New build, cylinders 3/4 not responding

[jason]

Only thing that worked for me was a smoke test. Have a friend that vapes blow down each throat. You’ll see it quick like.

[TonkaJim]

Update

Last night i tried the following:
- sprayed the intake manifold with carb cleaner at both the head and carb connection... no change in engine speed.
- swapped the 3/4 wires (although i knew the wiring was correct)... worse;
- pulled the rocker... all looks OK (except a potential issue with a push rod, see below)
- moved the fuel pressure gauge to the 3/4 side... pressure is same as 1/2

I forgot to bring home the thermal camera, so no temp measurements... going to try tonight.

Since popping and backfiring is a sign of running lean, I backed out the idle mixture screw to 3.5 turns which seemed to respond better to the throttle, but not as good as #3/4. But, when I tried to tune the carbs, there was no engine speed response to adjusting the mixture screws. Also, the 3/4 side was popping pretty loudly when I had the mixture rich... so bad i thought there might be some loose metal inside the valve cover.

So... any thoughts? I'm at a loss. It's not the carbs; it's not manifold leaks; it's not fuel supply; doesn't seem to be rockers/lifters; it's not compression...

I did find one unusual item, not sure if it's a big issue or not. The end of one of the pushrods looks like it's been pushed into the pushrod tube a little bit. It was for intake of #4. Here are some pics... some are a little blurry, but it still shows the deformation at the end.

BTW, the head is a 042 101 375 2 with some other casted and stamped marks... I think its a Mofoco 042 head, but not sure.

Thanks!

j
_________________
'72 Karmann Ghia stock Ravenna Green (1992 - 1999)
'72 Karmann Ghia modified Ravenna Green (2019-)

[Nitramrebrab72]

Oh dear it looks like it has come up solid against something. Probably the valve against the piston for some reason. What you could do with is a vacuum leak tester that's the only way to test if the valve is seating air tight.A compression tester will give an overall idea of things but will not necessarily pick up a slight leak. Are you sure it wasn't even slightly down on no. 4

[[email protected]]

[Nitramrebrab72]

I hope I am wrong and that the valve isn't damaged. Who rebuilt the engine? I noticed that the heads have been fitted with non original type washes. They should be the hardended type they are a bit larger hardened and a lot thicker. Those washers tend to bend and allow the nuts to sink over time. Nothing to do with your problem but just a mark of poor workmanship. A set only costz around 55 cents a piece.

[TonkaJim]

Thanks for all the suggestions. Yeah, push rod isn't good. I need to figure out what caused that.

Unfortunately, I don't know who re-built the engine... previous owner can't remember. Since they're JCS heads, it might be a JCS engine, but they've already told me that they don't have any records beyond year and a few months back.

I'll take a look at the valves/lifters again, but I'm thinking I need to pull the head. Can I do that with the engine in the car? Can I just remove the fan shroud, front & left tin, intake manifold and carb, exhaust, etc. or do I need to drop the engine?

Thanks,

j
_________________
'72 Karmann Ghia stock Ravenna Green (1992 - 1999)
'72 Karmann Ghia modified Ravenna Green (2019-)

[Nitramrebrab72]

Possibly the pushrod wasn't properly seated in the cam follower during the rebuild. And either damaged tightning up the cylinder head or by rotating the flywheel during the rebuild with it like that . The collision with the piston eventually seating it properly before the final valve adjustment
There also seems to be a lot of extra thread on the cylinder head studs and looking at the no 3+4 cylinders they seem to have one less cooling fin than the 1+2 but the photo is not clear enough to be sure. Its probably just an impression.

[TonkaJim]

Well, I answered my own question... no you can't completely remove a cylinder head w/o pulling the engine. Although, I was able to get about 3” of clearance between the head and cylinders to take some pics. What I found…
- #3 - piston head has black oily residue; same with intake valve
- #4 - piston head has some curved scratches on it; valves look ok.

Thoughts?

_________________
'72 Karmann Ghia stock Ravenna Green (1992 - 1999)
'72 Karmann Ghia modified Ravenna Green (2019-)

[69aircooled]

You've checked quite a bit here.
Have you verified that the ground strap on this car is in good shape?

[TonkaJim]

[Nitramrebrab72]

Those scratchs are weird, are they on the no. 4 and intake valve side? I tried replicating a valve contacting the piston and being able to make these marks and it is possible for the top moon 1/3 mark to be made and the side one as well but It depends on the valve angle.
I can't see any engine builder knowingly fitting pistons deeply scratched like that and the chances of fitting them without noticing would be like 1 in 100,000 and if it's on the side damaged pushrod side of no. 4 that's like making it a 1 in 800'000 so chances are the damaged occured after fitting the head.
If that is the case then I suspect an ever so slightly damaged valve edge.
I would strongly advise getting a vacuum test at a valve shop.
Here is pic of a valve vacuum tester they comes with different adapters suction pads and tha vacuum test can also be done from the intake/exhaust ports for testing complete engines.

[TonkaJim]

Thanks, I'll do the vacuum test this weekend and tell you how it goes...

