Why would my idle rise after riding for a half hour?

Jetting, Reeds, Air Filters, etc.

Why would my idle rise after riding for a half hour?

Postby doolin64 » Wed Jun 29, 2016 6:37 am

Cross posting a bit from Thumpertalk,

I had my first real ride on my bike the other day. I have a few carburetor related questions.

I noticed this problem before I rejetted, the bike seemed to drip fuel out of the overflow at times. Usually noticed when I leaned it on it's kickstand. I always shut the fuel off when I'm done so I never had any leaking in my shop that I noticed. But yesterday while out on my ride, I stopped to setup the camera for some video and while the bike was idling I noticed fuel dripping out of the overflow. I noticed it too on a failed attempt over a tractor tire. Is it carb overflow hose routing? Float? Or is this normal?

The other thing that happened was as I rode on throughout the day, my idle seemed to pick up. So I backed down the idle adjustment screw. I just don't understand why it wasn't an issue early on. I made sure my throttle wasn't sticking. All was good there.

Currently the carb has the stock pilot, an NECJ needle and a 162 main jet. The air screw is turned out about 2.5 to 2.75 turns. I'm right around sea level give our take a few 100 feet. Temps were around 80F and fairly dry.

Any help would be greatly appreciated!
doolin64
 
Posts: 96
Joined: Thu Feb 18, 2016 8:29 pm

Re: Why would my idle rise after riding for a half hour?

Postby Clearvu1 » Wed Jun 29, 2016 10:01 am

Is this a 300RR? Many, if not most of these bikes need the float level adjusted to stop the overflow issue. It's not a big deal, do a search and you'll find lots of results. Usually an increase in idle is due to a lean condition which could be caused by an air leak somewhere in the system. Check your fittings for a loose bolt and try spraying ether around the carb boots and manifold and listen for a change in idle speed to identify where the problem is. Worst case it could be a leaking crank seal, that usually is very noticeable causing very high idle speed.
Clearvu1
 
Posts: 210
Joined: Mon Oct 05, 2015 7:46 am

Re: Why would my idle rise after riding for a half hour?

Postby doolin64 » Wed Jun 29, 2016 10:56 am

Thank you. This is a 300RR. I'll try what you suggested.
doolin64
 
Posts: 96
Joined: Thu Feb 18, 2016 8:29 pm

Re: Why would my idle rise after riding for a half hour?

Postby GMP » Fri Jul 29, 2016 5:41 am

Float is probably high yes but thats not the cause of your hanging idle. Your a touch lean on the bottom, adjust the air screw and go to the 38 pilot if needed. The NECJ is great, I run it too, but some bikes @ sea level need the 38 over the 35.
Glenn
'13 Beta 300RR Racing
GMP
 
Posts: 2128
Joined: Wed Jul 31, 2013 5:25 am

Re: Why would my idle rise after riding for a half hour?

Postby chrisinflight » Fri Jul 29, 2016 2:40 pm

Set the float level and the higher idle can be sorted with turning the air-screw in by half turn at a time. I run necj #3, 162 & 35 at sea level to 500m. I need to swing between between 1.5 turns to 2.5 turns depending on temps. and humidity.
chrisinflight
 
Posts: 49
Joined: Sun May 22, 2016 6:38 am

Re: Why would my idle rise after riding for a half hour?

Postby ricoyam » Sat Jul 30, 2016 5:00 pm

All engines run more efficiently when fully warmed up. The rise in idle speed could simply be the engine reaching a more efficient temp. If you set the idle speed after starting after dechoking you will notice this.
Rick "Rico" Yamane
'15 430 RS
+20 or so others
S.F. Peninsula
Mechanic/Restorer Chris Carter Motorcycle Collection
ricoyam
 
Posts: 514
Joined: Mon Nov 18, 2013 12:45 am

Re: Why would my idle rise after riding for a half hour?

Postby markbxr400 » Fri Aug 24, 2018 9:18 am

Know it's an old thread, but just bought a new 18 XTrainer. Dealer told me to expect idle to be crap for the first tank of fuel, then to rise and be ok once I refuel. He said, in addition to the oil injection, they add oil to the first tank of fuel as well to help with the break-in. This causes the idle to drop off. Once that tank is gone, he told me to expect the idle to rise. Told me also to expect a higher level of spooge out of the exhaust right up front. Will see what happens.
2018 Beta XTrainer, 2017 Montesa Cota 300RR, 2017 Montesa Cota 4RT260, 2013 Yamaha Super Tenere, 2006 CRF230, 2007 Honda CRF70, 2018 OSET 12.5R for the GK's
markbxr400
 
Posts: 41
Joined: Sat Sep 23, 2017 7:38 pm

Re: Why would my idle rise after riding for a half hour?

Postby 74ossaguy » Mon Jan 21, 2019 8:12 am

its always possible there could be a little debris in, on, around the float valve needle. Worth a look at least.
74ossaguy
 
Posts: 18
Joined: Wed May 10, 2017 9:17 am


Return to Intake/Carburetion - 2 stroke

Who is online

Users browsing this forum: No registered users and 17 guests

cron