K5's with Carburetors (want your opinions)

[79rustyk10]

https://cliffshighperformance.com

They have a really interesting forum, and a lot of parts.

I forget who advertised ethanol compatible qjet parts. I think it was cliffs, but it might be quadrajetpower.com as well.

 

[mrk5]

I would definitely do ethanol free if it sits for long periods. My buddy's TBI truck sat for probably nearly a year and it had a no-fuel issue. We had to do a lot of troubleshooting before we figured out it was the connection at the top of the sending unit had corroded. I'm thinking it was due to the ethanol in the fuel.

I remember when I was in the Navy in the 90's I would leave my 79 K10 sitting for the 6 months I was on deployment and it always started fine. I don't think they were putting ethanol in the gas back then, tho.

My 66 has the factory fuel system and carb and it has a fuel filter under the cab before the mechanical pump and it seems to work fine. I switched the carb on my 73 for a newer carb and I used a filter in between the pump and carb.

For me one of the big things would be the ethanol free fuel.

 

[diesel4me]

I have notice in small engines,that sit a lot and often get the most damage from ethanol,the 2 cycle carbs like weed whackers and chain saws usually take longer to gum up than 4 strokes run on ethanol gas,probably the 2 cycle oil helps delay the souring of the fuel..

I left my chain saw half full of gas last fall and it was hard to start the other day,I had to use ether to get it to fire up,but once it ran it seemed ok,it was a bit boggy until it warmed up and I did open the high speed mixture screw a tad (something that almost always has to be done each time I use it when the temperature is different than the last time I used it)..I didn't have any 2 cycle oil last time I used it ,I put SAE 30 in with the gas instead..

I have been putting a little Marvel Mystery Oil or ATF in my tractors gas tanks if I park them without running them out of gas..so far they seem to have had no harmful effects from ethanol..yet..
I think the oil coats the insides of the fuel system parts and doesn't let the ethanol eat away at it right away..

Some carbs I have run dry before storing the tractors have started turning white & pasty inside,so even if you drain the fuel it is still possible for it to eat the zinc casting..It is a toss up whether running them dry or leaving gas with some oil or stabilizer works "best"..

There are specific fuel treatments and stabilizers for ethanol gas--"regular" Sta-Bil and others that dont mention ethanol on the label are not very effective,if at all..

I have had many old rubber hoses either turn to black bubble gum inside or get hard as rock and brittle and crack or snap in half if you bend them though..
I have been putting Tygon fuel line on them as I replace the hoses when they are due--its expensive but worth it..
Ethanol gas can turn sour in as little as 30 days,but 90 days or more is when the most problems start showing up..
Here I think they now put 15% ethanol in the gas,it was 10%,(might still be,I don't know if they passed the higher content into law )--but I also feel they do not test or regulate samples often,and it is a good bet some gas with a lot more than 15% gets delivered and used by us..

 

[Chief Brody]

Might want to check the vacuum advance if it has the old can style --if the diaphragm failed it wont get advanced at idle (when hooked to manifold vacuum),and that could cause a bog on acceleration..

Usually when an accelerator pump doesn't work well it'll want to bag down badly and almost stall when you stab the throttle fast,especially under a load..if you see two streams squirt out into the venturi when you work the throttle by hand it is probably OK..
Low fuel pressure can cause a bog too..usually a bad fuel pump shows up by hard starts with long cranking periods to get it fired up after sitting first..

I'll pull the distributor cap off and see if the vacuum advance does anything with suction

 

[diesel4me]

If its hooked to manifold vacuum ,it should make the idle speed drop some when you take the hose off it at idle,if its working..
Sometimes they'll still work even if the diaphragm has a small tear or hole though,to test it for that you can see if it'll hold suction with a mighty-vac pump tool ,or just use your mouth ,see if it holds a vacuum,or if it bleeds off..

Wont hurt to make sure the mechanical advance weights aren't "stuck" too while your looking at the distributor,,turning the rotor by hand,it should snap back when released if the weights & springs are working ok..

 

[FAB454]

Old gas?
Have you pulled the plus to look at them?

 

[Chief Brody]

The gas isn't old...I added at least 15 gallons of new 100% gasoline

 

[Chief Brody]

But it wouldn't hurt to do a complete tuneup I guess...

 

[Chief Brody]

If its hooked to manifold vacuum ,it should make the idle speed drop some when you take the hose off it at idle,if its working..
Sometimes they'll still work even if the diaphragm has a small tear or hole though,to test it for that you can see if it'll hold suction with a mighty-vac pump tool ,or just use your mouth ,see if it holds a vacuum,or if it bleeds off..

Wont hurt to make sure the mechanical advance weights aren't "stuck" too while your looking at the distributor,,turning the rotor by hand,it should snap back when released if the weights & springs are working ok..

If they are stuck is it ok to use PB Blaster or something or is it time to replace?

 

[tenderfoot]

I've been in the same boat for a while now. I just haven't been able to get to anymore possibilities for extensive other projects. But I'm leaning towards an ignition issue myself. Soooo......

 

[diesel4me]

If they are stuck is it ok to use PB Blaster or something or is it time to replace?

You can use a little PB or WD-40 on them--if the weights are rusty it is best to take the springs off (note which one went where,it matters),and use some sandpaper or a wire brush on them--inspect the pivot pins they ride on for wear,often they get worn and let the weights stick..

I don't think this is your problem,but it doesn't hurt to check anyways,and make sure everything under the distributor cap looks good..sometimes the contacts in the cap fuzz up with corrosion after sitting,that can make the spark weaker at the plugs--caps can carbon track or crack too--but normally parts don't go sour from sitting,a tune up shouldn't be a must unless it was due for one before it was parked..
Fuel system parts are more likely to be the issue in that case..

