Revs not falling immediately when rolling of teh throttle

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SteveR
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Revs not falling immediately when rolling of teh throttle

Post by SteveR » Sun Apr 23, 2017 4:45 pm

Took the Honda NX400 (XR400 motor) out for a back lane bimble with a couple of green lanes for good measure this afternoon. Not had it out much over Winter, as I had knee issue and when fit, I was using the lightweight AJP...

I noticed last week, that when rolling off the throttle from cruising speeds, say 5K, the engine just holds on to the last few revs for a shade longer than I like before dropping to tickover speed. This messes with what is usually good engine braking. This was quite obvious again today, and so good on a green lane descent either!! :unsure:

Carb?? Or valves???

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The Sarge
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Re: Revs not falling immediately when rolling of teh throttle

Post by The Sarge » Sun Apr 23, 2017 4:53 pm

Steve, your not riding a CCM450 are you ?? :whistle: :whistle:

daytona-supersport
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Re: Revs not falling immediately when rolling of teh throttle

Post by daytona-supersport » Sun Apr 23, 2017 4:53 pm

Check throttle returning fully. Slide not sticking near to the closed position.
Check for air leak from carb to cyl head.
Check float valve is clean and clear. Too high a fuel can cause problems.

Doubt if it's an ignition or valve issue. But why not check the valve clearances when the tank is off.

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Re: Revs not falling immediately when rolling of teh throttle

Post by SteveR » Sun Apr 23, 2017 4:55 pm

The Sarge wrote:Steve, your not riding a CCM450 are you ?? :whistle: :whistle:
My test ride(s) were enough to persuade me that on the whole, an old a/c carbed Honda suited my laid back slow riding style better. Sarge B)

SteveR
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Re: Revs not falling immediately when rolling of teh throttle

Post by SteveR » Sun Apr 23, 2017 4:58 pm

daytona-supersport wrote:Check throttle returning fully. Slide not sticking near to the closed position.
Check for air leak from carb to cyl head.
Check float valve is clean and clear. Too high a fuel can cause problems.

Doubt if it's an ignition or valve issue. But why not check the valve clearances when the tank is off.
Cheers for that, in theory, the Valves should be OK... done about 200 miles ago before an abandoned trip to the HISS last year.

I'll go through your suggestions, sticky throttle somewhere is my guess, possibly from gunky overwintered fuel...? I had treated the tankful left after a siphoning out, but some had been there a few weeks/months when I come to think of it... :unsure:

Might be worth some fuel system cleaner being run through "just in case"?

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Re: Revs not falling immediately when rolling of teh throttle

Post by DavidS » Sun Apr 23, 2017 5:03 pm

Cruddy fuel gunging everything up I reckon as a favourite.
2019 Triumph T120 Black and 2015 Husky FE450

SteveR
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Re: Revs not falling immediately when rolling of teh throttle

Post by SteveR » Sun Apr 23, 2017 5:15 pm

DavidS wrote:Cruddy fuel gunging everything up I reckon as a favourite.
I have some Redex system cleaner that can go in the tank!! (thumbs)

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Re: Revs not falling immediately when rolling of teh throttle

Post by Stewie » Sun Apr 23, 2017 5:42 pm

If it's just on the roll off, is the throttle cable a double with a return, worth cleaning and greasing the throttle cables so the twist should snap back, also never hurts to give the carb a good clean if it's been stood a while, even if its just fuel cleaner (thumbs)

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Re: Revs not falling immediately when rolling of teh throttle

Post by SteveR » Sun Apr 23, 2017 8:42 pm

Stewie wrote:If it's just on the roll off, is the throttle cable a double with a return, worth cleaning and greasing the throttle cables so the twist should snap back, also never hurts to give the carb a good clean if it's been stood a while, even if its just fuel cleaner (thumbs)
Cheers for the thoughts Stewie. Old fashioned single wire throttle and I try to lube the throttle body and tube itself regularly, bit reluctant to lube the cable in case it sucks in dust off-road... Might be worth a squirt of GT85 through the cable oiler I agree. The bike is 2003 and although it has only been used since 2014, it's still old!!

Redex is poised :-)

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Re: Revs not falling immediately when rolling of teh throttle

Post by Durham » Mon Apr 24, 2017 5:50 am

Happened to me yesterday on my CCM450 Sarge. Is this a known issue?

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