TheSamba.com :: View topic - Carb problem - Engine Starts, revs and dies

Fri Jan 11, 2019 10:33 am

Greetings Samba members

After searching thoroughly the forum, I have given up and decided to post my problem.

My beatiful baby is 1969 beetle. 1600cc DP, Carb is 30pic (No choke whatsoever) Electronic Ignition running strong.

The problem as follows:
It starts fine, then after a few seconds it just dies, as if lack of/too much fuel. After a while, it starts again with the exact same symptom. I tried accelerating and it seems to rev and liven up but it still dies. If I start it again and hit the gas pedal several times when it wants to die, it seems to avoid dying (it only sputters) **Here is the best part** and revs back up normally o.O, but it only runs good and dies just the same after a few seconds. Puzzling.

I have been fixated that is a carb issue. BUT here is what I have checked and covered so far.

I have thoroughly cleaned the carb several times (thoroughly means carb cleaner, hot water with some vinegar, as per suggestion seen on the forum). All the passages are flowing nicely, no clogs at all. Float level was one of the suggestions, and it has been modified thinking of an overflow. Same thing.

Valves have been gapped at 0.006, spark plugs are clean, wires are new, dizzy cap is clean, no cracks, rotor is new. Fuel pump and rod are excellent. (Tested them starting the car with the hose on a separate can, fuel pumps greatly and it died just as the same, and when it died the bowl still had gas in it).

Checked for vacuum leaks long time ago when it used run for a longer time before sputtering, and found none. Haven't been able to check them again due to not running long enough.

I have rulled out electrical because it keeps running and only fails because of carb/fuel delivery, but can't pinpoint how/when/where.

I now remain at your mercy, please HELP!

Fri Jan 11, 2019 11:51 am

Hola!

I know you said the carburetor is clean but if I was in your shoes, I would try swapping the carb with a spare.

Do you know anyone with a bug who would let you swap out the carb if you asked? Any VW clubs around that may have a few carbs laying around you can buy cheap.

PS: best of luck with the crisis in Venezuela.

Fri Jan 11, 2019 12:02 pm

Vacuum leak or clogged main jet.

Fri Jan 11, 2019 2:10 pm

jb17atita wrote: I have thoroughly cleaned the carb several times (thoroughly means carb cleaner, hot water with some vinegar, as per suggestion seen on the forum). All the passages are flowing nicely, no clogs at all.
This method of cleaning is good but does not ensure the passages are clear. You need to use a compressor to blow the passages clear.
How do you know the passages are flowing nicely? Even a small amount of dust/dirt in the idle passages could prevent the proper fuel flow. This is why compressed air is used to blow the passages out from the carb throat back towards the bowl.
Also remove the idle jet on the right side of the carb and blow it clear as well as flush the passages in the hole it sits in.
It helps to draw lines on the head of the jet showing the direction of the lateral passages. When you install the jet, make sure one of the passage lines is oriented vertically as this is the direction of the flow thru the jet.

jb17atita wrote: Checked for vacuum leaks long time ago when it used run for a longer time before sputtering, and found none. Haven't been able to check them again due to not running long enough.
Use the fast idle cam to hold the throttle open. This should increase the idle rpms enough to keep the engine idling on its own.

Using the small red straw, spray carb cleaner and focus the spray at the point where the throttle shaft comes out of the carb body. You will need to spray at the gap between the carb body and the arms of the throttle shaft.
If the idle changes at all (up or down) when you spray... you have a leak.

Sat Jan 12, 2019 4:28 pm

I am having the same issue, but I haven't done any investigation yet.

The messages here give me direction.

Thanks

Sun Jan 13, 2019 5:28 pm

joey1320 wrote: Hola!

I know you said the carburetor is clean but if I was in your shoes, I would try swapping the carb with a spare.

Do you know anyone with a bug who would let you swap out the carb if you asked? Any VW clubs around that may have a few carbs laying around you can buy cheap.

