Topic: 71' cb750 Carb jetting

[zuehl666]

I'm trying to get my K1 running well. I've got these Lynx filters with 3/8" coarse uni foam, oiled with uni filter oil. Stock carbs, CycleX electronic ignition and coil.


I've got a 4 to 1 with a reverse cone and small baffle inside.


Im running NGK D8EA plugs, they are reading a bit lean. The tips are grey. Ive got 120 mains 40 idle jets. Needle is on the middle clip position. I just ordered 125 mains. does anyone have a similar setup? What jets are you running?

[lucky]

Good photo of the bike!

For all practical purposes you have "pods" (a non stock nonrestrictive filter).

I would certainly use the 125 main jets you have already oredered but that will only help WOT. (Wide open throttle).

The needle clip on the slide needle was 3 or middle groove stock... so you will need to move the clip down one notch. Move it to the 4th groove down from the top of the needle.

I would change the idle jet to a #42.
You could try the #40 stock idle jet but I just think it could be lean and cause some hesitation when quickly opening the throttle which you don't want.
At least on this set of carbs the idle jet is threaded into the carb. Easy install.

Put the mixture screw at one turn open.
If there is any popping then Try 1-1/4 turns open.

After all of this is done sync all of the carbs idles.

Just stick with the stock type spark plugs.

[zuehl666]

Good photo of the bike!

For all practical purposes you have "pods" (a non stock nonrestrictive filter).

I would certainly use the 125 main jets you have already oredered but that will only help WOT. (Wide open throttle).

The needle clip on the slide needle was 3 or middle groove stock... so you will need to move the clip down one notch. Move it to the 4th groove down from the top of the needle.

I would change the idle jet to a #42.
You could try the #40 stock idle jet but I just think it could be lean and cause some hesitation when quickly opening the throttle which you don't want.
At least on this set of carbs the idle jet is threaded into the carb. Easy install.

Put the mixture screw at one turn open.
If there is any popping then Try 1-1/4 turns open.

After all of this is done sync all of the carbs idles.

Thanks! thats very helpful. I'll let you know how it works out.

[lucky]

Good photo of the bike!

For all practical purposes you have "pods" (a non stock nonrestrictive filter).

I would certainly use the 125 main jets you have already oredered but that will only help WOT. (Wide open throttle).

The needle clip on the slide needle was 3 or middle groove stock... so you will need to move the clip down one notch. Move it to the 4th groove down from the top of the needle.

I would change the idle jet to a #42.
You could try the #40 stock idle jet but I just think it could be lean and cause some hesitation when quickly opening the throttle which you don't want.
At least on this set of carbs the idle jet is threaded into the carb. Easy install.

Put the mixture screw at one turn open.
If there is any popping then Try 1-1/4 turns open.

After all of this is done sync all of the carbs idles.

Thanks! thats very helpful. I'll let you know how it works out.

Thanks for letting us know what happens. I am keeping a data base (list really),
and it has some gaps.

Many owners get info, then we never hear from them again.

[zuehl666]

Good photo of the bike!

For all practical purposes you have "pods" (a non stock nonrestrictive filter).

I would certainly use the 125 main jets you have already oredered but that will only help WOT. (Wide open throttle).

The needle clip on the slide needle was 3 or middle groove stock... so you will need to move the clip down one notch. Move it to the 4th groove down from the top of the needle.

I would change the idle jet to a #42.
You could try the #40 stock idle jet but I just think it could be lean and cause some hesitation when quickly opening the throttle which you don't want.
At least on this set of carbs the idle jet is threaded into the carb. Easy install.

Put the mixture screw at one turn open.
If there is any popping then Try 1-1/4 turns open.

After all of this is done sync all of the carbs idles.

Thanks! thats very helpful. I'll let you know how it works out.

Thanks for letting us know what happens. I am keeping a data base (list really),
and it has some gaps.

Many owners get info, then we never hear from them again.

OK, so it took forever to get my jets in the mail and I decided to move the needles to the 2nd from the bottom clip position and test it with the stock 120 mains, It went from slightly lean to too rich. That had me a little confused why, I even tried taking the baffle out of my pipe. So when the 125's finally arrived the other night I was just comparing them to the 120's and I dont know if its just the fact that they are darker in color, but the 120's seem to have a larger if not same size hole? I started to think maybe someone had drilled them out at some point. I ended up putting the needle clip back it position 3 and installing the 125s but ran out of time. I'll try riding it saturday and see how it goes.

[lucky]

Good photo of the bike!

For all practical purposes you have "pods" (a non stock nonrestrictive filter).

I would certainly use the 125 main jets you have already oredered but that will only help WOT. (Wide open throttle).

The needle clip on the slide needle was 3 or middle groove stock... so you will need to move the clip down one notch. Move it to the 4th groove down from the top of the needle.

I would change the idle jet to a #42.
You could try the #40 stock idle jet but I just think it could be lean and cause some hesitation when quickly opening the throttle which you don't want.
At least on this set of carbs the idle jet is threaded into the carb. Easy install.

