Diagnostic time (again) :(

[hamz9561]

Always use a decent fuel. Traxxas isn't on the list of the ones most here would recommend.

 

[Mickstix]

Only about a half gallon to go and I can switch up to a better brand! Weather changed for the worse again today.. Raining and barely out of the 50's.. Not supposed to warm back up till Sunday.. Will give the latest report next chance I get!

 

[RC Addict]

Hate to beat the proverbial dead horse but I really don't think you are going to have any better luck till the fuel is switched. I am not saying that is the only issue you are having, but it is a BIG one. Good luck.

 

[Mickstix]

Hey, I hope your right! Nothing I'd like more than to have it be a fuel quality issue! Unfortunately it's looking like early next week before I'll be able to get back on it..

 

[Mickstix]

Ran the car again today! Also got some new fuel and a MC-59 plug.. (Didnt use either yet though) But the car ran fine, all beit for the high idle.. I'd mentioned the last time I ran it the idle behaved for about 5-10 minutes before it started the chattering sound.. Well, today it went the whole tank of fuel w/o doing it.. I didnt even try to lower the idle today, just ran it up and down the street and slightly tuned it a little.. It's actually tuned a little rich now.. Temps when I checked were only 180 or so.. The idle didnt chatter or pull the car, but it's still a little higher than I'd like, but I really think all the probs were because it wasn't fully broken in?? Seems to be doing better and better with each passing tank of fuel now.. I didnt refuel it, I just put the piston at BDC and parked it.. (Didnt want to ruin a good day) LOL.. But they didnt have an Sidewinder or Boyd's fuel, but they did have Odonnell Racing 20%, so I got that.. Dont know if I paid too much or not, but it was 23.99/gallon.. I got the only gallon they had left.. They also had some called Coolfuel, and another brand with 3 letters in the name but I can't rember what it was.. Oh and the Traxxas and a few Heli and 4 cycle fuels.. I think the MC-59 was like 7 or 8$.. Not much of a deal I'm sure, but who cares..

 

[RC Addict]

Actually the fuel is about the price it should be. Glow plugs get marked up quite a bit. Try to buy in bulk online if possible to get the best price on them.

 

[Mickstix]

Yea, I like to help out the local shops as much as I can, but your right, online is the way to go to save some $$!!

 

[Mickstix]

I tell ya, I dont know if it's this way on all nitro engines, but on my SH .28, the HSN can wreak havoc on the tune!! Today I was running the car and when doing my high speed pulls the revs would hang for a few seconds after I let off the throttle. (As per the "let the engine tell ya" performance tune thread I know that the HSN was too lean) so I start richening it up a bit at a time.. Well all of a sudden the things actinging like it did before, where I couldnt touch the throttle and it'd just bog and shut off.. I started leaning the LSN like before, and it wasn't making any difference.. Then I remembered I'd richened the HSN, so I put it back to where it was and all was good again.. I've heard of engines being tempremental and only taking small adjustments to effect the tune, but damn.. This thing can go from too lean to too rich within an 1/8 of a turn! But anyway, she's still doing pretty good and eatin fuel.. I just need to be very precise with my adjustments else I'll be out in left field again, real quick.. So it appears that ontop of not being fully broken in, an overly rich HSN can cause all sorts of issues, even on the low/idle end of the throttle input.. Hope that bit of info may help someone down the road, who's having similar issues to what I was..

 

[MotoGod]

Generally speaking, once you get your base tune down pat....you will only need to adjust the HSN within +/- 2 hours or so of your base tune, unless the weather is DRASTICALLY different from when you got to your base tune. 1 hour shouldn't bring your engine from being "too rich" to being "too lean" though. If it does....something else is out of whack. 1 hour may be the difference between running like a raped ape, and just running very well though, but hey...all engines are different ;-)

I know on the Alpha Plus S852 that I am currently running, it finally "broke in" and dropped it's nuts during my second qualifier. It started sputtering and running really really rich right after the 3 min warmup had completed. I ran the entire race that way, and she never flamed out....or lost too too much power. Once we were done...I leaned the HSN by @ 2 hours....and never touched it again for Qual 3 or the main. It was running very very well and came off my Main temping at 210 degrees...so I had PLENTY more I could have leaned it out before being "too lean".

