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carb info and tunning guide!

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lincsrc View Drop Down
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    Posted: 23 March 2006 at 10:44pm

STICKY THIS ONE PLS!

hope it helps new and old r/c peeps out.

The question seems to keep popping up about Carb adjustments- what does it do, which do I adjust first, etc.. Here a basic guide explaining the internal carb components, what they're responsible for, and how to tune it properly.

Assuming you're at the manufacturers recommended starting point with the idle opening gap already set and the engine running- the first thing that must be set is the HSN. The HSN (main needle) controls the maximum amount of fuel flow through the fuel inlet/spray bar. Since it does control total fuel flow- the HSN setting WILL AFFECT the LSN setting. Therefore, you MUST adjust this setting 1st before finalizing your LSN adjustment. Setting your LSN 1st will only cause you to have to reset it again once you alter you HSN adjustments. You must typically match this maximum fuel flow through the carb with the maximum amount of air flow through the carb. Maximum airflow through the carb can only be achieved with the carb at WOT and the engine at max RPM. It doesn't matter how fast you accellerate at this point- just get the engine to maximum RPM's doing several high speed passes and make a judgement based on maximum speed and smoke trail. Adjustments should be made at hourly incriments. Once you get to a point where top speed is no longer improving, richen the HSN between 1/8-1/4 of a turn out just to ensure adequate lubrication at that maximum speed.
*If the engine suddenly cuts out at high RPM's - you too lean

*If the engine lacks high RPM response with excessive smoke- your too rich

If your engine's is starting to run excessively hot even while your fuel mixture is excessively rich...try switching to a cooler glow plug, one step cooler than the one your using. ( If your using Dynamite plugs like an MC-59, switch to an MC8, then to an MC9 if necc- if your using OS plugs and using an OS8, switch to an OSA5, and then to an OSR5 if neccesary. DO NOT JUMP FROM ONE MANUFACTURER TO ANOTHER WHEN EXPERIMENTING WITH GLOW PLUG HEAT RANGE. THERE IS NO INDUSTRY STANDARD FOR THEM TO COMPLY WITH SO KNOWING WHICH PLUG IS HOTTER THAN THE OTHER BASED ON IT'S GIVEN RATING IS NOT SOMETHING THAT CAN BE DONE BETWEEN 2 MANUFACTURERS)


When the throttle is anywhere between 1/2 open to fully closed, the LSN enters the fuel inlet/spray bar and restricts the amount of fuel that can flow through it. Less fuel is required at this point since the smaller carb opening is also restricting the amount of air that can flow through the carb. The deeper the LSN enters the fuel inlet, the more it restricts fuel flow- to match the restricted air flow.

There are many methods people use to set their LSN. For me- I typically clear out the engine by doing a high speed run, bring the truck in and allow it to idle, then watch and see how it responds at idle speeds. If the idle speed drops right away or slowly drops within a few seconds ( or if temperatures start to drop too fast) = the LSN is too rich allowing too much fuel through which is loading up the engine lowering it's RPM. If it starts to climb in RPM ( or if temperatures also start to climb) then it's set too lean. Adjustments should be made at hourly incriments with a high speed run in between each adjustment to clear out the engine. Once I get the engine to idle for at least 20 seconds or so without excessive load up, once again, I'll clear out the engine, bring it in and idle the engine for 5-10 seconds- then hit the throttle to watch how it accellerates. It should accellerate smoothly and powerfully from idle all the way to max RPM's with a nice healthy smoke trail leaving the exhaust. Even finer LSN adjustments can made in even smaller incriments to fine tune this setting. Once your satisfied with your overall performance- you can adjust the idle speed ( if neccesary) by using the Idle stop screw. This basically adjusts how far the carb's slide barrel will close. The LSN will affect the idle speed/quality if it's not set correctly- so it is important you're able to achieve and hold a steady idle at the manufactures suggested setting (usually at around 2mm) before making it's final adjustment. Remember- you're not entering a contest which engine can hold the lowest idle speed so just set it to where it's comfortably below clutch engagement to prevent premature clutch wear.

