This is for you guys out there looking for more performance...

[Wolfslash16]

Well, after I read the threads in where people were fighting over weather or not a stock TRX 2.5 (Or 3.3, they are the EXACT SAME) and I thought I'd put a end to it all. I had a spare carb left over, and I got out a drill to bore out the carb opening to make it larger. (In other words, get more power) After I drilled it out, I screwed in the lsn ALOT to make up for destroying the lsn's seat, and I put it in my slayer. All I can say is WWOOOOOOOOOOOOOOOOOOOOOOWWWWWWWWW!!!!!!!!!!!!!!! I can now wheelie up and down the street, get to the top speed alot faster, and it just gave it alot more power overall! On the down side, the idle is a little rough from ruining the lsn's seat) BEST. MOD. EVER!! PM me if you have any questions! (Ps These pics are showing a stock carb vs the one I bored out)This is the stock carb bore...And this is the bore after I bored a carb out!

[Wolfslash16]

Oh did I forget to mention this mod to add a TON power is FREE?!?

[1979chevy.]

That looks really good, make sure to keep an eye on your engine's vitals though.

[1979chevy.]

That looks really good, make sure to keep an eye on your engine's vitals though.

[Nitronaught]

Adding more air,,,, I take it you needed to richen up the needles a bit to compensate for that?

I have one suggestion... Make sure you do some high rpm runs back to back and immediately check the temps...

You are not the first person to try this.... Last person I dealt with that did the same type of mod had a high RPM lean issue they were not aware of and the engine would get very hot on a high rpm pass..... Engine life went out the window...

Just something to be aware of...

[lubecakes]

Did you have to hit the lsn seat? It looks like something a guy could do without ruining the lsn seat.

[Wolfslash16]

LOL, Ya, I could have bored it out and saved the lsn seat, I was just tired and in a hurry to see if it would work, and I went too quick and the drill went all of the way through.

[Wolfslash16]

To what nitronaught said, yes the temps do tend to get a litter higher (give or take 20F) but when you said "adding more air will lean it out" that got me thinking... what if I made the fuel inlet hole larger so more fuel can get in and fix the lean issue? Hmmmm... I know what I'm going to do today...

[lubecakes]

It won't help, unless you drill the needle housing itself. You should be able to richen the needle with good results.

[Nitronaught]

To what nitronaught said, yes the temps do tend to get a litter higher (give or take 20F) but when you said "adding more air will lean it out" that got me thinking... what if I made the fuel inlet hole larger so more fuel can get in and fix the lean issue? Hmmmm... I know what I'm going to do today...

Just remember the Wolf,,,, More air = lean,,, all's you've done is add more air...

It won't help, unless you drill the needle housing itself. You should be able to richen the needle with good results.

There is a way they calculate the amount of fuel to be delivered from the carbs venturi, and that is not from the HSN housing it's been messed up if the hole was drilled larger... It's smoothness and shape is metered to the amount of air flow on a flowbench.... It's kind of a science. Just like re-jetting any carb...

Richening up the needles would be as far as I would take it.... But it's not my RC... I just wanted to add this info,,, it's kind of something you need to keep in mind when dealing with these carbs....

I found much better results by not touching my carb like this, but doing a fuel porting job on the sleeve.... WAY MUCH MORE FUEL FLOW!!!! And a pretty good jump in torque... Had to reset my shift points because the added torque was making it shift way too soon. A sure sign of added torque is when the shift point drops from an engine mod...

OH and one last thing,,, a nitro engine will run like a spanked monkey when too lean,,,, just before it starts to lose performance and fail..... I've damaged a $400.00 racing engine thinking it was running like it was on steroids only to find out I was too lean... Found out too late...

[lubecakes]

Actually NN, I was referring to the holes in the outside of the housing, where the banjo fitting goes.

[Nitronaught]

Actually NN, I was referring to the holes in the outside of the housing, where the banjo fitting goes.

I think you mis-understood.... The venturi opens into the throat of the carb.... When yo put a drill down the carb throat you are actually burring up and deforming the shape of it.... So the atomization of the fuel is not as consistent....

I don't think opening the fuel intake hole under the banjo is going to provide more fuel flow,,,, the venturi is going to be the main decider in that area.... You know a lot on 1:1 engines, so maybe if I referenced a 1:1 carb it might clear things up a little more.. When rebuilding a carb for more performance, not swapping out the jets of the carb will not alow more fuel flow into the intake, Ok maybe a wee bit more but you get my drift... Then if you put a Big carb on an engine with the stock intake it is not going to perform as near as well as a car that has the intake manifold and the heads upgraded/modified to get that fuel into the combustion chamber (this is what fuel porting is doing with the sleeve basically).


This is just my experience, I've got a lot of respect for your input lubecakes, so I hope our differences here are not taken personal.... I just feel many people read these posts besides us, getting ALL the fact out there is important with this expensive hobby... Just my 0.02 ya know...

[Wolfslash16]

When rebuilding a carb for more performance, not swapping out the jets of the carb will not alow more fuel flow into the intake, Ok maybe a wee bit more but you get my drift... Then if you put a Big carb on an engine with the stock intake it is not going to perform as near as well as a car that has the intake manifold and the heads upgraded/modified to get that fuel into the combustion chamber

Ya, I understand what you mean buy this Nitronaught, It would be like taking a minivan engine and sticking a dodge charger's 440 hemi intake and carb on to the minivan's engine. It wouldn't do too much good, now would it? The only reason I did this mod in the first place is to see what would happen if I bored it out, and what kind of performance gains/losses it would give me.

Couple questions: I haven't looked into the barrel itself for a while, but is it possible to bore out the Traxxas carb to say, 7 or 8mm? I may head to the LHS and buy one to try.

