Author Topic: 2000 Concours only runs well on PRIME  (Read 544 times)

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Offline Richie

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2000 Concours only runs well on PRIME
« on: September 08, 2018, 10:02:46 pm »
Hello,
First time posting here!
I’ve been reading this forum for a couple months now, and it has helped immensely in restoring a salvage 2000 Concours I got for $300. It was crashed in 2007 and sat in a shed since then. Carbs were gummed up beyond belief, gas tank was essentially filled with brown Jell-O, and it leaked coolant like it was seemingly designed to do so.
I have been working on it constantly for a couple months, and I’ve finally got it running well. (Spark plugs are correct color, carbs are synced perfectly, valves adjusted, coolant system cleaned, all fluids changed, bodywork repaired and painted, etc.)
However, it only runs perfectly when the petcock is set to PRIME. When it is set to ON, there in a very noticeable hesistation when applying throttle. It bogs down for a half second or even shuts off with sudden revving. On PRIME however, a quick blip revs it straight to 5000 rpm in under half a second.

I am hoping you can help me figure out what’s causing the apparent fuel starvation. I replaced the petcock hoping that was the issue, but no dice. The vacuum line has good, strong suction, so I don’t think it is a vacuum issue.
I did install an in-line high flow fuel filter to ensure no stray debris could clog the carbs again, but the issue persists even with the filter removed.

I appreciate any help, thank you.

Offline Harry Martin

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Re: 2000 Concours only runs well on PRIME
« Reply #1 on: September 08, 2018, 10:19:54 pm »
So, you say PRIME only? RES and ON cause hesitation. Vacuum strong and replaced the petcock.

Is the vacuum strong at the petcock?

I'm not sure what to think of this. Either the replacment petcock is bad, or there is no vacuum for the petcock to function properly.
Even if I pinch off the fuel, there is usually enough fuel in the carbs to run a bit without fuel starvation.

I'm sure I'll be corrected on this by someone.
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Offline Richie

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Re: 2000 Concours only runs well on PRIME
« Reply #2 on: September 08, 2018, 10:53:03 pm »
The vacuum seems very strong at the petcock. I synced the carbs so I know the vacuum is the same at all 4 vacuum ports(about 20cmHg)
It will idle when set to ON, and will accelerate with very slow throttle application.With fast throttle application, it will bog/hesitate for a half second before revving, or it will simply die.

Oh, and I forgot to mention, if it is running in the ON position, and then I switch to PRIME, it takes about 30 seconds for it to take effect, and vice versa.
« Last Edit: September 08, 2018, 11:34:37 pm by Richie »

Offline Harry Martin

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Re: 2000 Concours only runs well on PRIME
« Reply #3 on: September 09, 2018, 12:20:21 am »
The vacuum seems very strong at the petcock. I synced the carbs so I know the vacuum is the same at all 4 vacuum ports(about 20cmHg)
It will idle when set to ON, and will accelerate with very slow throttle application.With fast throttle application, it will bog/hesitate for a half second before revving, or it will simply die.

Oh, and I forgot to mention, if it is running in the ON position, and then I switch to PRIME, it takes about 30 seconds for it to take effect, and vice versa.

Just to be sure, can you report the vacuum reading at the petcock using a gauge?
I could then compare to my C10.
« Last Edit: September 09, 2018, 12:23:52 am by Harry Martin »
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Offline Richie

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Re: 2000 Concours only runs well on PRIME
« Reply #4 on: September 09, 2018, 12:40:19 am »
Right now it’s showing about 15cmHg @ 1100 RPM

Offline Harry Martin

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Re: 2000 Concours only runs well on PRIME
« Reply #5 on: September 09, 2018, 02:57:09 am »
I just remembered...I removed the vacuum from my petcock and converted it using Murph's Kits.
It's 100% manual operation now. The vacuum at that point is plugged. Sorry.

It now has OFF/ON/RES. You have to remember to shut it OFF when done riding.

The kit overides/bypasses the spring loaded diaphram that opens/closes the ON/RES valve.
If there is insufficient vacuum, fuel could get cutoff.
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Offline Richie

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Re: 2000 Concours only runs well on PRIME
« Reply #6 on: September 09, 2018, 03:02:48 am »
Wouldn't leaving it on PRIME be the same as using a manual peacock set to ON?

