Topic: running rich

[evinrude7]

been chasing a rich condition in my carbs.  currently the 657 carbs i have on the bike are clean, floats set with clear tube method, 105 mains, 40 slow, needle at 4th position with a stock airbox.  idle screws set around 1.  it is my understanding that the idle screws don't affect anything beyond sitting still and idling.  bike was recently tuned up.  last two times i had someone riding on a bike behind me they said it smells rich.  vacuum synced the carbs a while back.  idles very smooth and runs very well.  brass was had from jetsrus and i specified and paid for genuine keihin.

what else can i adjust or change to fix the rich condition?  thinking of pulling them off and going though them again.  could i have set the slides too high while bench syncing and then when vacuum syncing ending up with them even higher when adjusting to #2?

[robvangulik]

Syncing has no influence on possibly running rich, it is making sure all cylinders run at the same power. Compared to modern bikes our sohc's always run (and smell) a bit rich as there is no computer trying to run as clean as possible.

[tlbranth]

I don't know what a 657 carb is but my K0 runs rich. I made it a lot better by lowering the fuel level slightly and lowering the needles one notch. The idle mixture, on my bike anyway, most definitely DOES affect mixture well above idle.
The needles and bits they go into wear out a bit and let more fuel in. Lowering the needle is the only way I know of to alleviate this problem since replacements (from Honda anyway) are no longer available.
Another problem I had was using what turned out to be an Emgo air filter. It made a difference when I switched to K&N.

[PeWe]

Can be too high fuel level in float bowls as mentioned.

Air screws probably right at 1 turn out.
They effect cruising in 60Mph (100 kmh) which I noticed when I verified them on my K2 with stock K6 carbs.
I set them way too lean (1 1/2) and it resulted in same behavior as it was time for reserve when crusing in even speed without acceleration.  Reduced until it disappeared and slightly more which ended up in around 1 turn out.

Ignition is properly set too?Choke is opened on all carbs?

 Too easy to forget open them. I have forgot them at 1/3 closed several times which work fine until the throttles opens more than the choke that will cause rich.

[Jerry Rxman Griffin aka MuthaF'er]

750F needles (75/76 anyway) should be in the 3rd/middle slot for factory specs. That would be in the range your buddy is smelling on normal riding.

[evinrude7]

I don't know what a 657 carb is but my K0 runs rich. I made it a lot better by lowering the fuel level slightly and lowering the needles one notch. The idle mixture, on my bike anyway, most definitely DOES affect mixture well above idle.
The needles and bits they go into wear out a bit and let more fuel in. Lowering the needle is the only way I know of to alleviate this problem since replacements (from Honda anyway) are no longer available.
Another problem I had was using what turned out to be an Emgo air filter. It made a difference when I switched to K&N.

The 657s among other models are the round tops. I've a K&N air filter in there.  So you went to 5th position on needles? Didn't lean it out too much?

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[evinrude7]

Can be too high fuel level in float bowls as mentioned.

Air screws probably right at 1 turn out.
They effect cruising in 60Mph (100 kmh) which I noticed when I verified them on my K2 with stock K6 carbs.
I set them way too lean (1 1/2) and it resulted in same behavior as it was time for reserve when crusing in even speed without acceleration.  Reduced until it disappeared and slightly more which ended up in around 1 turn out.

Ignition is properly set too?Choke is opened on all carbs?

 Too easy to forget open them. I have forgot them at 1/3 closed several times which work fine until the throttles opens more than the choke that will cause rich.

Ignition is as close as I could get it with a light. Advance looks good too.

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[evinrude7]

750F needles (75/76 anyway) should be in the 3rd/middle slot for factory specs. That would be in the range your buddy is smelling on normal riding.

I have a K Jerry.

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[evinrude7]

Now that I think back. When I set the floats with a homemade gauge to 26mm I didn't have this problem. When I clear tubed them they were a few mm shy of "optimum" level. Raised them to about 3-4mm below the rim. They don't overflow.

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[jonda500]

I don't know what a 657 carb is but my K0 runs rich. I made it a lot better by lowering the fuel level slightly and lowering the needles one notch. The idle mixture, on my bike anyway, most definitely DOES affect mixture well above idle.
The needles and bits they go into wear out a bit and let more fuel in. Lowering the needle is the only way I know of to alleviate this problem since replacements (from Honda anyway) are no longer available.
Another problem I had was using what turned out to be an Emgo air filter. It made a difference when I switched to K&N.

The 657s among other models are the round tops. I've a K&N air filter in there.  So you went to 5th position on needles? Didn't lean it out too much?

