First off, very, very sorry if someone has covered all this in another post. I certainly couldn't find it if they did.

Having problems with The Hulk and in need of a bit of advice. Engine is idling rough (coughing and farting and spluttering more so when cold but also a bit when warmed up) and hesitating really bad (to the point of almost stalling) when I start putting on the gas to get moving. It'll run ragged and backfire occasionally when I'm driving down the road and will eventually get a little better but will still run rough.

A little about the truck. Running a stock (pretty sure it's 100% stock but not sure) 390 with a Holley 650cfm four barrel carb and pick-up style distributor. It's got 3.43 gears in the rear diff.

I rebuilt the carb last year after the power valve failed and it was flooding. It ran well for a while but after I changed the timing chain and timed the engine (12 degrees BTDC as was suggested to me) it was left standing for a good 4 months while the body work got sorted out. I figured it was due to old gas in the lines etc and ran seafoam through the gas tank which helped a little but not a lot.

I've gone through the setup instructions from Holley and am at a loss as to what I need to do next to sort this out. I don't know what accelerator pump nozzles are in there right now, but I wouldn't think they were the culprits as it was running fine before. It's got the electric choke but being in Florida I wouldn't think it would need much choke for getting it started. The only other thing is that the vacuum lines were all over the place and I've just run them correctly (as suggested by Holley) but I replaced a lot of the lines when I did this. There were ports uncovered but I've now capped them so I would have thought I was making improvements not mistakes.

HELP!!!

 

Hello Kierobi,

If I understand you correctly, this was the first time driving The Hulk since changing the timing chain and vacuum lines ?

Is the backfiring through the carb or exhaust ?

If yes, triple check that your distributor is installed correctly (I.E. that the rotor was in fact pointing at the no. 1 HT lead at TDC before you set it to 12 degrees BTC.)

(12 degrees at idle is fine.)

Also check that your HT leads are all in the correct firing order.

Triple check your vacuum lines. E.G. Is the PCV valve connected to the back of the carb.

"There were ports uncovered" !!??
Surely this wasn't before you change things ?

 

Hey FMJ,

No this wasn't the first time driving since I'd done the timing chain but it has been doing it since I did the chain.

The backfiring is coming through the carb and not the exhaust. You can really hear the "ping" off the air filter lid in the cab when it does it.

How would I check the distributor position? Is it a case of barring the engine over to TDC on the flywheel marking and then checking where the rotor is with the cap off? And is there a diagram with the distributor connections for each cylinder so I can check if they are connected right?

The vacuum lines were all over the place and the timed spark advance and the air cleaner ports were not capped or connected. And there was an open connection on a "tree" connection in the manifold. Power brakes line was connected to manifold with three other lines including PCV. Got the power brakes connected to the back of the carb, vacuum advance connected to distributor and the air cleaner line capped for now. PCV is connected properly as well now. So yeah uncovered ports was before I changed things.

Going to check all vacuum lines again when I can but the only other thing I can think to do is run through the setup all over again and see if it sorts it out. Is this a similar setup to what you're running? If so what nozzles do you have in? Otherwise reading about it I might have to change the accelerator pump?

Thanks for taking the time to help me out and read through all my drivel!

 

Sounds like a timing issue check that the wires are connected to their respective cylinders. Also as far as I'm aware the Brake booster should be connected to the intake and the PCV connected to the back of the carb.

 

I'll check the wiring for the spark plug supplies when I can get my hands on it next (next week) but I'll look for a connection diagram before that so I can go over it.

I found a vacuum connection diagram from Holley and there it said to connect brake booster to back of carb and PCV to the left side when looking at it from the front. Will have to go over the lines and check them all out

 

Never mind just found the diagram for the spark connections and the how to in how to set the distributor up. Something else to tinker with seeing as the timing chain was done and all.

 

Hi Kierobi,

Yes, check the dizzy position as you described.

(By flywheel I assume you mean the balancer.)

Did you check your timing after all vacuum lines/ports were connected or blocked off ?

Is your dizzy connected to timed or manifold vacuum ?
If manifold, did you block that off before setting the timing ?
(If timed, it would make no difference.)

I have a 351c, so completely different to the 390, but 100% the same in principle.

You can run the power booster to the back of the carb, or to the manifold (the Tree connection you mentioned).

You can run the pcv valve to the back of the carb or to the front of the carb (as per your Holley diagram).

Uncap the air cleaner line !!
The engine needs clean air, so fit a stand alone breather, or fit a tube to the base of the air cleaner.
(The pcv system can't work properly without clean air.)

If the tranny is an auto, fit a line from the Tree to it.

If you have an EGR circuit, I have no idea what vacuum is needed on it.
(Luckily we don't have the emissions limits down here in The Deep South. )

Your initial rough running you mentioned was more than likely caused by vacuum leaks (I.E. all the open vacuum ports you've now capped).

If you want to quickly check your accelerator pump, remove the air filter (engine off of course!), manually open the throttle while looking down into the carb, and you should see 2 lines of gas dancing their way into the manifold.

Enjoy the tinkering.

