unresolved engine/tuning problems

[noidle22]

hi, i've got a gs racing avenger which from the start has been a tool of a thing to use.
initially it was going well, broke in fine and ran well for months, then the front diff shattered and the steering servo broke. since then it's been an endless stream of problems.

i've attempted a retune multiple times but each time it gets worse and worse, this is probably my fault. it blows a ton of smoke and fuel under acceleration, if i try and lean out the HSN it has no apparent effect until it starts sounding terrible and doesn't back off revs when i let the throttle go. i followed the flowchart guide for tuning but it hasn't helped. it won't idle for even 10 seconds so i can't get it up to operating temperature to tune it anyway lately . if i hold the revs up it works but this's getting a bit tedious. i tried leaning out the LSN to improve my idle, this is similar to the HSN, it has no effect until it gets to a point where the car just wont start, if i richen it out again it'll return to idling for about 10-20 seconds.

if on a good day it wants to run and i put up with it blowing heaps of smoke and running poorly, it runs through about a quarter to a third of a tank then stalls. no matter what i try it wont restart. if i try priming it again the carb feels like it's got a ton of backpressure that's stopping it accepting fuel and the fuel line is full of bubbles, i can also hear a kind of bubbling gurgling noise coming from the carb at this point as well, i heard something about the fuel boiling in the carb?

the fuel tank has no air leak, there may be cause for concern where the line joins the pipe cos there's fuel residue around the nipple but it's always been like that even when it was running well. i will seal up the engine when i get a chance and see if that helps but as of now i really dont know what to do.

is there anything else i can do/check?

thanks, and sorry if this's in some other thread somewhere, i wanted a thread that contained all my random problems

 

[mtaylortank]

try leaning it out somemore you might be flooding it out when you give full throttle and that would make it keap stallin and u said something about alot of smoke.. you get alot of smoke from either bad fuel or to rich.....

 

[hamz9561]

First of all, you need to make sure that the trim on the throttle is all the way down. Next with the filter off, check to see that there is about 1 mm of opening in the throttle body (about the thickness of a credit card). After sealing the engine and letting it sit overnight, reset the needles back to factory and re-tune your engine. Remember that you need to keep them temps between 220 and 240.

 

[bgbdwlf2500]

Sounds like it just needs to be sealed and then everything set back to factory settings. Fuel boiling is a sure sign of being too lean and even though its blowing smoke its still lean. My brothers Revo did the same thing, blowing smoke but the temp was 400 degrees. With an air leak the needles do what you describe, very little until it wont start

 

[pipisugbo]

I'm not sure fuel boiling is a definite sign of overheating. Methanol boils at 149ºF and nitromethane boils at ~100ºF. My motor typically runs between 220-260º and I almost always hear a little gurgling going on when I shut it down.

 

[bgbdwlf2500]

Well, when its boiling it wont flow into the carb which is why you can't restart the engine until it cools down.

 

[noidle22]

Hm, i see. Well my fuel is a little old as well because i went a fair while without running it so i'll make sure to buy some more fuel before i run it again. @ Hamz9561, my trim is always set all the way down and my throttle clearance has been the proper gap all the time, i'll do the whole factory retune again though like you suggested. I've ordered a temp gun and it should be here in 2 to 3 days, it's a public holiday today though so postage isn't happening and i can't go to the hardware store to buy some silicone sealant

Fuel boiling is a sure sign of being too lean and even though its blowing smoke its still lean.

when its boiling it wont flow into the carb which is why you can't restart the engine until it cools down.

This is what was confusing me because i thought it was running fairly rich because of the smoke and wouldn't be hitting very high temps, but if this is the case then it makes sense. And that would explain the reason it has no chance of restarting when hot, too hot :\

Edit: just pulled the exhaust off the engine and there was a lot of wear and a large rip in the gasket so at least i know where one problem was

 

[bgbdwlf2500]

That rip in the gasket was helping you to lose backpressure in turn running lean because there was not enough pressure in the fuel tank. most fuels these days have way to much oil so you can still be running lean with a good smoke trail

 

[NTC3 Guy]

Check your Glow plug, and replace reset the carb to factory settings including the idle screw. Check you fuel lines they may be worn and not sealing good.

