Main Air Jet Question

While cleaning my carbs, I found that the main air jet in all four carbs is a #36. I'm assuming that they swapped one of the air compensator jets for the stock main air jet since one of my air compensator jets on each carb is a #50. The #50 jet has a much smaller hole than the #36 jet. What effect would that #36 jet have on my bike? My bike has always run pretty good up until about 6000 rpms and then just doesn't want to pull like it should. Could that #36 main air jet be causing that? I'm going to switch it back to stock but was just curious what symptoms the large #36 main air jet would create. Thanks.

 

The smaller the air jet, the richer it will be. Read as... the smaller the air jet, the smaller the air that is used to atomize the fuel within the circuit.

Different air/fuel jet combinations are used in CV carbs to "tune" the fuel delivery to the combustion chamber. After I installed pods on my bike, I had to tune by trial and error with many combinations of air and fuel jets. I believe I am one of the few here that took to tuning the carbs with pods to this level.

I achieved excelent power and drivability when I lived in NV. Now that I am in TX, the tuning has begun again. It runs ok now. However, there is a slight richness in the transition from 1/4 to 1/2 throttle. By altering the fuel/air jets and repositioning the needle height, I will find the perfect balance again.

 

In case you are lookin at the label in the service manual for what is the main air jet; that diagram is wrong.
Below is correct.


I don't have my list with me (I'm traveling), but from memory your pilot air jet should be around a 205, and the main air should be a 50 (but wait for someone with info on hand to chime in).

 

Yep, I've referred to that diagram in my reading. Thanks. 205 and 50 are what the factory service manual and the Church of Clean information says it should be. I'm not sure why someone had the #36 air compensator jet in there in all four carbs instead of the #50. It's opening is much larger than the #50 jet. Does the main air jet control low or high speed operation or is that not how it works?

 

Main air controls the air that is mixed with the main fuel jet (~2k to top end).
Pilot air does the same for the pilot fuel jet (off idle to ~2k).
Your 36 should be smaller than the 50 if it is a Hitachi jet. Personaly I would junk the weird #36 jets and get the correct ones.

 

http://xjbikes.wikidot.com/carb-specs

Years & Models: 1982-3 XJ650 Maxim USA models
Carb Manufacturer: Hitachi
Carb Series: HSC32
Carb Model ID: 5N800
Main FUEL Jet Size: #110
Pilot FUEL Jet Size: #40
Main AIR Jet Size: #50
Pilot AIR Jet Size: #205
AIR COMPENSATOR Jet Size: #36
Starter FUEL Jet Size: #40 (non-replaceable, in float bowl)
Main jet NEEDLE ID: #Y-10
Main needle JET Size: #3.2mm (the main needle JET is also known as the "power valve" or "emulsion tube").
Fuel Level in float bowls: 3mm +/- 1mm (.118" +/- .039")
Idle RPM's: 1,050 rpms

 

According to the Church of Clean information, the #36 jets are the air compensator jets that fit in the intake of the carb body and they are always #36. In each of my carbs, one of the air compensator jets is a #50 so I'm thinking that somebody switched one of the #36 air compensator jets with the #50 main air jet for some reason. I'm not sure about how the numbers work but in previous posts, Len has made comments about the #36 jets being large and easy to clean. I'm thinking there's really no relation to the number of the air compensator jets as compared to the main air jet. I'll try to get a pic to show the differences. I would love for someone who has a Hitachi carb to compare the #36 air compensator jet to the #50 main air jet to make sure I have the right ones.

 

hatachi jets are based on drill size
mikuni on fuel flow

 

Here's a couple of pics comparing the 3. One is taken from the top of the jets and the other is from the bottom. Sorry for the rotation.




The #36 jets that were in the main air jet position match the other #36 air compensator jets that are in the intake part of the carb body.

 

I had to place an order from Len for something else and took the opportunity to ask him about the air compensator jets. I showed him the pictures I posted above and he said the #50 main air jet looks right. He also said this about the #36 air compensator jets, "the #36 compensator jets use some other formula for their "size" numbering that does not correspond with the main/pilot air jet number, that's why it is so huge with such a low "size" number!" So, I guess somebody just switched them in my carbs either accidentally or on purpose. I'm guessing with such a large main air jet in there that it was running really lean in the upper rpms. Maybe that's why it didn't run too good above 6000 rpms. Can't wait to get everything back together and see how it responds.

 

I thought you were only talking about the air jets in the top hat. Apologies.

 

Well, I am really. Somebody had taken one of the #36 air compensator jets in each carb and swapped it with the #50 main air jet under the top hat. I'm not sure how my bike ran as good as it did with an air jet with such a large opening in there as the main air jet. I'm going to put the #50 jet back where it should go under the top hat and the #36 air compensator jet back in its spot.