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TOPIC: Throttle Hanging Open (Adjustment help requested)

Throttle Hanging Open (Adjustment help requested) 2 months 3 weeks ago #23142

  • mizztheman
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I had exactly the same problem when I set up my carbs. Made a big difference when I followed the instructions in the service manual. I’ll see if I can dig the page out of the manual when I get home.

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Throttle Hanging Open (Adjustment help requested) 2 months 3 weeks ago #23149

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kawboy wrote: I'm looking at the choke cam and the profile doesn't look right. It appears to be teepee'd. Scotch?
First thing I noticed as well - by the first picture. The second (better) picture shows this - although not as "tee-pee'd as much as the first picture suggested.
Non the less, sliding the choke cam out of the way proves a misalignment with it when it's tightened. This is due to some previous set-screw dimpling in the "V" of the choke actuating shaft.
Before we continue: If you are experiencing Hard-Starts and/or anything other then a smooth idle then now is the time to install NEW idle-jets to cure the idle issue. www.kz1300.com/index.php/forum/carburato...le-jets-vs-old#20859
Hard starts can be cured by installing a choke-air restrictor:


At this point, regardless of what you do or have done - Verify that the "Ball-seat" is correctly seated in the Link Rod !
Then: Start by paying close attention to the three choke lifting arms ! All three should start to contact the top of the "spool" at exactly the same time. My experience with rebuilding carbs when I receive them is that 2 are "timed" - the remaining one is either "early" or "late".


NOTE: A carb. rebuilding service provider states: " One more thing that a lot of people aren't aware of is that the start valve (aka choke) lifters look identical at a glance but they're not. If you install one of them upside down, its partner start valve won't close all the way and that carb body will be uncontrollably rich. You'll chase a non-existent jetting problem to no avail."
This is false !! If this was the case, Mikuni would have marked the lifters with an "UP" mark !
This "condition" is from nothing more than the choke shaft having been dimpled from previous assemblies - and they always are. If the point of the set-screw is not retuned to the original divot, misalignment is guaranteed. The choke shaft needs to be removed and the high-spots around the divots, filed down. You can't do anything with the actual "divot"/depression. This is where some patience is required. Place the 3 lifters on a flat surface and confirm their arms are parallel.

The material is relatively soft so it's easy to realign them. With the shaft and lifters still off the carbs start playing the Shell-Game. Slide the lifting arms into their respective positions and "lightly" snug the set screws on all three. Place the shaft and snugged arms on a flat surface. All of the lifter arms must rest on the flat surface. If they don't, Swap them around - Turn them over if required and re-snug their screws. Repeat the process until they all align. The set-crews must be returned to the same divot. This in itself, can be tricky but is important !
This is the time to confirm that all three choke-plungers lift easily and most importantly - close - freely ! The Lifting Spools should "float" on the choke plunger. If not - correct this. Polishing the plunger stem will often look after this but: I've actually had to ream ( NOT DRILL) some spools that would still not slide up and down freely. This is important ! Also: The parallel arms of each lifter must not pinch the spool ! Spread the arms as required.
When you're satisfied with the lifter positions identify them as Left, Center and Right for future positioning reference.
Reinstall the choke rod with the lifters and fast-idle cam. Snug the set screws. Check the lifter timing with the choke lever. The lifters should make contact with the spools and start the lift at the same time ! If they appear to the eye to be "timed" - you're good !
Your fast-idle cam position is clearly misaligning due to the same condition. With the choke lever fully OFF and with no other obstructions, the Fast Idle roller must be OFF the cam. ie: A mere .010" is all that's required. In the choke OFF position the roller should be closer to the end of the cam then in your photos. If this is not the case then try this: Loosen the set-screw slightly and re-snug while pushing down firmly on the cam lobe. Check to see if this repositioned the cam, relative to the roller. It usually works, for me.
By now you should have the idea of what we're trying to achieve.
Now a "Static Sync." Cut a strip of writing/printer paper about 1/4" wide and about 6" long and crack the throttle plates to insert this paper so it is trapped between a throttle-plate and the venturi. Either venturi per carb. Adjust the sync. adjustment screw until there is some "drag" on the paper when you pull the paper out. Adjust the three carbs sync-screws so the resistance to pulling this paper strip out, feels the same. Snug the lock-nuts. This will set the throttle plates close to where they need to be for the vacuum sync. This "gap" is minimal but critical.
At this point you should be able to adjust the idle knob (between the left and center carb just for clarity) to get the .54mm clearance indicated in the manual (E21 - page 50?). This is an arbitrary setting for now and will likely change once the set-up and vacuum sync has been completed.
If you've done all of this correctly you should see the following:
1) With the choke OFF, the roller should be now be near/over the end of the cam lobe but not touching the lobe. This is the function of the Fast Idle adjusting screw (#30). Adjust this screw to get the roller off the lobe when the choke is OFF.
2) With the Choke fully ON, the roller should be sitting in the "valley" of the lobe. This is critical so that the throttle plates are closed to their maximum - just that slight gap as adjusted with the paper strip.
All of this should have eliminated your original problem plus reduced further set-up issues. The vacuum Sync can now be done. You should be able to adjust the sync to get 8" to 9" Hg vacuum but do not be alarmed if you can only sync to 7" Hg. This reading will be determined by the overall condition of the engine. On a cautionary level - If you are not careful and you are forcing the maximum vacuum readings you will inevitably over tighten the sync-screws and cause the linkage to bind. This is the reason the manual indicates turning IN the sync adjusting screws till they stop and then backing them out 1 1/2 turns. The 1 1/2 turns gives some room for syncing without binding. Note: The Enriching Valve starts to move at approx. 10" Hg, is half closed at approx. 18" and fully closed at 22" Hg. If you're using standard engine vacuum gauges IGNORE the nomenclature on the dial as it's not applicable to our engines.
That's it ! hope I've helped.
1980 KZ 1300 sr# KZT30A-009997
Always High - Know Fear !
The following user(s) said Thank You: zed_thirteen, Kawboy, mizztheman, A1, propav8r

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Last edit: by scotch.

Throttle Hanging Open (Adjustment help requested) 2 months 3 weeks ago #23150

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I don’t think you need a copy of the manual after Scotch put up that post.

What a Gent.

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Throttle Hanging Open (Adjustment help requested) 2 months 3 weeks ago #23151

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Lol, yeah, great info in there, thanks a bunch Scotch.

What do y'all mean by a "teepeed" choke cam? just that it comes to a point?

Should I give ti a few easy strokes with a file or just leave it be?

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Throttle Hanging Open (Adjustment help requested) 2 months 3 weeks ago #23152

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definition : Tee Pee
- What you evacuate after drinking tea
- What Survivalists use for shelter
- Another word for "ass-wipe"
:woohoo:


or in this case - The high resting point of one part on another, relative to the correct position.
Do not attempt to correct this problem by re-indexing the cam lobe with a file !
1980 KZ 1300 sr# KZT30A-009997
Always High - Know Fear !

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Last edit: by scotch.

Throttle Hanging Open (Adjustment help requested) 2 months 3 weeks ago #23153

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You Army Navy guys have an acronym for everything. And I suppose you have an AN spec for the TP (toilet paper)?
1980 KZ1300 B2 converting to an A2.

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