Air Leak Trouble Shooting - New-B, Please help !

[stickmansav25]

Hi Everybody - first post
Does anyone know of a trouble shooting (yes go here, no go here) sheet or protocol I can follow to source the problem of my irratic, high revving savage.
It started in both my cars(an old pirate buggy) at the same time !
The symptom is as follows;Radio off - throttle fully closed
It fires up and just rev's to no end - kinda' like a critical mass thing
I've done a lot a reading in your forum and I am about to walk thru' the various procedures but I am starting to wonder if tainted gas would ever cause this same issue (both cars are doing it and we just switched to a new gallon of fuel)
please offer any comment

thanks in advance
and be good
Stickman

 

[Diver6127]

Someone posted one up a while ago and luckily I saved it. It comes in handy and is very good. It's basically a flow chart.

I'm sorry, I forgot who did it but I certainly don't take credit.

 

[stickmansav25]

this is fantastic - double thanx to you and the original author. I guess I'll start from scratch and see if I can get it to idle again and then move on from there. Any comments on the symptoms of bad gas ? Thanx again

 

[Diver6127]

WHOA, Stickman ... I just realized you are asking on how to find air leaks. What I gave you was a tuning flow chart. Here's how to diagnose an airleak AFTER you check your fuel tank and fuel line ...

1. Buy some Nitro Blast
2. spray in verious areas of the engine (base of the carb; HSN & LSN; Under the cooling head; behind the collet; back plate)
3. Do each area one at a time. Where you spray and the engine dies is where the airleak is

Other things that can be used is WD40, Carb Cleaner Electric motor cleaner
Just remember, Do things one at a time but first check for a cracked or poorly sealed tank via the o-ring and pinholes in the fuel line.

and Welcome to RCNT

 

[stickmansav25]

bin thru' the lines and tank so far, it's just that I can't get the thing to settle down to actually do the diagnostics you suggest. Have you heard(or read) that bad gas would cause the same symptom . . . . it's just that both cars started acting up at the same time ? ? ?

 

[Diver6127]

Have you checked you throttle/brake trim? Bring it down as well as trying ot turn down the idle on the carb. If it's still the same, get the can ready to do some quick spraying. It helps if you have some help you.

Since you stated that both cars started doing it at the same time, I would suspect that it's the radio (if they're both on the same radio).

 

[RatzoRC]

That was a great diagram!
I saved it so I can pass it on as well.
Thanks for the re-post Diver.

 

[stickmansav25]

Our own diagnostic prowess ? ? had us shutting the radios off and running them as if we were breaking them in(with the servo not activqated at all and the carbs closed) and they still buggered off. I reset all the settings to 'slightly rich'. you can actually push the carb in 'til close and still the same deal. Does a 'flame out' last for ever ? Have I hurt my needle maybe when checking the mixture(don't tighten too much)? Is Jeff gonna' make the chase ? ? ! !

 

[olds97_lss]

Bad gas, air leak, bad glow plug, dead engine (worn out piston/sleeve) will all produce very erratic results when trying to run Nitro.

"Does a flame out last forever?" I'm not sure what you mean here. Do you mean, if an engine "flames out", are the effects permanent? If so, not usually, but it depends on the type of flame out. If you hit 500 degrees, flamed out, then more than likely, it be dead. 300 degrees and lower is acceptable a few times on most engines without to bad of after effects.

 

[stickmansav25]

I've been killing the motor before it get's too far gone. I've got my carb tore apart now on the computer table and I'm thinkin' the LSN was WAY too far in - I couldn't find a stop point ! It was really deep in the barrel ! Could it be I frigged it up ? Is there a starting point as to how many threads are showing or 'flush of the barrel type of thing for a good rich start point ? I've even went thru' my photos but no carb shots - and thanks for all your help, guys !

 

[Tarant]

factory setting are a 3 needles flush, but that is breakin settings, to run the factory settings are the same but the HSN is 1 1/2 turns in,

But this is just a starting point my needles are way off yet my savy runs great.

also do the uniflow tank mod cause if your tank (the stock tank) has a nasty habit of running lean when the tank gets half way empty.


https://www.rcnitrotalk.com/forum/showthread.php?t=20546&highlight=uniflow

 

[stickmansav25]

what does three needles flush mean ? I'm looking down the throat and have the idle set to about 1mm, LSN is flush, HSN is at 3 turns out. I'm gonna' her back together and try everything. Hey . . . can I buy just the needle, the barrel or the whole carb ?
this is the stock Nitro Star BTW

 

[olds97_lss]

As you screw the LSN in, it will actually push the carb barrol out once it hits bottom. I think by 3 needles flush, he means the mid speed is flush with the carb, the HSN is flush with the carb and the LSN is flush with the thing it screws into. That should be really rich on all counts.

From what I've read, you shouldn't adjust the MSN (mid speed). This actually adjusts where the fuel is released down the carb throat.

After setting all needles flush, you will probably need to screw at least the HSN in some to get any performance out of it. The LSN should only be messed with once you can get a high speed pass out of the engine cleanly (no gurgle or dieing at WOT). Then you mess with the LSN to get the engine to run clean on take off. To see of the LSN is in the ballpark, get it warmed up and running. After a high speed run, bring it back to you and pinch the fuel line to the carb about 2-3 inches from the carb. It should rev up and die around 4-6 seconds. If it dies sooner, the LSN is still to lean (hard to believe at break in settings). If it dies later, the LSN is to rich. Adjust accordingly. Clockwise leans it, counter clock wise richens it.

Hope this helps.

 

[Silent]

Check for Air Leaks

Heres how I check for those pesky air leaks.......

* mix up a little soapy water is a dish
* take the engine in hand and close off the exhaust and carb with your fingers.
* attach a new section of fuel tubing to the fuel inlet
* and BLOW as you paint (with small brush) the various parts with soapy water. Around the backing plate, base of the carb, carb bolt, needles, fuel inlet, and head. You'll see the bubbles.

Seal the leaks using a high-temp silicone sealer as a gasket between the parts, and you'll have a consistant running engine. I've found airleaks on brand-new motors out of the box like that.

 

[Tarant]

No when I said all 3 needls flush I ment the HSN,LSN and idle screw, their sould be a 1mm-2mm gap in your carb throat

 

[stickmansav25]

O.K., I've got all the needles set to their starting points. Gonna reassemble tonight and give it a go. Given the plant is out right now i'll check for leaks, as Silent suggests, then If I can get it idling I'll spray the components as it is running. Here's hoping my next reply is the 'problem solved' one that I've seen throughout this forum !!You guys have bin' a great help ! - Oh-Oh ! the boss is comin' ! !
thanx again
and be good
Stickman

 

[olds97_lss]

No when I said all 3 needls flush I ment the HSN,LSN and idle screw, their sould be a 1mm-2mm gap in your carb throat

Sorry about that Tarant. I know that a few of HPI's engines have a mid speed needle that people make the fatal mistake of trying to adjust...

 

[stickmansav25]

Many Thanks

Thanks to all that posted replies. The bubble test worked on both cars and the problem was at the base of the carb(on both cars) - tons of air !
Used the rtv silicone (actually removed the upper gaskets), let it set for ten minutes to skin over and re-installed. Brought the needles out to flush and they fired up. Used the spreadsheet for tuning and they're flying. Even put a 49 tooth spur gear on the savage and it's now pullin' wheelies !
Special thanx to members; SILENT, Diver 6127 and Tarrant !

thanks again
and be good
Stickman