I was just answering Double G's question. And besides, the carb had a HUGE crack under the hsn, and I was going to throw it out anyway. (I had to use alot of superglue to fix the crack) The mod I did only gave me a great top end power gain, but it completly ruined the idle. The slide is only slightly larger in diamter than the bore of the carb, so when you bore out the carb's throat, air will leak around the slide rendering the carb useless. That's part of the reason the idle was ruined, not the top end power. That's why you have to have a carb with the approprate slide diameter. There is really no way to mod a stock carb with good results, unless you replace the slide with a larger diameter, which is not practical, if even possbile. It is WAY cheaper and easier to buy a new carb with a larger bore and venturi. (Maybe a losi 3.4 carb?) I just hope this clears things up a little bit

[Nitronaught]

Yeah,,, I just don't want someone who's not aware of what a lean condition can do to their $150.00 engine before they start to decide to grab the drill.....

It's great to experiment... I've done a lot with 2 stroke carbs on Gokarts, Gopeds and played around with these RC carbs... They are not as tuneable as a 1:1 carb... PRobably too expensive to make a carb that small with interchangeable jetting, etc...

My Non-Traxxas BB Truggy racing engine actually has inserts to cut down or increase the throat size. They are color coded according to their diameter.... When I use the one with the smaller diameter, I have to lean up the needles,,, and it performs way too snappy for a tight racing circuit, also harder to tune.... But it's designed with these inserts in mind and you have to use one or the other or it won't run worth a darn at all cause of too much air flow and not enough fuel to match....

[jato flash]

Good info guys, I have a Losi carb on my 3.3 and it works great. Granted you have to take a little time to tune, but once dialed in, awesome. Good carb for the price, and holds a pretty good tune.

[Redsawacs]

I skimmed the comments above and I didnt see anyone talk about "Jets". well, the idea is, the fuel is metered entering the carb throat and you can only adjust it so far with the needle before you need a larger "Jet" to compensate.

Unless you open the flow of fuel equal to the flow of air, you will always have a lean mixture on the high end as, I believe, Nitronaught mentioned above.

"Red"

[Nitronaught]

I skimmed the comments above and I didnt see anyone talk about "Jets".

Unless you open the flow of fuel equal to the flow of air, you will always have a lean mixture on the high end as, I believe, Nitronaught mentioned above.

"Red"

The venturi is the opening in the carb that would be the same as a jet.... Jet's are usually removeable, the venturi opening on a composite carb is not a separate piece. When the throat of the carb was drilled larger the end of the venturi/jet was affected by the drilling since it is horizontal and the throat is vertical the drill bit must have chewed at it a bit...

But jetting was referred to.... These Nitro RC carbs just don't have interchangeable jet's the venturi is doing that part.

[lubecakes]

The "jets" in this case would be the needles, that's all there is to it.....and the venturi is where the air goes in.

Post #9 was a response to Wolfslash when he stated this: "what if I made the fuel inlet hole larger so more fuel can get in and fix the lean issue"? I responded with: It won't help, unless you drill the needle housing itself. You should be able to richen the needle with good results.
I don't know why you went on about venturis, I was talking about opening up the smallest part of the fuel system.

[Nitronaught]

The "jets" in this case would be the needles, that's all there is to it.....and the venturi is where the air goes in.

I don't know why you went on about venturis, I was talking about opening up the smallest part of the fuel system.

You are right, the jets are basically the needles within reason... But they are also pretty precise measurement and your O-rings and needles would need to be of different size since they are the parts that seem to be the bottleneck in the fuel flow of a carb....

And you know very well that the size and design of the venturi area is what atomizes the fuel, make that inlet opening larger without making a change to the venturi area and all's your going to be doing is learning where the sweet spot is on your carb,,, if you did not drill out too much of coarse...

If the carb is max'd out and needs all this attention, why is it when I ported my engine with the same carb and same everything else am I getting more power and better performance?? All's I did was increase the fuel flow efficiency of the engine itself... If the carb was that restricting, I'd not be seeing the performance increases that I have...

[lubecakes]

I would never try to mod a carb lol.
The principles are slightly different from these little carbs to a gasoline carb. In a gasoline carb the fuel gets into a chamber and needs suction to pull it further along. In a nitro the fuel is being pushed directly through the "jets" and then suction comes in to play. IMO, It's more like a throttle body fuel injection than carburation.

[Wolfslash16]

Wow. I just wanted to show everyone what would happen if you bored a trx carb out. I'm not complaing, just comenting. Good info though, This exact kind of topic is EXACTLY why nitro will always be more involving and more realilistic! =]

[Nitronaught]

I would never try to mod a carb lol.
The principles are slightly different from these little carbs to a gasoline carb. In a gasoline carb the fuel gets into a chamber and needs suction to pull it further along. In a nitro the fuel is being pushed directly through the "jets" and then suction comes in to play. IMO, It's more like a throttle body fuel injection than carburation.

Ah sort of,,,, The fuel is pressurized to make it from the tank to the carb, from there the crankshaft creates a vacume affect as the fuel get's pulled into the crankshaft and out the back end of the crankshaft to go through the lower end and up the posrts of the piston sleeve into the combustion chamber... This way the fuel/oil blend goes through the entire engine and lubricates the internals...

They are WAY different than 1:1 carbs 2 stroke or 4 stroke engines... They have fuel pumps and diaphragms at least....

It is posts like this that I learn a lot from others, including yourself!!

[lubecakes]

Yeah I was just trying to say that the fuel gets pushed through the needles instead of sucked like a 1:1 carb. That's the main difference in terms of principles. Don't ever think that I haven't learned anything from you either buddy.