 

[noidle22]

Yeah i noticed that my fuel lines are a bit dodgy lately, i have some good quality stuff that i ordered a while back that i'll use. Pulled the head off yesterday and my plug looked as i thought, not too worn out but with signs of running rich, it's been the second glow plug ever in this engine so it would be due for a replacement, will get something good quality.
Engines don't seem to be liking me lately, one of my injectors in my real car had an issue today so i'm hoping it doesn't turn out to be anything serious.

 

[noidle22]

well i'm resurrecting this thread because the car's at the state now that i've done everything suggested in this thread and nothing's changed. it has taken a while to get to this stage as i've been doing a lot of other non-RC things.

as a side note, i went to start it about 3 weeks ago, nearly had it started when the pull starter string snapped .
i was pretty devo but i went online to buy a replacement and then saw that the replacements were like $25 which was pretty steep i thought. the idea of electric starting had always interested me so i searched around and read up about a system called TigerDrive. i suppose many of you have heard about it/used it before. seeing as it cost about $35 for the starter and starter wand thing shipped to Australia, and the positive reviews i'd read about it, i gave it a go.

got it all fitted up this afternoon, was a really easy bolt-on install with no problems at all. i have the starting hole thing pointed out to the left of the car cos that was the only place that was easily accessible. i was just using my 14.4V cordless drill set on the lowest torque setting for the starting. primed the engine, put the starter wand thing in, drill on and bam, started within a second from cold. i was pretty happy with the performance, ease of install and price. if anyone was considering the tigerdrive system, i'd highly recommend it. of course, i'm yet to see how well the starting gears last or if they strip quickly, i hope they don't :S.

here's a link to the website if anyone's interested: Sullivan TigerDrive

so anyway, moving onto the more pressing issues once the engine had started. what i've done since last posting here is:
seal engine, new fuel lines, new glow plug, new exhaust gasket, new cable ties on header to muffler joiner cos they were a bit loose, retuned.
when the engines cool it's all ok, the revs return to normal, but once it heats up a bit the revs just run really high at idle. turning the idle control on the transmitter all the way down makes no difference, the only way i can make the revs drop a bit is if i actually push on the end of the carb and force it closed a little bit more.
could this be an issue with the low speed needle then, as it is right where i'm manually pushing the carb in? might i have just not tuned the engine properly again? as far as i can see, this engine doesn't have an idle speed screw. it's a GS Racing B03 engine.

thanks for reading.

 

[RevoJoe]

Sounds like this Avenger of yours is a bit of a lemon. Theres just some cars that will never work right. Sell the cursed thing, and buy something different.

But, lets just try and fix it first...

Everything I'm reading, describes a lean condition.

Are you tuning the engine while it still 'cool' or are you also tuning it once its warmed up? To me it sounds like the engine is leaning out once it gets hot. An incorrect tune will do this. Obviously your needing to tinker with the needles to get it to start, but you'll definitely have to re-tweak them once the engine warms up.

I'm willing to bet my left one, that your carby DOES have an idle screw. Its more than likely just sitting in an obscure place, and is hard to see. If its the engine I'm thing of, the idle screw will be quite small, like the size of a grub screw, and hiding around the back of the carby. Take this Revo one for example.

The idle screw is somewhat camouflaged by the carby housing. I think yours might look similar to this. If you can't find it, pull out the carb so you can get a closer look. From what I'm reading, your gonna to have to adjust it, so you'll need to find it.

If you've got the tune right, your idle revs should change quite easily on the idle screw.

Tuning tip for ya:

Go and get some new fuel. Old fuel will never tune right. Opt for a No.8 plug. Thats the best rating for Australian climates.

Start at the HSN first, get your top end right, then move to your LSN, and get your bottom end right. If you need to use the transmitter trim or the trigger to hold revs up while tuning the LSN, thats fine, cause all your doing is simulating partial throttle. Once your needles are savvy, adjust your idle screw. Once this, is done you may have to ever so slightly re-adjust the LSN, so it idles and takes off a little cleaner.

Once you get a good tune in, starting next time round should be pretty easy, to the point that your shouldn't even need to adjust the needles to start it.

See how you go. If you can't get any joy, throw up a reply and we'll see what else we can do.

