What's the diagnosis: fuel starvation, bad idle, running hot.

[willincalgary]

Interesting drive through Wyoming today. Started off with a little light offroading and then followed it up with a short highway drive.
Symptoms started at the stop sign to get on the highway. Idle was terrible. Not just the usual miss but lugging along at around 3-400 rpm. Sort of amazes me it can idle that low. Suspected a plugged idle jet which I removed and cleared with no noticeable improvement.
Next symptom was a loss of power at high RPM when accelerating or climbing hills. Fuel starvation could have several causes.
The final symptom was the engine was running hotter than usual. Normally it cruises along the interstate at 82 degrees C peaking at 85. Today it was crusing at 87 and peaking at 95.
I put these symptoms together and suspected a sticky needle valve in the carburetor. I have a Weber and had a problem with a rusty gas tank until about a year ago. Always plugging things and sticking the needle valve.
The way I see it the level of the fuel bowl was low giving me a bad idle and causing the engine to run lean and overheat. It would also explain the fuel starvation if the valve wouldn't open fully. I have cleaned out the carb, which had a bit of junk in it, and cycled the needle valve a bunch of times. This cleared up the idle and fuel starvation. I haven't flogged it on the highway yet to see.
Agree with the diagnosis. Alternatives? Doing a lot of driving these days and would like to nip this issue in the bud.
Will

www.cambrianadventures.blogspot.ca (http://www.cambrianadventures.blogspot.ca)

[Alk-3]

this sounds like an ignition problem to me. Maybe try cleaning the contacts of the distributer, and check the points etc. Pull the plugs and see if you are running lean. It might be that you're running rich due to poor ignition not burning up the fuel, and a rich fuel mixture will cause you to run hot.. or so I experienced just last weekend…
every time I think I have a fuel problem, it turns out to be ignition.

[SafeAirOne]

Well...like you say, an excessively lean mixture will cause all those symptoms. A timing problem could cause some of those symptoms.

Based on your assessment of a lean mixture, the trick is to find the cause. The list of possibilities, off the top of my head:


Fuel tank un-vented
Clogged Pickup tube/screen
Other fuel line obstruction
Clogged fuel filter
Failing uplift pump
Float valve issue
Other obstruction in carb
Vacuum leak
Carb mating surfaces leaking
Carb metering jet clogged or incorrect
Carb mixture valves obstructed/mis-adjusted



Those are some of the issues that can affect mixture. There's probably more though...

[slorocco]

Sounds like a reasonable diagnosis. Also need to account for some significant changes in altitude which could be a contributing factor with the fuel air ratio.

BTW, enjoyed reading the blog. Some of those pics around Cody and the reservoir are less than 5 minutes from my house up on the Southfork Rd. I know another rover owner that is a year round resident in Cody. He is also a retired Park Ranger. Very helpful guy.

[martindktm]

I had a similar issue that started maybe 2 weeks ago... And what solve my problem was to remove the cheapo new mechanical fuel pump I had put when I rebuilt the truck a year and a half ago and installed back the 38 years old AC mechanical pump that was originally on the truck...No more cutting, great idle and no fuel starving.

[Broadstone]

Give it a quick gravity feed, or hook up an auxillary gas supply to draw from with a clean fuel line direct to the carb. and see what happens.

[willincalgary]

Getting fuel starvation problems again so I bought and installed an electric pump. Now have new tank, pickup tube, hoses through an electric fuel pump and straight to the carb. Still having starvation issues. Also noticed today that the carb is leaking a bit of fuel from the accelerator pump linkage. Could this be indicative of bigger problems in the carb that could be causing my issues or is this another issue? I think I'm going to have to sit in Glenwood Springs, CO over the weekend waiting for parts. The truck just isn't reliable enough on the interstate. Also still running a bit hot.

[jonnyc]

Check all the parts stores in town. See if they have a one-bbl. Rochester carb for a 1951 Chevy 216. If they have a rebuild kit, you might get lucky in a local boneyard.

[SafeAirOne]

Hmm...Is there a fuel filter somewhere in the plumbing? By your description, it almost sounds as if you're running cruddy fuel from the brand new pickup through brand new lines to a brand new electric pump then directly into the carb. I'm confident that you installed a filter before the pump, but just didn't mention it.

Is your problem instantaneous from initial startup, or does it get worse as your driving time increases?

As a side note, as your elevation increases, I'd expect the mixture to get RICHER and figure you'd be getting the old black smoke from the tailpipe at higher elevations, as opposed to getting a leaner mixture.

[Alaskan Rover]

Getting fuel starvation problems again so I bought and installed an electric pump. Now have new tank, pickup tube, hoses through an electric fuel pump and straight to the carb. Still having starvation issues. Also noticed today that the carb is leaking a bit of fuel from the accelerator pump linkage. Could this be indicative of bigger problems in the carb that could be causing my issues or is this another issue? I think I'm going to have to sit in Glenwood Springs, CO over the weekend waiting for parts. The truck just isn't reliable enough on the interstate. Also still running a b hot.

If you are running a generator, I'd be fairly wary of an electric fuel pump as a permanemt install. Those times when you're running headlights, wipers, defroster may cause a battery deficit, as the genny isn't putting back enogh juice into the battery...your electric fuel pump might not get the energy it needs at such times.

What's your strategy on running a 50 mph vintage rover on the interstate...or are you lucky enough to have a Fairey overdrive? My strategy is to use my hazard lamps at all times and keep one eye peeled on the rearview mirror and hope for the best!

5/5 on the Rochester one-barrel...I've had one for 25 years on my series IIA, although it needs work now. Highest mileage I've yet attained with that Rochester is 22 mpg, which is far better than a webber VB or zenith. No tailwind, either!

[Andrew IIA]

My SIIA (2.25 with weber 2bbl) has been having a similar sounding fuel starvation issue. I tinkered with it for a month: cleaned carb jets and choke, lubed linkage, replaced coil, checked in-tank fuel pickup (clean), and was suspecting a failed (mech) fuel pump. Turned out to be a big vacuum leak due to failed intake manifold gasket (diagnosed and now being replaced by local mechanic).

Good luck with it ! Best, Andrew