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Tower .75 Carb fit--Help

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Old 09-02-2006, 08:27 PM
  #1
Bigshark
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Default Tower .75 Carb fit--Help

Based on the numerous positive threads here on RC Universe I decided on a Tower .75 engine as my first foray into glow powered flight. Everything looks and fits terrific except the carb. There is one o-ring at the bottom of the hole the carb fits into and one at the top that is attached to the carb. The carburetor will not fit completely into the hole. By forcing it down in the hole, while tightening the lock nut I can get it to seat fairly tightly. Is this normal? Should it slide in completely and not need pressure to stay on tightly?

Thanks,
Rich
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Old 09-02-2006, 08:39 PM
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Default RE: Tower .75 Carb fit--Help

Yiou should put pressure on it to compress the O-ring for a good seal. A quarter works pretty well to hold down on the carb while you tighten the draw bar. Many people also put some silicone or hi-temp gasket material on the o-ring to insure a goos seal.
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Old 09-03-2006, 12:23 AM
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Default RE: Tower .75 Carb fit--Help

The carb needs to be mashed down tight on the o-ring, or you can have
problems. I have used a small piece of plywood on the carb, and a small
clamp to hold it down tight untill I tightened the clamping screw.

FBD.
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Old 09-03-2006, 03:31 PM
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Default RE: Tower .75 Carb fit--Help

Wow this thing is louder than I thought it'd be. It ran beautifully! Attached the glow starter, hit the prop once, and bang. It scared the heck out of me. I stopped it by taking the glow starter off too early and then flooded it about three times before getting a feel for this beast. I didn't get all the way through the set up but it seems to idle nicely at low speed and the response to the throttle is nearly instant. My ears are still ringing.

Granted I REALLY flooded it the first time but should fuel be leaking from the front of the engine where the crankshaft exits the block? Also the first tank of fuel was run pretty rich and then leaned out according to the instructions. How long should a 24oz tank last at full throttle on this engine? This one lasted maybe five minutes once I got it started. Again granted there was a bit of a puddle on the floor of my shed due to the three times I flooded it.

Thanks again,
Rich
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Old 09-03-2006, 05:55 PM
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Default RE: Tower .75 Carb fit--Help

You should not run the engine inside a shed. The exhaust gases are not good for you. I know a couple of people who wear earplugs when they run in their engines.

If 24 ounces only lasted 5 minutes you are running soggy rich. Once broken in, and leaned for flight, a 14 ounce tank should give you over 10 minutes at full throttle.

Most glow engines seem to drip through the front bearing if they are full of fuel.
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Old 09-03-2006, 08:32 PM
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Default RE: Tower .75 Carb fit--Help

Even in the Tower web page photos, the carburettor is not properly seated... It is loose in the .61 too.

It is not pressed against the O-ring, but is several milimeters above it.

See photo.
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Old 09-05-2006, 09:49 AM
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Default RE: Tower .75 Carb fit--Help

Bigshark, in your original post you mentioned that there were two 0-rings on your carb. There should only be one where the carb fits up to the case. If there are indeed two rings, this would explain why you can't get it seated properly and would also account for all the flooding that you mentioned. My .75 gets about 12- 15 minutes on a 12 oz. tank depending on throttle control. Hope this helps.

Blue Skies, Green Lights
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Old 09-05-2006, 10:46 AM
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Default RE: Tower .75 Carb fit--Help

Your carb should press down on the o-ring. If it won't you might want to warm up the engine just a bit and make sure the carb base is smooth with fine sandpaper (make sure to rinse). You may want to use JB Weld on the muffler to keep it from vibrating loose and keep all the exhaust going out the end. The engine runs great when adjusted properly but if not you will complain as other do. A very good engine for the price.
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Old 09-05-2006, 10:57 AM
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Default RE: Tower .75 Carb fit--Help

On my .75 there is also and o-ring or seal at the bottom of the hole the carb fits into. I believe I have the carb mashed down far enough to compress both. Other than flooding it three times and running it probably richer than necessary (per the instructions) it ran great.

Next time I'll fill the 24oz tank completely, get the high end needle fully adjusted, and I'll check the run time.
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Old 09-05-2006, 11:04 AM
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Default RE: Tower .75 Carb fit--Help


Quote:
ORIGINAL: buzzingb

You may want to use JB Weld on the muffler to keep it from vibrating loose and keep all the exhaust going out the end. The engine runs great when adjusted properly but if not you will complain as other do. A very good engine for the price.

I took the advise of some others here at RCU and used High temp silicone RTV on the muffler mount and on the ported back part of the muffer. Naturally the one part of the muffler that was glued from the factory leaked like a sieve......
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Old 09-05-2006, 11:10 AM
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Default RE: Tower .75 Carb fit--Help


Quote:
ORIGINAL: carrellh

You should not run the engine inside a shed. The exhaust gases are not good for you. I know a couple of people who wear earplugs when they run in their engines.

If 24 ounces only lasted 5 minutes you are running soggy rich. Once broken in, and leaned for flight, a 14 ounce tank should give you over 10 minutes at full throttle.

Most glow engines seem to drip through the front bearing if they are full of fuel.

