Topic: 2nd opinion on carbs needed

[zerodaydave]

Hey guys -

I just got back from a 2100 mile road trip. Bike did great and would rev clean through with the exception of cutting out quickly from 3/4 to wot. It ran the best at 6500ft, cold temps, which I assume means my mixture is off.

I live in SLC at 4500ft.

My carbs are 064A on a Honda CB750K4.

My main jet was 102 on the trip increased to 105 stock now which is when the problem started. Pilot is 40 (replaced old pilots with new 40s.) Both are Kehnin stamped.

Cleaned emulsion tubes and mixture screws.

Float height 26mm.

Not sure about needle height (which I should check I'm sure.).

3k tune up was just performed. Valves, timing, cam chain, carb synced with new jets 105, 40.

I'm running k&n pods and a 4 in 1.

My issue is ever since putting in the new jets (which are stock) and after all the maintenance my bike idles great (perfect actually) but the moment I put on any throttle it acts like the mixture is rich and just bogs down at any throttle position. What's really strange is in order for the bike not to completely shut down I have to ride with the choke on but even then it's not really rideable. Its confusing because I feel like the mixture is rich. It has rich symptoms but I have to use the choke to keep it going. Makes no sense.

New plugs are a nice tan too.

Should I run the 102s? I was worried it might run lean but I did just do a 2100 mile road trip with that set up and the bike really ran great at other elevations (6500ft). Not mine (4500ft) haha.

I've tried fiddling with the mixture screws 3/4, 1, 1 1/8, 1 1/4. Nothing helps.

Isn't running less than stock a bad idea with pods, 4 in 1, and an altitude of 4500ft.

I'm thinking about checking the needle height but I'm at a point where I'm just hesitant about fiddling with the needle and thinking about going back to 102s.

Kind of confused here on where to go. Bike can't make it down the street and was puking gas out of carb 4 on the side of the road. Checked the float as well and all is good. Even temps on all pipes.

Any guidance?

[scottly]

Hey guys -

 Bike can't make it down the street and was puking gas out of carb 4 on the side of the road. Checked the float as well and all is good.
Any guidance?

Puking gas out of carb #4 is a sign.

[eigenvector]

Having to use choke is a big indicator that it isn't rich.

If you run with choke on and the plugs are a nice tan - you're way too lean.

[zerodaydave]

I know that's what's confusing me. I increased the jet size to stock from when the bike was running really good on a main jet size down from stock and now it's running so lean it can't run? Mixture screws are of no help.

[TwoTired]

It ran the best at 6500ft, cold temps, which I assume means my mixture is off.

Higher altitudes mean less oxygen available, and going leaner makes the the engine run better.

I'm running k&n pods and a 4 in 1.

"Pods" generally shorten the intake tract and bring outside atmospheric pressure closer to the carb throat.  Raising the pressure in the carb throat means less fuel can be pushed through fuel metering jets.  Pods and an open 4 into 1 usually lean any of the stock metering device selections.

My issue is ever since putting in the new jets (which are stock) and after all the maintenance my bike idles great (perfect actually) but the moment I put on any throttle it acts like the mixture is rich and just bogs down at any throttle position.

What makes you think the stumble is from an over rich condition?

My metric is related to how the engine recovers from the stumble.  If it burbles back to producing power, the mixture was too rich during stumble.  If the engine recovers cleanly, like it was suddenly switched back on, it was too lean during the stumble.

You should describe to us how the engine recovered after the "bog".

What's really strange is in order for the bike not to completely shut down I have to ride with the choke on but even then it's not really rideable. Its confusing because I feel like the mixture is rich. It has rich symptoms but I have to use the choke to keep it going. Makes no sense.

What are these "rich symptoms" you've identified?  Explain those, and elaborate.

Needing choke to run is an indicator of a too lean mixture.  Of course with the choke butterflies closed the engine can't breathe and get much oxygen to make power.

Isn't running less than stock a bad idea with pods, 4 in 1, and an altitude of 4500ft.

Well, er, yes.  But, so is running pods if you don't have to, imo.

Bike can't make it down the street and was puking gas out of carb 4 on the side of the road

Isn't that a pretty clear indicator of something to investigate and fix?  You could well have multiple problems to solve.  Some of which just might be self inflicted by choosing Pods.  But, if you like sorting out the fuctional engineering changes you've made to the bike, you can learn a lot about engine tuning and just what they need to run properly.

Cheers,

[scottly]

Is it still pissing gas out of the #4 carb? Did you F something up when you changed the jets? Have you done a clear tube test on the fuel levels in the float bowls?
The mixture screws are for idle, and have little effect at larger throttle openings. 

[zerodaydave]

No it's not passing gas any longer on carb 4.

I haven't performed a clear tube test yet.

I was messing around with the mixture screws because I understand it they effect idle to some acceleration off of idle.

It's totally possible that I screwed something up.

[zerodaydave]

It ran the best at 6500ft, cold temps, which I assume means my mixture is off.

Higher altitudes mean less oxygen available, and going leaner makes the the engine run better.

I'm running k&n pods and a 4 in 1.

"Pods" generally shorten the intake tract and bring outside atmospheric pressure closer to the carb throat.  Raising the pressure in the carb throat means less fuel can be pushed through fuel metering jets.  Pods and an open 4 into 1 usually lean any of the stock metering device selections.

