Setting up a PHBG carb for the first time, any tips?

extremeodd

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Strange, I drilled out one of my duplicate jets to roughly 100 (.991mm + it wiggling a tiny bit) and I'm getting literally the same results as before on the plug chop(the post before the most recent one with pictures) except the motor is even cooler yet and the exhaust is starting to smoke at WOT. Maybe I need to try a cooler plug for getting the plug chop reading then swap back to the hotter one for daily use.

EDIT: Went for another WOT ride and it doesn't really seem to be smoking now. One tip I saw (not sure if it works for WOT) is to try to pull on the choke while testing different RPMS, if it runs better you need a larger jet, if it runs worse your either about right or a bit rich. When I was at ~8400 rpm (maxed out) I lightly pulled on the choke (damn plastic thing came off, so now its all but useless) stem and when I felt it move the bike immediately lost power and regained it the moment I let go of the choke.

Might try drilling out the jet past 100 but I already used my largest bit to make it 100, I'm sure I could waller it out without much issue.
 
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CrazyDan

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Are you using an expansion chamber? You might not need such a large jet with a proper expansion chamber since it will scavenge better.
 

extremeodd

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Im running a zeda motorsports poor boy motor See it here (heavily ported, different piston), zeda intake See it here, an mz65 pipe, a KTM 50sx carb See it here (phbg), and a super free flowing air filter See it here. Running an approx 100 jet, AN atomizer (unknown size) and 45 idle jet.

I'm starting to think my issue is the jet atomizer, it appears to be of the AN style for 4 Stroke setups. But to change over they say you must change the bushing. I don't have a bushing, I'm starting to think this is a weird clone carb. Any way to help improve the AN atomizer if I cannot swap it out? Also there are no numbers stamped anywhere on the atomizer.

The guide says the AU atomizers will stick up 2-3mm and the AN will be flush. But my AN sticks up 2-3mm and there is no bushing to be removed.

In this cutaway you can see the bushing
87748


On mine, instead of this bushing it's simply the housing itself that is threaded to accept the AN atomizer. The last two pictures show what it looks like installed. Sticks up just like an AU but without the cutout. Would blocking the holes in the side of the AN atomizer help or do anything? Nevermind that question, they make a HUGE difference according to the Dellorto manual

There are several sideholes (6) in the atomiser(5), communicating with the air intake (2).
On opening the throttle fuel metered by the main Jet (3) flows into the atomiser where it mixes with air drawn through the side holes of the atomiser and the resulting fuel-air emulsion flows into the barrel (4) where it further mixes with air coming from the main Intake (1).
So this would be why even with a 100 jet I'm running lean at full throttle. Guess I'm soldering some holes tomorrow.

EDIT: Went ahead and soldered up all the holes, let's hope and pray the little dots of solder in the holes don't vibrate loose. If it wasn't 1am I'd go for a test ride to see how it's changed. It's not unheard of for people to drop over a dozen jets going from a "AN atomizer" to a "AU atomizer" so I'm hoping my "rich everywhere but WOT" issue is addressed now.
From the looks of how this Dellorto replica is built, converting from a "an" to a "au" is as simple as filling the numerous (far more than a factory AN) holes and possibly grinding out part of the 'dish' so its C shaped. It's a heck of a lot cheaper than swapping bushing/atomizers, that's for sure. Not to mention that I'm 90% sure that I couldn't put a replacement AN atomizer in as mine is coarse threaded and all of the pictures I've seen are fine threaded. Hopefully I won't have any need to adjust its size.
 

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extremeodd

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After soldering up the holes in the AN atomizer last night, I checked it again today and my soldering job wasn't the best. 3 of the plugs fell out when pushed on with a micro drill bit.
So I cleaned the hell out of it, used the exact hole size micro bit to clear away any oxides and I soldered it again. However I was running into an issue where solder was filling up the inside of the atomizer. So I found a drill bit that is slightly smaller than the jet end of the atomizer, slid it in and put it in my cheap electric drill.
That way when I was done soldering, I could slowly spin the bit and clear out the solder. In theory this would have worked perfectly if I would have had a drill bit depth stopper attached. It decided to bite in and before I knew it, it had pulled itself through the other end.

Now my mystery AN atomizer went from being very lean to beyond stupidly rich which is to be expected when you kinda negate the needle's ability to regulate fuel.
To top it off, I can't buy a replacement. Because my carb is a replica, it doesn't utilize the AN/AU bushing. Instead they drill/tap the case where the bushing would be to accommodate their custom version of the AN atomizer. It's made slightly longer so that the atomizer itself sticks up into the throat, but instead of the 'C' shape the AUs have, its a full circle. It also uses coarse threads instead of the fine ones Dellorto used which makes replacing the atomizer with anything off the shelf basically impossible (I cannot find clone parts anywhere).

