Topic: bike running way too rich after exhaust added

[miller_87]

Okay, here's my problem...I got a 1973 honda cb500/4 last year and the guy who previous owned it put a 4-2 turnout exhaust on with no baffles or any kind of air restriction.  The bike had decent power, but on the low end letting the clutch out, you could feel it was a little rough.  I was only getting around 33 miles per gallon, and the plugs were always fairly black so I figured he had re-jetted the carbs on there.  When I had checked, they were the the stock jets and needle position.  I was always told putting on an exhaust with no baffles would make the engine run rich, but the plugs were always blackened.  Well, I decided to go with a MAC 4-1 to quiet the bike down.  Went out for a quarter mile run and couldnt get it out of first because it was running so rich.  I had to keep it in the lower rpms because the plugs were getting fouled if I tried to rev it up.  Within the quarter mile run all four cylinders were pretty well fouled.  I decided to order in some 80 main jets with 38 slow jets.  Does this setup seem very odd to anybody else?  I would think something is very wrong here considering the main jets were 100's and slows were 40's, but there is no way it will run good like that.  It just seems like 80's would be very lean.  Please, somebody let me know what you think about this carb setup.

[miller_87]

Somebody out there must be running a 4-1 baffled exhaust that knows the answer to this jetting question...or maybe can let me know why my bike was running somewhat rich with the 4-2 turnouts with stock jetting?  If I recall correctly...any kind of a air leak by the carbs would cause the bike to run lean correct?

[78_SaltLick]

good lord i know nothing about bikes, but it sounds kinda like my same problem. guy before me put 4 into 1 pipes on it, no baffles straight pipe and i think by what ive been hearing its running extremely rich. Runs like #$%* in lower RPM's, exaust pipe literally has an inch of soot you can wipe out with your finger.

[TwoTired]

Okay, this is going to sound repetative.  But, the discovery process is often that, only with a different example of the same machine.

1. What is tune up history, and what was your check list of items for the tune up?
2. Do you have the correct spark plugs installed?  State plug brand, type, and gap setting.
3. What air filter do you have?  Has it been cleaned?  When was it last replaced?
4. Are you certain that the choke butterflies are opening fully?
5. Were you reading the correct part of the plug for combustion deposits; the center electrode insulator?

Don't mess with the carbs until all the tune up items have been properly addressed first.

6. Did you verify that the jets in your carbs weren't drilled to a larger diameter?  Or, cleaned so aggressively that the orifice is larger than what the number stamping is?
7. Are your idle air bleed screws solid or hollow?  What is their setting?
8. Do you still have the stock slide needles?  Have they been replaced with ones of a different taper profile?
9. Have you checked the float height?  And, that the float needles will, indeed, close off fuel flow into the float bowls?
10. Have you measured the fuel level in the bowls when fully filled?
11. Have you checked for fuel contamination (rust scale) that might block the float valves from closing?  (drain the carb bowls into a clean container.)
12.  Each carb body flange has a stamped number on the top right hand side.  What is yours?
13. Have you removed the emulsion tubes behind the main jet and cleaned the cross drilled holes?

Let us know what you find.

Cheers,

[scunny]

TwoTireds list is pretty comprehensive, it will be a tuning issue I'm sure.
I have run 4into1s on CB500's a GS1000 and a GS650 with stock air filters and with pods, with and without baffles, depending on the class I was racing in, and I never had a major issue with jetting, maybe a notch here or a rise in main jet, but never a large change. Check all the other tuning tips before playing with your carbs. Take your air fiter out, does it rev quicker but lack grunt ?

[miller_87]

1.  My tune up history for the bike is when I got it, carbs were cleaned and rebuilt, new air filter, new spark plugs(matched with stock numbers), new intake valves, new head and base gaskets...and just the standard cleaning of everything.
2.  Yes, correct sparkplugs, I dont know the numbers off hand, but they are matched with the book and also same numbers as previous plugs in there.
3.  Not stock air filter.  It is an aftermarket foam kind...but that would cause it to run leaner...
4.  Yes, choke butterflies are fully open
5.  And yes, I was reading the correct part of the plug...black in color by the way
6.  No, jets werent drilled
7.  Idle air bleed screws are out 1 turn
8.  Yes, still stock main needles
9.  Yes, floats are shutting off fuel correctly
10.  have not measured fuel level in bowls when fully filled, but they arent leaking and seem to be shutting off fine
11.  New gas lines, fuel filters, and tank has been cleaned
12.  Dont know
13.  Havent removed emulsion tubes

So far, this is what I can tell you.  Just seems odd to me with those aftermarket turnouts without baffles that the plugs would have been running dark.  Also seems odd that adding a 4-1 baffled MAC exhaust would restrict the air that much and make it run that much more rich to foul all four plugs in such a short distance. 

[TwoTired]

1.  My tune up history for the bike is when I got it, carbs were cleaned and rebuilt, new air filter, new spark plugs(matched with stock numbers), new intake valves, new head and base gaskets...and just the standard cleaning of everything.

