mikekosatka

My Feedback: (7)

He guys,
I had to take the butterfly disk (throttle valve) off the throttle shaft to slide the shaft out of the carb, (part way not completely out) so that I could put a connecter on for the cable. Any way, did that and screwed the disk/butterfly back on, BUT the carb doesn't want to idle, even with the idle stop screw completely removed. My question is , Does the orintation of the disk matter? there a few stampings on it but I could not discern any up/ down, etc. differences. At 3800 rpm, the plane would never land while running!!!
Mike
Part numbers 14 and 13 on drawing,

JoeAirPort

My Feedback: (41)

Yes the disk notch should match up with the jet on the carb. I kept track of the orientation when I took mine off. If that disk is not on just right the disk won't fit in the carb right and the throttle won't close completely.

mikekosatka

My Feedback: (7)

Thanks Joe
Mike

pe reivers

The disk has a bevel, and should be fitted the right way so the bevel face can snug up to the bore. It takes some light fiddling with the setup to get it snug before you tighten the screw.
When fitted the right way, the disk cutout will be located where the idle jets are.

mikekosatka

My Feedback: (7)

One of the best things about RCU is the community. Some of you guys have helped a lot of us out over and over again. I know I appriciate it.
THANKS
Miike

Bob Pastorello

My Feedback: (198)

You are sure right!

But neither Pe nor Joe mentioned the HORRORS of that swaged screw fatiguing the shaft through removal and reinstallation.... ON SOME WALBROS this is a death sentence. There are threads to be found where adjusting that plate by removal of the screw has resulted in the purchase of a new engine (or at least the payment for an extensively-repaired and internally-severely-damaged USED engine).

Some of the Walbro shafts don't have enough meat to tolerate that screw coming and going, particularly if the threads exposed on the initial install were swaged like most of them are. Removing that screw strips out a LOT of the meat of the shaft hole and weakens it severely, which also forces one to rely overly-much on the holding strength of retaining compound or Loctite.

I know I'll take some shots for bringing this up, as it sounds like you have a good solution to re-adjusting that plate. But in all good conscience, I couldn't read of your repair without telling the tale of the ingested carb-butterfly-screw.

NO criticism to either Pe or JoeAP, they both know a lot, and are good guys..... sometimes I just have to be "Chicken Little"....

pe reivers

Bob,
Are you suggesting to use new parts whenever you disassemble the throttle butterfly?
Too much torque also will kill the new parts, because the construction is delicate whichever way you look at it, swaged screw or new.
I always wipe the thread with locktite before fitting it, and apply just enough torque to make it stick. Too much locktite would also cause heaps of problems, and the cure might well be worse than the desease.[&o]

Bob Pastorello

My Feedback: (198)

I have limited experience with doing this, but the ONE failure of the screw to remain tight did it for me. My understanding is that not all screws are swaged behind that shaft where the threads are protruding, but I could be incorrect. I've been told that ALL of those that are held by screws in brass shafts ARE swaged.

So yes, I would recommend a new shaft and screw, for sure.

pe reivers

So far, all carbs I worked on had swaged screws. Surely something to consider, and check well.
I always have been able to use the old shafts with good results. Guess I have been lucky.

Bob Pastorello

My Feedback: (198)

Pe - you are too skilled and knowledgeable for your success to be luck. I'd be more inclined to think that *my* disaster was due to my own fumble-thumbs, but it is still an area to be sure about, cross-check, and verify.

That .02 brass screw can end up costing a bloody fortune.

Big_Bird

My Feedback: (1)

Bob, I 100% agree with you. If you need to take the screw out of the shaft out then have a new shaft ready to put back in with a new screw. Then use red Loctite. Be sure the disk is seated properly before the Loctite sets up. My experience is that all Walbro carburetors have a swagged screw. What I've found is when the screw is removed the swag will often cause the shaft to crack through the thin threaded area. This may not be readily apparent unless you use a magnifying glass and a bright light. At a minimum you will severely weaken the shaft due to brass removal. When your engine is running and it ingests the screw it is the kiss of death for the engine. Been there done that. Same goes for the choke shaft screw.

pe reivers

The Tillotson carbs are better in this respect. They use smaller gauge screws in a steel shaft. I do agree, that the Walbro is critical.

Truckracer

My Feedback: (19)

The amount of swaging on the throttle plate screws on the Walbro carbs seems to vary quite a bit from carb to carb. Some easily tolerate removal and reuse of all parts where others have the screw thread end swaged so much that it will indeed destroy the shaft when removed. You just have to use good judgement whether the parts are OK for reuse. I have also seen guys push so hard on their screwdriver that they bend the shaft where the screw goes through and any bending will fracture the shaft making it prone to failure at a later date. Again, a component inspection and good judgement is in order to determine whether the parts are reusable. A blanket statement that parts are not reusable is just not in order here.

Bob Pastorello

My Feedback: (198)

TR - I think it's an "opinion" thing. To me, the unknown risk of invisible stress damage warranted my statement of "replace the parts". Like many things in our game, this is another one of "measured risk" (or in this case, "unknown risk").

A good inspection and evaluation is always a good idea. Some may actually know what to look for...

