SpontaniousCombustion

Hello and thank you for taking the time to read this post.

I recently have gotten my 1/6 Protech Promax nitro RC car running to a reasonable setting, considering it did not run at all when I found it. How ever, the engine with make a strange rev noise every now and then and hold it. I have attached a video of it occurring so you guys can better see what the problem seems to be. If possible I would also like to know if the car is sounding correct at all, I am fairly new to this nitro RC cars and it is my very first car.

Link: https://youtu.be/L3zTnRbj9fQ

A few example of the noises occur at the time-marks:
0:33 - 0:35
0:37 - 0:40
0:44 - 0:46

1:38 is a good example too.

Thank you. I hope you come back with good news.

1QwkSport2.5r

Fuel mixture is too lean. When he exhaust note sounds chattery and the idle hangs, your needles are too lean.

SpontaniousCombustion

Hello, how would I go about changing this to the correct setting?

1QwkSport2.5r

The proper way to do it is start with a rich needle setting and work leaner. I would be richening both needles a half turn or so. Once the engine is warmed up well - one tank should do it, lean the high speed needle 1/16th turn at a time with a WOT run between each adjustment until it's revving up cleanly. Then adjust your idle mixture in the same small increments until you get a nice transition from idle to WOT. If after a WOT pass the idle hangs a bit before dropping, the high speed is too lean. If the engine cuts out going from idle to WOT, the idle is too lean. Ideally you want the idle mixture set rich enough that it slightly loads up after a long idle - 15-20 seconds. It should be a bit smokey and burbly after a long idle. If it revs clean and snappy after a long idle, the idle is too lean.

cbaker65

Ok...ive seen enough!
the car should have been going with that rev!

Your cltutch or your spur gear is not right!....

1QwkSport2.5r

Not necessarily. A heavier spring or clutch shoe will require more throttle to engage... Not uncommon on larger scale cars and clutches.

Clearly the engine sounds lean which will cause the spikes in rpm (surging). This isn't to say the clutch may not need attention too, but the topic is related to the engine not being 'right'. I think it best to tackle one problem at a time.

SpontaniousCombustion

Okay thank you all for your replies I'm glad the people of this forum help each other out. So it sounds like quite a few things need to be done to my car for it to be running like it used to back in the day. I am new to this sport and I don't really know much about the terminology and when it comes to tuning to car and fiddling with screws and servos I don't really have much of an idea of what I am doing unfortunately.... for example "Start with a rich needle"

I have no idea how to do this, I've checked videos and seen how they do it but it always just seems to end badly with the car then not wanting to start again. I don't really know what to do...

I have taken some photos of the cars engine to kind of show you what has been done and to see if it even look remotely correct.

This is what I believe to be the LSN (See picture 4 for an explenation)
This is the screw that I believe to be the HSN
This is the screw I believe to be the Idle Scew
As you can see, on the sliding part of the carburetor this is where I have seen most of the LSN to be located. However mine does not have a screw here at all, I am left with just a round circle plate rather than being something I can adjust.
This is the air filter of the car at the current time. It's not in the best condition at all, in fact, it's as good as nothing but a new one is on order and I am just awaiting its arrival. I was wondering if this had something to do with it maybe? Maybe it is getting too much air intake or some dirt is causing some damage somewhere along the lines. I have also noticed that the fuel lines would always be soaked in fuel after a run so this shows some kind of indication that there is a hole along the fuel lines somewhere but I have also ordered some new fuel lines just encase, it is due for some too.

I hope these pictures and video are providing you guys with enough information. I am happy to take photos or make videos if they are needed. Thank you for taking the time to help me.

1QwkSport2.5r

Generally, the screw shown in pic 1 is the midrange adjustment, however it possibly may be the idle mixture needle/LSN. It appears the end of the slide valve where the idle mixture screw typically is has some sort of sealant or cement crammed in where the needle would normally be. You can confirm where the idle needle really is by removing the air filter and while looking down the carb throat, move the slide valve in and out. Generally the needle will move with the slide valve in and out of the discharge orifice which is typically on the same side as the fuel inlet/HSN valve.

FWIW - richer needle settings are counter clockwise and vice versa for leaner. It helps to have a baseline where the needle valves should be, but some of the knockoff brands have horrible documention (or none at all), so it's tough to know where to start. This is more critical if the engine won't start and run on its own - since you're does, there's no sense in messing with it. Richen the needle to start with and work from there.

SpontaniousCombustion

Hello.

Which needle do I ritchen, the LSN or the HSN. I feel silly for not knowing the answer to these questions, I am sorry if they are stupid question but I literally have no idea what I am doing..

I have uploaded a video of me sliding the slide valve back and forth, this is the direction the small in went in. It seemed to be the side towards the servo which I found strange because there is no screw on that side as shown in picture 4.

Link: https://www.youtube.com/watch?v=OH2Y...ature=youtu.be

1QwkSport2.5r

It appears the LSN is indeed in the carb slide though there seems to be some cement or some foreign substance covering the screw head. Look in the end of the carb slide. It is a white substance. See if you can pick it out to find the screw. Very rarely would they have a slide valve carburetor without a low speed needle. The screw on the outside of the fuel inlet side (the one you thought was the LSN) should usually be set flush with the housing. This adjustment is to adjust the midrange mixture - vary rarely is this adjusted.

For getting a better running setting, I would Richen both the LSN and HSN and work it down from there.

