Here's a vid from the 170MJ watching the clear bowl. The video isn't very clear because the GoPro doesn't want to focus that close, but you can see fuel level fine. One time it decides to drain the bowl and another it seems like it could go all day.
Not sure why 2nd run didn't drain it, so it seems like it is only draining it randomly
That's what I don't get. I even got variations when testing flow. I can see in there and there's nothing floating around in the tank. Pretty sure the outlet was clean. Cap on or off didn't matter. Not much left with a simple gravity feed setup... unless the RC-One changes gravity. Maybe that's actually how the front end gets up so easily?
I don't disagree that a level carb is more ideal... but why does everyone else use them like this on all sorts of setups and I don't hear about such an issue... and again possibly more importantly is why does it work most of the time and then sometimes it doesn't?
I thought maybe the float was sticking as Scott said too, but I watched the vid a couple of times where it drains and it seems like it wasn't stuck to me. It's down where it should be letting fuel in and still draining. There are 2 crappy things about the angle here. First, the main jet is basically in the center and the highest fuel level is at the front (of the scoot) so it's not benefitting from the most fuel access. Second, the floats are where the highest level of fuel is, so they are more likely to stay higher than they would if level. If there's any good thing, at least fuel does slosh backwards on acceleration to some degree... but that seems mostly at launch when fuel levels are always fine anyway.
I really don't want to level the carb out by changing things around just because I don't see why mine needs this. Something else has to be happening. I should probably drain the whole tank again and run something through the barb on the tank. I wouldn't even think it should be that though, because my fuel lines and filter look filled. I'd figure that volume should cover an acceleration run... I guess unless it were totally blocked and holding fuel due to lack of venting, which I don't really think is happening.
Based on previous observations, I don't think I can raise the float height to any significant degree without getting back into overflow problems.
Last Edit: Aug 11, 2022 13:09:01 GMT -5 by 90GTVert
I've had fuel filters do stupid things stopping fuel flow randomly causing a few race losses,may be worth a try to dump the filter and see how it acts..Large screen type filters worked best for us..
I can try it. The last one was a simple screen. This is a Malossi screen filter. They're not much more than a large mesh strainer. I've used sintered bronze a lot and even paper at some points, both of which seem more restrictive. No problems then... but I guess most of my carbs use 90-110 jets, not 150-170 and not a silly angle.
What about automotive fuel filters? Or maybe run two of em parallel? Btw, doesn't the fuel cock in the tank also has a filter? They're made to flow fuel for a stock 50cc. Maybe get rid of that one first.
Test 1 : tank > 1/4" hose > 1/4" shutoff > 3/16" hose 425ml So, removing the filter jumped flow up from 175 at best to 425ml! I wasn't ready to accept that a simple strainer type screen filter was that restrictive. I initially had it running straight down from the barb, and questioned if routing it roughly 90 degrees bent right out of the barb could be the restriction. Zip tied it up that way, as it normally is, and it made no difference.
Test 2 : tank > 1/4" hose > 1/4" shutoff > 3/16" hose > 1/4" mesh filter (no hose on outlet) 375ml It looked like the filter restricted flow by about 50ml in 30 seconds. Still way more flow than I had, so something else was going on.
Test 3 : tank > 1/4" hose > 1/4" shutoff > 3/16" hose > 1/4" mesh filter > 3/16" hose 450ml Now it's flowing more with the filter and the 3/6" hose on the end than it was with just the hose coming from the shutoff and no filter at all!
Then I wanted to try putting 1/4" hose back between the shutoff and filter and using 3/16" after. At this point I'm suspicious that the large hose before the filter and small after causes a restriction. Maybe back pressure or head pressure or whatever it's called? I went to pull the 3/16" hose off of the Malossi filter and it ripped the end off of the filter. Perfect.
I didn't have any other 1/4" filter like it. I did have the Malossi filter labeled 6mm, which actually matches up to 3/16" well. The 8mm, is really ~1/4" which is why it's labeled that way to make sizing more clear. I zip tied the 1/4" hose on the filter from the shutoff to make it seal and see if I could test my theory with the smaller filter or not.
Test 4 : tank > 1/4" hose > 1/4" shutoff > 1/4" hose > 3/16" mesh filter > 3/16" hose 375ml Back to where I was with no hose on the outlet of the 1/4" filter, so I thought this may also improve by switching to smaller hose pre-filter.
Test 5 : tank > 1/4" hose > 1/4" shutoff > 3/16" hose > 3/16" mesh filter > 3/16" hose 450ml Boom! Right back to the high flow numbers by adding what I would have thought would be a more restrictive hose.
