im not sure how to go about geting this right

[tothemax1984]

Hi i have a cen magnum monster truck. It is a used truck and i looked it over there seems to be no issues. Im starting to think it has to do with a tune issue. It was used in another state and now its in ny where it is cold. Here is the issue when ever i start the truck it wont idle i have to give it gas and when ever i let off the gas i can here the rpm's drop so much and when i bring it in to idle it will die. I tryed to lean the low end, i try to lean the high end . The carb has a 1mm opening its kinda open alittle more then that to tell ya the truth i have not tuched that yet. when ever it dies i can not restart it for nothing. I know it might be running on the rich side its spiting alot of fuel out of the tune pipe. I dont think its a linkage issue or idle issue.Im thinking mayb air leak but i cant even get the motor hot enough to really do any leaning to the high end. i have to hold the gas down well i bring her in to lean it out. please help thanks

[HPI HIGH]

If it is an air leak on the engine it will idle very high.if air leak is on fuel tank and lines it will just shut off . Niether uaslly cause flooding.

[jaylude22]

My first question would be the following: Does it feel like it has any compression? When you turn the flywheel of the engine to the point where the piston reachs top dead center(TDC), you should feel a signifigant thump when the piston passes that point. If you don't feel that thump, tuning the engine will be difficult if not impossible.

After determining that the compression is good, the next step is to get that idle gap set appropriately. A 1mm gap, or more, is open too far. Typically, you're looking to be in the neighborhood of .8mm or roughly the thickness of a credit card. In order to keep the engine running with the smaller idle gap, you'll probably need to lean the low speed needle(LSN) signifigantly. At this point, it sounds like the LSN is way too rich and someone has tried to compensate for that with a large idle gap. Because there's so much fuel going into the carb now(because of the rich LSN), the large idle gap is necessary to mix alot of air with that fuel. Once you reduce that air supply by reducing the idle gap, you'll need to match that decrease in air available with less fuel by leaning out the LSN. Any time you have raw fuel spitting out of your pipe, it's too rich.

Give those suggestions a try and let us know what the outcome is. I'll try looking for any videos that are currently available online that may be of help. Good luck!

[jaylude22]

Here's a link that may be of assistance: http://www.brccc.co.za/downloads/CarbTechSecrets.doc

[tothemax1984]

the carb is open way to much so i should close that a bit and lean the low end. Should i do that befor i start the truck?

[jaylude22]

I'd do it first, no need to wait until it's running. You can then make small adjustments once the engine is running. Keep us posted :thumbs:

[tothemax1984]

Ok sounds good, i just checked the carb is open so much, i wana run on the rich side but im sure i have to lean it out the high end and low end as well. Its alittle to cold here today and its geting late.. (watching football lol). Ill try tomrrow after noon and post back .. Thanks guys for your help i hope to get it going.

[jaylude22]

No problem, that's what we're here for :D

[Ovaloldtimer]

Read over this a few time's
http://mrcr.ca/Documents/Ron%20Paris%20-%20Racing%20and%20General%20Tips.htm

[tothemax1984]

Well i tryed to close the carb and for some reason now its alittle more closed up but when i press the brake the gap becomes smaller then it would at idle is that ok there is still a small opeing?

[jaylude22]

The idle gap should be set to the .8mm, which means that no matter what position your throttle servo is in, that gap never becomes less than .8mm. If the gap becomes less than that, the engine will die. This video may help: http://www.youtube.com/watch?v=hqLcyobUK4w

The author of that video has quite a number of videos that can be helpful in day to day r/c issues you may encounter.

[tothemax1984]

The idle gap should be set to the .8mm, which means that no matter what position your throttle servo is in, that gap never becomes less than .8mm. If the gap becomes less than that, the engine will die. This video may help: http://www.youtube.com/watch?v=hqLcyobUK4w

The author of that video has quite a number of videos that can be helpful in day to day r/c issues you may encounter.
thank you i thought it might be a link issue as well i will have to give it all a try tomrrow its just it gets me so mad when im out there and it wont start nor will it idle right. Ill let u guys no tomrrow thanks

[nitroRCs]

hey man...if the carb is closing more when break is applied just simply ajust the throttle trim so it dosent do it!...i had the same trouble on my car :)

[jaylude22]

hey man...if the carb is closing more when break is applied just simply ajust the throttle trim so it dosent do it!...i had the same trouble on my car :)
That's not the right way to do it. The idle needs to be MECHANICALLY set by adjusting the idle stop screw. Once it's mechanically set, there's no way that the servo can close it beyond the point it needs to be to maintain an idle.

[tothemax1984]

I have a update so i took off the servo horn and closed the carb up ok that went fine. I had the remote set at 0 and i put the linkage back on and when i went to move the servo the carb did nothing. It would not move open no more it was like stuck. So i try to open the carb up with the idle screw that did nothing. This thing is is giveing me such a headache its not even funny.I think im makin it harder then it has to be at this time lol.

[jaylude22]

If you screwed the idle screw in while the carb was fully closed, then that's probably the problem. Try unscrewsing the idle screw, then pulling the carb open. If that allows the carb to function again, post it here and we'll take it from there.

[tothemax1984]

If you screwed the idle screw in while the carb was fully closed, then that's probably the problem. Try unscrewsing the idle screw, then pulling the carb open. If that allows the carb to function again, post it here and we'll take it from there.
should i turn the idle screw well the carb is closed or open?

[jaylude22]

Unscrew it first, then if the carb will open and close once unscrewed, hold the carb open while screwing the idle stop in. Then close the carb. Repeat these steps until you get the idle gap you need.

[tothemax1984]

Thanks man see the idle screw is not doing nothing, when i put the linkage all back and move the servo the whole carb moves but it does not open. Its all most like its stuck im gona keep workin on it threw the day