ferdinand.

[No photos- and I have a digital camera. How lame.]

9/29/00

slowly dialing it in.

Ok, here's what happened in the last few weeks.

Bought the 70/1 slides. There is /5 accelerator pump ramp (for an explanation of ramp characteristics (see here) according to Mr. Herdan at Herdan's. Never had to use them, though, since I seemed to get somewhere with...
K16 needles (see here for a Dellorto needle chart). Here's the story. Even with the 60 pilot jets and needles at the leanest position, the colortunes were showing a very yellow (rich) mixturnd needles at the leanest position, the colortunes were showing a very yellow (rich) mixture, getting worse as the throttle opened up to about 1/4 open (can't go much higher than that with the colortune). The stocks taper from a 2.45 mm diameter to 1.5 over 39 mm. The K16 go from 2.5mm to 1.75 over 39mm, so they should be (and are) leaner over the whole range, and get leaner at a faster rate than the stock K4 (0.09 mm reduction in diameter per mm lift, vs. stock value of 0.12). Well, they ended up being a bit too lean, even after swapping in richer 70 pilot jets. It idles at around 1.25 turns out, but is quite sensitive (which I'm told is a possible sign of a too-large pilot jet- maybe need to drop to a 65- a side point). I've had to add a couple of washers to bring up the needles 2 mm. At 1.3 mm things were fine after the bike heated up but there was a real lag while cold- a classic sign of lean running.
I'm thinking this may work out. If I get a $25 windfall and want to blow it on more needles (to get away from the hack of using washers) I could go for K92 or K94, which go from 2.50 to 1.65. This slope is 0.11 mm diameter/mm lift, which is a bit leaner but much closer to the stock 0.12 mm/mm. But what the hell. How much can you obsess about this? (answer: lots.)

as in the carbs suck too much fuel. the carbs have been running rich and now that i've started my postdoc at e been running rich and now that i've started my postdoc at TMSI, i don't have much time. but i think i've narrowed it down.

well, fixed the head gasket leak on the left cylinder. turns out while i was screwing with the valve seat replacement i grunged up the mating surface. a little JB weld and some careful grinding brought the surface flat again, and with a new head gasket the leak is gone.

Here's how carb things went:

main jets- seem ok at 155. full power doesn't come on with "full throttle" until around 3500 RPM, which seems a bit late- but there are two factors to consider. (1) the cam is supposedly a 336, which produced peak torque at a slightly higher rpm (2) the throttle cam on this BMW doesn't completely open the slides (!) so I'm really not only testing the main jets. blew $10 on 170s (no 165s in stock) but "full" throttle ran much worse so I'm back to 155s. maybe i'll drop 'em down to 150s or so later..
pilot jets- put in the 70s, and got proper idle at 1.25 turns out. before i was out at 2.75 turns, almost near 3, past which is the zone of badness according to various Dellorto tuning guides i've seen out on the web. but then i borrowed bruce's colortune kit, and visualized a richness of epic proportions at anything above idle. dammit! even pulling the needles all the way out didn't eliminate rich condition. so i put the 60s back in (again, $8 go bye-bye/buy-buy), and 60s back in (again, $8 go bye-bye/buy-buy), and pull the mixture screws out to 2.75 or so.

So I'm going to try two things:

K3 needles.(cheap) Since the first 1/4 throttle opening doesn't really get you into the taper zone of the needles, one way to lean things out is to get needles with a bigger cross section at the top. K3 needles are the same as K4 (stock) needles, except the tops are 2.50 mm instead of 2.45 mm diameter. i could get a smaller needle jet, but then I'm afraid of screwing with main jet operation zone.
slide change. (expensive) yeah, costly, but all indications are that the cutaway is too low (60/5 now; 5 refers to accelerator pump slope, 60 means 6.0mm cutaway at intake side of slide). going to a bigger cutaway means lower velocity under slide at small throttle openings which means less vacuuum which means less fuel which means leaner. I figure go up to a 70/5, and if that's too lean in the 0+ to 1/4 range then i can compensate with richer needle position or pilot jets. If i didn't ride so much in this throttle zone i wouldn't bother.