SpontaniousCombustion

Hello, I have checked the manual and found the name and explosive diagram to my engine however I don't seem to see the LSN or the HSN or even the Idle screw anywhere on it. In the picture it shows that the screw hole where the LSN would usually be is also blocked up and not there.

Here is the engine that is inside my car.
This is the explosive diagram of it.
And here are the lables as to which parts are which.

I hope the photos are clear enough for you to see and that you can make more sense of this.

1QwkSport2.5r

The photos are fine, but the exploded view seems a bit vague and seems to not show all of the parts. I would suggest picking the white stuff out of the end of the throttle slide to see if there is a screw in there to adjust the idle mixture. I have a hunch the factory that made the engine put the screw in a preset spot and sealed it in for some reason... If for some reason there is no adjustment screw in there, then they may have made it as a single needle unit (which would be very odd given the design of the carb). If the latter is the case, richening the main needle a half turn as outlined earlier would be the thing to do and run the car again.

SpontaniousCombustion

Hello,

Unfortunately no matter how hard I tried I could not manage to find a LSN anywhere on the car at all. I have looked countless times in the manual and cannot find anything and to top it all off, one of the bolts that connect the pullstart to the engine have gone missing so the pull start is kind of hanging on with just the 3 screws at the moment. It just seems to be problem after problem with this car and finding spare parts for it is near enough impossible... I don't know whether to abandon the project or not... parts are unavaliable, parts are not working correctly, it's unlike any other car. It just seems to be a car that's going to be problem after problem no matter what I do to it... I can't find 6 x 6 M2 bolts anywhere to replace the ones that have come out and gone missing so now the car is undrivable.

1QwkSport2.5r

Where are you located?

SpontaniousCombustion

I am located in Bedford, England. There is not even any RC shop near me that I can take it too. I traveled 30mins to a shop and it went in for a service. All they did was change the glowplug and nothing else they didn't tell me what I needed to do or anything. This was a few weeks back when I first got the car.

cbaker65

When you get rc's used an they've set for along time ,they should be gone through & cleaned ,especially the fuel tank.
Also when they set ,the O-rings & seals tend to dry out crack & leak on the needles.

That's nothing but a common 21 size engine ,most of that size usually take the same size screws!
What Ive seen of the vid an noticed off the top ,was the high rev an the car should have already started
to take off.
If your getting fuel leakage all over then you got a bad leak some where.
A nitro engine rely's on the pressure from the fuel tank ,if its leaking ,then the engine is not
getting the proper fuel .
A carb tune is useless with a leaking tank ,fuel line ,needles O-rings or a loose cylinder head!

1QwkSport2.5r

O-rings on the needle valves will leak fuel out, not air in. Most often, dried out o-rings allow the needle to screw itself in (or out in some cases). Also, the tank gets very little if any pressure until it's at half throttle or higher generally. I think it might be beneficial to find someone near you that can help you work on it - someone with experience.

cbaker65

Again ,let me refraise this!

If the pressure from engine { VIA} to the muffler [ VIA ] to the tank is not enough or the tank
is not getting the pressure ,then its not pushing enough fuel to the carb.!

An also ,if the internal filter on the tank is clogged ,it will restrict the proper flow of fuel for
the engine.!

People always attack the carb adjustments when theres other factors involved!

I did not say anything about an air leak!....

Once you check the lines an tank ,an make sure everythings good ,then you tune ,RULE OF THUMB IN MY BOOKS!...

SpontaniousCombustion

Hello,

Seeking someone with experience is a good idea but the last time I did that they completely scammed me, took my money and left me with a car that doesn't work still which really sucks and puts me off to taking it to someone a bit more. I really do not know what to do about the car..

cbaker65

Well ,Like I said ,If your fuel tank is not clogged ,because they do have an enteral filter in them ,so they need to be cleaned!
If fuel sets in the tank for a long time ,the fuel residue becomes like a molasses.

An also ,if the lid of the tank doesn't seal ,you will lose the pressure that is required to feed the engine!

You said that you always have wet fuel on the parts!

If you go back an check those things first ,it will make it easier to isolate the problems!...

SpontaniousCombustion

Hello,

Some new fuel lines came this morning and I have just attached them to the car. However I cannot test or run the car at the moment as I am finding it difficult to find some M2 6x6 bolts to reconnect the lose pullstart. Every model shop I have called have said they do not stock them size bolts. Once I somehow manage to find some screws I will go over the car and check to see if anything looks out of the ordinary.

cbaker65

Great...

In the meantime ,you can pull the tank ,clean it out with hot soapy water ,an you can dry it out inside by putting a piece of paper towel
inside an shake the tank hard.

Then with the fuel lines on the tank ,blow on the line that attaches to the muffler while pinching the line off that goes to
the carb. ,It should hold the pressure that you blow in ,an not leak out of the lid seal or fuel lines.

That's what I would do first!...

SpontaniousCombustion

Okay thank you I shall do that in the meantime. I must say a big thank you to Cbaker65 and 1QWKsport2.5r for taking your time to help me with this troublesome car and being patient with me as I am new to all of this. I shall clean out the fuel tank etc now and hopefully pick up some bolts on the way home after work tomorrow.

cbaker65

Cool!

I'm not here to undermine anyone ,infact ,I agree with what 1QWKsport has said an with a +1 ,its just theres other things
that need to be done other than the engine an that's the fuel supply & pressure that people don't stop an think about.

But anyway,I hope you get it running !..

SpontaniousCombustion

Thank you, I shall keep you posted tomorrow after work. (: