New engine build stumbles, misses. Sometimes.

[BruceJ]

Hey all,

Have about 250 miles on my 40hp 1385 "Big Bore" engine. Seems to be running well most of the time -- smooth, good power, and cooling well (in spite of 90+ degree heat). But sometimes there is a stumbling/missing/misfire that is really annoying. Plus I want to figure out what's causing it -- it's trying to tell me something.

It doesn't do it all the time. Sometimes I'll run around town, errand type stuff, and it's great. Other times not so much.

Usually it does it under load, like when accelerating in second. But sometimes it does it just cruising at, say 45 or 50. Just a little "burp" then it's fine. Other times is continues for a while.

It might be getting slowly worse but am unsure about that. It might just be that the original "oh my God I can't believe I'm actually driving this thing after six freakin' years" is starting to wear off, and I'm better attuned to things. It is annoying, it ain't right, but doesn't seem to sap power or cause cooling issues.

Also, this usually happens when the engine is warm, but not exclusively.

Things I've tried / looked at.
- Bowl of carb (rebuilt Solex 28 PICT-1) had a little bit of sediment, so I drained it and cleaned it out. Needle valve is good, and the float floats.
- Took cap off top of rebuilt Pierburg pump. Screen was clear. I haven't done a pressure test on it, but using a glass container pressure looks okay when cranking the engine over
- Blue coil and leads are new, in that they have less than 500 miles on them, but have been sitting in a box for about 6 years. Will check for spark next chance I get.
- Spark plugs (NGK BR6HS) seem fine. Double-checked gap to .025". Just a little bit of black powdery deposit on rim and maybe the first thread, but all else clear.
- I checked the valve gap multiple times. Set at .006, with very little change.
- Points gap on rebuilt Bosch ZV/PAU 4R5 distributor at .016", and dwell checks good. No noticeable crack in the cap.
- Timing. Have varied between 7.5 and 10BTDC with no noticeable difference in anything. Shows about 30 degrees at full advance. No pinging either way.
- All new fuel lines exc in the tunnel, which was given carb cleaner and compressed air.
- OG tank was given the full POR-15 resto treatment.

Things I'm thinking I'll try next:
- Checking for intake leak (need more carb cleaner/starter fluid).
- Pulling in-line fuel filter (yes -- it's underneath, not upstairs with the engine).
- Fuel tank, as I said, was redone, but sat empty for quite some time. Wondering if condensation gathered in there, and this water is still getting kicked around in the system somewhere.

Wondering if anyone has else has any ideas, like an "oh, yeah, that same exact thing was happening to me" kind of thing.

Thanks

[grandpa pete]

Check intake leak. . There are several types of intake gaskets depending on your year. Are you shure you removed the old " crush washer " before you put in the new one ??...common mistake
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[wcfvw69]

If you can rule out a vacuum leak at the intake manifold and at the carb mount, I'd inspect your plug wires. Is anything arcing? Are all your electrical connections tight? How old is your coil? Are your plug wires laying on top of each other or anything else? I had similar symptoms one time and I wasn't sure if it was fuel/carb or electrical. While I was trouble shooting it, it got dark and I saw a fairly new Bosch plug wire arcing.

How does it idle? Any issues there? If you rev it up in the engine compartment, can you get it to do the same symptoms?
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[rockerarm]

Hi. Your description of your concern stated "under load". I have seen ignition components be the cause here. Can you swap out parts with a known good running car here, versus replacing parts needlessly? You can use a dvom to check the plug wire connectors and wires individually.
Fuel system related- good fuel flow to the pump and a clear filter?
When you do your next valve adjustment press down on the valve spring retainer to assure no springs are broken or very weak.
Just some basics to consider.
Bill.

[txoval]

Is it a single backfire? Or does the engine start running rough?

[OLD VW NUT]

I'm going to guess it may be carb icing or the main jet is too small for the increase in displacement. Without good carb heat you can get icing even in 90* weather. A motor running lean may not be overheating but it will at times 'lay over' - stumble then go on like everything is fine. Usually this will happen at part throttle while maintaining speed.
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[Dr OnHolliday]

Dump the resistor sparkplugs...
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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

[BruceJ]

Man, thanks all for some great ideas for things to check!

Won't be able to get back at it till Thursday, if then. But last night I did manage to go for spin to warm it up, and then park in a dark place and peer around in the engine compartment. It was nearly pitch-black but I couldn't see any visible arcing at all. It idles nice, revs fine and I don't think it's missing when I work the throttle by hand. Also, it has never backfired, and I wouldn't describe it as running "rough" -- it's a smooth a silk until --burp-- a few times and then smooth again for a while.

