Chainsaw Porting Theory

[Redfin]

Good stuff fellas, good stuff.

 

[Terry Syd]

The 460 carb has some big air bleed holes. The stock spring is rather light, so this carb has a lot of potential for a heavier spring and more flow in the low speed circuit. It could become THE carb for big bore saws that use the HD carb configuration.

EDIT: I'm running it on a 64cc 029 and I have the auxiliary jet blocked off (I got it too big and the idle was crap). However, on a bigger saw I would work with the metering spring to see if I could get the fuel flow I needed. I could then drill the auxiliary jet to add a bit more if needed. The only thing I don't like is the position of the discharge for the auxiliary jet, it sits too close to the throttle plate. If the idle became a problem, it may need to have the discharge port for the jet drilled at an angle to get it away from the throttle plate.

 

[mdavlee]

I'm going to try to fit a rwj4 on mine when I get the time.

 

[Deets066]

I would like to try modding this WJ 17 on my hybrid. Low side is 1-3/4 out and the high is 1-1/2 turns out. Saw behaves really good with snappy throttle response. But I think there is more to be had

 

[drf256]

Ok that makes sense.
Earlier I think terry mentioned the transition holes acted as air bleeds until the butterfly opened. This is what I don't get. I thought you meant you drilled another hole down to the fuel reservoir....
Do these holes actually bleed air into the carb body?


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Dan, these pics may help us all understand.

 

[paragonbuilder]

View attachment 26182 View attachment 26183 View attachment 26184
Dan, these pics may help us all understand.

Thanks Al!
That helps me a lot. It's got my wheels turning again...


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[Terry Syd]

Here's an illustrative chart that gives the concepts of fuel air ratio to horsepower. The EPA wants to keep you down in the lean range where the engine will still run, but with less power and less emissions. I have a preference to the higher end of the curve.

 

[MustangMike]

Why the dumb EPA can't learn to test based on productivity instead of just engine size is beyond me. It makes no sense to cut emissions by 20% if it now takes 40% longer to finish the job! It's stupid I tell ya, just plain stupid!

 

[Mastermind]

Rich, I saw in the tech section under carburetors that your now having to work with Zamas that aren't 'twin jet'. Bugger, those were easy to mod, hopefully you will get your head around the newer type carbs.

Here's something I've run into when modding the 460 carb. I like the 460 carb because it has the largest venturi of the HD series (17.45mm) plus an offset main discharge nozzle - I think it will flow the best of that range of carbs.

The 460 carb is an EPA carb. I had originally thought that the small jet in the carb was a restriction on the low speed circuit - it isn't. Turns out it is an 'auxilliary' jet like on the twin jet Zamas. Unfortunately, it sits too close to the throttle plate and can cause problems with the idle, especially when it gets drilled larger (I don't know what the max size should be...)

Then I thought "where in the Hell is the source of fuel for the low speed circuit??" - I found it, I had to punch out the main discharge nozzle. You wouldn't believe it, the low speed circuit takes it fuel from the high speed circuit. There is a passage way drilled into the nozzle tunnel that leads to the low speed circuit.

I plugged the passage in the nozzle tunnel with some GB Weld, put the nozzle back in and then drilled a 1mm hole in the wetside just in front of the low speed needle seat in order to feed fuel to the needle. It completely changed the way the carb worked, it went pig rich immediately.

Not only is the idle more stable, but the max RPM is more stable. I'm going to do some more work with the metering springs, but I think I'm on the home stretch with this carb.

I thought you might like the information about where the low speed circuit picks up it's fuel as you may run into the same configuration in other carbs.

Lots of newer carbs are like this Terry. The 3120 carbs I do are the same way. Everything goes thur the main jet, to the metering nozzle area, then on to the low side and welch plug area.

 

[riverrat2]

Lots of newer carbs are like this Terry. The 3120 carbs I do are the same way. Everything goes thur the main jet, to the metering nozzle area, then on to the low side and welch plug area.

Happy 4th everyone,,,, If you know a veteran,,, Give them a hug or handshake, and tell them thanks,,, cause I sure do!!!

and Thank You Randy for fixing the carby on me 312o!!!! WOOT WOOT!!!!!

 

[MustangMike]

My friend Harold, he did 3 tours in Nam, says that I am the only one who ever sent him a Veteran's Day card. I used to send them every year, but no one has them any more, sad!

