Hd18b in my ms460

[MG porting]

The only difference in tuning at half a turn and farther out is how quick it adjusts. The same amount of fuel is needed with the same size Venturi whether it’s 1/2 turn or 3.5 turns or am I thinking wrong here!?

Depends on carb I'm not finished testing Lighting Performance is going to check and see if he has a smaller jet for me to put in the hd18b and I'll go back and put it back in and do more testing.

 

[huskihl]

The only difference in tuning at half a turn and farther out is how quick it adjusts. The same amount of fuel is needed with the same size Venturi whether it’s 1/2 turn or 3.5 turns or am I thinking wrong here!?

Nah you’re right I think

 

[huskihl]

The only difference in tuning at half a turn and farther out is how quick it adjusts. The same amount of fuel is needed with the same size Venturi whether it’s 1/2 turn or 3.5 turns or am I thinking wrong here!?

I think the metering needle and pop off would have more to do with running lean after a long cut. Or it heated up and wasn’t tuned rich enough to start with

 

[mdavlee]

I think the metering needle and pop off would have more to do with running lean after a long cut. Or it heated up and wasn’t tuned rich enough to start with

Yes. The jet can’t let what isn’t there through it. I swapped to .74 jets in WJ69 a couple times. All it did was move where it turned to. It is more responsive under 1.5 turns than 3-5 turns out like I’ve had RWJ-4.

 

[MG porting]

The key thing is having the right jet size so that you have a good adjustability for what the saw wants and for elivashun which is kinda a pain around my parts of the woods because elivashun can go from 50 foot above sea level to 4,000 foot above sea level so finding a good setup is King. I know some of you guys probably think I'm crazy or don't know my ass from a hole in ground but that's ok I not really out to prove you wrong or out to prove I know more than you I'm just doing something that to me if it works and work good then why not I've seen a lot of crazy *s-word in my time that you wouldn't think it would work and then find out that it did indeed work and worked good.

 

[Wonkydonkey]

The only difference in tuning at half a turn and farther out is how quick it adjusts. The same amount of fuel is needed with the same size Venturi whether it’s 1/2 turn or 3.5 turns or am I thinking wrong here!?

I think your right.. but having read the last poastin... I thinkin even an mtronic May have trouble at that elevation deviations.. 50 -4000 ...

 

[mdavlee]

I think your right.. but having read the last poastin... I thinkin even an mtronic May have trouble at that elevation deviations.. 50 -4000 ...

They don’t normally. I’ve run them from 840-3700 in a matter of days

 

[MustangMike]

I believe I was told that the HD-50 (461 Carb) has different internal ports than the other carbs.

Anyone have any information about this?

Also, what would happen if you slightly enlarged the venture on the smaller venture carbs?

I've been warned about playing with this stuff, but I ask anyway. Also, on some carbs the tubes stick out much further than others. Thoughts about modifying that?

 

[MG porting]

I believe I was told that the HD-50 (461 Carb) has different internal ports than the other carbs.

Anyone have any information about this?

Also, what would happen if you slightly enlarged the venture on the smaller venture carbs?

I've been warned about playing with this stuff, but I ask anyway. Also, on some carbs the tubes stick out much further than others. Thoughts about modifying that?

Some times you can take the tubs out without them braking but it's a 50-50 shot you can make the Venturi bigger but if there's anything kind of casting flaw you'll find it and hit a passeg that you won't be able to pach up.

 

[MustangMike]

Only one response … the silence is deafening! I may just have to play and see what happens, I did buy several of those ZAMA produced Walbro clones.

They work well, but the venture looks tight and they may be limiting my performance.

I'm just trying to think of the best way to do it. It would be easier if it were an uninterrupted circle, but it is not.

 

[drf256]

I believe I was told that the HD-50 (461 Carb) has different internal ports than the other carbs.

Anyone have any information about this?

Also, what would happen if you slightly enlarged the venture on the smaller venture carbs?

I've been warned about playing with this stuff, but I ask anyway. Also, on some carbs the tubes stick out much further than others. Thoughts about modifying that?

Only one response … the silence is deafening! I may just have to play and see what happens, I did buy several of those ZAMA produced Walbro clones.

They work well, but the venture looks tight and they may be limiting my performance.

I'm just trying to think of the best way to do it. It would be easier if it were an uninterrupted circle, but it is not.

I’ve been told that the 461 has a different midrange fuel ramp. Could be that the transition holes under the Welch plug are larger, IDK. I’ve never had much luck with the HD50. Have one here that I could never get to run right Mike-it’s yours if you want it. Shafts all swapped out already to standard 044 stuff.

