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Post by ancorder on Aug 6, 2010 0:07:05 GMT -5
I know there are a thousand carb-related threads... bear with me.
I've got two scoots: one is a 2006 Schwinn Graduate 150, the other is a 2006 TNG Milano 150. They're essentially the same scooter. The Schwinn runs great right, but the Milano, well, not so much.
I got the Milano a little over a year ago from a couple who couldn't get it running right. They'd pretty well torn everything apart, so I spent a couple of months last summer putting it all back together. New fuel lines, vacuum lines, intake manifold, fuel filter, all that jazz. Never got it running great; it would start up and idle just fine, but if I jerked on the throttle it would smother it and die out. I could ease on the throttle and get it about to half throttle (maybe 3000 rpms, best guess), but no more. This was about 30 mph on flat ground. I figured there was something I'd missed, and it was getting late in the season, so I just put it away.
Unfortunately, I didn't have a garage, so it sat outside all winter. This spring it wouldn't start, and had gas coming out the airbox. My fault for not winterizing properly. So in between moving and starting a new job, I took the carb off and cleaned it piece-by-piece, according to Big Guy's guide. That sucker shined when I was done with it. I remounted it, dropped a teaspoon of gas in the bowl, and boom, it started right up. Idled great. Went ot pull on the throttle and it acted just like it did last year: pull on it quickly, and it would kill it; roll it on slow, and it would go up to about 3k and top out. If I hold it there (about 1/2 open), it slows down a little over the course of 5-10 seconds.
Weird. So I checked every line, intake manifold, airbox for holes, found nada. Plug was very dark, indicating it's running rich. Adjusted the air/fuel screw to a leaner burn, but didn't seem to have any effect on idle speed or throttle reaction. (I eventually set a/f and idle back to normal.) Seems to me like it's not getting enough air, or it's getting too much fuel. I tried dismounting the airbox and leaving the carb open to the air, but still ran rich and bogged at 1/2 throttle.
I'm at a loss. All I can figure is that the enrichener isn't getting current (thus not closing off the extra fuel supply), or just plan ain't working. What also points me in this direction is that it started right up and the idle speed never slowed down as it warmed up. But is that extra bit of fuel really enough to cause it to bog so severely? It's puzzling to me.
Tomorrow I plan to swap the known good enrichener off the Schwinn and see if it makes a difference, but right now I'm wondering if anyone else has further thoughts, or thinks I'm barking up the wrong tree.
Cheers, y'all.
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Post by flyangler on Aug 6, 2010 4:56:16 GMT -5
You may want to adjust the valves if only to eliminate that possibility.
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Post by Bluefront on Aug 6, 2010 5:34:05 GMT -5
Ever try to adjust the float level? It should be about 18mm, although the specs vary, depending on the particular service manual. In the photo I'm using a Honda tool, but a normal rule can be used.  If this measurement is off enough (either high or low).....it can cause all sorts of running problems. |
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Post by pentode on Aug 6, 2010 7:54:57 GMT -5
bluefront,, I have also seen methods of checking the float while holding the carb so the float is verticle. Is there a prefered way ?.
I sure enjoyed reading your posts on rehabing your scooter. I learned a lot.
Thanks.
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Post by Bluefront on Aug 6, 2010 9:27:55 GMT -5
^^^^^Depends. You watch the little spring-loaded pin when you flip the carb over. If you see the pin depressing under the weight of the float, you should measure with the carb sideways, and the pin not depressed.
My carb does not depress the pin when I measure it this way.....so the measurement is accurate. It's easier to do it this way also. Sometimes the one float is of a different height than the other......in that case I split the difference.
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Post by ancorder on Aug 6, 2010 10:18:58 GMT -5
flyangler-- I did actually adjust the valves, and they are set same as the Schwinn: .004 and .005
bluefront, I'm not entirely sure I grasp the what and how of measuring the float, but I'll pole around elsewhere on the forums when I get home tonight and make sure I understand what I'm doing. Am I measuring how high the float is relative to the housing when the float is resting (not depressed)? And measuring off in which direction would cause a rich mixture?
Though I'll probably just swap the enricheners first, because that'll be easiest.