Small increments are best when trying to get that perfect tune down, but if you are pissing fuel out the exhaust at idle.... 1 hour leaner isn't going to make it stop blowing raw fuel alltogether...so you are perfectly safe to lean it more than 1 hour at a time depending on how much fuel it's spitting and such. A lot of the tuning idiosyncrasies can be solved by listening and running the engine. I over-leaned my engine during the first half gallon....found out by revving it and hearing it starve for fuel and "lean bogging". Richened it up 2 hours....ran great, but a tad too cold at 190. Leaned it another 1 hour or so....ran wonderful and cleared 200 degrees without a problem.

Now I am by no means an expert tuner, but I have screwed up enough tunes thus far to slowly figure out WHY I screwed them up...and how to fix them. I have done a LOT of trial and error with tuning in the past year. So I'd like to think I'm an OK tuner....but still learning something everytime I pick up a screwdriver.

 

[Mickstix]

Hmm. Maybe I was misreading the lean HSN condition? (While at full throttle it wouldnt sputter or lean bog, but when I let off the throttle (after a 4-5 second full pull) it would just hang at the revs it was at, and flame out if I didnt give it some throttle again) But all told, a 1/4 of a turn "rich" on the HSN made it go from running pretty good, to not at all.. But ontop of everything else, this SH .28 isnt exactly an italian racing beast.. lol.. I'm just happy the thing will stay running at this point.. Weathers about 5* warmer than it was, but not enough to drastically alter the tune, I dont think?

 

[MotoGod]

Well remember, the HSN controls fuel delivery at @ 1/4 throttle on up to wide open. The LSN controls fuel delivery at 1/4 throttle down to idle. So if you are going wide open and you let off the throttle....it's your LSN that is now controlling the mixture.

Here is a good test to perform:

-Start the rig up and warm it up on your starter box (or just something to get the wheels off the ground if you have a pull start).

-Warm it up completely to operating temp

-Grab a handful of throttle a few times, then let off the throttle completely.

What does the engine do?

1. Does the idle drop immediately down to a consistent and controlled idle?

2. Does the idle stay up fairly high for a number of seconds before falling back to a consistent idle? If so, how long does it take for it to drop down to a "normal" idle?

If you are in condition #1, you are probably OK on your LSN tune. With the car running, pinch off your fuel line. The engine should idle up and die pretty quickly, within maybe 2-4 seconds.

If you are in condition #2, your LSN might be too rich causing it to 4 cycle idle and burn off all the excess fuel in the crankcase...causing the idle to go way up until the extra fuel is burnt off...then it returns to normal idle. Lean your LSN 1 hour at a time until you get a consistent idle going. You should be able to rev it up to wide open and let off the throttle...and the engine should fall IMMEDIATELY back to a normal idle...or very close to immediately anyway.

Also keep in mind that the HSN controls overall fuel delivery to the engine. So if you lean the HSN, you are in effect also leaning the LSN by a tiny bit as well since the LSN pretty much overrides the HSN at 1/4 throttle and under.

It's a very delicate balancing act. Also remember, as you lean your LSN your idle will most likely go up, and you will need to adjust the idle screw accordingly to get a nice idle out of it. Never use the LSN to control your idle or you will end up overly lean.

 

[Mickstix]

Well that's my problem, I have both needles out of tune, and I can't seem do get either adjusted properly before I'm having to mess with the other.. I was doing the exact test you mentioned.. I get it up to temp, and do a full speed pass (about 4 seconds) at full throttle.. Soon as I let off the throttle it drops "just a few rpms" and hangs there for about 3 or 4 seconds and then shuts off like its out of fuel.. If I didnt know better I'd think the throttle was stuck open, but it's not.. I took that as the HSN being too lean, but when I richened it up it started effecting the tune at idle.. I was never able to get it up to speed after richening the HSN, it would sputter and die as soon as I tried to give it the throttle..(But it did idle good, for a change) Anyway, I started leaning the LSN (like I had to before) but that wasn't even helping.. Only thing that helped was to lean the HSN back to where I had it.. I'm tellin ya, this motor has a mind of its own, and it's mission in life is to mess with me! But I'll get it.. I at leat got it to where it'll run, it just needs a messaging.. (I'm hopin for a happy ending)

 

[MotoGod]

Is your idle gap set correctly? Does it die when you get on the brakes? If you were closer to Raleigh I'd say bring it by....but Florida might be a bit of a drive. lol

 

