GT Batman

I am having a problem that I do not have any idea what is causing it. My problem is that after getting my truck up to 1/4-3/4 speed it wants to keep increasing it's speed even with the throttle closed. It is not every time, but it happens 80% of the time. I have confirmed that the throttle is close as I would put the truck against a wall and watch as it seemed to magically accelerate without the throttle opening. I have tried turning the Idle sqrew down with no luck. This problem is kind of hard to describle. My first thought was a shoe dragging, but that wouldn't be the case as the engine is reving up like I am giving it throttle. This is a big problem as the braks don't work well when the "magic" throttle is being applied. This has nothing to do with the slipper as the truck does it when it is stationary, usually after I give it a little throttle. I took everything apart and everything looks good, so I can't even guess as to why it is doing this.

Here was my last test:
1. I placed the truck against my car's tires so it could not move.
2. I gave the truck about 1/4 throttle.
3. I let go of the throttle and observe the throttle fully returns and is not stuck open.
4. I can see the truck jumping and the engine reving as if I am giving it throttle.
5. I finally called it a day when the engine started to sound like full throttle and not stop even though the linkage never moved.

I hope someone can help

Just to make sure for tomorrow, I am changing the collet, flywheel, clutchbell, bearings, and shoe springs. This will at least eliminate these as possible reasons.

PillowPants

Sounds like a classic case of dying servo batteries. How old are the ones you have in there?

LoSiSuPeRtRuCk

My Feedback: (-1)

so your saying after you hit the brakes and the throttle is closed it still wants to accelerate? this is def. weird. im trying to think of what it could be. take the muffler off and look at the carb when its closed and see if it shuts all the way. if it isnt getting gas i cant see how its doing this.

Devilmanak

My Feedback: (1)

You have an air leak at the base of your carb, probably. Check to make sure it is seated and the pinch bolt is tight. THen check your head bolts, then your backplate bolts. I would bet that you find some loose fasteners. That is the only way that the engine can rev with the throttle closed, air has to be coming in somewhere.

LoSiSuPeRtRuCk

My Feedback: (-1)

yea i was gonna say this too. but i dont see how this would be effected by an air leak. i always thought an air leak would cause an engine to run high temps and erratic, but not accelerate off the gas?

GT Batman

TheHamburglar, I'm not sure how servo batteries have anything to do with it as the throttle is NOT moving, anf my pack is fully charged

LoSiSuPeRtRuCk , yes this is really weird. I did take off the air filter and seen that the carb setting was definetly back to idle, but sure enough, it wants to accelerate[X(]

Devilmanak, my carb appears to be seated tightly, as well as the sqrew, but I like your logic and it seems to be the only explanation. All bolts "appear" to be tight, is there any way to test for air leaks? Like putting a inner tube is sopy water?

Thank you all for your help

RCtruckRacer

Just a guess, how about a faulty o-ring on the HSN? i.e. when carb open and goes to closed, part of o-ring sticks out and lets fuel through? Just a thought

GT Batman

lstRacerX, is this something I could see happening? Also, what type of high temp sealant should I use? Can you tell me a brand name and where to get it? I might as well seal everything as well...however, I don't want it to be sealed so tight I can never remove it

RCtruckRacer

Easiest way to tell if the seals/o-rings on the needles are bad is to just unscrew them all the way out. As a precaution from tearing them on the way out, I would buy a new set of o-rings anyway. They are only a couple of bucks.

I found I had a similar problem when my HSN felt a little loose at one spot when turning. I was setting everything back to stock and noticed that the stiffness went away while turning the HSN at one particular spot. The O-ring had a kink in it and didn't seal very well. I didn't experience your problem though, hence the guess part.

For the sealer I use Permatex ultra copper sensor safe. You can find it any just about any automotive store. It's silicone and easy to remove when needed.

GT Batman

I will pick up some sealer on the way home. I will inspect the truck and report back. I read posts about air bubble in the fuel tank, but after plugging the primer they still had the problem, but might this be a possibility?

geide

I had the LHS work on my 1/10th scale LOSI once. The way he determined that there was a serious air leak was to plug the carb air intake with his finger. the car continued to run. He then proceeded to seal the engine and all was working fine.

