Carburetors flat off idle response

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Jetdr
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Carburetors flat off idle response

#1

Post by Jetdr »

Ok, I have read everything I can find on the slow response off idle. I have ultrasonically cleaned the Carbs, I have replaced the felt seals on the throttle shafts, I have triple checked every jet, Immulsion tube, and every brass piece with a 20x lighted magnifying glass. I have used no less than 10 cans of carburetor cleaner and brake cleaner to blow through every orifice in each carburetor. I have just about worn out my two stage 60 gallon compressor blowing these carbs out. Every jet and every piece has been meticulously installed back in the absolutely correct location. Of course all Randakk parts. The floats are set at EXACTLY 21 mm all across the deck. The carburetors sync out perfectly and the engine runs as smooth as it did when it was new.

From idle... when I twist the throttle, I have this hesitation that’s driving me crazy!!

This is on a 76 LTD with the 756A carburetors. The off idle air jet is a 115 jet not a 110 jet. I did do the solder up and redrill the jets out with a #59 drill bit per the Randakk website and I had absolutely no changes. So I pulled the jets out and heated the solder back out and I get the exact same response.

What have I missed? I have 40 plus years playing with this kind of stuff but I certainly do not know everything!!!
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desertrefugee
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Re: Carburetors flat off idle response

#2

Post by desertrefugee »

The slides in their bores need to be smooth as silk. If there's a delay in slide movement in response to that quick vacuum loss, a lean condition results. Sounds like this might be the only thing you haven't mentioned. I believe Randakk speaks to this on his website and recommends some sort of polishing. I've never polished (or needed to), but I always make sure the slides go back into the same pot they came from and that their action is smooth as glass...
- Life is not about waiting for the storms to pass. It's about learning to ride in the rain.
Jetdr
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Re: Carburetors flat off idle response

#3

Post by Jetdr »

Thanks Desertrefugee. I even balanced the CV slides. They are smooth as silk.

I think I’ve got it fixed actually.

So I followed Randakks instructions to a tee. Since I have a 76 with 115 air jets I used a #59 drill bit after I soldered up the jets. That didn’t seem to fix the problem so I desoldered the jets and tried it that way. Well it seemed react the same way. So... I figured what the heck.. I resoldered up the jets and used a .08mm which is dang close to a #62 drill bit. Put it all back together and that did it!! I now have very good throttle response and the engine just runs and sounds perfect!! I drove the bike around for about 10 or so miles, stopping and going and all is well. The LTD is smooth and perfect!!
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flyin900
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Re: Carburetors flat off idle response

#4

Post by flyin900 »

So I have a similar situation with my 76 which I also did the shaft felts and a proper cleaning and carb rebuild. I did a #60 drill on the off idle air jet, as I couldn't find a #59 at my supplier. So a couple of questions as to moving to a #62 sized air jet as the fix that seemed to work for you.

By reducing the jet opening to a #62 from a #59 as suggested as the off idle fix I would think you are running the circuit richer with less air flowing through the smaller jet size.

Is the #62 size drill bit equivalent to the #110 air jet used in the other model years that are not the 1976 model?

I would like to find some jets that are either a correct size already, or another used set that I can modify and try without pulling the carbs and changing the current #60 sized ones I have in there presently.
Current Bikes:

1966 CL77 - Honda 305cc - Dual purpose - "Gentleman's Scrambler" was a period moniker.
1967 CL175K0 - Low production number with #802 engine serial- winter 2019/2020 full restoration.
1972 CB350F - Baby Four with low mileage - Cosmetic refresh to the next level 2021/2022.
1978 CB550K - Very original bike with only 7499 Km. from new - light cleanup and refresh done.
1983 CB1100F - Canadian model - DOHC Supersport in pristine low kilometre condition from new.
1984 GL1200 - Standard model in showroom condition - two owner bike from new.
1984 CX650E - Restored summer 2017 - a rare Eurosport model - excellent one owner bike.
kenai
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Re: Carburetors flat off idle response

#5

Post by kenai »

Sounds like you have solved the flat spot. How many turns out are your idle jet screws -factory generally holds for 11/2 turns off bottom. Moving out more enriches the entire rpm range thru the three small holes below the pluck...tweaking the idle air feed would also richen up the mixture thru the entire rpm range. Which approach would be best... more gas or less air?? Sounds like less air when the butterfly is first opened - off idle- and the carbs go lean might be the stronger approach.....
2 - 1979 GL1000
1 - 1978
1 - 1977
1 for parts
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gltriker
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Re: Carburetors flat off idle response

#6

Post by gltriker »

