Duane,
Surprised you didn't run into Lee and his family back in 91-92 as he was around that area at that time. He later moved to Texas I believe shortly afterward. I'll have to dig up the mag and post some information. The mods on the sleeve came from Lee.
Here are the mod's from Jack:
Here's the article that goes with those drawings Mark. And thanks for posting those.
CALIFORNIA MOD
This modification for your K&B 3.5 is inexpensive and easy to do. It's for those of you who can't afford the expense of a tuned pipe and special carburetor. The "Cal Mod" is not only economical, it also greatly enhances your engines performance. All it takes is some much less expensive accessories and some bench work on your part.
This method of modifying the K&B 3.5 goes back to the late 70's, when it was introduced in NAMBA district 19. (Southern California in particular). A tuned pipe for an O.B. engine was unknown at the time, and the use of an inboard tuned pipe was out of the question. Too much overhang, that would throw off the balance was the popular belief. So we decided to enlarge the exhaust area in the lower unit to relieve the exhaust restriction. By doing this we eliminated the source for pressure to the fuel tank. So
now we had to find a new source. The obvious place was from the engine itself. After a couple of tries at different locations on the crankcase, we settled on drawing from one of the mounting lugs. This produced sufficient pressure for full throttle running, but was way too much at idle speeds causing the engine to easily over flood and quit. The carburetor was collecting too much fuel. The solution was to remove the carburetor, and install a K&B speed needle valve assembly. By removing the carburetor, the excess fuel that was flooding the engine could now spill out of the short venturi. To control the engine speed, we installed a slide throttle that at the time only K&B was manufacturing. Since then, there are only two sources for outboard slide throttle assemblies. They are available in kit form from: 1.) Prather products, Mod engine kit #8400 2.) 707 Specialties, kit # 3.5 ETA.
The "Cal Mod" increases top RPM by quite a margin. As an example, my best older style engine, (10mm crankshaft), bolted to a hydro, was tached at 23,000 RPM at the 1982 Namba Nationals. The time was 84.70 seconds. A national record on the NAMBA 9/10 mile, 5 lap oval course. With the introduction of the larger 13mm crankshaft by K&B, the speeds and times have been enhanced. The most recent record is 75.07 sec. by Mark Grimm of the Los Angeles area.
The "Cal Mod" is still preferred and very popular in Southern California to this day, and is widely used in the A (3.5) modified O.B. tunnel and hydro classes.
DIS-ASSEMBLY:
Dis-assemble the engine and lower unit completely. Remove the carburetor and set screws from the front plate, as well as the exhaust adapter from the crankcase. Moving to the lower unit, first remove the prop shaft assembly, remembering that it has a lefthanded thread. The pressure fitting is no longer of any use, remove it.
MODIFY THE LOWER UNIT:
Using a file, or a dremel type tool with a rotary cutter, remove the material that forms the four exhaust holes on the lower unit. Remove enough material from both halves to make the new exhaust outlet at least 7/32" wide. Sand smooth and polish the entire exhaust channel. The back edges of the new exhaust outlet may become ragged. Smooth them with a fine tooth file for esthetics. (Refer to the lower unit drawings.)
This next modification is strictly your option, but I recommend it for added performance. It involves removing area from the skeg, and it will take some careful cutting, shaping, and sharpening. Using a hack saw, band saw or Dremel, remove material from the front of the skeg starting at the top leading edge and leaving it 1/2" at the very bottom. Using a course file to start with, carefully, and equally, remove material from both sides of the skeg so the leading edge will not become off center. Smooth with a finer tooth file or course grit sand paper, finish sand with wet 320 or 400 grit wet or dry, leaving the leading edge fairly sharp and smooth. Comment: This modification reduces drag on the skeg adding to your engines performance
Wash both halves, re-assemble the lower unit completely and set aside.
CRANKCASE PRESSURE TAP:
A special 4-40 thread pressure fitting is included in the exhaust throttle kits available from the two manufacturers mentioned. Drilling and tapping on the crankcase is required to accept the pressure fitting. Hold the crankcase in a small vice and drill a # 43 hole in the center of the left engine mounting lug. This is definitely the most difficult part of the Cal modification. Be extremely careful here, the lug is fairly narrow and the hole must be absolutely centered. If you are not confident that you can do it, I suggest that you get some help. After the hole is drilled, counter sink it fairly deep. This will allow the pressure fitting to seat completely. Thread the hole with a 4-40 Tap.
Caution! When installing, do not over tighten the pressure fitting, it may break off.
To remove aluminum chips, wash the crankcase in hot soapy water, and dry.
Re-assemble the engine completely and before joining it to the lower unit, install the slide throttle on the crankcase and the needle valve assembly to the front plate. A good needle valve setting to start with is about 3 1/2 turns open.
Good Luck and good racing