FYI;  Part of the tuneup ( 3000 miles/6 mos), is gapping the points, checking/setting spark timing, tappet adjustment, cam chain tensioning, and cleaning/replacing the air filter.

2.  Yes, correct sparkplugs, I dont know the numbers off hand, but they are matched with the book and also same numbers as previous plugs in there.

If there is an R in plug number it's the wrong one and the standard plug for a 750 is NGK D8EA which is too cold for the 550 and won't allow the plugs to self clean unless you drive it 80 mph for 30 minutes on a 100 degree F day.  I've found several Cb550s with the wrong plugs installed and had parts counter men sell me the wrong ones for this bike.  But, if you're confident about your plugs...

3.  Not stock air filter.  It is an aftermarket foam kind...but that would cause it to run leaner...

No. Not if it was over oiled, packed too tightly or clogged with dust etc.
Do the test where you temporarily REMOVE the filter, and tell us if the run symptoms change.

5.  And yes, I was reading the correct part of the plug...black in color by the way

Base ring black is okay, center electrode insulator black is not.

6.  No, jets werent drilled

Never in the bike's history? How did you measure them?

7.  Idle air bleed screws are out 1 turn

You're side steping questions.  That's fine if you wish to side step issues.  But, the wrong bleed screws can seriously screw up mixtures.  If they are the stock hollow ones they are set on the rich side of the stock adjustment range, which by the way, is now likely irrelevant with the filter and exhaust changes.  If someone put air bleed screws in there from an F model bike they'd be solid and way more sensitive to adjust.  You'll need to find the proper idle air screw setting for your non-stock setup.

8.  Yes, still stock main needles

Okay, I believe you didn't change them.  Do you know they are original to the bike?

9.  Yes, floats are shutting off fuel correctly
10.  have not measured fuel level in bowls when fully filled, but they arent leaking and seem to be shutting off fine

High fuel levels will richen up the entire range of carb operation.   This is a carb fine tuning aspect, and not simply pass/fail.

11.  New gas lines, fuel filters, and tank has been cleaned
12.  Dont know

What? And, you won't bother to look at your bike?  Am I to assume you don't care either?  If you've only had it for a year.  How do you know you have the original carbs on the bike?

13.  Havent removed emulsion tubes

Clogged emulsion tubes will deprive the air premix before injection into the carbs causing a rich condition while operating on the mains and slide needles.

So far, this is what I can tell you.  Just seems odd to me with those aftermarket turnouts without baffles that the plugs would have been running dark.  Also seems odd that adding a 4-1 baffled MAC exhaust would restrict the air that much and make it run that much more rich to foul all four plugs in such a short distance. 

I believe you are barking up the wrong tree blaming the exhaust for your running rich problems.  For as long as you have had the bike it has run rich, so you tell us, and changing the exhaust didn't impact that trend.  More likely you have an air filtration or carb cleaning/tuning issue, I think.  But, hey, what do I know?

If you don't want to seriously address the checklist I provided, that's certainly your option.  I'll step aside and let others help you.  Perhaps others will provide you with the information you want to hear and in form more pleasing.

Best of luck!

[miller_87]

1.  Yes, I gapped points, checked spark timeing, tappet adjustment, and cam chain tension when I replaced head and base gaskets.
2.  Yes, there was an R but the numbers matched.  I was told the R just means restrictor or something like that for electronic equipement.
3.  It is a brand new filter, just put it on, didnt oil yet, not packed to tight or clogged
5.  Read center electrode
6.  No, jets werent drilled...refere to number one where I said carbs were cleaned and rebuilt...which meant new jets in the rebuild kit.
7.  I'm assuming they are the same as stock since they were in the rebuild kit...i believe they were hollow, but can't guarantee it till i look.
8.  Yes, they are original to the bike.
9.  Well, the floats werent stuck when i rebuilt the carbs...they are shutting off, as to say they are at the correct position, I'm just assuming because there has never been an issue with them and the first time carbs were taken apart were by me.
11.  Okay, I'm sorry I didnt have the opportunity to look tonight.  The bike is out in my grandpas shop which I did not have access to tonight.  It is out there because that's where I put the new exhaust on, after it was on, it was running too rich, so I pulled the carbs to pull the jets so I could order new ones...couldnt exactly drive it home with the carbs out...cut me some slack here...I've worked on enough engines and this is the first problem that I'm not sure to fix...I'm not some idiot that doesnt know how to pull apart an engine and carbs and correctly put it back together.  I know how to work on this stuff, just not sure as to the stock setup of these and as to why the engine is running rich and fouling out plugs.

[DammitDan]

Don't take offense miller... a lot of people who come onto these forums ask the exact same questions before they even search the thousands of previous posts that may be similar.  To top it off, after they ask the exact same questions they brush off possible answers because it would be too hard or time consuming (or money consuming) for them.  So in effect, they never should have asked if all they want to do is treat the symptoms but ignore the disease.

