flyday58 Posted March 21, 2012 Posted March 21, 2012 Heidi, The DT is doing pretty well these days, just a few issues. One of these is that under leisurely acceleration, she kind of sputters along, always increasing revs but acting like I just woke her up and she's reluctant to respond to my gentle carress. Ooh. If I insist and dial on the throttle, she responds willingly, indeed, voraciously with no hesitation. Clean, smooth, robust acceleration. The original carb died from varnish cancer, so the one I have now is one of those ebay $40 specials, ostensibly for my model. I did install the correct slide and needle, which survived the old carb and the clip is in the correct position. I wouldn't think my woes are electrical or cdi in nature, given the performance when I wrap the twisty-thingy to go fast. Throttle. Couldn't remember for a sec... Also cruising at 30, 40, 50 mph is sputter-less unless I feather the throttle. Also also, mine doesn't idle nearly as smoothly as oldbikerehab's does, and if I adjust the idle much below 1500 it will bog and die. Played with the idle air screw but standard to 1and a half turns works best. Also also also, after riding a bit then coming to a stop, idle will be around 2000 rpm, then drift down to 1400-1500 after 10 to 20 seconds, sometimes revving a little to 1600 on its own before decreasing again. I've looked for air leaks around the carb, reeds, crank, cylinder. Do to the wonderful ETHANOL MANDATE in this country our petrol is not it's all cracked up to be, but I saw a station down the road today advertising 100% petrol, no ethanol, so that's what I will put in the tank for the forseeable future. So. Ideas on my sputtering? Should I try to procure an OEM carb? Anything I might have missed?
Moderator Airhead Posted March 21, 2012 Moderator Posted March 21, 2012 morning Richard Have you set the air mixture screw? screwed too far in it should give a rough lumpy idle, too far out should cause the engine speed to increase and be smoother, the right place to be is just where the roughness disappears. if it doesnt follow this pattern then the pilot jet size should be re-selected based on what you find how bad is the original carb? I have an ultrasonic cleaner and compressed air available, if you want to send it me i'll have a look-see?
flyday58 Posted March 21, 2012 Author Posted March 21, 2012 morning Richard Have you set the air mixture screw? .screwed too far in it should give a rough lumpy idle, too far out should cause the engine speed to increase and be smoother, the right place to be is just where the roughness disappears. if it doesnt follow this pattern then the pilot jet size should be re-selected based on what you find Played with the idle air screw but standard to 1and a half turns works best how bad is the original carb? I have an ultrasonic cleaner and compressed air available, if you want to send it me i'll have a look-see? The original carb died from varnish cancer Hey Paul, As you see, the air screw is pretty much spot on, altho I will check it again. The varnish in the carb combined with what I can only assume is the ethanol-based petrol available here caused what looked like intergranular corrosion within the float chamber. One of the pillars holding the float pin broke off, so really there was nothing salvageable. I could have removed the jets, but I tossed it before joining this forum with all the excellent info available. Had I known I would have removed the jets, at least. I just returned from the petrol station down the road with a 5-gallon can full of no-ethanol 87 octane petrol. I drained the old stuff and added the new, but had to get under cover due to severe weather moving in. I don't think it will impact the sputtering but at least it should cut down on corrosion of my metal parts. Also going to purchase some of that see-thru vinyl tubing for the fuel and oil lines so I canobserve my petrol and lube oil status. Great idea. If I figure out how I will post a short vid of the sputtering I mean. Maybe it's just a two-strokeism...
