She Be Lean

QI have an '84 Camaro with a 350 that has been bored and flat-decked. It has World Sportsman II 72cc heads, a Lunati Voodoo cam (PN 60101), Speed-Pro flat-top pistons, an Edelbrock Performer RPM intake, and a Holley 670 Street Avenger carb. The distributor is a stock HEI with vacuum advance out of a '77 Camaro. It runs great when the weather is warm, but as soon as it cools down to 55 degrees, it surges cruising down the road and falls on its face when accelerating, and I have to ride the clutch when I take off or it will die. I have considered fuel injection, but it is a little cost-prohibitive. Also, I'm going to install a Mallory Hyfire 6 EXL soon, but I don't know if that will help or not. Can you please give me some ideas on what I can do to give it better cold-weather driv-ability? I don't want my car to have to sit for six months every year. Thank you very much for any help. Mike Kennedy Via email

A What you have is a lean condition. When the ambient temperature is higher than 55 degrees, you have just enough fuel to satisfy the engine's fueling requirements. When the temp drops, the air density increases and you have more oxygen in the inlet air. This leads to the lean surge you're feeling, the bog when you try to accelerate, and the stumble on take-off while slipping the clutch. Going to a stronger, hotter ignition system can help fire a lean mixture. But it sounds like you need to increase your jetting.

First, make sure that when the carb was installed, the float level and idle feed screws were set properly. If the float level is low or the idle feeds are on the lean side, this would also give you lean stumble conditions. Check out Honey's online FAQs for the correct information on adjusting your Holley 4150 model carb. If the adjustments are correct, we'd increase the primary jet size by two. I would also increase the accelerator squirter from the factory 0.028 inch up to 0.031 inch. This will aid in the initial step on the throttle. With these two changes, you should be able to make it through the winter.

Also, if your calibration is this sen-

sitive, we bet it's too lean for max performance during the summer. Adjusting the jetting of a carburetor is a very subjective adjustment based on the experience of the tuner. The folks at Innovate Motorsports have brought us affordable wideband O2 sensors to help dramatically with any tuning. The LC-1 kit gives you the wideband O2, wiring, software (PC), and cabling to your PC to know for sure that you have the proper calibration. Also offered are dash-mounted gauges to give you convenient, real-time AFR. Check out Innovate's online forums to help the novice tuner dial in his car. SOURCES:,


QI'm building a '58 Chevy Apache frame-off resto. I want to step up to the plate by going green. Do you guys have any idea where I can get the kit/ equipment for CNG conversion for a Chevy short-block? I figure I might as well step into tomorrow and get cheaper fuel at the same time. Also, I'd be able to fill 'er up at home. Is it possible you guys could do an article on a small-block CNG conversion? What do you say? By the way, keep up the good work! James Walter Via email

ACGN is sure a hot topic these days. T. Boon Pickens is going on TV and telling everyone that we could be running on CNG today. That's the truth, but the likelihood of everyone doing it is another story. Also, outfitting older vehicles is a challenge compared with the late-model EFI vehicles. We dug around for a while and will list several websites where you can do some research. After you've looked into natural gas, you can decide if it's for you.

One of your comments is that you could fuel your truck at home. While this is technically true, the compressor to do this today is around $4,500. This price is just for the compressor, not any of the conversion components and the fuel storage tanks that are DOT-legal. These fuel tanks are made from composite material and hold the natural gas under a working pressure of 3,600 psi. A tank that would hold the equivalent of 10 gallons of gas is priced around $2,800. The conversion kits we found online were from all around the world. The prices varied, but they come in around $1,800 for EFI systems, higher for carbureted systems. There have been tremendous advancements in the EFI side of the conversion market. There are systems available that are OBD II compliant and can be installed on current-model-year vehicles and retain the factory warranty!

Check out the sites below for more information. If you would like to speak with someone in person, give Impco Technologies a call (714.656.1200). Impco has been the premier mixer and regulator manufacturer for propane conversions ever since propane came into favor. I worked with the company years ago on a CNG project in the Texas Panhandle, where Don Hardy Race Cars was outfitting irrigation pump engines to run on natural gas. CNG is being used all around the globe to fuel cars and industry. As for CHP doing a conversion story, it may be a little early in the learning curve. We'll have to wait and see. SOURCES:,,,,, technocarb. com,

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