Kenai is pointing out something that is often overlooked in the quest to address this topic.
It has been noted many times, in many knowledgeable discussions, that enrichening each carburetor's pilot fuel delivery volume adjustment screw, beyond the specified Honda FSM initial setting, is consistently beneficial towards helping address a flat off idle acceleration complaint. The pilot fuel is introduced into the carburetor throat downstream of the throttle plate out of the easily fouled brass tube. (also, the troublesome return to idle complaint is generally eliminated, too)
Typically, with one additional counterclockwise turn of the pilot fuel volume delivery screw, the complaint is magically diminished. Utilizing the quite easily performed dynamic idle drop procedure will demonstrate how the pilot fuel delivery adjusting screw will affect the engine's very low RPM running behavior.
Although one might hesitate enrichening the pilot fuel screw, I believe, at least from my experience with my completely stock '75 GL1000's engine, that it's almost impossible to create an excessively rich engine running condition, before the screw's oring appears and no longer sufficiently seals the adjustment screw in its bore. If I remember correctly, Mike Nixon recommends 3 turns, maximum, from the seat as an initial set point. On my trike's stock carburetors, not too far beyond that set point, the pilot fuel adjuster needle screw suddenly feels very loose.

And, for what it's worth, I also feel that the presently very cold atmospheric conditions hinders the tuner's ability to heat the entire engine sufficiently towards creating the desirable conditions to perform meaningfull carburation adjustments.

note: The carburetors on the trike's engine are '76 LTD spec. number units that have had the specified off-idle hesitation slow air jet correction performed, too. ;)

Another note: As recommended by Mike Nixon, set the intake and exhaust valve lash clearance to 0.006 inch. Doing so on my trike's engine was notably beneficial in several performance categories. tumb2
Cliff (74yrs ;) )

Keep your eyes and ears open and you'll learn something new, everyday. tumb2

New users please visit our "Shop Talk" for common tips and help: <---jdvorchak
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RE: a thorough fuel tank cleaning
"And your carbs will thank you. They no longer live down stream from a sewage plant." -gregforesi tumb2
"Can't see the paint when your looking thru the handlebars..........." -Oldewing ;)
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Cliff

'75 GL1000 home built trike; http://www.ngwclub.com/forum/viewtopic.php?f=30&t=39996
October,2017 BOTM :shock: https://nakedgoldwingsclub.com/forum/page/Welcome

previous rides:
1953 H-D Servi-car, naked, 1969-1978 (serial#53G1559 committed to memory!)
1980 CB900 Custom (triked) 1997-2003 .... R.I.P.
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robin1731
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Re: Carburetors flat off idle response

#7

Post by robin1731 »

gltriker wrote:Kenai is pointing out something that is often overlooked in the quest to address this topic.
It has been noted many times, in many knowledgeable discussions, that enrichening each carburetor's pilot fuel delivery volume adjustment screw, beyond the specified Honda FSM initial setting, is consistently beneficial towards helping address a flat off idle acceleration complaint. The pilot fuel is introduced into the carburetor throat downstream of the throttle plate out of the easily fouled brass tube. (also, the troublesome return to idle complaint is generally eliminated, too)
Typically, with one additional counterclockwise turn of the pilot fuel volume delivery screw, the complaint is magically diminished. Utilizing the quite easily performed dynamic idle drop procedure will demonstrate how the pilot fuel delivery adjusting screw will affect the engine's very low RPM running behavior.
Although one might hesitate enrichening the pilot fuel screw, I believe, at least from my experience with my completely stock '75 GL1000's engine, that it's almost impossible to create an excessively rich engine running condition, before the screw's oring appears and no longer sufficiently seals the adjustment screw in its bore. If I remember correctly, Mike Nixon recommends 3 turns, maximum, from the seat as an initial set point. On my trike's stock carburetors, not too far beyond that set point, the pilot fuel adjuster needle screw suddenly feels very loose.Rule of thumb is if the mixture screws need more than three turns to run correctly then it's time to change the pilot jet.

And, for what it's worth, I also feel that the presently very cold atmospheric conditions hinders the tuner's ability to heat the entire engine sufficiently towards creating the desirable conditions to perform meaningfull carburation adjustments.Doesn't matter how warm you get the engine. The outside air temp will determine how the carbs want to be set. I never do any mixture adjustments, screws or jets, below 60 degrees. Even better if it's 65-70. If you set them when air temp is 40, 50 even 60, once it gets to 80 or 90 the carbs will be too rich. Even setting them in a warm shop when outside temp is colder you will not get them where they need to be for all season riding.

note: The carburetors on the trike's engine are '76 LTD spec. number units that have had the specified off-idle hesitation slow air jet correction performed, too. ;)That should be done on all carbs where Randakk recommends it. ;)