flyday58 Posted March 22, 2012 Author Posted March 22, 2012 Upon further review... Tried a few things this evening after the weather calmed down. Too many things, actually. 1. Drained the fuel tank and refilled with the non-ethanol stuff. 2. Replaced the correct slide and needle from the old carb with the set that came with the after-market carb, thinking that maybe the makers had it right. I could not get the thing to idle without turning the idle set screw almost all the way in. Air mixture screw made no diff whatsoever except for 4 or 5 turns out, then she stalled. So back with the salvaged slide and needle with the correct cutaway and proper part # on the needle. I tried one step rich, then one step lean, bike just wouldn't idle. So needle clip back on 3. Revs don't want to decrease back to idle. After revving in neutral to about 5000, revs drop to 3000 then only slowly taper off to 2000. If I set the idle screw to 1500, she stalls after a few seconds. Kicker: I took it for a spin up the road anyway. No sputter. Just smooth acceleration. only letting off the throttle she won't slow down because the revs hang at 3000. It reminds me of how it acts when the fuel tap is off and it's starving for fuel. Yet hard acceleration was perfect. Bugger. I am going to look again at the posts explaining the different parts in the carb that perform at different throttle settings to see if I can figure this out. I will also put the old petrol back in and see how she runs. I will probably disassemble the carb this weekend to cover all the bases. I love this stuff!
flyday58 Posted March 22, 2012 Author Posted March 22, 2012 Upon even further review... In looking at what I bought on ebay, the carb I purchased was generic covering years 1976 to 1981. So I'm thinking the jets, slide, needle, float height, etc. are all just "close enough". Guess I'll start fishing for a 2A7-specific model. Thought 40USD was too good!
Moderator Airhead Posted March 22, 2012 Moderator Posted March 22, 2012 can you fit the pilot jet from your old carb into the new one, sounds to me like the pilot is too small in the new carb there is a number stamped into the jet, something like 22.5, 25, 27.5 etc...you need a bigger one than the one fitted, be very cautious about lowering the needle you may make it run lean...ohh it will feel ok but it may begin to overheat and risk heat seizures and other nasties
oldbikerehab Posted March 22, 2012 Posted March 22, 2012 Heidi, The DT is doing pretty well these days, just a few issues. One of these is that under leisurely acceleration, she kind of sputters along, always increasing revs but acting like I just woke her up and she's reluctant to respond to my gentle carress. Ooh. If I insist and dial on the throttle, she responds willingly, indeed, voraciously with no hesitation. Clean, smooth, robust acceleration. The original carb died from varnish cancer, so the one I have now is one of those ebay $40 specials, ostensibly for my model. I did install the correct slide and needle, which survived the old carb and the clip is in the correct position. I wouldn't think my woes are electrical or cdi in nature, given the performance when I wrap the twisty-thingy to go fast. Throttle. Couldn't remember for a sec... Also cruising at 30, 40, 50 mph is sputter-less unless I feather the throttle. Also also, mine doesn't idle nearly as smoothly as oldbikerehab's does, and if I adjust the idle much below 1500 it will bog and die. Played with the idle air screw but standard to 1and a half turns works best. Also also also, after riding a bit then coming to a stop, idle will be around 2000 rpm, then drift down to 1400-1500 after 10 to 20 seconds, sometimes revving a little to 1600 on its own before decreasing again. I've looked for air leaks around the carb, reeds, crank, cylinder. Do to the wonderful ETHANOL MANDATE in this country our petrol is not it's all cracked up to be, but I saw a station down the road today advertising 100% petrol, no ethanol, so that's what I will put in the tank for the forseeable future. So. Ideas on my sputtering? Should I try to procure an OEM carb? Anything I might have missed? I have the same generic carb unmodified on my DT and have the same sputter in first and second gear. Once I'm out in the powerband I don't really notice it. I have my idle set around 1,400-1,500 and noticed yesterday that it likes to climb to 2,000 at stop lights like yours as well. Mind doesn't die with the idle below 1,400 but it sounds like it's on the verge so I keep it a little high and tbh, I haven't really left it below 1,500 to find out. When one of the mechanics dialed in my carb at the bike shop, he was mumbling and counting, and at one point said that the adjustments on the generic weren't quite what he remembered for the Mikuni, but it sounds like you've worked the air and throttle screws. Btw, my throttle screw is in almost all the way, much tighter than the Mikuni when I bought the bike, and the air screw is out about 4 1/2 turns, waaay more than the 1 1/4 recommended. I did notice a slight improvement after refueling with pure gas and gapping my plug to max spec. The rain has settled in here for the next few days so I won't be doing any more experiments for a bit but I'll keep you posted and keep an eye on what you discover. Other than the fact that we are both using the same aftermarket carb, I wonder if the fact that we both have lowered our final drive gear ratio with sprocket modifications could be causing sputtering in lower gears? It is kind of like we are starting out in 2nd or 3rd gear. But that wouldn't explain your idle troubles .
