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Old 03-12-2009, 07:02 AM   #1
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Default HELP, Losi 8 rtr mach 427 tuning gremlins.

I recently baught a losi 8 rtr, with the mach 427. I got it broke in just fine with 5 tanks of gas. took to track on a 32 degree day took me 5 hours to get it running, I finally did but when I go hard on the throttle the motor would stay revving when I let off the throttle. So came home tore the bug apart cleaned and lock titied al screws. Last night I fired her up again same temp outside so didnt adjust anything at first, it started doing the same thing revving high when I let off the throttle. We took carb off and set idle screw to 1 mm opening on the sleeve. Still doing the same thing. The sleeve on the carb is not sticking its going all the way back just keeps revving real hard. Anyone got any ideas? Anyone got a losi 8 rtr that can give methere settings to try. right now I'm at 3 out on lsn, 2-1/2 on hsn, and the carb 1mm open on idle screw. I've got 3 other cars and been running nitro for about 8 years but this one has me stumped!

Thanks in advance.
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Old 03-12-2009, 07:14 AM   #2
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You might have 1 of 3 things wrong!
1. You might have a airleak
2. Your tuning could be way out of wack
3. Try using a throttle return spring.

It sounds like a airleak. If your carb is closing right after you let off the gas then air is getting in from some where else. That does not sound that common for the Machs. It a great engine.

Make sure your carb stop screw is in the slot and double check for any leaks..
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Old 03-12-2009, 07:44 AM   #3
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Trips thanks dog, I am using return spring. One thing we did notice last night was the fuel line that goes on the nipple for the carb is extremely loose fitting on there. Could that cause an airleak? I mean it goes on and comes off real easy.
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Old 03-12-2009, 07:55 AM   #4
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If it revs real high at idle (carb open 1mm) you need to richen the low speed needle until you get a noticable drop in rpms or you'll hurt your engine. There may be another cause to your problem like sucking air from the fuel line or tank but you still need to protect it from running lean. If you do find another problem and fix it, then you can lean the carb back out.
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Old 03-12-2009, 07:56 AM   #5
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I dont think that would cause a airleak. I think that would just not generate vaccuum to keep the engine running and get fuel to it, but then again it might make it go really lean if it slide off. I would think it would just die tho. Replace your fuel line or use a tiny ziptie to the needle nipple.
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Old 03-12-2009, 07:58 AM   #6
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also check your low speed needle. Is it flush with the housing or is it all the way in??
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Old 03-12-2009, 07:58 AM   #7
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we did richen up the low end substantially, enough were it was boggin down giving it throttle, still when i blow it out and rev it up it still stays revving hard. I'm telling you i have tuned the traxxas 2.5 motor for years and it is a pain in the ass. All I've read is how easy the mach is to tune and run. Just getting frustrated. Honestly after thinking about that fuel line some more, just sliding on that nipple real easy I think thats the problem.
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Old 03-12-2009, 08:00 AM   #8
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Trip I'm at work now. You going to be on here tonight so I can pick your brain while I have the car infront of me?
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Old 03-12-2009, 08:15 AM   #9
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Sure man. I be on around 7-8. Have you tried going back to factory settings
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Old 03-12-2009, 08:18 AM   #10
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I am really new to Nitro RC, and I mean really new, like I just ordered a Losi 8ight T and havn't even got it yet new, but I have a butload of experience with motorcycle tuning and engines. When finding an air leak on my Banshee I will spray wd40 or equivelent around until the RPM's Drop. It would probably be easier if you had someone to help hold the car so you could spray around.
If the car doesn't wind up without giving it any gas then it doesn't sound like an air leak to me. Normally an air leak would make it rev up without giving it throttle. Good luck, let me know what the problem is when you figure it out.
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Old 03-12-2009, 08:58 AM   #11
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Quote:
Originally Posted by TRIPC View Post
Sure man. I be on around 7-8. Have you tried going back to factory settings

Thanks trips, Yeah we went to factory settings last night. It's almost like the throttle is sticking, the sleeve is all the way back we even tried pushing in with fingers and it's closed. grrrrrrrrrrrrrrrr!
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Old 03-12-2009, 10:36 PM   #12
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Your idle screw might have broken off at the tip. I had the same thing happen to me at about a gallon on my mach. If you slide the carb out half way does it wiggle back and forth and up and down. Mine did the same thing and it was the tip of the idle screw that had broken off.
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Old 03-13-2009, 12:49 AM   #13
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What about the o ring on the high speed needle. I have a losi 8 b and its been nothing but easy to start.

Unscrew the entire high speed needle and take it out. Put some lube on it and make sure the ring is good. I had this problem with my sons hyper 7. Not sure if this could be the problem though. I am sure you have also checked the back plate for fit?
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Old 03-13-2009, 04:24 AM   #14
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pull the motor

put the piston a bdc. open carb needles, put a piece of fuel line on the carb fuel inlet. cover the carb intake and exaust port with your fingers and blow into the fuel line, have someone with a small modelers paint brush ,brush soapy water on your motor and u will see any leaks. make sure to check the block also. i have seen one with a cracked block do the same thing.

427 is a very good motor and easy to tune.
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Old 03-13-2009, 07:51 AM   #15
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Quote:
Originally Posted by GNS Racing 86 View Post
pull the motor

put the piston a bdc. open carb needles, put a piece of fuel line on the carb fuel inlet. cover the carb intake and exaust port with your fingers and blow into the fuel line, have someone with a small modelers paint brush ,brush soapy water on your motor and u will see any leaks. make sure to check the block also. i have seen one with a cracked block do the same thing.

427 is a very good motor and easy to tune.

Did this last night no air leaks that I saw, we also pulled the complete high speed needle and both o rindgs are in good shape all looks well. I will reinstall tonight and work some more I did notice my slide was about 3mm out!!!! So I reset that to 1mm and I am going to get new fuel line today cause the fuel line that came on it fits loose on the fitting of the hsn.
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