 

[ramack]

As you mostly know my passion was in restoring my Blazer to factory stock. That meant getting a Rochester Quadrajet. I didn't modify any of the fuel delivery system.
Fast forward almost 5 years and it has not been driven as much as I like because of a lot of things...but those aren't important.

I would be interested in hearing your opinions, particularly those that still have carbs.

1. Do you still use the factory Quadrajet fuel filter? What is your experience with replacement intervals and any issues with the stock filter or those with the anti flowback valve.

Yes, still use the inline carb filter. Both my '77 (non-cat) and '79 (cat) have stock carbs. I've rebuilt the carb on the '77, recently bought/installed a rebuilt carb from National Carb in FL. Since owning the '79, I have had nothing but trouble getting the '79 to pass emissions tests, until I installed the reman'd carb.

I've never replaced the filters unless I take off the fuel line. Then it's only because I have it apart. I think I've changed the filter on the '77 once in the +20 yrs I've owned it.

2. Those of you who have trucks with carbs and are not daily drivers, what have you seen as regards to truck setting for maybe months?

If the '79 sits for more than a couple weeks, I have to pump on gas pedal, probably 5-10 times, then it starts right up.

Flat spots on the tires go away within a couple blocks.

The '77 hadn't been started in 3 years the last time I started it to split some firewood. So I poured , maybe a 1/2 cup of fuel down the carb and it fired right up.

3. What carb products do you use? cleaners..etc..

BG 44K

But haven't put any in since installing the reman carb last fall.

4. How many of you went with an external fuel filter and have you put it on the suction side (between the tank and the fuel pump (mechanical)?

N/A

5. What "tune up" items go bad when the truck is sitting for weeks at a time?

I can't remember the last time I "tuned" the '77...
The '79 I would replace plugs almost every other year because of fouling due to what I suspected was caused by the PITA, POS stock carb. I haven't had to do anything since the carb installation.

Thanks for your input in advance.

My pleasure.

 

[Joel Wilson]

I had a 76 C20 and currently have a 77 GMC Jimmy and both have an additional fuel filter after fuel pump but before the carb. I did this so I wouldn't have to worry about stripping the threads or anything and it started getting hard to find those in carb fuel filters. The 77 also has a check valve before the carb which seems to help with start up. Both vehicles had/have stock fuel pumps, but VERY hot ignitions.

The 77 GMC ended up having almost a full tank of year old fuel by the time I got it back on the road and it still ran. Ran like crap, but it did run. It ran better after I ran a whole lot carb cleaner, Seafoam, and some octane boost through it before I finally ran 2 tanks of fuel thru it. Now it's fine, except for the smoked driveline... In retrospect, if i knew that I was going to have the vehicle sit for awhile, I would put some sort of fuel stabilizer in it to help stop the fuel decomposing thing. Another note, my 76 really seemed to enjoy the Marvel Mystery oil in the fuel, it seemed to smooth things out a bit.

Joel
norcal

As you mostly know my passion was in restoring my Blazer to factory stock. That meant getting a Rochester Quadrajet. I didn't modify any of the fuel delivery system.
Fast forward almost 5 years and it has not been driven as much as I like because of a lot of things...but those aren't important.

I would be interested in hearing your opinions, particularly those that still have carbs.

1. Do you still use the factory Quadrajet fuel filter? What is your experience with replacement intervals and any issues with the stock filter or those with the anti flowback valve.

2. Those of you who have trucks with carbs and are not daily drivers, what have you seen as regards to truck setting for maybe months?

3. What carb products do you use? cleaners..etc..

4. How many of you went with an external fuel filter and have you put it on the suction side (between the tank and the fuel pump (mechanical)?

5. What "tune up" items go bad when the truck is sitting for weeks at a time?


Thanks for your input in advance.

 

[Mastiff]

Thanks ethanal lobby.

 

[blazer74]

https://cliffshighperformance.com

Everything he sells is the best for ethanol.
Like was said he has a Quadrajet forum that is very informational. Takes a bit to get a response sometimes.
How does it idle, check your choke pull off the same way as your vac can, see if it hold vac and stays retracted.
Certainly could be idle tubes or channels have crud in them. Stumbling on accel sounds lean to me.
Basic tuneup first. Wouldn’t rule out a plug or wire.

 

[Chief Brody]

Life got in the way of looking at the distributor this weekend, however it will give me the opportunity to get a 1 inch combination stubby wrench, which will make my life easier with the fuel filter replacement.
Should be here tomorrow.

 

[Chief Brody]

Finally got back to this today.

I replaced the fuel filter again to one that doesn't have the flap and I put a new spring in it.
Started it up to see if maybe the flapped fuel filter was causing some of the hesitation.
The hesitation was still there.

 

[Chief Brody]

Then I took the distributor cap off and checked the vacuum advance diaphram. It was working.

You can see here:

 

[Chief Brody]

Then I looked at the distributor cap and it looks like tartar on the inside contacts...like the kind the dentist scrapes off your teeth...it was white crust. I cleaned them off with a flathead screwdriver.

Then I put the rotor and cap back on and started it.

It idled very smooth. BUT...when I punched it, it would bog and actually died once.

Then I smell gasoline very strong.

 

[Chief Brody]

I looked under the hood again and this time I saw gas leaking under the filter housing I thought. I got my camera and took photos because it sees better than I can.

You can see the fuel coming out of the fuel line fitting: