Troubleshooting ideas on Qjet UPDATE still have problems

[mrk5]

Okay, Saturday on our trail run my truck started running chitty. Wouldn't idle, and I had to adjust the curb idle way up to keep it running. It was kinda what I would describe as "loading up". It smelled rich, too. Engine temp was normal 180°. It was running fine at the start of the trail, but I shut it off at one point, restarted and it was running like poopoo. Never had any problems restarting the truck, just keeping it running.

Course the next day we get in to drive 3hours home, the truck runs fine all day.

This happened one other time running around town all day, stop and go. The truck started running bad. It was parked for several days and the next time I drove it, it was running fine.

The carb was rebuilt in January and has only a couple hundred miles on it.

Here's some of my thoughts:
Vapor lock
Fuel pump is borderline, and when idling a lot it starts to fall behind.
Float sticking.
Float level too high.
Something other than the carb.

 

[dyeager535]

Vapor lock and fuel pump would be the last likely culprits IMO.

Fuel pump failures seem to be abrupt and positive (they fail and don't work) and vapor lock seems to be blamed for a lot of issues when it's not. If you've got the fuel return line setup, vapor lock is even more unlikely. It does happen, but it's not common.

The other options are possible, with a float issue sometimes the fuel will start to end up in the air cleaner...you can check for that easily of course.

Could also be an ignition issue, with it intermittent as it is, you'll need to check the stuff when it's happening. Problem when hot is commonly an electronic issue such as module, coil, etc., vs. plug wires, plugs, etc. Especially if intermittent. You have a plug issue at one point for example, it's very likely it's going to be 100% consistent.

 

[Hogback Fabrication]

Your float could have sunk as well (even the phenolic ones can absorb gas and sink).

 

[mrk5]

Thanks for the ideas.

I didn't think vapor lock seemed realistic because it restarted easily.

Good point on the plugs and wires.

I think I will check out the float.

Sounds like it may be kinda what I was afraid of. Wait til it happens again and trouble shoot from there. But at least this will help me narrow it down some. That's why in some ways I was actually disappointed when the truck was running just fine yesterday.

Reason I'm thinking this could be carb related is because this started happening after I changed carbs.

 

[diesel4me]

sounds like...

Water in the fuel is a possibility--makes it run poorly under load and die at idle,after it warms up its not so severe...try adding isopropanol dry gas,see if that helps...could have been the carb icing up too,if it was below 50 degrees with high humidity..dry gas helps stop that too...

 

[85mudblazin]

Funny you posted this, this happened to me last weekend to, idle went way down to the point it was lamost stalling, I cracked on the idle screw till it compressed the spring all the way and it still had a low idle, I continued wheelin and later in the day it kicked back up to a high idle since I had cranked down the idle screw so much, back off the idle screw and it runs just like normal again. I have no idea what was going on all I could come up with was there was a vaccum leak somewhere that just worked its self out.

 

[mrk5]

Actually I bet your problem was that some debris got into the idle circuit and then worked it's way out.

If you're luckier than me, It'll never happen again.

 

[mrk5]

Well it happened again.

Did a test trail run after re-routing the fuel inlet to carb, replaced fuel filter, and relocated the coil. Figured I'd try easier stuff first.

When the truck started running rough I checked the voltage to the distributor and coil and both were 13.8V. The coil was only warm to the touch. The filter was full of fuel. I also checked the torque on the carb mounting bolts. No problem there.

I drove the truck about 1/2 hour down the interstate, and when we stopped at the gas station the truck was running fine.

So it has to do with stop and go or slow speed driving. Twice on the trail now, and once around town (which was the only time it's been driven around town). The problem has occured at 5000ft & 10,500ft, so I don't think it's altitude.

Now I'm wondering if it is "loading up". I noticed I have the timing set at 14* and the idle mixture was set with this initial timing. I'm wondering if I need to retard the timing back to 10-12* (what I've been recommended to run at 5000ft), and readjust the idle mixture at that initial timing which will lean it out some.

 

[pauly383]

Strange as it sounds , my original one did that , and you know what I found , pieces of the charcoal from the cannister in my fuel bowl .

Another cannister and it hasn't done it since 2001

 

[mrk5]

I don't have any of that emissions crap. Maybe I should check for debris in the bowl, though.