75 bug 1600 twin port backfires

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Nick555
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75 bug 1600 twin port backfires

Post by Nick555 » Sat Aug 31, 2019 10:27 am

HI all

my 1600 twin port bug starts and seems to idle well but then when she drives it backfires and the car jerks, i seem to think it could be the carbs or coil that is giving issues but im not mechanically inclined enough to troubleshoot this myself, is there any one in the germistion/edenvale area that is willing to help me out im willing to pay for the service or if any one has any suggestions a noob like me can try it would be much appreciated .

thanks in advance :)



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Re: 75 bug 1600 twin port backfires

Post by retrovan » Sat Aug 31, 2019 12:29 pm

Try Vdubtech their add is running at the bottom of the screen.

Good Luck.

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Re: 75 bug 1600 twin port backfires

Post by Nick555 » Mon Sep 02, 2019 10:00 am

i was hoping someone could do it privately

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Re: 75 bug 1600 twin port backfires

Post by Ricoffy » Tue Sep 03, 2019 8:03 am

Nick, test the coil and condenser, this you can do with an inexpensive test light.

For the coil, first remove the lead wire going to the centre of the dizzy's cap, hold it about 1/2cm from a grounded metal object and have someone crank the motor. If you see a nice blue spark, 90% chance is that your coil is fine.

Check the condenser with a simple test light:
Remove distributor cap.
First, make sure the condenser is connected to the points properly.
Turn crankshaft until the points are fully open (any cylinder).
Disconnect the LT (green) wire from the coil.
Connect a test lamp wire to the ignition coil terminal and the other lead to the distributor wire.
Switch on the ignition. If the lamp lights, the condenser is grounded internally and must be replaced.
Now reconnect the distributor wire to the coil.
Pull the main high tension wire from the coil, and with the ignition on, turn the engine over. The spark should jump a 1/4 inch gap to earth. If it won't jump this distance, replace the condenser.

If you have done the above, roll up your sleeves and remove the heads - see if the valves seat properly. This may also cause your engine to backfire under load.
Trust me, I'm a doctor...

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Re: 75 bug 1600 twin port backfires

Post by Nick555 » Thu Sep 05, 2019 3:33 pm

Ricoffy wrote:
Tue Sep 03, 2019 8:03 am
Nick, test the coil and condenser, this you can do with an inexpensive test light.

For the coil, first remove the lead wire going to the centre of the dizzy's cap, hold it about 1/2cm from a grounded metal object and have someone crank the motor. If you see a nice blue spark, 90% chance is that your coil is fine.

Check the condenser with a simple test light:
Remove distributor cap.
First, make sure the condenser is connected to the points properly.
Turn crankshaft until the points are fully open (any cylinder).
Disconnect the LT (green) wire from the coil.
Connect a test lamp wire to the ignition coil terminal and the other lead to the distributor wire.
Switch on the ignition. If the lamp lights, the condenser is grounded internally and must be replaced.
Now reconnect the distributor wire to the coil.
Pull the main high tension wire from the coil, and with the ignition on, turn the engine over. The spark should jump a 1/4 inch gap to earth. If it won't jump this distance, replace the condenser.

If you have done the above, roll up your sleeves and remove the heads - see if the valves seat properly. This may also cause your engine to backfire under load.
thanks bud i appreciate all the effort you put into this reply but in the end i let vdubtech have a look and it turned out to be quite a few issues glad i let the pros do it tbh

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Re: 75 bug 1600 twin port backfires

Post by 73type2 » Thu Sep 05, 2019 3:45 pm

Nick555 wrote:
Thu Sep 05, 2019 3:33 pm
... in the end i let vdubtech have a look and it turned out to be quite a few issues ...
For the sake of continuity of this thread it would be interesting to know the outcome. Others might be having similar issues and could learn from your experience.

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Re: 75 bug 1600 twin port backfires

Post by Nick555 » Thu Sep 05, 2019 6:01 pm

73type2 wrote:
Thu Sep 05, 2019 3:45 pm
Nick555 wrote:
Thu Sep 05, 2019 3:33 pm
... in the end i let vdubtech have a look and it turned out to be quite a few issues ...
For the sake of continuity of this thread it would be interesting to know the outcome. Others might be having similar issues and could learn from your experience.
well the main issue was the gent who serviced my bug before (who i might add is refusing to take my calls) put the spark plug at the top right of the engine in skew and damaged the threads, from what i understand vdubtech had to drop the engine sort out the thread put new spark plugs, set the timings and valves , additional to that and unrelated to the initial query they are also sorting out my fuel gauge as it does not read at all and set my brakes .