Gary

GT Batman

geide,
good idea. I was able to stop the engine by putting my finger over the exhaust.....is that the same as your carb suggestion?
Thanks

benifur

My Feedback: (4)

I've never tried to fire one up with out the airfilter. Did it fire rite up or did he have to mess with it to get it to fire? I've found intake leaks on my harley with starter fluid but I don't think I want to try that on my nitos

GT Batman

Ok, I tried a few of your suggestions without any luck This thing also seems to heat up to 280-300 range rather easy and I had the body off and it was only 70F here. I am sure it is running rich as I see allot of smoke the entire time I am on the throttle.

Ok, about my testing. When it does its magic throttle, it has a high pitch sound and seems to be equivalent to when the truck flips upside down, but it stays constant. Also, there is little or no smoke coming out while it is doing this. I can just feel heat and a little fuel, but mostly heat from the exhaust.

I pulled the air filter and covered it and it dies instantly. I removed the fuel filter and ran a new line directly to the carb, checked to make sure the fule tank was sealed, and no luck. I thun pulled the HSN assemblly off, but I seen no O-ring, just a metal washer. I removed the HSN and it's casing, I didn't try and take out the needle itself.

So I am totally confused. I bought some sensor-safe Ultra Copper High temp RTV silicone and am applying it around the carb and backplate as we speak. But I can not see haw there was any leak around the carb, that thing was in there really tight and the O-Ring appeared tight to the crank. I haven't gotten to the backplate yet, so I will see if it was loose.

Any more ideas based on my new findings?

LoSiSuPeRtRuCk

My Feedback: (-1)

turn down your idle screw and richen your lsn.

geide

No, it is not the same thing at all. If you put you finger over the exhaust the engine will always kill. If you put it over the carb, and the engine keeps running there has to be an air leak. The engine cannot run without air.

Gary

bentgear

Are you sure the carb is fully closing as in viewing it while running with the air filter off. Sounds like the sticking throttle servo saver problem to me.

Ed M.

RCtruckRacer

When I suggested to unscrew the HSN I meant that literally. Put your tuning scewdriver on the adustment needle and unscrew it - all the way. I am sorry I wasn't clear!!![]

BTW if you did/do have an air leak in the back plate (or anywhere else), it does not have to be loose.

RCtruckRacer

Oh, I hate to ask this, but you did put the HSN assembly back on so that the nipple was pointing in the same direction it was before?

GT Batman

Actually, I moved the nipple from it's original factory orientation as it was pointintg almost at the engine. Why does this matter? I don't see how it has any effect on the needle setting?

Yes, I can definitly confinrm that while "catching" the truck while it is doing it "magic throttle" with the air filter off, that the throttle was fully closed. And even if the throttle was sticking, it would close when I apply the breaks.

And I have turned the idele sqrew down by over a full turn and I maybe ay 1-2mm gap now. When I try and riched the LSN is will not stay running. That is why I thought it was rich, and the fact that I get allot of smoke when the throttle is applied. Maybe turn Idle up and richen LSN?

I was hoping to run this in the race today...but I guess I will have to enter my (original) T-MAXX I migth not finish last as other racers usually break

gunslinger686

Just throwing this out there ,,,bad fuel,,,glowplug or glowplug washer.

benifur

My Feedback: (4)

there sould be 2 of them metal washer one on each side of the fuel inlet nipple. I have put silicone on them when sealing up an engine that was giving me fits awhile back. I sounds like a air leak to me . I had a fuel line break on my savage not all the way just enough to suck air and it took off like a rocket. it took a fence to stop it . So i'm thinking with high temps and you say you have it rich it has to be getting air somewhere.

benifur

My Feedback: (4)

Are we talking about a Mach? If we are heres a idea
http://www.killerhobbies.com/Browse_...1_26_-_SWK8008
I have one of these they are great carbs. and If your has a leak you can't find, it could be end of problem.

GT Batman

I have the .28 Novarossi. Would the soprtswerk carb be good for it as well? My patience is really wearing thin with this truck....2 different engine...same problems. I would have to start thinking this truck is the common factor. I could never keep the temps down on the mach, and the same with the Nova, that would be acceptable id I wasn't getting the "magic throttle".

Does anyone know the stock needle settings for the nova? I am thinking about going back to stock and see if the magic throttle exists.

BTW, I only finished 6 laps down in a oval race with my old original T-MAXX. That was with flipping 4 different times too. I hope I can get the LST going before next race

benifur

My Feedback: (4)

This is what my Novarossi .28 8 port was set at out of the box this doesn't mean it's right but it was where it was at and where I broke it in at. HSN 4 turns out from bottom LSN 4 1/4 turns out. mines a N528XRS. how hot does it want to run ?