The Barzu Bike - XJ750

dynojet uses their own sizing. A 120 mikuni or keihin jet is not the same size as a 120 dynojet jet. I found a chart one time that crossed regular jet sizes with dynojet sizes and they were way different.

This is not the chart I originally found but...
Dynojet vs. Mikuni chart

here's another I found
Dynojet size chart

 

No kidding. Nicely done Earz. I've bookmarked it, good reference. This begs the question though, did I go too high on my #45 pilots since I used the formula assuming the #136 dynojets are in fact #136? How does that actually compare to the stock #120's? In other words, if I'm not really up 16 from the stock 120's then what? I might scale back the pilots, no?

 

I'm gonna send Crath an email and see what his thoughts are...

 

Personally - I would go by dynojets instructions. If they don't say anything about changing pilot jets - I would leave the stock ones in there. They are changing needles and enlarging the slide lift holes to compensate for any extra required fuel at idle/low rpm's. You said you were really rich at idle. I'd put the stock pilots back in and set the mixture screws to DJ specs and run it. You may need to tune further since you are running open headers, but I doubt that you will need to go quite as large on the pilots. Maybe 1 size up.

 

This is copied out of chacal's catalog. Remember- this is figured using hitachi sized jets. Since dynojet does not offer/supply pilot jets - you may still need to change these from stock. Start by running stock pilots and if need be - I think I have a set of 42 pilots that I ordered but didn't need that I could send you. If they work - throw a few bucks my way. If they don't - send them back in case I need them in the future.

 

Earz, I'll hit you up for those pilots...but not just yet. I used Chacals formula to up my pilots, but at the time I did not know that DJ sizes aren't the same. I'll turn in the mixture screws a bit. Currently they're out 3 whole turns. (per DJ) If Chacal sees this he's gonna cringe. I'm not going to get too excited about this until the colortune comes in. I'll leave things the way they are, because the slide holes and needles have been modified as well. Once the colortune is done, I'll report back in and we'll take it from there. Maybe today I can finish the tank and take it out for a ride so I can gauge where it's at altogether and not just at idle. I love the tweaking and the bike sounds badass.

 

Barzu, you've come a long way fast. keep us 750cc owners posted. Great info in this thread altogether. Bike sounds great.

 

What part of chicago you guys from? Im in chicago as well. Barzu great information your thread as well. I want to run straight headers as well but im very skeptical on messing with those carbs. Any advice you can give me on the carbs or how would I factor in the altitude for chicago? Thanks dude.

 

Sal97,

what is the intake/exhaust configuration on your bike in the picture?

Also, what is the brand of whitewalls you have?

 

Barzu, bike is coming along nice, you got a great deal for that 750. Congrats, sounds like you really love it.

In my opinion, there is really no "guide" that is going to tell you the exactly what size jets are right for your bike. But it will give you a starting point. The best thing to do is tune the bike professionally on a dyno with a 5 oor 3 gas analyzer. This involves using a sniffer in each of the four pipes one by one to see what is actually coming out of each cylinder throughout the entire RPM range. By knowing what gasses and at what percentages of these gasses are coming out the tail pipe(CO2, NO, 02, etc), you will know if the bike is running rich, lean, or stoichiometric.

For example, you can have two 1982 XJ750s sitting side by side, with the exact same mods, but I guarantee you they will require slightly different size jet to get them dialed in 100% correctly. Guides are good enough to get you going.

In your particular situation, your main and pilot jets sound a little large. You are best to run the bike on a dyno with someone that really knows how to tune well.

I personally took mine to a friends shop and ran it on the dyno.

 

crath, after you had it dyno'd did it run correctly, I was reading on another thread that you had a hard time with the idle or something?

 

That bike never has idles correctly day to day. Everyday, depending on tempature and humidity, I had to adjust the idle. But that is an easy twist on a knob at a stop light, so it doesnt bother me.

Considering I run the bike balls to the wall 98% of the time, I set the carbs up to run well at mid-high rpms, where it matters, not idle.

 

Thanks Crath! Can any of you dudes recommend a friends shop thats in the Yorkville area of Chicago with a dyno? I'd like to keep the business in the "family" if you know what I mean. I fired the bike up again today and got it to idle perfectly at 1K or so. It sounds mean as hell. I'm passing on finishing the tank today and just slapping that thing on. I'll have to take it off to color tune anyway. I've got to be honest here, I just want to take this bastard out for a ride. I'm so excited that I have a knot in my throat. I'm taking it out this afternoon and going for a two hour ride or so. I'll let you dudes know how it runs. Or if you don't hear from me, it means that the bike broke down and I got kidnapped by some hot chicks and will have to be their love slave for the rest of my life.

Sent an email out to DynoJet giving them my exact specs, let's see what they come back with as suggestions for the pilots. I do agree that I'll probably have to scale them back to 42/43's.

 

Yorkville, eh? I was just there a few months ago for the Road Block car show at Lyon Farm. I took my XJ there for the show. I rode around Yorkville a bit too. I found some yuppie subdivision to raise hell in - very fun!

I don't know of any shops around that area to take your bike to though.

 

You were probably in my yuppy subdivision. So I took the bike for a spin around the neighborhood. Crap. It idles great, but rides like dog poop. I stalled twice while giving it gas. Need to pull the spark plugs and see what's going on in there...

 

Barzu- I found my pilot jets. I have 40's (you said you damaged yours) and 42's. I almost bet that dynojet is going to tell you to run the stock size jets. If you want to try them, PM me your address and I'll send them to you. Like I said - if they work, send me a few bucks. If they don't, send 'em back.

 

Earz, send the the 40's please. I PM'd you my address. I just talked with Dale at DynoJet support, and the pilot jets are not to be touched. Crap. So there you go, if anyone needs some 45's, lemme know and I'll shoot them over to you.

 

I have to agree with ya there Crath you don't beat your budy's idling around town. :lol:

 

Just my 2 cents had the 750 til it blew, so threw in the 650 running 43p and 128m, 2nd to last clip on the needle and is running great. I can tune it too lean to too rich within a half a turn.

Def sounds its a lil rich if strong idle but no pep, good luck man like Crath said not much to these bikes but going inside the carbs a billion times to get it right. Oh and looks good too!

 

So let us put this issue to rest a bit for now, until I get Earzs' pilots. Lets talk about the 750 gaydlebars. What the crap?! I want to put a straight pipe drag bar on this. Anyone found any 1" or 2" risers that fit this thing? The current bars are sorta like clipons, except waaaay more homosexual (not that there's anything wrong with that if it's your thing)

What do you kids have to say about that?

I can post pics if you'd like...