Now, off to work, where I'll ponder the scooter all day instead of getting anything done...
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Post by Bluefront on Aug 6, 2010 14:02:04 GMT -5
 The 18mm spec would be from the base to the top edge of the float(s). If that measurement was 25mm for instance, your float setting would be low (lean). If the measurement was 15mm the float setting would be too high and the setting would be rich. Tricky I know..... Sometimes the floats leak.....upsets the spec and the float level is too high (rich). You can take the float off the carb and shake it.....if there's any gasoline in the floats, it'll splash around. |
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Post by sprocket on Aug 6, 2010 15:24:23 GMT -5
This is the first I have ever heard of a float effecting how rich an engine runs. Rich or lean is handled by the jets, the air/mixture adjustments and the throttle needle.
All the float does is to open and close the gas flow from the fuel line to the float chamber where the gas is sucked up through the jets.
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Post by Bluefront on Aug 6, 2010 15:46:44 GMT -5
^^^^^Apparently it has to do with the level of the gas in the bowl......how far under gas the main jet is located. If for instance the level is very low in the bowl, it's more difficult for the engine to suck up the fuel (lean). Something along those lines anyway.....  The bad part about this.....if you diagnose a lean condition, you could enlarge the main jet which would help somewhat, but the problem would never be cured. It's best to check/adjust the level when you have the float bowl off....like every time. That's what I was always told when I started messing with cycle carbs. If you have a bad float (leaking), the gas level in the bowl is high (rich).....if you come to a fast stop, the gas moves forward in the bowl possibly making the problem worse, and the engine dies. It's definitely something to check if you're having carb issues.... |
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Post by sprocket on Aug 6, 2010 16:03:30 GMT -5
>> Something along those lines anyway....
OK, I see what you mean in regards to lean. The gas level falls below the jet intake for a few seconds and the engine starves of gas, then the float opens the gas supply and the jet can suck it again.
This is not 'lean' it is fuel starvation...
I just tried this on an old 4 stroke generator engine I have. I adjusted the carb float to make it drop the fuel level below the jets.
It doesn't run lean, it runs intermittently. Like it runs OK for about a minute then it starts to die and looses power, then it picks up gas and runs OK for another 45 seconds or so and then starts to die again.
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Post by Bluefront on Aug 6, 2010 19:45:53 GMT -5
^^^^^In that case, if you would keep raising the float level, you'd reach a point that the engine wouldn't quite be starving for gas any longer, but wouldn't quite have enough to run correctly.....lean. On the other end of the adjustment, the setup is running rich, right before the gas over-flows the bowl. It's not hard to adjust the float level, as long as the float itself is ok (not leaking). The float needle actually seating properly, is another related issue.  |
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Post by catbird on Aug 6, 2010 20:53:39 GMT -5
Here's some food for thought... www.factorypro.com/tech/carbtun.html float height has everything to do w/ carb tune and jetting Have an ITA 150 , came out of the crate not running worth a .... Hard to start, if it did took for ever to warm up(had to ease throttle in, couldn't just give it gas w/o stalling, blah,blah) . Carb was a no name chinese brand. Drilled idle screw,adjusted ,no help. called seller, sent warranty carb (Keihin, now were talking) still lean out of box but would finally start run and take throttle,just lean. installed 40 pilot, 115 main. Easy start,enrichment circuit kicks in for a short time. Changed whole driving experience. Would finally have smooth idle, serious acceleration, 62-65 (grade dependant, rider 6'3" 220 using speedo,don't care for watching GPS while I'm a gettin' it) Reading alot of people having problem with giving scooter throttle. With what I've experienced I would have say start looking at the carb itself specially if you have chinese carb. Engine's are pretty good but only as good as fuel delivery will let it. |
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Post by catbird on Aug 6, 2010 20:55:26 GMT -5
oopps forgot. Valve adjust is a critical step PRIOR to any jetting you may do to the carb.