Rcpilot

My Feedback: (78)

It's easy to check and see if you have a swadge screw. On the opposite end of the throttle arm is usually the little stop part that hits the idle adjustment screw (most of us just remove this screw). There is a little metal plate that moves back and forth on the shaft. It is usually secured with a small screw. Just take that screw out and now you can rotate the throttle shaft all the way around. Now you can inspect the screw to see if it's been flared out on the end.

If it's flared out, Just hit the end of it with the dremel and a cutting wheel. Slice/grind the end of the screw off. Now blast the area with carb-n-choke cleaner to remove metal dust. The screw should back out without destroying the soft threads in the brass shaft..

When you put it back together, use red loctite. Clean all the threads in the shaft AND on the new screw with a toothbrush and some more carb-n-choke cleaner. Get all the oil off. Loctite is worthless if the threads are covered with oil.

mikekosatka

My Feedback: (7)

I did as suggested ( align the cut-out on the disk with the 3 fuel holes (tiny!) and the carb idles down nicely... With the brand new Brillelli 26cc after 320z of gas thru it, it idles at 2300-2400. top RPM is about 7700-7900 RPM. BUT there is a significant miss present at all speeds. I have a optical kill switch in the circuit and the light blinks with every miss. I tried adjusting high and low speed screws per walbro instructions ( run 2 minutes untill warmed up, take up to top speed and adjust hi speed screw for top rpm, then cut throttle slowly untill it "4 strokes" and adjust low speed untill 4 stoke goes away then repeat slower and slower. No real difference. I understand missing can be a voltage thing, so I'm going to a) swap my batteries around to put my 5 cell in ignition, 4 cell for servos, if no result b) take kill switch out of circuit, c) buy a new race prepped big bore walbro off ebay?
My gas is fresh 89 octane and the oil is fresh mixed 40:1 per Brillelli.
THANKS for previous and (hopefully) future help.
Mike

pe reivers

yep, E-bay is the best source for quality stuff. Guys sell there because whatever they sell is so good they want to part with it.

Your ignition misses can be a lot of things. Check your wiring. One line may be broken, and make intermittent contact by engine vibrations. Also cells connectors have been know to fail, switches loose steady contackt etc.
If all is OK, the ignition may be at fault. Put it in very soft foam and use no tie-wraps, but rubber bands to keep it in place.

Big_Bird

My Feedback: (1)

The first thing that I would do is take that optical switch out of the circuit.

mikekosatka

My Feedback: (7)

Okay.
here's the latest on my miss in my 26cc Brillelli with walbro carb.
I isolated each piece starting by running the battery straight to ignition, no switch or anything... still misses, so I didn't worry about any of the other components. It occurs to me that I should have switched batterys also at that point, just incase its a battery short between cells or in the wiring... I'll try that Sunday. BUT THE GOOD NEWS IS that I maidened the Jerry's Big Boy thursday, and Dang that plane flys nicely. Even with a miss the engine runs reliably and I really think that this plane will be one of my favorites. If I can't get this miss gone ( Sunday all the gasser guys will be at the field, and I'll let them twist some screws) I will buy a S&S ignition. Maybe a new sparkplug first and switch from the 25:1 mix to 40:1, since it's pretty well broken in.
Mike

Big_Bird

My Feedback: (1)

The plug gap should be about 0.020". Seems to me that you might have a faulty ignition or sensor. Do you have a friend with the same ignition that you could borrow?

Tired Old Man

My Feedback: (1)

Uhhh, has anyone yet thought of calling Scott at Brillelli about the ignition? He's pretty good at taking care of stuff that might be broken.

mikekosatka

My Feedback: (7)

I did talk to Bill at CH Ignitions today ( he started the company about 25 years ago and seems like a great guy) and we talked about 20 minutes. He said most ignition problems are battery related, to try a loaded voltage check if possable. Because the miss is at all RPM levels, he suspects that it's a too advanced issue, but also suggested checking the gap between the magnet and the hall sensor, so I have several things to check. BTW, I pulled the plug and replaced it...it was black, not the pretty tan it should be, but running the 25:1 fuel to break it in is probably responsable. Anyway, put in a diamond tip Evolution plug and mixed up a fresh batch of fuel at 40:1 so tomorrow I'll see how it all works out.
I didn't bother Scott at Brillelli yet 'cause he is so busy I feel guilty taking up his time. But he is great with the service...can't praise those guys enough.
Mike

pe reivers

A black plug is not caused by oil content, but by a rich mixture or a cold plug. Reducing the oil will only worsen that condition, because the fuel viscosity will be reduced as well.
Running as much as 10% of oil can still produce a nice tan plug, though color may change due to type of gas and type of oil.

ljones5000

My Feedback: (2)

Off subject a bit but you mentioned the Evolution plug.. I went to buy a NGK, the auto parts didn't have them but the Evolution package indicated it would sub for what I wanted. I didn't buy it because no "R" in the name. Is the Evolution plug a resistor plug, anyone know?

pe reivers

If it is a garden type plug, with conical seat and 14mm thread, it must be an R-type, or the ignitions of Evolution will act up in strange ways.
if it is the new 10mm plug for ICU ignitions that replaces the NGK CM6, it is a non-resistor plug.