'85 Honda Nighthawk throttle problem. - Motorcycle-Journal Forums

wapam · 06-08-2007, 11:32 PM

With the engine running and in neutral, if I rev the throttle and then release it, the throttle grip and carb linkage all snaps back but the engine speed takes a few seconds to decrease back down to idle.

Likewise when I am riding and I squeeze in the clutch and release the throttle the engine revs way up and takes a few seconds to decrease. Hard to make a nice smooth shift.

Carbs have been cleaned and bike runs well otherwise.

Thank you for any opinions.

**Clint** · 06-08-2007, 11:52 PM

Welcome. I'd look for a vacuum leak. Check the hoses for cracks. Could also be a timing issue, but I'm not experienced with that.

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robertc729 · 06-09-2007, 12:07 AM

DrBob · 06-09-2007, 12:33 AM

Either a vacuum leak or an intake leak (either between a carb and a manifold or a manifold and a head). Check for visible leaks, and with the bike running spray a little WD-40 around the intake manifolds. If the idle changed, you found your leak.

Easy Rider · 06-09-2007, 11:27 AM

Quote:

Originally Posted by wapam

With the engine running and in neutral, if I rev the throttle and then release it, the throttle grip and carb linkage all snaps back but the engine speed takes a few seconds to decrease back down to idle.

Likewise when I am riding and I squeeze in the clutch and release the throttle the engine revs way up and takes a few seconds to decrease. Hard to make a nice smooth shift.

Had one. Mine did that a LITTLE too. More on the order of 1/2 to 1 sec.
I think many high compression engines are done that way on purpose so that you don't abruptly close the throttle and lock the back wheel. That delay was much less on my Kawi 600-4 because it has a "slip clutch".

Hard to tell without being there if your situation is "normal" or not. If it is not working right, my guess is that the fix would probably be fairly easy, quick and inexpensive. Alas, I don't know what controls the throttle down timing. A visit to a dealer might be in order.

Sounds like you need to work on your timing a bit. Close the throttle BEFORE you pull in the clutch.

wapam · 06-09-2007, 12:12 PM

Thanks for all the advice. Just curious, is this problem called a "hanging throttle"?

Thanks again.

wapam · 06-09-2007, 12:17 PM

Oops, I meant "hanging idle".

Thank you.

**Clint** · 06-09-2007, 01:11 PM

Sure.

wapam · 06-10-2007, 01:20 PM

So to clarify, I'm looking for a leak on the engine side of the carb NOT the air box side??

Thanks.

2005GZ250 · 06-10-2007, 08:04 PM

Yes check from the carbs to the cylinder head. On my '73 Suzuki GT750 if the idle mixture screws are not set right it will do the same thing as your nighthawk and will also surge on deceleration.

wapam · 06-10-2007, 11:15 PM

Thanks for all the help, I'll keep you posted.

wapam · 06-13-2007, 11:24 PM

Well, I got it fixed! Just had to tighten the clamps on the boots from the carb's to the engine. Easy fix if you know where to look and thanks to the great people on this site...I did!!

Thanks again.

2005GZ250 · 06-14-2007, 08:13 PM

Glad that you found the problem!

06-08-2007, 11:32 PM	#1 (permalink)
wapam Where Am I ? Joined: Jun 2007 Bike: '85 Nighthawk, '80 Yamaha 1100 Special Location: MN Posts: 38	'85 Honda Nighthawk throttle problem. With the engine running and in neutral, if I rev the throttle and then release it, the throttle grip and carb linkage all snaps back but the engine speed takes a few seconds to decrease back down to idle. Likewise when I am riding and I squeeze in the clutch and release the throttle the engine revs way up and takes a few seconds to decrease. Hard to make a nice smooth shift. Carbs have been cleaned and bike runs well otherwise. Thank you for any opinions.

06-09-2007, 12:33 AM	#4 (permalink)
DrBob In The Zone Joined: May 2004 Bike: several Location: Decatur, GA Posts: 2,763	Either a vacuum leak or an intake leak (either between a carb and a manifold or a manifold and a head). Check for visible leaks, and with the bike running spray a little WD-40 around the intake manifolds. If the idle changed, you found your leak. __________________ Dream like you'll live forever, live like you'll die tomorrow. You MUST obey the pug dog!

06-10-2007, 08:04 PM	#10 (permalink)
2005GZ250 Fender Buffer Joined: Sep 2005 Bike: 2005 GZ250 1973 "heavyoldandslow" GT750 Location: Roland, AR Posts: 439	Yes check from the carbs to the cylinder head. On my '73 Suzuki GT750 if the idle mixture screws are not set right it will do the same thing as your nighthawk and will also surge on deceleration. __________________ I only ride 'em. I don't know what makes 'em work. Oddball: Donald Sutherland, Kelly's Heroes 1970

06-14-2007, 08:13 PM	#13 (permalink)
2005GZ250 Fender Buffer Joined: Sep 2005 Bike: 2005 GZ250 1973 "heavyoldandslow" GT750 Location: Roland, AR Posts: 439	Glad that you found the problem! __________________ I only ride 'em. I don't know what makes 'em work. Oddball: Donald Sutherland, Kelly's Heroes 1970

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06-09-2007, 12:07 AM	#3 (permalink)
robertc729 Forensic Bug Splatter Analyst Joined: Mar 2006 Bike: 05 Boulevard C50 LE, 06 S40 (wife's bike) Location: Lexington, KY Posts: 4,086

06-09-2007, 12:12 PM	#6 (permalink)
wapam Where Am I ? Joined: Jun 2007 Bike: '85 Nighthawk, '80 Yamaha 1100 Special Location: MN Posts: 38	Thanks for all the advice. Just curious, is this problem called a "hanging throttle"? Thanks again.

06-09-2007, 12:17 PM	#7 (permalink)
wapam Where Am I ? Joined: Jun 2007 Bike: '85 Nighthawk, '80 Yamaha 1100 Special Location: MN Posts: 38	Oops, I meant "hanging idle". Thank you.

06-10-2007, 01:20 PM	#9 (permalink)
wapam Where Am I ? Joined: Jun 2007 Bike: '85 Nighthawk, '80 Yamaha 1100 Special Location: MN Posts: 38	So to clarify, I'm looking for a leak on the engine side of the carb NOT the air box side?? Thanks.

06-10-2007, 11:15 PM	#11 (permalink)
wapam Where Am I ? Joined: Jun 2007 Bike: '85 Nighthawk, '80 Yamaha 1100 Special Location: MN Posts: 38	Thanks for all the help, I'll keep you posted.

06-13-2007, 11:24 PM	#12 (permalink)
wapam Where Am I ? Joined: Jun 2007 Bike: '85 Nighthawk, '80 Yamaha 1100 Special Location: MN Posts: 38	Well, I got it fixed! Just had to tighten the clamps on the boots from the carb's to the engine. Easy fix if you know where to look and thanks to the great people on this site...I did!! Thanks again.

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