I think enlarging a smaller bore carb isn’t done much for this model cause it’s just not worth the work of doing it. You can usually find a junker oem HD for around $25 with the larger Venturi. You can tap the main nozzle through the bore if you want a perfect circle to play with. Very often there is a hidden passage under the Venturi that you will find the hard way when you try to open it.

The nozzle sticking out into the bore more on some models is interesting to me as well. It has to make some fuel ramp differences.

Remember what a Venturi does, it creates negative pressure/vacuum to pull fuel from the nozzle. If it’s oversized for a certain displacement saw, it will create less negative pressure and pull less fuel, so a richer jet will be needed. It’s counterintuitive. Everyone looks for a fatter jet on a bigger saw, more displacement more fuel right? Wrong, the bigger saw will pull more air through the Venturi and increase the negative pressure. It will pull more fuel from the same size jet as a smaller saw. When I did Duane’s 026 with the 044 carb I learned this. I drilled the jet to near 80 to make it run right. My hybrid runs a 72 jet.

 

[mdavlee]

I’ve had some saws tune leaner after porting than before. I never would have thought that. A couple suck the choke shut on Zama carbs as well.

 

[huskyboy]

I’m wondering if the intake port shape, duration and how much it was widened has something to do with how the carb responds. If the port is enlarged, effectively we are loosing velocity and increased the duration. Therefore that should require more fuel?

 

[drf256]

I think velocity in a port has more to do with responsiveness and resistance to falling out of the power band.

A huge intake port will flow the most overall, but if it’s in a worksaw that has a sudden increased load applied with a long bar, it will cause saw to bog out. That same port will probably make more peak power in a 12 x 12 cant cutter.

One size doesn’t fit all.

Personally I try not to make intake ports any larger than 100% of carb bore. I think the saws run better there. But I don’t build race saws.

 

[MustangMike]

I have widened and flattened several intake ports w/o any decrease in responsiveness. It is different than a car, the intake just feeds the crankcase, not the combustion chamber. On a saw that is dictated by the transfers - and they are the "dark world" in my mind. My thoughts on intake and exhaust are a lot more solidified.

 

[MustangMike]

On the carburetor, I have several of the ZAMA produced Walbro clones from D Dave. They run very well, but the venture seems a little tighter than an HD-16 even though the incoming port is the same size.

I'm thinking they may be prefect for a 440, but the hybrids may need a little more air/fuel. My thought is the additional volume (flow) of the hybrid will allow me to open up the venture a bit and still create sufficient vacuum to pull the fuel.

My ported hybreds seem to be limited in RPMs and I'm thinking this may be why.

Thanks for the offer on the HD-50 Al, but I already have one here. I had purchased 2 from D Dave, and the only saw that liked it was the ported 460 you did for me. All my working Walbro's are in use, but maybe I should pull one from another saw and see if it makes a difference.

FYI, my "unsnorkled" ZAMAs (that came on early 044s) also seem to have a tight venture, but they don't have that fuel tube protruding, so it may be a wash. My testing with my 10 mm 044 did not show any improvement with a snorkel Walbro carb.

Back to Taxes for now, but the wheels are turning!

 

[RI Chevy]

I think the HD11A was a great carb!

 

[MustangMike]

I’ve never had much luck with the HD50. Have one here that I could never get to run right Mike-it’s yours if you want it.

Thanks for waking me up Al. I do have an HD-50 still in the box and I should put it on and see what happens. That will be my next step. It was only used briefly when I did carb tests on other saws. Sometimes, you just overlook the obvious!

Unfortunately, it will likely take a while. Even though they extended the deadline, my phone has been ringing off the hook the last few days.

Yea, I got them on 2 saws, should have bought more of them before they vanished, but who knew?

 

[MustangMike]

Hey, I just want to thank everyone for starting and participating, and posting information in this thread.

It woke me up to the fact that some carbs have tighter venture's than others and that it was contributing to a lack of performance with the AM 440 Big Bore saws I have been building.

It also forced me to "take the plunge" to modify a carb for the first time … and the results were well worth it (at least on my second try).

I also thank D Dave for having had these low cost carbs available in the past, glad I loaded up on them, they work well and are 1/4 the price of OEM.

This is yet another example of the collective knowledge of those on this site helping to improve the performance of my saw.

THANKS TO ALL!!!

 

[MustangMike]

I think the HD11A was a great carb!

Yes, but they are NLA. HD-14s are still available, I guess that is the best choice from what I have read here (and re read so I start absorbing it).

Good thread!