Note: the ability to hold a prolonged and reliable idle is greatly affected by the heat range of the glow plug.. the hotter the better as far as idle quality. As far as high speed/max RPM running- the heat range of the glow plug will affect overall timing advance in which a hot plug might overadvance the timing causing detonation and/or reduced power output- the key is to experiment with something that will give you the perfect balance for overall bashing- cold plugs for tracks with long straightaways and extended high RPM use, and med/hot plugs in tight tracks where lots of decelerating at closed throttle followed by WOT acceleration is performed.

The Midrange adjustment does NOT control an actual needle- nor can it be set rich or lean (LSN shape and design has more of an impact as to how much more gradual fuel flow is allowed through the fuel inlet at mid throttle). It actually controls at what point of the carb opening, the LSN fully leaves the fuel inlet. Since the HSN should typically be set slightly on the rich side- the point at which the LSN leaves the fuel inlet will create a sudden small rush of fuel. This sudden richness can be beneficial to expert tuners by manipulating at what point it occurs in the throttle opening. To adjust the Midrange point, both the Mid and the LSN need to be rotated TOGETHER in opposite directions. In the picture below, this transition point takes place at 1/2 carb opening. If you want the transition point to happen at a later throttle opening- you'll need to adjust the mid range clockwise (deeper) into the carb body while adjusting the LSN counterclockwise in the same amount of turns. If you fail to adjust the LSN at the same time- you will affect your Low speed setting. The opposite holds true if you want the transition to occur at an earlier throttle opening. The affect of the Midrange adjustment is very minimal and is better off being left at the manufacturers base settings.

Remember- there are other factors involved in maintaining and regulating operating temperatures of your engine- while a excessively lean or rich mixtures will affect your overall operating temps- it is NOT the only factor involved. If your engine is approaching excessively hot temperatures while still spewing out lots of raw fuel/oil out of the exhaust due to an excessively rich fuel mixture, there is likely to be another problem with your engine (air leak, too high or too low compression ratio, wrong glow plug heat range, etc). Engines are set up and shimmed at the factory to work in most/average operating enviroments. If you live in an area that is always excessively hot (95F +), it may be neccesary to ADD an addition shim to reduce the compression of the engine to keep everything in safe operating range. If you live in area that are excessively cold year around...you might even want to consider removing the thinnest shim (.1mm) to INCREASE compression or even consider using higher nitromethane content to keep temperatures up where they need to be.

Good Luck!

below is t2boats own guide to tuning.

hiya, i thought we may aswell keep all the tuning info together so here's the other lot:

it's best to tune an engine when it's warm. so start it and let it run for a few minutes (they don't take long to heat up).

the carb settings are unique for each engine, yes, in more or less the same region (number of turns on the screw) but there might be a little difference. i run a few cars, one in particular i can compare as there's another fella on here who has the same truck but uses different settings on his carb and they're the same engine too. for example his truck doesn't run as rich as mine...

if you're having probs trying to set the engine up revert back to the factory settings which are (or should be) written in the instructions somewhere. the engine will still run on a rich setting! not touching the bottom end (really you shouldn't have to touch this needle) gradually screw in the high speed needle by 1/8th of a turn each time

when u hear the car bog down and possibly cut out, it's running too rich

when the car just cuts out, it's too lean

there are a few other points to remember n all:

outside temperature, if it's hot: use a cold plug, if it's mild: use a cool plug, if it's cold: use a warm plug.

now depending on what fuel u are using will depend on what plug you'll need to put in.

using a high nitro content, like 25% fuel would require a cooler plug in order to keep the running temp down, as it burns very hot..however, u also need to consider the outside temp you're running the car in. it's a compromise

once you've finished setting the high speed needle (as you lean the engine out you'll notice the revs are capable of getting higher, but be careful not to go too high) it's time to do the low speed setting.

