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dan7uk
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« on: June 26, 2025, 05:30:14 AM » |
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While riding, when I release the throttle and pull in the clutch to shift, the bike keeps a fast rpm for a couple of seconds before dropping to normal. Does this when going thru the gears, up shifting or down shifting.
I adjusted the throttle free play and it had no effect. Any suggestions?
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« Last Edit: June 26, 2025, 05:33:39 AM by dan7uk »
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98valk
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« Reply #1 on: June 26, 2025, 05:45:45 AM » |
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idle mixture screws or and mostly there is a vacuum link. PAIRS valve vacuum hoses or the normally intake manifold unused vacuum port caps are leaking. http://www.factorypro.com/tech/tech_tuning_procedures/tuning_carbtune,CV,lower_rpm_engines.html |
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1998 Std/Tourer, 2007 DR200SE, 1981 CB900C 10speed
1973 Duster 340 4-speed rare A/C, 2001 F250 4x4 7.3L, 6sp
"Our Constitution was made only for a Moral and Religious people. It is wholly inadequate to the goverment of any other."
John Adams 10/11/1798
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h13man
Member
Posts: 1771
To everything there is an exception.
Indiana NW Central Flatlands
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« Reply #2 on: June 26, 2025, 08:27:39 AM » |
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I'd say a vacuum leak. I'd replace all lines as they are 30'ish years old and depending on care/storage in its previous life.
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Mooskee
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« Reply #3 on: June 26, 2025, 10:47:08 AM » |
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+1 on most likely a vacuum leak.
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WintrSol
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« Reply #4 on: June 26, 2025, 02:04:30 PM » |
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Also +1 on vacuum leak. Lean engines tend to 'throttle hang', and when the vacuum spikes, even a tiny leak will contribute to this. You can test this without moving; raise rpm to about 3k and quickly close the throttle. It should quickly return to idle, if not, it is too lean. If it drops lower than comes back, too rich, but it doesn't sound like the problem here.
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98 Honda Valkyrie GL1500CT Tourer
Photo of my FIL Jack, in honor of his WWII service
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dan7uk
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« Reply #5 on: June 26, 2025, 04:32:02 PM » |
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This bike is a 99 interstate and I picked it up about two months ago. I'm sure the bike hasn't been desmog in its 26 years. Seems everyone who posted is in agreement on a vacuum leak. I owned a 99 standard Valkyrie about 15 years ago and I put a desmog kit in it just for precaution. I guess I will be putting one in my current one.
Thanks for all who posted, I never thought of a vacuum leak could be causing my problem, are the red eye desmog kits still available? Have a link?
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98valk
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« Reply #6 on: June 26, 2025, 06:02:02 PM » |
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This bike is a 99 interstate and I picked it up about two months ago. I'm sure the bike hasn't been desmog in its 26 years. Seems everyone who posted is in agreement on a vacuum leak. I owned a 99 standard Valkyrie about 15 years ago and I put a desmog kit in it just for precaution. I guess I will be putting one in my current one.
Thanks for all who posted, I never thought of a vacuum leak could be causing my problem, are the red eye desmog kits still available? Have a link?
see my post how I did the desmog. first time I did the heads were on the engine. this was a set of ported heads so I did them before I installed the heads. https://www.valkyrieforum.com/bbs/index.php/topic,105991.0.html |
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1998 Std/Tourer, 2007 DR200SE, 1981 CB900C 10speed
1973 Duster 340 4-speed rare A/C, 2001 F250 4x4 7.3L, 6sp
"Our Constitution was made only for a Moral and Religious people. It is wholly inadequate to the goverment of any other."
John Adams 10/11/1798
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dan7uk
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« Reply #7 on: June 27, 2025, 04:06:22 AM » |
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98 Valk, I looked at your attachment didn't see anything about desog just work on your heads.
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SCain
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« Reply #8 on: June 27, 2025, 04:59:34 AM » |
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This bike is a 99 interstate and I picked it up about two months ago. I'm sure the bike hasn't been desmog in its 26 years. Seems everyone who posted is in agreement on a vacuum leak. I owned a 99 standard Valkyrie about 15 years ago and I put a desmog kit in it just for precaution. I guess I will be putting one in my current one.
Thanks for all who posted, I never thought of a vacuum leak could be causing my problem, are the red eye desmog kits still available? Have a link?
Look at the signature line for Mooskee, he is a VRCC vendor, sells a De-Smog kit on his web site. |
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Steve  |
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98valk
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« Reply #9 on: June 27, 2025, 02:17:40 PM » |
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98 Valk, I looked at your attachment didn't see anything about desog just work on your heads.
scroll down to Reply #15 and #16 here is my top desmog plugs. Used shortened 9/16" bolts. Fill the holes with quicksteel. Then some hi-temp silicone and install the bolts. |
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1998 Std/Tourer, 2007 DR200SE, 1981 CB900C 10speed
1973 Duster 340 4-speed rare A/C, 2001 F250 4x4 7.3L, 6sp
"Our Constitution was made only for a Moral and Religious people. It is wholly inadequate to the goverment of any other."
John Adams 10/11/1798
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indybobm
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« Reply #10 on: July 03, 2025, 05:27:18 AM » |
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Make sure that the carb butterlys are actually closing quickly and not hanging up a little when the throttle is closes.
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So many roads, so little time
VRCC # 5258
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Pluggy
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« Reply #11 on: July 03, 2025, 05:50:07 AM » |
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Make sure that the carb butterlys are actually closing quickly and not hanging up a little when the throttle is closes.
Yes. Stuck "Butterflies" was a problem on my 4 cylinder Honda. That bike has no vacuum system to fail. |
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Mooskee
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« Reply #12 on: July 03, 2025, 09:46:08 AM » |
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Make sure that the carb butterlys are actually closing quickly and not hanging up a little when the throttle is closes.
Yes. Stuck "Butterflies" was a problem on my 4 cylinder Honda. That bike has no vacuum system to fail. Routing of the throttle cables can cause it to close slowly upon letting off. Does it still do it if you twist the throttle closed? |
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WintrSol
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« Reply #13 on: July 03, 2025, 10:37:31 AM » |
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Routing of the throttle cables can cause it to close slowly upon letting off.
Does it still do it if you twist the throttle closed?
As can what you choose to lubricate them. |
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98 Honda Valkyrie GL1500CT Tourer
Photo of my FIL Jack, in honor of his WWII service
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dan7uk
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« Reply #14 on: July 05, 2025, 03:55:26 AM » |
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Make sure that the carb butterlys are actually closing quickly and not hanging up a little when the throttle is closes.
Yes. Stuck "Butterflies" was a problem on my 4 cylinder Honda. That bike has no vacuum system to fail. Routing of the throttle cables can cause it to close slowly upon letting off. Does it still do it if you twist the throttle closed? I will check them when I am installing a desmog kit next week. |
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