Issues with new Walbro HD-12B EPA

[slackinoff]

*Moderators - this might be more appropriate in the clone section, feel free to move pls*

Does anyone know if the Walbro HD-12B "EPA" has any differences from the non EPA version besides the limiting screws? This carb will not fully lean out, even with the high jet fully closed up (limiting caps are removed). The low jet is set to about one turn. I bought this carb brand new in box.

This is on a clone 372 OE - I built it last year and have been playing with. It doesn't have much run time. I swapped the Chinese copy on it last night and am going to run it after work today.....I never ran the saw with the included Chinese clone HD-12.

I will be kind of shocked if I can get the clone carb to lean out properly....it will make me think these EPA versions have another difference to them than just the limiting caps.

 

[slackinoff]

Well…..with the original clone HD-12 swapped over it runs exactly the same. I can close the high jet and it still four strokes. Low jet is at about 3/4 to one turn. Not sure what rpm it’s four stroking, but I would guess 11k, a bit above where it cuts at.

I’m just really perplexed at this point.

Could it be super wonky timing numbers? I’d imagine the possibility of two bad carbs is low.

 

[Ketchup]

Try a different coil?
Obstructed exhaust?
Seems unlikely that an EPA Carb would produce excess fuel.

 

[slackinoff]

Try a different coil?
Obstructed exhaust?
Seems unlikely that an EPA Carb would produce excess fuel.

Sorry accidentally posted before replying

Possibly on exhaust, see below. Yep I will snag another coil to try. It seems it could be ignition related. I agree on epa carb thoughts, plus it’s running the same with clone hd-12

 

[slackinoff]

@Ketchup - this is the only outlet on these clone mufflers. You think that might be so small it could cause this? It’s pretty darn small.

 

[Shane¹]

I wonder if it's the coil? I feel like some of the aftermarket coils break down at higher rpms

 

[Ketchup]

@Ketchup - this is the only outlet on these clone mufflers. You think that might be so small it could cause this? It’s pretty dang small and that same thought crossed my mind.

View attachment 394688

I doubt it, but it needs a bigger outlet anyway. My bet is on the coil. Timing is possible too.

 

[slackinoff]

@Shane¹ and @Ketchup Thank you for the help so far on this. Much appreciated. I am definitely going to try a coil. This coil fits a ton of saws so I don’t feel bad throwing that part at it.

I thought I had timed this cylinder but it’s not in my notes. Just in case if’s got some funky timing not jiving with that small ex outlet I went ahead and did a muffler modification. I did both bolt tubes like this.

 

[Ketchup]

@Shane¹ and @Ketchup Thank you for the help so far on this. Much appreciated. I am definitely going to try a coil. This coil fits a ton of saws so I don’t feel bad throwing that part at it.

I thought I had timed this cylinder but it’s not in my notes. Just in case if’s got some funky timing not jiving with that small ex outlet I went ahead and did a muffler modification. I did both bolt tubes like this.

View attachment 394708

Sleeper. Careful not to set anything on fire.

 

[slackinoff]

Sleeper. Careful not to set anything on fire.

Ha! That's funny yes I guess it is! Thank you for the reminder about setting anything on fire. I'm in East Texas, we don't get into burn ban territory that often. But still - good reminder thank you!

 

[slackinoff]

I just wanted to update this thread in case anyone also has issues similar to mine. Nothing helped get the max rpms up or the saw being a pooch.

The muffler mod helped, a new coil did nothing. I decided to just try a whole new AM cylinder. I went with a Laser #44337 (made in Taiwan) and it comes with a Highway piston. $35 shipped on eBay.

The timing numbers came out good. I’m hoping this will give me a fresh start.

Laser Pro #44337 Tiawan cylinder timing with no base gasket.

Exhaust 103
Transfers 128/128
Intake 73
Squish .023

I will post again after I get it installed and ran.

 

[slackinoff]

 

[Outback]

That's interesting. More pics of your jugs please. Seriously, that's whats important.

