Any carb gurus? Walbro HD

[Mastermind]

I'm finally getting pretty confident in my carb tweaks.

Rob, listen to Terry. He's a smart guy.

Sometimes replacing the main nozzle cures a lot of low speed issues without much drama. It has a check valve in it that prevents air flow back into the passages at idle. If that valve (just a flat disc of the same material the pump diaphragm is made from) is malformed or dried out it will leak, and you will never get a good idle.

 

[jmssaws]

I have no airleak,I had it in a bucket of water.

I can make it idle perfect but it will fat bog accelerating.
For it not to fat bog it's to lean to idle
I have a small zama I put on it and it runs perfect but less power.

 

[srcarr52]

I have no airleak,I had it in a bucket of water.

I can make it idle perfect but it will fat bog accelerating.
For it not to fat bog it's to lean to idle
I have a small zama I put on it and it runs perfect but less power.

How far is the butterfly open? It probably needs more bleed through the butterfly so it can be shut further closing off the transition fuel ports.

 

[jmssaws]

How far is the butterfly open? It probably needs more bleed through the butterfly so it can be shut further closing off the transition fuel ports.

It's open some,visible Crack

I'll try more

 

[srcarr52]

It's open some,visible Crack

I'll try more

On the adjuster how far up the ramp are you? Also where are you on the H and L adjusters when you have a good idle but it won't spool up nicely?

 

[mdavlee]

I have filed a notch for a 2nd bleed spot on some of these carbs

 

[jmssaws]

On the adjuster how far up the ramp are you? Also where are you on the H and L adjusters when you have a good idle but it won't spool up nicely?

Probably a turn or 2 on the ramp
It's .5 on the low and .75 on the high

If I turn the low a hair either way I get to lean or to fat.

Not a 1/4 or 1/16 of a turn I mean a hair

 

[srcarr52]

Probably a turn or 2 on the ramp
It's .5 on the low and .75 on the high

If I turn the low a hair either way I get to lean or to fat.

Not a 1/4 or 1/16 of a turn I mean a hair

Ok, now we are getting somewhere.

Seems like you may be on the low side of the butterfly opening suggesting it may have too much bleed but as long as it's not fully closed and you have to add fuel to get it to idle down you are probably ok.

0.5 and 0.75 on the screws suggests that you are getting too much fuel all the time. First I would check to make sure the needle is properly closing with a pop off gauge. Pump it up to 15-20 and tap the lever, it should seat and seal with over 5 psi left and hold nicely. There are many things that can cause them to leak a little. Sometimes the lever tips will be bent slightly different and side loading the needle, or they won't be flat enough and pushing the needle around in it's bore. Other times you may need to lap the needle seat to make it seal.

If it seals fine then you probably don't have enough pop off pressure or you have leaking welch plugs.

 

[tree monkey]

`oem or am kits?

 

[tree monkey]

ultrasonic cleaners will destroy the hs nozzle's

 

[jmssaws]

`oem or am kits?

Both.
No uc cleaner just gas.

The carb off my 460 works good on it

 

[Philbert]

ultrasonic cleaners will destroy the hs nozzle's

Can you elaborate on this Scott?
Does it matter what solvent you use?

Thanks.

Philbert

 

[Terry Syd]

Most as I recall would lean out at idle and still have a full well on the metering side

That seems to be consistent with a leaky check valve allowing some air into the nozzle tunnel. The low speed circuit is pulling the fuel and AIR into the chamber under the welch plug. The metering side will remain full of fuel as the air through the nozzle is getting pulled into the low speed circuit.

Check and see if the carb has the two holes in the nozzle tunnel. If so, try the mod I mentioned and see if it cures the problem (if it is a really, really bad check valve, air will eventually be pulled into the wet side).

If that fixes your problem, the next carb will be easier - you know where to plug and where to drill.

Then you can try drilling the auxiliary jet for the low speed circuit. With two carbs you can mod one to .3mm, check it with a stock carb, if the modded carb works better, then mod the stock carb to .35mm and again compare. Eventually, you will find the 'sweet spot' for the jet.

 

[jockeydeuce]

Some are worse than others. In fact I revisited some today on a 365 I just put together and the symptoms vary.

Are you saying if I give the low a stand alone circuit I won't have to replace the nozzle? I guess I need to find a source for nozzles too.

BTW. ..I looked through the pile and every last problem carb is an EPA HD-12B

 

[Terry Syd]

Are you saying if I give the low a stand alone circuit I won't have to replace the nozzle? I guess I need to find a source for nozzles too.

Try the mod and see if it works. It may only delay how long it takes before the carb starts leaning out at idle. The air will be going into the wetside instead of directly into the low speed circuit. It may be enough to make the carb usable. If it does delay the onset of the idle problem, then you have likely diagnosed the problem in the carb as a faulty check valve.

 

[tree monkey]

remove both needles
note the depth of the nozzle
drive the nozzle into the carb with a flat punch
put a piece of hose over the discharge end of the nozzle
put hose to mouth
suck, blow in hose
it's a one way valve
you should be able to suck air in, but not blow through it
if it fails, replace it
takes about 5 minutes to do

 

[460cixy]

Ok so I modded a carb just as terry suggested here's some pics to get the idea you can clearly see the hole I drilled to feed the idle circuit and the original hole before and after blocking also other parts of the idle and intermediate orifices as I'm running an alternative fuel for this saw and are now much larger also drilled the brass "booster" jet for the low speed and the same on the high speed side also opened up the orifice in the main jet not pictured

 

[Terry Syd]

Neat, I hope it works for the fuel you're running. Are you going to run the 10% nitro with methanol?

By the way, if you take a look at the area under the welch plug you will see how large and odd shaped it is. I think that is why the HD doesn't idle as well as a Zama. Zama uses a long thinner passage to the idle port so that the capillary action creates a 'freight train' of little bubbles to the idle port. That gives it a more uniform idle mixture. In the HD the bubbles of air can be quite large and all over the place.

I'm presently putting in a little steel 'pipe' in that area to see if I can tame the HD idle a bit.

 

[460cixy]

It's still all over the place but it's running ok I guess getting a good idle with meth is half the battle found an air leak this morning fixed that and it improved as expected but not great I think the pump side of it is struggling to keep up under wot too. Do you know if there is a rubber pump diaphragm available? The hard plastic ones I feel do t pump as much

 

[Terry Syd]

The pump diaphragm only works at idle. If you need more fuel at WOT then you may want to drill the auxiliary main jet a bit larger.