kiln

Thanks Cynic. This post provided more answers than what you could have imagened.

1="broken"=slightly dressed with a file to broke the sharp knife edge. 2=I do have the old piston and they both match except for the transfer ports on the piston skirt. And so the plot thickens with an answer and weird solution and a question. Allow me to elaborate.I have 3 carbs:A)old dt 125 carb B)new chinese carb and C)new mikuni carb. A) and C) gave the same results (bogs down and cannot idle even with idle screw fully turned in) but only B)works. Turns out that carb B)is a Keihin knockoff with an interresting setup: 5G4 Jet needle,O-2 Needle jet, 160 main jet,25pilot jet.This is exactly what is listed in this thread: (Thanks Cynic) listed for a Yamaha DT175A/B. Bike idles easily, can be adjusted and the idling goes up when choke is pulled. Maybe I will go leaner to 140/150 main jet, still need to test ride further. So my thinking is this:Order a 5G4 jet needle and O-2 Needle jet for carbs A) and C) and have 3 working carbs rather than only one chinese carb. Which brings me to the following question:Where to buy these items from and import them to South Africa? All suggestions welcome.

Piston got damaged when a bottom ring broke on one of the transfer port edges. I have subsequintly ever so slightly broken the sharp edges of the transfer ports that might have caused the ring to broke. I only had this Wiseco piston to run with, whilst I am waiting on a replacement from Yambits, 20 days delivery. I do not think the porting is an issue though since many recommended it here and on other forums.That is why I suspect that I must live with the no idling untill I can install the proper piston.I thought maybe someone else also had a similar experience.

I will change back to the original carb and post findings when I have done that.I changed it because i suspected it to be worn too much for it to idle properly, now it is the same with the new carb which is why I suspect the piston design, do you know if it is an "AHRMA" design?

It has run and when ridden, no problem, 96km/h, Ijust cannot get this setup to idle though. i have tried 22.5 and 25 pilot jet, no success.

I humbly appologise Oldgit.It is a 1979 DT 125. Standard barrel and standard piston size,used but rings end gap still within tolerance.Compression tested at 92PSI.As mentioned earlier piston is a Wiseco with halfround open port on piston skirt,previous "new" piston with twin port broke a ring near the exhaust port thus installing the Wiseco that I recieved with the barrel off a purchase made in the US.I have opened the exhaust port a little and polished it with a Dremel.Carb is a new Mikuni replacement from Japan and behaves exactly the same as the previous original Mikuni.Easy starting,no idling and idle screw screwed in fully. Intake rubber new without any leaks, tested with carb cleaner sprayed. Any suggestions or should I strip down the bottom end?

Houston, we have a problem....After setting up with a pilot jet of 25,main jet of 140 I am unable to get this bike to idle. Idle screw fully turned in, air screw 1.5 turns out warmed up and no idling on its own.Maybe it is the Wiseco piston in the bike, it does not have the twin ports on the skirt but rather a half round entry point. Would it be better to get a piston with the long twin ports? I have opened the exhaust port a little and polished it a bit, could this be the cause of the engine not idling? Carb is new & clean with k&n air cleaner in the air box and Booyesens reeds.Premix is at 33:1, i.e. 30ml/1liter fuel. Thanks for the input in advance.

