Hyosung SD50 won't start

[sheaiden]

Daughter bought what was listed as a 2007 Hyosung SD50 (sense), and I agreed to get it running for her, if I could.  It was running when we picked it up, put it on the trailer, when we got it home, it wouldn't start.  Checked spark (replaced spark plug because it was the wrong size, but spark was good), checked fuel filter (clean, was flowing past the in-line fuel filter), and checked vaccuum on the petcock tube.  All looked good.

I took off the air filter cover and discovered it didn't have an air filter.  when I sprayed some starter fluid in, the bike did start for about 5-10 seconds; this showed me it was able to run, and suggested to me that I needed to check the carb.

Carb was loose on one bolt, and when I took it all the way off, I noted the o-ring joining it to the engine was broken and "repaired" using some sort of rubber gunk.  

I took off the carb, cleaned it using the instructions in the Hyosung service manual, noted it appeared the jet was clogged, replaced the o-ring (had to use a generic nitrile one with the right measurements, couldn't find a local parts source).  After replacing it, the symptoms changed slightly: it still won't start on its own, but when I spray a bit of starter fluid in, it will run for up to 45-60 seconds, even making it through some revs, till suddenly it dies out.  Carb bowl fills appropriately, carb is solidly on the engine.  I've ruled out the petcock, the fuel filter and sieve, and the float.  Jets are clean now.  I'm guessing it was running when I picked it up and trailered it, but on the trailer ride home the carb shook loose because of the loose bolt and broke the seal.  

I'm wondering given the inexpert repair of the carb that I discovered, whether the mixture screw was set correctly; it was abnormally cold when we picked up the bike (about 45 degrees F), it's about 95 degrees F today.  This leaves me with a few questions:
1: how to verify good starting points for setting the idle and mixture screws
2: does any of this sound like it could be caused by not having an air filter on?  do I have to have the air box cover on? I have read some comments where people say it doesn't run without an air filter because it gets too lean.  
3: Are there any reliable places to buy parts for the SD50 line?  I tried placing a test order from hyosungcatalog.com (kickstand arm and headlight wire harness) to see if they would actually deliver, but they've still not shipped 3 weeks after I ordered.  I'm in MN (US), but willing to order from anyplace that might get me items within a week or two.  

I do notice that when I crank it, it sounds like there's a ringing metal sound (high pitch) while it cranks; I've not worked ever with 2-stroke, so I don't know if that's normal.  goes away when it actually starts.  

[geoffh]

Not familier  with the hyosund but generally, idle screw somewhere between 2 or 3 turns out from bottom, set the idle when it,s running , use a foam pad and cut one to shape, use the air box all the time, it is better to have it fitted on these little 2t they can be "fussy" .use the directory icon on this page to follow a no start check list, keep asking till it,s fixed.

Geoff

[pinkscoot]

Jun 22, 2022 15:06:14 GMT -5 geoffh said:

Not familier  with the hyosund but generally, idle screw somewhere between 2 or 3 turns out from bottom, set the idle when it,s running , use a foam pad and cut one to shape, use the air box all the time, it is better to have it fitted on these little 2t they can be "fussy" .use the directory icon on this page to follow a no start check list, keep asking till it,s fixed.

Geoff

Plus one on the no start check list 49ccscoot.proboards.com/thread/647?page=1 go all the way through and if you have questions just ask. I had a Hyosung with a bad ECU, they are proprietary and I'm not sure where you could get one now. I did a build thread on it the info on what I found is in there.

[sheaiden]

I actually started with the "no-start" checklist, I found it very helpful. here's the results that led me here:
Engine turns over fine, just doesn't start, so start with section 8:
Section 8: Fuel, Check. Kill Switch, this model doesn't have one (plus, it starts with starter fluid). Side note, in the place of a kill switch, it has a "kill the lights" switch. very odd, first time I've seen that. Alarm, n/a.
Section 9: Spark, check. (first thing I checked, actually; before I started researching on the internet)
Section 14: Compression, check (manually, not measured). Plus, it starts with starter fluid.
Section 16: Fuel
I may try getting fresh fuel, I'm using some non-oxy (91) that I picked up a season ago for my snowblower, so it's possible it's old. Still works fine in the snowblower, but it's worth trying fresh. I cleaned the carb just prior to me posting (my first trip through the checklist led me to that step), fuel filter is clean, fuel lines are providing fuel to carb bowl (after cranking the bowl has fuel in it to drain).

