Who has xj550 w/mikuni carbs and pods?What jets do you run?

I have an xj550. I recently did all the dirty work of rebuilding carbs, adjusting valves clearances, syncing carbs and color tuning and it runs and doesnt start without the assistance of starter fluid.

My question to you with the xj550 with mikuni carbs running pods is simply this: what jet combos are you running?

I run 117.5/37 now and cant help but think my issues could be solved if I go a bit larger in the main/pilot jet sizes. Yes, I'm aware of the jet sizing formula and that's what I tried to follow.

So again, if you have xj550 with pods, please share your jet sizes.

Thanks!

 

150 main jets??? Man, I'm thinkin of going to 125. 150 seems pretty big. Wonder if your bike runs alright with them?

 

Re: Who has xj550 w/mikuni carbs and pods?What jets do you r

Sounds good man, thanks!

 

Thanks for checking. Weird they dont have sizes stamped.

To get new jets, I just made an order with a user on this site that runs XJ4ever.com. His name is Chacal.

Here is the catalog: http://www.xjbikes.com/Forums/viewtopic/t=14561.html

here are the jets available: (you'll want to contact Chacal for pricing as they have changed since this catalog was posted.)

HCP6900 OEM Mikuni MAIN FUEL JET #105
HCP6901 OEM Mikuni MAIN FUEL JET #107.5
HCP6902 OEM Mikuni MAIN FUEL JET #110
HCP6903 OEM Mikuni MAIN FUEL JET #112.5
HCP6904 OEM Mikuni MAIN FUEL JET #115
HCP6905 OEM Mikuni MAIN FUEL JET #117.5
HCP6906 OEM Mikuni MAIN FUEL JET #120
HCP6908 OEM Mikuni MAIN FUEL JET #125
HCP6909 OEM Mikuni MAIN FUEL JET #127.5
HCP6910 OEM Mikuni MAIN FUEL JET #130
HCP6911 OEM Mikuni MAIN FUEL JET #132.5
HCP6912 OEM Mikuni MAIN FUEL JET #135
HCP6913 OEM Mikuni MAIN FUEL JET #137.5
HCP6914 OEM Mikuni MAIN FUEL JET #140
HCP6915 OEM Mikuni MAIN FUEL JET #142.5
HCP6916 OEM Mikuni MAIN FUEL JET #145
HCP6917 OEM Mikuni MAIN FUEL JET #147.5
HCP6918 OEM Mikuni MAIN FUEL JET #150

All of the above OEM Mikuni Main Fuel Jets are priced as follows:
$ 5.50 each
or
$ 18.00 per set of 4


HCP6919 Aftermarket Mikuni MAIN FUEL JET #90
HCP6920 Aftermarket Mikuni MAIN FUEL JET #95
HCP6921 Aftermarket Mikuni MAIN FUEL JET #100
HCP6922 Aftermarket Mikuni MAIN FUEL JET #102.5
HCP6923 Aftermarket Mikuni MAIN FUEL JET #105
HCP6924 Aftermarket Mikuni MAIN FUEL JET #107.5
HCP6925 Aftermarket Mikuni MAIN FUEL JET #110
HCP6926 Aftermarket Mikuni MAIN FUEL JET #112.5
HCP6927 Aftermarket Mikuni MAIN FUEL JET #115
HCP6928 Aftermarket Mikuni MAIN FUEL JET #117.5
HCP6929 Aftermarket Mikuni MAIN FUEL JET #120
HCP6930 Aftermarket Mikuni MAIN FUEL JET #122.5
HCP6931 Aftermarket Mikuni MAIN FUEL JET #125
HCP6932 Aftermarket Mikuni MAIN FUEL JET #127.5
HCP6933 Aftermarket Mikuni MAIN FUEL JET #130
HCP6934 Aftermarket Mikuni MAIN FUEL JET #135
HCP6936 Aftermarket Mikuni MAIN FUEL JET #140
HCP6937 Aftermarket Mikuni MAIN FUEL JET #142.5
HCP6938 Aftermarket Mikuni MAIN FUEL JET #145
HCP6939 Aftermarket Mikuni MAIN FUEL JET #147.5
HCP6940 Aftermarket Mikuni MAIN FUEL JET #150
HCP6941 Aftermarket Mikuni MAIN FUEL JET #152.5
HCP6942 Aftermarket Mikuni MAIN FUEL JET #155
HCP6943 Aftermarket Mikuni MAIN FUEL JET #157.5
HCP6944 Aftermarket Mikuni MAIN FUEL JET #160
HCP6945 Aftermarket Mikuni MAIN FUEL JET #165
HCP6946 Aftermarket Mikuni MAIN FUEL JET #170
HCP6947 Aftermarket Mikuni MAIN FUEL JET #175
HCP6948 Aftermarket Mikuni MAIN FUEL JET #180