flyday58 Posted March 22, 2012 Author Posted March 22, 2012 Other than the fact that we are both using the same aftermarket carb, I wonder if the fact that we both have lowered our final drive gear ratio with sprocket modifications could be causing sputtering in lower gears? It is kind of like we are starting out in 2nd or 3rd gear. But that wouldn't explain your idle troubles . My sputter was there before I changed sprockets, so I'd have to link it back to the carb. My idle set screw is nearly the same as yours, while the air mix screw I just left at 1 1/4 because it didn't seem to make any diff. To me it sounds like it's running lean at idle, but it's fine as I throttle it up. From the tech description in the Haynes UK manual, it's all tied to the pilot jet, so if I can today I will disassemble it and look at evrything with focus on the pilot jet. I may just chalk this one up and get an OEM carb.
oldbikerehab Posted March 22, 2012 Posted March 22, 2012 I sure hope that pilot jet works out for you. Otherwise that means I'll have to start looking into rebuilding my Mikuni asap since I won't be able to make the summer knowing there's a box of increased performance sitting idle in my shed.
Moderator Airhead Posted March 22, 2012 Moderator Posted March 22, 2012 My sputter was there before I changed sprockets, so I'd have to link it back to the carb. My idle set screw is nearly the same as yours, while the air mix screw I just left at 1 1/4 because it didn't seem to make any diff. To me it sounds like it's running lean at idle, but it's fine as I throttle it up. From the tech description in the Haynes UK manual, it's all tied to the pilot jet, so if I can today I will disassemble it and look at evrything with focus on the pilot jet. I may just chalk this one up and get an OEM carb. if you set your idle to the slowest you can get away with (hopefully 1500), then start turning your air screw in (clockwise)...this should start enriching the mixture and at some point the engine should start to stumble. If you find you can turn it to less than 1/2 a turn fron closed without causing a stumble then clearly the pilot jet is too small and incapable of enrichening the mixture enough...change it for a bigger one (they are cheap so buy the next two larger sizes)
Moderator Airhead Posted March 22, 2012 Moderator Posted March 22, 2012 or you could invest in one of these, you can see the colour (yes thats 'colour') of the combustion and you are looking for a blue flame yellow= rich, blue = good to go, white = lean (very bad) Gunsons colourtune or i send you mine to heathrow workshop?
flyday58 Posted March 23, 2012 Author Posted March 23, 2012 So disassembled the aftermarket made in ????? carb. Took some pics. First up: let's play 'Find the main Jet". Second: the idle air mixture screw: Third: the needle jet was not run all the way down. This is just a quality unit. The internal design of this thing is not like a Mikuni. Decided to go back with the needle and slide that came with it, but made a few msmts first. The needle that came with is long, slender and pointed. The Mikuni is shorter, wider and blunted at the end. The needle that came with is 1/16" longer than the Mikuni needle. The slide I can't see any diff. I compared it with the Mikuni 2.5 and a 2.0 I ended up with, and cannot see how they differ. I know they must, but I ain't seein it. Also found the old carb that I just KNEW I'd tossed (guess that makes me a tosser...). 2 pics: Whither the air screw? So oldbikerehab, whaddaya think?
flyday58 Posted March 23, 2012 Author Posted March 23, 2012 The needle jet I had removed in the 2nd pic...
oldbikerehab Posted March 23, 2012 Posted March 23, 2012 Honestly, I couldn't spot the air screw on your carb at first since it looks like yours has been stored in a bucket of grease and mud! LOL But it did get me to dig my Mikuni out to assess its condition and was yet another reminder of how much abuse these bikes and still be brought back from the dead. I'm sure under all that gunk is a much better carb than the knockoff. You might just be down to some elbow grease and a few (more) tiny parts to be ready for the races! I probably won't get back to much in depth wrenching or carb rebuilding for a few weeks when my new throttle cable comes in. I'll be following your lead to see how things work out though.