Another note: As recommended by Mike Nixon, set the intake and exhaust valve lash clearance to 0.006 inch. Doing so on my trike's engine was notably beneficial in several performance categories. tumb2
1976 Goldwing Super Sport
1985 Honda Elite
1976 KZ900 Dragbike
1992 ZX7 Dragbike (KZ900 style motor w/NOS)
and a rotation of various purchases
Randakk approved Carb Rebuilder
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flyin900
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Re: Carburetors flat off idle response

#8

Post by flyin900 »

Thanks for the input fellows. I won't be trying any adjustments until this spring when the temp is more normal and above 60F. The off idle response is not really that bad it just isn't where I would like it to be, yet it maybe normal for the GL1000 motors. I do need to give the motor some extra gas on most takeoffs above what I would consider normal compared to my other bikes. (These are more an 80's mix of Honda bikes with a somewhat newer and a different style of the CV carbs.)

The air mixture screws are currently set at factory specs, so I will start there and try to increase the turns out by one turn and see what that does to the issue. I do actually have a ColorTune plug that I will also place in each cylinder to get a reading on the idle colour of the mixture.

The bike runs very well otherwise and pulls hard right to red line, plus the spark plug colour is within the proper shade with no evidence of lean or rich conditions on any of the plugs.
Current Bikes:

1966 CL77 - Honda 305cc - Dual purpose - "Gentleman's Scrambler" was a period moniker.
1967 CL175K0 - Low production number with #802 engine serial- winter 2019/2020 full restoration.
1972 CB350F - Baby Four with low mileage - Cosmetic refresh to the next level 2021/2022.
1978 CB550K - Very original bike with only 7499 Km. from new - light cleanup and refresh done.
1983 CB1100F - Canadian model - DOHC Supersport in pristine low kilometre condition from new.
1984 GL1200 - Standard model in showroom condition - two owner bike from new.
1984 CX650E - Restored summer 2017 - a rare Eurosport model - excellent one owner bike.
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robin1731
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Re: Carburetors flat off idle response

#9

Post by robin1731 »

flyin900 wrote:Thanks for the input fellows. I won't be trying any adjustments until this spring when the temp is more normal and above 60F. The off idle response is not really that bad it just isn't where I would like it to be, yet it maybe normal for the GL1000 motors. I do need to give the motor some extra gas on most takeoffs above what I would consider normal compared to my other bikes. (These are more an 80's mix of Honda bikes with a somewhat newer and a different style of the CV carbs.)

The air mixture screws are currently set at factory specs, so I will start there and try to increase the turns out by one turn and see what that does to the issue. I do actually have a ColorTune plug that I will also place in each cylinder to get a reading on the idle colour of the mixture. As someone mentioned earlier the best way to adjust the mixture screws is using the idle drop method.

The bike runs very well otherwise and pulls hard right to red line, plus the spark plug colour is within the proper shade with no evidence of lean or rich conditions on any of the plugs. Are you checking the plugs at various rpm using a plug chop to di it?
1976 Goldwing Super Sport
1985 Honda Elite
1976 KZ900 Dragbike
1992 ZX7 Dragbike (KZ900 style motor w/NOS)
and a rotation of various purchases
Randakk approved Carb Rebuilder
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flyin900
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Posts: 1489
Joined: Sun Jan 10, 2010 3:50 pm
Location: Canada

Re: Carburetors flat off idle response

#10

Post by flyin900 »

Robin thank you, I will try the idle drop procedure when I do the other checks in the spring and I haven't tried the plug chop. Since the issue is only at take off and it's not a heavy bog, just a little more throttle needs to be applied to the launch taking the RPM between 1500 and 1800 to pull away smoothly.
I assumed this is the off idle issue that is talked about, since all my other bikes at 1200 -1500 rpm pull away nice and smooth. The GL1000 also will sometimes do this but more often than not you need to get the RPM a little higher to attain a smooth launch from a stop.
Once underway the bike pulls hard with no flat spots or other issues right to the red line. So either this is just the way these GL1000's are, or there is some slight tweaking that still needs to be done to the idle/air mixture circuit.
Current Bikes:

1966 CL77 - Honda 305cc - Dual purpose - "Gentleman's Scrambler" was a period moniker.
1967 CL175K0 - Low production number with #802 engine serial- winter 2019/2020 full restoration.
1972 CB350F - Baby Four with low mileage - Cosmetic refresh to the next level 2021/2022.
1978 CB550K - Very original bike with only 7499 Km. from new - light cleanup and refresh done.
1983 CB1100F - Canadian model - DOHC Supersport in pristine low kilometre condition from new.
1984 GL1200 - Standard model in showroom condition - two owner bike from new.
1984 CX650E - Restored summer 2017 - a rare Eurosport model - excellent one owner bike.
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