Ok, It's a .40 size Tower motor on an avistar. Suppoesd to be new when I got it. On a plane but never flown the plane had so many problems that I'm sure it had not flown much if any at all.
So much for background now the problem. It has had about 5 tanks of fuel run throught it and it still won't idle. it runs up on the high side real good. The carb has a little hole in the front that is for low speed air and a screw on the side that screws in and out to lean or fatten the idle mixture. NOW...... the thing will not idel without a glow stick unless the screw is turned out some 7 to 8 turns??? at 7 turns out is where the hole in front is completely open, thus no adjustment, it simply wont run unless the hole is totaly open.
Yes many glow plugs have been tried. With and without idle bar. better with idle bar but still won't run.
carb has been removed and cleaned, checked the O ring. seemed a little flat for an O ring but it seals fine.
Fuel Tank seems to be set up properly and new feed line installed.
And FAT!!!! Man does it like to be FAT. Fuel all over the place.
It seemd to be loading up at idle, when comming of full throttle it will run smooth for mear seconds and then load up and die.
The low end screw can be turned out untill the spring unloads and when the throttle is pushed to full the screw turns it self in till the spring loads and the screw stops but no difference what so ever.

Is it time to replace this thing?
It's new but second hand, does anyone know if tower has a workmanship warranty on their motors?

Thanks, Miloh.

Heres the carb and the hole, you can see the screw and spring on the left.

I don't know this engine or the carb but what looks odd to me is that the air bleed hole seems to be above the barrel, unless it slopes down instead of being drilled straight through as usual. It almost looks like the carb is on upside down but that can't be. About all you could do is drill the hole slightly larger to allow more air to go through it.

HMMMM............... I'll have to study on that but before throwing it out I will give it a try.

I was just playing with one of these the other day. If you are describing the screw on the left of the picture that stands at a nearly 90 degree angle to the muffler mounting screw then you are adjusting the idle SPEED not the idle MIXTURE. The mixture screw is an airbleed like you said. If in fact you have been using the correct adjustment I suspect the hole is clogged. The one I have runs like a baby. I wouldn't give up on it. Take care, Cliff

I have an older Magnum with an air bleed carb. I could take the screw out of the carb ( the one parallel with the throttle barrel) and the idle was still to rich. I drilled out the air bleed hole 2 drill sizes bigger and then I could adjust the mixture to get a good idle. There was an article in one of the R/C mags back then about making the hole in the barrel oval to do the same thing.

Yes the screw in the back of the carb that sticks UP is the idle speed and does nothing for the mixture. It also hold the barrel in place.

Dru.

Thanks guys for your help. I do know the difference in the two mentioned screws and should have pointed out the screw that can bearly be seen in this pict.
Someone else said to change fuel???? can't see how one fuel could have this effect and still run my super tiger .91 as good as it does. Byrons 15%
Still looking at my drill to, pretty tempting!!!!
Thanks, Miloh.

BTW I did take the carb off and made sure the hole was not blocked.

Miloh.

Here is the screw I've been twisting.

It's an air bleed carb. I have had engines with these carbs and you could throw the screw away and it would idle ok, or maybe slightly rich even then. Good advice in an earlier response about drilling the air bleed hole slightly larger if the engine is still rich on idle with the screw backed totally out.

Clair

OK!!!!!!!!!!!!!!! the drill is comming out tonight.
I'll let everyone know tomorrow evening how it worked.

Miloh.
BTW Azcat I did run it without the screw and it still slobbered all over the place! Thanks.

The first Magnum GP 40's were made by Thunder Tiger. I was always told that the Tower 40 was also. I know you can swap parts in the three engines.

More often than not, people speak more highly of this engine than they do the OS 40 LA.

You may want to remove the carb from the engine. Disassemble and clean it inside and out. It may possibly be assembled with the barrel upside down? Check and see if this is possible.

I had one a few years back and it always ran perfect with the screw half way accross the hole. It never gave any trouble so I never worked on it.

Enjoy

Jim

w8ye.

Thanks man, I did just that (clean it, completely disassembled) the barrel will not go in but one way. I also drilled the hole out one size up in standard drill bit sizes.
just got finished about 9:10 will try it tomorrow evening.
I robbed an O.S. LA 40 off a bud's plane today to try out, funny you should come along with this info now.
What have you heard about the thunder tiger .46 pro??

Miloh,

The Thunder Tiger PRO 46 is a standard of the model airplane engine industry. It stands right up there with the best 46 Schnurle ported ABC type ball bearing engines. I take it that you have an oportunity to obtain a used one? Just make sure it feels smooth when you turn it and that it has plenty of compression.

You will enjoy the TT PRO 46 engine. It's in a bigger league than your Tower GP 40 type engine. A new Thunder Tiger PRO 46 has a good price also.

