The Secret of Engine Tuning

Mac

New Member
Messages
4
Location
Worcester
Hi Everyone

I was wondering if anyone could offer me an idiots guide to engine tuning, as I would like to be able to do it myself.

I have recently purchased an FG Baja and its proving a little difficult for me.

Thanks!!

Mac
 

cyclops1970

Well-Known Member
Messages
628
Location
Hamilton Ontario Canada
copy'd from DDM's tech page
How should I adjust the jets on a Walbro Carburetor (WA-167 / WT-603 / WT-668 / WT-257 / WT-813, etc)?
These carburetors require regular adjustment to ensure peak performance, and also to avoid an unsafe lean condition, which can prematurely damage your engine. If you find your top-end RPM's have fallen off a bit, or if you experience lagging or surging, it is probably time to re-adjust the carb jets. To ensure max performance and engine life, follow this procedure:
1) Locate the low and high RPM jets on the side of the carb - they are usually marked with a L and a H. Turn both jets completely CLOCKWISE ( to the fully closed position).
2) Rotate the Low jet counter-clockwise to 1 and 1/4 turns open.
3) Rotate the High jet counter-clockwise to approx 1 and 3/8 turns open.
4) Now, start the engine. You may need to turn the Low jet slightly one way or the other for the engine to start.
5) Adjust the Low jet as desired until the idle is where you like it. Turning clockwise ("CLOSING" THE JET) will produce a higher idle, and counterclockwise ("OPENING" THE JET) will produce a lower idle (and eventually flood and the engine will kill, if you turn it too far).
6) Open the throttle lever to full blast. Adjust the High jet until you get maximum RPMs. Note: this will probably be REALLY LOUD. Listen for the highest-pitched whine to tell you where max RPMs are hit. AFTER YOU FIND THE MAX RPM SETTING, TURN THE HIGH JET COUNTER-CLOCKWISE ("OPEN" THE JET) APPROX 1/16TH OF A TURN TO ENSURE YOU HAVE SUFFICIENT GAS/OIL MIX TO COOL THE ENGINE PROPERLY.

Note: The above are just general guidelines. You may need to adjust both the H and L screws once you begin driving, depending on engine loading, altitude, humidity, etc. The trick is to find settings that work well for you, and stick with them.

Here is some helpful information regarding common carburetor tuning problems:

If your engine stutters at full throttle and cannot reach full RPMs:
The high jet is too far open. Close the jet by turning it clockwise slightly, and then ride-test. If no improvement, repeat until desired results are achieved. Once you have found a workable setting, open the jet approx 1/16 of a turn to ensure sufficient fuel/air mix.

If your engine bogs out when transitioning from low speed:
The high jet is too far closed. Open the jet by turning it counterclockwise until you are at least 1 1/2 turns open, and then gradually close the jet until performance is as desired. Poor engine compression, blocked exhausts, and very heavy engine loading can all also cause bogging.

If your engine idles very fast and kills if you attempt to slow the idle:
You may have an air leak in your intake. An easy way to check for leaks is to spray the intake manifold and area surrounding it with WD-40. If the idle changes after you spray the WD-40, there is an air leak. Common areas for leaks are between the manifold and the cylinder, and between the carb and the intake manifold. Inspect the manifold, carb gasket, and intake gasket for cracks or other signs of damage, and replace if necessary.

If your engine idles but then slowly kills:
Your low jet is too far open. Close the low jet by turning it clockwise until a stable idle is achieved.

What are the recommended carburetor needle settings for my engine?
DDM recommends the following tuning as a STARTING POINT for tuning your engine:
G230RC / G260RC / CY23RC / CY26RC / CY27RC / CY29RC / GP290 engines: 1 and 1/4 L, 1 and 3/8 H.

and link http://www.davesmotors.com/rccar-faq.htm
 

Timmahh

Bajastafarian Madnes
PLUS member
Messages
3,374
Location
Michigan
here is the tuning sheet you would get if you purchased an ESP modified motor.
Doug has wrote up a very very good tuning guide. this is how ive been tuning for a long time. it works very well, and if you keep up with maintenance and checkups. the motor should last a long time with only a periodic ring change.

