Nagging Carbureted Engine Issue

[bobblefrog]

I'm going to try a third mechanic this morning and thought I'd throw this out there as I'm starting to feel a little pessimistic.  Juno has a new carb and been tuned etc.  But I'm finding about three - four hours into driving (with stops of course) she starts missing/surging on acceleration up rises.  

My mechanic found a loose spark plug wire before I left so thought we had it, but had some minor stumbling the first day and was pretty bad the second day when I limped into my destination (a truck stop).  There I stayed two nights and the mechanic there checked my spark plug wires, distributor wires and vacuum pressure.  With no other ideas he went ahead and installed a new fuel filter (which had already been changed this summer - but you never know).

Again, four hours down the road, same issue.

I've got a locking gas cap so in case it was a venting problem (84 dodge ram 350) have just been snugging it rather than clicking it now.  But again yesterday just as I got to my destination it did it again (just a minor bit - but did do it).  It was colder yesterday than it has been.  When it's bad it will also do it from a start/stop like from a traffic light after I pull off freeway.  Seems a little rough idling.

My only other symptom that may or may not correlate is it starts great cold (2 pumps and starts right up) but not after it's been running and then off five minutes.  The only way I can start it then is to act like it's flooded and press accelerator to the floor to get it turn over.  Also I do seem to get the tiniest bit of surging / hesitation from a stop (usually warm).  But not quite the stumbling described above.

I've learned it helps on the rises to get a running start and keep a firm pressure on the accelerator.

Anyway - today if they can talk to me I'm going to see if they can check the distributor (maybe just pull the cap and look for signs of any residue), ask about vapor lock/venting and maybe pull and check the plugs?  Or even pull the top of the carb and see what might be happening when I try to start it - might give a clue.

Used these guys on the way out from denver when the accelerator pump on old carb went out (or at least that was their diagnosis - they said as long as he babied it he could limp on to NC and he did).  

Have no clue if this has been since the new carb was put on - since it takes awhile to start happening I may just now be finding out.

Throwing it out and will update if I find solution.  Hasn't stranded me but sure is wearing on the nerves!!

 

[highdesertranger]

what carb? sounds a lot like vapor lock to me. highdesertranger

 

[Van Man Dave]

Elevation change can cause a lot of similar issues with my old carbureted van.
Have you been seeing a lot of elevation difference in your travels?

At sea level my van runs lean and is hard to start, stumbles on accelleration, etc.
At high mountain elevations the van runs rich and is hard to start, stumbles, etc...
At 3-5000 feet the van runs like a dream, no issues at all.

 

[jonsun]

cold starting well then stumbling when hot means its rich. did they put a new carb plate on it? they can warp ever so slightly and when hot start leaking air. Or you can have a manifold gasket going bad leaking when heat soaked. Mechanic should be able to look at the plugs and see an air/fuel issue.

when you start a carbed engine cold you pump once and that closes the choke. pumping anymore does nothing because there's no fuel delivery until the engine is turning over and actuating the fuel pump.

 

[UptownSport]

it starts great cold (2 pumps and starts right up) but not after it's been running and then off five minutes.  The only way I can start it then is to act like it's flooded

Act like it's flooded? I'd assume it is.
Five minutes isn't long enough for heat soak.

After four hours, however, points to some type of heat issue- to be master of obvious.
So you could have two, or multiple issues.

Many of these things, like checking wires and such are easily within an average person's capability.
Even the carburetor is easy to disassemble.

But, there could be 50 good suggestions here, but still never guess what it is.

There used to be a valve on the exhaust manifold which would open as engine warmed up.
It could be that that's stuck closed- IF it has one. Look, and see if it has one, then grasp the counterweight and see if it turns.
obv when cold, LoL

Thermoquads would have the little bowls fall off- I'm not sure this actually affected anything, but you could disassemble and glue it back on.

Other than that, they were really good carburetors I wouldn't suggest replacing it unless there's a clear fault.

Again, though, could give fifty guesses and still wouldn't be right.
It's always best to do a systematic troubleshoot- get a troubleshooting diagram and go down it.

 

[jonsun]

that EFE valve works off the cold vacuum switch. when the engine heats up the switch turns vacuum off. If the switch goes bad no vacuum gets applied and the valve simply doesnt function. If it's stuck all you have to do to check is suck on the vacuum line and you'll be able to tell if it's actuating. Same with the EGR valve. (which works off the hot vacuum switch.)

So when your mechanic checked the vacuum did he check the hot and cold system? For instance if the hot switch stopped working it will fail to advance the timing after warm making it harder to start. The cold system is there for emissions to help heat the engine up. The distributor is set retarded and the EFE/EGR system is actuated. Once hot those switch off and vacuum advance kicks in.

 

[UptownSport]

If it's stuck all you have to do to check is suck on the vacuum line

Not sure I follow- Maybe a picture of you demonstrating? LoL

Those valves will break off the shaft, too. Can't see that w/o removing downpipe.