So the game plan is to try to jet down enough that it's not running stupid rich (dropped from a 100 to an 87) since the needle cannot even start to provide any restriction. If that seems like a fail then I will try to remake the ring I drilled out with solder. If that fails I can get another one of these crappy copies for $22.75 and try again but instead of solder, using JB weld or something to plug the holes since I could stuff the inside with something to keep the JB weld from seeping in past the holes. However I'm looking at aliexpress and I can grab a PHBG 19/21 racing clone for roughly $30 shipped.

I would move away to the VM18 but even if I purchase another $22.75 clone, I'm only in for about $86. Which is including purchasing jets from 70-100, a set of #61-#80 micro drill bits, a set of pin vices, and solder. Taking a look at eBay the current cheapest vm18 is $61.52, however if I was buying a vm18 I'd be grabbing the clamp on since I have the ZMS intake that matches its size when the bushing is removed. Those are running at roughly $80-85 shipped plus however much I'd be spending on jets.

Since I've spent roughly the cost of 2 of these clones in parts and tools and have gotten a very strong grasp on how to tune one of these bastards now, I'm probably going to stick with these random PHBG carbs for now. If I can't manage to get the atomizer under control (I'm sure I can) I'll swap out the carb/intake for the stock and NT to get by.

Whenever my paycheck decides to hit my bank, I'll pull the trigger on this AliExpress 21mm PHBG racing carb with the au262 atomizer. It comes with a 92 main, 50 idle, 60 starter, 40 slide and w7 needle. Basically the same thing as what treatland is selling, but for half the price (and a 20-30 day wait). All I'll need to source for it is a pull choke to replace the cable choke, the one on my clone just removes the black pull cap when you try to use it.

If I would have known ordering this damn $22 carb would have lead down such a rabbit hole, I'd have gotten a vm18 or vm20 instead. I'm in too deep to quit now haha.


EDIT: My plan to solder up the atomizer and drill it would have been a complete success, except for one thing.
I was using the needle as a drill bit (very light pressure) to give it the perfect clearance/fit for the taper and when I was 95% of the way done, the needle stuck to the solder, and it broke at the bottom clip position (I had it too shallow in the chuck and all of the force went through the clip area).
Back to the stock intake and NT I go :(.
When payday hits, I'm going to order a few needles along with that aliexpress racing phbg. Might try to see about putting either a dot of solder on the jet where it broke so it'll sit as if it's in its richest needle setting, then I could solder rejet the atomizer to match the now slightly shorter needle. Or I might try my hand at soldering the broken piece back on if I can find it.

EDIT 2: Did some measuring (yay on screen apps) and the needle the clone came with is a W20. Also found the piece that broke off, it snapped where it's the thinnest on the richest adjustment. Since this needle doesn't have to endure much strain, I'm going to try and solder the pieces together. Worst case the fix breaks from vibration and I lose the engine for the rest of my maybe mile ride.
 
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extremeodd

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It's the ever rare triple post. Soldering the needle worked perfectly to fix it and after a touch of filing it slips right into the slide without issue. Getting the atomizer back into the 260x range has been a trial, I think I've got it up to roughly 255 as the widest part of the needle can now wiggle just a touch. In trying to widen the hole evenly I've managed to make it tapered which might help compensate for the smaller than stock opening.

Slapped it all together with a 96 main jet and the needle on the 2nd from the richest setting (now my lowest setting due to soldering) she seems to be running much better. Still loses power and sputters hard around 7900 rpm so I need to figure that out.

My idle is still being a bugger and I have very little power below 3k but that's due to the pilot still being a bit too large. Soldered/drilled my 50 to a 45 which helped some but it's still really hard to get a smooth idle at 2k rpm. It's either 4 stroking at 2k or running smooth at near 3k no matter what combo of setting I use on the two screws.

It's now been 4-5 hours since I typed the stuff above (forgot to hit post reply) and I've managed to open up the atomizer just a hair more with some tightly rolled up sandpaper. With a 100 jet (I think) it seems to be running fairly rich at WOT. It starts sputtering around 7k and cannot rev any higher, I've not really been able to discern what a 'rev limiting' lean/rich condition sounds like. The sputtering I'm hearing almost sounds like really fast 2 stroking. Either way, it's fully drivable and it seems like I've at least eliminated the bad 4 stroking/loading up I'd get when cruising at 5k rpm for more than 100ft.
 