PS: best of luck with the crisis in Venezuela.

¡Hola, Joey!

Thank you for your reply.
We are doing the best we can with the crisis. It's not so bad but it's not any good. Thanks for your wishes.

Yes, that is one my last resorts, swapping the carb, I'm expecting a used one over the weekend to try that.

TDCTDI wrote: Vacuum leak or clogged main jet.

Main jet is almost pristine, so I'm leaning towards vacuum leak which is what I haven't been able to check (and also seem a logical culprit considering the symptoms).

Ashman40, as I said, I haven't been able to check for vacuum leaks actively because the engine does not hold for more than 30 secs on.

I spent this Sunday trying to check for any vacuum space statically (i.e. without cranking the engine, especially because the battery lost the juice due to many crankings and no charging). I disassembled the intake manifold, check the rubber boots -No cracks- Resealed the end castings to the heads (put one metal gasket and one paper gasket in-between and light coat of RTV silicon between everygasket).
Again, I did not fire it up because of lack of better battery and the carb is in the ICU.

I expect to pick up the other carb tomorrow and charge the battery.
I'll keep you posted.
Thanks all for your replies and suggestions.

Here's a pic of the current heart (excuse the mess)

Mon Jan 14, 2019 9:27 am

Any chance you can post a video showing you start the engine and it running until it dies? I'm interested in "how" it does? It is a "slow death" from lack of fuel? Or is it an instant death like someone turned off the ignition switch? Watching/hearing and the engine as it dies could confirm which of the above is your situation.

Fuel from fuel pump fills the carb's fuel bowl. The engine should run for a few minutes with just the fuel in the bowl. Since you are only getting 30sec of run time it suggests you are running off just the fuel squirted from the accelerator pump into the intake. Once this dries up the engine sputters to a stop.

Try two things... loosen the (small) volume mixture screw on the left side of the carb so it is four turns out from fully seated.
Loosed the (large) bypass screw, also on the left side, four turns out from fully seated.
Loosen the screw at the top end of the throttle arm until (at rest) it is NOT touching the fast idle cam. Tighten it in until it just contacts the lowest level of the cam. Tighten 1/2-turn more to slightly open the throttle plate.

These settings should be VEY rich, but should get your engine started and running off the fuel in the bowl. Check that the fuel level in the bowl is correct.

Last resort Tip: Try doing a "poor man's tune up". Get the engine started. Rev the engine rpms up high. Slam your hand over the carb opening to block ALL airflow. This creates a huge vacuum inside the carb throat which should SUCK all passages clear. This can sometimes clear slightly blocked passages. Warning, if you have any slight vacuum leaks... this could open them up even more. This could be good as it may help you more easily find them.

Mon Jan 14, 2019 7:54 pm

ashman40 wrote: Any chance you can post a video showing you start the engine and it running until it dies? I'm interested in "how" it does? It is a "slow death" from lack of fuel? Or is it an instant death like someone turned off the ignition switch? Watching/hearing and the engine as it dies could confirm which of the above is your situation.

Yes, I'll try posting it, I did try to record something but my "phone stand" was not as sturdy as I needed.
It is not exactly instant death, but slow death only avoided by hitting the gas pedal several times -emphasis on several.

ashman40 wrote: Try two things... loosen the (small) volume mixture screw on the left side of the carb so it is four turns out from fully seated.
Loosed the (large) bypass screw, also on the left side, four turns out from fully seated.
Loosen the screw at the top end of the throttle arm until (at rest) it is NOT touching the fast idle cam. Tighten it in until it just contacts the lowest level of the cam. Tighten 1/2-turn more to slightly open the throttle plate.

My carb is a 30pic, so no bypas screw, mine only has one screw on the left side, which is issually set to 1 1/2 turns from the close position. I have also set this screw to over two turns with no difference in the outcome.

ashman40 wrote: Last resort Tip: Try doing a "poor man's tune up"...
Will do it next time it fires up, and does not die in the time between me hitting starting it and going to the back.

