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1600 Backfires
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malander
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PostPosted: Fri Jul 30, 2010 9:09 am    Post subject: 1600 Backfires Reply with quote

Bought a '66 running rough. It has a 1600 stock in it.OK, I timed it, new points gapped to 16, fresh plugs gapped to 26, new plug wires and condenser, cap and rotor are fine. It has a 34 pict 3 on it, I tightened the carb and manifold down, where do I go from here? compression check? Carb rebuild? New gaskets? It is backfiring like mad in 1st and 2nd, lack good power.
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Hammarlund
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PostPosted: Fri Jul 30, 2010 10:06 am    Post subject: Reply with quote

Welcome to the Samba.

Unfortunately, the problem you are describing could be caused by many things. In no particular order:

(1) Is there condensation forming on the manifold? It only takes a second to look and see.

(2) Is the motor missing at idle or under no load conditions, or only misfiring under load? Is the spark strong and blue, or weak and yellow?

(3) Can you borrow a known good carburetor and put it on your car? This will isolate the carb as a potential source of trouble.

(4) Didn't you do a compression check before you bought the car? If not, I would certainly do one now, as many of these cars are sold because the engine is worn out and the previous owner does not have the desire/funds to replace it. However, rarely will anyone admit this is why they are selling the car. Also, check the crank pulley for excessive endplay.

(5) What kind of distributor do you have, and how are you timing it?

(6) Have you adjusted the valves?

I realize this is a lot of stuff to check. So, start with the easy ones (checking for condensation, making sure you are setting the timing in a manner appropriate to your distributor) and go from there.

In any event, I would do a compression check, now. There is no point throwing new parts at this engine if it is worn out.

Good luck. Post back with more information about the type of engine (single or dual port) type of distributor and method of timing the distributor, previous owner's given reason for selling the car, etc, and maybe some of the items can be stricken off the list.

Almost forgot: if this is your first air-cooled VW, read your Owner's Manual right away. You will find it in the Technical pull down menu above. In addition, you will want John Muir's How to Keep Your Volkswagen Alive as a sort of primer, and the Bentley Manual to use as a shop manual. Your 1600 is of course not stock, VW had a 1300 in American cars in '66, but most of the information in the above references is still valid.
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malander
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PostPosted: Fri Jul 30, 2010 11:04 am    Post subject: Reply with quote

I'm running an 09 dist at 10 degrees. I'll check compression today as well as distributor advance at 2500 prm. Also, I have a 34 pict 3 paired with the 09, I have read this is also a problem at low end. I have also read that soldering the air hole in the bottom plate / butterfly "fixes" the 34/3 - 09 compatability problem, any rewason not to do the "fix" ?

Car idles fine, starts up like a champ, only backfies and stumbles in 1st and 2nd. Valves have been adjusted to .006 cold, I'll check spark as coil is the only ignition item I have not checked yet.

No condensation in the manifold. everything esle checks, on to compression test and advance. Thanks!


Last edited by malander on Fri Jul 30, 2010 11:07 am; edited 1 time in total
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PostPosted: Fri Jul 30, 2010 11:07 am    Post subject: Reply with quote

Hammarlund wrote:
...

(6) Have you adjusted the valves? ...



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malander
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PostPosted: Fri Jul 30, 2010 11:09 am    Post subject: Reply with quote

Yep, .006 cold.
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Hammarlund
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PostPosted: Fri Jul 30, 2010 11:36 am    Post subject: Reply with quote

Do you by any chance mean the 009 distributor? I am unfamiliar with any 09 type.

The most common types of 009 should be timed so that they advance 32 degrees or so at 3250 or 3500 rpm, and then checked at idle to make sure the timing is reasonable at low rpms. It should be static timed only in order to get the car to start.

Lots of people are prejudiced against the 009. It does have its drawbacks, but I've run one for years with no real problems. I don't know how compatible the 009 and the 34 would be; someone else will have to answer that one.

I do think that if one has a nice matching numbers car the original carb, one is better off with a stock distributor; but I am running a Frankenmotor, like yours (in a '66, yet!).

Common wisdom says compression problems are more likely to manifest themselves as stumbling in third and fourth than first and second, so hopefully your compression is okay; but I would check it anyway. One needs to establish a baseline...

But I hope and believe if you set the timing correctly you will see a big improvement in driveability on this car.
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malander
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PostPosted: Fri Jul 30, 2010 3:14 pm    Post subject: Reply with quote

I made a wire for the connection from the coil to the electric valve ( ? ) on the side of the carb, that helped. But still backfires at partial throttle.

The car is a baja, it runs an open exhaust which I plan on replacing with a "quiet" baja muffler / header system.

Compression is 95 -105 in each cylinder , plugs are dry but black a sooty. I'm going to check advance timing tonight ( my light is too weak to see the numbers in daylight) and see if I get 30- 32 @ 3000 + RPM. My next step is to rebuild the 34/3 carb and shut off the hole in the butterfly as mentioned in an article I read on making the 009 dist. and this carb compatible...
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Hammarlund
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PostPosted: Sat Jul 31, 2010 8:08 am    Post subject: Reply with quote

Yeah, the wire you fixed was probably either to the choke (right side of the carb, front is front) or the fuel cutoff solenoid (left side). If it was the choke, read up on the adjustment procedure and adjust it properly.

You do have to adjust it periodically, especially whenever there is a big change in temperature.

That open exhaust may well be the problem. I've seen engines in the past that would missfire due to an exhaust leak (or running without a muffler!) causing insufficient back pressure, although I've never experienced this personally on a VW.

One of the things I don't like about an aftermarket exhaust is that they usually do a poor/non-existent job of getting heat to the manifold through the risers. which results in condensation forming on the inside and outside of the manifold. This can cause driveability problems in traffic, and usually the carb is adjusted to run slightly rich in an unsuccessful attempt to eliminate the problem, which causes excessive carbon buildup, which plugs the risers, which causes less heat to be transfered...this may account for your sooty plugs.
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