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most ppl in here (but not all) number the needle slots 1 to 5 with #1 being closer to the top or blunt end and #5 the bottom or pointy end - so #5 is the richest setting and #1 is the leanest.
John
so to lower the needles one notch you raise the clips from #4 to #3.

[tlbranth]

I don't know what a 657 carb is but my K0 runs rich. I made it a lot better by lowering the fuel level slightly and lowering the needles one notch. The idle mixture, on my bike anyway, most definitely DOES affect mixture well above idle.
The needles and bits they go into wear out a bit and let more fuel in. Lowering the needle is the only way I know of to alleviate this problem since replacements (from Honda anyway) are no longer available.
Another problem I had was using what turned out to be an Emgo air filter. It made a difference when I switched to K&N.

The 657s among other models are the round tops. I've a K&N air filter in there.  So you went to 5th position on needles? Didn't lean it out too much?

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No, standard is #3 groove. I moved the clips to #2 groove (second from the top). It leaned things out some but it's still a tad rich.

[evinrude7]

I don't know what a 657 carb is but my K0 runs rich. I made it a lot better by lowering the fuel level slightly and lowering the needles one notch. The idle mixture, on my bike anyway, most definitely DOES affect mixture well above idle.
The needles and bits they go into wear out a bit and let more fuel in. Lowering the needle is the only way I know of to alleviate this problem since replacements (from Honda anyway) are no longer available.
Another problem I had was using what turned out to be an Emgo air filter. It made a difference when I switched to K&N.

The 657s among other models are the round tops. I've a K&N air filter in there.  So you went to 5th position on needles? Didn't lean it out too much?

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most ppl in here (but not all) number the needle slots 1 to 5 with #1 being closer to the top or blunt end and #5 the bottom or pointy end - so #5 is the richest setting and #1 is the leanest.
John
so to lower the needles one notch you raise the clips from #4 to #3.

 

i'm one from the top (highest position). my understanding is the higher on the needle it sits the higher the number and the leaner it is.  which goes with what you are saying as far as lean/rich with just a different number orientation.  hondachopper.com calls the notches out the way i am explaining it.  my year bike and carbs call for number 4 position.  with your number layout i'd be at 2 or 3.  much much richer.  no?

[evinrude7]

Can be too high fuel level in float bowls as mentioned.

Air screws probably right at 1 turn out.
They effect cruising in 60Mph (100 kmh) which I noticed when I verified them on my K2 with stock K6 carbs.
I set them way too lean (1 1/2) and it resulted in same behavior as it was time for reserve when crusing in even speed without acceleration.  Reduced until it disappeared and slightly more which ended up in around 1 turn out.

Ignition is properly set too?Choke is opened on all carbs?

 Too easy to forget open them. I have forgot them at 1/3 closed several times which work fine until the throttles opens more than the choke that will cause rich.

out (counter clockwise) is rich because you are forcing more air through the idle circuit which brings on more fuel.  no? 

[jonda500]

I haven't read where any one had to go to the leanest (top slots) needle setting, but it is apparently common to have to use leaner than stock settings on old carbs.
I actually have a set of 657 carbs(cb750K) that I got from a cb550K I used to have and while they may have been changed when the PO fitted them to the 550, they have the needles set at the second richest position and worked well (on my 500 fitted with pod air filters).
Both of my 500K's have the needles there too (second from the bottom) but for one I have had to go two sizes smaller pilot jets (from #40 to #35).
I am certain turning the air screws out (anti clockwise) leans out the mixture (I think of it like a small controllable vacuum leak!)  and +1 -not just at idle, they do affect the response as you open the throttle too.
John

[evinrude7]

i'm where the red mark is on the photo. 

[tlbranth]

i'm where the red mark is on the photo.

Try putting the clip in the top notch.

[PeWe]

i'm where the red mark is on the photo.

That is 2nd slot from top which should cause lean midrange. This together with the other settings will guarantee a very dull midrange. Not much happen when twisting the throttle, right?

My K2 with same type of carbs, stock airbox and Yamiya no numbers 4-4 (like HM300) have:
Pilot 40
Air screws 1 turn out
Needles 4th notch from top
Main 115.
Live at 30-40 meters above sea level.

Less breathing exhaust smaller main jets.
If using restrictive HM 341 4-4 maybe 105 main and needles 3rd from top as stock had.

[Henning]

Also consider going with a smaller idle jet - 38 and 35 are available - it makes a surprisingly big difference to the overall mix. I fought rich running for a long time and the only thing that helped in the end was the smaller jets, currently 35's. There was a looong thread about this a while ago, mainly about stumble off idle, but the bottom line is that both punters went with smaller idle jets and it solved their issues.