8/28/00

fun with shop presses.

found out why there was a river leak on the left side cylinder base. it turns out the cast-iron barrel lining wasn't flat with the aluminum cylinder mating surface, and the raised lining lip prevented a proper seal.ng surface, and the raised lining lip prevented a proper seal. a chance to try out the fancy new 6 ton shop press from harbor freight. i figure i'll press the barrel lining down just a bit so that the case mating surface is flat. just lay a flat aluminum bar across the barrel lining and press down. i mean, cast iron is strong, right?
Answer: cast iron linings are brittle. verrry brittle.
so, i replaced the barrels with the nikasil/galnikal ones from the original '88 block. why the hesitation before? well, i had '78 pistons of the "B" size class (93.970 mm) matched to the "B" bore '78 cylinders (94.015 to 94.025 mm). the nikasil '88 barrels are "C" class, which is 94.025-94.035 mm. well, shit. in my desperation, i did the quick back-of-the-envelope worst case calculation. if my pistons were at their low end (say 93.960, worn to the "A" class size), and the bore was at the large end (94.035), that'd give a piston-to-cylinder clearance of (94.035 - 93.960)/2 ~ 0.039 mm, which is well within the maximum specified clearance of 0.080 mm. shee-it, what was i afraid of?

fun with carbs.

got jets from munroe, couldn't wait for darwin to order. (sorry, as a proud american i'm addicted to instant gratification). as suggested, stuck with stock R90S specs: main = 155, pilot = 60, k4 needle, 2.60 needle jet. plopped 'em in, running not much different than before. but now leaks are mostly gone, ent than before. but now leaks are mostly gone, so i can concentrate on tuning. (yeah, i know, i need to replace head gasket to be dead on, but i just wanna get ballpark).
need to go out tomorrow and do some 3/4 to full throttle tests to see if i'm running rich or lean, and then deal with pilot/idle jets. right now, engine runs better as mixture screw goes from 1 1/4 to 1 1/2 turns, and stays steady as i pull it out even further, past 1 3/4. it should bog down as i pull it out further as it gets richer. do i need a bigger pilot jet? it runs smoothly around 1 1/2 - 1 3/4, but maybe i need to step up a size to get that "further out bog down". how about an air leak? not sure, not symptoms of runnin lean. need to check carefully tomorrow. shouldn't be, assuming the "looking new" carbs are not leaky. but i guess we know what THAT assumption necessitates- yep, a carb rebuild. but they look so good, i just have to ignore that possibility for now. of course, all of the above data is to be interpreted oppositely if i'm mistaken, and the fuel mixture screw (richer as the screw is turned out) is really an air mixture screw (leaner as the screw is turned out). not sure which is the case for my PHM carbs. ain't life grand?
for now got the throttle cables "balanced" as close as possible by watching slide movement and syncing them. so neat to see little pumpers squeeze a jet of gas into the carb throat everytime i open the te carb throat everytime i open the throttle. ooo, those little pumpers.

fun with paint.

$6.00 paint job done. wait until i get the pictures. the faring, after mounted, is slightly askew, perfectly matching the deameanor of the mechanic-on-premises. no plans for straightening. (afraid of what the shop press will break next time.)

8/22/00

he's on his way. before i made it out to the west coast, here was the situation...

background.

