Ignition Troubleshooting

[mat in tn]

very often the vacuum gauge can be used to test fuel pressure but not for fi. low pressure only. I recommend driving this as much as you can. I know it does not make sense if you have something else that gets 35 mpg but it needs to be driven. I generally rotate between two trucks for this reason. I'm not getting rid of my OG but my "dolly" gets better mpg and is a whole lot of fun to drive. I try to keep stabilizer in my builds that set for long periods.

[Bullnose Gator]

I've been driving it exclusively this week since I got it running again. I keep having to tweak the fuel bowl levels because it seems to run fine for a long while and then have some intermittent hesitations, but I think I'm getting it more dialed in.  

[Gary Lewis]

You may have issues with the gas in the tank.  You might try a bottle of Heet or somesuch.  But it'll be best if you can burn out all of the old gas and go with new - w/o ethanol.

[Bullnose Gator]

I guess I should have thought of that before I topped it off last night .  I also didn't think to go with ethanol free.  I've never heard of those, do they sell them at regular auto parts stores?  I'll try that, a few long country drives, and a fresh tank of ethanol free and see if that helps, thanks.

[Gary Lewis]

If you topped it off with ethanol then that may help clean the system out.  The issue is that ethanol-laced gas goes "off" quickly.  But fresh ethanol helps clean things up.

And if you have ethanol you don't need the Heet as it'll do much the same as Heet.

[Bullnose Gator]

Good news is that it has kept running.  Not so great part is that it still doesn't run as smooth or strong as it used to, it still sputters some in 3rd and 4th gear and takes a good 3-5 mins of me giving it just a little gas when starting from cold for it to not stall out.  

The rear fuel bowl seems to be the symptom/cause.  I've adjusted the needle and seat up and down repeatedly and the position that makes it run the best is when I adjust it down so low that the adjusting nut can't even grab it anymore and I have to use needle nose pliers if I want to back it out.  

On to my questions:
1) What are the chances the rear fuel bowl float is causing this?  
2) Since I know the issue is carb related, I'm considering getting a carb kit and doing my first carb rebuild (mainly for the learning experience).  What is the success/fail rate for first timers doing that?  I'm not afraid of destroying the carb, I'll replace it if I need to, I just don't want to waste my time rebuilding it if it's an advanced skill kind of project that won't benefit me.  

Thanks for any input and apologies for bringing this post back to life (again)!

[rcarlisle]

I'm glad you keep bringing it back.  A chance for all of us to learn.   What I read says you have a choke issue happening.   Did you get the new carb in/on yet?  Didn't you order one a while back?

When I was messing with my choke originally, I had some issues with the fueling being off and the engine would chugga a lot.  To get mine where it is now (reasonably okay), it took a LOT of trips around the block and adjusting.   And I aslo found, my test loop wasn't quite long enough.   If the choke isn't opening, it will make hte truck run far too rich, which can result in stumbling.  As can not enough choke.  IF the choke is doing odd things, the truck won't run right till choke is off.   IF it runs right then.

Does it still do it's bad things when completely warm?

Is this an original for the truck carb?   the 4 barrel is a little beyond what I'm familiar with so I may be off.  But I'd be looking at choke first to make sure the truck isn't running poorly because of choke plate position.

[Bullnose Gator]

rcarlisle wrote

I'm glad you keep bringing it back.  A chance for all of us to learn.   What I read says you have a choke issue happening.   Did you get the new carb in/on yet?  Didn't you order one a while back?

When I was messing with my choke originally, I had some issues with the fueling being off and the engine would chugga a lot.  To get mine where it is now (reasonably okay), it took a LOT of trips around the block and adjusting.   And I aslo found, my test loop wasn't quite long enough.   If the choke isn't opening, it will make hte truck run far too rich, which can result in stumbling.  As can not enough choke.  IF the choke is doing odd things, the truck won't run right till choke is off.   IF it runs right then.

Does it still do it's bad things when completely warm?

Is this an original for the truck carb?   the 4 barrel is a little beyond what I'm familiar with so I may be off.  But I'd be looking at choke first to make sure the truck isn't running poorly because of choke plate position.

I returned the new carb i ordered because I was able to get her running again with the current carb, which i'm pretty certain is the original.  I have not adjusted the choke at all (nor do I really know how to), but how likely is it that the choke can get "off" from where it was several months ago when things were running good? It has a hard time when it first starts, then runs it's best (depending on where I've adjusted the rear fuel bowl to on that particular drive) once it's warmed up/hot.  On a long drive last week (30ish miles) it seemed to start running a little rougher towards the end.

[rcarlisle]

I agree the choke should not have changed and the 4 bbl guys will have to help if that's where it is.    You're in FL so I don't know what the difference in temps are for summer to wnter - some guys have to make a slight adjustment. Might make a difference?  Slight?  

Is it possible on your carb to disable the entire secondary circuit in some way?

As for rebuilding carbs, it isn't a really big deal.   You want everything super clean - all the passages need to flow freely and any moving parts need to move freely.  Floats need to float and move freely and the passages need to flow correctly.   All that comes from everything being super clean.  And maybe new parts if there is excessive wear or floats aren't floating.  

BUt anyone with a little know how should be fine on a first time rebuild.   Be organized and clean.   And try to lay it all out on a bench where you can work from start to finish without disturbing the porject where you might lose parts.   Get some sort of organizing device, muffin pan, storage box with little dividers, etc. to keep track of parts.  Take photos as you go of where everything is.  tape labels if you need them.  