 

Yeah sorry, coming from the UK and with work I'm used to calling it a flywheel! LOL. Timing was done before I figured out I had a load of vacuum connection problems so that definitely needs to be done again. Dizzy WAS connected to manifold but is now connected to timed port as Holley recommend. Timing was done with it on manifold and connected so think that's going to make a difference when I re time it thinking about it.

The two vacuum lines I now have runningn to manifold are the AC/heater controls and the auto tranny line. I don't have an EGR circuit as far as I can see and I'm not going to fit one either as it's not a requirement for Florida. I intend to run a vacuum line to the base of the air cleaner once I fit the new one and connect it up. In the meantime I'll uncap that port and see what happens.

Checked the carb accelerator pump like you said when I was messing an out with it last and got two nice squirts of gas so think I should be ok there then.

From what you've told me sounds as though I have to check the dizzy position and timing and redo them both now I have the vacuum lines sorted.

 

UK to Florida. Good move !

I went UK to South Africa.

Here's the good news, the engine is probably at least 10 degrees retarded, which is significant.

Vacuum advance adds between 10 and 20 degrees to idle timing, so, at 12 degrees idle, you should see between 22 and 32 degrees when using the timing light with manifold timing connected.
(That's why it needed to be disconnected when setting the timing.)

Before you do anything else, check your timing again.
Now that you have the vac advance on timed, which doesn't effect idle timing, you'll see the true idle timing.

I assume you had to increase the carb idle screw when you went to timed.

Once your problems are sorted, run it with timed vac advance, and then run it with manifold advance, and see which one you prefer.

Don't leave the hole open in the valve cover, tape a bit of extractor fan filter, or equivalent, over it to stop any crap gettin' in.

 

If you timed it when you had a major vacuum leak and had vacuum hooked to the distributor advance? You probably set the timing too far advanced initially, and then when you fixed the vacuum leak, you would probably have more advance kicking in earlier, so your timing would be too advanced across the board. That would perfectly describe your symptoms - hesitation, backfiring through the carb, running marginally better when warmed up but still not great, etc. You can retime it with a timing light or a vacuum gauge, but when you do so, unplug the distributor vacuum line and plug it FIRST to keep any vacuum advance out of the picture. Then when you get it where it needs to be, reconnect the vacuum. Most of your problems should disappear.

 

Yeah moved to Florida as that's where my wife's from. We had homes in no th UK and Florida and so it was a bit of a no-brainer. Plus would never have gotten my hands on a big block V8 in the UK without paying through the nose for it! Whereabouts in South Africa? We were there January/February this year on a five and half week long road trip and friends wedding. Such a cool country.

Seriously guys, thanks for all the advice. As soon as I'm home again next week I'll re time and see how it goes. Having the descriptions you've all given me I makes a lot of sense for the timing to be the issue (well actually me going into it half cocked and timing it wrong but you know what I mean). Will keep you posted on how it goes but am open to more suggestions as they come!

 

Ok, I have to say it, I'm jealous !
But firstly, congrats on meeting and marrying ''Mrs Kierobi''.
Having a V8 truck in the UK is a waste of time coz the roads are mostly choc-a-block, and the cities and villages have crappy little roads.

And let's not forget about the gazillion speed cameras !

I'm jealous coz you're right smack in the land of V8 trucks, with massive open spaces, and all of the parts you need can be got in the country you live in !

I feel better now, thanks for listening. LOL

I've been in Cape Town for the past 13 years, and 12 years in Johannesburg (Jhb) before that.

Cape Town is right smack in the middle of some glorious countryside with great cruising roads.

(Hmmm, now that I think about it, I'm only jealous of the parts available locally to you.)

I've driven the truck up to Jhb a few times which is a +/-2,000 mile round trip, and I loved the open traffic free drive on each trip.

You chose the right time to visit as Jan/Feb is the best weather. I trust you got to visit Cape Town.

Enough about that.

Did you fit a double chain timing kit ? (I assume yes)
And did you time it at zero ?
(I.E. the kits come with 4 degrees BTDC, zero, and 4 degrees ATDC)

Also, given that your vacuum system was up to sh$t, chances are that the pcv valve is old.
I'd fit a new one, especially as they're dirt cheap.
Just make sure that it is specifically for a 390.

Laterz.

 

OK, so want to start off by apologizing for bringing up an old thread and for not replying in the first place. Bit of a d##k move there.

Just got home from work (I work at sea and am gone for months at a time) to find that my wife, her family and the neighbors all chipped in and got the upholstery redone in the truck. Talk about being gobsmacked! I had no clue this was coming and it was my Christmas present that they managed to keep secret because I was away over Christmas and New Years again. Think I'm blessed with wife, family and friends!

But back on track. Still having problems with the carb stuttering, although MUCH improved since when I left it (wife also replaced battery and it's not nearly as bad on the crank up now). I'm beginning to think I'll have to rebuild the carb again which isn't a big deal. BUT (there's always a catch). When I was last messing about with it, I lost the c-pin that was keeping the throttle linkage attached to the plate on the carb and now I'm home, can't for the life of me remember which hole it was in!?!?! Does it make a huge difference? I put it through with a cable tie before I left and it runs, but am wondering if this could be the cause of the rough take off now?

Sorry to be bombarding you with my coming home and rough idling story, but constantly in search for answers!