matteo_galet

Hello everybody
I'm new to this forum, and I'm from Italy so close an eye on my english...
Few months ago I bought from the bay a Losi Aftershock LE for about 300€.
Since it's my first experience in nitro RC world, I had a very hard time to get it tuned after break-in procedure.
This summer, with school not longer keeping me away from my truck, I had more time to work on it and I finally got it to run quite good.
I feel I'm next to the perfect tuning, but there are still some issues to deal with.
In fact the engine stalls after 10 minutes of bashing, and is hard to restart.
I noticed there are lots of bubbles in the fuel line entering the carburetor, and when removing the air filter after the engine has stopped I can see, whenever I open the throttle slider a bit, lot of fuel evaporating/burning in carb's air intake. When I return the slider to idle position the fuels keep burning until there is no more left and air bubble are pushed back in fuel line to the fuel filter and then to the fuel tank.
As recommended by every forum online, I already removed the stock fuel primer.
I also covered with tape the fuel filter, thinking it was boiling fuel by becoming too hot due to its position next to engine's head (the plastic filter already shown some small wear due to the heat). No improvements at all...
I know the carb boiling fuel is result of an over-heated engine, but in fact I'm pretty on the rich side - engine goes 4 stroke when cold, makes LOT of smoke and spits LOT of fuel on the ground.
By the way, the hotter it gets, the less the smoke and oil on ground... of course it burns half the fuel in the carb, so I must stay that rich or the engine would be starved for fuel

So what is this situation symptom of and what do you suggest doing?

I really appreciate your help...
Thank guys!!!

HerrSavage

Try an OS A5(cold) glowplug.

cummins driver

My Feedback: (31)

I had this problem on my Losi LST2, and my father in law had the same issue with his LST2 with the 427's. His Mach .26 in his LST1 also had the issue.

What you need to do is buy an insulated carburetor - or one that is partially composite. The composite isnt an insulator like aluminum is, and thats why the stock all aluminum carb has the fuel boiling problem. I put a picco .28 Carburetor on my 427, and I put an Ofna Force .28 carburetor (bought new on ebay for like $12) on my father in law's 427 and both engines run and tune 10 times better now. The engines run consistant now and dont die with the hard start issue like you mentioned. They arent pig rich when they are first started like they used to be. With the stock carb, I had to tune the engine rich so it ran horrible for the first several minutes until it got good and hot, then when it got hot it would run decent again with the exception of stalling as it boiled the fuel. Neither truck does any of that anymore and its a quick, and reliatively cheap fix. Let me know if you need any help or more info on it[8D]

Here is one that would work. Cant find a cheap one like i found for my father in law:
http://cgi.ebay.com/Ofna-PICCO-28-P3...item4cf909712f

And here is a picture of the picco carb in mine. Excuse how dirty it is[X(]

matteo_galet

@HerrSavage
Thanks for the suggestion, but since it's pretty hot here in italy I'm already running a pretty cold glow plug; I can't tell the number as I thrown the package away and the glow plug doesn't have any number on its body.

@cummind driver
It makes me happy knowing that somebody has already had my same issues
Well, this isn't funny at all, but finding solutions for a common problem is way easier.
Anyway, when you say "insulated carburetor" do you mean airtight or heat-insulated?
I think you mean the plastic carb can't reach such that temperature to boil fuel... am I correct?
By the way, I noticed on my carb dust cover (the plastic thing in blue on the throttle slider) a little hole; can it have been the cause of a potential air leak, maybe causing all my problems?
I already proceeded with airtightening the engine and the carb collar and needles, with red RTV (gasket maker).
But, I don't want to run the monster until I buy a new dust cover - just in case that hole was the problem - then I'll keep you up to dateandif what I did don't help I'll buy a new carb as you suggested.

Thanks again for the help, I really appreciated it.
Bye!

PS: not need to feel sorry for the dirty carb - when I first had fun bashing around with the AFT I learned how fastly they get dirt as hell

cummins driver

My Feedback: (31)

Hope those highlited parts answer your questions good. The problem is just that the aluminum carburetor absorbs the same amount of heat as the engine block. The composite carburetor doesnt absorb heat since plastic is an insulator, not a conductor(like aluminum). Now; I have had some engines with aluminum carburetors that dont boil the fuel. I dont know why some do it and some dont, but every SH based engine I have owned has had this problem, and a composite carburetor will fix it. Definately keep us updated!

HerrSavage

No engine runs well immediately. They all need to warm up. I've never had serious issues with SH engines. NEVER the restart issue. That's a tuning issue, or something else.. I even sold an old Mach 427 a few years ago with a new Aftershock carb, and it ran great(have video somewhere...)

But if a Force 28 carb is cheap and really does make a difference, go for it..

Still, if you can get an OS A5, try it(preferably with an oilier fuel.. - for bashing..)

