Colder plugs for 912 engine

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Steven Scott
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Colder plugs for 912 engine

#1 Post by Steven Scott »

Here in Las Vegas we are already experiencing 100 degree days. My 912 engine with new Weber 40 IDFs in a '51 coupe pops significantly at 55-70 mph after the heads get good and hot. Idles and accelerates fine, but at part throttle (intermediate metering) the gas is probably boiling in the bowls. The plan is to add two insulating blocks to the carb bases and pitch the metal bases that came with the Webers. I changed out the WR7BPs plugs for a set of WR5BCs that I had and felt like it made an improvement...to a point. The popping resumed, but not as soon as with the hotter plugs. My question is whether Bosch makes a colder plug than the WR5BC or (Platinum) and if anyone thinks there is value to going colder. I really can't take a road trip with this problem. Steve in Las Vegas

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Greg Bryan
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Re: Colder plugs for 912 engine

#2 Post by Greg Bryan »

Steve - I can't help but think there is something other than spark plug heat ranges going on with your car. I know there are a lot of 356s running around in the southwest . . .
Maybe some of the hot weather folks could share their setups.
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Re: Colder plugs for 912 engine

#3 Post by Kevin Wills »

What jets and e-tubes are you running?

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Steve Proctor
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Re: Colder plugs for 912 engine

#4 Post by Steve Proctor »

Yeah, I would say something else is going on. Here in Tucson and across the desert, I don't know anyone that doesn't run standard tuning specifications. I recall a convoy in 1998 across the desert to the San Diego WCH in 110* temperatures. All the cars were running hot and then we started the climb up over the mountain into CA. Guys complained that their temp gauges got up high in the range, but no adverse running situations due to the heat. One guy had an issue, but not related to the temp.

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Re: Colder plugs for 912 engine

#5 Post by Steven Scott »

Men: Thanks to all for considering my question about the fuel feed issues with my 912 engine. Kevin, the carbs are new Webers which are jetted for general use and had been operating just fine until this summer...I would need to research the factors. Like many questions that get posted, I probably haven't disclosed everything that could be factors to why this engine started acting up under intermediate metering. For now, I ordered up an electric fuel pump and accessories and new insulating carb-to-intake manifold gaskets. Now, at least, the gas will be routed to the carbs without going to the engine case first. I have a remote oil cooler and filter setup, so the oil temp hasn't been remarkable (185-200 degrees) at freeway/open road speeds, but that doesn't mean things aren't getting too hot in the engine compartment, which seems to be the obvious issue. I do have an a/c system, so there is a cooling grid under the factory opening, so I'm sucking air across the warm grid, but the lid is also louvered, for what that may be worth. The thing is, this phenom is new. It hasn't done this before and I have been on the road for two years...just not in as hot weather as this summer. I guess I'm answering my own questions here, just wondering what others would do about it. Does the use of lead substitute and octane booster cause gas to be more volatile? Thanks everyone. Steve

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C J Murray
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Re: Colder plugs for 912 engine

#6 Post by C J Murray »

Check your ignition timing. Retarded timing can cause overheating. If you run points then a worn rubbing block can cause the points to close and timing to retard.
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Martin Benade
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Re: Colder plugs for 912 engine

#7 Post by Martin Benade »

correct plug heat range generally involves being cold enough not to cause pre ignition and hot enough not to get dirty and fouled. Not pre igniting and not yet fouled, they all run about the same.
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Greg Scallon
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Re: Colder plugs for 912 engine

#8 Post by Greg Scallon »

And I would certainly suggest finding out what jets you're running in those Webers. I just installed a new pair of 48 IDFs on a VW 2332 I built and not only did I have to re-jet the carbs but I had to pull them completely apart to re-set the float levels and clean them prior to use. They were dirty and the floats were set way off from the factory.

I would suggest that you may be running lean in your mid-range. When temps get hot, you're carbs start popping.

