Engine trouble, Fuel starvation or ignition problem

[Eddie DVK]

Ok,

After I got my new MOT, I started to drive my beetle a bit more often to see if everything works properly.
But after a week of regularly driving, something strange occurs, after a mile of driving it starts to misfire above 3000 RPMs.
This is in every gear.

Strange but did a lot of test drives to look what the problem is, but after every check I took it for a drive.
And the problem is still there.

First the ignition-
1. checked the valves (adjustment) - ok
2. checked the ignition timing - ok
3. checked the ignition module - ok
4. checked the coil - ok
5. checked the cables / leads - ok

Now the Fuel system-
1. took out all jets and blown them with air pressure
2. checked the fuel pressure - ok  (have a permanent fuel pressure gauge on my adjuster)
3. adjusted the fuel pressure a bit higher from 0.25 to 0.30 bar.

But the problem is still here...
It looks like a fuel starvation problem..
Does somebody recognize this?

The only thing to do now is to teardown my carbs.

But I wanted to ask you guys first before I do that.

Help appreciated

Regards Edgar

PS I drive this configuration for 4 to 5 years without trouble.

[Tobi/DFL]

Hi Edgar,

I had a similar problem some years ago. The engine idled okay and driving slowly with low revs was no problem but as soon as I pushed the pedal a little harder the car bogged heavily. After some days of searching for the mistake I found out that one cable shoe had a contact problem. Obviously the resistance got too big when I tried to drive a little faster.
Maybe you have a similar problem.

Good luck!

Tobi

[Rocket Ron]

Try driving with the fuel cap off (with not too much fuel in the tank) to see if it's fuel tank breathing issue

Also worth checking the filters at the tank and any others inline you may have

I've had both problems and it's not until you load the fuel system that you see any issues

What carbs are you running ?

[Eddie DVK]

Hi Toby,

Thanks for the reply, the strange part is I can rev it to 4000-5000 RPMs on the first mile of driving.
But after that I can just rev it until 2000-3000 and when I gif it a little bit of gas, it starts to bog and stumble..
And I have changed and tested every cable one by one.
But will test this again. thanks.

Hy Ron,

I use 40mm webers.
I use a filter before my electric pump and Filter King intergrated filter Fuel regulator in the engine compartment..
The only thing I can t check is the fuel pressure gauge when I am driving because it is in the engine compartement.
Butt will check those filters..
Ok will try to drive with out fuelcap and test this..

Thanks.
 

[Eddie DVK]

More suggestions appreciated 

[modnrod]

Maybe time for a few long shots?
 

Pull the dizzy cap off and spray contact cleaner in there.........sometimes you can get a build up of dust and static under the cap.

I've had a very similar problem once when the ignition coil started to break down, almost exactly the same. It tested fine on a meter, but replaced it and problem fixed. Borrow one and test it anyway.

Only when the engine gets warm, but not cold? A cracked spark plug will do that too.

Sometimes when fuel sits around it gums up and varnishes, especially high aromatics (high octane). Strip the fuel lines off the motor, especially cleaning bits like any T-pieces. Your electric filter will also have varnishes in it, it too was sitting around with stale fuel. My best guess is stale fuel and varnish somewhere to be honest.
Try blowing carby cleaner through the fuel lines after you've taken off the pump and filter for cleaning.

[JABa-daba-dooo]

Hi,
First thing that comes to mind is a defective coil with a fracture in a winding inside the coil.
To me it sounds like this occurs only when the coil has operating temperature.
Works fine until it gets a little extra load. At higher loads the fracture in the coil may act as a switch and turn the power off and on through the coil and engine can bog and stumble.

Try a different coil that's my suggestion.

JAB-Tuning

[Martin S.]

When was the last time you replaced the plug wires? It's not easy to tell if they are no good other than misfiring on acceleration under load, as they could look ok on the outside but be bad/burnt out inside.
Also, check your gas tank for crap floating around. It could plug the drain at the bottom and then unplug as you drive around. Remove tank, swish gas around and blow out with air and replace, easy and gives peace of mind.

[HERB]

Do you have the factory screen on the fuel tank outlet? If so, pull it out and check, it maybe be plugged up not allowing the volume of fuel needed. It's often overlooked and caused me many headaches. I had a "miss fire" that drove me nuts and I checked all ign. related parts before someone suggested I check the in tank filter screen which was almost totally plugged.

[Larry S]

I had a bad set of spark plug wires once that caused this issue. i tried a new coil, unhooked the tach, ran new wires to the coil, just about everything and it turned out to be the wires.took me a week to figure it out.

[Jim Ratto]

Hi Toby,

Thanks for the reply, the strange part is I can rev it to 4000-5000 RPMs on the first mile of driving.
But after that I can just rev it until 2000-3000 and when I gif it a little bit of gas, it starts to bog and stumble..


[/quote









When it does the above, after a mile or so, immediately kill fuel pump/engine and coast to side of road (safely). Remove air filters and watch down throats of carbs and open linkage. See if accelerator pumps are injecting fuel or not. If not, your float bowls are empty or fuel level is (really) low. If the fuel levels go low, the engine will run on idle circuit, but fuel level in emulsion tube wells will be too low to begin emitting fuel/air mix at duct in auxiliary venturies. If this is the case, you have an issue with needle valve, float or both.

Check it out and let us know.

Jim

[Jim Ratto]

Hi Toby,

Thanks for the reply, the strange part is I can rev it to 4000-5000 RPMs on the first mile of driving.
But after that I can just rev it until 2000-3000 and when I gif it a little bit of gas, it starts to bog and stumble..

When it does the above, after a mile or so, immediately kill fuel pump/engine and coast to side of road (safely). Remove air filters and watch down throats of carbs and open linkage. See if accelerator pumps are injecting fuel or not. If not, your float bowls are empty or fuel level is (really) low. If the fuel levels go low, the engine will run on idle circuit, but fuel level in emulsion tube wells will be too low to begin emitting fuel/air mix at duct in auxiliary venturies. If this is the case, you have an issue with needle valve, float or both.

Check it out and let us know.

Jim

[andrewlandon67]

I definitely agree with Jim on this. Accelerator pumps should definitely be checked. If they're not working, if they're not working, and it's not what Jim specified, then make sure the diaphragms are intact and the pumps are adjusted properly.

[Eddie DVK]

Ok thanks for all the Replies.

I did check all the sparkplug wires... one by one, but haven t tested the coil yet. will test that also.

I think I still have the filterscreen in my fuel tank outlet. Will have a look at that.

I am testing it step by step, so all the fuel suggestions I will try those after the ignition testing.

Will keep you posted.

Regards Edgar

[Jim Ratto]

I don't think the accelerator pumps are the cause of this issue, I'm just suggesting you can use their function, pretty easily, to see if your fuel levels are too low. The car will run on the idle circuit, it sounds like to me, but once you get to 3K or so, it falls flat... right? Sounds like main circuit is failing to come in. Main jets don't plug (usually) so I would suspect something is keeping your fuel level too low in bowls.

Jim

[HERB]

Any updates on your engine issue?

[Eddie DVK]

Ok I think I found the problem...

I am a little embarrassed to say but, checked all the sparkcables but didn t check the cable from distributor to coil  ,
because I didn t had a spare for that... Tried an old one.. and the problem was gone.

So bought a new set of cables... ditched the silicone ones... they seem to brake faster for some reason.. not the first set...
Haven t attached the new cables yet, but as soon as I have i keep you guys noticed.

Thanks for the help...

Regards Edgar

[Martin S.]

hheh love it when I'm right!