Some jetting advice

NewHavenMike

1976 XS360C
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Hey guys,

So I thought Id take some "pre tune" notes on the setup I am running right now.

I took it for a ride the other day where I could really stretch its legs and see how my bike performs.

I was hitting a flat spot around 5k and it would just stumble. So, I raised the needle one notch and now it pulls fine and it stumbles at 7k. This is where I stopped and figured I need to go bigger on the main jets..

The bike is jetted like so, unmodified by me.
Mains-135
Pilot-25
4fp21 needle, X-6

stock airboxs, crappy shorty mufflers that I repacked with fiberglass.

Thats pretty much the stock setup for the 360s..

However, I notice that the stock pilot jet is supposed to be 17.5 according to my Haynes manual.
Should I be worried about this jet being too big or do you think a 25 size pilot can still be compensated by the idle mix screw?

I did notice after I took it out for a few miles, It would not idle.. Which I think its too rich on idle. I could smell gas. I had the idle screws out 3.5 turns. I could only get it to start if I had the throttle wide open and only then it would just idle for a minute or so before it picked up again..

This is on top of having a cold idle that will hang at 3k when i rev it up..

Im thinking I can tun the idle screw in to 1 turn, and lower the float levels and see what happens..

I know these jetting posts are very tired at this point, Im doing a ton of research and reading all over the place. I think im on the right track here Id just like some confirmation on the direction om going.

Thanks.
 
The 17.5 pilot jets are not the same as the ones used in other bs34 carbs. They where only use in a few different carbs of the time and are no longer used. My guess is your using the wrong style and causing your idle or even upper rpm issues as your soaking the plugs at idle.
 
I know the mufflers are garbage, among the worst. I needed something quick.... I was able to run through 3rd gear up to 9k with no problems.. I didnt realize that the regulator I was using wasnt operational so I wasnt getting a charge either.. Does the stator/ alternator add that much resistance to the engine?

I looked at the slow jets and they are the solid ones with no holes on the side.
IMG_0057.JPG
 
I ordered new emulsion tubes, O-rings and two sizes of mains. The other hardware on the carbs was from the Keyster rebuild kit. I checked for airleaks and they are synced.

I have idle screws out 3 turns and i have to have the idle set screw in quite a bit before it holds an idle. Certainly more than one turn after the set screw makes contact with the throttle. When my order comes in I will break down the carbs completely and clean even more. The buttferlys have a bit of tarnish on the sides as well as the bore. Its more like stains because I cant feel them and the screws on the butterflys will not budge one bit..
 
What does the end of the pilot jet look like? I was not aware of those style jets where made in that size from mikuni. The jets need to have the open ends. Where did you find xs360 emulsion tubes?

DSC02811.jpg
 
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It seems that i should get new butterfly shaft seals. I could blow right into the carb bore on the right carb.. is a leak acceptable here or should it be sealed tight? Its a moving part so id expect a little leak.
 
XSChris, I came across another thread that I believe you posted in about this and came into a link that was emulsion tubes from Mikes XS. I probably wont need them now that it seems they arent the right ones.. It doesnt hurt to have a bunch of stuff for experimenting. Now I find out that the jets on MikesXS are not Mikuni brand so they are junk I guess..?

The science behind carburetors and emulsion and all that is insane.. Something so simple too. I just want the thing to run at its best and have a stable idle at a stoplight.

The O-rings on the emulsions tubes were completely shot, they cracked off. I didnt realize that there is a such an opening going right into the fuel bowls and you can get passive air if those o rings are bad.. This could be causing the high idle..?IMG_0059.JPG

Another thing I noticed with the emulsion tube and the fuel bowl....IMG_0063.JPG IMG_0064.JPG Does positioning the E-tube matter?

and the pilot jet,IMG_0069.JPG
 
O-rings need to seal. If you have never replaced the butterfly seals it would be a good idea to do it, but no they won't be an air tight seal. There will be a good one under vacuum. Use mikuni jets if you can people have found a lot of manufacturing errors with china made ones. Mikes don't sell the x-6 tube but a z-8 that some say is close but still off from the stock one. Position of the tube don't matter. I notice a lot of calcification and some rust in them bowls, you need to clean them more. I would go back to the stock pilot jets. I run xs360 carbs on a few of my bikes and even with pods on the stock H-pipe and free flow mufflers I use stock jets. These type of carbs run rich to start with.
 