Then I was really disappointed that I couldn't see what the effect would be having the larger filter with hose diameters changing since I couldn't find any more 1/4" filters. I went to check the shed, because the mowers use 1/4" fuel filters and I had one around. It was a paper type, not the screen. Eh. We'll see. I angered the wasps above the shed door on the way out and one stung me in the neck. Small price to pay for the test filter I was after.
Test 5 : tank > 1/4" hose > 1/4" shutoff > 1/4" hose > 1/4" paper filter > 3/16" hose 450ml OK, maybe not. This seems fine with the mismatch on each end of the filter.
Test 6 : tank > 1/4" hose > 1/4" shutoff > 3/16" hose > 1/4" paper filter > 3/16" hose 450ml No change.
This was 3x or more the average flow from prior testing, so good enough for me. I wanted to do one more test to see if having the hose a bit more straight down than my usual routing was a major restriction. That flowed 425ml. Makes sense I guess. Going much more straight down would seem like an advantage in a gravity feed fuel system. Still, tons more flow than I had.
At this point, I'm guessing my bowl emptying issues will be cured, but no test runs yet. You can just look at the fuel coming out of the hose and clearly see the difference from the past tests or watch how quickly it fills a container. It's obvious.
I also noticed that the 1/4" mesh filter would not fill during tests with 1/4" before it and 3/16" after. Then with 3/16" on both sides, the filter would fill and stay full. The paper filter didn't seem to care. Maybe because the paper element offers some sort of restriction or isolation that the screen doesn't or maybe something else I'm missing in the design.
The main thing that I learned here is to match fuel hose size on both sides of a filter. Even with paper, after seeing this I would still match it. Again, I can't tell you technically why, but it appears that some sort of resistance or pressure is better than just an open hose. Another one of those times where relying on intuition fails me, thinkng that bigger wherever it'll fit flows more.
I'm also probably not going to bother buying costly scoot/moto filters anymore. I'll just pick up auto/mower filters like most people seem to do anyway. Now I'm just hoping the one on there isn't junk. I had a Kohler filter that's a monster and then some no-name filter. I have had generic filters come apart while riding, so I guess I should make sure I have enough hose under the seat to reach from shutoff to carb just in case.
TLDR : Match hose sizes on both sides of the filter and maybe don't bother with expensive scooter/motorcycle filters over cheaper name brand automotive/mower stuff.
Last Edit: Aug 12, 2022 13:06:12 GMT -5 by 90GTVert
It seems pretty conclusive. So hopefully it's solved. 👍
Yamaha Aerox NS50 2016 project Yamaha Aerox NS50 2016 Piaggio Typhoon 2019: Great scooter, poorly built (sold) Yamaha Slider 2002: The problem child (sold) Yamaha BWS NG: The Family affair (son now owns) Yamaha Aerox YQ50 2008: The fast one (sold) Yamaha Jog RR 2004: The first one (sold)
Mrs Bud 10/06/22 you are not going to pull that engine apart and put lots of new bits in it, are you?
I was excited for Saturday. I had plenty of fuel flow and a day that was in the low-mid 80s with low humidity. A nice change from the weather for the last month or so and much closer to where I prefer to test main jets. The dragy said density altitude was at 836ft on my first runs. I've been seeing it 1700-1800ft most of the time. Just for reference, actual elevation is barely above sea level at 40-50ft. My excitement turned into loathing by the end of the day.
I started out with the 170 MJ in the clear float bowl. I assumed I'd need no larger than 160, but I wanted to start big. It was too rich. Sputtering on takeoff and didn't clear out for a bit. Not good results, but not awful.
I swapped in a 165 MJ. Somehow it got worse. Still sputtering and it was about a half second slower in the 1/8 mile.
I had been using a 160 main jet before attempting to tune, and it would take off clean when I rolled in. Not that far off. I had also rode it with the 170 on the test that I posted some video from a few days ago. It was worse now. It struggled to clear out, even with me getting to WOT more quickly than normal. That made me suspect either a float height issue or a fouled plug. I didn't worry too much about the plug, because the first took 300+ miles to totally foul and at least a couple hundred before I noticed any obvious symptoms and this plug had 50 or less miles on it. Doesn't mean it's good for sure, but I didn't swap it out.
I tried setting the float height to 21mm, to hopefully lower the fuel level. Turned the fuel on and the bowl didn't fill at all. What? I found that the plastic bowl will bind up the floats when tightened. It didn't seem to do this when first installed, but it definitely is now.
