WHY they need a return from the filter to the tank. So does anyone have a theory or know why they did this? Does this mechanical fuel pump create that much pressure that a return is required?

Being I have been driving it without the correct fuel filter, in theory, what problems would this cause? Would it push fuel past the float and needle causing a slight richening ofbthe fuel air mixture?

I also pulled a plug and the plug looked good to me. It was a little more tan on one side than the other.
 
The fuel return goes a long way in reducing vapor lock. ;)
Make sure you have the return line fitting of the filter, at the 12 o'clock position.

LG
 
Ok.

I have ran quite a few cars and trucks with mechanical pumps and never have had a return line to the tanks. Even with high volume pumps.
 
AMC did this as common practice throughout their entire line.
It's a very good idea.
LG
 
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