AF05E Malossi 47 mm BBK installed

[tlthehun]

Thank you for existence of this forum and Red Eft Performance for your roles in getting my 1988 SA50 Elite running again relatively quickly.

The engine dropped a piston pin circlip which embedded itself in the piston, collapsed the ring lands, broke both of the rings and cut a groove in the cylinder.

The oem cylinder is still listed at Honda but was backordered and the parts guy couldn't say whether it would ever be available so after a bunch of reading and conversations with myself, I ordered a Malossi 47mm (64.9 cc) BBK from Red Eft Performance. As others have stated, Keith rocks and I was surprised to find the BBK landing on my doorstep in California, two days after it was shipped out from the opposite coast.

I'll work on this post over the following days and weeks but I wanted to mention that the main jet supplied with the Malossi kit is visibly larger than the stock Keihin #88. The only thing that I had that was small enough to get some sort of measurement with was a spool of .032 inch (0.8128 mm) safety wire which was an easy "go" with the Malossi main jet but was a "no go" with the #88 Keihin.

Spending time jetting was my biggest concern with going with a BBK but considering a few things in retrospect, worrying that the main jet supplied by Malossi was going to be too small is the least of the potential problems. That Malossi can design, engineer, manufacture and market a two stroke cylinder and cylinder head (with Viton O-ring), bundle it with two sets of reeds (one fiberglass (two petal, not for my reed block) the other other carbon fiber (three petal to replace my oem metal reed)), all the required gaskets and well written instructions that include guidance on raising the needle and even specify the octane requirement but somehow then blow it on the main jet in a country where everybody owns a scooter seems very improbable.

There is so much more compression now that, without a battery, my battery charger that has a 50 amp "start" function was unable provide enough current to the starter to crank the engine over. Prior to the BBK, it handled it effortlessly.

Once I switched to the kickstarter and the caburetor was primed, she fired right up.

Edit 2012 06 04 22:51 PDT

I grabbed a caliper and measured the main jets using the pics above, finding 23.88 and 25.33 mm. The Malossi kit jet is about 6% larger ID than the #88 Keihin which calculates to about 12.4% more area.

Extrapolating from wheelman111's charts and info (http://www.hondaspree.net/phpBB3/viewto ... =8&t=12839) the #88 Keihin is about 0.033 inch. 106% of 0.033 inch is 0.035 inch and a #92.5 (marked 92 or 93 IIRC) Keihin.

Wheelman111 found that Keihin MJs are numbered close to their inside diameter in millimeters and I seem to remember arriving at the same conclusion a number of years ago when I was racing an NSR50. By that, 106% of a #88 would be a "#93.8" so at least a #92.5, again.

[LMH]

I got an AF05e with a malossi BBK on it for free because he didnt chamfer the bore, make sure you chamfer the ports or you will have the cylinder chip away at the ports, scar the piston and bore and ruin it. I wouldnt use the stock carb if possible either. At least use a 100 jet, that malossi jet isnt good to use, or bore it out.

[smokindon]

I got an AF05e with a malossi BBK on it for free because he didnt chamfer the bore, make sure you chamfer the ports or you will have the cylinder chip away at the ports, scar the piston and bore and ruin it. I wouldnt use the stock carb if possible either. At least use a 100 jet, that malossi jet isnt good to use, or bore it out.

What carb would you recommend running? My float sunk in the stock carb and I'm looking to upgrade.

I have the same setup but I'm running a 90 jet in the stock carb if that helps the OP. I didn't chamfer anything but it runs great.

Sent from my MB855 using Tapatalk 2

[tlthehun]

I have the same setup but I'm running a 90 jet in the stock carb if that helps the OP. I didn't chamfer anything but it runs great.

Thanks, someone here had already advised a 90 main jet with the stock airbox so I'm pretty comfortable with the Malossi mj as it is clearly larger than a #88 Keihin and if it is only one step larger it would be equivalent to a #90 and knowing that the #90 has worked for you is reassuring.

I know that there's a main jet chart somewhere on this forum, I'll check that later to take a guess at what size it is equivalent to.

[tlthehun]

I did have to slot my stock exhaust's mounting holes to work with the BBK. If I had drilled perfectly, then new holes would have been all that was required.

I first attached the pipe to the cylinder and decided on the ideal position, then marked with a punch what I guessed to be the center of the threaded holes in the engine, drilled with a 3/8" drill bit, filed as necessary to slot and bolted on with two washers, one about the same size as the bolts and another larger one to spread the load as well as cover the slots.

[tlthehun]

When I obtained the SA50, I transported it on its side in the back of my truck, which saturated the stock air filter with 2T oil. The air filter may or may not have been usable before that but by the time I got around to making the SA50 run, the air filter had disintegrated. With the stock top end, I ran around for awhile with the airbox and no air filter and also with a piece of foam stuffed in the airbox. It seemed to be stronger with the foam but it ran okay with the unfiltered airbox.

