Backfring

Bugboy · Post by **Bugboy** » Thu Mar 01, 2007 10:58 am

Hey guys have this problem with my bug. She seems to be backfiring a helluva lot. I have changed my sparkplugs and completely stripped the carb and cleaned it out. She ran well last nite for abit then the backfiring started again. I seem to think that it could be a clogged petrol filter? Haven't checked yet but she seems to be spitting out quite alot of dirt. I mean I drove to work from home (Athlone to Pinelands) and she was sputtering all the way even gave her some gas to clear things out but she just kept on. Please help.

Post by **Tony Z** » Thu Mar 01, 2007 11:18 am

what else have you done to the car recently?? Are you 100% sure that the plug wires are connected the right way?? Are you 100% sure that all the plugs and plug wires are properly connected - sometimes you put on a wire and it feels like its home, but its not, they almost "click" into place.
Are the plug wires in good condition.
Points and condensor... when was the last time you replaced these? Have you checked for corrosion of the points? Have you got spark to all the plugs? are you 100% sure?
Is the rotor good?
is the dizzy cap good? Contacts good? No cracks?

The dirt could be poorly burned fuel

Post by **fig** » Thu Mar 01, 2007 11:29 am

There are several causes of backfiring:

The first thing to check is for holes in your exhaust.

Also check ignition timing and valve clearances.

The most serious cause of backfiring is burnt valves. You do change the oil and reset valve clearances every 5,000km, don't you? To check for burnt valves do a compression check. No3 is the usual culprit.

In general, NEVER mess with your carb until after you have exhausted (scuse the pun) all other possibilities.

Bugboy · Post by **Bugboy** » Thu Mar 01, 2007 11:39 am

Well I havent changed the points and condenser recently.They have been in there about 4months now. Rotor needs to be replaced though. Have made sure that all plug wires are properly in heard the click. Also labelled them before I removed them. Then I have sealed up all holes in my exhaust about two days ago. As for regular oil changes have done one about a month and a half ago,as for valve clearances haven't removed the heads yet to check on that. Also now that you mentioned timing there is a bit of a miss ,not bad but it is present.

Post by **Tony Z** » Thu Mar 01, 2007 11:44 am

Get a timing light and check your timing....
You admit you need a new rotor
Get a manual or download a basic one and set your valve clearances.

A general rule to remember is........
If you think its your carb, its not. Look elsewhere.

Bugboy · Post by **Bugboy** » Thu Mar 01, 2007 11:50 am

Okay will do that.

Post by **fig** » Thu Mar 01, 2007 11:51 am

You don't need to remove the heads to check valve clearances; just the tappet covers.

Correct valve clearances are absolutely critical to the good health and longevity of your engine.

Another thing to check is for hairline cracks in your rotor and distributor cap. These will show themselves through carbon "tracking" along the crack, which causes the ignition spark to short circuit, either to earth or to one of the other spark plugs.

Post by **fig** » Thu Mar 01, 2007 11:53 am

BTW, if the backfiring is through your carb rather than from the exhaust, then don't drive the car until you have fixed it. Backfires through the carb are a not uncommon cause of ACVW engine fires.

Post by **eben** » Thu Mar 01, 2007 2:47 pm

i'll blame the condensor 9/10 times... it drove me crazy...

Bugboy · Post by **Bugboy** » Thu Mar 01, 2007 4:38 pm

Havent thought about the condenser though. What is its function if you dont mind my asking?

Post by **eben** » Thu Mar 01, 2007 7:33 pm

If i remember its either to make sure a big enough charge builds up in the coil or to prevent excessive arcing at the points....

Bugboy · Post by **Bugboy** » Fri Mar 02, 2007 8:14 am

Oh ok. I have now changed the condenser as well as the plug leads and she still gives a bit of a backfire. So now I have to check valve clearances and timing to make sure everythings as per specs. A buddy of mine(sufficiently knowledgeable on VW's) reckons that I should also check the heads and see if there are no cracks. Could this also be a potentential symptom?

Post by **Tony Z** » Fri Mar 02, 2007 2:27 pm

dont worry about the heads until you have done a proper service. Work through the simple things first.

The only reason a beetle is unreliable is because people dont spend money on them.
I have done about 160 000 km in mine and I can still count how many times it has broken down... once when I didnt tighten my dizzy clamp propely, once when I sucked a rag into the fan housing and pulled out the genny mount from the case and 2 sets of electronic ignitions, then once when a wire extension I made worked its way loose. And now, broken cam follower. But thats it, because I maintain my car myself and look after it. 10 years and 160k km's. I even did a CPT JHB trip without any problems.

Bugboy · Post by **Bugboy** » Mon Mar 05, 2007 4:12 pm

Hey Tony had the timing set and she's going like a boeing. Did splutter abit but seems everythings cleared out now and she has a real smooth now. I suppose it was high time I changed all the ignition components again. Oh the furthest I went with my bug was like Strand but on my way home my generator bearing seized on me . Have since then moved to an alternator. Would like to build another engine someday and bring back the Genie just because its some piece of hardware.

Post by **Tony Z** » Mon Mar 05, 2007 4:21 pm

Really glad to hear it. Simple mechanics involved, and the difference it makes is unreal.