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sputters and backfires under acceleration 1600DP PICT34 009
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HapyBus
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PostPosted: Wed Mar 02, 2011 3:06 pm    Post subject: sputters and backfires under acceleration 1600DP PICT34 009 Reply with quote

Gents, and any laides present,
I have tried earnestly to search for my solution. It has been said that it may be a fuel delivery issue. I changed the fuel filter, I removed the carb and cleaned and blew out all jets. I have adjusted the valves twice in a day and half, I have used Bentely to properly adjust the carb.

what it is.. 1600 DP, fresh heads, pistons and cylinders, less than 150 miles. All new ignition, wires, points, condnsor, cap rotor, plugs.

The set up is a Pict34, 009. I have dwell set at 48*, and timing is at 26* full advance.

It starts at merely a bump of a key, well almos Smile it idles fine, you can hear the choke work. After idleing awhile it likes to die.

Under heavy accleration, it sputters, shudders, coughs and spits, and the warmer it gets, the worse everything is. I pulled over on my shake down rides, and it idles fine, but when I give it gas it really was a backfiring.

I let it cool a bit, took it back to the garage at low rpm, and it stutters, but got me to the shop.

Condidered replacing the fuel pump, but as I thought about how it gets worse with the warmer temps, I chose to ask you all first.

Thank you for reading
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busman78
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PostPosted: Wed Mar 02, 2011 3:16 pm    Post subject: Reply with quote

First off your total advance is too low.
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PostPosted: Wed Mar 02, 2011 4:49 pm    Post subject: Reply with quote

Start by looking down the carb when the engines off and opening the throttle, does the bent brass thing give a good squirt of gas?
After that try another rotor in the distributor if you're sure the points and dwell are good.
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Desertbusman
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PostPosted: Wed Mar 02, 2011 5:02 pm    Post subject: Reply with quote

Why 26 degrees? I don't think I've ever heard of that recommendation. In the 28-30 range is what the majority of us use.
Do as BD says. If the problem remains try adjusting the accelerator pump volume both more and also less. Tweek, drive and tweek and drive and see if it makes an improvement.
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PostPosted: Wed Mar 02, 2011 6:44 pm    Post subject: Reply with quote

Desertbusman, this wrenching is not natural to me, and certainly troubleshooting is greek. I have all my books out, read what people have to say, and then take advice from either the more experienced here on Samba or trusted friends. One such trusted friend, builds engines, and is very good at the air cooled engines, suggested that he runs his 009 at 26. So I tried it as well. Unfortunately, tis engine is just going back together after a refresh, and I have no data tio compare to, with the exception of an 009 I am running in another application, and it does fine. The other engines in my herd have either DVDA or SVDA.

The feedback that seems to be consistent is fuel starvation...I read in previous archives about a dirty filter..changed it. Tomorrow I will look at the fuel inlet/outlet and see what may be hiding in the screen. If that passes, I will change the fuel pump. from there, I dunno... tried throwing different coils at it already..not certain if they are good or not, just different
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Randy in Maine
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PostPosted: Wed Mar 02, 2011 7:31 pm    Post subject: Reply with quote

Have you checked the fuel pressure (after the pump) and the carb float level?
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PostPosted: Wed Mar 02, 2011 8:14 pm    Post subject: Reply with quote

I would go with the suggestion to see if the accelerator pump works. I would also watch the timing from idle to 3500 RPM and make sure it goes back to around 10 degrees at idle and up to 28 degrees at 3500 RPM then returns when you let off the throttle. If it works Ok and the accelerator jet pumps then you may have a vacuum leak somewhere.
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Last edited by SGKent on Wed Mar 02, 2011 9:01 pm; edited 1 time in total
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Desertbusman
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PostPosted: Wed Mar 02, 2011 8:18 pm    Post subject: Reply with quote

Quote:
Under heavy accleration, it sputters, shudders, coughs and spits,


You need to explain it some more. Here's why.
There is a difference between heavy acceleration and running it at a fast speed after you are through accelerating. You didn't say that it runs bad when it finally reaches a higher speed and you are no longer accelerating.
If it does run bad at a high speed that changes the picture and it might be a bad pump or clogged filter type problem .
As soon as you hit the pedal hard it is not running off of the fuel pump, but rather the gas that has already filled the carb. Once the carb volume is depleated then it would sputter and probably stall. But it takes quite a while for the carb gas to become depleated. Totally remove the fuel supply from a carb and it will probably run for half a minute or so.
But to go from a normal throttle opening to a big throttle opening does need the extra spurt of gas from the accelerator pump during that transition. Without the right amount of spurt it will stutter and all that.

So if you can get past your acceleration period and get it up to a reasonably high speed and if it isn't sputtering it is getting sufficient flow from the pump and filter. At the higher speed is where it requires the greatest amount of gas supply.

All this also points out the need for correct float setting.
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PostPosted: Thu Mar 03, 2011 5:10 am    Post subject: Reply with quote

Desertbusman, As for the symptoms, I refer to heavy throttle as going through the gears, between 2 and 3 its real rough, and at crusing speed, consistent throttle, say 60 mph, it has light jerk until warm, then its all herky jerky at cruising speed.. Then after say 5 miles, it is really rough and will not get out of its own way.