[Jerry Rxman Griffin aka MuthaF'er]

Can be too high fuel level in float bowls as mentioned.

Air screws probably right at 1 turn out.
They effect cruising in 60Mph (100 kmh) which I noticed when I verified them on my K2 with stock K6 carbs.
I set them way too lean (1 1/2) and it resulted in same behavior as it was time for reserve when crusing in even speed without acceleration.  Reduced until it disappeared and slightly more which ended up in around 1 turn out.

Ignition is properly set too?Choke is opened on all carbs?

 Too easy to forget open them. I have forgot them at 1/3 closed several times which work fine until the throttles opens more than the choke that will cause rich.

out (counter clockwise) is rich because you are forcing more air through the idle circuit which brings on more fuel.  no?

No. It brings more air as you stated

[evinrude7]

i'm where the red mark is on the photo.

That is 2nd slot from top which should cause lean midrange. This together with the other settings will guarantee a very dull midrange. Not much happen when twisting the throttle, right?

My K2 with same type of carbs, stock airbox and Yamiya no numbers 4-4 (like HM300) have:
Pilot 40
Air screws 1 turn out
Needles 4th notch from top
Main 115.
Live at 30-40 meters above sea level.

Less breathing exhaust smaller main jets.
If using restrictive HM 341 4-4 maybe 105 main and needles 3rd from top as stock had.

no flat midrange.  bike pulls well all the way through. 

[evinrude7]

Also consider going with a smaller idle jet - 38 and 35 are available - it makes a surprisingly big difference to the overall mix. I fought rich running for a long time and the only thing that helped in the end was the smaller jets, currently 35's. There was a looong thread about this a while ago, mainly about stumble off idle, but the bottom line is that both punters went with smaller idle jets and it solved their issues.

might try that.  don't have any stumble off idle. 

[seanbarney41]

Is it killing off spark plugs?  If no, and it's running so good, why mess around?

[evinrude7]

Is it killing off spark plugs?  If no, and it's running so good, why mess around?

No not fouling plugs. Would be nice to get it right.

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[Maraakate]

Is it killing off spark plugs?  If no, and it's running so good, why mess around?

I agree, if it's slightly rich but not affecting performance, MPG, excessive fumes, etc. then I'd just leave it be.

[evinrude7]

Excessive fumes to those behind me
 

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[Maraakate]

Excessive fumes to those behind me
 

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What colour?  Can you see it when idling?

[evinrude7]

Excessive fumes to those behind me
 

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What colour?  Can you see it when idling?

No


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[Maraakate]

Excessive fumes to those behind me
 

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What colour?  Can you see it when idling?

No


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Can you see it at all, at any time?  Have you personally smelled the exhaust (carefully, obviously)?  If the plugs are in order in the picture, I'd say the 2-3 look pretty good and I'd live with it.  1-4 look slightly sooty, but probably OK.  Since it's 1-4 related it could be 1-4 points and/or ignition coil/caps/etc.

You could also try the "dollar bill test" if you have some currency large enough to cover the exhaust hole and see if it stains the bill.  See: https://mechanics.stackexchange.com/questions/23418/what-is-the-dollar-bill-test

[Maraakate]

This could be incidental, and I assume you already checked... but there is absolutely no air leaks from 1 and 4?  You checked top, bottom, left, and right with some PB Blaster at the airbox and intake side?

Still operating on the assumption that the outer two plugs are 1-4 and that it's probably ignition related, gap may be slightly off for 1-4.  Did you use a timing light to verify the timing?  There is some test procedures in the service manual to test the coils.  You'd have to look it up as I don't know what points to probe or what the values are supposed to be.

[evinrude7]

Excessive fumes to those behind me
 

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What colour?  Can you see it when idling?

No


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Can you see it at all, at any time?  Have you personally smelled the exhaust (carefully, obviously)?  If the plugs are in order in the picture, I'd say the 2-3 look pretty good and I'd live with it.  1-4 look slightly sooty, but probably OK.  Since it's 1-4 related it could be 1-4 points and/or ignition coil/caps/etc.

You could also try the "dollar bill test" if you have some currency large enough to cover the exhaust hole and see if it stains the bill.

I have smelled it before but didn't seem overwhelming to me. The two riders that mentioned it said they definitely noticed it. The first guy was during a continuing ed riders course. He kind of made a big stink about it. Lots of idling while waiting in line and pulling away. The other dude was this past weekend. I lead the first 75 miles and he mentioned it was tough to be close behind. I did notice him staying off my tail. We spoke about possible reasons for the issue. I'm not thrilled w the plug colors but yeah 44 year old bike. First thing I checked was points. I reckon I could test the coils and condensers.


