Carb Jet sizes

[mac11]

I wanted to confirm the carb jet sizing for the bs34. The numbers i found searching this site are as follows:

Main Jet:

142.5​

Pilot Jet:

42.5​

Pilot Air Jet:

45​

And what I found in my carbs

Main Jet:

135​

Pilot Jet:

42.5​

Pilot Air Jet:

155​

I guess this rediculous Pilot Air Jet explanins why I can't get the thing to do a damn thing regardless of adjustment to float height or pilot air screw setting.

 

[drewpy]

man that air jet is huge! I recon the PO put in a mains instead

 

[xschris]

The 80-82 models have 155's in it. The 77-79 models have 170's that is correct These are pilot air jets not pilot fuel jets. The pic is of the jets the one on the left is the 77-79 model bs34's sohc xs400 then the 80-82 in the middle and last is a pilot fuel jet used in both sets. The pilot fuel jet goes inside of the carb.

 

[drewpy]

just checked the yam manual (should have done that first) it says 155 air for xs400 H and SH

 

[mac11]

Thank for the info guys.

Yes I know I'm looking at the point air jets when looking at the 155 and 170 sizing that I have. good to know my pilot air jets are correctly sized. Don't know why the literature I was looking at was so far off on that.

And both Sets of carbs had 42.5 pilot fuel jets.

So can I ask to reconfirm the main fuel jet sizing? I currently have a pair each of 132.5 and 135.

I've an open exhaust but was planning on using factory air boxes so I thought the standard size main fuel jets should be able to be used. Please correct me if I'm wrong?

Thanks guys.

Mac

Posted via Mobile

 

[bcware]

Don't mess with the pilot air jet.

42.5 is the stock pilot fuel jet, but I use a 45 with stock airbox and tiny mufflers on my 1978.

137.5 is stock for mains on my 1978, but size varies a lot by year. With stock airbox and tiny mufflers I have been running 145 mains for 2000 miles this season. The 145s have turned out to be a little too small (pops near redline and plugs look a little too light), so today I switched to 150. For me this is 5 sizes larger on the mains for just free flowing exhaust! I have yet to test ride the 150s, but I can provide an update this week.

 

[trailguide4678]

Pilot air seems WAY to large. Haynes manual calls for 45. Others are within range.
sizes will depend on which particular model bike you have...Haynes gives a breakdown by model and which sizes are standard...

I wanted to confirm the carb jet sizing for the bs34. The numbers i found searching this site are as follows:

Main Jet:

142.5​

Pilot Jet:

42.5​

Pilot Air Jet:

45​

And what I found in my carbs

Main Jet:

135​

Pilot Jet:

42.5​

Pilot Air Jet:

155​

I guess this rediculous Pilot Air Jet explanins why I can't get the thing to do a damn thing regardless of adjustment to float height or pilot air screw setting.

 

[bcware]

The pilot air jet is large; the Hayne's is inconsistent with how they label some of the jets in the manual.

 

[robbiecampbellsoup]

Anyone have any positive sources for the stock pilot air jet in an 83 Maxim DOHC?

Mine appears to be 170 on both sides - but idles very lean.

The other jets are stock with the exception of the pilot fuel jets at 45 each.

 

[xschris]

Should be 170. Have you adjusted you floats? What do you have your idle mix screws set at?

 

[robbiecampbellsoup]

Should be 170. Have you adjusted you floats? What do you have your idle mix screws set at?

Plastic floats adjusted to 22.6mm (they were at ~27 by the previous owner)

In this video: Youtube; My Bike idling and being revved

Idle mix is at 3.5 turns out. Main jets are stock. Pilot jets are 45. Air jets are 170. My right cylinder plug is perfect, left is black with sut and a bit wet. Have yet to do compression test.

I've just cleaned the carbs, and I'm hesitating putting them back in as I may as well get rid of the airbox, put on Uni pod filters (I may copy 16VGTIDave's crank-case breather mod as well). I would be rejetting to 142.5 mains, up one on the needle, and 47.5 Pilots.