[Dr OnHolliday]

"R" in sparkplug designation (model #?) = resistor.
_________________
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

[BruceJ]

Okay, finally had some time to play around with this. So far, nothing has helped but at least I'm eliminating some things. What I've done/checked:

1. Changed out NGK BR6HS plugs with B5HS (non-resistor type).
2. Swapped coil and ignition wire set with known good ones.
3. Double-checked valve gap, also looking for loose or broken springs. Don't know that I'd be able to recognize a loose one or not, but all were impossible to move by hand so I'm gonna guess they're tight and therefore fine.
4. Swapped out the fuel filter (next to clutch lever) with new one, and also drained lines a little to check for water. Couldn't find any. Also, ran a new hard line from the firewall to the pump, fastened to left side of shroud, above the head, as per stock (?). (Didn't help any, but sure tidies things up a bit!).
5. Made sure all exhaust connections were tight.
6. Finally, sprayed generous amounts of ether starting fluid onto the intake manifold while the engine was running, focusing especially on the carb/manifold and manifold/head joints. No change in idle noted.

As I said, nothing worked. As a matter of fact, it seems like it's getting worse, to the point where I won't take the car anywhere until I fix this. Expanding a bit on the symptoms:

Seems to idle smooth, pulls in 1st okay, but can tell right off the bat accelerating through 2nd and 3rd. Cruising along in 3rd and 4th, spontaneously misfires and/or stumbles once or twice, say, every minute or so. Sometimes worse than others. Now seems to happen both first thing and when fully warmed up.

Another thing I've noticed: on rare occasions, especially rolling down hill and engine braking in 3rd, I'll hear a sharp --tink-- just once, maybe twice, and then it quits. Hesitant to call this a backfire, because there's no KAPOW!, just that little metallic sound. The first time I thought it was just road junk getting thrown into a fender, but now I'm not so sure. Has only done this a few times and is very hard to replicate. Not sure which side -- sounds like the left, but since that's where I'm sitting, who knows?

Not sure where to go from here. Swap out the distributor? Something with the distributor drive shaft? Double-triple check the fuel pump with an actual pressure gauge?

Could my grounding strap -- present, though cruddy -- be the culprit?

Also, am still mulling about the carb (28 PICT-1) jetting, but am a stranger to the dark art of carb jetting so am seeking ideas here. Going from an 1192 to a 1385, would this automatically mean I need a bigger main jet? Mine has a 122.5 -- what was stock?

This leads me to The Thing I Should Have Mentioned #1: The old engine, when I tore it down, I found to have the 83mm kit, i.e.., a 1385. And, now that I'm thinking about it, that engine had misfiring problems too. But with all the other problems the car had at the time (six years ago!) this was the least of my worries and I kinda sorta forgot about it. It was running the same carb I'm using now, with the same jetting -- but I've rebuilt it and had the throttle shaft rebushed by a pro.

Thing I Should Have Mentioned #2: The new build has a Scat C-25 camshaft. I know they say the camshaft should be the -last- thing one should mess with, but a trusted friend recommended this as a mild alternative, and has seen it work with the 1385 before. Camshaft specs are over my head; but, if this cam has slightly more overlap, should I definitely consider a bigger main jet?

And how does the fact that I'm now running a vacuum advance distributor, versus the old .009, come into play (i.e., now using the vacuum port on the carb)?

Not sure where to go from here . . .

[BruceJ]

Answering one of my own questions, but coming up with another.

I have a spare old and dusty 40-hp motor, mostly complete. Appears to be mostly stock, too, but hard to say what's inside.

It's equipped with a 28 PICT-1. I pulled the main jet and it's a 122.5. So, if this engine is indeed stock, then this is my answer, re, what was stock for that carb. This engine also has a different distributor than then one I'm running -- a small "biscuit" versus the larger one on my new engine. Can't find any numbers on it -- could be an aftermarket, but definitely not a .009-type.

One thing I noticed on this spare engine, though, is that both vacuum ports (the one at the carb and the one on the biscuit) have have the little brass restrictor in place, whereas my current engine has neither restrictor. What does this mean? Did the small-canister setups need the restrictors?

Grasping at straws here, and being a chronic insomniac I sometimes overthink things, but sometimes the obvious eludes.

[wcfvw69]

Reading your symptoms, it's either electrical or fuel in my mind. You've changed the coil, wires, plugs. You stated the points and condenser are good.

Have you looked up that distributor on OLDVOLKS.com to verify what the static timing should be? http://www.oldvolkshome.com/ovhignbo.htm

You didn't list the Bosch full number for that distributor. Is it the correct distributor match for that carb so you can rule out a vacuum signal issue between the two? You said it has a vacuum can. Is the can good? You've sucked on the hose with the distributor cap off and watched the advance plate move in the distributor? Have you held your tongue over it to insure the vacuum can will hold the vacuum?

