SwampNut Posted February 13 Share Posted February 13 I am giving up on it. My priorities would be reliable and easy starting. Don't care about MPG or max power. Mikuni TM40: Inexpensive, generally easy to tune, not the most powerful or best MPG. XRsonly.com sells it as a kit with the adapter and multiple jets, but shows out of stock. I can get the carb and jets from other sources, but still also need an airbox adapter. @IcePrick has one on his XR400 and likes it a lot. This is valuable info and makes it my top choice. The forums seem to just see this is a good solid carb nothing that stands out. Lectron: Expensive. First-kick starts. Hard to tune sometimes. Works at any altitude even laying on its side. Edelbrock: Some love it and some hate it, inexpensive, can be tweaky to tune at first. Quote Link to comment Share on other sites More sharing options...
IcePrick Posted February 13 Share Posted February 13 When I did my Mikuni on the XR4, I just installed it and set the idle. Never had to play with it at all beyond that. As far as first kick, yes - cycle throttle twice, choke to full, find the notch at TDC, kick it like you mean it, and it will light. If it's been sitting for months, maybe cycle the kick starter through a few times before whacking the throttle as above. Hot starts, leave the choke off and don't touch the throttle. If it lays on its side for a bit whilst you've taken a dirt nap, get it upright, pull the decomp, kick it through about 10 times with the throttle open, it may take a couple kicks with the decomp off to clear the fuel before it will light. Completely changed the XR4 from temperamental and finicky to reliable and simple. Improvement throughout the throttle range, particularly transitioning from idle and any time going to full throttle from anywhere else - that little squirt of gas is a miracle. Quote Link to comment Share on other sites More sharing options...
SwampNut Posted February 13 Author Share Posted February 13 Weird, they recommend the 40mm for the 650R and 42mm for the much lower powered L model. Quote Link to comment Share on other sites More sharing options...
IcePrick Posted February 13 Share Posted February 13 Just now, SwampNut said: Weird, they recommend the 40mm for the 650R and 42mm for the much lower powered L model. It's about double the weight, takes more gas to drag that around. Quote Link to comment Share on other sites More sharing options...
SwampNut Posted February 13 Author Share Posted February 13 1 Quote Link to comment Share on other sites More sharing options...
superhawk996 Posted February 14 Share Posted February 14 I went looking to see if I could find a reason for the 40 vs 42mm and instead ran into a video about how much the Mikuni sucks and why you should use the stocker. Then in the comments were several people agreeing, then a bunch asking those people if they'd sell them their used Mikuni. And several that love their Mikuni. So basically, about the same you were finding in your searches. Quote Link to comment Share on other sites More sharing options...
SwampNut Posted February 14 Author Share Posted February 14 What kind of oil were they using, and what was their preferred carry caliber? 2 Quote Link to comment Share on other sites More sharing options...
superhawk996 Posted February 14 Share Posted February 14 10w-40 and 10mm/40 Quote Link to comment Share on other sites More sharing options...
superhawk996 Posted February 15 Share Posted February 15 One of the YT professionals I reached out to said that he's encountered this a few times and the problem was the seat. The seats are often too hard to replace and he described his method of polishing it that has worked for him. IIRC the previous needle was all metal, no rubber coating, so I can imagine that it would be more prone mar the seat surface after lots of vibration and bouncing. Funny that the XR and R5 both had perplexing carb issues. The R5 still occasionally drips from the overflow, but it finally runs so I'm ignoring that for now. And I just received some pure castor oil to add to my home brewed gasoline to hopefully get all the right smells. Maybe lubricating the gas will cure the float issue 😁 Quote Link to comment Share on other sites More sharing options...
tomek Posted February 15 Share Posted February 15 (edited) I'd check stator. Is it kick start? I have old school air-cooled xr600r. 628 actually. Dual carbs. I got it used of course, somehow came with street plates. In Illinois. Anyway, it was difficult to start as fuck till I troubleshooted stator. It was out of specs. Starting is easy now on new stator. Edited February 15 by tomek 1 Quote Link to comment Share on other sites More sharing options...
SwampNut Posted February 15 Author Share Posted February 15 12 hours ago, superhawk996 said: IIRC the previous needle was all metal, no rubber coating, Rubber also, but it likely was aftermarket. I had this from Walt, but then thought, the rubber should seal... That's a bummer. It's seems like when carbs act like that the only fix is a new one. As a last ditch effort, I take a q-tip and cut the stalk at a sharp angle and chuck it up in a drill. Spray the float seat with wd40 and place the sharp tip into the seat hole and polish it with light pressure for a few minutes or until the stalk breaks. If that doesn't fix it, new carb time, or if the seat is replaceable, new needle and seat time. Quote Link to comment Share on other sites More sharing options...
superhawk996 Posted February 15 Share Posted February 15 10 minutes ago, tomek said: I'd check stator. Is it kick start? I have old school air-cooled xr600r. 628 actually. Dual carbs. I got it used of course, somehow came with street plates. In Illinois. Anyway, it was difficult to start as fuck till I troubleshooted stator. It was out of specs. Starting is easy now on new stator. The carb issue is that the bowl overfills and spills from the overflow. It's inconsistent, but persistent. We've been in the carb 15-ish times, find nothing wrong, installed a new needle, no change. It's almost always fine when the carb is re-assembled, take a short ride, usually fine on the ride. A moment after you stop it starts flowing. Quote Link to comment Share on other sites More sharing options...