if there's 2 needles which are opposite one another on the side of the carb, they are low speed settings and only 1 should be adjusted... it's usually the larger brass screw.

leave the truck to idle for about 10seconds then suddenly blip the throttle to full. if the engine bogs down with a delay then it is running too rich. the transition from low speed to high is not good enough. screw in the low end needle 1/8th of a turn and repeat the blip!

should the engine cut out when you blip it, it's too lean, so unscrew the bottom end 1/8th turn and repeat the process

when the engine is capable of being quickly accelerated without any bogging or cutting out then the bottom end is fine, you can then again fiddle with the high speed screw for a better top speed if you wish

little tip for racing: raise the idle speed to just below where the clutch bites, this reduces the time on the starting grid, just a slight rise in rpm and it's away! good take offs..

pls feel free to add any other bits of info you feel may help others out or any problems youve had and how you have solved them. 



Edited by lincsrc
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ultrapeter View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ultrapeter Quote  Post ReplyReply Direct Link To This Post Posted: 09 April 2006 at 9:20pm
very good instructions,i have just run my havocs engine in but in still revs very high when sitting ilde.what do you suggest.

Edited by ultrapeter
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lincsrc View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote lincsrc Quote  Post ReplyReply Direct Link To This Post Posted: 09 April 2006 at 9:30pm

this may be a stupid question but have you adjusted the idle screw to try and lower it or maybe the trim on your controller is set high

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Post Options Post Options   Thanks (0) Thanks(0)   Quote ultrapeter Quote  Post ReplyReply Direct Link To This Post Posted: 09 April 2006 at 9:47pm
trim set low have idle screwn set out.if i set it out more it does not fire up
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lincsrc View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote lincsrc Quote  Post ReplyReply Direct Link To This Post Posted: 09 April 2006 at 10:04pm

at this time of year nitros are harder to start but if you need the wider idle gap for starting then use the trim on the comtroller to open the throttle a little to get it running and then back it off when it is nice and warm and then you can set your idle right.

dont try and get the idle as low as it will go just get it low enough to not engage the clutch and move the truck with the brakes off.once youve got your idle set right you can start to tune for performance.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote newboyaustin Quote  Post ReplyReply Direct Link To This Post Posted: 25 April 2006 at 6:24pm

i got a fusion and when it is idle it spits out a load of fuel, i know coz the ground was wet and now i got a fuel patches on the road, is this normal or does it need tweeking, i've made several adjusts ment but it still seems to spit out quite a bit of petrol,wot should i do

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Post Options Post Options   Thanks (0) Thanks(0)   Quote markjordan Quote  Post ReplyReply Direct Link To This Post Posted: 30 April 2006 at 11:33am
I have a schumacher havoc and it cuts out at nearly high speed what is the reason for this happening 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote newboyaustin Quote  Post ReplyReply Direct Link To This Post Posted: 30 April 2006 at 12:58pm
high speed mixtur needs tweeking a bit, u need to unsrew the high speed mixture!! 1/8 of a turn untill its good!!!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote GBDUO Quote  Post ReplyReply Direct Link To This Post Posted: 30 April 2006 at 7:31pm

Do you have the new exhaust restrictors in your exhaust?  Contact Schumacher as it sounds like you need them!

Graham

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Post Options Post Options   Thanks (0) Thanks(0)   Quote xtr 3e Quote  Post ReplyReply Direct Link To This Post Posted: 30 April 2006 at 9:15pm

I have got the xtr and i have a small problem the engine was set and some one has fiddled with it at my cousins.I need to know the setting to get it running again it runs but then when i give it full throttle it loses power and starts to splutter and not work then cut out.If i only give it 1/10th of power then it works really well wot is happening. can anyone help me?

