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45cc Homelite needle valve 'covers' & adjustment

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Old 06-07-2005, 09:51 AM
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Deadeye
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Default 45cc Homelite needle valve 'covers' & adjustment

As some of you may know, I converted the new style (had to make a carb adapter) 45cc homey for a 80" Byron's CAP-21 some time ago. Before the maiden flight, the engine ran well, even if transition from idle to full was a little slow. After my botched landing on maiden (little damage, broke prop, bent my gear), the engine now runs crappy. Transitition is terrible, and full throttle chokes itself out after just a few seconds. I have twidilled with the needles till I'm blue in the face to no avail. The engine came from a chainsaw, and the needle valves has those little plastic 'limiter covers', for a lack of a better term. They only allow about a half a turn or less on both high and low. What I have figured is the high speed, is in the red cover, and is closest to the head. The idle needle, in the white cover, is farthest from the head. Is that right? Chainsaw instructions were not clear on this.

Can these 'limiters' be removed? Is it just a standard steel needle screw with spring under them? How does one remove them? What's a good starting point on adjustment for these at 3500 feet? Thanks guys!
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Old 06-07-2005, 10:27 AM
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Default RE: 45cc Homelite needle valve 'covers' & adjustment

Hi,
My Homey 33cc has a walbro carb. Some of the engines I am told come with Zama carbs. If the plastic won't pull steight out, you have to use x-acto knift and a pair of small wire cutters to remove the plastic. After it is removed, you will find two needles with no screw driver slot (Walbro). I took my moto tool with a cutting disk and cut a neat slot accross both of them. This allows me to adjust them normally. Male sure that all of your carb gaskets aren't leaking and everything is lined up properly. The pulse port if it goes through the manifold could be blocked. Good luck.

Dave
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Old 06-07-2005, 10:28 AM
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Default RE: 45cc Homelite needle valve 'covers' & adjustment

Hi,

You just pull those little plastic caps straight off. There is a standard adjustment screw under each one. If you look closely, there will be an "L" and a "H" embossed on the carb right above or below each needle. (For "High" and "Low") However, something obviously happened in the crash to change something. Either some dirt got in the carb, fuel line got pinched, or something. You need to find this problem first. Shake the plane and see if you hear your clunk tube in the fuel tank moving properly. It could have jammed itself forward, kinking the tubing in the tank, and/or blocking off the clunk against the tank.

The needles themselves shouldn't be very far from where the plastic limiters allowed them to be. If you have to move the needles a lot, look for another problem.

Good luck, and let us know what happpens,
AV8TOR
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Old 06-07-2005, 03:24 PM
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Default RE: 45cc Homelite needle valve 'covers' & adjustment

My first thoughts were a sheared or badly bent key.

I have nearly sheared them off on lawn mowers by striking something hidden in the grass. They actually had an offset in them.

It's an easy thing to check.
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Old 06-07-2005, 04:26 PM
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Default RE: 45cc Homelite needle valve 'covers' & adjustment

Yep, been there, done that too!

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Old 06-07-2005, 04:35 PM
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Default RE: 45cc Homelite needle valve 'covers' & adjustment


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ORIGINAL: Ralphbf

My first thoughts were a sheared or badly bent key.

I have nearly sheared them off on lawn mowers by striking something hidden in the grass. They actually had an offset in them.

It's an easy thing to check.
Key, eh? I never thought of that. It is possible since my prop did indeed strike the ground on my botched landing. I hope to hell it isn't, though, as this a cast in key.
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Old 06-07-2005, 04:43 PM
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Default RE: 45cc Homelite needle valve 'covers' & adjustment

Not to worry. I don't think this is your problem but if it is, just clean up the crankshaft and the flywheel really well, add a few drops of Loctite, line it up carefully, and bolt it together. It will work fine. The key doesn't really "hold" anything, it's just there to line you up conveniently. The taper on the crank/flywheel interface is what holds.