Hope the following "Mikuni Jetting" info will be of assistence: To summarise various parts of the carb work as follows: From cold, closed to 1/4 throttle, choke and idle jet. When started, closed to 1/8 throttle idlejet and air screw. 1/8 to 1/4 throttle, slide cutaway. 1/4 to 3/4 throttle, needlejet (atomiser) needle position and taper of needle. 3/4 to full throttle, main jet and power jet if used. NOTE: The power jet only works when the engine is revving flat. All it does is allows a smaller main jet to be used which weakens off low down carburation. The power jet substitutes the main jet size when the engine is revving high. Both main and power jet should add together to a normal main jet size. Below is a more comprehensive and definitive guide to jetting your carb. JETTING - Getting the most out of your bike By Don K. Courtney For whatever reason it becomes necessary to re-jet a carburetor, it is without a doubt a nightmare if you do not have a procedure to follow. The following is nothing more than a technique, procedure, steps or whatever you want to call it to help identify and isolate the carburetor circuit involved. You can only begin re-jetting your carburetor if the following conditions are met: 1. Top end is in good condition. 2. Bottom end is in good condition. Crank seals. 3. Spark plugs, air filters, reeds and so on. If your bike's motor is not mechanically sound, then all the jetting in the world will not help. With all of the above conditions met, you should be able to jet your carburetor following these steps: Step 1: DETERMINE THE CORRECT NEEDLE AND OR NEEDLE JET. Whether or not your carburetor is a MIKUNI or a KEIHIN, it does not matter. This is the most important step in jetting your carburetor--period! 1. Remove the main jet. 2. Place needle clip in mid-position. 3. Start motor and run it on the stand. Condition: Motor running and main jet out. Needle or needle jet is correct: Carburetor should run clean to approximately 3/4 throttle. From 3/4 throttle to full throttle, the motor should start to break up as a result of too rich condition. Correction: None needed. Condition: Needle or needle jet is too rich. Carburetor runs clean to approximately 1/2 throttle but breaks up before 3/4 throttle as a result of too rich condition. Correction: Mikuni replace needle jet with next leaner and test again. Keihin replace needle with next leaner diameter and test again. Condition: Needle or needle jet is too lean: Carburetor runs clean beyond 3/4 throttle and has an erratic throttle response. Correction: Mikuni replace needle jet with next richer and test again. Keihin replace needle with next richer diameter and test again. The emphasis here is to find the correct needle or needle jet diameter, which will allow more fuel to pass than is needed but not so much that the needle itself has no control below 3/4 throttle. Step 2: DETERMINE THE CORRECT PILOT JET. 1. Make sure the bike is warmed up if at all possible. 2. Main jet out. 3. Needle clip in mid position. 4. Turn air screw all the way in then 1/4 turn out. 5. Start motor and run it on the stand. 6. Adjust idle so the bike will just barely idle. Condition: Motor running and main jet out. PILOT JET CORRECT: With one hand on the throttle maintaining RPM at approximately 1/8 throttle, turn air screw 1/4 turn at a time clock wise until you bottom it out. Motor should become slightly erratic and you should have to play with throttle to maintain RPM. Start turning air screw counter clock wise, 1/4 turn at a time until you have reached 2 3/4 turns out. Between 1 1/4 and 2 1/4 turns, your motor should have reached its highest RPM maintaining a steady throttle. Adjust air screw again between 1 1/4 and 2 1/4 until you have determined highest RPM. Quick throttle response should be clean without bog. PILOT JET TO RICH: RPM does not reach a peak between 1 1/4 and 2 1/4 turns, stays the same or keeps rising out to 2 3/4 turns. Correction: Mikuni replace pilot jet with next leaner and test again. Keihin replace pilot jet with next leaner and test again. PILOT JET TO LEAN: RPM does not become erratic and motor maintains throttle when air screw is turned all the way clockwise. Correction: Mikuni replace pilot jet with next richer and test again. Keihin replace pilot jet with next richer and test again. Remember, with a steady throttle approximately 1/8, there should be a distinct difference in RPM from 1 1/4 turns to 2 1/4 turns if the pilot jet is correct. The emphasis here is to find a pilot jet that will run crisp without bog and without the main jet. Step 3: DETERMINE THE CORRECT MAIN JET. The main jet selection process is easy once you have the correct needle diameter or needle jet. You now only have to correct a rich condition from 3/4 throttle on up and you know what a rich condition sounds like. Your pilot circuit is correct and without bog. 1. Replace main jet with one that is at least two sizes smaller. 2. Needle clip in mid position. 3. Start motor and run it on the stand. By replacing the main jet with one that is too small, you are looking for a condition that is too lean. You adjust your main jet from a too small to lean condition. Condition: Motor running and main jet in. MAIN JET CORRECT: Carburetor should run clean and crisp to full throttle. Correction: None needed. MAIN JET TOO RICH: RPM reaches a peak slowly with a deep sound. Excess fuel and oil mixture at end of silencer. Spark plug fowls easily and is dark in color. Correction: Mikuni replace main jet with next leaner and test again. Keihin replace main jet with next leaner and test again. MAIN JET TOO LEAN: RPM reaches a peak quickly but erratic. A quick full snap open of throttle causes the motor to hesitate BEWAH sound or a complete bog. Motor sounds like it has a ring to it. End of silencer white. Spark plug is white in color. Correction: Mikuni replace main jet with next richer until the BEWAH bog just barely goes away, then replace the main jet with the next richer and run it. Keihin replace main jet with next richer until the BEWAH bog just barely goes away, then replace the main jet with the next richer and run it. The emphasis here is find a main jet that is just rich enough to allow you snap the throttle wide open without the motor bogging as a result of the main being too lean. Should be a quick crisp throttle with no hesitation. Step 4: DETERMINE THE CORRECT NEEDLE TAPER AND CUT AWAY. This step in the jetting process can be made very simple if you remain close to stock. However, your needle taper is adjusted for 1/2 throttle to 3/4 throttle. Start off with a rich taper (shallow taper angle) and keep going leaner (steeper taper angle) until it will not maintain constant RPM at 1/2 throttle (runs erratic). Go back to the leanest taper angle that ran the smoothest at 1/2 to 3/4 throttle and that should be the correct taper. The needle taper final test should be under track conditions with the greatest effect entering and exiting corners. Do not change the needle diameter or needle jet size during this process because that has already been determined. Adjust taper and throttle cut away only. Throttle cut away effects from idle to 1/4 throttle. The correct cut away will maintain steady 1/8 throttle with quick throttle response. Generally the stock cut away is very close. Experiment with different cut away until it maintains the best response to 1/4 throttle. QUICK TIPS: Keep it simple, buy the optional OEM needles or needle jets that are available, as this may speed up the taper selection process. Don't skip any steps or you're just guessing. FINAL THOUGHTS: That's it, if you spend the time jetting correctly, the benefits you will gain definitely out-weigh way the time spent. Take the guesswork out jetting by following a procedure that has been given or one you have laid out yourself. Keep the black magic process out of your tuning tricks and you will be better off for it.