One other item that I forgot to mention is that the gasket between the manifold and head was soaked with gas and fell apart when I took of the manifold. This is the second gasket that this has happened to... seems that gasoline is pooling in one of the intake ports.

My current hypothesis is that the #4 intake valve isn't opening due to the damaged pushrod which was damaged when the valve hit the piston. So, I'm also going to try to check the valve lift this weekend to see if this is true.

Thanks again for all the help!

j
_________________
'72 Karmann Ghia stock Ravenna Green (1992 - 1999)
'72 Karmann Ghia modified Ravenna Green (2019-)

[jason]

You had good compression. Check the fuel and fire. Either a vacuum leak or spark issue. The pushrod was probably when they put the ends in, hit too hard.

[Nitramrebrab72]

[nsracing]

If you have compression in all four cylinders, why pull the heads? This is not a mechanical issue at all.

It either fuel or electric. Did you check the wires? and plug connectors?

Was the exhaust pipes hot on all 4? or is the problem side 3/4 side ever got hot exhaust pipes.

You could have just ruled out the wires and they are firing the plugs then just check the fuel supply. Are the bowls full? When you did the synchronization, were all the throats all flowing the same w/ the linkage disconnected?

And why were you timing the engine when you have cylinders that are cold? Put in a timing say zero...let the motor run and warm up, make sure all cylinders are firing = HOT exhausts. Grab hold of the pipe w/ your bare hand and see if it sizzles. If your hand burns, then that cylinder is working.

I don't think you needed to dismantle the motor at all.

[Nitramrebrab72]

[nsracing]

If you have compression then the valves and seats are intact.

The pushrod may be from a lousy installation of tip. Looks like someone just clobbered the tip on there. You get this when you use a hacksaw to cut the pushrod tube. It should be cut w/ some precision --lathe or equivalent.

Not sure what those marks are on the pistons. But if the rockers and pushrods disconnected while running you will get those. And obviously not enough that the valves did not hit at all.

I tell ya...these 'experts' come here and help out.

[busey]

[nsracing]

So the #3/#4 cylinders are cold even when wide-open throttle?

If you cleaned the mains, then set the idle past the idle circuits and draw from the mains. This should be 1200 RPM or so. Once the throttle plates are off the idle circuits, you will be drawing fuel from the mains. See if the pipes get hot. If they are HOT at that high idle speed then your problem is in the idle circuit. Clean/ check the idle jets. They could be having some tiny dirt or something in there.

When you have cleaned the idle jets, back down on the idle to say 900-1000 RPM and see if the pipes are still hot.

Isolate the carbs - unhook the linkage from one of the carbs. Work on the carb that has issue. If one side already got HOT pipes -leave that side alone and unhook it from the linkage. Figure out what is wrong w/ the COLD side.

make sure the wires/ plug ends are snug in there.

Try that and come back here and tell us what you find.

[TonkaJim]

Thanks everyone for your assistance...

This weekend, I pulled the engine and both heads. I didn't notice anything unusual... the tops of all the piston heads are unmarked (the "scratches" on #4 disappeared once I wiped away the crud) and no indication of damage to the valves. I also took a look a better look at "jammed" #4 intake push rod... well, it's the exact same length as all the others and appears to be structurally sound (the bulging is probably due to poor craftsmanship?).

A couple of items I noticed ...

- Cylinders did not appear to have any gasketing at the head. Is this normal? Manuals mentioned a "paper gasket" when reinstalling the heads. It looks like red gasket maker "good" was used at the block, but I didn't pull the cylinders to investigate.

- The dual carbs (EMPI 40 HPMX) are snug against the fan shroud... OK, more than snug... I had to hammer the fan shroud to allow the carbs to sit flush on the heads. I also had to do the same for the left air cleaner base so it would sit flush on the carb (right was snug, but I got it on). I don't know if this situation existed before or if it has to do with how I reinstalled the fan shroud. My bet is that it did (to some degree, I just didn't notice). So, are there smaller fan shrouds I can use, or do I need to live with the "field adjustments" I did?

So, I put it back together... and guess what? Issue fixed... sort of. Cylinders #3/4 are now responding to the throttle, but still have an excessive amount of popping and backfiring through the carburetors, on both sides now. I've confirmed the timing (5 deg ATDC @ idle), sync'd the carbs and adjusted the idle speed and mixture. Timing helps, but idle adjustments don't seem to do much.

OK, so, since the valve/piston/pushrod hypothesis didn't turn out to be the cause, I'm wondering if one of the issues has been air leakage at the manifold/head connection due to the fan shroud preventing proper carb/manifold installation. I did the carb cleaner spray test earlier with no reaction, but...

Another item regarding the carburetors... in order to get it to idle, I have to turn the idle speed screws in about 4 turns. Is this an indication of anything? All the instructions I've seen tell me to start at 1/4-1/2 turn in, but I can't hold an idle at this setting. Does this have to do with jetting?

Anyway... thanks in advance for any assistance! I'm thinking I might have to get some professional help (both for me and the Ghia) soon...
_________________
'72 Karmann Ghia stock Ravenna Green (1992 - 1999)
'72 Karmann Ghia modified Ravenna Green (2019-)