Tech Talk: April 2026

Intermittent Hesitation

Jon, on a mildly built 1776cc engine running dual carbs, what is the most effective way to diagnose an intermittent hesitation that only appears under light throttle? How do ignition timing, progression circuit tuning, vacuum leaks, and fuel pressure interplay in this scenario, and what step-by-step approach would you recommend to isolate the root cause without simply swapping parts? Thank you.

— Mark Jensen — Portland, OR

Mark, you didn't say what kind of dual carbs you are running, but I'll try to help. The first thing to check would be the function of the pump jets. With the engine off, use a good flashlight and see if the pump jets are giving a good squirt when the throttle is actuated. If not, find out why and correct it.

If the problem is intermittent as you say it is, then timing or a vacuum leak probably aren't an issue. Of course, it won't hurt to check these though. Regardless of what kind of carbs you have, it's generally best to keep the fuel pressure under 3 pounds. See your Robert Bentley manual if you need to lower the pressure.

If for example the problem only happens on a freeway drive, then fuel volume may be too low. This is independent of fuel pressure, although they can be related. Remember that even though you are getting maximum fuel economy at freeway speeds, you are also using more gallons per hour than around town. Here again, there is a test for volume in the Bentley manual.

Lastly, you can learn a lot by just inspecting your spark plugs. If they are super clean and white, your fuel mixture may be too lean. If they are sooty, the mixture is rich, and this can cause a hesitation when you accelerate. The cure could be as simple as a new set of plugs.

Generator to Alternator

Hello Jon, I'm converting from a generator to an alternator on a 12-volt system. What wiring changes are absolutely critical to "get it right" the first time? How do differences in charging characteristics, regulator design, and grounding affect overall reliability? Also, what are the most common mistakes that lead to overcharging, warning light issues, or premature component failure? Any input would be greatly appreciated. Thank you.

— Luis Ramirez — San Antonio, TX

Luis, the wiring changes on a typical Bug are fairly simple. Locate the regulator under the rear seat. You'll see a blue or green small wire coming in from the front of the car's loom. This is the one that you'll connect to the alternator's small terminal. You can re-use one of the generator's wires for this purpose. Just connect them at the regulator. For the positive connection, you'll be combining the two heavy red wires at the regulator. Next, you'll run another heavy red wire from the alternator down to the positive starter lug. This connects to the battery so that the system can charge.

Even the cheapest alternators charge at 50 amps or so, compared to the generator's 30 amps; the battery charges much faster and things generally get brighter when the car is running.

I would say that for ultimate reliability and ease of service, the generator with regulator is your best bet. Why? Because they are easily serviced. If you have a regulator failure, it's right there under the rear seat. If the regulator (inside the alternator body) fails, you have no choice but to remove the alternator and get an entire replacement unit.

If you do go with an alternator, remember that the warning light on the dashboard (speedo) must be in working order. Since it connects to the regulator by that small wire, it needs a small voltage signal to tell the alternator to start charging. A burned-out bulb means no charging!

Deck Height

Hi Jon. When setting deck height and compression ratio on a performance air-cooled engine, how do you balance power, detonation resistance, and long-term reliability — especially when using today's lower-octane pump fuels? What role do combustion chamber design, camshaft selection, and ignition timing play in determining a safe yet responsive setup for street-driven applications? Thanks.

— Daniel Fischer — Munich, Germany

Daniel, most Type 1 VWs have a deck clearance of roughly .070" which yields a compression ratio of around 7-to-1. This can work with regular gas, but mid-grade gas is a safer bet.

Ignition timing is something that you won't want to reinvent, so stick with a distributor that has about 20 degrees or so built in. Time at 7 to 9 degrees idling, and 30 degrees when fully revved up.

There's nothing wrong with the VW's combustion chamber design, but it's important to have someone "cc" the chamber volume so that you can calculate your true compression ratio. If you don't have the tools, have a shop do that for you prior to the build.

Lastly, if you are using a stock camshaft, you have to be careful with the amount of compression you set up. Less overlap (i.e. stock cam) will tend to detonate more under harsh conditions. If you choose some kind of a "hot rod cam", you can sneak up on the compression ratio safely without detonation being a problem. The more overlap the cam has, the more pumping losses you will get at low engine speeds. This translates into less chance of detonation.

High-Temp Oil

Jon, for air-cooled engines experiencing high oil temperatures on freeway drives, what diagnostic steps should be taken before adding external oil coolers? How do factors such as engine tin completeness, ignition timing, fuel mixture, compression ratio, and fan shroud design influence cooling efficiency? And when is an auxiliary cooler truly necessary rather than a band-aid? Thank you!

— Oliver Hughes — Bristol, UK

Oliver, every single thing you mention in your message is important! The most important thing is probably having complete and good-fitting engine tin. Keep the timing under 30 degrees, the compression under 7-to-1, and use a genuine VW fan shroud and fan if available.

One of the more common causes of overheating is an object stuck in the cooling fan. This can be as small as a tiny leaf, or as large as a shop rag. Anything at all in the fan can cause loss of air flow.

We once had a car in the shop with chronic overheating. Dismantling the engine completely didn't show that the builder had done anything wrong. Upon reassembly of the engine tin, we noticed a small length of 10-gauge wire that had gotten stuck down in the crevice of the fan blades. Once removed, the car's overheating problems were solved!