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Post by Bluefront on Aug 7, 2010 4:20:26 GMT -5
^^^^^ That CV carb tuning page is about like I've always approached jetting issues......except I always adjust the float level to specs while I'm doing the main jet change. Normally the float level spec in the manual, would be the optimal setting, without needing any further tweaking. Pretty good explanations on that link..... |
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Post by catbird on Aug 7, 2010 7:46:39 GMT -5
using my last mulligan.....brain typo on jetting, currently 40 pilot, 112 main
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Post by sprocket on Aug 7, 2010 13:39:32 GMT -5
Have you adjusted the diaphragm throttle needle? It would be my first choice before messing with the jetting?
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Post by ancorder on Aug 8, 2010 12:34:24 GMT -5
Float level (to my best discernment) doesn't seem to be a problem. Adjusted it both ways and didn't have any noticeable effect. Swapped enricheners and also had no effect. Here's my next thought:
You know how we all hate it when somebody starts a diagnostic thread and doesn't provide ALL the info? Well, I'm sort of guilty. That is, my muffler's got a hell of a rattle (always has since I got it), and I assume there are some busted baffles in there. Would it be possible that those baffles are stuck in such a way that they're preventing the relief of pressure when I up the throttle? I don't know if that makes sense, but I'm starting to get antsy. I do have one of those briggs & stratton lawnmower muffles and a piece of steel coupling, and I'd been planning on doing that muffler mod anyway. I was just waiting to get the scooter running right first, because I know it's always best to make sure you're running well BEFORE you start doing mods.
Anyway, should I go ahead and swap the muffler? Any chance that'll take care of things?
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Post by sprocket on Aug 8, 2010 14:19:20 GMT -5
I have seen this a couple of times. Pull the air filter off the carb and try it...
I doubt it is the muffler, but it could be blocked preventing the exhaust from escaping...
Undo the muffler from the exhaust pipe and try it...
So its either no air getting into the engine or no exhaust getting out...
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Post by ancorder on Aug 8, 2010 14:57:41 GMT -5
Sprocket, I tried pulling the air filter (and then the whole airbox) off the carb a couple of days ago, but to no avail. Still idled fine but bogged when I throttled up.
I can't remove the muffler from the exhaust pipe, and I don't want to remove the whole pipe from the head, so I think I'll just swap mufflers, even though it'll probably mean needing to get a couple new smash gaskets. Probably isn't the problem, but it's not very time-consuming, so I figure I might as well try it out.
Just had a family emergency (great uncle had an accident and passed away last night), so this project may be slow in coming together over the next few days. If any of y'all are the praying sort, I would appreciate your thoughts. Grandma's having a bit of a tough time.
Anyway, I'll probably have some time to go out and swap mufflers this afternoon, and I'll report back if I notice a difference.
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Post by sprocket on Aug 8, 2010 15:02:13 GMT -5
Sorry about your loss...
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Post by ancorder on Aug 8, 2010 17:43:55 GMT -5
So, I ham-handedly rigged the new muffler up. when I pulled the old one off, the muffler just about fell off the header pipe, so if that wasn't the cause, it was about to become a problem.
the trouble is that the threaded coupler didn't fit perfectly over the header pipe, so it was only about 80-90% sealed. I tried it out anyway, and aside from being a bit obnoxious (good thing i've gotten used to wearing earplugs when riding), it seemed a bit more responsive on the throttle. still bogged down a fair bit about a third of the way up, but I didn't want to roll it too hard since I haven't rigged up a bracket for the new exhaust yet.
I guess in sum, I'm not sure if I've made an improvement or not. When I pulled the exhaust off, I did note that the copper smash gasket had a small point of dark burn, which was also evident on the head of the pipe. So I think I had a bit of air escaping there, which wasn't helping, and probably wasn't doing my valves any good. So I don't know if I fixed anything or not, but I do have a much lighter muffler and the need to find a muffler shop to weld the coupling on tomorrow...
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Post by sprocket on Aug 8, 2010 18:49:36 GMT -5
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Post by ziao on Aug 9, 2010 9:57:39 GMT -5
Go ahead and order like three gasket sets that come with that copper ring. I ordered a mrp gasket set with 0-ring only to have a bolt come loose the next day and copper ring fell out.
These are easy to lose if your header pipe is loose, its hard getting the header pipe good and tightened just make sure its on very tight!