extremeodd

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Finally got around to messing with the bike for 20 mins today. Dropped from the 98 that was in there to a 94 which helped give it some more power and let it rev slightly higher. Swapped that for a 90 and yet more power and now I'm back to where it's always cut out (on both the NT and the PHBG) 8600rpm. Sadly due to removing the bowl 30+ times, the gasket is about shot so I'll need to be replacing that along with the gasket under the slide cap. Can't wait until I get my hands on the racing version, the twist off top and quick change jet bolt will make tuning a touch easier.
 

darwin

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WOW, from the cutaway it looks like such a simple creature but we know it's not from your troubles. I've never had so much trouble as you have had, knock on wood. W/4 strokes mostly the carbs are plugnplay as long as their clean inside. Good luck and hope you get it right soon.
 

extremeodd

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I appreciate the kind words. From everything that I've read, carburetors are carburetors with the few exceptions of stuff like the PHBGs who have a few specific configurations. If I would have grabbed a Mikuni vm18, none of this would have been an issue but I would be in for more money than I currently am, despite all the issues.

The cutaway is fairly simple because this is a simple carb, however, all of my issues are stemming from the center brass bit that screws into that other brass bit. My crappy knockoff doesn't have the "other brass bit" and threads directly into the carb body.
Where the blue line is drawn is where an air pathway is (they missed it when cutting that example in half).
The brass bushing has a big hole on one side for that extra air pathway.
On a 2 stroke, you can see how the air is forced up since the threading for the atomizer is below the blue line. This seems to be set up to help atomize the mixture better and/or to help with 2 stoke blowback by directing air around the nozzle of the atomizer, also keep in mind the 2 stroke bushing is C shaped with an opening towards the motor.

On the 4 stroke atomizer, the threading is ABOVE that outlet, forcing the air downwards and into the holes in the side of the atomizer. This is to lean out the mixture on sudden WOT conditions.
Because I cannot swap out that brass bushing, even with the holes on the atomizer soldered, it's going to cause issues as that effectively eliminates that air pathway.

With all that said, despite being a simple carb there are 10 items a person can either adjust or change out to tune the carb. Idle/pilot jet, main jet, atomizer, atomizer bushing, choke jet, slide, needle, needle clip position, idle fuel screw, idle air screw. If you buy a nongarbage example all you really gotta worry about is the main jet, needle clip position, and the 2 screws.

These Dellortos are the only small carbs that I've seen come with a "4 stroke" and a "2 stroke" setup, typically it's just a matter of jetting and blocking off oil/vacuum lines.

Today I ordered the aliexpress 21mm racing clone and a pack of needles so I can swap this useless fat w20 for a far more usable w7.

Despite how much trouble I've had, and how "janky" my current setup is, this thing pulls freaking hard compared to the stock NT. With all of the proper parts, it should be nicer yet.

The reason I keep posting on this thread, with all this information, is to hopefully help out someone down the road. If this thread would have already existed, I would have come across it in my searches and saved myself a lot of time. Unfortunately, all the information found here cannot be located in any one place. Everything in this thread came from different forums, some from moped army, some from a random ktm50 forum, etc etc.
 
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extremeodd

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This probably will be the last update until I get my 21mm PHBG racing clone from China in a month or so.

The needle set came in today and I figured out that my w20 needle is actually is some weird size. It's the same tip end as a w7 (approx 1.4mm) but with over 20mm of taper.

Tried out the w11, w5, w7 needles on various clip settings and the best setup so far seems to be the w5 on the 2nd from the richest notch. This was going purely off of head temp (after redline for 1/4+ mile), exhaust smoke volume, max achievable rpm (and accompanying noise), and 'seat of the pants feel'.

With it being 106f right now I have to run fairly rich to keep the motor from getting too terribly hot. The highest I read was about 460f on the leanest notch on the w11 needle (1.8mm tip, 2.5mm shaft 86-8700 rpm) and my last run on the current w5 2nd from richest notch (1.4mm tip, 2.46mm shaft 83-8400rpm) was about 4-420f.

The biggest difference I've noticed has been my low end is actually usable now. Before if you were trying to accelerate from 2k rpm, it was not happening because of how stupidly early it was getting on the needle. Now with an 18mm taper, it actually accelerates, albeit not very fast, but it can pull from that low without roasting the clutch. Also, it strangely idles better now, despite the slightly smaller diameter (2.46 vs 2.50mm) which probably has something to due with how long the taper was on the old needle. *MID POST EDIT* Just double checked the measurements on that needle and the taper is easily 24-26mm if not longer. That would explain the low-end power issues.

I might get around to dropping my jet size to the next one down but it's forecasted to be over 100f until August 29th where it should finally drop down to only 98f for a couple of days before going back up to over 100f. Working on anything out in the garage in that heat just plain sucks.