If you still have trouble with your Tower 40, See if the LA 40 carb will fit and try it in your Tower?

Keep in mind that your Tower 40 is no longer being made and that parts may be hard to come by? The newer Thunder Tiger GP42 (though a good engine) is made a lot different. I doubt if anything will interchange between the two?

Enjoy,

Jim

Was thinking about buying a new one (tt .46) this plane was bought on a whim. I have a nice cessna 182 with a Super Tiger .91 and plan to fly larger planes like that but have been out of the hobbie a while and this avistar was just the ticket to get my chops back up. hate to put a new motor on it just to fly it for a couple months, but also can't get any good flight time with it running like this. I am getting good a dead stick landings though LOL!!!
We will see how this mod works soon and go from there.

Thanks, Miloh.

you need more air at idle, drilling the hole one size larger should fix it. If it is still rich, then try hte next larger size after that.

Ok guys this hole drilling thing is the ticket. ran 3 or 4 tanks throught it this afternoon and it will now idle just fine.
Now it's slobbering a little at 3/4 throttle but I will get this corectted next time out.

Thanks everybody!!!!!!!!! Miloh.

Is this advice for the TT Pro 46 or the Tower 46? I have a TT Pro 46 and it also appears to running rich at idle. I'm a little nervous about drilling a hole in the carb body, not knowing what size of hole, location etc. []

The engine that we were originally talking about was the Tower 40. It had a look alike in the Thunder Tiger GP40. They are old engines that are not made anymore. There were also some comparisons with the OS 40 LA series which is currently made. These engines all have air bleed carbs that are a completely different ball game than the carb that comes on the Thunder Tiger PRO 46.

Someone asked about the TT PRO 46 as to whether it was a good engine or not and it is.

I'll give someone else the opportunity to tell you how to readjust your low speed mixture needle on your TT PRO 46. If there's no response, I will be back.

DON'T BE DRILLING ANY HOLES

Enjoy,

Jim

Uh- no drilling necessary...

Inside the throttle arm is the low speed needle go 1/4 turn clockwise (lean) until you can go from a long idle 30 seconds maybe, to full throttle as fast as you can move the stick without the engine blubbering (flooded)

Someone will wander in with a page long version I suppose-

W8YE is always the man to so he WILL be back-

later

That doesn't sound right. You better have a spare carb...

You have 3 screws. An idle set, a low-speed mixture and a high-speed mixture. The picture you sent shows what look to be the idle set screw and the low speed air mixture. Not sure which is which but it seems to be you need to figure that out first if nothing is blocked.

If you idle is not set right, you may be trying to adjust the air-bleed mixture to a place where the idle is not...if you know what I mean.

The idle set screw will just keep increasing the idle but when the engine is running, the air mixture may "sound" like its doing the same thing. You need to find the documentation!!...but you have to get the low-speed air mixture and high-speed fuel mixture in the "ball-park" first. Typically 1 1/2-2 turns out on the high speed mix and 2 turns out on the low speed mix. Then I would adjust the idle up fairly high...because that screw is probably not documented. Follow the directions to adjust the low speed air mix, then follow the instructions to adjust the high speed needle setting. Then lower the idle to what you expect...and double check the other two settings.

I believe someone has screwed up your idle set screw.

ComCity, Things are getting all messed up here. GX Ame has a Thunder Tiger PRO 46 which does not have an airbleed. He also has not posted a picture.

The tuning information you gave is very good though.

I must admit that this is the beginning of a new thread starting about 4 posts back but right now I have no way to split or combine threads. So I thought we would just go with it the way it is.

w8ye

Sorry, I didn't see the thread switch. I still have a hard time believing that I would need to drill a hole in the carb that the engine manufacturer matched to the engine. Now, if it was switched out for an after market carb....maybe.

I think people sometimes don't realize is that all of the mixture controls overlap to some degree and if things get totally out of whack, things won't seem to be working anymore the way the book says. And, in that case, you HAVE TO start over....

I mean, for example, take an engine perfectly tuned. I could set the idle set screw down so the engine idles faster and then then open the air bleed or low throttle mixture screw to slow the low end back-down to idle... what I end up with is a screwed up setting but at the same RPM idle I just had before; however, a screwed up setting that is unreliable.

Getting things out of whack...can happen on an air-bleed carb or a true air mixture screw setting....

I started this post about a tower .40, I did find after going through all the screw turning the following did correct the problem.
Remember I have been working with small engines like this for quite some time and this engine simply did not have enough latitude on the low end for adjustment so I enlarged the air bleed hole in the front of the carb and got the range needed for the engine to be adjusted properly. This only after knowing of several people trying the same thing first.
I tried everything before drilling and the engine would simply not run right but after the drilling it runs beautiful.

Miloh.