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Old 06-07-2005, 05:04 PM
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Default RE: 45cc Homelite needle valve 'covers' & adjustment

I peered behind the flywheel, and saw my key, It looks OK from that side, but it's at least a two beer job to get it all apart...possibly three . It will have to wait til I'm done with work for the day. Thanks for the reply.
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Old 06-08-2005, 09:19 AM
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Default RE: 45cc Homelite needle valve 'covers' & adjustment

Pulled the flywheel, key looks fine. I finally got the red and white needle caps off, and found the embossed 'L' on my Zama carb. Engine is running pretty good right now, idles good, throttles good up until about 80%, then it just kind of soggs out. A quick throttle back to 80% or so keeps it from dying, but I'm not getting my full RPMs. Tried leaning and richining the high end, to no avail. Some further tuning tips would be greatly appreciated by me. Do low and high need to be adjusted together on an engine like this? My only other experience with a gasser is a Quadra, and I've never had to adjust it. Thanks gents!
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Old 06-08-2005, 02:00 PM
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Default RE: 45cc Homelite needle valve 'covers' & adjustment

When you rev up the motor to the point where it starts to fade try choking it.

If it picks up it's a fuel problem, if not then it may be an ignition problem.
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Old 06-08-2005, 02:10 PM
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Default RE: 45cc Homelite needle valve 'covers' & adjustment

Hi, Here's a copy and past of a post I did yesterday for a fellow with a similar problem...

Look for any possible airleaks in the fuel system. These engines will not pump gas well with even a tiny air leak. I use safety wire to wrap and secure each connection. The ZAMA carbs are a copy of the Walbros and work fine in my experience as long as they have both the high and low speed adjustable needles. I would rebuild it and check the adjustment on the regulator arm.

Note: It is easy to get your needles all crossed up on these engines as one affects the other unlike most glow engines. You can get yourself into a position where the high needle is screwed in too far, and the idle out too far, and it will act just like yours. Start over with both needles screwed out 1 1/2 turns. Adjust the idle for a good transition to higher throttle, then do the high needle, then check the idle again, etc. Small changes....

Here's a site with a great download for instructions on adjusting these engines/carbs: http://www.bmeengine.com/html/manual.htm

Good luck, and let us know how it goes...
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Old 06-08-2005, 08:14 PM
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Default RE: 45cc Homelite needle valve 'covers' & adjustment

AV8tor might have given you a clue, with engine not running, check the throttle plate and watch to see if your servo is opening it to far past dead center,this would cause the condition you have if it is going past dead center .



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Old 06-08-2005, 11:45 PM
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Default RE: 45cc Homelite needle valve 'covers' & adjustment

Yes, and I have had this happen. The problem though, is that you need to check that with the engine running! When I had that problem, it was really perplexing. The throttle worked just fine on static tests, but it had just enough slop in the linkage that when the engine was running, the engine vacuum would pull the throttle plate past full open and start to close it a little bit. Took me a while to find that little problem...

Good thought.

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Old 06-09-2005, 12:17 AM
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Default RE: 45cc Homelite needle valve 'covers' & adjustment

So what you guys are saying, is that it is possible for the butterfly throttle opening to go past 90 degrees, and actually choke off the air as if it wasn't quite up to full throttle? Like a reverse action kind of thing? I will check for that and post back my results. It may take a day or two, as my calendar is filled up right now. I'm hoping to get some time this weekend.
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Old 06-09-2005, 08:38 PM
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Default RE: 45cc Homelite needle valve 'covers' & adjustment

Yes, exactly. Now this won't usually occur unless the carb has been modified. There is a stop, that both limits the butterfly to full throttle and no more, and also serves as the idle stop. But a lot of us cut this stop off, and use the transmitter trim to set the idle. That way you can just use full down trim to shut off the engine like most people do with glow engines. (Also there is less chance of the throttle binding at full throttle.) However, the down side to that is you need to check and set full throttle properly also, so that it can't go too far and actually start closing down the carb throat.