I hadn't actually planned on being in the shed while it was running But even with a the use of a few hefty compression clamps I was concerned that the test stand would go for a short flight.

My strongest electric, geared, sailplane motor is a freaking toy by comparison. A Kyosho Endoplasma geared 3.8 to 1 on 7 good sub-c cells will pull a two meter sailplane up at a 60-75 degree angle. This thing is freakishly powerful by comparison.
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Old 09-05-2006, 12:59 PM
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Default RE: Tower .75 Carb fit--Help

The silicon that I have tried didn't seem to stick very well and after a while it came off and seemed to soften up due to the fuel. It is better than nothing and will help. I have even used the JB on the muffler to engine joint with great success. It will part if you want to remove the muffler. I haven't had very good results with the JB repairing broken parts however. Some swear by this stuff, but not me. I use it only on limited applications.

The 75 will require some runin time so be patient and get the needles adjusted as needed. It will take about a gallon of in air running to get it set in.
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Old 10-07-2006, 04:19 PM
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Default RE: Tower .75 Carb fit--Help

More newbie questions (while my Tower . 75 is still on the test stand, as somewhere in the Czech Republic or China or who knows where someone is putting together my backordered Senior Telemaster ARF.)

I've run about a half gallon of 10% Omega (with a couple extra ounces of castor added) through my .75 and the beast runs beautifully at full throttle. One flip to start and off it goes. I've yet to play too much with the needles. The high speed is set to keep it rich enough to pass the pinch test throughout the use of a tank of fuel. It really does lean out a bit as the tank empties.

As far as the idle, it idles beautifully at what seems to be a fairly low speed. There is a pronounced stumble when going from idle to full throttle. Using a 24oz tank and playing with it the entire 25 or 30 minutes, I was unable to get the engine to stop but just stumble, even after an extended idle. Should I worry about fooling with the idle mixure and low speed needle or just leave well enough alone
? I'm pretty certain it's flyable as it is...
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Old 10-07-2006, 05:14 PM
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Default RE: Tower .75 Carb fit--Help

Leave it....it's a bit rich on the low end, but that's what you want at
first. You can fine tune it later, after you get more fuel through it.

FBD.
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Old 10-07-2006, 06:58 PM
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Default RE: Tower .75 Carb fit--Help

I've noticed that my TH .75 engines don't like to have the low end tweaked for about a gallon. Seams weird to me. It's an ABC engine. You'd think after 3 or 4 tanks it would be good to go. Every one of those engines that I've tried to lean the low end for perfect transition gave me fits. I finally learned on about the fourth engine to just lean them a bit for decent idle and rough transition and fly them for about a gallon or two before I finally tweak the low end perfect. After a gallon or two--lean it in and they idle and transition perfectly. [sm=spinnyeyes.gif]
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Old 10-07-2006, 10:08 PM
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Default RE: Tower .75 Carb fit--Help

Just a quick one to put my .02 in. I had trouble with my first TH 75 with not being able to shut it down with the trim at the end of the flight in my 4 * 60, using a 12/6 prop. Bax had me establish an idle at about 23-2400 and have a reliable transition, and after a good break in period it was easy to fly reliabily, and still idle slowly enough to land...and you know how a 4 * floats. It's going onto the Venture 60 I've been building for the past few months. Clint[&:]
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Old 10-08-2006, 08:24 AM
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Default RE: Tower .75 Carb fit--Help


Quote:
ORIGINAL: Bigshark

Granted I REALLY flooded it the first time but should fuel be leaking from the front of the engine where the crankshaft exits the block? Also the first tank of fuel was run pretty rich and then leaned out according to the instructions. How long should a 24oz tank last at full throttle on this engine? This one lasted maybe five minutes once I got it started. Again granted there was a bit of a puddle on the floor of my shed due to the three times I flooded it.
The answer to this question is yes, especially if flooded. When the engine is leaned out a bit, the wet nose may go away. But the idea is to get the lube to flow up to the bearing in the front of the engine by providing a lower pressur path to the outside world. Most front bearings only have shields which are not repeat not seals and those provide a leakage path (and that's good). Some front bearing do have a seal on the outer face and do not leak as much.

Enjoy your engine.

Chip
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Old 10-09-2006, 11:36 AM
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Default RE: Tower .75 Carb fit--Help

Thanks for the responses all. The Hobby Lobby Senior Telemasters are backordered till 10/20 so I may have a bit more than a gallon through this engine by then. I REALLY need to invest in a tach. The idle seems solid and will go on forever with just a hair line crack showing through the top if the carb. The transition to full power isn't perfect but it is flyable. It starts so easily and runs a full throttle so nice I'm reluctant to mess with it.

The one thing I haven't done yet is try it at different attitudes. I'll have to wait for the plane for that testing .

To Chip: I was flooding the CRUD out of my poor motor. With no experience, I primed the bloody thing until it was full. It was leaking from the front bearing and sptting fuel out of the carb when flipping it over. After clearing flooded engines three times I got wise . These buggers are quite alot easier to flood than the other small engines I've dealt with in chainsaws and weedeaters........

To Clint: I know what you mean about floaters. This engine is going into a Senior Telemaster. Hopefully it won't float much further than my sailplanes on landing or I'll need a bigger field......
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