Put the mixture screw at one turn open.
If there is any popping then Try 1-1/4 turns open.

After all of this is done sync all of the carbs idles.

Thanks! thats very helpful. I'll let you know how it works out.

Thanks for letting us know what happens. I am keeping a data base (list really),
and it has some gaps.

Many owners get info, then we never hear from them again.

OK, so it took forever to get my jets in the mail and I decided to move the needles to the 2nd from the bottom clip position and test it with the stock 120 mains, It went from slightly lean to too rich. That had me a little confused why, I even tried taking the baffle out of my pipe. So when the 125's finally arrived the other night I was just comparing them to the 120's and I dont know if its just the fact that they are darker in color, but the 120's seem to have a larger if not same size hole? I started to think maybe someone had drilled them out at some point. I ended up putting the needle clip back it position 3 and installing the 125s but ran out of time. I'll try riding it saturday and see how it goes.

You cannot SEE .005 thousandths. You would need some way to measure that.
Remember that the main jet is not going to affect 1/4-3/4 throttle very much at all .

If it has hesitation when giving it quick throttle then you need to deal with the slide needle. With pods and aftermarket exhaust you cannot expect the midrange to be rich enough unless you make an adjustment.
Forget about plugs or plug chops right now.

Just get it to run right. No popping on decell, and no hesitation on giving it quick throttle.

Get that part right first,.. before worrying about plug color.

[zuehl666]

Good photo of the bike!

For all practical purposes you have "pods" (a non stock nonrestrictive filter).

I would certainly use the 125 main jets you have already oredered but that will only help WOT. (Wide open throttle).

The needle clip on the slide needle was 3 or middle groove stock... so you will need to move the clip down one notch. Move it to the 4th groove down from the top of the needle.

I would change the idle jet to a #42.
You could try the #40 stock idle jet but I just think it could be lean and cause some hesitation when quickly opening the throttle which you don't want.
At least on this set of carbs the idle jet is threaded into the carb. Easy install.

Put the mixture screw at one turn open.
If there is any popping then Try 1-1/4 turns open.

After all of this is done sync all of the carbs idles.

Thanks! thats very helpful. I'll let you know how it works out.

Thanks for letting us know what happens. I am keeping a data base (list really),
and it has some gaps.

Many owners get info, then we never hear from them again.

OK, so it took forever to get my jets in the mail and I decided to move the needles to the 2nd from the bottom clip position and test it with the stock 120 mains, It went from slightly lean to too rich. That had me a little confused why, I even tried taking the baffle out of my pipe. So when the 125's finally arrived the other night I was just comparing them to the 120's and I dont know if its just the fact that they are darker in color, but the 120's seem to have a larger if not same size hole? I started to think maybe someone had drilled them out at some point. I ended up putting the needle clip back it position 3 and installing the 125s but ran out of time. I'll try riding it saturday and see how it goes.

You cannot SEE .005 thousandths. You would need some way to measure that.
Remember that the main jet is not going to affect 1/4-3/4 throttle very much at all .

If it has hesitation when giving it quick throttle then you need to deal with the slide needle. With pods and aftermarket exhaust you cannot expect the midrange to be rich enough unless you make an adjustment.
Forget about plugs or plug chops right now.

Just get it to run right. No popping on decell, and no hesitation on giving it quick throttle.

Get that part right first,.. before worrying about plug color.

Thanks, I'll have to take it for a ride saturday and see how it runs.

[lucky]

How does it run just sitting in the garage?

No point in taking it out on the road if it will
 not run right while sitting in the garage.

[neilc]

I am running pods and 4into 2 exaust with 120 mains and 40 slow jet with middle  clip position and running rich

[zuehl666]

I am running pods and 4into 2 exaust with 120 mains and 40 slow jet with middle  clip position and running rich

When I had my clip in the middle the tip of the plug was grey, moved it down one to richen it a bit and it was too rich at that point. So I put the clip back to the middle and put 125 mains in hoping that it will get just a little more gas at highway speed and even it out a bit. I'll let you know if that works.

[zuehl666]

How does it run just sitting in the garage?

No point in taking it out on the road if it will
 not run right while sitting in the garage.

It runs fine, Idles without popping, I can give it a quick rev and it seems ok but will pop a bit coming back down from higher rpm. That was with 120 main, 40 slow, Screw 1 turn out, and clip 4th from top. I rode it a bit like that and when I checked the plugs after about 30 highway miles they were black. I haven't had anytime to get into the garage and run it again, Hoping tomorrow or sunday I can do that with the way I have them setup now. 40 slow,125 main, and 3rd clip. The float levels are stock.

[neilc]

Thats whaty 3 settings are the bike runs great but fouls plugs after 50iles so still have to figure that out.

[lucky]

I would get it to run right. No popping and good acceleration at top end, with no end in sight.  No hesitation at all, Then I would worry about the plugs.

[saltcitycafe]

Did you ever get this worked out? I have a 71 750 as well and will be assembling and firing it up in the next few months so I would like to know where you ended up

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