Linhai Bighorn 260cc 2x4

[MechanicallyMinded]

Hello everyone,
I have a older model Linhai Bighorn 260 2x4. I bought this bike cheap, quite some time ago. It was in a field stripped with nipples still on the tires. I have slowly tinkered my way back to a complete bike. Rode it and was completely disgusted with how it ran.

Before I go much farther let me say, this is my "loaner or secondary" bike. Nice to 2up with the wife and stuff. It doesn't see much use, but I do want it to be amateur proof, for a buddy or two.

Now, the hardened duct work cracked and things got bad. The manifold cracked and it was worse.

Ordered new intake manifold for rocketa/manco. Fit great, re-installed and ran like mud. Backfiring, spitting raw gas, erratic idle. I knew I needed a re-jetting and I despise these carbs. I took it off, pulled the jets, put the jets in a bag and the carb in the trash! Much better!

Ordered a 30mm pwk flat slide, jet kit, pvc for ducting, and began my adventure.

I have a decent running bike right now on a 140 main. Problem is I am having a hard time telling what my secondary is doing. I do not know if the slide needle has clip grooves or not, haven't made it that far yet.
Starts good. Seems to idle slightly rich, loads up at idle over time, and just as the throttle is first pressed it stumbles until the needle is picked up. After that, throttle rolls on and off smooth and W.O.T. is better than ever. Thing sounds like a jet ski.

My question is has anyone gotten a good base with a pwk on a 260 linhai.

It looks like I will land mid spectrum on the main, but very lean on my secondary. Is this a usual characteristic for this engine? It goes against what I want to do from habit. Even worse, that means the carb shipped with a too small main, and a too large secondary. Sounds off too... I assume it was aimed toward a 90-150cc expansion explosion diversion converter. Either way, it might run 8n ford that way.

What diameter carb and jets are you running? Don't get wrong, it is wayyyy nicer than before, but still... not RIGHT. I will swap more jets tomorrow. And I will post up some pics of what I have done.
Sitting on a 140 main and 40 secondary. Seems to want leaner at idle. Choppy and loads up after 20 seconds or so.

Thanks for taking the time to read! I expect my personal pan pizza coupon now.

[MechanicallyMinded]

Easily resize photos on mobile?

Pwk 30mm (specifically the black/red one.) Pwk jet set. 2" pvc elbows for ductwork into airbox. Cone filter, "auto cold air intake type". The air box has no lid, and is functioning as a splash guard only. The pvc extends into the box.
I found a nice clear fuel line in the fuel line section of oreilly auto, even thin spring clamps to all fit perfect. The line is snug on the carb, tight with the clamp, but stretches to fit an inline filter to coincide with the fuel tank outlet size.
I am running a single line, no fuel pump, gravity feed with a screen type filter.

Stock pwk 30mm jetting as shipped was main 124. Secondary 34. Started and high idle cold, as it warmed up it died. Takes no throttle. Obviously lean.

With no baseline, I randomly selected a 155 main. As expected, started, high idle with seemingly no adjustment on air screw. Flat spot at less than 10% throttle, stumbles. Old black plug got darker. Bike would rev between 30-70% throttle.

Installed a 140 main. Bike started with high idle. Flat spot below 10% throttle. 30-70% throttle and W.O.T was improved. Bike was able to move. WOT pull and shutdown reveals no noticable color change to OLD plug, which is already hard to read. I have 2 new plugs saved for when we get closer.

Moving forward, secondary was 34 stock, again with no baseline, tossed a 52 in it. Obviously rich. Hard to start, requiring throttle. No adjustment on air screw. At idle it loads up and requires a brap-itty-brapp-brap of the throttle. Flat spot at less than 10% throttle, 30-70% throttle and W.O.T reasonably unchanged.

Dropped secondary from 52 to 45. Starts poorly on it's own. Idles for approximately 20 seconds before loading up and beginning to stumble. Brap-itty-brap some more. Flat spot at 10% and less throttle. 30-70% and WOT

At this point, I disassembled to the throttle slide needle, 5 grooves. In middle position, there was the clip. Pulled clip and put it on the next groove to make the needle higher. Then searched the ground for the tiny clip for 10 mins. Reinstalled. Flat spot at 10% and less throttle gone. Bike will creep along and runs decent from off idle to WOT. Getting closer.

Dropped secondary from 45 to 40. Starts decent on it's own. Idles slightly erratic, doesn't want to idle down without stalling. A small amount of change on the air screw when nearly out.

Dropped secondary jet from 40 to 38. Bike starts on it's own flawlessly first or second hit. Flat spot off idle to 10% throttle is gone. 30%-70% throttle and WOT are better than ever. Adjustment appeared closer to 3 to 4 turns out on air screw. Getting closer!

Currently this is where I am today. I am dropping from 38 to 35 on the secondary now to try. I live inside city limits and it is difficult to get any decent run time in the yard. I leap in and out of the street without fenders. The neighbors do not understand my jetting efforts.

If the 35 secondary will get my air screw adjustment closer to 2-3 turns out it will be very close to right. Even now it runs better than ever. Wife and I, even 2up-ed for a 30 min ride earlier and I have 15% more power than ever before. We creeped through fresh logging and buzzed gy6 style on the asphalt. Still can't stabilize the idle at very low rpms yet, too rich at idle.

I will have to go to another location with my 2 new plugs, I will be doing an idle only plug check and a WOT pull and shutdown plug check to really sight this in. So far, I am more happy than ever with this pwk conversation.

I will update on what I find and what jets specifically work for me. I am approximately 700 foot above sea level.

[MechanicallyMinded]

Alright, today my pwk 30mm on my older Linhai big horn 260 atv is sitting at a 140 main jet, 35 secondary, and the throttle blade needle is second from the LOWEST setting. Air mixture screw is between 1.75 and 2.25 rounds out, still playing with it.

This is a good baseline. Bike runs excellent, idles great, throttles amazingly, loves W.O.T. and happily returns to a stable idle. I am ready for my new plug shutdown checks. I am approximately 500-700 foot above sea level. To be honest, it is the best it has ever ran. I would be fully satisfied to leave it the way it is, except for I want confirmation of a clean plug, off principle.

I hope someone else finds this useful. Again pwk 30mm 140 main, 35 secondary, 2nd to lowest needle setting. 2" pvc ducting into air box, with a large automotive style cone filter. Good starting baseline for Linhai Bighorn 260 Atv.

[MechanicallyMinded]

Man...

[MechanicallyMinded]

After a plug check, bike is all around lean. A quick main jet bump should suffice. Although weather has not permitted me to carry on, as of yet. I think five or 10 points should work. I will try ten, it's easier to drop size for confirmation, if needed.