flyday58

Okay, what's the CORRECT redline for a '73 RT3 tacho? Even pics of bikes on the internet vary.

Cold and wet here, too, but Sunday night. Been up about 24 hours now so going horizontal soon. Will look up those two sites when I wake up in about 7 hours, thanks for the links, Paul. 2Wheels, you're my kind of nutcase! I appreciate the humour from the proper side of the Atlantic.

I am currently running it on non-ethanol petrol, 87 octane. But I still think today's formula differs from 30-40 years ago. What time is it over there, shouldn't you people still be in bed? It's 1822 Sunday evening here in Tokyo/Narita...

Float height checked and double-checked at 21mm. Just put a new #140 main jet in, pilot jet is also the recommended one. Will lift the needle when I get home Tuesday. Do you think the extra bore is requiring more fuel? Maybe today's petrol is formulated to burn hotter to burn more completely to save our little planet? Apparently this set-up worked in '78 but not '12.

Inclined to go with 2 Wheels' interpretation! Don't I wish... That's what I came up with also: too lean, too hot. I deliberately left out the high heat - I had to test y'alls savvy. Well done, all! So. The carb is stock, has all stock parts. The cylinder and piston are .50 over, so bigger jets nessa? Still can't get it to idle like I want, it's fine around 1800, but one tiny fraction more and the idle drops and keeps dropping. Yeah, yeah, I know. Clean the carb again again again. Will also lookit the gas cap. And I guess I will have to man up and buy a DTI checker-thingy like Paul sez, 'specially with an RT3 derelict in the stable and a CS5 on initial approach... Oh, and Paul, nice signature above your icon, except...

Not too much info to start on this one, just want your gut feelings. Without knowing specifics, what would you think of an air-cooled two-stroke running fine, revving normally, after about 15 minutes of riding at 50 mph, starts fading, losing power, not accelerating with more throttle, then quickly bogging and for all the world sounding like it is seizing up? Luckily I had turned around and headed home; when it quit, I was only a half mile away, downhill. As it slowed from around 35 where it quit, clutch in, it felt hard to downshift to get it into neutral, not at all like when it's running. (This could just be incidental, like that extra info they give my kids in math problems that they don't need!) (The info, not the problems.) After getting home I let it sit a few minutes, then manned up and tried to turn it over. To my surprise, it wasn't froze up, and there were no metallic crunching sounds from within the case. Dropped it in gear and tried rocking to see if the tranny had gone, with predictable results - it wouldn't move. But again, no clunking metal noises. So I tried to start it. Fired right up like nothing untoward had happened. Rode it down to the end of our street, about 3/8's of a mile, it shifted fine thru all the gears, revved to 5000 like normal. Rode back home, no changes, still running fine: no strange, unwanted noises, all is well. Based on this info alone, what would you think could be the cause? I will tell you this was the first run with the replacement Mikuni carb with proper jets/needle/slide installed and 21mm float height. Also removed the suction pipe I installed because it wouldn't rev over about 5500 without cutting out, even in neutral. After removal it would rev to redline and more. Not that I would do that...

It just followed me home, Ma. Can I keep it, puh-LEEZ???

Thanks Paul, good idea on holding the carb at an angle. My needle jet does screw in, and the air jet was clogged. I managed to sand down a sewing needle to get it to poke thru enough to dislodge the schmutz that was in there, and the WD40 cleaned it out. Now I have a nice stream flowing thru the air jet. Nope, I didn't jam the needle thru, just gently poked - didn't want to screw up the jet size. All ports now seem to be open. So next week, and the new parts. Hopefully they will arrive before I leave town.

Emulsion tube is in good shape as is the passage. I have a diff tube than in the pic but I get the idea. As for o-rings, I have none, nor does the parts list show any. I thought that odd, what's to keep gas and air from leaking? I got the air screw to emulsion tube hole cleared. Now I'm just Waitng for parts next week. What about float height, pin depressed or just touching?

(Heavy sigh) Not as sputter-free as it started out. After a few rides the sputter has started again. AND I cnnot get it to idle properly. If I set it to 1800-2000 it idles mostly fine, some hunting, but once I set it to 1500 or below, it slowly bogs then dies. REALLY irritating, this. Removed the side cover, there was a little oil film in the bottom. Removed the magneto, the crank seal is dry, no dampness of any kind, so I don't see that the seal could be leaking causing my probs. I think the film is WD40 I was using to try to find any leaks on the carb. I know some of it ran down into the case. So removed the carb again. Well, first time for THIS carb. There was fuel puddled around the air screw inlet hole. I thought, hmm, that probably should not be. Disassembled the carb for a really good look. I can see that the air screw hole has a port straight thru to the needle jet, so I tried to blow air thru it with a plastic WD40 pipe. Nada. Tried to spray WD40 thru it. Nada. Got my junk Mikuni and tried spraying WD40 thru it, success! So I know the new one is clogged. Will work on getting it open today. Found the main jet says 120. Saw it before but ignored it in the interest of seeing how well it performed, It won't rev much over 6500 under load, New proper 140 on order. On setting the float height: I measured 24mm with the float just touching the needle plunger. Do I need to measure with the plunger depressed, or just touching the tip of the plunger? I did the latter, which is how I've always done it, and set it to 21mm. But the fuel in the intake made me wonder if it's too high. But the air screw hole is clogged, so that is where I think that fuel came from. Ordered a new needle and seat anyway. Hopefully sometime next week I will get the parts in and can continue my saga. Will still consider the crank seals and reeds if I still have the probs. The spark plug looked good btw, clean and a dull brownish.

A spectacular looking DT! Love the "YBU?" license plate. 2 q's: what tyres do you run, and where do you get your petrol tank and seat covers?

Last one is cos Locomotive Breath is screamin' on the stereo... Gents, it was the carb. Sputter no more. The carb I bought on ebay cured my problems, except can't get it to idle like I want. The OEM unit had some water in it and had begun the corrsion process, but it was all superficial and cleaned up nicely. The slide was correct, but the needle was almost a full cm longer than the 4J13; I put my old slide/needle combo in. I will remove the drain plug sporadically over the next few weeks to drain out any accumulation of crud and see if all is well. For now I'm happy with the results, just wish I hadn't wasted money on the aftermarket carb. That thing didn't even fit in the filter box correctly, wouldn't go all the way in. Wait, did I mention ?

"Ground control to Major Tom..."

This is why I come to this site, cos you people have all these little jewels. Thanks for the linky, great stuff. Always been a sucker for sexy cutaways! On the way to Tokyo now, oem carb should arrive while I am away.

Indeed. There's a pic somewhere in the post of my air screw, and the o-ring is cut on it. I reassembled it gingerly with a dab of grease to ease insertion (??). It ran a little better until I rode it, then it was back to the same. Awaiting an OEM carb for installation the end of the week.

I tried it already, and it REALLY didn't like it. So I tried it up a notch, also to no avail. I know it should not affect idle doing that, but I could not keep the bike running in either postion without revving constantly. This is a very temperamental carburettor.

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!

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!

The needle jet I had removed in the 2nd pic...

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?

Yes, all that was done on original assembly. Being a old git mech I am fairly fastidious to that sort of thing. Anal is a word I think that sums it up.

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.

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!

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!

Paul, is this procurable or did you make it?