Good luck,
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Old 08-21-2005, 03:06 PM
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Default RE: 45cc Homelite needle valve 'covers' & adjustment

After 2 months of shelving this project, I'm back at it, tearing my hair out. Since both H and L needles have to be set totgether, and I've never done that, I ask you guys for help once again.

H and L needles both screwed in, then screwed out 1 1/2 turns. Engine fires up and idles great. As I advance throttle, it struggles, and half throttle it dies. If I cover the carb hole with my thumb, it spools right up. This indicates too much fuel, right? So then I tighten the H end? How much, and how much does the L need to be adjusted? Thanks guys, too windy to fly this afternoon, but would like to give this plane it's second only flight this evening.
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Old 08-21-2005, 04:18 PM
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Default RE: 45cc Homelite needle valve 'covers' & adjustment

Nope, covering the carb with your finger enrichens the mixture, indicating you're running lean, (without the finger). You need to open the needles.

You set the idle mixture rich enough that the engine doesn't stumble when you accelerate, then you set the high speed for just below peak rpms. Then check the idle mix again. You have to juggle back and forth like this until you get it right as one needle affects the other, unlike most glow engine carbs. Try starting with both your needles about two turns out, and go from there. The good news is, that once you get it set, you will probably never have to fool with it again, as these engines aren't finicky about needle settings once properly set up.

Good luck and hang in there, it's worth it.
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Old 08-22-2005, 09:25 PM
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Default RE: 45cc Homelite needle valve 'covers' & adjustment

Deadeye
Since the crash, have you noticed any fuel leakage from either the case or head gaskets? (Going thru the hair pulling on a 21cc Echo at present. Soft tidal flat, too many RPMs, and inexperience..
Had a few leaky gaskets so cut some out and replaced them all other than exhaust. Then still would not idle down without dying. Opened Walbro and found a mess in screen filter. Cleaned screen and flushed tank and installed another in-line filter (DuBro gas) between tank and engine; first is filtering tank fill line. Still would not idle. Friend observed last nite that I had enough flex in Sullivan Golden Rod throttle linkage that it took 3 clicks of trim to see movement at the carb. Added some supports to GRod, reduced expo setting and now each click is responsive at carb. (wished I had checked the expo PRIOR to the support addition)

a tip that works for me on adjusting. I file a small perimetrer notch midway 90 degrees from slot. This becomes my reference point for when I start adjusting. I use clock face notations (H @ 2:00 L @ 6:30 etc) I record the starting locations and and note CCW (Richen) CC (Lean) and new position. Run and record and repeat.
When finished I note the rpm both high and low. If I suspect a carb is not running right I can check the notebook and see if somehow the settings got moved.



av8tor1977
I have a similar high end problem. The last 15-20% or so of throttle advance to a full 90 degree butterfly, I get a RPM drop.
I noticed this prior to current idle problems but it is still present. I have a Walbro 167a, 11.1mm installed. What characteritics would a too large of carb venturi exhibit?
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Old 08-22-2005, 11:11 PM
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Default RE: 45cc Homelite needle valve 'covers' & adjustment

Well, too large a carb will do that, and an 11mm carb is a bit big for a 21cc. Try closing the choke a bit at full throttle and see if it picks up. If you're lean, it will. Then you will know to open the high speed needle a bit. If that doesn't help, try a 10mm carb.

Good luck,
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Old 08-27-2005, 06:30 PM
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Default RE: 45cc Homelite needle valve 'covers' & adjustment

2 turns out on both L and H seems to be the sweet spot for me. Just a hair leanier than 2 full turns on the H, and L is exactly two turns. It seems to be running great now, and this plane will get flight #2 tommorow. I'm flying all 11 of my airframes this weekend, it will be the last to go up tommorow evening or late afternoon. Thanks for the help, fellas. It is really appreciated.
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