79 kz750 jet size?

Hi, I'm helping a buddy with is 79 kz750. He has a stock airbox with straight pipes. I have no idea what size jets are in the carbs now but I'd like to know what size you think he should run with his current setup. Any help would be awesome. Thanks

Stock jets are 45 pilot and 125 mains. I would recommend going to 50 on pilots because that improves performance even with stock setup. The factory pilots were too lean for smog restriction, 50's ran better on mine with every exhaust I have run over the last 30 years.

As for mains with straight pipes: probably at least 135, maybe more. He will also have to screw around with the needles no end and it will probably never run right across the full range.

I'm old and lazy and time is more valuable than money so your friend might want to drop about $175 on a set of MAC pipes and then he won't have to screw with the carbs for the next six months. The MACs run perfect with a 50 pilot and 125 main.

If he is dead set on straight pipes and needs main jets, here is the only place I know that still sells the mains for the BS-38 Mikunis that came on the '79 KZ750 twin:


www.allensperformance.co.uk/mikjets.html


You want this one: N100606-SIZE


This place claims to have them as well:

www.motorcyclecarbs.com/search.cfm

Do a search for : n100.606

I ordered mine from motorcyclecarbs.com
still tinkering with it though since I put on K&N pod filters

Hey Bountyhunter, all the advice you gave was for a twin, right? I have a 4 cylinder 750 (80) and am always looking for improvements. (That's where most my problems also occur )

apbling wrote:

Hey Bountyhunter, all the advice you gave was for a twin, right? I have a 4 cylinder 750 (80) and am always looking for improvements. (That's where most my problems also occur )

Yeah, twin. Disregard if it's a four.

I am a new member to the site. Still trying to use the computer. I just purchased a 1979 KZ 750 Twin. It has 30,000 miles and seemed to run good when I bought it two weeks ago in Atlanta ,GA. Started right up and I took a ten mile test ride. I live in Johnson City, TN and we have not seen the temperture above 32 degrees since I bought the bike. I can not get it started again. Gas is good, timing and points(new), battery new and fully charged, plugs are new. The spark seems to be weak (yellow and not blue).

Any sugestions? I keep the bike in an unheated building.

Hopper wrote:

I am a new member to the site. Still trying to use the computer. I just purchased a 1979 KZ 750 Twin. It has 30,000 miles and seemed to run good when I bought it two weeks ago in Atlanta ,GA. Started right up and I took a ten mile test ride. I live in Johnson City, TN and we have not seen the temperture above 32 degrees since I bought the bike. I can not get it started again. Gas is good, timing and points(new), battery new and fully charged, plugs are new. The spark seems to be weak (yellow and not blue).

Any sugestions? I keep the bike in an unheated building.

If points and plugs are good (and battery is strong) and you get a weak spark, the coil is suspect. Good news is Z1 Enterprises sells a new EMGO OEM type four ohm coil that will work perfectly for $36 (and that is cheap for a new coil). I am running it on my 750 twin and it really cranks the spark.

You should also check the voltage at the positive coil terminal and make sure it is over ten volts. If not, you may have wiring/fuse/switch/connector issues.