I've managed to fix all the error codes except 42 (rich Idle). It's blowing smoke at idle and this just started happening. I peeked down the carb while it was running and it's dumping fuel out of a side port and it seems excessive. This is not the accelerator pump port that is located in the center. This port is coming off the side of the throat. Does anyone know if this is where fuel is delivered when idling and how to adjust it?

I also leaned out the idle mixture solenoid with a jumper wire and it had no effect. I could hear the solenoid clicking so I know it's working. I'm wondering if something in the carb is broken but I'd like to see if anyone has any ideas before I take it apart. I'm guessing it's a mechanical problem and the computer can't compensate for it.

I also tried turning the mixture screw all the way in and it had not effect. Fuel was still dumping out of the port with the solenoid on full lean and screw all the way in.

It runs good otherwise, just terrible at idle.


EDIT: I watched a video and on the non feedback YFA, the port on the wall of throat is where the accelerator pump is discharging. If the feedback carb is similar, I'm thinking it's sucking fuel right through the accelerator pump and out the port.

Thanks.

 

Excellent trouble shooting!
Yes the little pipe sticking out of the upper wall, is the accelerator pump output port.
The square diaphragm in the accelerator pump is torn.
The diaphragm is part of the accelerator pump. It could also be the short black hose that connects the accelerator pump to the output tube.

Ask if you need more help.
Jim

 

Also, you can fix it on the truck, without needing to remove the the carb. As you are just needing to take the top of the carb off.

 

I am guessing your float level in the carb is too high. The most common cause is dirt from a dirty fuel tank holding the float needle open. Your float can also go bad and sink, but that is less common, but does happen once in awhile. If someone has been in there, they may have dislodged something or adjusted the float a little too high. When the float level is too high fuel spills over into the engine.

 

Thanks for the reply gentleman. I'm thinking I may want to remove the carb because I have hand issues (too much dirt biking) and seem to drop everything into a black hole. I'll tear it apart and see if I can figure out what's going on. I'm excited to fix this thing. I've tested every sensor and wire and want to be done with it.

EDIT: I think in my original post I referred to the solenoid on the carb as the idle mixture solenoid. It's actually called the feedback solenoid (fuel mixture). My mistake.

 

I'm glad I went through the headache though. I have a good understanding of the electrical. I found a problem that can creep up in the design due to age.

They daisy chain the signal return wires through the TPS, and other sensors all the way to the self test hookup. I found where the wires are doubled in sessors, they become oxidized and the resistance in the wire goes up. I discovered this when I did an ohm check from the computer connector to each sensor. I was getting above three ohms in places. Also, there's a factory splice in the harness for the signal return. It is not sealed and looks like it could get very corroded. I literally spayed these daisy chain and splice points with contact clean and the ohms changed!!

I'll snap a picture of what I'm talking about and update this thread.

I can't imagine all the folks that abandoned all hope over this and did away with this system.

 

Speaking of dropping things, be on the lookout for the BB size check valve and weight. It is used in the accelerator pump, after you take the top of the carb off, tip it over and they will fall out. Easy to lose, set them in a safe place.
When I first read your post I thought you may have the last computer control system that works.
I was always under the impression that the computer provided a ground for the solenoids, and the 12 volts supply power was daisy chained. But to be fair, I gave up on it fairly quickly as it wasn't cost effective to fix.
Good luck, Jim

 

I am sure a lot of 300 sixes where junked because of wiring and sensor issues. A good solid engine with a lousy control system which can ruin the whole show. But to be fair, the problem you have now can happen to any engine with a carb. If you find a lot of sediment and rust in the bottom of the bowl, it may be time for a new fuel tank. Very common problem and the tank used to be fairly cheap. But I haven't check the prices lately.

 

I pulled the carb out. It looks very clean inside. I put some fluid in the bowl and the power pump seems to work if I put my finger over the brass rod and check ball. I have no idea what the aluminum plug that I point to in the picture does. If I don't push down on the brass plug to seat the check ball, gas comes out the end of the plug and back into the bowl. This aluminum plug is in the way of one screw so it's hard to remove the power pump diaphragm.

Another interesting thing I noticed, on the downward movement of the power piston, gas comes out a nozzle further down the bore. On the upward stroke it comes out the upper nozzle.

The tube going from the power pump to the nozzle looks good and the pump seems to work.

The float looks good and the float pin is in very good condition.

Looking at the internals, I have no idea why gas is coming out the upper nozzle when the truck is idling. There's got to be some problem I can't see.

Thanks.

 

I think I figured it out. The lower nozzle applies vacuum to the bottom of diaphragm. I'm pushing fluid out of that port so the diaphragm must be leaking. After I pulled it out here is what I found. I'll order a kit and see if this fixes it.

Thanks for all the help.

 

Yeah those tears don't look great. Nice work on the troubleshooting.

 

I enjoy reading your posts. You take the time and effort to learn how it works, then use the knowledge to troubleshoot. It's a refreshing change from the usual posts....

Post 1: truck does run, then about 1 hours later...
Post 2: a very long list of parts that where just bought, to be installed all at once, hoping one of them will fix it.

I really have never seen the round silver thing, with the arrow in your photo. I was hoping someone else has some info, I don't.

Jim

 

Thanks for the compliment. I try to walk through my thinking process so in the future it may help someone. In the process, others can catch my mistakes. We'll see if it's fixed when I get my rebuild kit.

The aluminum disc unscrewed so i was able to diaphragm out. I think I have an idea about what it is. I think it smooths out (regulates) the stream from the accelerator pump. I suspect it has a small valve inside that opens when there's enough pressure but I'm not sure. I suspect it's an emissions thing. Probably to use only the necessary amount of fuel to get the job done. I've never seen it on any other carb.

 

I looked it up, it's called a temperature compensated pump. Not sure exactly how that one works, but I did mess with the same type of system on a 2150 2bbl. On the 2150 2bbl they had a extra vacuum port and vacuum line coming off the accelerator pump housing. When the engine is cold, the pump works like any other pump. When the engine is warm, there was a sensor that applied engine vacuum to that extra port on the pump. When it did this, it bled some of the fuel squirt back into the bowl to lessen the amount of fuel shot when the engine was warmer.

The 2150 worked on vacuum, not sure how the yfa compensator sensed temperature and worked. If it has a vacuum port on the side of the carb, then it worked just like the 2150, a sensor on the engine somewhere would apply vacuum to it when the engine was warm.

You are correct, it sounds like a emissions thing. I never have seen so many gizmos added to engines as a bandaid just so they would pass emissions testing. And nothing was consistent, this engine would have it's group of bandaids, another engine the same year would have it's group of vacuum lines and bandaids. I call the late 70's and 80's the dark ages of vehicle mechanics.

 

This is funny, sad and true. Off topic but my dad had 70 something chrysler cordoba that was beat to crap that he gave to me. It had the lean burn system. I remember when it broke and went into limp mode. I was younger at the time and didn't understand the computer controls. It used so much gas I finally packed the trunk with garbage from my chores and sold it to a guy for 100.00. He ended up junking it because he couldn't get it running right.