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General Category >> Rubber Side Down! >> Off-throttle to idle issue
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Message started by toddlamp8 on 10/31/07 at 12:01:12

Title: Off-throttle to idle issue
Post by toddlamp8 on 10/31/07 at 12:01:12

When i'm coming off of throttle to idle (say driving down the road coming to a stop sign) the RPMs drop down to about 800 before coming back up to normal idle. This only happen when i'm running at about 3000RPMs+ and pull the clutch in. The RPMs drop all the way down and then it returns to the set idle speed. I just recently rebuilt the carb and everything is clean. What's the deal? The slide is as clean as it's ever going to get but I figured if that was sticking I wouldn't get the drop,. Instead I would remain at higher RPMs.

What's the deal??

Title: Re: Off-throttle to idle issue
Post by toddlamp8 on 10/31/07 at 14:06:27

Anyone?

Title: Re: Off-throttle to idle issue
Post by verslagen1 on 10/31/07 at 14:47:23

I think that's normal.

Suddenly closing the throttle starves the engine of air to slow it down and the fuel/air ratio is optimized for idle, not for running full bore. So what does get in there is a little rich. And maybe wets the plug a little. So by the time it reaches idle itaint running so good. And the idle is going to be slow untill the excess can be burnt off. Returning it back to the set idle speed.

ok? ;D

Title: Re: Off-throttle to idle issue
Post by toddlamp8 on 10/31/07 at 14:50:53

Hmmm, I don't think it's normal since it never did it before. Plus it only happens when I come off the throttle AND pull the clutch lever. It does not do it when I just come off the throttle and slow down.

So some suggestions on what to change? Sometimes it gets to the point of stalling but thankfully that's rare. Regardless it very unnerving.

Title: Re: Off-throttle to idle issue
Post by Oldfeller2 on 10/31/07 at 14:55:05

I think the float bowl is a little low from the hard running and the idle suction on the petc0ck needle valve isn't enough flow for a fast refill on the float level -- temporary slow idle comes primarily from a slightly lower bowl level. Get same sort of action each time you try to run out of gas, don't you?

Plus engine is max hot from the exertion and all the running fits are a bit tighter right after you slow down (air flow goes down too).

Take your pick, or say it may be a combo of all the above. In any case it's normal enough on my bike.

Oldfeller

Title: Re: Off-throttle to idle issue
Post by Paladin on 10/31/07 at 14:59:32

Down to 800 and back up to idle? I'm idling at about 600!!

A sudden throttle closure will cause an engine to stall out. (some?) Automotive carbs have (had?) a thing called a dashpot that would delay full closure so as to not stall the engine. On the Savage I'll blip the throttle lightly to stop from stalling out. But as noted, I'm idling obscenely low. If you have recently rebuilt the carb it is probably closing smoother and faster.

Title: Re: Off-throttle to idle issue
Post by toddlamp8 on 10/31/07 at 15:02:24

I run my petc0ck on prime all the time to avoid any issues from the On/Res petc0ck so that can't be it.

I guess I could re-adjust the floats a hair higher to give the bowl a bit more fuel.

Title: Re: Off-throttle to idle issue
Post by Oldfeller2 on 10/31/07 at 15:03:05

Idle is supposed to be at least 1000 rpm to keep from oil starving the cam bearings. (or so they say ....)

Mine gets "even" sounding at 1150 - 1200 rpm, any less than that is irregular and lumpy sounding.

600 would be very low sounding to me -- literally.

Oldfeller

Title: Re: Off-throttle to idle issue
Post by toddlamp8 on 10/31/07 at 15:04:07

Paladin wrote:

Wow, that is low. Idle should be ~1,100RPMs (at least that's what it says on my front manufaturers plate).

Title: Re: Off-throttle to idle issue
Post by T-Mack1 on 10/31/07 at 18:00:42

I noticed mine does this when it's just barely warmed up. It even stalls if I let off the throttle and hit the clutch. Idles at around 900. Once I ride another 10-15 minutes it goes away and idle is 1100.

Paladin,
I have an oil pressure gauge on mine (off the test port). With 10W40 MC oil, at idle and outside air at 80 F, bike warmed after 20 minutes of riding, the oil pressure at 1000 rpm was only 2 -4 psig. Yes,....2 psig..... scary!!! I don't think I want to know what 600 RPM would give. Sure hope you're running 20W50....

Title: Re: Off-throttle to idle issue
Post by toddlamp8 on 10/31/07 at 18:56:41

This happens even after highway riding so I know it's been warmed up. I've been setting my idle to ~1,250-1,300RPMs so that when it drops I don't stall. All the diaphrams seem free from holes, air filter is new, and I just cleaned the carb, so i'm at a loss.

Title: Re: Off-throttle to idle issue
Post by toddlamp8 on 10/31/07 at 20:09:19

Fun fun fun, coming back from work tonight I was taking an exit in 4th gear (86') from 5000RPM, pulled the clutch and she stalled. Started up no problem, but still, that SHOULDN'T happen.

