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time for a new engine?

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dragonlike76

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  1. Bashing
try to keep this brief. i hav about 2 gallons thru truck now. only uprgades are alum a-arms, and aftermarket air filter and steel spur 72t. after i first broke in truck it had all kinds of power and would pull wheelies constantly. after the mistake of letting a friend try to tune it (idiot even messed wit shift point and messed up tranny).gave up on old tranny and baught a new one with f.o.c. conversion already done(ebay). truck sat for a year or so till recently. it fires right up with no problem but tried everything and can't seem to get this thing running right now. started 4 turns out hsn. now at about 3 1/4 seems to have more lleft in it but temps are running between 260 and 300 now (thats with no body on and about 75-80 degrees outside). it shifts almost instantly at full throt take off (but shifts great if i richen it back up though) and just has no power to it. no low end torque or high end speed. i tore down the motor and it doesn't seem bad no scarring, alittle discolored on top of head. no air leaks, good hoses, just doesn't want to take a tune. has solid stream of blue smoke even at full throttle pass. i can't get any good performance out of this thing. so is it just time for a rebuild or upgrade motor(something easier to tune)?

forgot to mention it is a 2.5 model 4910 running 20% taxxas fuel
 
My reply to this would be, as long as you have good compression, the engine should be ok. Just sounds like a tuning issue. my friend was running his the other day and it seemed to be real responsive at first. Then, 2 or 3 tanks later, it was bogging at full throttle take off. We thought it might have been running hot. It was warm outside. But, it seemed like when he stopped, and let it cool between tanks, it ran great. Got hot, ran like crap. Don't know.....wish I could help ya more.
 
well I'm gonna try this i had a spare carb laying around so i switched them but have to wait till payday to get fuel(used the last of it today). i know its late on the weekend so hoping to get some suggesions from all of you later. anything that may help tuning or ideas for a powerful easier to tune motor (if there is such a thing). ty
 
How old was your fuel? If you let it sit out for a while, it will absorb moisture kind of like brake fluid...if that makes sense.
 
fuel was only a few days old, just baught a quart of it last weekend when i started tryin to tune it.
 
Did you store the engine with after-run oil in it? Was the tank and fuel lines empty? Also, all of my traxxas motors have run in the 290-300 range. For some reason they like that temp range.
 
you never mentioned setting on the low side needle. typically a nice rich LSN will bring the temps down.
 
have always used afterrun oil since it was new i really dont think its a problem with the motor I'm almost positive its a tune issue of some sort I'm just lost no adjustment seems to help. lsn is set that the pinch test shuts off at 2 1/2 to 3 secs.. and i realize these motors run hot but I've never had it run consistenly in the 300's like this. and to have no excellaration or speed confuses me if it was on the lean side that would explain the temp but if i richen it even the slightest 16th the thing barely wants to move.
 
I'd tear it apart and seal it before going any further, just to eliminate the possibility of air leaks. Running rich + high temps usually equals an air leak. Make sure the head bolts are tight as well. Also make sure the hsn housing isn't leaking. Don't over tighten it if it is. They strip easy.
 
slipper clutch is all the way tightened then backed off 1/4 turn its good. i seled the engine before the last run tore it down sealed carb and back plate.i do believe the old hsn may have been strippe but havent been able to test the new carb yet. I'm out a fuel and dont get paid till friday. gonna try it this saturday and i will post how it goes.i aprriciate all the help guys. most of it i have already tried but thats why I'm here hoping someone can think of what i havent lol. last bit one guy at work told me to shorten my fuel line to get a more consistant flow. does that seem right? ok thanks let you know after this weekend how it goes.
 
Metalhead Matt said:
I missed that you sealed it in the above post.:) Are you getting a ton of smoke? Raw fuel coming out of the exhaust?
Click to expand...

yes smokes is constant an solid and their is som much fuel coming out of the exhaust that I'm only getting maybe 5 minutes of run time out of the thing. i went thru a quart in an hour trying to tune this thing and that was with no speed or power 3 1/2 to 3 turns out on hsn and skywards of 310 on engine temp
 
Kinda sounds like a cracked block. Any fuel accumulating where the head sits on the block or around the bearings? Trying to think of other places it could be sucking air...
 
no hfuel around head but I'm not completly rulling out an air leak.guess I'm gonna just have to try it this weekend and go from there. what is a good direct drop in replacement motor for these things wit no other changes. so many choices. id really prefer input on what others are using instead of i heard this one or that one lol.
 
The 3.3 is an excellent upgrade from the 2.5 it drops right in without any changes at all! The header, clutch, and ez start bolt right up and so does the motor mount.
 
Wouldn't mind throwing my 2-cents in...

Seems you need to be completely satisfied that there's no air leaks before going any further.

Take out your 'sealed' engine. remove pipe and manifold. Remove filter and neck from carb. Get yourself a spray bottle with soapy water in it. Get a spare piece of fuel line on the carb fuel inlet and put other end in your mouth.

Holding the engine in your left hand put your thumb air tight over exhaust port (manifold removed) and your finger air tight over carb inlet. Blow through fuel tube. Hard. If your bloated cheeks are collapsing, the air is going somewhere! If so pick up the spray bottle in right hand and blow again while spraying one short spray on any point you suspect; carb, front bearing, back plate, etc. anywhere you like. Any tiny air leak will bubble up. Dry that area with kitchen roll.

You can check for any leaks like this and a least this will eliminate/diagnose one of the more common problems with these engines.

It worked for me when I had a brand new engine. Turned out to be the crank as air leak was between crank and inner face of front bearing.

Adam
 

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