Day One - New Project

[Bullfrog]

With the pilot air passage cleared, what air screw setting worked out to be the best?
Ed

[hodakamax]

Hey Ed, kinda vague, but about two turns out.

Max

[Bullfrog]

OK. Yes there is a LOT of "feel" (actually "hear") to tuning the pilot air screw. But if you set your idle speed with the idle speed adjusting screw, then make a 1/4 turn adjustment on the pilot air screw then wait for something to happen (idle speed decrease or increase) . . . you'll slowly "dial in" on the pilot air screw setting which provides the best idle (probably the fastest idle) without changing the idle speed screw. That pilot air screw setting which ends up being the best (fastest) idle setting is your best setting. Just be sure to approach things in about 1/4 turn increments with a wait for the idle to stabilize.

Generally, if it "dials in" between one and two turns out, you've got the right pilot jet. More than two turns out indicates that a leaner pilot jet is needed (ie, you are "leaning out" a too rich jet with excessive pilot air). Less than one turn out indicates that a richer pilot jet is needed (ie, you are "richening up" a too lean jet by excessively choking off pilot air). Right now you seem to be on the ragged edge where a 20 might be better - but that sort of defies the logic(and actual history) that reeded engines require richer jetting than piston port . . . and since my trials bike is happiest with 25 or 30 pilot (with the same carb) . . . it would seem best to stick with the 25 for now.

And yup, the next step would be to go to the 2.0 slide, I'm pretty sure I have a "loaner" 2.0 slide if you need to borrow one for tuning (probably a 1.5 too) - but I'd need it (them) back once you get the tuning dialed in. Let me know.
Ed

[hodakamax]

Hey thanks Ed. I'll probably fiddle with it tomorrow and give you a report. I'll try your method of 1/4 turns and waiting for it to stabilize. That would be great on the loaners, see what you have, I appreciate it!

Max

[Bill2001]

Bullfrog-- my '72 Wombat 94 uses the long pilot jet, both the original and replacement carbs. And thanks for the write up on pilot-jet tuning. I have ben using the "find the sweet spot" 4-stroke method.

A big yep on crud in the passages/drillways. My original carb had so much corrosion from being left sitting with water that I decided to replace insted of fiddling around with it.

Carbs cn be a pain, but once clean and set up properly, they can be a joy.

[Bullfrog]

Hot diggity! A short tour thru the basement parts mine revealed an ore pocket which contained a selection of slides to fit the 24mm carb! So I could loan out any or all of the following slides: #1.0, #1.5, #2.0 and #2.5
Ed

[hodakamax]

Yay! I've got the 2.5, how about the 2.0, 1.5 and even the 1.0. I'll test and return! Thanks! Address coming on PM.

Max

[Bullfrog]

Awlright!
Ed
PS: I'll look to see if I might happen to have an ore pocket of pilot jets too.

[Bullfrog]

The pilot jets are hiding from me, but the slides were delivered to the Post Office just in time to make it on the mail truck heading out of town at noon. They should arrive in KS by Wed. or Thurs.

Have fun tuning!
Ed

[hodakamax]

Thanks Ed!, I'll keep you posted.

Max

[hodakamax]

Ah, Ed's goodies have arrived.

Strange how getting use to a totally new creation seems to follow Murphy's Law. What can go wrong, will go wrong. One of the quirks I discovered is if you leave it idling on concrete and go to get a screwdriver for needed adjustments, it will walk off the kick stand, fall and break the clutch lever. Stupid but funny. Anyway, back to tuning! (I thought the Gang would like that story somehow).

Maxie

[Bullfrog]

Show of hands - who thought, "Oh good, its not only me."?
Ed

[hodakamax]

Also funny Ed. Hmm, raining, project on hold.

Max

[matt glascock]

Hey Maxie and Ed, mine walk backward when I leave them idling on the stand. Is this the standard progression for unattended bike migration? I watched it walk off an uneven slab on my driveway as I was bringing up the portable air compressor, then the world went into slow motion as it fell over and took out a blinker lens and mirror. As this was in process, my brother cupped his mouth, threw his head back, and yelled "TIMMMMMMMMBERRRRRRR!!!". Helpful.

