03' RC51 Erratic Idle

[weasel]

03' RC51 Erratic Idle *Solved*

*Fixed*

Howdy folks. It's been a while but I need help from my old friends

I went for a short ride the other day. 35-65mph for 10 miles and everything was fine. I stopped for about 15 minutes and when I started it back up the RPMS's went to 5k then started bouncing between 3000 & 3500 RPMs constantly.

I limped home but can't figure out what's wrong.

I've had it for about 1000 miles and this is the first issue (17k total miles). It has a PCIII & I tried zeroing it out and adjusting the throttle position.

All the vacuum & fuel hoses look brand new. The previous owner switched out the throttle bodies a few years ago.

The fuel pressure regulator's not leaking.

The battery's at 14.34v at idle. I haven't tested the RR yet.

Throttle cable needs to be lubed, but it's not sticking.

Here's some vids.

Warmed up and going from 3000 to 3500 RPMs
Short: https://youtu.be/H4zHXCgPysc

Cold start. Okay until I touch the throttle and it revs to 5k
Long: https://youtu.be/eV__F387hVc

kthanksbye

 

[NSR500]

Similar symptoms to what I experienced with one of my bikes. Turned out to be a bad battery in my case.
As explained to me:
Your 14.3v at idle is what the reg/rec is feeding the battery. At load your motor wants to pull more voltage and the battery can’t charge and deliver the voltage required in a stable manner.

 

[weasel]

Interesting. Battery with the bike off is at 12.64v

Thx NSR

Similar symptoms to what I experienced with one of my bikes. Turned out to be a bad battery in my case.
As explained to me:
Your 14.3v at idle is what the reg/rec is feeding the battery. At load your motor wants to pull more voltage and the battery can’t charge and deliver the voltage required in a stable manner.

 

[Tom G]

Similar symptoms to what I experienced with one of my bikes. Turned out to be a bad battery in my case.
As explained to me:
Your 14.3v at idle is what the reg/rec is feeding the battery. At load your motor wants to pull more voltage and the battery can’t charge and deliver the voltage required in a stable manner.

At higher RPM the alternator delivers more power, but the regulator should keep it constant. 14.34V looks good.

 

[weasel]

At higher RPM the alternator delivers more power, but the regulator should keep it constant. 14.34V looks good.

So maybe the RR is revving the bike? I've had a lot of them fail. Usually they just kill the battery or catch on fire.

Thx Tom

 

[DannoXYZ]

vacuum leak, no way to "tune" around physical issue.

Also remove PC, best to program maps in ECU directly.

 

[weasel]

LMAO, I removed the side fairings and can't see where the PC's plugged in. I really really don't want to have to remove the air box. It's a total PITA on my bike.

I'm not even sure how to find a vacuum leak

Thx, Danno

vacuum leak, no way to "tune" around physical issue.

Also remove PC, best to program maps in ECU directly.

 

[motomania2007]

Easiest way to find a vaccum leak is to start the bike and then use something like carb cleaner, wd-40 or something similar with a straw. Selectively squirt the carb cleaner at suspected/possible leaks. If the engine tempo changes when you squirt, you found a vacuum leak.

 

[scootergmc]

OK harkening back to my RC51 days- but is the PC grounded directly to the battery?

 

[DannoXYZ]

If you've got large or multiple leaks, spray may not detect them all, unless you got 5 cans and 5 hands.

First confirm presence of leak first. Connect vacuum-gauge to intake manifold and measure vacuum between throttle-butterfly and intake-valves. Refer to manual for proper vacuum amount with warmed up engine.

Then locate leak next. I find spraying is too difficult, especially for beginners who can't detect changes in engine-note easily. Even more difficult with erratic idle, how do you know if change was from spray or randomness in idle?

A more reliable and definite way is to plug exhaust and pressurize intake slightly 2-5psi. Then spray soapy water around all seams and clamps. Leaks will show up as bubbles on outside. Often at multiple locations. And you can take your time, bubbles aren't going to disappear.

 

[weasel]

OK harkening back to my RC51 days- but is the PC grounded directly to the battery?

Well there's a black wire connected to the negative terminal but I'm not sure what it is.

Looks like I'll be vacuum leak hunting this weekend

Thanks

 

[DannoXYZ]

also measure TPS output at idle.

If there's idle-switch in TPS, make sure it's activate when throttle is closed.

Fast-idle adjustment on left

Flapper-valve adjustment on right

Lots of vacuum-hoses that may be leaking, unplugged or cracked.

test disconnecting plug from idle-valve. Remove and clean idle-valve.

I know it looks like big job, many, many issues like yours has been solved by removing PC... maybe as last resort.

 

[CDONA]

Easiest way to find a vaccum leak is to start the bike and then use something like carb cleaner, wd-40 or something similar with a straw. Selectively squirt the carb cleaner at suspected/possible leaks. If the engine tempo changes when you squirt, you found a vacuum leak.

I was taught to use water, non flammable, it will do the same as the stuff listed above without the mess

 

[weasel]

Weird, I disconnected the battery yesterday and today it's barely cranking. I did remove the black wire from the neg terminal that I 'think' is to the PC :shrug

Thanks for all the info.

 

[buellistic]

I was taught to use water, non flammable, it will do the same as the stuff listed above without the mess

I found a old propane torch with a vacuum line attached works best.
You can wiggle the hose anywhere.
Spraying carb cleaner can go Bad Fast.

 

[weasel]

It probably is a vacuum leak but I find it strange that after 1000 miles, that I go for a 10 mile ride with no problems, sit for a little bit & then start it up with a vacuum leak all of a sudden.

Like I said, all the hoses that I can see under the tank are pristine.

 

[DannoXYZ]

Rubber hoses and manifolds may seal when cold. But softens up after warm-up and may leak then.

 

[kuksul08]

MAP sensor is a common one.

Did you try the onboard diagnostics?

 

[weasel]

MAP sensor is a common one.

Did you try the onboard diagnostics?

I reset the throttle position and MAP. I think.
It was my first time trying the PCIII software.

I'm checking for a vacuum leaks today, and testing the RR and TPS.

Thx,

 

[Tom G]

Weird, I disconnected the battery yesterday and today it's barely cranking. I did remove the black wire from the neg terminal that I 'think' is to the PC :shrug

Thanks for all the info.

When you say barely cranking, is the battery still good? Fully charged? I replaced my battery recently at the age of 3 years, cranking was weak when the bike was sitting for 2-3 weeks and normal when it was ridden/charged recently. My GS has a car style alternator, they usually last forever, so slightly different then yours.