Now that I've actually spent money and time on the BBK, I found that the airbox's rubber airboot wasn't sealing properly or even adequately to the carburetor and I reasoned that I could fix two problems with one stone by ordering a clamp on air filter. Amazon.com continues to amaze (Amazen?) and $14.22 and two days later I now have a UNI UP-4112 1" ID foam air filter clamped into place. I tried heating the gray bodywork with a heat gun to create a bulge that would clear the air filter when the suspension compresses but that just thinned it out so I hurriedly cut out a piece of it with a combination of a heated utility knife and a hacksaw blade. I'll clean it up later.

I oiled the Uni filter with Uni filter oil. It's nowhere near saturated but I had in the past when I was racing an NSR50 used a Uni with no oil so I'm sure proper oiling is adding a bit of restriction and, more importantly, filtration for thousands of miles of street use.

With the BBK, stock airbox and no air filter I was getting a bit of lean surge at part throttle so before I rode with the Uni, I raised the needle beyond the bottom groove by adding two of the smallest washers that I could find in my garage, which amounted to raising the needle another 1.92 mm.

Today, I bought the smallest washers that I could find locally, which are #2 stainless steel measuring about 2.40 ID x 6.30 OD x 0.50T mm to replace the previous lockwashers that I had found.

A stack of four of the #2 washers measured to be about 2.41 mm and I used those to shim the needle. A quick ride around my house feels a little less powerful than the 1.92 mm shimming but I'm going to leave it alone until it's broken in and I switch from the current Chevron 91 : Valvoline 2T petroleum conventional oil (to seat the rings) @ 32:1 back to my usual 2T mix of Chevron (octane TBD, I'll probably start with 91, then try 89 and will hopefully be able to use 87 more so that I can share fuel than to save 20 cents a gallon) plus Redline Two Stroke Race synthetic. With race two strokes, I've been mixing at 30:1. With the SA50, chainsaw, blower and weedwacker, I've been at 50:1. I'm generally all for more oil but I'm aware of the potentially lean pilot circuit so more fuel and less oil sounds like a good idea for the SA50. Feedback will be appreciated!

pics:

[Ben L.]

Please keep us updated on your trial and error. I am preparing to do this swap in the very near future. It looks real nice so far! Thanks!

[tlthehun]

Malossi kit parts baggy contents: reeds, exhaust studs, main jet.

[tlthehun]

Malossi BBK cylinder head parts: cylinder head, O-ring, bolts, washers.

[tlthehun]

kit gaskets: cylinder base, stock head and exhaust

[tlthehun]

Survived durability testing yesterday evening.

I took the SA50 with me to work so that I could attend a nearby meeting without having to drive my 7000 pound work van. I unexpectedly spent 10-15 minutes climbing really steep residential streets. I tried to be as gentle as possible but near to full throttle was necessary at times.

I'd say the top end is broken in now!

Topped off tank that was maybe 1/4 full with Chevron 87 @ 50:1 with Redline so the current fuel is about 46:1 88 octane. It feels a little rich and didn't blow up today, either.

[tlthehun]

Survived severe durability testing today. Freeway was a mess so I rode the scooter on backroads to a meeting.

42.7 miles, much of it full throttle and uphill, highest speed according to GPS = 42.3 mph.

I took it easy on downhills and maybe 6 times cut the ignition with the throttle closed and over 35 mph indicated on the speedo for addtional cooling / less heat and also a number of times opened the throttle while ignition off for even more fuel to pass through unburned.

More stressful ride than I've been exposed to on two wheels with an engine as the posted speed limit 45-55 mph for most of my ride so I had to take to the paved shoulder a number of times and wave cars past. The SA50 will be sticking to around town use from now on.

Topped off fuel tank before and after, measuring 2180cc of fuel used to top off afterwards so 74.1 mpg if the odometer is accurate. Seems pretty good for how much time I spent at 3/4 to WOT.

Like I stated in an earlier post, I like more oil in my fuel so I will probably flip the whole scooter plus yard equipment 50:1 communal fuel and run everything on 32:1 with Redline Two Stroke Race synthetic 2T oil.

[Wheelman-111]

Greetings:

Sounds like yoou don't have a CHT Gauge yet.
Now might be a good time to check plug color.
If it's Brown, it'll Stick Around. If it's White, expect Explosions Bright.

[mmeadows]

hey man any update? was your motor fine with no breaking in? did you wire your oil pump open or get rid of it?

[tlthehun]

hey man any update? was your motor fine with no breaking in? did you wire your oil pump open or get rid of it?

It's running great. I did actually break the top end in some, heat cycles, gradually harder and harder use but I did use it harder than intended sooner than intended.

I removed the shaft from the oil pump and am using pre-mix as mentioned earlier in this thread.

I owe this thread some attention, I'll add more info soon.