ok for awhile now my truck has kinda been running a little rough when it idles. you have to feather the gas at stop signs and stuff. yesterday when me and my uncle where at Dairy Queen in the parking lot it cut itself off. I started it and took off. pulling out of the driveway at work yesterday it stalled again. I started it and drove home. when I got home I told my dad what is going on and told him to listen how rough it's idling. he said, "that sounds pretty bad!" we opened the hood and investigated for a couple minutes. my dad called his buddy and the guy said it sounds like the diaphram inside the fuel pump is broke. so we got a new fuel pump on and got it running. it was running better than it has in 3 months. my dad told me to let it idle for about 3-5 minutes. at about the 4th minute I reached on the carb and revved it 2 times. after that it never idled the same. it would idle so rough and then die.

I cleaned the spark plugs several months ago and since then it has been doing this but not this bad.

last night me and my brother were gonna go see a movie. dad got the truck running real smooth but then he revved it and it stalled. to get it running that smooth he cleaned one of the fuel lines.

I don't know what to try anymore. we haven't changed anything except the fuel pump. fuel filter looks clean but it might not be. could it be that I put one of the spark plug wires back on the wrong spark plug? bad spark plugs? carb needs adjusting? new fuel filter? new distributor?

let me know what y'all think.

thanks for help on this very much!!!

 

I remember your other thread not too long ago about it starting to run funny randomly, sounds like that was a precursor to this. You either have a vacuum leak or a fuel issue. First check for vacuum leaks by idling the motor and spraying a can of carb spray at suspect areas. If the idle goes up, that spot is a leak. Common places are the carburetor base gasket and the power brake booster.

Also could be a fuel issue. Float level may be too low or it could be doing the exact opposite and flooding. You need to pull the air cleaner off the motor the next time it cuts out and look down the throat of the carburetor to see how it looks and then report back. If you can start it up easily after it cuts out, it's probably not flooded. You can try adjusting your idle mixture and speed, but if the carb has never been opened before and it all of the sudden started this like day\night difference, then it's probably time to just rebuild it. I honestly think it is a float issue as a result of varnish or debris which is one of the number one indicators it's time for a carb rebuild.

You'll want to check the basics like plug wire order and timing first just in case, but my experience points to carb rebuild time.

 

found no evidence of vacuum leak around motor, but we were unable to let truck idle while spraying carb cleaner. we had to hold the gas slightly. no increase in throttle. couldn't spray carb cleaner around brake booster due to manual brakes.

carb appears to be clean. with motor running intermittent stream of gas out of jet (1 bbl carb). with motor off jet still pumps gas into carb chamber. starts up easily after it stalls. very light mist of white smoke (NO FLAMES )

 

anything? anyone?

 

fmc400 sounds about right with an incorrect float level adjustment.
Your statement "with motor off jet still pumps gas into carb chamber. starts up easily after it stalls."
Would indicate this, though I know not what jet you are refering to. Jets are internal.
If the booster is leaking gas into the venturi, then you will have found your problem. Further investigation to the carb will determine what has to be done.
Sounds like fmc400 is right on the money here, and the carb is due for some maintanance.
Rebuilds are easy, and you might find the problem when you tear it apart.
Might be something as simple as dirt or small debris in the bowl that is contaminating the needle and seat. This will allow an uncontrolled wmount of fuel to drip into the venturi and cause all sorts of trouble.

 

so carb rebuild would be the best?

 

ok, it's decided that we're gonna take off the new feul pump, put the old one back on, and rebuild the carb.

my dad wants to express a deep thanks to y'all that helped or were about to help.

 

Sidebar note:

If the fuel pump had gone bad? CHANGE YOUR OIL ASAP!! When the mechanical fuel pump fails it has a nasty habit of dumping raw fuel into the oil system of the truck.

S-

 

I agree with Tedybear. It's a must.

Also, you can't tell if a carb is clean by looking at it on the outside. You have to physically go through it. Inside are many internal passages that are prone to varnish buildup. But I'm glad to hear you're going to rebuild it. Make sure you do it the right way - which means soaking it with Chem Dip and then spraying it off with carb spray. Many people only use the carb spray and then post back complaining that the rebuild didn't help. Also, if you have a new fuel pump, you might as well leave it on there anyways.

 

Could not agree more!

Both Tedybear, and fmc have hit it out of the park.
Change the oil, and leave the new pump. Would hate to see you put the old one back on, and have it fail in a few miles.
New is good, and it is already in there, so run with it.
Good luck.

 

I assume you did check the fuel filter.
I like to install a clear plastic filter underneath the back of the truck in the rubber hose coming out of the fuel tank. You have to climb under the truck to check it but you would be surprised how much trash is in the gasoline we buy. I want to catch the trash before it gets into the main fuel line and accumulates.
The only problem I have had is in the cold of winter the water caught in the filter can freeze and stop the flow of fuel. I always keep a spare filter in the glove box in case this happens.
I didn't come up with this, most Toyota trucks have a filter near the fuel tank from the factory.

 

I'm betting on debris in the carb. Rebuilding it should be straight forward. I think this will fix your problem. Ever think of doing an intake swap and a 2 barrel?. It'll wake that baby up!

 

the thing is the old pump was still working fine. we changed it cause my dad's friend said that's what he thought was going wrong and it turned out that wasn't the case.

later I'm gonna search for a rebuild kit on the internet. LMC has the kit for 73-78 300s and NPD has it for the 300 but not for 79. I guess I'll check the sponsors, too. gonna be driving dad's '01 chevy 2500HD 4x4. that means I'm just another normal vehicle not a classic.

 

For a carb rebuild kit - if this is the 300 and it's stock, it will have a "list number" stamped on the throttle body of the carb. You need to give that number to a local parts shop and have them cross reference it in a book to find your rebuild kit. I don't advise you buy it off the internet because of the plethora of calibrations available for those carbs and all the different requirements of each rebuild kit. Don't buy a "one size fits all" from LMC. Napa has the best rebuild kits, although they're a little more expensive.

 

Did you check plugs, plug wires, and cap and rotor first? Might as well do easy stuff first.

When you cleaned those plugs did you check the gap?