Jetting a Type 1 Engine

by Eugene Palmer

Several messages recently have raised the concern in my mind that folks are not jetting their VW's to reflect changes made to the engines. Allow me to recommend some guidelines. My experience is limited to the upright and type 3 engines, but I've no doubt the same principles apply to the type 4 pancake.

Stone Cold Dead Stock, this means stock engine size, air cleaners, exhaust, compression, distributor, fuel, etc.

Hey, use the stock jet size, which is 125 for the 34 PICT-3. If it still seems hot, go to 127.5.

ANY SINGLE THING other than stock, Berg Semi-Hemi heads, 009 distributor, extractor exhaust, etc.

127.5-130 mains minimum

ANY TWO OR MORE THINGS other than stock,

135 mains

SUPER STOCK, Berg Semi-Hemi heads, 6.9:1 CR, dual carbs, paper or screen air cleaners, 009 distributor, Pertronix or other CDI ignition, single or dual extractor exhaust, ratio rockers. 140 mains minimum, I have these in my engine and, even without the ratio rockers, it's still not quite enough. I'm trying 142's and 147's soon (can't find 145's), I'll let you know. Also refer to the Hot-VW's article on the SCAT stock engine with dished pistons (lower CR) that recommends the same thing. They stopped at 140 but I think 145 is supported when the timing is advanced to take advantage of the lower CR. Hot-VW's didn't do that, or didn't talk about it.

LARGER ENGINES 1641-1776, Depending on the fuel delivery system and other components, but even with stock carbs and exhaust, please start at....... 150 mains and work up from there, if it's a super set-up with dual carbs and extractor, it will easily support 160, 165 or even 170 mains.

BIG ENGINES 1776-1980, I think you're getting the picture here, MORE FUEL, start at 160 mains, 170 if it's a super set-up.

Taller Soapbox here: I burnt up a 1776 engine on 130 mains and a round silver "pressure regulator"(read restricted) set at 2.5 PSI. I believe they were both responsible for the extreme exhaust temperature and resulting melted heat exchangers, burnt valves, cracked heads and scorched cylinders. I once returned a pair of Kadrons because they "wouldn't make power" on a large engine. They were simply not jetted high enough. I've read everything Berg ever published and I believe when he says he can lean out the mix on a lowered CR engine it's because his initial jetting was way higher than us backyard types ever imagined. When I tried the 130 mains (perfect right out of the box, guy on the phone said so) in the Weber dual 34 ICT's on my super stock 6.9:1 CR engine, it had nasty intake backfiring, the classic lean condition symptom. No amount of idle jet changes would help, only until I went to the 140's did it settle down. When I tried the stock carb on this engine it ran hot and was horribly lean. I couldn't seem to find larger Solex jets. The Dellorto manual says a "race ready" 1600cc engine is jetted 160 or higher, and that jetting is mostly related to venturi size. When I hear about 1641's with 110 or 120 mains that positively scream, I cring and imagine the exhaust valves red hot on their seats, and then the inevitable failure at 9435 miles.

I have an 02 sensor at the merge point of the exhaust and I'm finding that the mixture changes even with the level of fuel in the tank. When it's full, the mix is richer than when it's near empty. I also think the outside temperature causes changes, when it's summer and hot it's leaner than when it's cooler. The first ten minutes of driving are richer than later on, and I have the thermostat and flaps in operation. It seems ridiculous but if I really were serious I would change both the jets (richer) and spark plugs (colder) before heading out for the mountains from the city. Folks seem to think their fuel mileage will get better with leaner jets, I beg to differ, you weaken the engine when you do this and it loses it's efficiency, not being able to make the amount of power it could were it supplied with sufficient fuel. I believe there is also a small amount of evaporative cooling effect that helps keep engine temps down. Be very careful when relying on the spark plug color, unless it was taken out hot off the highway, you not likely to get an accurate color. I don't believe that the level of pollution out of a lean engine is less than that of a properly jetted engine.

The VW loves fuel and must have it to run cool and strong. Bergs jetting was a proprietary secret, and I think it's because he ran on the rich side of everything, though I don't believe even they are sending out carb kits rich enough for what people are putting together. Closely check your fuel lines, pump, and filter for weakiness and restrictions. If you've made ANY changes to your engine, check those jets, bump them up.

But, of course, don't believe anybody, think for yourself.

Regarding steering play, please check all related components before charging into adjusting the steering box itself. As mentioned in previous posts, the draglink ends. But also, all four tie-rod ends, the king pin bushings (the ones center of the front beam), the actual mounting bolts and frame around the steering box for looseness or cracking, the dampner, the rubber isolation ring above the box, and very importantly, the ball joints or in the case of splitties, the king pins and associated bushings out at the wheels. Also very importantly, the wheel bearings, and wheels and tires. The steering box comes last. I've had very little success adjusting the actual box, whenever I've tried, there inevitably ends up being a tight spot or bind somewhere in the travel, not good or worth it. Replace the lube if you want, but don't do anything drastic to the box, if it's bad, replace it.