My only other thoughts are you've got some crap in that carb in one of the circuits or possibly, under load, your fuel pump isn't producing enough fuel to keep the fuel bowl in the carb full. I had a fuel pump start to get weak and it's symptoms were I couldn't accelerate well at higher RPM ranges while driving it. I don't think it's the main jet. You're in the range for the jet size.
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Decades of VW and VW parts restoration experience.
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**Restored German Bosch distributors for sale or I can restore yours**
**Restored German Pierburg fuel pumps for sale or I can restore yours**
**Restored Porsche fuel pumps or I can restore yours**
**Restored Porsche distributors or I can restore yours**

[Cusser]

I'd start at the beginning. Check/clean plugs, adjust valves, check points gap and timing.

And make sure that the timing does advance to give you 30 degrees total advance at about 3500 rpm.
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1970 VW (owned since 1972) and 1971 VW Convertible (owned since 1976), second owner of each. The '71 now has the 1835 engine, swapped from the '70. Second owner of each. 1988 Mazda B2200 truck, 1998 Frontier, 2014 Yukon, 2004 Frontier King Cab. All manual transmission except for the Yukon. http://www.thesamba.com/vw/forum/album_page.php?pic_id=335294 http://www.thesamba.com/vw/forum/album_page.php?pic_id=335297

[BruceJ]

Thanks Bill and Cusser for keeping me focused here. Lying awake at night thinking of worst-case, apocalyptic scenarios is not productive. Gotta keep from wandering further afield . . .

Yes I have visited the OldVolks site. My car's a '65 but the case is from '63, with late 40-hp heads (the good ones). Either way, the ZV/PAU 4R5 is either listed as stock or "can use". However, looking closer I did notice that the vacuum cannister is one number different, with different pressure requirements. The can on my spare motor is definitely smaller. Will try to get a closer look at the numbers.

First I'm going to triple-check the timing to make sure it's good -- and yes, I'll triple-check that vacuum. Even if it's fine though, I may swap it out for my old/spare .009. Not as a permanenant choice, but just to see what happens.

If that doesn't work I'll go over the carb again, then the fuel pump. I'm also thinking ignition or fuel, but it's good to hear from you more experienced guys that you're thinking the same thing.

Thanks, and will report back!

The

[Cusser]

Yeah, does not seem to be "internal engine" at all, unless the valve clearances are out of whack.

Remember: 0.006 inches when cold, each one checked/adjusted when THAT piston is on ITS TDC !!!
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1970 VW (owned since 1972) and 1971 VW Convertible (owned since 1976), second owner of each. The '71 now has the 1835 engine, swapped from the '70. Second owner of each. 1988 Mazda B2200 truck, 1998 Frontier, 2014 Yukon, 2004 Frontier King Cab. All manual transmission except for the Yukon. http://www.thesamba.com/vw/forum/album_page.php?pic_id=335294 http://www.thesamba.com/vw/forum/album_page.php?pic_id=335297

[Dr OnHolliday]

Go over the 009 with a fine tooth comb, and then install it. Good 009s run just fine...
_________________
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

[BruceJ]

After a month of Thursdays I think I've found the issue.

Does this look normal?

Doesn't look scorched or anything, almost like it's meant to be there. Or missing something?

Anyhow, I proceeded with my original plan, to put the old .009 in just to see what would happen. Cleaned it up, set the points, plugged the vac port in the carb, started it up, timed it to "all in" (around 30 deg BTDC @3500), checked the dwell, and drove it for 35 miles and it ran like a dream!

So, either that hole isn't normal, or something else was up with the distributor. But at least while I mull this, I can drive it again! Actually, if it's gonna run this well I might just keep the old .009 in there. Doesn't look as nice as the other original type, but if it runs well and not hurting anything, why not?

Thanks for all of your help!

[OLD VW NUT]

Yep - bad points will make for a crappy running motor and make all those running issues you described. If it were my car I'd ashcan the points and put a Pertronix ignition system in place. You'll never have to adjust points/timing unless you disturb the dist.

[KTPhil]

Check that you don't have a fuel smell in your oil. Your pump might be iffy with a leaky diaphragm, and in that case it's diluting your oil with gas.

Maybe your fuel pump rod is occasionally hanging up on the phenolic block. Check that it slides freely.

Some replacement point sets have that hole in them. It's supposed to help with arcing or bounce or something. No harm in it.

I didn't like the 009 on my 1385. It gave good high-rpm power, but it felt "peaky" and I had to keep revs up all the time. I had to shift more and it fouled my gas mileage and was noisy. I found an original "big can" distributor and it was much happier with it.

I'd try a slightly larger main jet, too. I believe stock 28 PICT carbs used a 122.5 main with a 140z air correction. Try a 125 main, especially with your 009 distributor.

What carb are you running? Those without the power fuel jet can run lean at high load/high rpm.

[Maddward]

Looks to me like your contact on the stationary side of your points came off