Hey guys. I recently made a great trade on a tower hobbies tower terror .25 truck.

It has the factory engine seen here:

http://www3.towerhobbies.com/cgi-bin...?&I=LXRCJ6&P=7

The engine itself seems to be mechanically great. Im just having a little bit of a hard time tuning it. I have sealed it up and I am pretty experienced with nitro engines and mechanics in general. I got the truck used obviously, and these engines are known for being finicky, however I enjoy tinkering with these things.

The main thing I cant quite figure out yet, is that it seems like richening the high speed needle plays a big role in how the truck idles. I can get it to idle pretty good, but richening the HSN will richen the bottom end enough that it wont idle. It seems to be pretty finicky about idling. If I could get it to idle consistently, I can tune the top end with no problem. At times it seems to have a bog in the mid range as well. It will jump off the line and about 1/3 through the RPM band it bogs/hesitates and then picks back up. I was getting low on fuel when it did this, but It doesent make sense fully to me why that would cause the mid range to be weak. The engine starts easy even hot and I was running it in 12* weather tonight with no real problems.

The high speed needle has a bad o-ring and ever so slightly leaks fuel past it, but i dont think this would be a big issue. Fuel lines are good and the exhaust is on tight. The engine also has a mid speed needle and I have messed with that some too. It makes a big difference in how the truck runs even just turning it slightly.

Basically the 2 problems I am having are the idle problem, and the bog at WOT in the mid range(which may have only been a low fuel issue?). Anyways, just looking for some ideas or things to try. Thanks

That O ring on the HSN is a big thing when it comes to tuning. You should replace it.

The HSN shouldn't affect idle. It passes a lot of fuel and should not pose a restriction that could affect the small amount of fuel the LSN passes.

I'd say your HSN is too lean. This is common enough when trying to compensate for a rich LSN.

This could also be causing your bogging issue.

To start, since it isn't stalling at WOT (although it might if you held it there long enough), I'd richen the HSN 1/4 turn, and then focus on tuning the LSN for the best launch. You can get the LSN close by listening to the idle for 20 seconds. It shouldn't go up or down over 20 seconds to be close. After final tuning for the best launch, it may change over a 20 second interval.

Anyway, I like the 20 second "listen for a consistent idle speed" better than the pinch test to get close.

And I have to add.....some engines are just plain weird.

Best of luck, and I'm a bit envious....I'd love to have a Tower Terror, but having to order parts from Tower isn't the best, as parts have to cross the border to get to me, and I seem to get charged way more than Tower says for those green checked replacement parts.

After some reading im thinking some fine tuning of the MSN could be the cause of my lean bog in the mid range. It may not be transitioning to full fuel fast enough to keep up with the demands of the engine.

However, the idle is just aggrovating. The idle gap is fine, and I have tried several things to get the idle right. I have had it lean enough to where it was cackling at idle and it would still die after idling just a few seconds. I have richened it up and it dies really quick then. It leaves a nice thick smoke trail and I believe the HSN has to be pretty close, however im not kidding about the idle changing with the setting of the HSN. It shouldnt and i dont see how it is physically possible, but it sure seems like it does. I consider myself pretty good at tuning a nitro engine, and this one isnt awful or anything, its just not quite what it should be IMO. The engine does have great power and RPM. I hope to be able to mess with it some tomorrow during the day. Its gonna be cold, but oh well, its worth a shot.

Well, this is a fun little truck. Honestly the only thing i dont like about it so far is that the tires dont have foams. I like the engine, and think it will be ok once i get it dialed in and the rest of the truck is extremely simple and well built. Thats one thing i really like about it. I dont like having to order all the parts from tower either because their standard shipping is $10 even if its a dogbone, but ebay has some parts for them so i guess i wont worry about that till I break it. I only have about $45 in the whole truck with 2.4 radio, so im extremely pleased with it

Thanks guys!

As controlliner said, fix the o ring. If the HSN leaks then everytime you touch it the leak will get better or worse, which will obviously affect the running at idle. O rings are cheap but as a simple test you could just remove the needle and put it back in with a lot of grease, this should give a temporary seal.
On the Ofna engines the midrange needle is very particular about its positioning, maybe this is the same story? For the Ofna engines you have to set the mid needle approximately flush then remove the HSN housing to line up the nearest hole in the mid needle.
Other things to check would be, correct head shims and plug (are they correct for your fuel and conditions).

There is no middle speed needle, its an adjustable spraybar. Unless you are compensating for a tuned pipe, you should not touch it. It should be flush with the carb body. If you do decide to adjust it, you need to adjust it in conjunction with the LSN. If you back the spraybar out half a turn, you need to bring the LSN in half a turn. All the "MSN" does is let you play with the powerband a little. Look down in the carb, you see the needle that pokes into the little tube? The needle is the LSN, and that little tube is the spraybar, which is attached to the adjustment slot on the outside.

Its called a mid speed needle even though it is the spray bar.


Anyways, it seems to be running good now. I have it idling pretty decent and I think the bog I was noticing is just the point where the clutch fully locks up. Its more noticeable on a single speed truck than a 2 speed because the lower 2st gear kind of covers it up on a 2 speed. It had some stuff in the HSN banjo that could have cause some problems and so i think its running like its supposed to now. [8D]

Eric

then you're running the high speed needle way too lean, it should have little effect on the settings that are further down the line.

If that's not it, then you must have an air leak

No, its not too lean up top. I found some gunk in the HSN banjo bolt when i took it loose and im thinking that was causing problems. Here it is running. Not perfect, but its running and idling pretty good now.

[youtube]http://www.youtube.com/watch?v=Latt9To4878[/youtube]

That sounded pretty damn close to perfect in my book, maybe a little lean, but pretty damn close!

Sounds good to me, and it's making plenty of smoke so I wouldn't be worried about engine life.

it does sound pretty good

I think its about right now. The center spur gear support bearings are locked up in it now and im wondering if they have been dragging, but they will be fixed by friday or saturday i hope and i should get to run it some more[8D]