I remember reading somewhere that hd12b's "can" flow more fuel than a hd6. However at the same time I read that hd12's have a shared circuit with the high and the low as one of the epa provisions. Maybe lean out the L and see if you can get control over the H. The worst you can do is bbq a cylinder or two. You have an extra already.

Have you considered wonky ignition timing? I advanced the timing on my clone flywheel/coil and it still sounds stockish. On my oem bottomed flywheel/coil combo's they sound spicy like they should with the same amount of advance. Since the chinese saws have a key it would be easier to grind her down and bump up the ignition timing. Is your second coil oem or chinesium. I bet the magnet location on the flywheel is suspect. I should probably put a light on a couple at some point.

I had an unmodified 262xp that would yank the rope out of my hand and that saw was the best one of the series I've owned. Let us know if better jugs improve your experience.

 

[Ketchup]

My friend has done tons of 372 and says the main nozzles go bad a lot. Ethanol, ultrasonic, aggressive compressed air or harsh brake cleaner can wreck the nozzle. Then they flood/run fat. I’m working on getting the nozzle part number.

 

[Outback]

They won't idle/run with a bad nozzle. This is what you want.

 

[legdelimber]

View attachment 398675

Slackinoff. I'm just now noticing a streak or something in your last image, looking at what I believe are the clutch side transfers. There's a streak between the the transfer opening, nearest to the intake side.
May just be my eyes, but it looks like it might lift the rings as the piston goes across it.
It's in the lower left area of the pic.

Can you feel it?
If so, Have you pushed (using piston) a ring on top of it and looked for a gap on either side
of the spot, between the ring and cylinder wall?

 

[slackinoff]

@legdelimber - streak is just something the camera is making look weird. No issues with it there.

@Outback - thanks for all the tips!
I tried everything tuning wise. I even tried the Zama C3M carb that came on the 365. It’s a “twin jet” C3M. Same issue as with the clone walbro and the oem walbro. Afterwards, I modified it according to the big C3M twin jet thread on arborist site. Haven’t tested it in the modified configuration, but I went ahead and plugged the high speed hole as suggested when you can’t close the high speed needle enough. This is all well documented in that thread and that mod will certainly get the saw to lean out properly. I’m confident in it. I got this cylinder before modifying the Zama C3M twin jet. Plugging the high speed hole would have fixed the issue I’m 99% sure. But anyways, there was nothing about the FT cylinder I liked. This Laser cylinder has way better transfers and basically everything else too.

Yep, I played with the ignition timing, advancing it past the point a key could be used. Ha that was fun.

Link to more pics of the laser cylinder, page 7.
https://opeforum.com/threads/aftermarket-cylinder-quality.26470/page-7

Twin jet how to modify thread. Link to the big original twin jet thread is linked in the thread below.
https://www.arboristsite.com/threads/zama-carb-mod-cliff-note-version.275905/

 

[slackinoff]

I’m about to install the new cylinder right now actually.

 

[slackinoff]

I know I’ve posted this in the aftermarket cylinder thread as well. But I figured since there was interest in the new Laser cylinder I’d post in both. This was from last night. About to go test!

 

[slackinoff]

I posted this in the aftermarket cylinder thread, but I need to say the same here incase anyone had similar issues. So after all that fussing about with clone HD carb vs real walbro HD12, tuning, coils, ignition timing, ect...it was just a bum cylinder.

Below is the first run with the Laser cylinder. Way way way better already. It never ran anywhere close to this (even without b&c....I've built enough 70cc saws I can tell).

The only problem I had was my modified Zama C3M was having low jet problems. I sort of expected this because of an isssue JB welding and re drilling a passage. It's fixable, but for now it is wearing an Un-Modified Zama C3M Twin Jet and that's ok. It still proves the cylinder was the problem all along.

I'm going to test this un-modified Zama C3M twin jet against an oem Walbro HD12, then finally against a properly modified C3M Twin Jet.