Carburetor frustrations

ImpulseRocket89

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Out of curiosity, is this the style of carb you have, and if yes is the screw circled in black the idle screw you are adjusting? I ask because generally if the idle mixture screw is located behind the throttle slide, it is a fuel screw and not an air screw. The more you turn it out, the more fuel you get. This may be why you are having so many issues.

It is also worth keeping in mind that, while the pilot jet size does affect the idle mixture fuel volume, you can have a 2 or 3 pilot jet sizes that are close to the right size that will allow an idle mixture screw setting to be reasonable and idle, but not run correctly at just off idle to 1/8th throttle. It's important to distinguish the two because a slightly too lean pilot, and a slightly too rich pilot, can both have idle mixture settings that fall within the reasonable range of adjustment. A good example of this was on one of my bikes with a Mikuni carb. A 25 pilot jet idled perfect with the idle mixture screw (fuel) turned out 2 turns, but at light steady throttle it would hesitate and stumble from being lean. A 30 pilot jet idled perfect at 1 1/4 turns out on the idle mixture screw, but was rich enough to turn the spark plug black. I had to run a 27.5 pilot jet to get a decent part throttle fueling and a good idle mixture.

Tuning rule of thumb with fuel screws. Less than 1 turn out from seated you need to drop down a jet size. More than 2 turns out from seated, up a size. Don't ignore those "half" sizes. like in my example above where the 27.5 jet worked the best - in Keihin terms, the jets that end in 2 or 8 are the "half" sizes between the 5's and 0's.
 

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noah9988

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Yes that's the carb I have, and no, that's what I was calling the air screw. Is it a fuel screw on these carbs?
 

ImpulseRocket89

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Yes that's the carb I have, and no, that's what I was calling the air screw. Is it a fuel screw on these carbs?
On every PZ carb I have ever worked on it is a fuel screw. And, as I stated before, as a general rule of thumb, if the idle mixture screw is before the slide it is an air screw, if it is after the slide, it is a fuel screw. I mean, it could be one of those weird exceptions since it is a clone carb. The bowl and float sure show that its possible lol.
 

EthanRevBike

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How should I go about repairing my “racing carb” choke unlock/lock. I bought a new carb and it sat around for a while and now the choke is broken.
 

DAMIEN1307

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If gas is leaking out the vent then the float needle isn't seating properly
Probably a speck of dirt.
And don't forget this little ditty from another thread about his carby Wrench...lol.

 

DMoore0079

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If you don't have any luck with the PZ carb, the $30 KTM50 clone carbs are a decent choice (Dellorto PHBG19 copy). It has a spigot mount, so you can mount it pretty easily with a section of hose and clamps. I used the 23mm OD intake for the G2 reed, which matches the spigot mount pretty much dead on. It uses 5mm threaded main jets (same as the NT carb), and pilot jets of any size you'd ever need are readily available through Treatland.

For ultimate ease of tunability, you can't beat a chainsaw carb. No jets to mess with - just a low and high speed mixture adjustment and idle. They do require some fabrication for the throttle linkage and intake and are slightly harder to start since they require choke for initial priming, but the benefits greatly outweigh the negatives IMO.
 
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