jetting seems SO close, yet not quite

[discochris]

Got the Mikuni clone reinstalled on the Enforcer...

Running a 115 main and 25 pilot. Needle in the middle position. Ebay exhaust. Stock airbox.


At around 900' above sea level.
Have tested a few different settings with idle screw and fuel/air screw.
Bike starts and idles just fine. Runs decent below half throttle, as soon as it gets to mid-throttle, it sputters and bogs.

I don't have a tach, so I can't tell you exactly what RPM it stumbles at. It feels so close, but still off. I've read most of the threads here, but can't decide which way to go next.

[wheelbender6]

Keep checking your spark plug. The electrode insulator should be tan in color when the jetting is right.

[Wild Dog]

Got the Mikuni clone reinstalled on the Enforcer...

Running a 115 main and 25 pilot. Needle in the middle position. Ebay exhaust. Stock airbox.



Did you check the spark plug? I bet it is crayon white.

[discochris]

http://https://chris-berg.smugmug.com/Motorcycles/Bashan-250/i-GLXWMkB/Ahere's the plug

[discochris]

I put in another plug and it ran much better, but this plug was brand new. I bought it last month when I bought the bike.

The stumble is still there.

[Megadan]

Make sure it isn't stuck at half choke. That fine til half theottle and then bog is exactly the issue you will run into if it is.

Also, that 115 may be a tad rich with a stock airbox. Have a 112.5 main jet?

[discochris]

Not at half choke. This is with choke off.
You think it's too rich with a 115? I was thinking it might be too lean, looking at the plug, and noticing the engine seeming pretty hot.

I don't have a 112.5, I have a 110...

[Megadan]

Not at half choke. This is with choke off.
You think it's too rich with a 115? I was thinking it might be too lean, looking at the plug, and noticing the engine seeming pretty hot.

I don't have a 112.5, I have a 110...

I live at 1100ft, a 27.5 pilot, needle 3rd slot, and a 115 main was what I ran with a pod filter and full exhaust in the warmer months. You might be fine with a 115, just a.thought since you have a stock airbox.

The only other thing I can think of is the float height might be off.

I only bring up the half.choke thing because it has bitten several members here, even me. Heck, I had the choke go to half on its own once when I hit a bump lol.

[discochris]

So I tried a 110 main. Bike ran EXTREMELY hot, and not well. Obviously lean.
Having already used the 115, I thought I would try a 120. No more stumble, bike pulls strong. Starts right up without needing choke.
(this was with the 25 pilot and the needle in the fourth position from the top.

However, idle was off - when I revved it in neutral, it wouldn't come back down, and it didn't idle well.

Turns out I appear to have lost the retaining clip that goes in the slide above the needle. Argh. I have no idea where it popped off to in the garage. I may end up having to order a whole new carb if I can't find it...

[Megadan]

So I tried a 110 main. Bike ran EXTREMELY hot, and not well. Obviously lean.
Having already used the 115, I thought I would try a 120. No more stumble, bike pulls strong. Starts right up without needing choke.
(this was with the 25 pilot and the needle in the fourth position from the top.

However, idle was off - when I revved it in neutral, it wouldn't come back down, and it didn't idle well.

Turns out I appear to have lost the retaining clip that goes in the slide above the needle. Argh. I have no idea where it popped off to in the garage. I may end up having to order a whole new carb if I can't find it...

The missing needle clip would definitely explain the part throttle weirdness. Glad to hear the 120 main worked out.

As far as needle cljps. https://www.amazon.com/MIKUNI-VM20-369-NEEDLE-CLIPS/dp/B003CJW4W8

Never hurts to have spares. ;)

[discochris]

Not the C-clip. Isn't there another retaining spring thingy that goes above that?

[Megadan]

Not the C-clip. Isn't there another retaining spring thingy that goes above that?

Ahh, you are talking about the V shaped retainer. You should be able to just borrow one from the stock PZ30 carburetor. They may be called different names, but they share quite a few parts.

[discochris]

Ahh, you are talking about the V shaped retainer. You should be able to just borrow one from the stock PZ30 carburetor. They may be called different names, but they share quite a few parts.

That's it! Thank you...

[Megadan]

That's it! Thank you...

Did that work out for you?

[discochris]

Still working on it. Didn't realize that I needed to plug off all the air box hose stuff with the new exhaust... It's getting closer.

[discochris]

So I think I'm close.
I'm running a 120 main and 27.5 pilot. Needle in the third position (middle). Bike starts right up on full choke, and as it warms, I can go to half and off. About 1.5 turns out on the air screw. All good news.

Still stock airbox and the ebay muffler.

However... I'm getting some backfire on decel from full throttle.
I can't possibly imagine with a 120 and 27.5 that I would be running lean, so I suspect I have an exhaust leak. I ordered a new gasket yesterday.

I did pick up a small tach to install to set the idle correctly.

I also need to check the valves again when the bike cools down. I set them when I first started working on the bike (they were tight as expected), but they seem particularly noisy now. Do these bikes tend to have a really noisy valve train?)

[discochris]

Took it out today. Starts, idles and runs well to mid-throttle. Bogs and dies closer to WOT and is backfiring on decel. Going to wait until the exhaust gasket gets here this week and make sure the other connections are sealed. If same results, going to go back down to 115 on main jet since needle and pilot seem to be doing their job.

This is certainly a learning experience. I've owned carbed bikes before, but have never really done this kind of tuning.

Took my big V-Strom out for a few hours for some two-wheel therapy...

[Wild Dog]

I also need to check the valves again when the bike cools down. I set them when I first started working on the bike (they were tight as expected), but they seem particularly noisy now. Do these bikes tend to have a really noisy valve train?)


What's the gap for In and Ex? They shouldn't be noisy.

[discochris]

What's the gap for In and Ex? They shouldn't be noisy. I set them to spec. But I need to double check. I believe I set them to .003.

[discochris]

Today's update. The valves were definitely off. Not sure how that happened - I might have not had it correct at TDC. Engine runs much quieter now. Starts and idles well. Runs well to half throttle still.
But is still bogging past 3/4 throttle and backfiring when I let off. Dropped the main back down to 115 and then 110 to test.

I'm almost positive the issue at this point is an exhaust leak. New copper gasket comes tomorrow and I have sealer for the two connection points.

[discochris]

It's fixed! But it wasn't anything I thought.
I pulled the exhaust, put in the new gasket, sealed the connection points.
Bike was still running like crap. Still stumbling, backfiring, dying. I was at the end of my rope.

But I had picked up a second Mikuni copy the other day for parts and because I thought I'd lost that piece that holds the needle down (which of course I later found.)

So I pulled it out of the box, put in a 115 and 25, 2.5 turns out and put it on the bike.
Adjusted the idle, and the bike runs perfectly now. No stumble. No backfire. Doesn't die.

I'm not positive what was wrong with the other carb (I suspect possibly a bad fuel-air screw), but thank you all for your help. This is one of the better and more supportive motorcycle sites on the web.