Good points, though-we'll be up to that 50 soon, LoL

 

[Vern]

First thing I'd want to know is was the carb replaced due to this current issue ? Second, is the replacement a remanufactured unit?

Vern

 

[UptownSport]

You can add fuel injection for about nothing.
A solder together DIY kit is $200

It's absolutely reliable.


But so is the Thermoquad, more or less.

I'd go do diagnosis before throwing that, or any other parts at it!!!
(Letalone new Thermoquads, LoL)

 

[Gideon33w]

what carb?  sounds a lot like vapor lock to me.  highdesertranger

Same thought. - Wrap your engine bay fuel lines in something heat resistant and see if there's an improvement. If so, def vapor locking. 
I'm no carb expert but ran into the same issue exactly as described in my old Datsun 620. Exaggerated because of Arizona heat too.

 

[Gideon33w]

Thinking back, on my old Datsun, the cure (95% cure anyways) was to reroute the fuel line and add some heat resistant wrap.
The stock fuel line location ensured A LOT of heat was dumped into the fuel which was causing my issue.
For some reason, the stock routing had the fuel live wrapping around things and had a upwards hump (you don't want those).

 

[jimindenver]

Possible weak fuel pump?

 

[steamjam1]

I've got a locking gas cap so in case it was a venting problem (84 dodge ram 350) have just been snugging it rather than clicking it now.  But again yesterday just as I got to my destination it did it again (just a minor bit - but did do it).  It was colder yesterday than it has been.  When it's bad it will also do it from a start/stop like from a traffic light after I pull off freeway.  Seems a little rough idling.

you have a 1984 Dodge B350.. Which means if its equipped with a 5.9L, when you remove the air cleaner you'll see a Thermalquad. The symptoms you describe is a classic plastic carb body first starting to warp problem. The only solution is to get an upgrade quadra-jet carb out of an '85-'88 van.

If you van has a 5.2L, then it'll come with a Carter BBD... Also JUNK..

 

[UptownSport]

Ball & Ball Dual was an excellent carb- as was the single.

Only thing i saw on the equally excellent thermoquad was aforementioned wells falling off. I never saw a warped one, but heard lots of people TALK about how plastic warps.
I never, really determined that the wells falling off were an actual problem.


Chrysler's partnering with Carter was one of the reasons for their reputation as 'go forever' cars in the sixties.

Later, they (and others) used a Holley of Weber design- my belief is this single item was cause for much derision of American car industry.

In any case, I'd be wont to suggest replacing anything without good justification.


It sounds like the broth's had too many, low quality cooks- if wires are left loose

Heat soak- up here that wouldn't occur with only five min of driving- i suppose i have no idea being from North 

But get a fuel pressure test- thatd be prudent to start sorting it out

 

[Gideon33w]

It sounds like the broth's had too many, low quality cooks- if wires are left loose

 
Haha, yeah, think we found one ...

 

[bobblefrog]

Hey all - want to thank everyone for input. I have my settings wrong so never realized I had replies to my post. My problem continued to worsen across the country (think I know a mechanic in every state now!) and my anxiety increased with travel so completely forgot about this thread. Wasn't til I was talking around HDR's campfire the other night that I realized I needed to go back and check all my posts to follow up...

THANK YOU.

So, it does seem I am dealing with a vapor lock and other issues - currently in AZ and for the time being, in cooler temps she's been running better. I don't expect the issue is solved although I have run 4 hours now at a time without issue. Still have the starting issue after it's warm and then off for more than five minutes, but that's just an annoyance now. What got bad was the surging on the rises. Had fuel filter replaced, vacuum pressure checked, the fuel line moved away from water pump and taped, another mechanic said there was no cure for vapor lock, poured in some ATF to my fuel tank and sent me on my way, a fuel pump replaced (helped greatly - it was leaking, didn't solve) and finally a distributor rotor (think from the noise that became a problem later in the series of events) and fan clutch replaced, some carb tuning and wiring fixed.

Things I'm considering in future - reworking the entire fuel line away from the hottest parts of the engine (and possibly replacing), putting a 3-way fuel filter closer to the carb to return vapor back to the tank and of course the fuel injection to replace the carb, although I've gotten differing opinions on that, as well. In the meantime I understand the issue and will adjust travel to work around it.

By freakish coincidence, I met the third owner in Denver (she recognized the rig in a grocery store parking lot and flagged me down). I mean I bought it in Denver but in a city that big, what's the chances? She had a much worse issue with it than I ever did. At that time she had an electric pump installed back by the gas tank (didn't solve issue from what I understand) but that has since been bypassed. The mechanic that replaced the fuel pump felt that the new fuel pumps generally solved the issue and it did help as I said. Surging not so bad, but the fan clutch was weak and even though my gauge wasn't showing overheating, it has been running a tic cooler ever since. Also am told those gauges weren't the most reliable.

FYI - carb was a new edelbrock - sorry, can't remember the model right off hand

 

[Weight]

My 87 B250 has a return line from the canister fuel filter that was designed to solve vapor lock. http://www.rockauto.com/en/moreinfo.php?pk=7574292&cc=1073382&jsn=476