Moderator Airhead Posted March 23, 2012 Moderator Posted March 23, 2012 So disassembled the aftermarket made in ????? carb. Took some pics. First up: let's play 'Find the main Jet". Second: the idle air mixture screw: Third: the needle jet was not run all the way down. This is just a quality unit. The internal design of this thing is not like a Mikuni. Decided to go back with the needle and slide that came with it, but made a few msmts first. The needle that came with is long, slender and pointed. The Mikuni is shorter, wider and blunted at the end. The needle that came with is 1/16" longer than the Mikuni needle. The slide I can't see any diff. I compared it with the Mikuni 2.5 and a 2.0 I ended up with, and cannot see how they differ. I know they must, but I ain't seein it. Also found the old carb that I just KNEW I'd tossed (guess that makes me a tosser...). 2 pics: Whither the air screw? So oldbikerehab, whaddaya think? so with the new carb i cannot see a main jet fitted...is there no screw thread below the needle jet? and the old carb air screw, it should be to the right and lower than the idle speed screw, can i see it under that crud? heres ours over here in UK, I checked the DT175E parts list and it's just the same by the look at it...see item 17
2 Wheels Posted March 23, 2012 Posted March 23, 2012 I would clean up the old carb and reinstall it,,,get new jets and whatever esle you need for it. That aftermarket carb looks like a toy one. Just my thaughts
flyday58 Posted March 24, 2012 Author Posted March 24, 2012 The old carb is no more. Bereft of life, it rests in peace. This is an un-carb. If I hadn't lifted it from the rubbish pile it would be pushing up the daisies! Sorry, lost it for a mo. Sadly the inside of the old carb disintegrated due to a mixture of old gas and water intrusion, perhaps from ethanol in the fuel. I've got the correct one on the way, should be here when I get back from the Far East late next week. Sir Paul, there is no main jet in the float chamber, as the pic shows, or rather, doesn't. Yes, the air screw is hidden beneath the crud on the old carb. This is the unit that I earlier said I no longer had. Turns out it was in the rubbish pile with the rusted stuff I couldn't salvage when I started this project, which, BTW, was back in 2001, not four or five years ago, like I thought. Honestly don't know where the time has gone. I run and I run to catch up with the sun but it's sinking... Oldbikerehab, it would probably be worth it to at least remove your air screw and check the condition of the o-ring. You see what mine looks like!
Moderator Airhead Posted March 24, 2012 Moderator Posted March 24, 2012 2001! and then one day you found...ten years had got behind you
flyday58 Posted March 24, 2012 Author Posted March 24, 2012 2001! and then one day you found...ten years had got behind you I was home 6 weeks straight after 9/11 and needed something to do, so I went to the junk yard and found this DT175. Called last week to see if they had anything like that anymore, but the place has changed hands and the guy evidently cleaned out the older stuff. Every year is getting shorter, plans come to naught, and so on. Today the toy carb (Thanks, 2 Wheels!) started dripping petrol from the bowl overflow and is also hanging on the corner of the bowl with the bike resting far to port on its side stand. There was no literature with the carb so I don't know the correct float height. Given the internal construction I wouldn't bet the Queen's knickers that the Mikuni settings would work. Will wait for the OEM unit to arrive instead of futzing with this one. I also discovered the engine won't rev over 6500 under load. It starts to break up a little and kind of acts like it has a governor built in. Again, hoping this is all due to the carb. I did go back to the ethanol-based fuel. The sputtering is more pronounced but the idle stopped hunting. Still won't idle for long at 1500, but that could be up to the o-ring on the air screw. Will continue this saga when the new(old) carb comes in. ALBATROSS!
Moderator Airhead Posted March 24, 2012 Moderator Posted March 24, 2012 yeah sounds pretty carb related, probably way too rich gives a kind of 4 stroking feel... a firing of every two revolutions
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