SwampNut Posted February 15 Author Share Posted February 15 I should go outside and check it.......no leak. Quote Link to comment Share on other sites More sharing options...
tomek Posted February 15 Share Posted February 15 (edited) Whatabout float valve, whatever proper name? Looks like worn out parts 2 and 4. Probably too much side to side movement, something touching something and it gets stuck, overflows, etc. But, yea, new carb is probably good idea. Edited February 15 by tomek Quote Link to comment Share on other sites More sharing options...
superhawk996 Posted February 15 Share Posted February 15 5 minutes ago, SwampNut said: Rubber also, but it likely was aftermarket. I had this from Walt, but then thought, the rubber should seal... That's a bummer. It's seems like when carbs act like that the only fix is a new one. As a last ditch effort, I take a q-tip and cut the stalk at a sharp angle and chuck it up in a drill. Spray the float seat with wd40 and place the sharp tip into the seat hole and polish it with light pressure for a few minutes or until the stalk breaks. If that doesn't fix it, new carb time, or if the seat is replaceable, new needle and seat time. Very similar to what the YT guy told me, except he uses a pencil in a drill followed by a Q-tip in drill with polishing compound. Quote Link to comment Share on other sites More sharing options...
superhawk996 Posted February 15 Share Posted February 15 1 minute ago, tomek said: Whatabout float valve, whatever proper name? Looks like worn out parts 2 and 4. #2, what I called the needle, has been replaced. The only thing that goes wrong with floats is that they can perforate/crack and fill with gas, but then you get a consistent over-fill. Not in the photo, and unavailable according to Carlos, is the seat and that's what we've been discussing polishing. I never got a good look at it and didn't suspect it because they "never" wear out, but apparently it's a thing with this carb. And I just realized that others probably never wear out because they're an easily replaced wear item that comes in most rebuild kits so they're rarely all that old. This one appears to be pressed in where others are threaded and have a hex or flats to grab with a wrench. Quote Link to comment Share on other sites More sharing options...
tomek Posted February 15 Share Posted February 15 So you guys got new needle but old seat. And seat is pressed in. Kinda like throwing new valve on not refinished seat in cylinder head. Not ideal. Was it leaking with old valve? Maybe run some fine valve lapping compound? Quote Link to comment Share on other sites More sharing options...
superhawk996 Posted February 15 Share Posted February 15 12 minutes ago, SwampNut said: I should go outside and check it.......no leak. Take a 30 second ride to remind yourself why you ordered a new one....tho it would probably be now that it decides to not leak. Or maybe I ran it out of gas with the 57 bowl removals 😂 I hadn't fired up the 400 since Ocotillo and the gas was smelling not so great, but it fired right up after I remembered how to use the choke. It happens to have a Mikuni pumper, probably a smaller copy of what you ordered. I had to re-learn that full choke is a hair too much, it has to be pulled to the second detent, but not into it. Or half choke and a pump of the throttle. I'll have to bring it next time so we can compare them, I haven't ridden it other than one lap of the driveway. It doesn't seem to have that magical floating suspension feel of the 650, but seems decent. Quote Link to comment Share on other sites More sharing options...
SwampNut Posted February 15 Author Share Posted February 15 Even the floats are hard to get because "they never go bad" according to our biggest dirt bike shop. I hope Al gets past the hangover today and finally ships the fucking carb. 5 minutes ago, superhawk996 said: It happens to have a Mikuni pumper, probably a smaller copy of what you ordered. Probably what Mike has on his. Quote Link to comment Share on other sites More sharing options...
superhawk996 Posted February 15 Share Posted February 15 1 minute ago, tomek said: So you guys got new needle but old seat. And seat is pressed in. Kinda like throwing new valve on not refinished seat in cylinder head. Not ideal. Was it leaking with old valve? Maybe run some fine valve lapping compound? It was leaking, but it had some stuff in it that I suspect was particles off the petcock rubber so I figured it would be fine once that was replaced and it was cleaned out. Before learning of the seat issue we had planned for Carlos to give it to me because I had to experiment and find out WTF was going on. Fine lapping compound is my plan, maybe followed by polishing compound, unless he decides to do the experiment instead. If I can grab the old needle in a drill I'll use that for the polishing to know that the angle is correct. Quote Link to comment Share on other sites More sharing options...
tomek Posted February 15 Share Posted February 15 Well, good luck. It would suck to be forced to replace carb due to float valve issue. I'd examine bowls for signs of float making contact with it. 1 Quote Link to comment Share on other sites More sharing options...
superhawk996 Posted February 16 Share Posted February 16 8 hours ago, tomek said: I'd examine bowls for signs of float making contact with it. I suspected that because the 'toe' of the floats looked really close to the bowl. There were no marks on the bowl or floats, but I tweaked them a bit to make extra clearance just to be sure. Quote Link to comment Share on other sites More sharing options...
SwampNut Posted February 22 Author Share Posted February 22 I discovered that the valves appear to be pretty tight, managed to lose my feeler gauge, find it, lose it again, then gave up and went to bed and ordered a nice pre-bent one that I'll need anyway. I don't have any of the offset box wrenches which I think is the only way to get to the exhaust side without removing the radiator. The manuals says, "Trust us, it's harder to do this with the radiator on than just removing the radiator." Challenge accepted. I need to get some work done then go figure out whether I need tools, or just remove the radiator, or what. Amazon delivery by 3pm if I order by 10am. Also, this is one big motherfucker of a carb. Quote Link to comment Share on other sites More sharing options...
IcePrick Posted February 22 Share Posted February 22 Nice, I see you opted for the Trump Edition wrenches. You going for the matching sneakers? 3 Quote Link to comment Share on other sites More sharing options...
SwampNut Posted February 22 Author Share Posted February 22 I heard morans are paying $1900 for those, would make great riding boots I suppose. I'd get all the attention pulling up to the gay bar. Quote Link to comment Share on other sites More sharing options...
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