All of the above Aftermarket Mikuni Main Fuel Jets are priced as follows:
$ 2.50 each
or
$ 9.75 per set of 4

Thanks

 

right on.. so ya went with 122.5? i just bought 125 to replace my 117.5
and replacing my 37.5 pilot jets with 40 - let me know your results

 

I hear ya on both points - i bought my bike for $50, but put in over $500 in parts and tools.
These are like toys. I'm 6'4" 250lbs and its an interesting ride to say the least.

 

Re: Who has xj550 w/mikuni carbs and pods?What jets do you r

That is damn nice! Believe me, if I could, I would!
Im pretty sure I couldn't make it happen, but what ya askin?


I did have some progress on my 550 today. I installed my new #40 pilot jets, #125 fuel jets and new choke cable and the bike fires up without any starting fluid. I'm gonna sync the carbs and color tune and see how it goes now.

I did just see notice that my fuel tank is rusted all over on the inside, so I gotta figure that out.

Nice bike man

 

Re: Who has xj550 w/mikuni carbs and pods?What jets do you r

That is really nice. If i could, I would.

Let me know how raising the floats helps your situation. Im running 125 mains and 40 pilots and it seems to run well. It seems to start on occasion all by it self just fine. I found that if i dont start it at least once a day, then i need starting fluid. BUT I did find that i can cover one or two of the carbs with my hands while cranking and it will fire up without starting fluid. Im not sure what that indicates. Keep me posted on your float findings.

 

Right on! Awesome you got it working. I haven't tried pulling away in any gears other than first and second. I'll have to try 6th. There are some technical guides on setting the float heights. I have gone through them a couple times in order to get as close as I can.

I think i'd be set if it werent for the cold start thing.

The stock pilot jet size is a #35. They are really thin in that hole just behind where the mains are. Its imperative to have a screwdriver that fits so they dont strip.. I found out the hard way and had to replace the ones i had in there when i rebuilt the carbs. They look like 3/4 inch long missle.. some thread at the back end and a tiny hole in the tip. My originals were so bad, i didnt know there were even holes in there.

Im up to a #40 pilot jet now hoping that would allow just a bit more fuel through the pilot circuit during startup. It seems to have helped marginally. I wonder if I should try going back to stock to see if there is an improvement. maybe i need to go bigger on the pilots.

Wonder what size you have in your carbs?

 

dragsta, if changing your fuel level helped, you should report what the fuel height measurement (clear tube method) is, as it would give members a number to shoot for.

Also, just from personal experience, you can raise the fuel level too high (I made a mistake wrt what point I was supposed to be measuring it on a different model's carbs) such that they over flow. Measuring the fuel height will ensure they don't over flow, in addition to giving another data point.

 

Riiiggghht.

Mikunis, right? Float level spec is +/- 1mm. It may run "bitchin" but it also may be running lean OR piddling extra gas into the crankcase. It'll run just GREAT right until it blows up if either of those conditions exist.

The "clear tube method" is best performed with the carbs OFF the bike, and mounted level. And if done correctly, the results have a predictable, positive result-- your floats end up in spec.

I've been following this thread without saying anything, waiting to see if any of you fighting with a 550 had bothered to check your valve clearances yet. Or done a proper vacuum sync, with the YICS blocked correctly. Doesn't seem to be the case.

See, the key to re-tuning for pods and exhaust mods is to have everything else 100%, so you know that you're not dealing with effects that have nothing to do with your mods.

Otherwise, you'll be at this for a while.

