74 Sport Carb Jetting

[dden]

Hi guys, getting my 74 sport ready for riding. The previous owner had K&N filter on it, and also said he cleaned the carbs before i bought it as it had been sitting for a while. They are original PHF 32's

It is now setup with the original open stacks with the mesh screen. an just isn't running right. doesn't want to idle and has some flat spots.

I decided to take the carbs apart, reclean them and find out what jetting and settings it was setup with. Here is what i found

Idle Jet - 70
Main - 148
Atomizer - AB265
Needle Valve Assembly 250 with black tip
Pump Jet - 35
70/2 Slide
K5 Needle set with the clip on the top ring so the needle ends up the furthest down into the carb
10 Gram Float
Choke Jet - 75

Idle Screw 2.25 turns out
Mix Screw 1.75 turns out

The main seems too big, any suggestions on known good setups? Also what was stock? I only found a few references int eh 750 Bible, not the entire carb setup. It was also for 72-73 sports and if i remember correctly the 74 had different cams. I could be wrong about that...

Thanks
Dan

[wdietz186]

The idle jet is a bit big, IIRC they were 60 or 65's
Mains were usually in the 125 area but the factory often jetted the bikes individually.
Before you go too deeply into the jetting make absolutely sure the valve adjustment is correct,the ignition is timed correctly and producing a good spark,the battery is good[under about 11v the bike will run like poop] and the carb insulators are sealing well. A check of the valve guide condition would be prudent too.

[machten]

I run the stock setup and it works very well. My Sport will start with choke first kick after one priming kick with choke per cylinder, start, turn off choke and idle steadily immediately.

I'd say a 148 main is way too big unless you are running some very funky cam grind and big bore. I'd go back to a 125 which was stock with conti's and bell mouths. Some people ran with 128 in the vertical carb to run cooler to compensate for less airflow. But no more. The idle should be a 65 and the needle a K17. With your current setup in a stock Sport, I'd expect you're running rich all the way through throttle progression. You're running on the top slot of a richer needle to compensate for the over fueling main, pilot and needle, but it isn't enough and your progression would be all mixed up yielding flat spots. Your plugs would tell the story. Are they sooty?

Also, the slides should be 70/1 (70) rather than 70/2. No difference to pumper ramp length on the slides, but the 70/2 ramp starts 3mm higher which will delay your pumper coming to the party. Probably no big deal though. The pumper jet of 35 is correct from memory.

I agree with Bill's comments below, but I reckon your main, pilot and needle will be causing you problems.

Kev

[dden]

thanks for the information. I did some searching for that sk17 needle and did not find it available. But during the search i came across a few pages that say the sk17 spec was a mistake in teh original ducati manuals and made its way into several other books. Supposedly the K5 needle is correct. I also find the slide 70/2 as stock but that may have been a mistake as well.

I ordered some mains in the 115 122 125, 128 range. and some 65 and 70 idles. Ill jet it down to where it was "supposed" to be and adjust from there. Slides are harder to find these days but i'll keep my eyes open for the 70/1 and 60/1 as its reported to help.

Good advice on checking timing and valves. That was already on the list and will be done before the rejet.

[machten]

I did some searching for that sk17 needle and did not find it available. But during the search i came across a few pages that say the sk17 spec was a mistake in teh original ducati manuals and made its way into several other books. Supposedly the K5 needle is correct. I also find the slide 70/2 as stock but that may have been a mistake as well.

I know a K6 needle works well too in the middle slot and is readily available. I wouldn't worry about replacing the slides at this stage if they are serviceable. They are expensive and I don't think you'll notice the difference much if at at all. Changing those jets will make the biggest difference by far. Then see how the K5 and 70/2 run with them.

Good luck!!!

Kev

[dden]

Runs MUCH better after carb cleaning and change to the main jets. Thanks for the info guys.