Also beware of damaging your engine shroud (plastic cover). With the header not connected 100% hot gas gets out and starts to melt the shroud.
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Post by catbird on Aug 9, 2010 15:45:12 GMT -5
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Post by njyuriy on Aug 13, 2010 0:22:31 GMT -5
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Post by ancorder on Aug 22, 2010 17:12:59 GMT -5
Okay, sorry it's been a while. What with funeral arrangements and family traveling and all that stuff, time has been short. Anyway, I got myself a couple of high-performance exhaust gaskets and got the mower muffler welded to the header pipe, so my exhaust system is in much better shape now.
Still bogging down at less than half throttle. I'm just about to head outside to swap the carburetor off my Schwinn onto the TNG and see if it helps. If it does, then at least I've eliminated everything else, and I just need to figure out what the hell's wrong with my carb. If it doesn't help, well, I'm not sure what's next.
Also, I noticed yesterday when I was running the TNG that there was a sort of whirring noise coming from the head (I think). Not super loud, and it didn't vary with throttle or operating temp. I'm not sure what it is, or if it's normal; it's rare for me to have all the plastics off to where I can even hear such a thing. Anybody know what that might be?
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Post by als01seville on Aug 22, 2010 17:41:08 GMT -5
Scootercromeparts they are way out of site on their prices.
Alleyoop
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Post by sprocket on Aug 22, 2010 17:48:57 GMT -5
>>If it doesn't help, well, I'm not sure what's next.
Change the fuel filter. Get one for a riding mower. It could simply be fuel starvation
causing the problem. For $5 why not?
>>> there was a sort of whirring noise coming from the head
You running a EGR valve cover? They sometimes make a sound as they open and close.
Also, if you have an emission re-breather system they can make a noise.
I removed all the sh^t from mine...It made absolutely no difference in performance
but it is less to go wrong...
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Post by ancorder on Aug 22, 2010 22:14:54 GMT -5
I changed teh fuel filter the last time I was out there since I had another one on hand. Didn't change anything.
As for the whining noise, I think it's normal. I pulled the plastics off my Schwinn and it sounded about the same, so I'm not worried about it.
Now, I swapped the carb off the Schwinn (which was unbranded) and plopped it on the TNG (which had a Mikuni carb on it, strangely enough), and the darn thing ran to WOT without any bogging whatsoever. So it seems there's something internally biffed with my carb. Whether it's the jetting or what, I don't know, but it's the problem. I guess I'll open up both the carbs and see if I can tell what each has for jets. Ran out of daylight to do so tonight, though.
And of course an afternoon of tinkering wouldn't be complete without a new symptom/problem. I've got that new lawnmower muffler on the scoot, and when I revved it up all the way, it backfired on deceleration like you would not believe. I thought I was getting shot at. So, yeah. The higher I revved the engine, the louder the backfire. So I put the old copper smash gasket back on (since it sort of fits up inside the housing) and also used the new high performance gasket, and that seemed to help a little, but I wasn't brave enought o take it all the way to WOT to see how bad the backfire would be. I can say, though, that there were some small backfires on deceleration even from half throttle. Not bad, but definitely noticeable.
Is this just from the new muffler, or have I got something else going on?
If I can figure out how to properly bypass all the emissions crap I may do that, but I'm trying not to get too many things going at once.
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Post by sprocket on Aug 23, 2010 11:07:55 GMT -5
Sorry, I forget was this a new scooter muffler?
If not, then you probably don't have enough back pressure, or the manifold is not sealed totally or you are running way rich...
Backfiring is caused by unburned fuel entering the exhaust. If there is a hole where air can get in it mixes with the fuel and the hot pipe or exhaust valve cause the gas to explode in the exhaust pipe and sometimes the muffler.
>>The higher I revved the engine, the louder the backfire.
Yup, this is because more unburned fuel is getting into the exhaust system...
Try pulling off the air cleaner and see what happens. This should lean the engine and stop the backfiring , at least to some extent.
If this is the case...then you need to get to the throttle needle in the top of the carb and raise the C-clip on the needle one space up, away from the tip.
This will lean the entire throttle range.
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