1977 Bus backfired through the intake plenum on startup

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1funbug
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1977 Bus backfired through the intake plenum on startup

Post by 1funbug » Tue Sep 25, 2018 7:26 am

I have been blessed with a Westy that has provided only minor issues requiring troubleshoot for as long as I've owned it (twelve years). The fuel injection is completely stock. We also shared a visit from Colin this summer. It's a strong running bus, until. Yesterday, leaving from work, I cranked the engine. It fired up, then immediately backfired for the first time ever, and died. In disbelief, I cranked it again with an identical result. I had it towed back to my house, about 7 miles. I inspected the engine bay and found one hose detached at both points lying of to the side and another disconnected.

In the Ratwell photo, "C" was completely detached, "E" was disconnected at the decel valve. I believe it backfired through the intake plenum and popped those hoses off.

My next step is to pull the valve covers off and check the valves. What else should I do before attempting to fire it up again?

Matt Harrell

UPDATE:
valve gap all good. I was specifically looking at intake valves. One needed tightening 1/8 turn. Cap, Rotor, points look healthy. Crank is easy to turn by wrench (during valve adjustment).
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Amskeptic
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Re: 1977 Bus backfired through the intake plenum on startup

Post by Amskeptic » Wed Sep 26, 2018 5:46 pm

Classic symptom of a lean condition that may have arisen from a cracked vacuum hose, or a loose one, that led to more interesting results.

Check all hoses and start it up and see how it does.
Colin
BobD - 1978 Bus . . . . . . . . . . .111,130 miles
Chloe - 1970 bus . . . . . . . . . . . 206,787 miles
Naranja - 1977 Westfalia . . . . . 93,996 miles
Pluck - 1973 Squareback . . . . . 55,510 miles
Alexus - 1991 Lexus LS400 . . . 72,113 miles

1funbug
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Re: 1977 Bus backfired through the intake plenum on startup

Post by 1funbug » Wed Sep 26, 2018 5:49 pm

That's what I did. She is running fine again. Scared the crap out of me. Need a few more good quality hose clamps.

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Re: 1977 Bus backfired through the intake plenum on startup

Post by Amskeptic » Wed Sep 26, 2018 5:52 pm

1funbug wrote:
Wed Sep 26, 2018 5:49 pm
That's what I did. She is running fine again. Scared the crap out of me. Need a few more good quality hose clamps.

You should know that there was an epidemic of this back in the day from emission regulations. Porsche got so tired of blown up AFMs that they asked Bosch to make one with an anti-backfire pop-off valve. And Bosch did. And later, pop-off valve springs and circlips would get ingested in the engine costing ten times that of a new AFM.
Colin :blackeye:
BobD - 1978 Bus . . . . . . . . . . .111,130 miles
Chloe - 1970 bus . . . . . . . . . . . 206,787 miles
Naranja - 1977 Westfalia . . . . . 93,996 miles
Pluck - 1973 Squareback . . . . . 55,510 miles
Alexus - 1991 Lexus LS400 . . . 72,113 miles

1funbug
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Re: 1977 Bus backfired through the intake plenum on startup

Post by 1funbug » Wed Sep 26, 2018 5:58 pm

Well, ok. Thank you Jedi Master! It's a relief to know that it's very likely not a bigger problem.

PaducahFrank
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Re: 1977 Bus backfired through the intake plenum on startup

Post by PaducahFrank » Wed Oct 31, 2018 8:16 am

Our 1978 Bus just did the same thing! It was running like a champ when I parked it the other night. Came out the next morning and fired that sucker up, fired right up, backfired (I assume through the intake), then died. The clear hose that connects to the black rubber connector on the intake plenum had come off. I put it back on and all is well.

My question is, what caused it to backfire? It has not been backfiring at all. The only clue may be that it was a little cool our when I parked it that night but through the night a warm front came in and it was actually a little warmer and more humid in the morning.
Paducah Frank

1978 2.0 F.I. Non Cali Westfalia
1974 Triumph TR6
2005 Chevy Colorado

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Re: 1977 Bus backfired through the intake plenum on startup

Post by Amskeptic » Wed Oct 31, 2018 8:21 am

PaducahFrank wrote:
Wed Oct 31, 2018 8:16 am
Our 1978 Bus just did the same thing! It was running like a champ when I parked it the other night. Came out the next morning and fired that sucker up, fired right up, backfired (I assume through the intake), then died. The clear hose that connects to the black rubber connector on the intake plenum had come off. I put it back on and all is well.

My question is, what caused it to backfire? It has not been backfiring at all. The only clue may be that it was a little cool our when I parked it that night but through the night a warm front came in and it was actually a little warmer and more humid in the morning.


Check spark plug wires for crossing over each other. Make sure point gap is good and condensor is snug, and primary wires at coil are snug.
In rare cases, intake valves can be a little varnished and they don't close well at cranking speed.
Colin
BobD - 1978 Bus . . . . . . . . . . .111,130 miles
Chloe - 1970 bus . . . . . . . . . . . 206,787 miles
Naranja - 1977 Westfalia . . . . . 93,996 miles
Pluck - 1973 Squareback . . . . . 55,510 miles
Alexus - 1991 Lexus LS400 . . . 72,113 miles

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