Bug loses power

[jshbrgs07]

Had my 68bug clearance set at 4 thou inch and adjusted timing accordingly, she purrs beautifully and runs smoothly the thing is just today after getting stuck in traffic for almost 2hrs, on 1st gear when I stepped on the accelerator she suddenly loses power and turns off but all lights are on, triedto start the ar but all she does is crank and would not start..had to give a push to start. After a mile she just turns off again and had to give another push and runs, upon shifting to 3rd gear she loses power so I shifted down and she roars back to life and shifted to 3rd and responded smoothly after a mile she started to lose power again and had to shift a gear down back to 3rd then 2nd gear gave a strong rev and shifted back to 3rd and she responded well again,. I have a 68 beetle.

Thoughts pls? TIA

[Stray Catalyst]

.004 is too tight, IMHO - you're better off setting the valves to .006. If you can push start it but not start it with the starter, it's a strange symptom. What carb(s) are you using, and what distributor? Is there fuel in the filter? Is the engine unusually hot when it quits?

[Marc]

Your symptom could be fuel-starvation rather than ignition - the classic syndrome is that after sustained high fuel demand the tank filter will plug, but when the car sits idle/fuel demand is reduced gravity takes over and the crud falls back to the bottom of the tank until the next time you're on the highway for a while.
Changing gears changes the engine RPM at a given roadspeed so the mechanical fuel pump stroke rate changes, which can sometimes help for a short time. A problem with the fuel tank vent system gives an identical symptom, but simply leaving the cap loose "cures" it.
.004" is just fine provided you are adjusting your valves at the recommended 3000mi interval. The spec was only expanded to .006" in deference to the American market, where the typical motorist is less assiduous about maintenance than they are in Europe - too many customer complaints about burnt exhaust valves from people who'd never read their owner's manual. There was never an intake-valve-related reason for the change - personally I use .004" intake and .006" exhaust, which typically is good for 5-6000mi...YMMV.

[aussiebug]

I thought much the same as Marc. Possibly a blocked in-tank filter. Another possibility is a blocked or partly blocked idle jet, or if you still have the original 30pict/2 carb, the idle cutoff solenoid, which screws into the back of the idle jet on these carbs, might not be working properly. Running when the revs are high could mean it's running on the main jet but not at lower revs on the idle jet.

And I also agree with Marc on the tappet settings. I have used 4 thou on all engines since 1970, check them every 3thousand miles, and have never had a problem.

[jshbrgs07]

Thank you for the input. I think I found the culprit already. It is the new gasoline Im using now, it is a 91 ron with a special mix in it, the same thing happened with my 74 beetle after loading the same gasoline. Id better go back to my old gas station.

[Marc]

Not likely. It's been known to happen that fuel with a high alcohol content can cause a "crud burst" by loosening corrosion from the walls of the tank, thus freeing it to clog up the strainer in the bottom of the tank and/or any inline filter(s) present..."cleansing" agents ostensibly intended to clean fuel injectors will have the same effect - but once that's taken place, merely switching back to a less corrosive fuel won't fix anything, the strainer/filter needs to be cleaned/replaced.

[aussiebug]

it is a 91 ron with a special mix in it, the same thing happened with my 74 beetle after loading the same gasoline.

I presume you mean it's E10 or similar - has alcohol in it. That would not normally produce the symptoms you describe - it's more likely to make the engine a little sluggish, and run a little hot.

Alcohol contains almost 40% USED oxygen which can't be burnt again, so it has less "fuel" in the fuel. Adding some to gasoline means it's clean burning which is good for reduced emissions, but it also means it makes the engine run a little lean (E10 makes the engine run 4% lean). Modern FI cars with engine computers can adjust the mixture on the run, but a carburettor can't - the jets in the carb supply a VOLUME of fuel, but they don't know what the energy value of that fuel is.

The answer (if you HAVE to use E10 or a similar fuel) is to enrichen the main jet (by two sizes for E10, each 2.5 step in the Solex jet sizes alters fuel flow by about 2%), and maybe the idle jet too (this is not so critical), from the usual 55 to say a 60. That will get the mixture back into balance (or close to it) and the engine will be happier for it.

[E_bug]

I remember when i lived on the east coast that we got the Winterised mix fuel.
The gas stations changed over about this time of the year if i remember correct.

[jshbrgs07]

for some reason the bug just got back to its normal self after a few days of full throttle and endless revving while on the streets. My bug is a 68' 1200cc with a main jet of 122.5 as for my idle jet im not sure which is it because when I opened my carb i see a bent tube with a marking 50 on it and a jet that looks like a the main jet with a 60 on it.

[Marc]

You didn't say which carb you have, but on most Solexes the idle jet is external, screwed into the RH side of the carb - expect it to be a g55 (or thereabouts).
You may have had a piece of crud blocking the inlet valve ("float valve" in the carb top) that's finally flushed through. Could be the end of story, or it could be lurking in the bottom of the bowl waiting to get sucked into the main jet or accelerator pump...
There's still a possibility that the pickup screen at the bottom of the tank was getting plugged up, and the junk that was doing it has finally settled down and stuck to the tank walls again. You may find out next time you drive on the highway for a while.
I would toss a new fuel filter on, unless you can tell for sure by inspection that there's no hole in the media.

[jshbrgs07]

I will have the fuel tank drained and cleaned and replace the filter to be sure it wont happen again. Thanks for the advice. My carb is a solex h-30-pic. Could not find the specifics of it on the internet. But someone told me it is similar with a 30 Pict/1 or 30pict/2 but with a manual choke.