Good luck with your investigation. These kinds of things can be frustrating when you're in the middle of them but more often than not they're rewarding once you've figured things out.

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Re: Colder plugs for 912 engine

#9 Post by Steven Scott »

Thx, again, Greg, Martin, and Cliff. I tried larger (25) main jets which, I think size 24 came in the Webers. Car ran badly with larger mains. This '51 is a restored (for street use) SCCA E-Production car last raced in the mid-'60's, so it came lowered, widened, dual mount late trans, brakes, louvered, 912 engine, late gauges, etc. Bringing an old racer back to street use is harder than one thinks since everything is either gone, substituted, cut off, drilled out, deleted, reinforced, or reshaped. I know I'm thwarting the air flow cooling with the a/c grid over the air inlet to the engine compartment. I thought the louvers would compensate. It has a fully electronic ignition system and no distributor, but we tried various timing settings to no avail. I've made the problem with the a/c, which was installed by an experienced 356 guy in Las Vegas. Most of the year this engine hardly gets up to 185 degrees. Martin, you are right, the plugs are hardly the issue (I'm from Cleveland, too). Greg, do you have a jet size in mind to address the mid-range leaness? I'll get the electric fuel pump in and report back. Thanks for your insight, guys. Steve

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Re: Colder plugs for 912 engine

#10 Post by C J Murray »

Hi Steven,

Weber idf 40s could have various sizes of venturis but 28mm and 32mm are common. Main jets usually fall into the 115-125 range. Air jets, 170-180 range. Idle jets in the 50-60 range. Emulsion tubes are controversial, F7, F11, or ???????

Idle jets control up until near 3000rpm. Mains are chosen by which one works best in the 3-4000 range. Air correction jets control 4000+rpm and WOT.

All jet testing should be done at steady throttle, NO MOVEMENT, in the rpm range that the jet controls.

Accel pumps are fine tuned after the jet sizes are finalized. Make them richer or leaner, evenly by number of turns, until response to throttle movement is best.

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Re: Colder plugs for 912 engine

#11 Post by Greg Scallon »

Steven.
I'm afraid that no, I don't have any specific jetting sizes in mind since I've never used Webers on a 356 engine. With Cliff on the thread though you have an excellent resource who does know a lot about the subject. I'm sure you'll figure out your problem. Good luck.

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Re: Colder plugs for 912 engine

#12 Post by Mike Horton »

If you don't have them, get a set of the thick phenolic heat barriers to go between the manifolds, and carburetors, this 10% ethanol fuel is far more volatile that anything in the past, and on shut down in your weather, the heat soaks will empty the float bowls fairly quickly. The 10% ethanol requires individual car/engine combo carb tuning...
Mike

Do a search for Weber carb jetting, there are many posts on that subject here, and study the tech articles which apply... have fun!
Mike

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Re: Colder plugs for 912 engine

#13 Post by Steven Scott »

Special "Thanks" to Mike Horton, Greg Bryan, Steve Proctor, CJ Murrey, Greg Scallon, and others who sent me advice on getting my 912 engine to run right in my '51 ex-SCCA coupe. I learned from each of your comments. I was going in the wrong direction with my poor running issues, for sure. Mike fwd me a number of carb tuning articles, of note was Tony Simeon's detailed publication about Webers which totally put me on the right track.
Many things were amiss by putting new Weber 40 IDFs on the car right out of the box!
Tony's article detailed setting the float levels which were way off (and probably 50% of my issues); changing to 32mm venturis; 0.04mm accel pump jets; 1.35 main jets; 0.50 idle jets; and much thicker heat barriers (from the old Solexs) DID THE TRICK!!!
I can't believe it is the same engine. Significantly more low-end torque, tractibility, and lots more smooth power thru the gears.
Thanks, Everyone! I hope to meet anyone who is coming to the WCH in Santa Fe. I will be showing at the Concours (Outlaw class), My car is the Pasha Red Pre-A #10971.
Steve Scott, Las Vegas, NV :D

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