Tue Jan 15, 2019 5:22 am

Quote: Fuel from fuel pump fills the carb's fuel bowl. The engine should run for a few minutes with just the fuel in the bowl. Since you are only getting 30sec of run time it suggests you are running off just the fuel squirted from the accelerator pump into the intake. Once this dries up the engine sputters to a stop.

This was checked by removing the hose from the pump to the carb. It ran and when it died, it still had fuel in the bowl.
I also removed the top part of the carb, in that moment my wife could help me with cranking the engine so I could see the problem first hand. Same thing happened: It ran and when it died, it still had fuel in the bowl.

Here's a couple of pics of the carb showing its unique characteristics. In this side of the world, it is the most common type of carb we have (being from Brazil), but I have barely seen it in thesamba.com

Tue Jan 15, 2019 6:53 am

Have you tried adjusting the mixture screw?

Does it change how the engine runs when you do? If not then there is a blockage in the idle circuit, or a vacuum leak, or the throttle plate is incorrectly set.

By your description, it sounds like the carburetor is too lean, thus the reason that it continues to run when you blip the throttle. The accelerator pump gives it just enough fuel to satisfy the stoichiometric ratios necessary to run, until it's depleted.

If you want to do this on the car, remove the top of the carb, remove the drain plug at the bottom of the fuel bowl & drain fuel, & remove the main jet. Then remove the air correction jet/ emulsion tube (at 12o'clock in the top of the carburetor throat, DO NOT DROP IT into the carb), use compressed air and/or carb cleaner to blow the passage clear & check if air/carb cleaner is flowing back out of the float bowl. Make sure that the emulsion tube is clean also.

It's up to you if you want to remove & clean the pilot jet while you're there.

Tue Jan 15, 2019 6:56 am

Here is the little video I could record on my cellphone. It's pretty low quality but it is what I got.

Tue Jan 15, 2019 7:15 am

Yeah, you're running out of fuel. If there is fuel in the bowl, check the main jet in the bottom of the fuel bowl & force air back through the idle jet passage.

Tue Jan 15, 2019 8:42 am

TDCTDI wrote: Have you tried adjusting the mixture screw?

Does it change how the engine runs when you do? If not then there is a blockage in the idle circuit, or a vacuum leak, or the throttle plate is incorrectly set.

By your description, it sounds like the carburetor is too lean, thus the reason that it continues to run when you blip the throttle. The accelerator pump gives it just enough fuel to satisfy the stoichiometric ratios necessary to run, until it's depleted.

If you want to do this on the car, remove the top of the carb, remove the drain plug at the bottom of the fuel bowl & drain fuel, & remove the main jet. Then remove the air correction jet/ emulsion tube (at 12o'clock in the top of the carburetor throat, DO NOT DROP IT into the carb), use compressed air and/or carb cleaner to blow the passage clear & check if air/carb cleaner is flowing back out of the float bowl. Make sure that the emulsion tube is clean also.

It's up to you if you want to remove & clean the pilot jet while you're there.

Yes, I tried. No change.
I did all those steps, repeatedly, before posting.
Your explination is something I have thougt of too, hence my repeated blowing/cleaning the carb

TDCTDI wrote: Yeah, you're running out of fuel. If there is fuel in the bowl, check the main jet in the bottom of the fuel bowl & force air back through the idle jet passage.

Done, way before posting.

That is why it is so puzzling.

Tue Jan 15, 2019 4:56 pm

What do the spark plugs look like? Rich or lean?

My gut is lean, like no gas, but I have been wrong before.

So, if you could post up a picture of the plugs.

Beyond that. Can you keep the car running if you spray carb cleaner into the carburetor opening? That would tell you either the car will continue to run and that you are having a fuel delivery issue or if it dies, that you have a spark issue. We have seen several faulty condensers recently. Might be worth a shot!