 

gary

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Post Options Post Options   Thanks (0) Thanks(0)   Quote newboyaustin Quote  Post ReplyReply Direct Link To This Post Posted: 30 April 2006 at 10:25pm
yeah as i said, high speed mixture needs sorting and the low 1 maybe!!!!!!!!!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote GBDUO Quote  Post ReplyReply Direct Link To This Post Posted: 30 April 2006 at 11:24pm

HSN: 2 1/2 to 2 3/4 from fully screwed in 

LSN: 2-3 mm from flush

Idle: 2mm gap

I could have sworn this was answered in the OP...

Graham



Edited by GBDUO
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lincsrc View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote lincsrc Quote  Post ReplyReply Direct Link To This Post Posted: 01 May 2006 at 1:21am
your right mate all the info needed to get your engine running sweet and problem solving is up there to read but is a lot to read at once.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote MATT 06 Quote  Post ReplyReply Direct Link To This Post Posted: 02 May 2006 at 11:28am
WHAT IS THE RIGHT PEAK TO TUNE TO
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Post Options Post Options   Thanks (0) Thanks(0)   Quote GBDUO Quote  Post ReplyReply Direct Link To This Post Posted: 02 May 2006 at 12:51pm

Say what!?

Right peak???

Graham

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Post Options Post Options   Thanks (0) Thanks(0)   Quote blade954 Quote  Post ReplyReply Direct Link To This Post Posted: 21 June 2006 at 1:43pm

Hey guys i just put a picco carb on the TTr .21 with low & high end adjustments, with the option of changing throats in the carby, Its composite and is a direct change over and really helped crispen and liven the TTr .21 up... An easy to tune carb as well..

I was a bit sceptical on the picco due to hearing they are hard to tune and so on but really they are easy to tune, just no as big movments as the ttr carb even 1/2 a mm will make a difference and it holds its tune quiet well...

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Post Options Post Options   Thanks (0) Thanks(0)   Quote mrmaggoo Quote  Post ReplyReply Direct Link To This Post Posted: 26 July 2006 at 7:10am

Hi, I'm new to all this.  Does anyone have a picture of a Thunder Tiger .21 with the screws that need adjusting labled.  I tried setting my car (XTR-3e) to standard last night and now it won't start so I have obviously done something wrong,

cheers

 

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Post Options Post Options   Thanks (0) Thanks(0)   Quote GBDUO Quote  Post ReplyReply Direct Link To This Post Posted: 26 July 2006 at 10:48pm

Hi mate,

These are the best i could find i am afraid!  Most of my pics are with the carbs of for some reason!

http://photo-origin.tickle.com/image/130/7/5/O/130754727O019 056455.jpg

http://photo-origin.tickle.com/image/130/7/5/O/130754785O830 793483.jpg

Sorry about the small size and crapness of the photos!  Basically the screw with the brass surround is the HSN, the one which is huge and perpendicular to the carb slightly below the HSN is the idle and the tiny black screw below the idle is the LSN.

If you scroll up, i have posted the factory settings, do this on each of the needles and it should fire into life.  If it doesn't it is probably something else!  Is your glowheater warm, does your glow plug work, have you primed the engine properly?

Graham

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Post Options Post Options   Thanks (0) Thanks(0)   Quote mrmaggoo Quote  Post ReplyReply Direct Link To This Post Posted: 27 July 2006 at 7:23am

thanks for that mate.  Made the adjustments last night, but I tihnk it was an air bubble in the fuel line that was stopping it starting.  I squeezed it a few time a it started fine.  Where did you get that filter and the aluminium hop-ups from?  Does it make much difference?

cheers

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Post Options Post Options   Thanks (0) Thanks(0)   Quote mrmaggoo Quote  Post ReplyReply Direct Link To This Post Posted: 27 July 2006 at 8:40am
Also, in your description of how the screws are set you said that the LSN should be set 2-3mm from flush.  I can't set mine like this as there is a spring there that stops it going this far in??
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