[Mickstix]

Gap is correct, but it still idles too high.. Brakes dont effect it, it stays running.. Here's the info I was using, to adjust the HSN, but now that I look at it again, I'm not sure the LSN was adjusted properly to begin with, so that might be throwin it off.. Your suggestion that the LSN was too rich makes sence.. I just wish I could get one needle or the other adjusted correctly, then it'd be pretty easy to adjust the other one.. Oh, here's the post I was going off of:

"To give an explanation to what is happening is simple. If your HSN is too lean, after a wot pass when you let off the throttle the engine is still lean causing the idle to hang and idle high until the LSN has a chance to take over and meter the right amount of fuel to bring the idle down to normal running speed (given the LSN is set correctly)"

ANyway, I wonder if I could just start the thing and let it warm up, then just do the pinch test over and over until I had the LSN right? (Can the HSN affect the pinch test of the LSN?) That might be my next move.. Today when I did the pinch, it took like 3-4 seconds to die, and reved up pretty good at the end.. (a little more rev than it should, and took appx a second longer than it should, to die) And yea, Raleigh is a bit far for a tune up.. But I'm gettin it at least "in the ballpark" now.. If I just keep swingin I'll eventually hit the damn thing... Hopefully!!

 

[MotoGod]

It's typically better to tune your HSN first, since it affects both needles. The LSN will only affect itself and your engine's idle speed. If you're still stuck....I can always hop on the phone with ya and listen to what it's doing and maybe give you a hand.

Nitro tuning is a serious headache when you're learning, but once you get the hang of it, it's really not too bad at all.

 

[Mickstix]

Thanks for the offer!! I just might take ya up on it if I continue to have probs dialing it in.. But the weathers finally warmed up, and the suns out, so I'm refreshed and good for another couple tries before I throw in the towel! Thanks again for all the info and help! It's very much appreciated!!

 

[MotoGod]

Anytime Mick. I was you a mere 6-8 months or so ago ;-) Struggling to get my engines in tune....my problem was used engines though! Trying to tune a dead engine is a futile effort. haha

Good luck with it!

 

[Mickstix]

hehe, yea I hear that! Also, tryin to start a glow engine with a dead ignitor can be troublesome too.. Car ran pretty damn good this afternoon!! It does something weird though, (I know, imagine that.. lol) Anyway, if I do say a 4-5 second full throttle pass, and let off the throttle and just let it coast, the idle drops initially, but then it picks up (or hangs) and the engine runs at a sustained rpm for about 3 or 4 seconds, then it kind starts poppin or missin?? Ever heard of that before? I think my LSN is probably still a little rich (one or both needles are still rich cause it's only getting up to around 190*) But I wonder if a rich LSN could cause this? It'll only do that if I do a sustained full throttle pass.. Just grabbing throttle and letting off within a second or two and it doesn't do it.. Any ideas?

 

[MotoGod]

A rich LSN will definitely cause the engine to "idle up" after you rev it up a bit. Lean it 1 hour at a time until the idle no longer goes up and down anymore. This may bring the idle up higher, but use the idle screw to bring it back down again.

Actually now that I read it all again....this only happens after a wide open pass....so it could just be your HSN set too rich, especially if you are only getting to 190*.

What I have seen in my engines, and a few buddies is that when the LSN is too rich we can rev the engine on the starter box then let off the throttle. As soon as we do it will maintain a low idle for 1-2 seconds...then act like someone cranked the idle screw up a few turns....then it will settle back down again. Leaning the LSN a little at a time keeps the idle up at the higher point longer...until it finally doesn't go up and down at all anymore. First time I did this I thought I was leaning the LSN WAY too far, but in the end...I was just REALLY REALLY rich.

 

[Mickstix]

Cool, I'll try leaning the LSN first and see what it does.. Reason I'm thinkin it's the low needle is it runs pretty good (almost too good) on top, so I figure if the HSN was rich it wouldnt attain the RPMs I'm getting? But who knows, it could be anything with this motor.. lol.. I'm just affraid once I get the LSN leaned correctly I'm going to have the same issue as before, where the idle is so high it sounds like its being strangled and wanting to drive off by itself.. But maybe the idle screw will have an effect this time? Last time I got it running decent I ziptied the aircleaner on so I'd quit pulling it off and double checking my gap every 5 seconds.. lol.. Thanks again bud!