Offline Harry Martin

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Re: 2000 Concours only runs well on PRIME
« Reply #7 on: September 09, 2018, 03:19:39 am »
In reality, yes. However, you have no way to shut off the fuel now.

If the diaphragm fails, you get a gas leak and is a common point of failure.
When the vacuum shuts off, the spring loaded diaphragm IS SUPPOSED to cut off the fuel preventing a fuel leak, or the dreaded hydrolock that can destroy your engine.

Search the forum on this topic and you will find no end to the horrors of what can happen.

Some folks just install a manual valve or convert their petcocks like i did so that you can actually turn off the gas.
A further step, and well worth the investment, is to install overflow tubes in each carburetor to prevent the hydrolock.

Steve can help you with this at https://sites.google.com/site/shoodabenengineering/home
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Offline Richie

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Re: 2000 Concours only runs well on PRIME
« Reply #8 on: September 09, 2018, 03:30:08 am »
I actually installed an inline fuel valve right next to the petcock for shutting off the fuel, as I’ve seen a lot about hydro lock on these bikes. The petcock doesn’t seem to have any leaking issues right now, but I figured it’s better to be safe.

Offline Outback Jon

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Re: 2000 Concours only runs well on PRIME
« Reply #9 on: September 09, 2018, 05:58:32 am »
I actually installed an inline fuel valve right next to the petcock for shutting off the fuel, as I’ve seen a lot about hydro lock on these bikes. The petcock doesn’t seem to have any leaking issues right now, but I figured it’s better to be safe.
That might be your problem.  The C10 doesn't like any restriction on the line going to the carbs.  Although that type of restriction usually results in problems with high speed operation, not just revving the bike.
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Online Bud

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Re: 2000 Concours only runs well on PRIME
« Reply #10 on: September 09, 2018, 09:10:18 am »
Sounds like the same problem Trav is having in the 2006 running poorly making me sad thread.  You can have good vacuum from the vacuum line, but if there is a pinhole in diaphram, it can cause running problems.

http://forum.cog-online.org/concours-c10-zg1000-general-chat-and-tech/06'-zg1000-running-badly-making-me-sad/

Offline GeorgeRYoung

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Re: 2000 Concours only runs well on PRIME
« Reply #11 on: September 09, 2018, 01:10:48 pm »
Messy suggestion.

Remove the gas line from the petcock to the carbs. Remove the petcock vacuum line from the engine.

In the ON position, if you suck on the vacuum line, does gas come out the petcock? If not, the petcock is faulty.

Does your mouth fill with gas? If yes, there's a leak in the diaphragm.

Offline Richie

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Re: 2000 Concours only runs well on PRIME
« Reply #12 on: September 09, 2018, 05:01:21 pm »
Just tried it; when I suck on the vacuum line, fuel pours out very fast, and none comes out of the vacuum line.
It seems the petcock is fine, which means I’m really out of ideas.
Maybe I’ll just run it on PRIME, as long as that won’t harm it.

Offline Richie

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Re: 2000 Concours only runs well on PRIME
« Reply #13 on: September 09, 2018, 05:38:32 pm »
Just noticed a significant kink in the fuel line after the fuel filter... replaced the line and routed it a different way to ensure to kinks... NO EFFECT.

I’m at a loss.

Offline Richie

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Re: 2000 Concours only runs well on PRIME
« Reply #14 on: September 09, 2018, 06:16:13 pm »
Okay... new information has revealed itself.
It runs perfectly fine on RES.
The fact that it only runs well on PRIME and RES leads me to believe that the problem should disappear with a full tank of gas, as there will be more of a gravity feed effect. The question is, why is the amount of fuel in the tank having this significant of an effect?

Offline Harry Martin

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Re: 2000 Concours only runs well on PRIME
« Reply #15 on: September 09, 2018, 06:21:48 pm »
Okay... new information has revealed itself.
It runs perfectly fine on RES.
The fact that it only runs well on PRIME and RES leads me to believe that the problem should disappear with a full tank of gas, as there will be more of a gravity feed effect. The question is, why is the amount of fuel in the tank having this significant of an effect?