 

[noidle22]

thanks for the reply revojoe, i managed to find the idle speed screw it was the same place it is on that carby you posted. i had looked for it before but somehow had just not seen it.

i took it for a drive just then and tuned it a bit and yea it does seem to be leaning out once it gets hot (yes i wait for it to heat up before fiddling with needles). i had it when it was fairly warm but not overly hot idling quite well, it'd drop itself off the throttle and idle normally, but soon after it got worse and worse. it blows tons of smoke under acceleration but on the overrun when you let off the throttle at high speed you can hear it making an almost limiter-bounce noise. once stopped it revs like crazy.

i put my hand in front of the exhaust pipe and it didn't feel like there was much exhaust pressure there at all, i guess this is a symptom of the lean condition. i got the HSN sorted more or less, the leaner i went on it the worse the revs became so i stopped. i tried screwing in the idle speed screw and it helped, but only for a short time. after a while it just revved back up to what it used to be at like i hadn't even touched the screw at all. i'll have another go on the weekend but for now i'm pretty over it.

 

[RevoJoe]

thanks for the reply revojoe, i managed to find the idle speed screw it was the same place it is on that carby you posted. i had looked for it before but somehow had just not seen it.

i took it for a drive just then and tuned it a bit and yea it does seem to be leaning out once it gets hot (yes i wait for it to heat up before fiddling with needles). i had it when it was fairly warm but not overly hot idling quite well, it'd drop itself off the throttle and idle normally, but soon after it got worse and worse. it blows tons of smoke under acceleration but on the overrun when you let off the throttle at high speed you can hear it making an almost limiter-bounce noise. once stopped it revs like crazy.

i put my hand in front of the exhaust pipe and it didn't feel like there was much exhaust pressure there at all, i guess this is a symptom of the lean condition. i got the HSN sorted more or less, the leaner i went on it the worse the revs became so i stopped. i tried screwing in the idle speed screw and it helped, but only for a short time. after a while it just revved back up to what it used to be at like i hadn't even touched the screw at all. i'll have another go on the weekend but for now i'm pretty over it.

Yeah, I know the feeling.

How does the engine react to adjustments on the LSN. Does it make much difference? If its too rich, you should see it idle like crap and choke up when taking off, or it will just stall completely. When you start leaning it off, the idle revs should pick up a touch, and take off cleaner. If you keep leaning off the LSN, it will eventually get to the point where the idle gets bit too high, and the engine will cut out, when trying to get going.

Is that happening with yours?

Ok. HSN. So your screwing the needle in and the revs are getting higher.

Obviously its leaning off, but what do you mean. Do the revs increase while its just sitting there while you lean off the HSN? Or does the idle stay where it is as you adjust the HSN, and its just hitting a higher note when you give it the beans?

If you are adjusting the HSN, and the idle revs are going up really high, either your screwing it in way too far, or there is a bigger problem. Ideally, the most a HSN needs to go in is 2mm below the lip of the HSN sleeve... if you get what I mean there. Anymore than that is getting excessive.

I'm pressuming here that you've tried tuning the engine from factory state> As in, setting the needles back to factory specs, and going from there?

From here, if tuning the needles are only making things worse, and leaning the engine out further, we can only presume that the engine is doing one of two things:
- Its not drawing in enough fuel,
- Or its drawing in too much air.

I'm inclined to go with the former.

From what I've read, the engine is sealed, and all gaskets are intact, so it can't be drawing in excess air.... unless....
Have your checked the carby base oring? (the one the seals in between the bottom of the carby and the crankcase.) There might also be a crack in the carby housing itself. This can sometimes cause excess draw-in.

If there is no possible place for excess air to be drawn in, it has to be a partially blocked carby jet. If you think that this might be the case, strip the carby down, flush it through, and see what happens.

They only other thing that has any chance of explaining this is compression.

See if you can find a tear-down of the engine. (all I could find was a basic user manual) Theoratically, there should be a thin washer that sits between the head and the top of the block. If this is missing, it will increase the compression. Having said that though, I've never seen a nitro engine react that bad to a missing swish.

I can't really think of anything outside of what I've written here, unless your fuel has some spastic amount of nitro in it, but if something comes to mind, ill let you know.