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[evinrude7]

This could be incidental, and I assume you already checked... but there is absolutely no air leaks from 1 and 4?  You checked top, bottom, left, and right with some PB Blaster at the airbox and intake side?

Still operating on the assumption that the outer two plugs are 1-4 and that it's probably ignition related, gap may be slightly off for 1-4.  Did you use a timing light to verify the timing?  There is some test procedures in the service manual to test the coils.  You'd have to look it up as I don't know what points to probe or what the values are supposed to be.

Yes done with a light. I'll check for air leaks.

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[evinrude7]

I'll need to verify this but I do have some decel popping which is a whole lot quieter and dull with the diffusers on these 341s. Need to verify if it's coming from 1 and 4. Almost certain about 1.

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[Maraakate]

You also mention a K&N air filter in there.  For #$%*s and giggles have you tried going back to the original air filter?  Sometimes they can make things overly rich if it's excessively oiled.  It may also change the air/fuel ratio which means having to experiment with jets, which may be "fun" to you but it's not to me.

For what it's worth, and I have not verified this, but I've heard plenty of anecdotal evidence from Hondaman on these forums that air leaks on these particular type of carbs used on the SOHC4's will actually cause a rich condition.  If there is an air leak and this is true, then that could be the issue.

Also, keep in mind that coils can read good on a meter, but may not show a problem until they get warmed up and then the resistance changes and causes funny things to happen.  You can always swap the coil from one side to the other and see if the plug colours move from 1-4 to 2-3.

Condensor is probably OK.  A lot of people blame them, but they seem to be fairly reliable if the bike is stock.  There's a few tests you can do, but the easiest one is to run the bike with the cover off in a dimly light area or at night and see if the points are excessively arcing.  If they are you can get still get new OEM condensors or you can buy Hondaman's transitorized ignition box which bypasses the condensors, but keeps the points.  This will prevent the points from wearing out further, eliminating the arcing.

Some slight decel popping is probably normal IF these carbs don't have an air cut-off valve.  I don't know if they do, but if it's mid 70s then I would say probably not.  Someone else will have to chime in on that because I don't know what a total stock mid-70s era 750 is supposed to sound like during decel.  From what I have read on here though, it is apparently normal and that the stock exhaust was designed to hide it quite a bit.

[Maraakate]

See http://www.dansmc.com/carb15.htm for more info on air cut-off valves if you are interested.

[evinrude7]

You also mention a K&N air filter in there.  For #$%*s and giggles have you tried going back to the original air filter?  Sometimes they can make things overly rich if it's excessively oiled.  It may also change the air/fuel ratio which means having to experiment with jets, which may be "fun" to you but it's not to me.

For what it's worth, and I have not verified this, but I've heard plenty of anecdotal evidence from Hondaman on these forums that air leaks on these particular type of carbs used on the SOHC4's will actually cause a rich condition.  If there is an air leak and this is true, then that could be the issue.

Also, keep in mind that coils can read good on a meter, but may not show a problem until they get warmed up and then the resistance changes and causes funny things to happen.  You can always swap the coil from one side to the other and see if the plug colours move from 1-4 to 2-3.

Condensor is probably OK.  A lot of people blame them, but they seem to be fairly reliable if the bike is stock.  There's a few tests you can do, but the easiest one is to run the bike with the cover off in a dimly light area or at night and see if the points are excessively arcing.  If they are you can get still get new OEM condensors or you can buy Hondaman's transitorized ignition box which bypasses the condensors, but keeps the points.  This will prevent the points from wearing out further, eliminating the arcing.

Some slight decel popping is probably normal IF these carbs don't have an air cut-off valve.  I don't know if they do, but if it's mid 70s then I would say probably not.  Someone else will have to chime in on that because I don't know what a total stock mid-70s era 750 is supposed to sound like during decel.  From what I have read on here though, it is apparently normal and that the stock exhaust was designed to hide it quite a bit.

I have Mark's ignition on there. So it actually bypasses the condensers?  I don't believe I over oiled the air filter. Certainly not like I used to on my Jeeps.

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[evinrude7]

See http://www.dansmc.com/carb15.htm for more info on air cut-off valves if you are interested.

Thanks

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[Maraakate]

I have Mark's ignition on there. So it actually bypasses the condensers?  I don't believe I over oiled the air filter. Certainly not like I used to on my Jeeps.

I believe so.

[PeWe]

Needles are not stock?

[evinrude7]

Needles are not stock?

could be.  i need to pull the carbs apart when i have a few hours of free time.  going to look into all of these suggestions.  very appreciative of the replies.