bleach1

I have an Os 12tr and i am having the problem that at about 5 seconds after hitting full throttle the engine will start chocking and spluttering. After that i only have about 25% of my throttle before it starts doing that again. It just started doing it the other night at a race and has always been fine before that. The engine has had about 1.5 gallons of fuel ran through it.

popsracer

bleach1;

Sounds like the Main needle setting is too rich.

Many engines go rich as the piston and sleeve obtain final seating. Different brands of fuel and even air density can sometimes have drastic effects on tuning.

Think of the screwdriver slot in the needle as a hand on a Clock. Try closing the needle 2-3 hours (clockwise) and see how it effects the performance. If it gets better, you are going in the right direction.
Do this an hour or two at a time until the engines runs cleanly at full throttle, but still leaves a nice trail of smoke when driving the car/truck.

Bounty Hunter

Another thing to consider is that there may be a leak on one of the idle stop orings too. Plus it is always a good idea to know where your needle settings are (how many turns out the needle is from the fully closed position). That way if the needle settings seem like you are reeally off in order to get the engine to respond correctly then that may tip you off to a leak somewhere in the engine or the carb.

bleach1

i recently pulled the carbie off and chipped a little of the metal that sits on the seal. I used some auto sealant to seal it. How can i test if its leaking?

I actually just found a split in the fuel hose from the muffler back to the tank. I replaced the hose and it seems a bit better now. Could this problem cause this symptom?

GUNPOWDER

Yes, it could. I also had a similar problem, in my case the there was some dirt in the exhaust. I cleaned the exhaust and made sure that air flow was good.. It took a while to fix because I initially thought it was a tuning problem..

GUNPOWDER

Just thinking about this and related to my previous post, is it possible that any traces of metal went into the engine?? If so, metal traces could also stuck in the pipe, preventing proper air flow..??

BaxterC

I have another suggestion, look for blockages in the fuel system from the tank to the carb, including bothe the tank and the carb, if there is a small 'insignificant' blockage, the motor will get fuel properly, then when at full throttle, it will need more fuel than the blockage is able to give and then causes the problem you describes, I would suggest replcing ALL the pipes and check all the connections and fuel nipples and all the other little things.

Manticore

main needle too lean !!

bleach1

i seem to have fixed it. Replaced the hose from the muffler to the tank. It had like a tiny hairline split in it. Since i replaced it it did it a heap less then i played with the needle and it seems to be quite good now.

popsracer

bleach1;

One thing we all forgot to mention:

When is the last time you cleaned/replaced your Air filter?

A dirty filter can cause the symptoms you describe.

It seems like you have it running better now, but if you have not as yet, check the filter.

Bounty Hunter

So many things to check....how do you do it?

BaxterC

Hop on to a forum... no, sorry, I am wrong Hop onto RCTECH

Bounty Hunter

You know with SOOOO many helpful people trying to respond. Doesnt it seem a little daunting to someone that just needs a little help?

bleach1

thanx for the help everyone, but it was the hose from the muffler to the tank in the end. Im guessing that hose is there to help provide some fuel pressure at high rpm.

Bounty Hunter

Well if there is not enough pressure as the tank empties then you will start to lean out too much and the head temp will rise (actually the rising head temp will occur anyways). If there is too much pressure the engine will die out before all the fuel in the tank is expended. You have to find a happy medium. It is for this condition that you see a lot of 1/8 scale cars that use a gas chamber on the pressure line to try and equalize the pressure going into the tank.