I went back to the original aluminum bowl and set the float height to parallel at 19.5mm. I figured maybe the floats had been binding enough even before that they changed the height. Did another couple of test runs with the 165 MJ and it didn't change, or actually it got a little worse. Good runs are usually 2.6-2.8 0-30MPH and at this point it's going as slow as 3.7 0-30.
I'm thinking it has to be the float height. Could the better flow have changed it? Maybe good flow from gravity feed doesn't, but maybe if it was weak it could have? That doesn't sound right because I'd think even if it trickled in slowly it would require the same amount of fuel to make the float rise, but I really wasn't sure what else to think since I'm suddenly having rich conditions and suspecting float height right after improving fuel flow. Maybe the floats rise, but not as much can make it past the needle when flow isn't great as it rises so they never rise quite as much?
I decided to put the clear bowl back on and see if it could at least be useful for some tests to see if I could get the fuel height away from the top of the bowl a little. I checked again with the clear bowl and fuel was again very near the top of the bowl.
Then I tried something different. I've seen other people use water to test float height. I always thought it sounded like a bad idea, because water should be more dense. Water is over 8lb/gal and gasoline is something like 6lb/gal. Not sure where premix comes in, but I assume near gasoline. I would think this should throw off float height. Gotta try though. It sure would be nice not to spill gas/oil everywhere when testing.
It was a fail, as expected. Well, maybe not exactly as expected. Float height was lower. I was initially thinking that the dense liquid would push it higher. It seems to work the other way and it just takes less of the dense liquid to float the float; which made sense after thinking about that for a moment. As you can see, the level was quite different with water. There's also a pic to show my little bench test setup. I bent a straight pegboard hanger around a piece of tubing so it held a 150ml syringe and then attached hose and a shutoff to that. I even tested on the bench and the scoot both with premix to make sure the big 2.5 gallon tank above the carb didn't have any significant effect, but both seemed to level out the same.
OK, back to fuel and oil. I set the float height to 21mm. Still at the top of the bowl. 24mm and still up there. WTH? At this point I assume that the floats must still be sticking in the clear bowl, even with me barely tightening the bowl. The rods that the floats ride on are thicker in Malossi's clear bowl than the DellOrto original. The floats also sit closer to the plastic bowl... maybe because the plastic is thicker (I didn't actually check thickness). The net result is, the clear float bowl sucks. I've heard that you should only use them for testing, but I can't even get through a little testing without trouble. It was nice to see, but I would only suggest trying this if you are really having issues and can't get ahold of an extra drain plug to modify for testing.
I didn't want to mess with the clear bowl anymore. Too much of an unknown with just how much it could throw things off for tests. One good thing is that it came with it's own bowl bolt/main jet holder. The bolt did not fit the standard bowl though. The standard jet holder has a 9.9mm shoulder just below the head for a gasket to go around. The clear bowl's jet holder had an over 11mm shoulder that wouldn't fit into the aluminum bowl and it also had another ring below the threads that was too large to fit.
I stuck it in the lathe and took the shoulder down to 9.9mm and turned the other ring down so it wasn't an issue. I drilled through the hex end so I could very snugly fit a piece of a plastic barb in there. I had to push hard to get the barb to snap in and I used a little super glue around it for extra insurance. Not something that I'd trust for riding, but good enough to fit a hose on the end so I could watch fuel level with the original bowl.
At 24mm, fuel was still near the top of the bowl. It may have been a little lower, but it was at least close. I set it to 19mm and the fuel went right to the mark I put on the bowl for 24mm. Oh boy. I changed it way too much, so I figured fuel level would drop a lot. It filled really slowly... and eventually made it's way to the same height. Now I'm totally lost. Floats, needle and seat look OK. Didn't spend a long time, but nothing obvious.
I made sure the float arm was straight and set it roughly parallel again and decided to just put the regular bowl bolt on and put the 165 MJ back and see how it goes now. I put the carb on the scoot, turned the fuel on... and fuel poured out of the overflow quickly. I tapped the bowl just to be sure and it kept pouring out. Screw it. I'm lost. It was 7:30 at night at that point and I started on it around 10AM (with about a 1.5 hour break). I was very much over it. I'm about ready to put the Lectron on it at this point. The only other thought I had was to weigh the floats, but I don't really think anything is wrong there. I could have made a stupid mistake on assembly the last time since I was so fed up with it by then, but either way there's something that I'm missing or something strange. I must have been changing fuel level when I first got the carb, because it piddled and I adjusted it and then it ran out of fuel and then I got it to a point that basically worked.
Last Edit: Aug 14, 2022 11:44:40 GMT -5 by 90GTVert