Title: Re: Off-throttle to idle issue
Post by klx650sm2002 on 11/01/07 at 02:02:01

With tickover revs dropping then coming up suggests a rich mix.

Clive W :D

Title: Re: Off-throttle to idle issue
Post by Dynobob on 11/01/07 at 04:46:24

It's normal from what I've seen. After I rejetted, I noticed mine did that (the rpms dropped when returning to idle). I turned up the idle speed a bit and it's been fine.

Title: Re: Off-throttle to idle issue
Post by Trippah on 11/01/07 at 05:28:36

HI- foggy brain this am..too much Halloween I guess. Your idle drops way low, bike actually stalls when coming into a stop, but Only with the clutch pulled in. This is a little backwards=No? Usually a bike rpms fall when you come into a stop, then you engage the clutch taking the engine off load, allowing it to turn more freely(quicker) and the idle stays up and you don't stall.. Hmm
Forgive the dumb question..you are downshifting as you come into the stop situation? And you ride with the pet on pri to eliminate vacuum issues.. No kink in the fuel line..
Great question (not a great situation) Have you tried it with pet in on positon..maybe partiallly clogged pet unit..curious how it does on vacumn.
Good luck and keep us posted.

Title: Re: Off-throttle to idle issue
Post by Dr_Jim on 11/01/07 at 10:07:21

Title: Re: Off-throttle to idle issue
Post by toddlamp8 on 11/01/07 at 11:39:20

Thanks for the replys. I'm running a stock 86 carb with the 155 jet. There is only one way to install the clip so I know I didn't screw that up. I also recently installed a HD Dyna muffler and made no modification to the white spacer. The fuel lineis new. I will check the vacuum line tonight to see if it is damaged.

Title: Re: Off-throttle to idle issue
Post by Dynobob on 11/01/07 at 12:43:20

toddlamp8 wrote:

I also recently installed a HD Dyna muffler and made no modification to the white spacer.

I don't think an 86 has the white spacer. I could be wrong ;D With multiple grooves on the needle, it's not needed. I think the white spacer was added later to lean out the carb for those EPA folks. It also prevents the user from richening their carb.

Title: Re: Off-throttle to idle issue
Post by toddlamp8 on 11/01/07 at 12:51:45

When I look at the microfiche on RonAyers.com for the 86 carb the spacer is there.

Title: Re: Off-throttle to idle issue
Post by Trippah on 11/01/07 at 15:05:37

What a wonderful day at work ;) I think everyone is focused on the carb- which is reasonable. As a question, if the clutch load/no load IS the determining factor, would engine compression be an issue? If not under load, the engine should increase in revs..but if the compression wasn't right, wouldn't it fail to suck gas throught the carb? As a 61 year old newbie to mechanics, it is so daarrn confusing. >:(

Title: Re: Off-throttle to idle issue
Post by toddlamp8 on 11/01/07 at 15:11:53

On the way to work today I tried different RPMs and even at ~2500RPMs when the clutch was pulled in the RPMs dropped to ~750. It seems like the higher the RPMs i'm at when I pull the clutch lever the lower they drop before returning to a proper idle.

Title: Re: Off-throttle to idle issue
Post by barry68v10 on 11/01/07 at 15:15:01

My experience suggests that you're dealing with a rich mixture, but I don't see how that's possilble unless you simply have a worn out carb in dire need of replacement...

Title: Re: Off-throttle to idle issue
Post by toddlamp8 on 11/01/07 at 15:59:15

Would that have something to do with the pilot screw? I noticed that when I would adjust it the idle speed barely changed no matter how far in or out (unless it was all the way in, then it died). The oring is fine, just replaced actually.

Title: Re: Off-throttle to idle issue
Post by toddlamp8 on 11/01/07 at 16:34:50

Ok, well I took the advice of the forum, and went outsideto adjust the pilot screw in a little to lean out the idle and guess what, IT WORK! Preliminary tests show that my idle returns to where it should (pretty close at least). I'll see how it does on the highway ride home from work.

Thanks for the help!

Title: Re: Off-throttle to idle issue
Post by barry68v10 on 11/01/07 at 19:17:53

toddlamp8 wrote:

Oh, good. I guess I somehow missed the fact that you had adjusted the pilot screw...glad things seem to be fixed! Enjoy! ;D

Title: Re: Off-throttle to idle issue
Post by toddlamp8 on 11/02/07 at 11:22:15

Well it's kinda-sorta fixed. I may have adjusted it too much because I was shooting flames out everytime I came off the throttle!

Title: Re: Off-throttle to idle issue
Post by vtail on 11/02/07 at 11:29:15

Paladin wrote:

Down to 800 and back up to idle? I'm idling at about 600!!

From what I get Idle should be about 1200 as to get anough oil pressure to get oil to the cam. Most other stuff runs on roller or needlebearings and can servive on splash-oil ;)