1979 Yamaha xs750 carb jetting 

I never cease to be amazed at how many people go to change jets but don't know how to get a true reading on the mixture or I guess you would call it the science of rejetting. first it's a pretty common rule pr thumb that for pods you start out by go up 6 sizes in main jets and another 2 sizes when you add opened up exhaust and for every 3 sizes you increase the main jets you go up 1 size in pilot. also to test the mixture when changing main jets you find a straight away where you can open the bike up to about 3/4 of redline hold it there for a mile or so then hit the kill switch and coast to a stop then check the plug. riding around speeding up and slowing down and idling is a total waste of time because you your plug reading is going to reflect the mixture at the last speed you rode at not the actual mixture while in the main jet circuit. you need to isolate the fuel delivery circuits and check each of them individually so i guess that would also be the science of rejetting.....

I known this is an old paying, but I just wanna say thank you for uploading.

I just bought the stuff you finally ended up using. I wish I had the original air box really, but it came with these pods. Thanks for the posting man, I appreciate your time.

Quicker, easier way to check for leanness is to pull out the choke when it is stumbling at speed. If it runs better (by adding gas with choke) it is too lean. Repeat as necessary.

I own one and it has the air box and K&N filter. Never had any problems like you do. Remove the box, you get problems. I have 80,000 miles on her.

Great job. I had an 79 850 special.

you will find that to avoid overheating on the center cylinder you'll need to run that one just a little rich, granted I'm running the wisco bore kit on three n one with carbs from an 850 and jetted .

thanks very much for sharing I've just started my own xs750 build, so will remember this vid on ignition day I have also just bought a set of Triumph Trophy 900 carbs that are a perfect fit and from what I have read on the uk forums are a huge improvement in performance on the xs750

Very helpful video! Camcorders focus on the distance that the majority of the image is at (higher end cameras will give preference to objects in the middle of the frame) so if you pick an object up and hold it in front of the camera the background is still 75% of what you're filming so that's what the camera focuses on. Just leave the parts on the table so everything is the same distance away. It makes everything nice and simple for the autofocus!

love the flags!

I have an 82 XJ-750 Maxim that was doing the exact same thing, I didn't Jet it out though, I just opened the Pilot Jets up some and it smoothed right out.

Wow,you got that up on the center stand easier then I thought possible. Mine takes 2 plp to get it up on the stand.Perhaps its bent.

47.5 on the pilot fouls plugs after 1 week. dont go that fat. go 3 turns out on the mixture screw, and run a 43... stock jet size is 40 for the xs750

I use an aem wideband on the handle bars and a pyrometer on the pipes.

I have a xs850 carbs that are a bit different they are H5C-34mm Hitachi rather than the xs750 with HSC-32mm Mikuni. My carbs all together have 12 jets.

Normally if the spark is black so it means that ur engine need more air not less so u have to upgrade ur pods or to have bigger ones

awesome video!.So you went up 4 sizes on the main correct and you left the pods tapped up?? ive heard the rule of thumb is 5 sizes up if you have pods and free flow exhaust. I really like how when you changed a setting and then took us for a test ride.

Thank you for this video. Awesome

Helpful video! When you moved up to your final jet size did you leave the movable rings on the needles to the last spot you moved them? or back to the original spot? Thanks! Ross

You sir, are awesome ! :)

i got cheapo ebay pods. Im too lazy to put the air box back on. I'm just gonna make due with hesitation at high rpms. I hit highway speeds fast and fine.

ON MY 79 XS750 special im running 145main 43.5slo jets... got that same 3 into1, and I'm running naked uni pods (black inners) mechanical shutoff petcocks... the vacuum stocks are trash.

Hi, I would like to ask a question off topic please. I like the handle bars your using and would like to know what they are please and where to get them. Also, do they work OK with the shorter UK style throttle and clutch cables? Thanks in advance

Cheers mate

Where do you get your parts from I have a 1979 XS750 I'm restoring and need parts

Hello mate, i woudl like to know if that set of carbs can work for a Yamaha XS850? because i'm having problems with mine, and those are very rare and complex. in other hand i'm seeing that your carbs only have one jet i guessing is the main, where is the pilot or slow jet?

Das a 750, honestly if I were you I'd get a set of cvk's off a triumph sprint 98, headers and exhaust too. Carbs require mild tuning and are direct fit, the headers require minimal welding to the flanges and the crossover pipe doesn't have room for the center stand. However, makes it run quite a bit better though.

I might be buying one of these. I really like the look of them. The one I'm getting has been in storage for a long time, but the engine turns. What's an easy way to sinc the carbs after I rebuild them?

How did the plugs look after the 150 jetting on the main? I have a 79 xs special thats just a nightmare opened up the carb and they were already @150. The idle jets are all torn up from screwdrivering. Have no idea what size they are the jets are so beat.

Also how is your gearing after the upjetting? I seem to only get about 10 miles before shifting? It gets better when i adjust the a/f mix screws? About 20 mph on the gauge til 2nd gear

you got the tape on the wrong end

what kind of carb is that, hitachi?

So what did the plugs look like after the jetting

did you ensure float height was correct before altering your jets?

Hi can not seem to find timing marks to set it up. And on timing chain there is a discoloured link. Has that anything to do with it

Where did you order your jets from? I have the same bike

Hi can you tell me the torque settings on the head bolts please

what size cone filter are those?

look up "Gunson colortune"

Well, you have a nice garage and set of tools, your only lack in knowledge, take it to a good mechanic, he' ll save you a lot of headecks, masking tape?, really?, who are you?, an Ichiban brother?, is good to try but you have to know when to give up "NEVER GIVE UP" not allways work, good luck!!

47.5 on the pilot fouls plugs after 1 week. dont go that fat. go 3 turns out on the mixture screw, and run a 43... stock jet size is 40 for the xs750

ON MY 79 XS750 special im running 145main 43.5slo jets... got that same 3 into1, and I'm running naked uni pods (black inners) mechanical shutoff petcocks... the vacuum stocks are trash.