You may want a bucket of parts cleaner to dip things in over night if it's terrible.  be careful what you dip - some parts don't get dipping in carb cleaner.   But since it runs, it may just need some spray cleaner.   When I used to do motorcycle carbs, I used torch tip cleaners, wire strands, whatever to clean passages.  Plus some compressed air or carb cleaner squirted through.   Every passage goes somewhere.  

Pay attention to gaskets and parts as you dismantle it and make sure you have NEW parts that are identical.

Clean it all, replace parts, do float adjustments as needed.   Reassemble.   Pray a little maybe.  What can it hurt, right?  

[Bullnose Gator]

rcarlisle wrote

I agree the choke should not have changed and the 4 bbl guys will have to help if that's where it is.    You're in FL so I don't know what the difference in temps are for summer to wnter - some guys have to make a slight adjustment. Might make a difference?  Slight?  

Is it possible on your carb to disable the entire secondary circuit in some way?

As for rebuilding carbs, it isn't a really big deal.   You want everything super clean - all the passages need to flow freely and any moving parts need to move freely.  Floats need to float and move freely and the passages need to flow correctly.   All that comes from everything being super clean.  And maybe new parts if there is excessive wear or floats aren't floating.  

BUt anyone with a little know how should be fine on a first time rebuild.   Be organized and clean.   And try to lay it all out on a bench where you can work from start to finish without disturbing the porject where you might lose parts.   Get some sort of organizing device, muffin pan, storage box with little dividers, etc. to keep track of parts.  Take photos as you go of where everything is.  tape labels if you need them.  

You may want a bucket of parts cleaner to dip things in over night if it's terrible.  be careful what you dip - some parts don't get dipping in carb cleaner.   But since it runs, it may just need some spray cleaner.   When I used to do motorcycle carbs, I used torch tip cleaners, wire strands, whatever to clean passages.  Plus some compressed air or carb cleaner squirted through.   Every passage goes somewhere.  

Pay attention to gaskets and parts as you dismantle it and make sure you have NEW parts that are identical.

Clean it all, replace parts, do float adjustments as needed.   Reassemble.   Pray a little maybe.  What can it hurt, right?

Haha, you got that right.  I'm in Central Florida, so temperature isn't a big factor, but she definitely performs better the warmer she is.  I may start by replacing the rear fuel bowl float first and then move on to the rebuild attempt if that doesn't help.

[mat in tn]

before getting too far into the carb, let's be certain of a couple basics. if something changed its possible to be inside the carb but more likely not.  I would start by making sure that there are no vacuum leaks. the most likely examples would be deteriorated hoses, cracked hoses where they fit onto any components or cracked vacuum caps. missing even. loose carb mounting nuts is also a possibility although more common on the l6 models. identify all vacuum ports on either the intake manifold or carburetor. cap them all with new vinyl caps (the pretty colored ones) they do not dry rot and crack like rubber. mark all hoses that you remove so you can put them back exactly. then start and tune the engine. if it runs better then add one hose at a time until you have all done paying attention if it runs poorly again.
I say this because at idle you should not be able to change much by messing with the rear float level other than idle quality. and the fact that you can says that the needle and seat seem to be working as is the float. you should be setting the float with the sight screw removed and the fuel level just trickling at the bottom of the screw hole. engine running. you set the front the same way.

[Bullnose Gator]

I will certainly have more questions about the vacuum trouble shooting, but just to share more info about the rear bowl I'll share that when I adjust it to where the sight plug shows the fuel at just barely spilling out (a gentle rocking of the truck makes it lap out a trickle) it will idle ok for only a matter of a minute or so before stalling out.  When I adjust it back all the way down to where even a hard rock of the truck makes no fuel come out of the sight plug is when it runs its best.  the front bowl is at the perfect level and I stopped adjusting it weeks ago because it doesn't seem to be causing any change in performance.

[mat in tn]

this may seem odd. however. when you have it running, with the float level set, and it starts to run poorly after running for a moment. is that with the sight screw still out? if so, hold a finger closing it off while its running for a moment and see if the run quality changes. if it changes move your finger and see if it floods out. that will tell you the state of your needle and seat/float.

[FuzzFace2]

mat in tn wrote

this may seem odd. however. when you have it running, with the float level set, and it starts to run poorly after running for a moment. is that with the sight screw still out? if so, hold a finger closing it off while its running for a moment and see if the run quality changes. if it changes move your finger and see if it floods out. that will tell you the state of your needle and seat/float.

I would say also look down in the carb on the rear to see if fuel is dripping in.
No power valve in the rear so that cant be it.

I wonder if a gasket is causing fuel to leak when the level is up to the normal place?
I am guessing the carb uses a metering plate and not a block with jets as most Holley's do.
Wonder if the plate could be warped?

They are not hard to rebuild and if you follow what was posted you should be fine on the rebuild.
Dave ----

[Bullnose Gator]

So I ran it with the needle/seat raised to where fuel was just trickling out of the sight plug. As it was running a little rough I plugged the sight plug and it barely started running a little rougher. When I removed my finger fuel poured out.  I didn't notice any fuel in the rear barrels. Also, the choke stays in the 100% open position whether it's idling or revved.  How should the choke be positioned during a normal/healthy idle?

[mat in tn]

once warmed up the choke should be wide open, and the fast idle cam released. revving the engine should have no effect on choke position. other than releasing the choke on the first rev. if it was able to stack fuel to the point of flooding out when you removed your finger then the needle and seat are not shutting off the incoming fuel completely. that will be from too much fuel pressure or bad needle/seat of bad float. you were already looking in those areas and that should have proven that you are on the right track. when you remove the float, if it is brass shake it to see if there is any fuel sloshing around inside. if there is its trash. get another one. however changing the needle and seat is simple and done in place without disassembly of the carb so I would start there.