Fuel Issue?

[Nicholas D]

Hello all – So I finally found the perfect bus last November after looking for several, several years and couldn’t be happier. The PO took great care of it and it has needed only minimal maintenance (tires, basic tune up – valves, points, timing, etc) but has had a totally inconsistent issue that I wanted to see if anyone could offer any advice.

It runs just great 90% of the time but every so often it will start sputtering, lose power, and backfire intermittently. It seems to do it more often when it is held a higher rpm for a sustained amount of time. Usually, I am able to limp it to where I’m going, let it rest and it disappears for another two weeks or so.

All this points me to believe it is a fuel issue, like a dirty gas tank. It maintains good fuel pressure from what I can tell (can’t look at gauge when it’s actually happening), the fuel pump is working properly and I don’t see any gunk in the fuel filter. Rather than just throw parts at it and get a new tank, I wondered if anyone else could offer any insight for basic first steps in diagnoses or troubleshooting? I’ve had a bug (the same bug) since I started driving 25 years ago and feel pretty confident working on that, which is also a 1600dp, but my bus has duel carbs, which I’ve never dealt with. I’m a firm believer in starting with the low-hanging fruit first, but short of carb adjustment (which I don’t think it is because it runs fine when it runs fine) or either cleaning or replacing the tank, I’m at a loss…. Sorry for the length of the post and thanks!

[Wildthings]

If you think it's a fuel issue dump some fuel injection cleaner into the tank and see if that clears it up.

If your valves are hanging up in their guides because of ethanol laced fuel going sour then an upper cylinder lubricant might help.

[aeromech]

Try to run the tank down to right before empty. Disconnect the battery. Get a couple catch pans to hold the residual gasoline. Raise the rear of the bus and remove the right rear wheel so you have better access.

At this point you need to try and drain the tank. Don’t get gas in your eyes or ears. If any gets on your arms wash them with soap and water. Now, once the tank stops flowing go up and remove the fitting and nut from the tank outlet. There should also be a finger strainer up inside which pulls straight down. Plan ahead to replace the strainer.

So, the tank is empty (hopefully). Did any ugly looking crap come out? Is anything partially blocking the hole? Place a clean catch pan under the outlet and pour a gallon or two of fresh gas into the tank and see if debris comes out.

At this point if you had a borescope you might look inside and see what’s the condition. If it all looks good install the new strainer and reassemble everything.
_________________
Lead Mechanic: San Diego Air and Space Museum
Licensed Airframe and Powerplant Mechanic
Licensed Pilot (Single engine Land)
Boeing 727,737-200-300-400,757,767
Airbus A319,320,321
DC9/MD80
BAe146
Fokker F28/F100
VW type 1 1962,63,65,69,72
VW Type 2 1971 (3 ea.) 1978, 1969
VW Jetta
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Capable of leaping tall buildings in a single bound

[Wildthings]

[Nicholas D]

This is all great advice, thank you. I will definitely drain the tank down as you suggest once it gets low enough - it just got filled up last night. This may be another thing worth noting, my wife (whole stole the bus from me and drives it everyday) said it usually does the sputtering/poor running routine the first one or two times after it gets filled up.

It gets StarTron at every fill up and maybe it's just coincidental, but two of the times it ran rough were the only two times I'm aware of that it didn't get any StarTron.

Either way, thanks again and updates to come!

[aeromech]

I had some wounded travelers come through San Diego several years ago complaining of the bus running similarly to yours. Telford and I found a rag in the tank

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_________________
Lead Mechanic: San Diego Air and Space Museum
Licensed Airframe and Powerplant Mechanic
Licensed Pilot (Single engine Land)
Boeing 727,737-200-300-400,757,767
Airbus A319,320,321
DC9/MD80
BAe146
Fokker F28/F100
VW type 1 1962,63,65,69,72
VW Type 2 1971 (3 ea.) 1978, 1969
VW Jetta
VW Passat
Capable of leaping tall buildings in a single bound

[Nicholas D]

So aeromech just so I'm sure, once the tank is drained I need to remove the fitting and nut from the tank outlet? By this you mean where the fuel line comes out of the bottom (?) of the tank? I found the following on Bus Depot, is this what you're talking about?

https://www.busdepot.com/j11226

Thanks again, and my apologies for probably over thinking on my part.

[aeromech]

[Nicholas D]

Perfect, thanks! Guess all I can do now is run the gas out of it, headed camping for the weekend. Hope we make it!!

[aeromech]

Here's a trick. Hang a fuel container on the side of your bus. Run a hose to your engine. Be safe. This will tell you if the tank is your problem.
_________________
Lead Mechanic: San Diego Air and Space Museum
Licensed Airframe and Powerplant Mechanic
Licensed Pilot (Single engine Land)
Boeing 727,737-200-300-400,757,767
Airbus A319,320,321
DC9/MD80
BAe146
Fokker F28/F100
VW type 1 1962,63,65,69,72
VW Type 2 1971 (3 ea.) 1978, 1969
VW Jetta
VW Passat
Capable of leaping tall buildings in a single bound

[Jeff Geisen]

If I were in your situation I’d confirm dwell is at 50 degrees. If you’re good there, change the condenser to eliminate ignition probs.
_________________
I Corinthians 4: 1 thru 5

‘63 ragtop - ‘68 single cab

[Nicholas D]

Thanks for the tip Jeff. I actually just changed out the condenser a couple weeks ago. Noticed the rubber grommet that fits on the distributor body had come loose and the wire had fallen into the distributor a little. I figured that couldn't be helpful for ignition so I switched it. I do still need to double-check the dwell though.

[Jeff Geisen]

I appreciate you, you’re welcome.
_________________
I Corinthians 4: 1 thru 5

‘63 ragtop - ‘68 single cab

[jakokombi]

Could it be that the vapor recovery system is blocked off or plugged, thus creating a vacuum?
_________________
70 Sunroof Kombi
69 Tin Top
73 Thing
72 Baja

[aeromech]

[Nicholas D]

Update for my own benefit I suppose. I finally got a day off work and was able to remove the fuel line from bottom of tank (there was no strainer at all) and rinse with a few gallons of fresh gas. I also found a second , filthy, fuel filter under the bus (amazing what happens when I actually have the time to look). Cleaned tank, switched fuel filters and put some fresh gas in. The pictured junk came out of tank and although it's not a glove I suspect it could have been the culprit. We'll see! Thanks again for the advice!

[Wildthings]

In my opinion you are better off to run without the screen and cut the stand pipe so it is much shorter and V-notch what is left of it so it can't easily be blocked with a piece of plastic floating around in the tank. With the original stand pipe you can end up with an inch plus of water pooled in the bottom of the tank, something I would rather not have.

Since you have an inline filter the screen itself is redundant.

[Nicholas D]

Is the circle part the stand pipe? Pic is the one I replaced which is definitely shorter than what I put in. I get what you mean about having so much water in the tank with a taller stand pipe, and get the idea of cutting a notch to avoid blockage but wouldn't the screen negate any need to cut a notch and still filter any particles?

[Wildthings]