Tue Jan 15, 2019 10:07 pm

Agreed. It appears to be running only from the fuel being squirted by the accelerator pump and this may be flooding the intake. It also seems to be running very rough.

Any chance you can borrow a known good carb from someone? If it runs better w/ the borrowed carb you know it is your carb that is the problem.

If not, I would try Speedy Jim's troubleshooting for engine not running. Check that there isn't something else causing the engine to run rough.
http://www.speedyjim.net/htm/eng_strt.htm

Wed Jan 16, 2019 10:09 am

clean the idle jet, also, take out the idle mixture screw and blow in there

Wed Jan 16, 2019 4:41 pm

Hey, Jimbo!
For your pleasure.
Spark plugs from 1 and 2 cylinders

Spark plug from 4 cylinder (Number would not budge and my ratchet broke, Father has the good one :evil: ) BTW, more on this plug later.

Electrical issues have been discarded (more on that later on).

Thanks your for your imputs Jimbo and ashman40. I totally agreed, hence my buying another carb for testing.

After charging the battery, I tried with the same old carb.
Nothing, or should I say, same thing. Starts runs and dies.

Testing starts.
Slapped the secondary carb on the car. and.....

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IT FINALLY RUNS AS IT SHOULD!!! :D

It was indeed my old carb who was effing with me.
Now, the 4$ dollar question.... (that's what cost me the carb plus shipping, price to this date's currency exchange rate) Who in God's grace is the culprit?

With the "new" carb on, I swapped in:
1. Main jet from my old carb (it runs)
2. Pilot or idel jet from my old carb(it runs but suddenly it died)
He did not want to fire back up.
3. Swapped back the pilot jet from the "new" carb. Nada.
4. Swappend back the main jet from the "new" carb. Bingo! It runs, it fired right up. o.O Hmm.

40-year-experienced mechaninc doing his shade-tree session of mechanics on his own truck was helping, and he certified that my old main jet was no clogged. But...

After some test runs, I decided to put back my old carb on with the "new" main jet. Just the main jet, the rest was from my old carb.
And the puzzle ends...

NOW, IT RUNS!!! :D :D :D

I have a bit of misfiring on plug nº 4, but it runs!
BTW, Final inquiry. I need to get smaller nut spark plugs, I mean, the 5/8 ones, not the 13/16 ones. the cyclinder tins do not allow me to put in a bigger socket there. (I have tried, but...) What number and brand do you recomend? Regarding hving the heat range closer to our original application. I'd appreciate any help on this too.

One time it did not want to fire up, but it was due to some poor contact with dizzy wiring, but I fixed, and it runs!

I want to thank you all for pitching in and guiding me. Truly.
Sorry for the long post but, like many admins and moderators here, I hate when people doesn't report back saying when they solved it, and how they solved it.

Wed Jan 16, 2019 6:24 pm

That first picture of the two sparkplugs ... those two plugs look totally different. And they were on the same engine? On the same head even?

Max

Wed Jan 16, 2019 6:29 pm

Thanks for the pictures. You have three plugs showing in the pictures and they are all a different type and manufacturer. Highly recommend you get four plugs all the same.

Really odd regarding the main jet swapping, and the difference it has made. Sounds like the old one was clogging up the port, but the new does not. Really odd, but not the strangest thing I have seen or heard.

Glad that you got it! That is what is important. Now get 4 spark plugs that are all the same, adjust the valves cold. Then set the dwell, and timing. Then set throttle plate, idle speed and mixture. Repeat as necessary. Should be running great when you get all done.

Wed Jan 16, 2019 6:38 pm

Max Welton wrote: That first picture of the two sparkplugs ... those two plugs look totally different. And they were on the same engine? On the same head even?

Max

Hate to say it but ... these days in Caracas, he probably can't get new plugs. Unless he knows someone who knows someone who....