 

My "experience" that I was referring to was on 650 Turbo Seca carbs, which are Mikuni, but obviously not the same as 550s. I was measuring from the wrong point (3 distinct "steps" are found at the perimeter of the base of the carb body), but still, you could adjust the float high enough that it actually couldn't shut the fuel flow off because the float would contact the body before it could rise any higher.

dragsta, if you've adjusted a lot of floats that's fine, I don't doubt your abilities. Posting the actual measurements will help other members who are not as experienced (hence, why they are on the forum asking in the first place) get a better starting point for tuning with carbs. And if they lack the "feel" for those adjustments, measuring is the only way to be sure. You only need to level your bike side to side, and measure the fuel height at the middle of the side of the carb body (where the main needle is). Front to back level is not important.

I personally will never try pods, but the difficulties intrigue me. I'm an engineer by trade, and have a bachelors in aerospace, so I've taken several basic courses in aerodynamics and thermodynamics, and I can say that unless turbulence is the problem, I can't see a simple answer why pods are so difficult to tune with, other than the carbs have to be tuned in a highly non-linear way.

The way I see it, per carb, there are 8 variables that we can use to tune each carb. There is the pilot air/fuel jet, the main air/fuel jet, jet needle, emulsion tube, fuel height, and slide spring. Each of these contributes in a non-linear way to the fuel air mixture across the operating range (wrt mass flow) of the engine. I presume that Mikuni or Yamaha, actually test the engines with different settings, picking the ones that give it the performance they are looking for.

In order for members on this site to get the same result with pods, it's going to take a methodical approach, in which all of the data on those 8 parameters (per carb) in addition to the ACTUAL pods used, altitude, etc, are collected and tested in a repeatable way. If you make it work on your bike, fine, but for those that don't, your experience won't be very helpful unless you specify EXACTLY what you did, so the OP can try to reproduce your result.

Also, note that idle performance is not usually the concern with pods, it's lean top end that's scary, because that will damage an engine. Forcing these engines to idle really isn't that hard. Only a dyno can quantitatively tell you what your performance is across the operating range. Other than that, it's the highly subjective plug reading or butt dyno (which is less quantifiable and harder to repeat).

 

Quite the attraction.. Awesome you got your bike rollin, Dragsta.

Given the additional input, i would like to eliminate any assumption of cutting corners and clarify for the record that I have validated my valve clearances are in spec as I just replaced 6 of the 8 shims that were out of spec. I have bench synced and gauge synced my carbs with the yics tool purchased from Lin, and the quad carb sync quage set and I have also used my Gunson colortune set to colortune the plugs.

After each jet change, i resync my carbs with the yics port blocked followed by a colortune. I believe I have covered the bases so that I can focus on what is needed for the carbs. I cleaned my carbs followed by a few float wet sets set in spec per Clymer manual. multiple cleanings, including a complete dis-assembly and replacement of all parts including the throttle shaft seals. While disassembled, ive used carb cleaner, compressed air, carb dip and determination to clean all passages They each pass the clunk test. My my goal has been to eliminate all variables but the jets. due to modified frame, i cant use stock airbox.

So, again Dragsta.. good job. I am curious as to your pilot jet size. That seems to be the only thing i am unsure of between our setups. I have had luck with my bike firing up day after day, but if it sits for a couple days or longer, i need starting fluid or i can cover the carb inlets and it will usually start. I wonder if you let yours sit for a few days, if it will fire right up?

 

This might be an old thread, but I thought I would add my 10 cents on this and agree with bigfitz52.

I got a 81 XJ550 motor jammed into an ATV frame with the following specs:

UNI pods (chrome caps)
D&D drag megaphones (stright pipes).
115 mains.
40 pilots.
Dyna green coils.

I take a lot of pride in old Yamaha 2 valve motors. The ATV gets a full out of frame tuneup each winter (cleaning,valves checked, so on). It's put thru hell and back each summer being packed full of mud almost each weekend.

BUT....Even when its -5F outside I have never needed starting fluid to start the motor. So any of you that are using starting fluid might want to go down the list of tune-up items. The starting jets get their fuel right from the fuel bowl (for the most part) so I think you are chasing a larger problem than just rejetting.



http://www.youtube.com/watch?v=Sq5i1AqeBME

As the title of the video says, this should be the kind of idle you will get after everything is synced and EVERYTHING adjusted. This motor has 25k so you can hear the classic primary chain tensioner knock.