Topic: 1978 CB750K idle jet

[lucky]

I have a 1978 CB750 I am building into a cafe style bike.
I am a ex Honda mechanic.

What experience does any forum members have with removing the idle jet
On the 78 K model? So called Keyhole style carbs

There is no screwdriver slot and i heard they are pressed in.

If I run a stock engine, pod filters, and a kerker style exhaust what size mainjets will I need ?
It has 110 mains,  and the idle jets are not marked.

Will a pilot air screw adjustment take care of it?

[mrrch]

Grip lightly and twist out. Sirius Consoldated has optional sized jets push in slow jets if required.

[brewsky]

Cut a small piece of shoe leather to wrap around the jet and grab it with vice grips.

Kinda like pulling a tooth.....twist,  rock, and pull ....but start out gentle.

Soak in PB Blaster first.

[Flying J]

so what did you do at honda?

[dakota]

...

[lucky]

so what did you do at honda?

Who are you asking?

[TwoTired]

What experience does any forum members have with removing the idle jet
On the 78 K model? So called Keyhole style carbs

There is no screwdriver slot and i heard they are pressed in.

Twisting removes more metal then you want.  Best to avoid making the hole bigger or the jet smaller.  Less risk of them falling out latter.
Pull them straight out, as that is the way they were installed.

It's called a swagged fit, or swage fitting, btw.

We call them PD carbs in this forum, usually.

Cheers,

[Blitzburgh207]

...if you yank it more than twice you're playing with it

Grip lightly and twist out. Sirius Consoldated has optional sized jets push in slow jets if required.

Thanks! I want some new ones but couldn't remember the name of those guys

[BobbyR]

Get a good grip on the jets, with good pliers so you do not have to squeeze them oval, pull straight  up and a bit of wiggle gets then right out. Putting them back in be extra careful to get them nice and straight, and lightly tap back into place.

[lucky]

so what did you do at honda?

Sorry I did not get back to you right away.
I worked as a dealership mechanic in Tucson, Arizona at Muscleman's Honda store.
I also raced in the 250 class with a Ossa TT Special.

[cookindaddy]

Some have suggested parallel jaw pliers to pull on the jets without deforming them but these are hard to find. Once you get a good grip on them, they come straight out. I'd suggest twisting not rocking so you don't deform them.

Cleaning the idle jets is a bit of a trick, once you get them out. You should be able to see light through the idle jets and when you do, you will see that the hole down the length is unbelievably small, a few thou. Some have suggested passing a piece of small diameter wire through the hole, hopefully copper so it doesn't scratch the inside of the brass idle jet. Three of the four in mine were plugged solid. Bike ran much better with them clean.

Can't help with the main jet size.

[lucky]

I did pull out the push in style jets. Thanks everyone for the advice.
I added one .022 shim under each needle. that helped right off with the throttle response.
4 into 2 into 1 exhaust and no air filters. With pod filters on, it was even better.
Then I sent the slides to Cycle exchange and they cut a little off of the bottom of the slides and that was helpful to get the idle down also.

Still did not want to accelerate and I found out the fuel accelerator pump and nozzle system was not working.
I investigated all of that and got that all working.
Now I will put the carbs back on the engine with cut down slides.,one .022 shim under the needles and all nozzles squirting now and one step larger on the mains.

Should work well now. I am not worried about it being too rich believe me.
I am at sea level and I need all the fuel I can get.

[CustomUnderdog]

Hi Lucky, I read your post concerning the pilot jet on your CB750K. I am working on a CB750k 78' and would like to get the carbs right. Which size main jet size are you using and did you change the size of the pilot jet ?
 thanks Lucky

[flybox1]

Hi Lucky, I read your post concerning the pilot jet on your CB750K. I am working on a CB750k 78' and would like to get the carbs right. Which size main jet size are you using and did you change the size of the pilot jet ?
 thanks Lucky

we need to know what intake and exhaust you intend to use to accurately suggest jetting.
35pilot/110main is stock for the '78 750s.

[martin99]

Hey Lucky
My F2 runs pods and a Marshall Deeptone 4 into1. Don't know how that compares with a Kerker.
I've raised the needles (PD41s) by one clip position, essentially the same as you adding a shim. Mains are 130, pilots stock at 35 with IMS screws two turns out. Works for me, and without getting into the whole pods vs airbox debate, I would suggest that would give you a decent baseline for some finer tuning.

[flybox1]

this thread is 3+ years old.  I think lucky sold this bike even.
CustomUnderdog dug it up 

[martin99]

Ha ha! Didn't see that