SO here is the issue. I have a super reliable 93 carry F6A. Had GR rebuild the carb 4 years ago and has run like a top since. Can't say enough about their work there. Have not used the truck much over the winter. THe last couple of gallons of fuel in the tank are from about 6 months ago and it 87 octane. I know I know not a good choice. wasn't by design and I have been telling myself recently that I have to get that fuel ran through it soon as to avoid any bad gas issues etc. As spring progressed I had the truck out a very little bit. My son and I went on a 10 mile ride on a Saturday ran great. We went again on the next day and when we stopped I noticed that it idled a bit high at rest a few thousand, not dramatic but a little high. 2 days later I fired it up waited for it to worm up for a few minutes. Went to take off and it almost died when I let the clutch out. Hmm that's weird she never does that. Let the clutch out again and the same response. revved it up to get the rpms up let the clutch out and took off. Noticed that if I stab the gas pedal the engine wants to die and bog under a load. Also will not idle. pretty much wants to taper off and die immediately at idle. ran it for a mile or so and circled home. I took the carb boot off and noticed a bunch of dirt and fuel residue in the carb boot. Why do these trucks get so dirty there. I have noticed this before and cleaned it but with tight connections you should not get this grimy of residue at the carb like that. started it up and watched the choke plate. backing off normally with temp increasing etc. What I did notice is that the little accelerator pump? on the air cleaner side of the carb. WHen that is injecting fuel the truck revs up normally, when that stops pumping fuel like at idle and several other times in the observation it wants to bog out. I siphoned out all of the old fuel, will now add three gallons of fresh high octane fuel and go from there. Any thoughts. Just is one of those odd scenarios that one day its fine the next day its a 1300lb paper weight. And as with off fuel issues you are always guessing until it is fixed. Not like if a strut falls off, that a guy can see. I have a battery charger on it to ensure strong battery etc. Will replace fuel filter to ensure proper fuel pressure but from there I don't really have any ideas. All vac lines are on and tight. All are silicone type with very god seals. I don't think it is the idle selanoid because sometimes when it dies I can crank it and re fire it and it will idle fine for a couple seconds and die. Any thought are much appreciated.
To isolate that I took the inlet fuel line off and turned the key. Plenty of fuel spraying everywhere. However. When stabbing the accelerator to keep the engine running I noticed that the only time that the engine would run would be when the accelerator pump was running. You can tell when it is pumping by the sudden small diameter spray coming out of the lower nipple on the air filter side of the carb. Actually cool to watch work. When it was not spraying the motor would die out completely. I could resurect the rpms by stabbing the accelerator(accelerator pump comes to life). I researched the accelerator pump and found that it draws fuel from the bottom of the bowl. Unlike the main jet and emulsion tube and so forth. That tells me that the upper jets are plugged because anything that called for fuel through the top of the was not getting fuel? Now this is just an assumption but it was clear that the accelerator pump was getting plenty of fuel and nothing else was. I noticed the day b4 this occurred that the engine was running about4 or 500 over normal idle. Was there something plugging the air mixture passage? Creating a lean condition and a high idle? When I get the carb off these 2 areas are where I will be focusing on. Had this carb gone through 4 years ago but have run hundreds of gallons of fuel through it since. Thanks for the input. Any other ideas or am I just crazy thinkin here?
Took the carb off late last night. Will have some time to get the bowl off of it this evening. For eveyone out there who is perplexed by these complicated carbs....they are just a carb and nothing more. Dont bee intimidated by them because they are just a bunch of small passages and chambers like all other carbs just a little bigger.
So I peeled this carb apart. What a mess of dirt inside. Looked like someone tossed a couple pinches of black dirt in the bowl and ran the carb on the truck. black sediment all over in the carb. Along with that I found that the main jet was 90% plugged with an accumulation of dried dirt. I did order a rebuild kit from Gr which I am not impressed with. Half the parts for some aspects of the carb with none for others, along with a couple of the parts for certain areas. Conclusion is that I would chance a different supplier next time. I peeled apart the fuel filter and let it dry overnight. Hardly any evidence of any dirt in that filter. in fact none whatso ever on the paper element. After it dried overnight there was nothing more than a hint of dust in the sediment bowl. My next thought is that the hard fuel line on the frame rail from the pump to the carb is rotted on the inside. Only place corrosion or dirt could come from?. Took compressed air and applied to one end with a white rag one the other. Wha lah....nothing came out but a small bit of clean fuel? Where the heck is the sediment coming from??? Took off the inlet nipple at the carb to inspect the strainer screen inside the fuel inlet. This is your last protection against fuel contamination. Not a spec of dirt inside of it. What the heck where did the dirt come from with there being no trace as to where it came from. Only thing that could be was that 4 years ago when I sent this carb to GR to be rebuilt, they rebuilt it and never cleaned the dirt out of it. Who would do that you may ask. My same question but tell me if that was not the case where did all of that dirt come from? Any thoughts........ I'll have the carb on by end of the weekend and I will update the start up. Going to replace all the fuel lines and coolant lines while I'm in there being that it hopefully won't be off for many years but we will se.