 

[xschris]

No baffle in the muffler? With no back pressure that will cause tuning issues. Have you synced the carbs with a manometer yet?

 

[16VGTIDave]

Floats on DOHC's are set by measuring the fuel level in the float bowl. Detailed instruction are in Chapter 4 of the service manual.

I'm currently running 40 pilots, needle clips in (stock) middle slot, and 135 mains. DOHC's don't require as large jets as SOHC's due to the YICS system providing better fuel atomization. Don't make the mistake of trying to run SOHC sized jets as it will be too rich. And it sounds like you are already jetted too rich. With new plugs, the center electrode should have little to no colour and the surface of the plug that the ground electrode is welded to should be medium to dark grey, not black, after a 20 minute hard ride.

 

[robbiecampbellsoup]

I have no idea about the muffler - didn't put it on. I'm not sure how to even get into it.

Dave are you still running the Uni pods - your last post on that you had said you were running 47.5 Pilots, 140 mains.

I will be syncing them once they are installed back on the bike.

I'm trying to decide if I put the system back together - or do the intake modification and rejet and then try to tune it.

 

[16VGTIDave]

Like my signature says, I'm still running the UNI filters on stacks. How could I not? It's my design!

I have changed my mufflers to slightly quieter ones and have re-jetted as a result. I've been surprised how lean I can jet the bike now that I have some back pressure and have learned the correct way to read the plugs. Apparently, the extended nose plugs should be almost clean white as they are designed to get hot and burn off most deposits. I was jetting richer and richer to get some colour on the center electrode, as I'd been instructed to so many years ago. And this is, quite simply, the wrong way to read an extended nose spark plug. Lesson learned!

 

[sebasoleil]

My XS400 maxim 1983 DOHC Mukini 35mm setting without modification went i have it was:
Main = 127
Pilote = 45
Air = 170
Flotte = 22 mm
Needle at 3

Soon I will change air filter pod !!!!

 

[Unkle Crusty]

sebasoleil. Is yours a 5 or 6 speed? Also wondering if there is much difference in jet sizes. My 83 DOHC came with a worn out 6 speed motor. I put in a good 5 speed.
Just moments ago I put in two 125 mains. Switching to EMGO filters. This thing runs fine but did not like WOT. Plugs looked lean, so I went up in size to 140. Was way too rich and puking fuel back out the carbs. Will be running again soon.

Unkle Crusty

 

[16VGTIDave]

Maxim = 5 speed wide ratio, 16x35 final drive gears
Seca = 6 speed close ratio, 16x38 final drive gears

Otherwise, they are the same engine.

I'm currently running the following:
Main jets - 127.5
Needle clips - middle (stock)
Pilot jets - 40

 

[Unkle Crusty]

Thanks for that Dave.
I think mine had 17 35 with the 6 speed. Now I am at 16 35. Will revisit gearing once I get maximum revs at WOT in 5th. Going to try 125 mains to start with. I only have 1 each of the 127.5 and 130. Will find out soon enough. Waiting for the swing arm shaft to arrive. Been thinking about a grease fitting in the swing arm. Just reconnected the chain today. Decided it was easier to do in the vise, rather than put it on last.

Unkle Crusty

 

[16VGTIDave]

I have doubts that you will get above 9000 rpm in 5th, but I wish you luck! I can redline 3rd and 4th, but not 5th. Our bikes top speed is HP limited. And the bikes are aerodynamically challenged, as all naked bikes are.

Once I switched to pods, and later UNI filters on stacks, I found that the main jets could be matched, so I buy jets in pairs.

I considered a grease fitting on my swingarm as well, before I replaced the rear suspension. You will have to pump a lot of grease in there the first time, to fill the cavity. I'm also not sure how the seals will like having grease trying to push them out. But it does seem like a valid idea.