The tube for ON reaches up higher into the tank, thus if on the ragged edge of fuel level for that tube, you will experience fuel starvation until you switch to RES or PRIME.  :great:
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Offline Richie

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Re: 2000 Concours only runs well on PRIME
« Reply #17 on: September 09, 2018, 06:40:18 pm »
Ill fill it all the way up (have to use gas cans... bikes not registered) and see what happens. If it actually is just a matter of the fuel getting near the top of the tube, then I’ll be surprised that I’ve been able to idle it for a couple hours on the center stand without it dying.

Part of me hopes that is the problem, because then the bike will be perfect, and part of me hopes that is not the problem because I’ll feel and look like a real douche for going through all this to find that it’s low on gas. :/

Offline Richie

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Re: 2000 Concours only runs well on PRIME
« Reply #18 on: September 09, 2018, 07:16:29 pm »
Well I added 2 gallons and the problem improved, though it still runs better on RES...

Offline MAN OF BLUES

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Re: 2000 Concours only runs well on PRIME
« Reply #19 on: September 09, 2018, 07:45:35 pm »
....gas tank was essentially filled with brown Jell-O, .....

I know it's kind of late to say this, as you now have a pretty full fuel tank to mess with, but when you were cleaning it all up, did you by any chance dislodge the fuel screen inside the tank, and posssibly some of the tank spooge that was present, got itself lodged deep inside the "ON" fuel pickup tube in there??? Sounds like it did.



maybe drain the tank, and revisit that area, with the petcock removed, (also remove the fragile diaphragm first, to prevent damage)  and blow it out with compressed air, from the exit hole back into the tank side.... to insure it isn't blocked... because it seems to be a starvation thing that is hiding somewhere.

I've also seen diaphragms, as delivered, incorrectly assembled, where actually both of the 'rubber'diapragm petals(for lack of a better term, the rubber flappy parts) were located on one side of the plastic square 'plate', rendering it inopereable...when that flapped part is correctly assembled, there should be a rubber part on either side of the plastic 'frame' that holds it.

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Offline Richie

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Re: 2000 Concours only runs well on PRIME
« Reply #20 on: September 09, 2018, 11:32:52 pm »
Took the petcock out and cleaned it again... the filter was still in place, and it’s still doing the same thing. I guess I may not figure it out but it doesn’t really matter I suppose... no issue with running it on RES as the fuel gauge works perfectly fine and I always track my mileage. I just wonder... is the opening when set to RES larger than the tube when set to ON?

Offline KLRPhil

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Re: 2000 Concours only runs well on PRIME
« Reply #21 on: September 10, 2018, 01:28:13 am »
The fuel gauge works perfectly fine?  What is the secret there?  Has there been some modification?  Those things are notoriously inaccurate. 
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Offline Richie

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Re: 2000 Concours only runs well on PRIME
« Reply #22 on: September 10, 2018, 02:10:14 am »
Well I assume it is accurate as there was about a half gallon in there when I added an additional 2 and it is showing just under 1/3 full.

Offline connie_rider

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Re: 2000 Concours only runs well on PRIME
« Reply #23 on: September 10, 2018, 03:04:43 am »
I agree with MOB; This does sound like a fuel starvation problem in run position..
Sounds like a blockage in the "on" passages of the petcock.
The fact that it runs ok on Reserve confuses things..

1) I think you sed; your having the same basic problem with both petcocks?
2) When you change from prime to on, does the problem start immediately or does it take several minutes?
3) When the hesitation occurs in "on" position, will the engine eventually rev up?
OOp's; Just saw this.... and then I switch to PRIME, it takes about 30 seconds for it to take effect, and vice versa.
4) Disconnect the vacuum line from the petcock and plug it.
      Attach a hose and use a vacuum pump to pull vacuum to the petcock.
      Run the engine and see if the hesitation has changed.

Ride safe, Ted

PS:  Are you hooked to only 1 vacuum source? {vacuum hose should be hooked from #2 cylinder to petcock}.
          {Some have T'd their vacuum lines and tried using 2 cylinders to pull the vacuum}.
« Last Edit: September 10, 2018, 02:42:54 pm by connie_rider »
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Offline Richie

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Re: 2000 Concours only runs well on PRIME
« Reply #24 on: September 10, 2018, 06:51:02 pm »
Yes it’s the same issue with both petcocks, and manually sucking on the vacuum tube does not affect the issue.
And yes the vacuum line is only hooked up to the 2nd carb.