what happened to my tune?
 

i was running my truck the other day, (mach .26) and my high speed needle was set about 2.125 turns out. its been this way for a long time and ran great. however just like someone threw a light switch it ran extremely rich almost to the point where it wouldn't run. at full throttle it wouldn't even move. this happend immediately. i ended up turning the hsn in a full turn to get it to run good again. now its only a little over 1 turn out. what could have happened? i pulled the needle to see if it broke off or something, but everything looks good.
any input? thanks

replace your glow plug with the same plug that came out and put your HSN back to where it was. problem solved.

or your motor is finally broke in now!...back the HSN out about a full turn and lean the LSN about a half a turn and see what happens!...would a glow plug all of a sudden make a motor run rich?...usually if they are bad they dont let the motor run!

nope. plug go bad all the time and still glow. I see this happen all the time. OR here is one better! I bet you didnt know your glow plug gets its heat range from the initial glow of your glow starter. Meaning your plug runs off the initial glow it gets from your starter, SO guess what happens if your starter is almost dead? weak initial glow, resulting in what seems like a super cold plug..


Just because you plug glows in the starter in your hand, does not mean its still good.

I have seen this discussion before Joe and some people claim that the combustion is what keeps the plug hot while others agree with you. I would love to know the truth

I wouldn't post that if it wasn't a fact.

never hear of a plug causing this but thanks alot i'll try it.


nah. it has about 2 gallons through it. i did try the needle adjustments you posted though before i read this with no improvement. thanks though

finally some one else is having the same problem!!!! I have had this problem for a couple weeks now and i am about to give up, pack up and go electric (actually i am getting stuff together for electric conv). all three motors i have all the sudden they all started running ridiculously rich. I had to do the same thing, lean it, lean it, and lean it some more. Leaned it till the lsn was less then 2 turns out, same with hsn. DIdnt matter how rich or lean i tunned. It would always go to a heavy bog a die. I have changed P/S and rods, engines, pipes, plugs, nitro. The only thing i have not changed is the fuel tank. There are no bubbles what so ever. And there is not a airleak.

I have a pretty old ignitor (actually the first one i have ever had), It's the black ofna one, and the plugs are good.

It almost acts like it has a stretched or bent rod (well almost like that but add a terrible, terrible idle), but the rods are new. It's almost like someone put water in my fuel bottle. I am done with it.

I am holding out hope, that if i put a new plug with a new ignitor it will solve the problem. If not, i am done.

to the O.P., your problem does sound like a stretched rod. I had that happen before and replaced the rod and problem solved. But in my situation, it won't even stay running unless i have the throtle open some what. I have to set my trim like 6 ticks open to keep it running On every motor i have. And that is with a fairly wide idle gap.

try changing your air filter maybe too much oil.

check your pipe tip, it might be bent. had this happened to me once, a guy hit me from the side, the tip was bent and boom, the engine became rich immedietly.

Also the airfilter as Runninonmt said.

mine runs great though as long as i have it "leaned out" based on the needle position. however it still blows blue smoke like its normal. nor does it overheat.

fuel pressure
 

It could also be your exaust gaskets on your motor or your pipe or a broken fuel line or exaust pressure line most of the time this will cause your motor to go lean because of the lack of pressure but I have seen it cause the motor to just act bad. When ever I have a sudden tune issue and it is not the plug like Joe says I would start to look for pressure leaks.

just cleaned it off. i'll see how it is tomorrow with the new plug and cleaned air filter. i need to fix the steering servo horn first though.

if i just plug the fuel to carb line and blow in the pressure line, can i diagnose a pressure leak properly this way?