Engine Trouble 7000ft+ carb jet tuning help? I've tried almost everything.

[Lucknuts]

We live at between 6500 and 10,000 ft. here and I have tried everything I can find online to fix the "way too rich" situation to no avail. Help!

1. 3 times over every gasket is sealed every bolt is tight, including the carb to the carb pipe thing going into the head. Yes exhaust too.
2. The chain is straight as an arrow and perfectly tight.
3. All the electrical is functioning properly, getting great spark from this NGK plug.
4. Air filter is sealed, working and fully open.
5. Timing looks right doing TDC test and looking at magneto, comparing to online pics

The bike still 4 strokes when idling and bogs down when given gas.

So, must be too rich right?

6. Soldered the jet closed and poked tiny hole with high E string from guitar. Opposite problem.
7. Widened hole with pin and blow torch. Back to too rich again.
8. Inserted high E string into carb jet (after removing all solder and using original jet size): too rich
9. Doubled string: too rich
10. Used B string end #24 (then doubled): too rich still
11. B string with coiled wrapping (almost blocks jet entirely): won't start.

Can anyone tell me where to just buy a jet that is the correct size for my altitude? Please? It's fun for me to MacGyver stuff but this is too much.

Thanks

 

[Deleted member 12676]

there is no way to know what size jet you will need. Just buy a micro drill bit set and try different sizes. Where to buy a set and what steps to take to jet it correctly is on my site. (click signature link)
I was at 8500ft and had to solder the lower portion of the needle to get the jetting between idle and mid range correct. Getting top rpm jetting with the main jet is the easy part. I finally got a Dellorto SHA and was happy till I moved down to the coast where I could never get it jetted right. Now I use a fully adjustable Mikuni and am very happy.

 

[HeadSmess]

another alternative to soldering and drilling is using strands from the finest copper wire you can find. just keep soldering one in at a time til its right. the finer the wire, the better. use a very hot iron and only "tack" the ends out away from the jet hole.

for using a guitar string...hmmm... 020 would be around 0.5mm? high E is usually a 10, that would be 0.25mm. so id be fiddling with 18-22 guage if i was to try making holes that way... b or g... sometimes the inner strand of the wound strings is right...

i do use strings to guage my holes after drilling. invariably accurate


a set of microdrills from 0.3 to 1.3 in 0.05 increments should be around $20 on fleabay. you will need a pinchuck to hold them. id be trying 0.4 to 0.5 at first.


when you look at the slide, youll notice a cut away that faces the air filter. not the narrow angled slot for the idle screw thats opposite the slot for the cable/locating pin. you wont see these when the carbs assembled. its just a shallow angle on the front face/bottom edge, visible down the throat.


increasing this angle or its depth will lean the bottom end or idle out. avoid it, can be easy to go too far.

main jet is wide open throttle. the needle and its height, controlled by a small e-clip, is the mid range. the angled cutaway is the idle.

start with full throttle, get it right, move to mid, move to idle.

plug chops and reading a plug. get a new or clean plug. run it for a good mile at the throttle setting you want (liquid paper marks on the throttle grip and housing!) and hit the kill switch keeping the throttle in position. check plug. you want light tan, a vaguely rusty colour depending on fuel and oils and plug heat range. black is rich, or too cold a plug, bone white is too lean, too hot a plug (or just right if the mix is right). if its too lean it wont run. easy.

 

[Lucknuts]

Awesome info, thanks guys! Can't believe I didn't think of copper wire!

I only had a few odd extra strings around and I didn't want to take any off my guitars. I have loads of wire around here. Also, the drill bits are inexpensive and I've already soldered it closed again.

Unfortunately, home depot didn't have micro bits when I checked. So, the only place to get them is online? Bummer. I suppose I can wait until next weekend to finally ride it. Maybe I'll try the copper wire after all. And, a blowtorch seems to work way better than a soldering iron for this stuff if you guys haven't tried it.

 

[Lucknuts]

Also, if I'm going to spend over 20 bucks online for a micro drill set and tiny chuck, it seems I might be better off just buying a better carburetor.

If any of you guys want to recommend a better carb in the $20-40 range I appreciate it. Sorry, I haven't searched the forum that yet though. I'll do that as soon as I can. Thanks.

 

[Deleted member 12676]

all the cheap carbs give cheap performance and arent made well.

For $75 you can bolt on a Walbro carb from JNMotors but it don't allow an extended intake for low rpm power boost. A 18mm Mikjuni costs $70 but you need custom adaptors for it. A Dellorto SHA will bolt on but it is a headache because only adjustment is changing the main jet. And they eventually break where they clamp on.

 

[HeadSmess]

i like having the drills cus when you get a new carb, invariably, you still gotta use them?

new carb, old carb, it will still need jetting to suit your needs

jetting is worth learning.

imho, dont worry too much about carbs, other than some dialling in. which is what youve been doing.

the things mainly WOT any way, anything else is just puttering around, and with under 2 hp usually, throttle control isnt really an issue... at WOT, the stocker does fine.

all my mucking with fancy carbs has made me draw one conclusion...keep it stock.


remember! KISS!

hehehe, im only at 250m or summink

 

[Deleted member 12676]

my experience is the opposite.
the 12mm Dellorto gave me 8% more top speed than the stock 14mm NT carb. Both were jetted for max speed.
A good quality carb just does a better job of atomizing the gas. The gas is entering the air stream thru 3 or 4 holes in the Dellorto, whereas the NT has only one big entrance hole. Obviously the one with the more holes is going to do a better job of atomizing. Although I dislike the Dellorto SHA for its inability to completely tune, I really like its design with multiple entrance holes for the gas. That is one advantage it has over a normal carb with two entrance points. I hope to experiment with the 16mm SHA in the near future.

 

[Lucknuts]

Whaaa? Cheap freaking engine, why would I pay about the same price I got the thing for, for a carb?

See, that's the problem when people take something way too seriously; Clever marketers make y'all look like fools paying crazy money with too high a markup because it makes you feel cool.

Anyway, I've almost got this turd tuned. It's a lot of fun when it has power.

I started with two wires taken from a 16g strand. Then three, still too rich. Then I could barely fit the fourth and it ran just amazingly. Yet, when I checked the plug it was slightly white! Yikes, I thought the pipes were hotter than usual.

Poked it slightly with a pin to mash the copper a bit and make a slightly bigger hole. No love. Now it's too rich again. Frak.

I'm losing my mind over this stupid thing. It's supposed to be simple, yet it's far from that. It's supposed to be inexpensive but there's some kind of industry for this crap pushing gawd knows what for outrageous prices... have I missed any paradoxes?

These bikes are incredibly lame and yet people race them? Wow. I don't think I could be more confused about a subject after so much research? What is this some secret mason thing? Is there a union?

 

[Lucknuts]

Here's the nitty gritty: I have it close to tuned for this altitude, but apparently it'll 4 stroke and bog unless the jet is just shy of too lean. Apparently that's hard to get. And if I got tiny drillbits wouldn't they just break?

But, here's the thing. I made a stealth silencer to see if the noise I was hearing was the 4 stroking pinging or not. It's not! The freaking engine sounds like it's clattering and scraping and destroying itself and that's just idling.

As far as I remember from mopeds this isn't right. Sure the clutch makes a lot of noise which really sucks. But, it's not that. I can hear the piston going up ancarburetord down and it sounds like it's scraping and flopping around in there, slightly.

WTF is that? it's a metal scraping on metal sound, chug a chuga a slap slap chuga