Hello again all.I am very curious if anyone by chance would know what size the o-ring is that fit over the crank on the clutch side, the one underneath the primary gear bush? ID=? Thickness=?

Clive: Try to install a #25 pilot jet and #150 main jet. This solved my exact same problem m8.

Thanks Nev.I am fairly sure the back box is clear since it is homemade, i.e double pipe design-top in-bottom out, sort of a free flow type. I have been running rich for about 600km.

1 US Gallon = 3.785412 Liter 1 UK Gallon = 4.546092 Liter 1 US Liter = 1 UK Liter

Thanks 2-wheels. I just love how this bike takes to the open road in top gear. "Top Gear"...."2-wheels"...sounds like a very nice combination.

I must admit, 20:1 sounded awfully rich but then again isn't that lubrication all that is available for the crank & conrod bearings... Keeping that in mind I ran with that ratio and in hindsight, I now see the consequences of that methodology. I will reduce the jet size in conjunction with a ratio of 40:1 and report on that experiences after the weekend. Thanks again for all the feedback. Is there any favourite of gasoline type to use on our type bikes? I.E. Lead replacement or Unleaded fuel.

Thank you for your comments thus far. Oldgit:The plug chop was done after riding wot for about 1km or so, so the only other thing would be to look at the premix ratio which I had at 100ml/2l (20:1) Nev:I am familiar with the ratio program and thus ran with a mix 100ml/2l (20:1)as suggested on Dan's website.However looking at what you and Oldgit suggests: either 67ml/2l(30:1) or even 50ml/2l (40:1). Any other suggestions on Pre-mix ratios? What does the rest of the DT175/Dt125 enthusiasts use on a daily basis as a Pre-mix ratio?

Hi, This is directed to either oldgit/neo/cynic/anyone with experience on the topic Is it normal for carbon to form a layer on the head and piston crown within 600km of operation? Could it be that a)premix as at 20:1 is too much oil-plug chop revealed medium brown color,what should premix ratio be for a DT175? b)Main jet too large=160, idle jet=25-Normally main jet=140, idle jet=22.5 c)Unleaded fuel to be used rather than Lead Replacement Fuel Any advice on above welcome.

Looking at the crank on the clutch side, does anyone know the size of the o-ring between the bearing and gear spacer?

Hi there Oldgit.Did this mod make any significant change in performance? Does the air chamber need to be an exact size related to engine cc? Sure hope this will give a "powerband" to my dt175. Regards

Oldgitonabike:>Do you perhaps have more info on the exhaust porting bit, i.e. more pics on the procedure and more info on possible performance gains/losses after porting is done? Maybe a "Porting Post" please? Regards Kiln

Hi, If you wanted to convert to a 12v system, Ne0 have provided a workable solution in this post: Project Firefly It works really well and it is very easy to fit.

NE0, I just finished with the conversion! What a great success! Driving at night now is a pleasure and I can venture further after work without the fear of darkness catching up with me. Thank you so very much for the relevant info and I am sure that every DT owner out there would benefit from such a conversion as it is extremely easy and affordable to fit. Keep up the good posts! P.S. Can this post be "Pinned" in the Yamaha Workshop Forum please?

NE0, If at all possible, please include picture of the connectioins into the loom.I looked around on the net and I see aome inexpensive 12v regulator/rectifiers with 5 wires available for mainly the chinese GY6 engines.Only trouble is which wires are incoming and which are outgoing and how can this benefit us...(Wire colours are yellow,pink,green etc. I can't wait till the weekend as I would love to apply these alterations as soon as I have a chance. Thanks again for all your knowledge and research made available for all.

Great stuff Ne0! This exactly what I was looking for!I highly suspect my problem also lies with the 6v rectifier and seperate 12v regulator.Can you please give me direction to a model of 12v regulator/rectifier I can search for on eBay or even Yambits? Maybe you can include model or part numbers available in a project pdf download after the whole write up is complete? I can't wait for episode 6...sorry part6 etc.

Please let us know how it worked out for you.

Welcome NEO(belated)Indeed you have two very nice bikes, each with their own qualities.