Dies when I touch the throttle

The Bike: 1982 KZ 750 M1 CSR Twin. Original Airbox and carb.

The bike was mine back in 2001 - I moved to Florida and gave the bike to my uncle. My uncle had the bike between then and now who had much more experience than me with bikes. He passed recently and the bike is mine again.

When I got the bike back it had been sitting for a few months without being run. Got it to start but it was rough. When i touched the throttle it would die.

After searching around for a while i thought I found the problem. Pilot jet was clogged or malfunctioning in some other way. I took the carb apart and paid as much attention as I could to how things were set up and gave it a really solid cleaning.

I took off the bowls
I removed the top covers
I took out the pilot jets
I took out the main jets
I took out the emulsion tubes
I removed the vacuum pistons and checked the diaphragms for failures
I checked the floats

I cleaned everything as well as i could and reassembled it as to the specs in the service manual. I checked it twice if not three times and feel I did the reassembly as well as anyone else would. The jets and emulsion tube were very dirty and gunk covered. The jets looked more like caps and I couldnt see through them prior to the clean. They came out very clean and I thought I had solved my problem.

Today i put the carb assembly back on the bike and turned the gas to prime for a minute or so and the bike fired up shortly after. I had to play with the idle adjust screw some but eventually got it to about 1050 rpm idle without choke. Every 20 seconds or so it sounded like it skipped a beat but would then idle fine until the next little stutter. This is a much smoother run than I was getting prior to the cleaning.

But my problem remains about the same. I reach for the throttle, give the tiniest twist and i can hear it start to die. No rev, just die. It almost feels like it is running out of gas but it fires right back up again like nothing happened.

I sprayed around the carb holders with carb cleaner during idle to check for leaks. No noticable difference.

Clutch in or out it idles as described above. I didn't try it in gear. I didn't lift the kickstand because I don't believe I have a kick sensor.

Other observations that may or may not be related.
1] I'm getting a little more exhaust pressure out of the right side.
2]Plugs are brand new
3]Right plug and left plug wires are different from each other but both appear operational.
4]I replaced the fuel line with a 1/4" line i got from a local bike shop when I bought the plugs

Is there anything I'm overlooking? Am I down the right path thinking my issue is carb/pilot jet related? Has anyone experienced this before and or have advice?

Many Thanks in advance

-Adam

Good Fortune!

From what you describe it sounds like the pilot circuit is still plugged. You need to remove the pilot screws and make sure the passages are all clean. Also, all the various O-rings should be replaced since they are 35 years old now. Needless to say all the various other maintenance tasks should be updated on the bike as well. Things like valve adjustment, clean/replace the air filter, etc. Anything that is off on the maintenance can cause you to chase your tail regarding running problems.

So i took out the pilot screw and cleaned the snots out of the whole pilot circuit.

Now I have a completely different problem. I can't get it to drop under 5k rpm's!

I thought I was setting everything to the appropriate specs but now I'm not too sure.

I put the pilot jet in till it was snug then backed it out one full turn. (my manual says back it out the same number of turns that were counted during disassemble - but it was junked up during disassemble - i found on some thread here on most carbs it's less than two turns)

I put the pilot screw in all the way and then backed that out one and a half turns (my mikuni carb literature says it should be between 1 1/4 and 1 3/4 turns)

The only way i got the rpm's to lower was to partially block the air intake with the palm of my hand.

The idle adjust knob is set so the butterfly valves are closed. The throttle cable may even have a little sag in it.

I sprayed the carb holders with cleaner while it was running with not increase in RPM so i'm feeling confident i don't have an airleak there.

Any thoughts? Could my pilot jet be letting too much fuel through? Where would you go from here on your bike?

Try backing out the pilots screws to 2.5 turns and see what happens.

Intake leaks do not always respond to spraying crap on the boots.

Benjo wrote: I put the pilot jet in till it was snug then backed it out one full turn. (my manual says back it out the same number of turns that were counted during disassemble

You don't back out the pilot jets, snug them down and leave them snug.

Pilot screw... pilot jet. Do we have a component name issue?

missionkz wrote: Pilot screw... pilot jet. Do we have a component name issue?

My use of the terms is consistent with the diagram above which is consistent with the manual.

Benjo wrote: . . . I put the pilot jet in till it was snug then backed it out one full turn. (my manual says back it out the same number of turns that were counted during disassemble - but it was junked up during disassemble - i found on some thread here on most carbs it's less than two turns)

I put the pilot screw in all the way and then backed that out one and a half turns (my mikuni carb literature says it should be between 1 1/4 and 1 3/4 turns)there.

Any thoughts? Could my pilot jet be letting too much fuel through? . . . .

Benjo wrote:

missionkz wrote: Pilot screw... pilot jet. Do we have a component name issue?

My use of the terms is consistent with the diagram above which is consistent with the manual.

I suspect that the manual or other written reference is either misleading or being erroneously interpreted.

The pilot jet is itself part of the passageway in the pilot circuit. Pilot jets are available in various different sizes. The pilot jet is supposed to be fitted snugly, and supposed to remain snugly fitted.

The pilot screw is adjustable to regulate the volume of fuel mixture provided by the pilot circuit into the carb bore (after the fuel mixture has already passed through the snugly fitted pilot jet).





Good Fortune!

Thank you all for the help and clarification up to this point! I believe on of the resources was using the term pilot jet where they intended to use screw. I will spend some time on this this weekend and report any progress. Thank you again! Very grateful.

The adjustment screw on a carb is usually one of two types.

One type enables regulation of the amount of air entering the pilot circuit. It's usually a side-located screw. And is generally referred to as a Pilot Air Screw.





The other type -- usually located near the carb holder -- enables regulation of the amount of fuel mixture entering the pilot circuit. And is generally referred to as a Pilot Mixture Screw.

Here's a comparison between manual slide carbs of the difference between a pilot air screw and a pilot mixture screw.



Am thinking most if not all CV carbs have a pilot mixture screw (located near the carb holder).
And I don't recall off-hand a CV carb that has a pilot air screw.

May sometimes be called a Pilot Screw.





But we know in our hearts that it's really a Pilot Mixture Screw. :lol:



Good Fortune!

Patton, thank you for your thorough posts!

She is running very well at the moment! Thank you all for your insight.

This morning i took the carbs off again and went through them again.

I snugged the pilot jet as mentioned above - thank you for that!
I reset the pilot screw to the appropriate number of turns back
I checked the choke to make sure it wasn't sticking
I checked the floats to make sure they were also not sticking (i think this was the cause for my high rpm)

Reassebled and she fired right up and idled between 1k and 2k after warming up. Some minor adjustments and I think she's in great shape!

This afternoon I took her down the road and back and I am very pleased!

Thanks again - this forum was ahuge help!