Bike suddenly running rich

[DC Concours]

Hi guys,

My bike is getting lower mpg and seems to be running rich. What are the symptoms of a rich mixture in this bike and how can this happen suddenly? Is it time for a carb service?

[m in sc]

could... be.. check the air filter and air box 1st. mouse may have made a home in there.

'2 mouse jetting mod'. 

also check the vacuum line tot he petcock isn't leaking fuel. if the diaphragm is torn it can suck fuel into #2

[DC Concours]

Thanks. Checked and cleaned the air filter a couple of weeks ago when this all started suddenly. The filter was not that dirty.

It happens when I am rolling along at say 60mph, 6th gear.... and then want to accelerate. I give it gas or shift down to 5th and give it gas. The bike makes a breathy sound and shakes a little and slowly picks up. The acceleration is not crisp.

[turbojoe78]

DC, do you have overflow tubes?

If you do, remove the rubber overflow lines from the drain nipples on the carbs and put the petcock on prime without the bike running and see if any gas is coming out of any of the carbs.  You could have a float needle that's not sealing all the way letting too much gas into the fuel bowl.

How does the bike run just sitting at idle for a couple minutes?

[BruceR]

I was going to suggest checking plugs, plug wires, coils.  But the symptom doesn't sound like that.  Vacuum might be the culprit.  Hoping a carb guy responds soon to diagnose.  My approach would be to check the simple stuff first then send the carbs to some one to set up properly.

[DC Concours]

Thank you for your help Joe. The bike starts and idles perfectly. Runs well while on low speed jets.

Problem is during acceleration in higher speeds.

DC, do you have overflow tubes?

If you do, remove the rubber overflow lines from the drain nipples on the carbs and put the petcock on prime without the bike running and see if any gas is coming out of any of the carbs.  You could have a float needle that's not sealing all the way letting too much gas into the fuel bowl.

How does the bike run just sitting at idle for a couple minutes?

[DC Concours]

Thanks Bruce.

I really don't think the carbs are off but they should be vacuum checked. This all happened while my gas was winterized. I am on my first tank of non-winterized gas. Could water in the gas cause this?

I was going to suggest checking plugs, plug wires, coils.  But the symptom doesn't sound like that.  Vacuum might be the culprit.  Hoping a carb guy responds soon to diagnose.  My approach would be to check the simple stuff first then send the carbs to some one to set up properly.

[BruceR]

Try a 1/2 bottle of Techron in the gas?  After that you'll need to change the oil too I think.  If idle and part throttle are good I'd suspect something in the carbs.  Other than synching them on my '99 I never had to mess with mine.  Could be high speed circuit gummed up.  But I'd make sure you had good clean gas in it before doing anything else. 

[cra-z1000]

Drain the fuel and refill with fresh fuel . Could also be starvation if happenning only at higher speed acceleration . Check fuel line routing .

[Boomer]

The symptoms sound like a torn diaphragm to me which means one of the needles isn't lifting the same as the others.
What makes you think it's running rich? Can you smell gas in the exhaust?

[m in sc]

are you sure its rich? sounds more like fuel starvation with the added info of the 'at speed' symptoms as z-1000 says. check tank vent/petock flow etc. 

[DC Concours]

Hi guys,

I went for an investigative ride for this post...

This is what happens:
- when I grab a fistful (suddenly accelerate) in any gear over 30mph the bike seems to bog down
- especially noticeable around 3k+ rpm
- bike shakes
- sounds breathy
- gentle acceleration does not have any issues
- last fill up was yielding 32mpg. I normally get 38mpg mixed hwy/city
- I first noticed this about a month ago JUST after the bike was sputtering running out of gas and after I flipped to reserve
- This bogging and shaking happened a year ago for one day, but after I rode it hard for 15 mins it came back to normal the next day
- start/idle/low speed runs fine
- bike will roll in first gear w/o cutting even at 500rpm
- I have steve's 2 min mod and overflow tubes

[turbojoe78]

If you have fresh gas in it from this year, I would check the foam, or whatever you used to block part of your air box intake to make sure it's still in place.

Then whether that's good, or not, add a bottle of dry gas to a full tank (Heet or Iso-Heat) and run all of it through till close to reserve, then fill up with fresh gas.

[cra-z1000]

Hi guys,

I went for an investigative ride for this post...

This is what happens:
- when I grab a fistful (suddenly accelerate) in any gear over 30mph the bike seems to bog down
- especially noticeable around 3k+ rpm
- bike shakes
- sounds breathy
- gentle acceleration does not have any issues
- last fill up was yielding 32mpg. I normally get 38mpg mixed hwy/city
- I first noticed this about a month ago JUST after the bike was sputtering running out of gas and after I flipped to reserve
- This bogging and shaking happened a year ago for one day, but after I rode it hard for 15 mins it came back to normal the next day
- start/idle/low speed runs fine
- bike will roll in first gear w/o cutting even at 500rpm
- I have steve's 2 min mod and overflow tubes

What kind of fuel line is on it ? If it's that clear stuff it gets real flimsy when it heats up and can kink real easy . If there are tight bends in the line (any type of fuel line )you may have starvation when the tank is low on fuel since it is gravity fed . It may flow good enough at low speed but once the fuel demand comes up with the throttle it won't flow enough to keep up .

[DC Concours]

Turbojoe, I put my first tank of fresh gas last week. I will check the foam. It was ok last time I checked. I don't know if heet is carb safe. SISF is not a fan of putting these things in the tank.

craz1000, I have the OEM tubing and a inline filter. No tight bend and it has always been fine.

[turbojoe78]

DC, I know Steve's thoughts on fuel additives, that was why I suggested running it through.  You could also run your tank down to half, add a 1/2 bottle of Iso-Heat and ride the bike till you need to add fresh gas.  This is something MOB used to suggest for getting water out of you're tank.  Did you notice the problem after you put it on reserve?  Do you ride till you hit reserve a lot?  With my C10 I used to ride to reserve every tank so my petcock stayed exercised and I got the gas down to the lower corners of the tank.

[DC Concours]

Hi Turbo,

I think I will let a couple of tanks run through. I think there might might be water somewhere. I used to read MOB always talk about water in the tank. I will use Heet. You all like it.

This problem started after I moved to reserve on my ride back home. I exercise the reserve from time to time so it is used. Maybe not as much as you.

But the thing is wouldn't bad gas cause issues through all gears, speeds and rpms?

[cra-z1000]

Yeah it really should . I'm afraid it's time for carb cleaning . It's not that hard especially if you go by MOB's method in the Fall 06 Concourier . I've been doing mine for several years now with great success .

[m in sc]

crack the drains on the carbs and catch the mixture in a glass bottle. let sit, look for water. will be obvious. better than guessing.

remember: the main jet is the 'lowest' jet in the carb with the pilot being quite a bit higher. water settles to the bottom of the bowl/tank. 

[cra-z1000]

Hi Turbo,

I think I will let a couple of tanks run through. I think there might might be water somewhere. I used to read MOB always talk about water in the tank. I will use Heet. You all like it.

This problem started after I moved to reserve on my ride back home. I exercise the reserve from time to time so it is used. Maybe not as much as you.

But the thing is wouldn't bad gas cause issues through all gears, speeds and rpms?

If you do try Heet , be sure to get out and ride most of the tank out . Don't want to let that stuff sit long as it's harsh on float tips and the fuel will seperate again after some time .