[hodakamax]

Quick report. A sampling of slides from 2.5 to 1.0 resulted in the problem unchanged. From idle to just before mid range the engine is flat and struggling. The main is a 210 and obviously rich. I've been as low as a 150 but it was starting to sound a bit crisp but still with the problem of near stalling coming off of idle unchanged. A quick twist off of idle can kill the engine. I've also been to all the clips on the needle with changes to mid range but with the same persistent off idle problem. Baffling. The idle air is still vague but seems to idle best at about 2 1/2 turns with the 25 pilot. There still might be a passage closed somewhere, off with the carb for the umpteenth time. Grrr.

Max

[viclioce]

Keep going Max! You'll get there! ; D Victor

[Bullfrog]

While you have the carb off to re-check, double, triple and four-ful checking all passages and jets . . . take a peek at the starter circuit plunger. It has "soft" (slightly compliant) bottom face to help assure that the plunger seals off the circuit when it is in the "OFF" position. Is that black compliant face in good shape? Is the plunger snug in the bore? A good method for at least testing whether or not the starter plunger/starter circuit is causing problems is to coat the plunger with heavy grease to assure that it is sealing -- then check to see whether the carb is behaving differently.

Something just seems not right still.
Ed

[hodakamax]

This pathway is suspect from the intake to the pilot jet. I have no access to the right angle to the pilot jet marked in red without removing the factory brass plug at the pilot jet. I can get the monofilament from the intake to the red mark. A small flow is noted but it's difficult to tell if it's enough. Hmm.
Report--Max

Just got your report Ed. I did check the starter circuit first and the plunger is snug in the bore but the rubber face is somewhat hard and shaped into the seat. Quite possible the the rubber is not sealing. Weird!

[hodakamax]

A closer inspection of the plunger reveals an edge on the rubber that's probably keeping it from sealing. Here's some pix. Click to enlarge.

Max

[Bullfrog]

IF (repeat, if) the pilot air screw actually has a noticeable effect when tuned - then the pilot air passage is probably OK. But it is a question since you report pilot air tuning is so vague.

I'd sure try a smear of heavy grease on the end of that plunger to assure a seal there, then try to re-tune the pilot air screw. Having to go to 2+ turns out with the #25 just doesn't match previous experience and suggests fuel is being supplied by something else when it is not supposed to be.

Ed

[hodakamax]

Resurfaced the rubber face on the plunger, applied heavy grease, back to 2.5 slide. Same symptoms. It still vaguely needs 2-2 1/2 turns on the air screw. It dies with the air screw all the way in. It does seem to have extra smoke as it clears the flat spot like it may be too rich on the initial opening of the throttle, good mid range hit once it gets going. I'm done for the day and will have to think more on this one. Probably time to try a carb. I found a new spigot 24mm carb but I can't find a spigot for it. We'll keep after it!

Max

PS--and Ed, thanks for your help so far. I appreciate it!

[Bullfrog]

Trying a different (especially a "known good") carb seems reasonable - cuz things just aren't making sense - and they aren't dialing in as expected.

Soooooo . . . while following that "makes no sense" sort of thought . . . is there any chance that #25 pilot jet might have been modified by some DPO? (Dreaded Previous Owner) What if it is actually a #50 now?

Ed

[hodakamax]

Hey Ed, in answer to your question about the pilot jet the #25 jet appears to be stock or at least smaller than the new #40. I'm back apart studying the situation. I think a friend of mine who lives about two hours from me has a NOS 24mm carb from a model 93 box engine. At least he's looking for it. Meanwhile I'll stare blankly at the carb body I have and hope it gets well. I think I'm going to check the passages just one more time for laughs though. Any other ideas besides the NOS carb?

Thanks!

Max

[viclioce]

Max. The Model 93 carb I have also calls for a 25 pilot jet stock. I had a 40 in my original & it was way too rich. It would start without engaging the choke but as it warmed up it would flood out the motor. Changing back to the 25 allowed me to start with the choke engaged and turn it off as it warmed up. I also was able to set the air screw a 1.75 turns for a good mix. This is just some informational notes. I hope yours able to work this out. Good luck

[hodakamax]

Hey Victor, Thanks for the info to help solve the puzzle. Just another challenge!

Max