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Unfortunately, the 25 size pilot jets are all I have and I cant find any that are under a 30 size. When I last took my bike for a ride, I had the idle screw set to 1/4 turn out. Anything after 3 turns didnt make a difference so I screwed them in all the way. That made a difference. I left them at 1/4 turn out and I was still getting the high idle. I hope that O-ring is the culprit lol. Im on Jets R Us right now Im going to order a couple different sizes of mains. Ordering more than I think Ill need so if/when I decide to change mufflers/ airboxs, I have the jets ready to go

Ordering:
135 mains (stock)
137.5
140
142.5

Im gonna bring the "China mains" to work tonight. I have access to pin gauges and Im curious... its too bad that the original mains were frozen stuck in the bowls and the only way I could get them out was to use an awl.. I was not happy about it.

And what is this thing I keep seeing about drilling a hole in the round slide?!?!?! I see a kit for sale selling jets along with a drill bit! Its sounds like an easy way to ruin the roudslides
 
You can still get the 17.5 pilot jet in kits for the xs750. Might not be genuine Mikuni though.
Sucks to buy a whole kit but there were a few compatible parts.
 
And supposedly drilling out the slide results in faster throttle response.
Dynojet has a lot of kits for CV carbs that include the slide drill bit.

I couldn't find any hard evidence that it actually works.
 
Agree with the 76-77 xs750 pilot jets. The china jets from what I have seen have different shaped end nozzles than the mikuni jets have. I tossed the china jets out when I saw this. Stick to the real deal stuff.
 
Agree with the 76-77 xs750 pilot jets. The china jets from what I have seen have different shaped end nozzles than the mikuni jets have. I tossed the china jets out when I saw this. Stick to the real deal stuff.

Question is whats from china?

I just dealt with crap from K&L............purchased for the 1100 and well it would not run for nothing...........found a post on a forum saying they were junk. Well cleaned all the old stuff up really good and bam..............bike runs great.

I agree only deal with Mikuni factory stuff.
 
Real Mikini jets will have their stamp on the bottom. It will be a square stamp with a smaller square in it. So, a square within a square...

The china jets seem to have a symbol resembling a square within a triangle.
 
Ok, I was wrong. I looked at the fake jets again and they dont have anything other than the size on them. Its like the manufacturer will stamp the size in 3 spots on the jet and then they machine the middle and the cross cut in the bottom...

Ive done some more research and it seems that XS360s did come with #25 pilots installed.. My bikes serial # is in the low 300s so maybe they changed it down the line?
 
They list 17.5 and 25 for pilots and 120-140 for mains. I have taken apart more than a dozen sets of xs360 carbs (76-77) and have only found 17.5 and 135 jets in them. They may list more sizes for bikes sold in very high or low elevations or in states with high emissions standards.
 
Ok guys heres an update.. I installed the 140 mains and kept the 25 pilots.. Bike pulls good all the way to redline at like 3/4 throttle. If it give the throttle the extra turn, it starts to sputter...? Also, when I come to a stop it stalls, Its getting flooded. I think its partially because Im setting the carbs up when its cold and the settings are too high. Stupid me, I didnt realize that when Im setting the idle mix screws that you should set them to where the bike starts to idle low instead of high.. Im setting them too lean so I know that has something to do with it. I was also thinking of setting the float height a bit higher as to maybe prevent flooding. The floats look good and the needle/seats are new. Nothing is getting stuck open..

TODAY, I am up early and I have most of the day to tinker on.... The bike is a ton of fun to ride its just when Im at a stop sign or light I hate it lol.. My bike is definitely an attention getter and its the worst when your idling at 3500 or you cant get it to start because its flooded lol. Ive also noticed that when it idles high, if i snap the clutch, sometimes that will bring the idle back down, the stalling issue is sort of new..
 
Took it out for a good 40 miles today. I checked the timing and the right side was firing almost at TDC while the left was ok. Set timing and resynced the carbs which were also a bit off..

Some times the idle wants to drop to a stall and other times it will stay at 2500- 3000. I gonna tinker with the idle mix screws. The jets are #25 so i kind of figured id only have to have the screws no more than 2 turns out...?
 
With my 17.5 jets I run them at 1-1.5 turns out, even with pods and free flow exhausts. . Pull you screws and make sure the tips have not broken off in the bodies.
 
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