I will, however, swap out my 44t back to the 36t so I can get some better mileage and better top speed within the next day or two. Was only running a 44 because cruising at 20mph (when I ride with my pedal powered neighbor on 15+ mile rides) the super early needle was beyond painful.

The motor would get super loaded up on excess fuel-oil and just guzzled gas. Literally every 1/4 mile or so I'd have to clutch in and redline it over and over to clear out the crazy build up. Where running the 44t brought the rpms up just over 1k at 20mph and it wouldn't load up quite as bad. Now it'll happily cruise at 2k rpm without 4 stroking the entire f***ing time, let alone at ~4k rpm where the 36 likes to be at 20mph. I'm willing to bet I increased my mileage 25% or better with just a different needle. *MID POST EDIT* Maybe not on the mileage changing, I've seemingly used damn near half a tank in the last couple days and I've only ridden 10ish miles (3.5l tank).

That and when it comes in, I'll be installing that new carburetor because of TWO MORE MM OF OPENING BABY!!!
That and hopefully with the correct, non jerry-rigged atomizer/bushing combo, it'll run a touch better and be easier to tune.

I do have two questions/concerns:
1: Is it normal to only really need to use the first maybe 1/8th of the throttle? Like I can get to within a few miles an hour of topping out with seemingly very little throttle. Literally, 1/8-3/16 throttle is more than enough to get 80-90% of the way to redline, the only difference the rest of the throttle makes is how quickly I get there. Once it's there, I can maintain it with as little as 3/16 throttle and once at or basically on redline the last 20% of throttle keeps it there.
EDIT: Found a couple of very very informative threads about some of the various mechanics with these carbs and I forgot about the progression system. Because of my rather rich idle jet, the progression system is easily allowing enough fuel to get pulled as the RPMs increase without really needing to touch the throttle as it'll meet the fuel demands of the increased airflow.

2: Considering the ambient temperature is/will be 105F or higher for the next 2-3 months, what is a safe maximum temperature for these motors to run at? By maximum, I mean for a period of 1-2 mins of WOT before riding normally. The highest reading I got after going 1/4 mile WOT was 460f, I'm not sure at what temperatures these motors start to seize up at.
What would be a safe constant/running temperature?
After riding 3.5 miles home just after the sun started to set (104F), running it harder than normal, I got a reading of 365f or so. I've read that a constant 400-450f can be handled but I thought I'd ask. This is on a stock head, the temperature is being measured with an IR thermometer near or on the base of the spark plug, I've spray painted the head and plug with black paint to help with the accuracy of the reading (worst case, the gun is adjustable).
I'll be buying a CHT gauge with my next paycheck so I can keep an eye on temperatures, damn this PHX heat. Or I might spend the money instead on a 6cc fred head, better cooling = more better, right?

EDIT: Found this thread here talking about maximum CHTs and it sounds like I'm still quite within safe temperatures. Just got worried since it was finally getting hot enough to start to burn off some of the crap that has built up on it, along with the black spray paint (not high temp stuff). This gives me more confidence in going down a couple of jet sizes, I'm fairly certain that it's still far too rich at WOT.
EDIT 2: After blasting around for about 1.5 miles at 8k rpm or higher, I only reached a peak(ish) temp of 460f in 94f weather (I'll test in a few hrs when its 106-107). Since I won't be running that high rpm for any longer than that, I think I'm good to lean it out some more if it's really needed but I shouldn't have to.
 
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extremeodd

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It's the post you have been waiting for. The end of a saga: The alibaba 21mm PHBG racing clone has arrived.

This carb is so much nicer than the old one and it has the correct bushing/atomizer combo.

Tried running it with the stock 90 main/50 idle and it ran but was so rich it couldn't get above 6.2k RPM. Over the course of the last 3 hours I've stepped down one jet at a time all of the way down to a 72 main and soldered/drilled the idle to approx a 42. With a 76 main it would get to about 7200rpm before 4 stroking, dropping down 4 sizes to the 72 lets it get up to roughly 8k (don't have enough room in my neighborhood to fully top it out).

It still seems a little on the rich side, especially at low RPMs but overall this carb feels so much better when riding around. Not to mention how freaking easy changing the main jet is now, just undo the plug and change it! Thinking about changing the W7 out for a W11 to help lean out the top end a touch.

Gotta say that I'm surprised at how much I had to downjet moving from the ghetto 19mm PHBG to this higher quality 21mm. I guess the correct atomizer/bushing combo makes a world of a difference. Now I just gotta figure out a good intake runner length, I have about 8in on there right now. Everything I've read indicates that having the carb only 2-3in from the piston isn't great if your only revving up to 8k, but it feels like 8in was probably a bit too long.
 
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