All this talk about composite carbs is suspect and frankly disingenuous IMO - spread inititially by one person in particular, then picked up on and regurgitated by his sycophants. I have had like eight SH engines over the years, and no they don't idle fantastically, but for the money they have great power and reliability - AND they are easy to break in and tune. I run the cold plugs for better performance, and just live with having to blip the engines so they don't go out. I have raced like this, and my experience racing a Mach 427 in truggy was just as good as running the Picco P7.. Main difference was, I paid the same for both, but the Picco was used and had 2 1/2 gallons on it. Cuz new it would have cost 2 1/2 times more than a new Mach. We're not talking competitive buggy racing here either, but bashing an MT. If the cheap Force carb solves whatever "issues" you're having, great... If not, run a colder plug and maybe change your tune..

But to anybody else considering getting a new Losi MT, don't let these few people convince you that you have to have a new carb before you even get started. It's just not the case. The stock Losi 454 in the XXL will run perfectly fine.

matteo_galet

So HerrSavage I understand every engine has to warm up before running well, but i think having a pig rich tune, as rich as going 4stroke at start and bogging during runs, and already have the engine overheated... Well THAT is not a tuning issue I think.
But you already said it can be something else... was it generally talking or do you suggest other things to chech?


So you mean composite carbs are just a workaround and they don't solve the problem? I already thought this because the fuel path to the engine combustion chamber comprises other high-temperature parts of the engine, so if the fuel doesn't boil in a composite carb, it will do in the crankshaft or in the crankcase itself. Am I correct?

Anyway it makes me feel unlucky to know that those engines are so easy to tune - in fact mine seems to be the one less easy to tune!

Thanks anyway

HerrSavage

SH engines are extremely easy to tune. They should never bog - mine don't.

Again, try an OS A5!!

cummins driver

My Feedback: (31)

- It doesent take a lot of work to figure out that plastic is an insulator and aluminum is a conductor... Im not an advocate for anyone on these forums, I only talk about what I know from experience and what has worked for me. I didnt tell him to go buy a picco or novarossi, I simply suggested he buy a composite style carburetor since that is what has worked for both 427's I have worked on.

- The restart issue is not a tuning issue. Its the fact that the carb boils the fuel back into the line so fast once it warms up that its hard to prime it enough to get it to start quickly on a hot start.

- Yes the engine still has to warm up some before it runs good, but it only takes about a minute of running around. Before with the stock carb set to run good when the engine was warm, it would take at least 3 or 4 minutes of blubbering around pig rich before the carb would get warm enough to have the engine run fairly good for the rest of the tank.

- The SH engines are powerful and reliable. I dont deny that a bit. I really like my Mach 427, but in stock form, the carburetor makes it a pain to tune because of the way it boils the fuel when the carb gets hot. I had an O.S. A5 in my 427 and the fuel still boiled.

- You dont HAVE to have a new carburetor, but if you run the truck on hot days, you WILL have fuel boiling issues, its just inevitable. I dont know what your climate is like Herr, or how hot it gets where you are, but I never had a single problem from my SH engines in the cooler weather around here. But in the heat of the summer, all of my SH engines would boil the fuel. A composite carb is just a pretty cheap fix to really bring out the true potential of an otherwise great engine.

HerrSavage

Fair enough, if that's how it is. It very rarely gets over 80F here, and I've never had these issues. Still though, except for you and one other guy, I've never heard about them all that much either. Not trying to argue.., just saying.

And again, even when racing a 20 minute main on an 85F day - with an OS A5 plug and oily SW basher fuel, I was temping like 212 on a silver Mach. Have never experienced anything that made me think the fuel was boiling. Half-tank lean maybe, or just too lean a setting..

cummins driver

My Feedback: (31)

I thought about this myself. However, I think the problem is that the fuel spends a relatively long amount of time in the carburetor compared to the crankcase. The fuel has to run all the way through the carburetor and it is probably there for 3 or 4 seconds (just a guess) before it enters the airflow and gets drawn into the crankcase. Once it comes out into the airflow though, Id say its less than a second before it makes its way to the piston. Kind of like if you hold your hand in a fire for 4 seconds, its really going to hurt, compared to just running your hand through an open flame quickly and just barely feeling the heat. Thats my theory anyways; and im sure there is still a small amount of fuel that does boil off in the engine, but it wont cause the issues like it does when it boils in the carburetor.

cummins driver

My Feedback: (31)

I dont know what temperature nitro fuel boils at, but i would like to have a temperatue gun and do some testing. If i ever get one, ill put the stock carb back on my mach 427 and run it and see what temp the carburetor body is at when it starts boiling fuel, and compare it to the temperature of the engine itself as well.

supertib

Insulated carbs tune much nicer then non insulated, no question about it.........We just put a Picco carb on a Losi 350 from a RTR Losi 8 2.0and the engine ran piles better then it did on the original carb...It ran crisper, idled down better and picked up nearly 2 minutes of runtime...........