Monolever swingarm and 33/11 ratio final drive from a very low mileage 1995 R100RT.
a cheap 1989 R100RS for a foundation. Pluses:
- Monolever rear end
- Nikasil-lined barrels
- K-bike style front end (i.e. brakes that actually work)
- stock post-'81 light flywheel assembly
- electronic ignition (maintenance-free)
- did I mention it was cheap?
- cam has timing that the factory sport 336 cam has
Minuses:
- low-compression pistons
- 32 mm heads, which means (1) 32 mm Bing CV carbs (2) 32 mm exhaust headers (3) smaller intake valves. adequate, but bigger throat diameter would be nice for top end
- egregiously offensive short exhaust pipes with a huge collector box, in poor condition no less
- bad bearings in final drive (lots of play)
- flimsy, flexible front fender (i preferral drive (lots of play)
- flimsy, flexible front fender (i preferred my '78 RS's fiberglass one)
- electronic ignition (can't be repaired on the road)
- wheels are pretty boring
remains of my poor 1978 R100RS
- high-compression pistons
- 40 mm heads, with big 44 mm intake valves. valves were refaced with a 45 degree angle at the Yale machine shop.
- nicer pipes, both in design and condition (yes, even after being burnt in the accident.
RS fairing and mount
40mm Dellorto PHM carbs. very sexy, reserved for the phoenix bike.

what I did.

Here's what I did with it all...

replaced valve guides. heated them up to 500 degrees in the oven, drove out the old valve guides, drive in new ones from CC products.
moved to berkeley.
(attempted to) replace intake valve seats. dremeled a groove into old ones, popped them out with minimal damage to seat area in head. heated them up again to replace intake valve seats. completely screwed up one by driving the seat in cockeyed. excoriate myself, make mental note to buy shop press so that I never am stuck hammering crap with a socket as a drift- particularly when the parts are at broiling temps. other one is more or less ok. send off screwed head to Terrill's aluminum head repair in chico, ca. in less than 48 hours, the seat area is cut out to accept an oversize valve seat (of better material than stock, i might add). looks great, much kudos to Jay at the shop.
cut three angle seat shape into seat with the Neeway valve cutters. try to set them as close to the bottom of the valve face as possible for maximum contact diameter. make nice wide (2mm) seat widths at 45 degrees- no interference cut. want maximum heat transfer, i'm looking for longevity and reliability. i figure improving my riding skills with make me go faster than a full on line-contact, infinite-face radiused valve seat grind.
assembled heads with new stock springs, old retainers, rocker arms from the '89 RS with end block mounts from the '78 RS rockers to match the pillows on the old 40 mm RS heads.
honed cast-iron lined barrels from my old RS. would've stuck with nikasil barrels from the '89 RS, but need to use old ones to match my...
... cleaned up, high-compresson pistons from the '78 RS. put new rings (with 4-part oil ring, also from CC products) on and put the whole deal back on rods.
slapped top end back on. set clearances. noticed that the rocker arm geometries were way off- the contact on the valve step moved around a bit during the opening and closing, particularly on the exhaust valves. probably because i cut thevalves. probably because i cut them too much, so the valves sunk a bit into the head. should radius them so that the rocker arm geometry is square and contacting the center-line of the valve steam at half-valve depression (to minimize valve stem contact wander, as suggested on many websites such as here). too eager to see if bike runs with the new carbs...
put on new (to me) 40 mm Dellorto PHMs. jets (main and pilot) are a bit small (145 and 50, respectively, instead of 155 and 60 as suggested by Peter at Darwin motors in S.F.), but should work. has own cables, need to do some fidgeting and dremelling to fit stock throttle assembly.
oh yeah, replace headlight relay with 30 amp auto one from Radio shack. jumper 87 and 87a pins to get it working.
installed minimal upper fairing so that turn signals could be mounted.

results.

pulled on chokes. battery freshly topped off with trickle charger. bruce over to witness the event. leave carb air filters off for now. fires up after a few engine rotations, roars to life. louder than stock, certainly. IT WORKS! now, just need to go to Munroe motors in S.F. to get carb jets (and maybe new main needles and needle jets, too). also need to buy something from darwin as ted to buy something from darwin as thanks for help.

to do.

set ignition timing.
get proper jets, install uni air filters, then balance carbs.
fix rocker geometry before guides and/or valves are prematurely worn. maybe fiddle with old RS ones?

Last updated 9/29/00