Keep in mind that the low speed flows fuel from zero to about 1/3rd throttle opening. The high speed jets starts flowing from about 1/3rd throttle open to full throttle. Both jets flow fuel above 1/3rd throttle.
Set the high speed jet at least 2 turns out from bottom to start. Set the low speed jet at about 1&½ turns out. Warm the engine on the stand for a few min, rev the engine on the stand a bit while rough setting the low speed jet for idle to rev throttle response. Close the low speed too far, and the idle goes up from a lean condition. Open the low to far and the engine will run rich and die. Stay on the rich side, but make sure throttle response from idle is good. Continue to rev the engine above half throttle, but not holding it in any one position for the last few min, to run the engine with the high speed jet flowing. Shut it down, and check the plug color. The plug should be a dark color like a dark brown or black. The rich settings we start with could possibly foul a spark plug, so you might want to have a new plug or two on hand for tuning. This plug color is good for now, it means we are getting plenty of fuel--at least on the stand.
Now, it is time to run it and tune the high speed jet. Remove any body parts, or roll cage parts you need in order to access the plug easily. You will want to keep a plug wrench and a glove (that plug will be hot) in your pocket while you are out in the field tuning, You want to be able to access your plug easily. Run the Buggy. Run it for 10 sec min, at about ½ throttle after it is warmed up, and stop it at your feet. Quickly shut off the engine, and check the plug (don‘t let engine idle or use lower RPM‘s so the plug won‘t darken, and give you a false reading). If it is still dark in color, that is good for now. Now run the buggy again and use a little higher RPM. Check the plug again. Repeat while creeping up on full throttle, and check the plug often. Keep doing this until you are checking the plug with full throttle runs (you will need a lot of room), and the plug hopefully is on the dark side. If the plug is white, or light in color at any RPM, and you cant get a safe color to it by turning out the HS jet (over 2 turns out approx does not make any difference on the jet), stop running the engine. You most likely have a air leak or a dirty carb/filters, which can also cause a lean condition and damage the top end. If the plug is still dark after your going full throttle, you should be safe. You can start leaning out the high speed jet until the plug is a nice med chocolate brown color AT FULL THROTTLE. After that is done, you can fine set the low speed jet for best acceleration. Going richer on the low speed usually helps the jump off the line, but the idle may suffer.
Note- Make sure you use a tacky filter oil for the air filter or you will suck in dirt. A “Tacky foam air filter oil” can be purchased at any dirt bike shop. Fully saturate the filter element, and squeeze as much oil out of the filter as possible with paper towels. It makes no sense to tune the carb with a dirty filter, so use a clean one.
hth
Timmahh
 
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hellya

Well-Known Member
Messages
346
Location
washington
I run colmane and my plug barely change colors..its still nice and shinny, almost......:) 7 tanks later
 
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Timmahh

Bajastafarian Madnes
PLUS member
Messages
3,374
Location
Michigan
I run colmane and my plug barely change colors..its still nice and shinny, almost......:) 7 tanks later
ya, colemans is so much cleaner burning than gas, regardless of oil used. its not surprising it has very little deposits left behind.
been thinking of giving it a go.
 

Timmahh

Bajastafarian Madnes
PLUS member
Messages
3,374
Location
Michigan
fwiw pip,, the guide i posted is done on the first start of a new motor.

the guide and tuning sequance is the brakeing. once your done with this tuning guide (about 10 to 15 minutes worth of actual run time) just run it.
 

pipeous

Well-Known Member
Messages
3,269
Location
Surrey, BC, Canada
that's cool. I always seem to take the long route and follow the ONB break in method but it's hard to burn off 3 tanks of fuel at half throttle or less as it takes forever.... though I have never broken in a weedwacker or my leaf blower and they run 40-1 mix.

I am stepping out of the comfort zone and trying something new so that's a big step for an old fart that doesn't do change well LOL (I still break in nitros on the box too ;) )
 

Thunder9000

Member
Messages
10
Location
oneida
don't forget

its very important to keep the air filter clean and properly oiled,doesn't matter what other improvements you do if dirt is getting sucked in.
 

sickboy

Well-Known Member
Messages
938
Location
Netherlands
Hi yes you will have to re-tune the carb but if you don't learn now you will never get the hang of it just read the above and you will eventually get to grips with your carb and once you get the hang of it there no more to think about
 

kryptonite5b

Well-Known Member
Messages
534
Location
philipsburg pa.
I don't know where to post it but, here it goes. I am running a fuelie motor with the stock muffler, I now put the performace pipe on, do I need retune the engine? I really don't like messing with carbs.
yes you do, but you don't have to start all over. i just get it warm and adjust the high speed needle as needed.
 
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