Only half engine fires at idle (3 and 4) - Air inleakage ?

[el_fela]

Hi all,

my engine was rebuilt, I put together the long block (pistons, cylinders and heads). It works and it has only 50 miles.

The thing is that when idling, if I pull 1 and/or 2 spark plugs there is little or no change on rpm. If I pull 3 or 4 it dies. I hear some misfires, but overall 1 and 2 don't fire. But, if I open the bypass screw on the carb introducing more air, at some point 1 and 2 start firing, but then the idle is too fast by far.

The car runs great at higher RPM's, and I think overall runs pretty good, but I can tell there are misfires at low-mid RPM's.

I cheked/adjusted valves like 3 times, .004 or maybe .005 on all valves.

I've checked and changed all spark plugs and wires, dizzy parts (points, rotor, cap), etc.

Engine compression is not even, don't know why:

#3 - 110 #1 - 110
#4 - 130 #2 - 100

So I guess air inleakage, maybe related to a burnt valve/valve seat on #2, cause I don't see a problem where the manifold meets with the head. Beware, I'm not a mechanic; before I had my bug I knew nothing about cars, and I learned mostly on the internet and on thesamba.com.

I wanted to ask you guys, what could be wrong? How can I tell? Why do #1 and #2 fire when the bypass screw is opened? If there is an air inleakage, it should be on #1 and #2 side/head, right??

I really don't want to drop the engine without knowing what's going on. Any help will be ratly appreciated! I can't find the cause, it's driving me nuts and I'm worried I might break something.

Peace,

Felipe

[MacLeod Willy]

I doubt if its a burned valve at so little mileage. Sounds like it could be a vac leak at the intake and head. Propane can find the leak if you run it through a rubber hose and direct it around any fitting. The rpm jumps immediately, could be the problem.
I would also double check the points and for wear on the breaker plate.
The compression is at the widest range I would feel comfortable with, 20%. Better recheck that again.

[KTPhil]

Is it a dual port? If so, how is the rubber coupler between the runners and the center section of the intake manifold?

[el_fela]

I don't think I'll be able to get a propane torch. Anything else I could use? Nobody knows what "starter fluid" is in my country.

The engine is stock, so only 1 solex 28 pci carb. Dizzy is brasilian SVDA. Will check points again.

Things that happened:

- exahust valve for cyl #2 seems made of a different material and was machined and adapted for this engine beacause it was for a diffrerent car.

- rocker arm stud broke and engine run some minutes without rocker arm.

Thank you all.

[Cusser]

[MacLeod Willy]

You can use a rubber hose IE: (garden hose) about 2 foot long or so. Listen very closely to each connection. You can shove a smaller piece of short hose in the far end to pinpoint closer

[Dr OnHolliday]

Aerosol starter fluid = ether
_________________
1965 Type 1 sunroof Baja / about 70k miles on self-rebuilt '74 1600 and counting / SP heads and aftermarket valve keepers / non-doghouse shroud with external cooler and filter / 1.5 qt extended sump / Weber 32/36 DFAV progressive carb / 009 dist with Pertronix / 1.25 ratio rockers and ball adjusters / 1.5" stainless steel J-pipes and carbon steel baja exhaust

[Dr OnHolliday]

Sounds like you need to pull the heads and examine them or have an experienced machine shop examine them. Since you have a somewhat makeshift valve, who knows what other makeshift conditions you have.
_________________
1965 Type 1 sunroof Baja / about 70k miles on self-rebuilt '74 1600 and counting / SP heads and aftermarket valve keepers / non-doghouse shroud with external cooler and filter / 1.5 qt extended sump / Weber 32/36 DFAV progressive carb / 009 dist with Pertronix / 1.25 ratio rockers and ball adjusters / 1.5" stainless steel J-pipes and carbon steel baja exhaust

[el_fela]

Thank you all for your help!

To check for leaks I used a butane can for camping stoves. It seems there is a little increase in RPM when I spray some parts of the admission tube, like if there was a puncture or something, but I'm not completely sure. I will check that and when I can I will probably drop the engine.

Another VW bug mistery: while checking the distributor once again, I used the old rotor I had instead of the new one, which is a generic part . Magic ! No more pinging noises, car accelerates much smoother. I can't believe it, and there is not much difference between the 2 rotors. The old one has a narrower tip. Ow well, I don't expect an answer, just a comment

I will update sometime!

Felipe

[grandpa pete]

[tb03830]

Sounds like you have an air leak on the manifold. I doubt it is the valves. rotors will cause this also. The rotor was probably the cause but I suspect you still have a leak if the idle changes when you put the propane on the manifolds.
_________________
"Sic Vic Pacem, Para bellum - Pray for peace, prepare for war."

1964 Convertible Bug - 1600cc SP engine with a stock H30/31 Carb and SVDA Distributor - Swing Arm Highway Flyer Tranny, Gene Berg's Temperature Dipstick, 2.5" drop spindles, 2" narrowed adjustable front end. Chromed OEM fan tower.

[el_fela]

Carb cleaner, good tip. It didn't feel right holding that can, much less spraying it. Children, don't do this at home !

Just for the record, I still need high idle for the car to idle on all 4 cyls.

[Abscate]