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Old 07-09-2009, 07:40 PM   #1
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Default i loose low end power after warm up..

i never had problems tuning my on road, and im having a hard time getting my truggy w/ 24.7 motor running solid with 1/4 of a 150CC tank left.

the 1st 3/4 tank rips! and i still haven't been able to get my temps over 210. book on my motor is 240-250.

i think im ruffly 2.5 turns out on each needle. it runs great.. until i get through 3/4 of a tank. could it be that 1/4 tank sloshing around and leaning my LSN out? its the off the line power im loosing w/ 1/4 tank left.

any ideas?
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Old 07-09-2009, 09:05 PM   #2
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Sounds to me like the engine's heat soaking after 3/4 of a tank and the bottom end goes lean.
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Old 07-09-2009, 09:11 PM   #3
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Quote:
Originally Posted by builtb16a View Post
i never had problems tuning my on road, and im having a hard time getting my truggy w/ 24.7 motor running solid with 1/4 of a 150CC tank left.

the 1st 3/4 tank rips! and i still haven't been able to get my temps over 210. book on my motor is 240-250.

i think im ruffly 2.5 turns out on each needle. it runs great.. until i get through 3/4 of a tank. could it be that 1/4 tank sloshing around and leaning my LSN out? its the off the line power im loosing w/ 1/4 tank left.

any ideas?
those 247 engines like fuel on the low end and the losi leans out on the bottom side of the tank so its a double whammy



those engines are actually a little tricky to tune
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Old 07-09-2009, 09:11 PM   #4
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That or your tank is shot.May not be pressurizing enough
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Old 07-09-2009, 09:15 PM   #5
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i think it might be the fuel pick up. the truggy is a month old. ive put maybe a gallon of fuel through it. i might run it hard tomorrow... and then when it gets sluggish, top off the tank and see what happens.

if not.. might be looking for a new style tank.. if thats even possible?
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Old 07-09-2009, 09:23 PM   #6
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That sounds like a common problem with a lean low speed needle. With the temp in check you might just be over compensating for a rich high speed by leaning the low end to get power. I wouldn't jump to the conclusion of an air leak low in the tank unless you are getting a flameout problem when the tank is low. The other possibility is that your clutch springs may be starting to weaken. When they heat up they may lose some tension causing the clutch to engage too early which destroys your low end power. First thing I would do is richen the low end a bit.
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Old 07-09-2009, 09:46 PM   #7
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i think the LSN is right on point.. because 3 hours behind, and i was getting the high idle that would drop.. which i think means rich.

it scoots on a full tank. so tomorrow while its nice and hot, i'll be sure to be on a 1/2 tank or better.

is there tanks out there that have 2 pick ups? i know it would be kinda hard without sucking air, but what is the best tank on the market? or is it a common off road problem?

could i double my inlet fuel line? why do i see some people wrap coils and coils of fuel lines?
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Old 07-09-2009, 09:49 PM   #8
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you wrap the feed line making it longer that way when you flip upside down there is enough fuel in the line for the truck to run for a bit giving you enough time to flip it back over before it shuts off.
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Old 07-09-2009, 10:18 PM   #9
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If it's a Losi truggy, the fuel tank is very good. The clunk style tanks they have allow you to be upside down but still pick up fuel.
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Old 07-10-2009, 04:22 AM   #10
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start the truck with a 1/2 tank of fuel and see if it rips cold with a half tank like a full tank. If the truck is still running good when it runs out of gas, you know it's tune not tank, because you said it takes 3/4 tank to start doing it.
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Old 07-10-2009, 07:58 AM   #11
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Mine does this sometimes after the weather changes. I'll tune in the morning during practice and by noon when we're running quals, I'm bogging when I pull the trigger. It bogs, bogs, bogs, then takes off like a raped ape. I usually just richen the high speed two hours and it completely fixes the problem.
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Old 07-10-2009, 08:25 AM   #12
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Not sure if this is your case, but does your tank have a small drop in the rear bottom of the tank? losi has one that if the fuel pick up clunk is not sitting in it will flame out at around 1/4 tank from going lean and sucking air...if so make sure the clunk is just a hair off the back of the tank and sitting correctly...
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Old 07-10-2009, 08:37 AM   #13
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Just replace the tank and fuel tubing and be done with it. The first tank in my 2.0 truggy did not last long and maybe a gallon and then it started giving me all kinds of enging problems. I even switched engines before I finally found the problem and changed the tank. Do yourself a favor and change the tank.
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Old 07-10-2009, 08:46 AM   #14
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im going to try and diagnose before i start buying parts.

my next step is to see how my performance is at just over 1/4 tank. this seams to be my trouble area.. so if its rippin up the street one a cold engine with 1/4 tank left, there's something wrong with the tune.

a dog like yesterday on 1/4 tank, cold engine.. something wrong with the tank.
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Old 07-10-2009, 01:49 PM   #15
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well, it cant be the tank, i started with 1/2 tank, and ran it almost completly dry and didnt' have any low end loss untill i topped off the tank, adn got through 1/2 of that. so basicly, seams after about a full tank of run time, the engine gets hot, and starts to loose that low end power.

you can almost hear it struggle off the line. sounds rich, bogs and pops alot, but doens't stall.

also, on that 1st 10 mins of run time, 1/4 tank, whatever.. really ripped. once i noticed it started to bog down, and loose my low speed power, i topped off the tank, so it must be in the tune.

also, are these big block engines typically run for 1 tank full, before starting to get hot? is it best to give them a rest, or can you run tank after tank after tank?

after i let it cool down, 10 mins or so, start it back up.. 100% power again.

must be in the tune.. but can you run these big blocks 2 hours straight with respectable head temps?
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