Try starting fluid: as mentioned, it starts, so it says to clean the carb. I have, though I'm no expert, so I'll take it off and try again to make sure I didn't miss a plugged pathway or hole.

Air filter was not installed when I bought it, so I'm trying to source a new set of foam I can cut to size. It suggests setting my mixture settings, that's what I've been trying to figure out how to do.

Have not been able to check for reed valve. Will have to see if I have time to take it apart that far. Not sure, given the symptoms, how likely this is.

I think overall my problem is in the mixture; I've received the advice to put both idle and mixture screw all the way in, and then back the mixture screw out by 1/8th of a turn at a time, trying to start it in between all of the turns. Only other thing touched on that I didn't check is the reed valve. I've never worked with 2-strokes before, so I'm not familiar with what a reed valve is, but there's a section on removing and inspecting it in my service manual, and it gives me something to look up and learn about.

Edit:  I've been looking at the page here: www.49ccscoot.com/faq/carbtune.html to figure out the mixture, but I wasn't sure how to use it to find a starting point when I can't get it started...

[aeroxbud]

It's definitely worth checking the reed valve. It can cause starting issues.
It shouldn't be much harder than the carb to get to on most bikes.
You want to see the petals flat, sealed all the way round, and no light getting through.

[sheaiden]

For those following along: I finally got it running for an extended period of time. Reed valve was good, and I checked the oil flow as much as I could (mostly just made sure the tubes in and out were full of oil and it was flowing; don't have the measuring tool and I'd need to make sure it's running first to be exact).

On a hunch after putting it all together, I decided to test my theory that it was simply refusing to run because the air filter was missing. to simulate the restricted air flow of an air filter, I put my hand partially over the air intake in the air filter box, and shot a touch of starter fluid in to get it going. through just moving my fingers and restricting more and less air flow, I was able to sustain it running for a few minutes, though once I figured out the trick I stopped and let it die; I didn't want to damage the engine with constant changes between too lean and too rich.

So now I need to figure out how to source the air filter, source a generic piece of foam to make my own, or find an acceptable alternative (been thinking of those cone air filters that just clamp on the carb, replacing the air filter box). Still not sure why it ran at his place when I picked it up, though I did find dust and dirt in the air box, so it's possible it was clogged and was restricted because of that. who knows.

[jbjhillbilly]

Oiled foam will work fine. Pick some up at a shop that caters to motocross folks.

Uni Filter - BF-1 BF1 12" X 16" X 5/8" 65-PPI Green Fine Foam a.co/d/0vk7Eex

Pod filters are notoriously difficult to dial in.

[sheaiden]

Thanks! I'll check out that foam. Do I need to get the specific "foam oil" that they sell for an oiled foam filter? or is engine oil sufficient? I've tried searching, but I find conflicting information. also, the compartment for the filter is about an inch deep, and I have no idea how thick the OEM filter is. if that stuff is 5/8, should I double it up?

I did order a pod filter from Amazon, I figured if it doesn't work I'll return it; it gets here tomorrow, and looks like the filter foam will get here in about 4 days. I'll update if I get it running fully!

[sheaiden]

Another update: the pod I ordered arrived, the foam is supposed to arrive this next week. I was able to get it running for about 5 minutes with the pod, though I still needed to use the starter fluid to get it to start. as predicted, I had a hard time getting it to dial in to something stable; in the end it did just keep dying on me as I tinkered with the mix screw and the throttle stop screw. I think I'll just wait till the foam gets here, see it the way it's supposed to be, and in the mean time I may take the carb off and make sure it's indeed cleaned fully; it would be good to have my daughter see the whole process. being the non-expert I am, it's quite possible I missed a hole or port or something.