the black crap might actually be your old rubber fuel lines braking down over time. Did you replace them 4 years ago when you put the rebuilt carb on?
another thought... make sure you replace the old rubber lines with fresh (newly manufactured) hose specifically manufactured to be used for fuel lines. For any noobs, this is always printed right on outside of the new hose. One last suggestion, run some new gas (or even water) through the new hose prior to installing it. This should flush out any dust, etc. , that it picked up sitting on the shelf. The holes in the carb jets are usually so tiny, that they don't tolerate much debris before clogging. I still have a few carb'ed vehicles around the house so I recently invested in a new 1 gallon sized ultrasonic cleaning machine (about $100). After an hour soak in that machine with a solution of Simple Green & water , the carbs come out hospital room clean.
Yes all fuel lines were replaced 4years ago. Also if that was the case the strainer just inside of the inlet tube on the carburetor would have some black residue caught in it and mine was completely clean.
So I got that carb on Friday. Everything takes longer than you think. Replace all the fuel lines. all the vac lines on correctly. Fired it up. I was happy to see no leaks anywhere. fired right up. warmed up and started to stumble. Noticed that the choke plate ws not coming off like it should. ENded up flipping it up with my finger and then it took hold and. Started it up this morning at 32F. it starts right up but the idle up from the choke isn't seeming to be working like it was when I took it off. All the vac lines are correct all the coolant lines are on. Any ideas why this would be different now? Only thought is that the air mixture needs to be adjusted after the rebuild and that would change the idle speed etc? I'm kinda stumped as to why things would change when none of the linkages were disturbed.
You definitely need to adjust things. I did a thread on the basics a while back: https://minitrucktalk.com/threads/some-thoughts-on-carburetors.20150/
I disagree on that one but I could be wrong. If all you change is the diaphragms, gaskets and clean out the passages/jets etc there should be no real significant change the the operation to the carb. I didn't take off or adjust the linkages etc so everything is exact as it was when I pulled it off. I found the main jet completely plugged so that was my problem. I changed out the gaskets and diaphragms just because I was in there and don't want to be in there for a long time. Let me know your thoughts.
I’ve rebuilt a bunch of carbs, of just about any style you can think of down through the years. If I take them apart, I adjust them when I get them back on the vehicle. I have never had one just work right and be properly adjusted with out adjustment on the vehicle. If you pulled the idle mixture adjustment screw it will need to be readjusted. Took out the idle speed screw, choke high idle, or idle kick up for the A/C or alternator, they need to be adjusted. I used to “rebuild” Weber downdrafts on the car buy just pulling the jet holders and shooting carb or brake cleaner in to the passages, and then pulling of the vacuum hoses, and sticking the red straw in each of them to clear those passages. I didn’t even take them apart, or off the manifold, and they still needed adjustment when I got done with them. If good enough, is good enough, you might be able to get way without doing on the vehicle, dynamic adjustments and tuning. If you care about how it runs, you should adjust the carb.
I totally agree on the mixture adjustments. That will be the for sure one. I'll connect the airbox and look at it tonight
I connected the airbox and she is running horribly rich. Sputtering like an old airplane puffing blue smoke and struggling to run it's so rich. Black soot coming out the tailpipe. Jigs and fixtures was more than right about needing a tweeking. I am assuming it is in the mixture screw. First question is what do u guys use as a tool for that one. Can't even get a little ratchet in there with a drill bit. Secondly what do we find as a good starting point on that adjustment. Can't wait to get this dialled in,I have wood to cut before it warms up too much.
Seems like the best tool for the air mixture screw is a penny,dime, or a quarter. Just not much room in there for a tool. Couldn't even get my right angle carb tuning wrench in there. I turned the screw in one turn this morning before I left for work and it fired up yet struggled to idle at 300 rpm. Going to go in all the way and start backing it out tonight and we'll see how it goes. Had a feeling this was going to happen when I pulled the carb
300-RPM???? Idle should be some where around 900-rpm. You need to set the idle as low as you can get it to run smoothly, and then work the idle mixture screw in or out to get the best lean idle. Please read this thread. i explain how to set best lean idle: https://minitrucktalk.com/threads/some-thoughts-on-carburetors.20150/
Yeah that's how rich it's running. Mixture screw for this carb must be way to far out or rich. It's choking itself out. It was rich before I connected the airbox which limits air even more. Going to lean it out tonight and go from there. Like I stated before, no matter what I do to the carb mixture will more than likely change as it did here.