 

[Terry Syd]

My friend Harold, he did 3 tours in Nam, says that I am the only one who ever sent him a Veteran's Day card.

I did two hard tours in Nam and all I got was crap from people when I got back. It was 'politically correct' to act that way back then, now it is politically correct to say "thank you for your service". - I feel like telling those people to go fork themselves.

Lots of newer carbs are like this Terry. The 3120 carbs I do are the same way. Everything goes thur the main jet, to the metering nozzle area, then on to the low side and welch plug area.

I'm going to play around with this 460 carb and see where I can take it. I also have an HD-5 that appears to be designed the same way. We may be able to come up with a set of general mods that can defeat the EPA geniuses.

 

[CR888]

Yeah the Nam vets were treated disgracefully upon return here. It was totally wrong led by fools that had no understanding of the situation they faced. Fortunately public opinion has changed nowadays for good reason. Back to Walbro wizardry.

 

[MustangMike]

I did two hard tours in Nam and all I got was crap from people when I got back. It was 'politically correct' to act that way back then, now it is politically correct to say "thank you for your service". - I feel like telling those people to go fork themselves.

Well, Thank You for your service, some of us appreciate it. My friend Harold was spat on when he returned and he basically disappeared in CA for a few years after, and his tours were very tough as well, does not like to talk about it. He became, and still is, a workaholic. His wife credits me with finally getting him out of the house to do something besides work. He loves to go to my upstate property in the Catskills, very remote and scenic, and we do near impossible projects! He loves it.

 

[Mastermind]

I did two hard tours in Nam and all I got was crap from people when I got back. It was 'politically correct' to act that way back then, now it is politically correct to say "thank you for your service". - I feel like telling those people to go fork themselves.



I'm going to play around with this 460 carb and see where I can take it. I also have an HD-5 that appears to be designed the same way. We may be able to come up with a set of general mods that can defeat the EPA geniuses.

In my family it was never politically correct to be rude to anyone, and we were taught to respect our elders too. Once as a child my dad and I were walking into a store. On the way to the door we passed a group of older guys sitting on a bench in the shade of the building. I was in the lead, and only had candy on my mind. I never spoke a word to those guys, but dad said hello as we passed. Once we got thru the door, he slapped me across the back of the head. What did I do wrong? Then and there he taught me to never walk past my elders without acknowledging them, to always at least say hello, or ask if they were doing well. Those sort of lessons are sorely missed in my eyes. Maybe manners are making a come back Terry. Maybe that's what is changing....

I hope you do figure out those epa carbs. They can be a real pain to use on larger saws. The 395xp carbs too, I've tried using them on 65cc engines with mixed results......

 

[Brush Ape]

My Dad taught me to spring for a box of donuts when I go to the scrapyard. Dad said the world at large has a low opinion of those guy and the trash collectors, but those are the guys who would help you in a pinch. Go in there acting like a prick to cash in an electric motor and if they accept it, you'll get the rate based on the casting the outer shell is made of. Go in with donuts and some respect and get paid for its rate in copper. Need a 400 small block? 318? 220 throttle body? Third-gen tailgate? Short tail 700r4? Take donuts, a joke and a smile and your odds increase.

 

[jmssaws]

In my family it was never politically correct to be rude to anyone, and we were taught to respect our elders too. Once as a child my dad and I were walking into a store. On the way to the door we passed a group of older guys sitting on a bench in the shade of the building. I was in the lead, and only had candy on my mind. I never spoke a word to those guys, but dad said hello as we passed. Once we got thru the door, he slapped me across the back of the head. What did I do wrong? Then and there he taught me to never walk past my elders without acknowledging them, to always at least say hello, or ask if they were doing well. Those sort of lessons are sorely missed in my eyes. Maybe manners are making a come back Terry. Maybe that's what is changing....

I hope you do figure out those epa carbs. They can be a real pain to use on larger saws. The 395xp carbs too, I've tried using them on 65cc engines with mixed results......

I use sir and mam everytime I speak to someone, how often do you hear that anymore?

 

[paragonbuilder]

I use sir and mam everytime I speak to someone, how often do you hear that anymore?

I hate it when you call me ma'am...


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[jmssaws]

My dad comes from a different time and it's very obvious,he is a Cristian man in every way. Has only ever done the right thing. It takes dedication to be like him,nobody has time to be kind anymore.

 

[MarkEagleUSA]

nobody has time to be kind anymore.

Everyone has the time... most only choose to worry about themselves.