What I'm saying is, no one is saying you don't know what you're doing or that you're not willing to take the time to fix your bike.  What we are trying to do is cure the disease by starting at the best place to start, the diagnosis.  It's easy to make assumptions (such as that the non-stock airbox couldn't be causing the problem) and place immediate blame on the likely suspects (i.e. the exhaust).  I think that a little patience and some luck will solve this problem.

Just be glad it's not an electrical problem! 

 - Dan-0

[TwoTired]

2.  Yes, there was an R but the numbers matched.  I was told the R just means restrictor or something like that for electronic equipment.

The R means resistor, for suppressing radio interference.  The original spark plug caps have these resistors.  So, now you have two which lowers the spark voltage and intensity.  It might be contributing some to your "rich" issue.  But, if they are new and the correct heat range, should work.  Just don't expect 12000 miles from them unless you replace the plug caps with non-resistor.

6.  No, jets werent drilled...refere to number one where I said carbs were cleaned and rebuilt...which meant new jets in the rebuild kit.

Now see, you didn't tell about a rebuild kit before.  Did new slide needles also come in the kit and did you use them?

7.  I'm assuming they are the same as stock since they were in the rebuild kit...i believe they were hollow, but can't guarantee it till i look.
8.  Yes, they are original to the bike.

Then the carbs should be stamped 627B.   Did the kit you installed, specifically state it was for the 627B variants of this carb type?  There are 4 variants of this carb type including 022A, 069A, (and 087B, I think).  Some kit suppliers ignore the distinction between these models and the slide needles had slightly different tapers originally.

9.  Well, the floats werent stuck when i rebuilt the carbs...they are shutting off, as to say they are at the correct position, I'm just assuming because there has never been an issue with them and the first time carbs were taken apart were by me.

Well, you've had a mixture issue for a year now.  And, bowl fuel levels can effect mixtures.  Shouldn't you at least check the float setting to eliminate a possible cause, or at least add to the list of knowns?
If your kit also replaced the float needles and seats, then it was highly likely that the float height had to be reset for those new components.

11.  I'm not some idiot that doesnt know how to pull apart an engine and carbs and correctly put it back together.  I know how to work on this stuff, just not sure as to the stock setup of these and as to why the engine is running rich and fouling out plugs.

I never said you were.  But, setting up carbs is more than just putting bits together.  It's knowing tiny details about the components inside, what they do when, and where they are currently set, so they may be adjusted for the desired effect.
Did you use Honda carb kits or some other manufacturer?  Honda Carb components and book settings work well with their bikes in stock form.  Exhaust and intake modifications may require different settings and or internal carb components.

I'd still like to know if your emulsion tubes are clean and clear, and what slide needle taper you have.  These are going to have the biggest impact on 1/4 to 3/4 throttle settings.

Did you verify the carbs air jets were clear?   Just a thought...

[crazypj]

I never said you were.  But, setting up carbs is more than just putting bits together.  It's knowing tiny details about the components inside, what they do when, and where they are currently set, so they may be adjusted for the desired effect.
Did you use Honda carb kits or some other manufacturer?  Honda Carb components and book settings work well with their bikes in stock form.  Exhaust and intake modifications may require different settings and or internal carb components.

I'd still like to know if your emulsion tubes are clean and clear, and what slide needle taper you have.  These are going to have the biggest impact on 1/4 to 3/4 throttle settings.

Did you verify the carbs air jets were clear?   Just a thought...

Do you have standard air box with foam filter? foam filters dont last forever, after about 3 to 4 yrs the foam just gets old and can start to break down, clogging its-self up. Lot of people do float height incorrectly, carb should be at about 70degree angle to check it. Pod filters allow carbs to 'sink', causes rich mixture, emulsion tubes/ needle jets wear due to airflow 'pulling' them in towards cylinder, use magnifying glass to check.Air jets are also called air bleeds, in the airbox side of carb intake, if blocked or partially blocked your going to have problems.( a hole with a brass tube presssed in, blat some carb cleaner through them) set airscrews about 1.5 to 2 turns out from LIGHTLY seated. If this doesnt put you in the ball park there are other issues. It should never be neccessary to use 20% smaller main jets!
Sorry if this sounds too critical, or simplistic, no one knows your level of expertise
PJ

[HondaMan]

If the exhausts flow better than the stock setup, the result will be richer mix. This is because of the higher volumetric efficiency and increased air speed across the jet needle hole, causing increased fuel lift. The ultimate answer is a larger cutaway on the carb slide, but this is impractical for most home mechanics. That said:

1. Try running without the air filter in place: if this helps, then replace the filter element (if used). If it gets worse, install a paper (more restrictive) element. K&N filters flow better than foam ones, foam better than paper.
2. Lower the needles in the slides before changing main jets. With black plugs, start with 2 notches "higher" on the needle.
If this helps considerably, lower the main jet 20% and raise the needles back to where they were, then try again.
3. Repeat step 3 if still too rich. I roadraced the CB500 I had at a 70 mainjet, open megaphones, idle screw at 1-1/4 turns and a K&N air filter inside a stock airbox. Timing was +2 degrees from stock, plugs were D8E. RPMs were above 10,000.