[geoffh]

I take pictures of the two carb halves and cross the passages off as I clear them,practice stripping the carb has meant I can do this roadside with minimal tools it has saved me from  a few "walks of shame" . when the foam arrives box every thing up on the scoot as though you have finished it a loose clip can really mess things up.

Geoff

[repherence2]

Jul 10, 2022 23:01:32 GMT -5 sheaiden said:

Another update: ... as predicted, I had a hard time getting it to dial in to something stable; in the end it did just keep dying on me as I tinkered with the mix screw and the throttle stop screw. I think I'll just wait till the foam gets here, see it the way it's supposed to be, and in the mean time I may take the carb off and make sure it's indeed cleaned fully...

you are chasing the wind. 

with no "stock" filter element in the air box, of course it will be hard to start due to the air flow and air to fuel ratio in regards to the pilot jet because the resistance of the filter element is not present.  without a filter element, the stock pilot jetting is the wrong size.

yes, you can order some foam, but how do you know what the stock thickness and open cell size of the stock foam element was?  even more so, you will chase after the wind. 

most likely the bike ran when you picked it up because the air temperature was lower (45*) as opposed to your current temps of 95*.  that is big difference in humidity and air density.

there is so much information on this forum that has been posted.  a member posted his tried and true method of getting all sorts of 2 stroke engines to fire up.  if you search, the information is all here in the forum.

you should look into getting a Pilot jet kit and a Main jet kit for your carb.  you can run pod filter, aftermarket foam for air box, or no filter, but you still need to get the pilot/idle circuit of your carb in tune to get the bike running first.  lots of information on carb tuning as well in this forum, i highly suggest you read up and do some research.

you might as well get a cylinder head temp gauge as well before you end up soft seizing your engine or burning a hole in your piston while riding or "tuning" the carb.

[sheaiden]

Thanks to those who previously replied. I successfully got it running! Detailing my steps/stumblings here for future forum archeologists.

After reading through the carb tuning posts back at the beginning of this process, I originally thought the mixture needle tightening would make the mixture more rich (restrict air flow post jet). When I took the carb back apart, I traced the tubes again and saw I had made a mistake when I originally identified the pathways, turns out needle in is more lean (restricts extra fuel pre-jet). While waiting for the filter foam and oil to arrive, I discovered this, reversed my needle positioning, and got the engine to fire more reliably when I restricted the air flow with my hand. This made me more confident that once I got the foam to arrive it would work.

Once the foam arrived, I still had to start it using the starting fluid, but now knowing which direction was which on the mixture screw I was able to get it running long term. It would still not start on a cold start though.

Figured out that when I put the carb back together, I had put the auto-choke back in with the collar on the wrong groove (there were two that were right by each other and both fit, about 2 mm apart). As a result, the auto-choke was starting too low, and was essentially never opening. It appears the proper placement on the auto-choke that I have is on the bottom groove.

It now starts, and after some tests (and rereading the carb tuning posts), I was able to get it to let me accelerate to 30 (at first, it was idling fine, but would die when I opened the throttle too high).

I still have some dialing in to do, but I think actually getting the thing running is a success. Thanks for you guys' help!

Regarding the advice from repherence2 regarding getting replacement jet kits, or even just parts in general: the issue I've found is that there are precious few places that sell parts for this scooter. I don't know enough about this type of engine to know what after-market parts are compatible, and the originals are only sold at a few stores. When I tried ordering from one of them it took them 2 months to even acknowledge my order, then only sent half of it and didn't bother refunding my money till I told them I was looking into a credit card reversal. Noob mistake #2: don't buy a used bike without making sure parts are still readily available for it. Lesson learned, both me and my daughter.

[geoffh]

That's good news,if you post some pictures of the scoot and engine in particular one of our fine members will recognise it and be able to point you towards aftermarket goodies,have look for the chassis number and engine number and code,the dark winter nights are looming down.

Geoff