I pulled over, with it running, stuck my fat head into the engine bay, and hand throttled it, and there was immense back fire.
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Desertbusman
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PostPosted: Thu Mar 03, 2011 5:52 am    Post subject: Reply with quote

Hope you didn't singe your eyebrows.
Bentley 5-31 tells how to select the correct washer. The goal is to get the correct fuel level. The rebuild kit would also tell which washer to use.

From what you just described it probably rules out an accelerator pump issue. So the pump output, filter, and the other items that were mentioned might be the problem. Did you do the timing again? Did you do the other things that have been mentioned?

One thing you might consider is when you are up at speed and it is messing up real bad is to turn off the engine, immediatly take it out of gear, and coast to a stop in neutral so the pump won't be pumping and refilling the carb. Then take the air cleaner off and do the accelerator pump test like BD says. If it doesn't squirt there might not be sufficient gas in the carb. The other thing would be after you shut it off in that manner pull the top of the carb and measure the fuel level.
Also check the float needle in and out of the valve body for perfect smoothness. I had a similar problem once as yours and everything seemed good but finally found a little rough ridge on the needle valve that was causing it to hang up once in a while. It was a brand new valve also.
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The best thing that anyone can do for their Bay is get the Volkswagen of America Official Service Manual published by Robert Bentley. Without it the bus is pretty much doomed.
73kombi wrote:
when that red light goes on, you have to make a choice.
Amskeptic wrote:
I am not answering that.
Respectfully,
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Jody '71
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PostPosted: Thu Mar 03, 2011 7:00 am    Post subject: Reply with quote

Intake manifold icing can sometimes cause your symptoms. So can a clogged tank strainer. I'd time your 009 as suggested, that is higher than 26, like 28-30. And as mentioned your fuel pump pressure may not be correct.
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PostPosted: Thu Mar 03, 2011 8:28 am    Post subject: Reply with quote

I had a guy bring a car to me once that was running like this and when I checked I found he had a couple spark plug wires routed wrong. A backfire indicates to me that you're getting ignition at the wrong time.
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PostPosted: Thu Mar 03, 2011 10:01 am    Post subject: Reply with quote

aeromech wrote:
I had a guy bring a car to me once that was running like this and when I checked I found he had a couple spark plug wires routed wrong. A backfire indicates to me that you're getting ignition at the wrong time.


This is what I have been thinking too. Getting 2&4 backwards is easy to do, and easy to fix. Check to make sure that you have it right.
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PostPosted: Thu Mar 03, 2011 3:26 pm    Post subject: Reply with quote

Aeromech and Mountainminstrel I surely hope you are not right... I get enough grief for my ineptness as it is...

Thanks guys...going to go tinker now, 5:30 EST, Ill let you know what I find
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PostPosted: Thu Mar 03, 2011 3:29 pm    Post subject: Reply with quote

as I think this over more, I have put roughly 175 miles on this set up since the refresh... the first 100 miles were trouble free.

I noticed a slight mis however at crusing.

Thne we had to remove the engine due to the fan grinding on the shroud..replaced generators and fan set up.. engine back in and the trouble of the mis got increasingly worse.
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PostPosted: Thu Mar 03, 2011 7:02 pm    Post subject: sputtering and choking and backfiring issue solved Reply with quote

while there were many ideas, check fuel and spark (all that is involved with spark) one man had a story, of how it happened to him one time EXACTLY, the sputtering, the loss of power, the backfiring. He mis diagnosed it as a carb or fuel problem. He said that he had the condensor come loose from the coil, and it was shorting out.

I thought that was weird enough to check..just checking them did not tell me why to check them, cause I just put them in new in 120 miles ago. But the thought that I put them in loose, now that made perfect sense to me.

So first thing I do when I get to the shop, is crack my favorite adult beverage, reach around and check the condensor, and yes it wobbles.

We remove the distributor, tighten up the condensor, change rotors, for some reason this one looked tired (should have been a new one) re install the dizzy at 26*, and drove the hell out of it on a shake down ride...

and all seems to be right.

Thank You Desertbuusman and all for hanging in there with me. Thank you all for your thoughts.

Write to ya next time I have an issue!
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PostPosted: Fri Mar 04, 2011 9:06 am    Post subject: Reply with quote

37 deg total at 3k rpm all will be well again Very Happy
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PostPosted: Fri Mar 04, 2011 9:39 am    Post subject: Reply with quote

rivifunbus78 wrote:
37 deg total at 3k rpm all will be well again Very Happy


I don't know where that comes from, but you want this thing to be timed (vacuum hoses off) at about 28-32 BTDC when all of the centrifical advance is has to off is all in. It should be all in about 3500 RPMs or so, but you will be able to see with your timing light when the centrifical advance function in the distributor no longer has any more advance to give.

The intent here is to prevent pre-ignition, pinging or whatever you wish to call it. Too much advance it death to an aircooled VW engine. Too little advance (like 26) is also bad and will likely cause a lack of power, fuel combusting in the exhaust, and high oil temps
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PostPosted: Fri Mar 04, 2011 10:10 am    Post subject: Reply with quote

From where I am standing, the truth is that the bus didn't have the timing set correctly and still doesn't. I don't buy the "loose condensor" story and proof is the 37 degrees it is now timed to.
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Desertbusman
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PostPosted: Fri Mar 04, 2011 2:47 pm    Post subject: Reply with quote

And from where both you and I are standing, SG, both 26 and 37 are funny numbers. Or switching a couple plug wires and it only misses.
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when that red light goes on, you have to make a choice.
Amskeptic wrote:
I am not answering that.
Respectfully,
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