Get your SO or buddy to crank the wheel back and forth and check everything for play. Replace anything icky, tie rods are fairly cheap. Look closely at the center king pin (also called a swing arm pivot I think), there should be no rocking, this is all in the Muir book. One thing not mentioned in the Muir book is that if you do replace the king pin bushings you need to REMOVE THE GREASE NIPPLE! Nothing like bashing endlessly up into the bushings only to find you've been gouging a huge notch in the old bushing as you beat it past the bit of grease nipple that protrudes inside the beam. Without that thing in the way they come out like butter. After you get all that done, have it aligned at a shop, measuring across the tires just isn't accurate enough.

On the subject of ongoing jet changes, I re-installed the 60 idle jets (1600cc weber 34 ICT blah blah) and lo & behold, the light throttle and off idle response has indeed returned to it's previous smooth response. The running mix seems better too for some unknown reason. I'm trying to stick to one change at a time so thats the way I'll post them. Besides, I'm too busy to fool with the car, I've the luxury of being able to ride my bike to work these days and parking sucks.

(1971 Westy with super-stock 1600cc type 1 engine, Weber 34 ICT dual carbs)

Since I spouted off about the charge mix I thought I'd do further testing, and see just how rich I could go without producing black smoke, backfires, and horrible fuel mileage. Though I tried to do just one change at a time I couldn't quite pull it off, this is a work in progress.

I changed the mains to 147 (from 140), and while I was inside I couldn't help but change the air to 160 (from 150), and the idle down to 52 (from 60 in an effort to keep backfire/sputtering to a minimum). The 02 meter got richer around town, but there was now a stumble just off idle and in the super light throttle range. I ran the timing ahead to about 18-20 BTDC (from 15) on the 009/Pertronix. The stumble diminished but did not disappear. On a warmed up highway run (<10 miles) with the new advanced timing the 02 had only a barely noticeable richer reading, but even doing 75-80 mph the oil temp wasn't moving past 180, midday, at about 75 degrees F air temp. I think it has a bit better high speed power. This was already a pretty cool running engine and previously would've only hit about 200 under the same conditions. Downhill deceleration sputtering did not seem to change, it still has a slight spit, so much for the 52 idles.

This exhaust is a dual "quiet pack" extractor with very tight flange type fittings that I brazed on where the stock heat exchanger tips meet the extractor. I use the 15mm type head nut for maximum flange coverage wherever I can get them to fit, on the rest I use the stock 13mm nut. It's likely an engine with the leaky stock clamps, or any other leak, would have a nasty backfire under the same conditions.

I now imagine many of the list members out there ripping into their carbs and I must say BE CAREFUL, fuel and sparks don't mix! Keep that fire extinguisher charged and nearby, and either dis-connect the battery and/or be darn sure there are no sparks, electrical or mechanical, around your open carbs. Raw fuel is a pollutant, stick it back in the carb or in your spare fuel can.

Due to the heavier exhaust smell, I no longer believe that the richer mix does not pollute any more than the leaner mix. My nose tells me it does, perhaps it's the price for keeping the VW running cool.

Please also make very sure there are no vacuum leaks in your intake system. When I took the carbs out the little covers over the distributor vacuum take-off were badly disintegrated and must've been leaking air. It's very easy to do an intake install and have a leak. An old problem I ran into was when I tried to put a single port manifold back on an engine that had the cylinders shimmed out for lower compression. The engine was .120" wider and that was enough to make the intake manifold fail to mate properly with the port on the heads. I eventually went to dual carbs to solve the problem. I've also had to replace the hoses and check valve for the power brake system to insure there were no leaks. I always keep a spare check valve. The balance tube and fittings should be closely checked and tightened, a lesson I learned when I couldn't get a pair of Dellorto FRD's to perform until I fully bottomed the hose clamps on the balance tube. The next time I took off, the engine jumped to life as all the carb circuits became engorged. Use an oil spray to find leaks, if the idle changes, you know you've found a leak.

Next steps are to replace the 60 idle jet and make sure the stumble goes away (it should). I'll try to have a bit of patience and run a couple tanks through to get a sense of the mileage before I try the 155 mains. If I can finally get a rich highway reading, I'll try a CD ignition and maybe even the 1.4:1 rockers to see if the engine can use the fuel. Though I long ago promised myself I wouldn't use the 1.4:1 rockers on these heads because they don't have heavy duty springs, maybe just for little while.

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