RC51 issues clutch/fueling issues - Honda RC51 Forum : RC51 Motorcycle Forums
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post #1 of 16 (permalink) Old 06-21-2017, 11:09 AM Thread Starter
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RC51 issues clutch/fueling issues

I finally joined the family and bought my buddies old RC51. He'd had it parked for almost 10 years before I rescued it.
The issues i'm having are related to the clutch and the fueling.

With the clutch once the engine temp hit about 200F would begin to slip and then eventually slip so bad that the clutch wouldn't even engage. ie. bike is in 1st, clutch is out. bike will not move. If I let the bike cool down it would eventually engage again. I replaced the all the plates and springs with new equipment. There is a noticeable improvement as it's not slipping now but on a test ride yesterday the clutch eventually went so far out of adjustment that it only engaged at the extreme end of the lever.
I've not encountered this before with another hydraulic clutch. As I've replaced the plates and springs i'm left thinking there's something wrong with either the master cylinder or the slave cylinder?

During this last ride it seemed to operate ok, but again once it's hot there's problems under deceleration, at around 3000rpm it feels the bike is shutting off like it's stalling. You can pick the bike up with the throttle but the the engagement point is very harsh, the bike basically snaps back on, this certainly makes getting back on the throttle mid corner after a downshift very challenging. It also started stalling when approaching stop lights. it was easy to start up again. As long as you're on the throttle it seems to operate normally.
the bike has a pc2 and running 15/41 gearing. My research suggests that the fuel pump regulator might not be working properly. So I will do the nipple leak test, that and disconnecting the pc2.

I'm not a total newb, i've been wrenching on my own bikes since I started over 20 years ago, racing for 10. I rebuilt my SV650 race bike this year without a single mechanical issue but so far the RC has me banging my head against a wall. I'm looking for ideas on anything else I should be looking at..



thanks
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post #2 of 16 (permalink) Old 06-21-2017, 02:23 PM
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I think the source of your problems is in the second sentence concerning "He'd had it parked for almost 10 years before I rescued it".

It's possible the clutch fluid has absorbed a lot of water moisture which has sludged up in the line and not allowing full clutch release, or possibly blocking the relief ports to relieve pressure.
When the engine heats up, the fluid expands and has nowhere to go and caused clutch slippage.
I would try checking and bleeding the clutch line to check for milky fluid coming out.

A similar thing happened to my Hayabusa years ago, when a mechanic failed to installed the correct diaphragm on the clutch master cylinder, allowing it to absorb a huge amount of moisture over a short period of time.

The first symptom was a way stiffer clutch followed by engagement issues.
It was when I tried to bleed the clutch was when I discovered the cause, which pissed me mightily.
Took a bottle and a half of brake fluid clear all the crud out of the slave cylinder. It was nasty.
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post #3 of 16 (permalink) Old 06-21-2017, 02:44 PM Thread Starter
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Something i'm considering is rebuilding the master as well. A blockage on the relief port could certainly sound like the culprit. I've not rebuilt one before, can you detail where the relief port is found? either 28 or 29?
As for the fluid, it was flushed immediately when I got it and since then while dealing with this i've probably flushed it another three times.
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post #4 of 16 (permalink) Old 06-21-2017, 03:41 PM
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I might think about replacing the fuel filter as well. If it sat for years there is no telling what any remaining fuel left init would turn into.
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post #5 of 16 (permalink) Old 06-21-2017, 03:44 PM Thread Starter
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All the fuel was drained out of it before it was ran it but i'm absolutely concerned about the condition of fuel pump and filter. I'm really hoping to not have to go there though
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post #6 of 16 (permalink) Old 06-21-2017, 03:48 PM
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My bike had been sitting for a few years before I rescued it. I know you said you flushed the clutch several times, but it's probably time to rebuild the clutch master and slave cylinders. I had flushed once, still had problems, so ordered the OEM rebuild kits (very inexpensive, minimal parts to replace) and did it. Problem solved. Check out the peanut butter I found in my slave cylinder picture.
a) Clutch Master: Part #3 and maybe 28, 29, for the master - and maybe 8 for the cup reservoir,
b) Clutch Slave: Part# 6, 9, 13, (and I replaced the spring #8),
c) any decent quality DOT4 brake fluid.
optional: Spiegler steel braided clutch line

btw, clutch slave cylinder parts are located in the *left crankcase cover* section of the OEM catalogs.

Don't forget new crushwashers, and I always bleed air at the master (via the banjo bolt) as well as the slave.

Very high chance your fpr diaphragm is toast. You could be having problems with it even if it passes the so-called leak test.

I'm betting you used proper wet clutch MC oil, but my bike HATES 20W-50. 10w-30 or 10w-40 full syn would be my recommendation.
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post #7 of 16 (permalink) Old 06-21-2017, 04:22 PM Thread Starter
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You've pretty much got me convinced, so it looks like it's going to be another week waiting for parts. ugh I've order the master cylinder and slave rebuild kits and a FPR. The bike is running motul 5100 10w40. I always use Jaso ma spec oil in my bikes, either 10w40 or 15w40, no other grades.
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post #8 of 16 (permalink) Old 06-22-2017, 04:49 PM Thread Starter
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As I'm waiting for parts.. I did what I could while the kids were playing in the sun after work yesterday. Fuel Pressure Regulator passed the leaky nipple test, fwiw. I also removed the PC2. With it gone the fueling has dramatically improved and the ride to work was more pleasant, fuel seemed present throughout the rpm range nor was there any stalling. hopefully the ride home is just as good.
The clutch of course is only good for a bit
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post #9 of 16 (permalink) Old 06-22-2017, 07:29 PM
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Quote:
Originally Posted by jaybo View Post
I also removed the PC2. With it gone the fueling has dramatically improved and the ride to work was more pleasant, fuel seemed present throughout the rpm range nor was there any stalling.
The map in your PC could easily be corrupted if anyone used the buttons, ever, as I recently discovered. See this post: https://www.rc51forums.com/forums/11-...over-time.html

I think you should change the FPR regardless, as it's only a matter of time, and despite your nipple test, it might be bad because fuel gets past the diaphragm when there's 50 psi on one side and vacuum on the other. I recently had symptoms exactly like yours (and nipple drip), and the FPR solved it.

Also, I think a full rebuild of your hydraulics (master and slave), and a careful check of the clutch release rod will solve your odd problem.
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post #10 of 16 (permalink) Old 06-22-2017, 08:49 PM Thread Starter
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Yup got all the parts on the way. Thanks
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