I hope this was informative and could possibly assist someone in the future but it probably looks silly to someone who is aircooled savvy :wink:

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Re: 75 bug 1600 twin port backfires

Post by Ricoffy » Fri Sep 06, 2019 8:48 am

Nick555 wrote:
Thu Sep 05, 2019 3:33 pm
Ricoffy wrote:
Tue Sep 03, 2019 8:03 am
Nick, test the coil and condenser, this you can do with an inexpensive test light.

For the coil, first remove the lead wire going to the centre of the dizzy's cap, hold it about 1/2cm from a grounded metal object and have someone crank the motor. If you see a nice blue spark, 90% chance is that your coil is fine.

Check the condenser with a simple test light:
Remove distributor cap.
First, make sure the condenser is connected to the points properly.
Turn crankshaft until the points are fully open (any cylinder).
Disconnect the LT (green) wire from the coil.
Connect a test lamp wire to the ignition coil terminal and the other lead to the distributor wire.
Switch on the ignition. If the lamp lights, the condenser is grounded internally and must be replaced.
Now reconnect the distributor wire to the coil.
Pull the main high tension wire from the coil, and with the ignition on, turn the engine over. The spark should jump a 1/4 inch gap to earth. If it won't jump this distance, replace the condenser.

If you have done the above, roll up your sleeves and remove the heads - see if the valves seat properly. This may also cause your engine to backfire under load.
thanks bud i appreciate all the effort you put into this reply but in the end i let vdubtech have a look and it turned out to be quite a few issues glad i let the pros do it tbh
Glad to read you got it sorted.
Trust me, I'm a doctor...

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Re: 75 bug 1600 twin port backfires

Post by 73type2 » Fri Sep 06, 2019 9:36 am

Nick555 wrote:
Thu Sep 05, 2019 6:01 pm
I hope this was informative and could possibly assist someone in the future but it probably looks silly to someone who is aircooled savvy :wink:
Thanks for the feedback. It's not silly at all. It reminds me to always use a systematic approach when fault finding.

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Re: 75 bug 1600 twin port backfires

Post by jfe » Mon Sep 16, 2019 7:50 am

I want to jump on the wagon here please. I have similar issues that just doesn't resolve. I bought a recon motor and had it fitted by the workshop. From there it all started going wrong, I had a motor smoking from the breather, now I have a recon peace of sh....
Anyhow, it will idle perfect and same as it gets underload start to stutter under accelleration and backfire. I've had them then fit an electronic ignition system as apparently the coil and points were an issue. Ran great for the first 100m then worse than before. Next step, bought a new carb and fitted it to the motor plus cleaned out the tank and fitted a new fuel line from front to back. Improved 70% and by this time I've had it with the workshop.
Since I've found the "brand new" plug wires were not seated properly on the connectors on the distribution cap, crimped them to fit snugly and had another 10% improvement.
Now the car runs okay but it feels like it's running out of fuel as I drive, it will run well and the next moment give a jerk almost like when you turn off the ignition while driving and then go again. When decelerating it will also backfire. Checked timing marks and they are all aligned, didn't check with a timing light though.

My train of thought is 1. running out of fuel due to float level of new carb and the cut is just enough for it to fill again as it's almost rhythmic, 2. ignition system has gone bad and need to rewire from ignition all the way to the back, 3. the plug wires they fitted is a LOS and needs to be replaced by proper set like bogey.

Any advice will be appreciated please, if invested a load of money for the rebuild and it's slowly getting to me.

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Re: 75 bug 1600 twin port backfires

Post by 73type2 » Mon Sep 16, 2019 1:42 pm

I think you need to start a new thread for your car.

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Re: 75 bug 1600 twin port backfires

Post by Terry Phillips » Mon Sep 16, 2019 2:51 pm

Run a wire straight from the battery or starter direct to the + on the coil see from there it might be the ignition switch,do you have 20 keys on the key ring that wears the switch out to much weight. my 2c worth.

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Re: 75 bug 1600 twin port backfires

Post by Terry Phillips » Mon Sep 16, 2019 4:12 pm

Check the engine has a good earth from chassis,

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