My issue is ever since putting in the new jets (which are stock) and after all the maintenance my bike idles great (perfect actually) but the moment I put on any throttle it acts like the mixture is rich and just bogs down at any throttle position.

What makes you think the stumble is from an over rich condition?

My metric is related to how the engine recovers from the stumble.  If it burbles back to producing power, the mixture was too rich during stumble.  If the engine recovers cleanly, like it was suddenly switched back on, it was too lean during the stumble.

You should describe to us how the engine recovered after the "bog".

What's really strange is in order for the bike not to completely shut down I have to ride with the choke on but even then it's not really rideable. Its confusing because I feel like the mixture is rich. It has rich symptoms but I have to use the choke to keep it going. Makes no sense.

What are these "rich symptoms" you've identified?  Explain those, and elaborate.

Needing choke to run is an indicator of a too lean mixture.  Of course with the choke butterflies closed the engine can't breathe and get much oxygen to make power.

Isn't running less than stock a bad idea with pods, 4 in 1, and an altitude of 4500ft.

Well, er, yes.  But, so is running pods if you don't have to, imo.

Bike can't make it down the street and was puking gas out of carb 4 on the side of the road

Isn't that a pretty clear indicator of something to investigate and fix?  You could well have multiple problems to solve.  Some of which just might be self inflicted by choosing Pods.  But, if you like sorting out the fuctional engineering changes you've made to the bike, you can learn a lot about engine tuning and just what they need to run properly.

Cheers,

Hey Two Tired-

It never really produces any power it just sputters all through the throttle range and then eventually dies. If I turn on the choke all the way it will get better but still sputter. As I slowly disengage the choke while riding there is a point where it will have a burst of power. This is all happening over about a minute. By the end I'm holding the throttle wide open and barely doing 20mph. The bike will continue until it eventually dies. No power at all. Just lots of sputtering.

To be honest I'm still trying to get the feel of lean and rich symptoms. The choke seems like an indicator that it is indeed running lean but I increased the main jet size and replaced the old pilots so I'm just confused as to why it would be suddenly running so lean.

I think my next step is verify that the needle is in the 4th position. If it has 102s in it maybe it was leaned out?

[TwoTired]

I don't think you could have tan plug deposits if it is running rich.  They would be black and have soft carbon on them.

If you put in new spark plugs, do the run issues improve, at least temporarily?

Tell me about your ignition components.

I guess I don't know how to interpret "sputtering", related to rich or lean.  I would guess that's rich, but spark plugs would show black insulators.

Cheers,

[zerodaydave]

It's a dyna coil 5.0 ohm. The ignition system is less than a year old. No problems with it to date.

Added new plugs they are far from black. White to light tan. Run issues didn't improve at all with new plugs.

It's hard to describe sputtering over the internet. The bike idles fine. If I add any gas at all it will sputter and die. If I turn on the choke it will run. I can ride with a wot but can't even make it over 30mph. No power. It gets worse over time. Just sputtering and eventually difficulty starting.

[evinrude7]

It's a dyna coil 5.0 ohm. The ignition system is less than a year old. No problems with it to date.

Added new plugs they are far from black. White to light tan. Run issues didn't improve at all with new plugs.

It's hard to describe sputtering over the internet. The bike idles fine. If I add any gas at all it will sputter and die. If I turn on the choke it will run. I can ride with a wot but can't even make it over 30mph. No power. It gets worse over time. Just sputtering and eventually difficulty starting.

TT will have more knowledge than i can lay down here but what if you took some masking tape and blocked off part of the pod filters.  that will let you know if you're simply sucking too much air.  at least you'll find the problem.  it's my understanding with pods you have to over jet the carbs, adjust the needle height, etc to compensate for the non-stock air.   

[TwoTired]

It's a dyna coil 5.0 ohm. The ignition system is less than a year old. No problems with it to date.

Points or electronic?   Plug cap status?  What HT wires are you using?  Resistor plugs?
Can you measure the voltage that the coils are getting on the black/wht wires?

It's hard to describe sputtering over the internet. The bike idles fine. If I add any gas at all it will sputter and die. If I turn on the choke it will run. I can ride with a wot but can't even make it over 30mph. No power. It gets worse over time. Just sputtering and eventually difficulty starting.

What behavior changes occur when using only partial choke?

Is "sputtering" related to a random fire pattern?  Or does it seem like it just shut off when opening the throttle.

Can you describe how the engine recovers from the "sputtering"; clean running return, or random fire transition.

Cheers,

[zerodaydave]

It's a dyna coil 5.0 ohm. The ignition system is less than a year old. No problems with it to date.

Points or electronic?   Plug cap status?  What HT wires are you using?  Resistor plugs?
Can you measure the voltage that the coils are getting on the black/wht wires?

It's hard to describe sputtering over the internet. The bike idles fine. If I add any gas at all it will sputter and die. If I turn on the choke it will run. I can ride with a wot but can't even make it over 30mph. No power. It gets worse over time. Just sputtering and eventually difficulty starting.

What behavior changes occur when using only partial choke?

Is "sputtering" related to a random fire pattern?  Or does it seem like it just shut off when opening the throttle.

Can you describe how the engine recovers from the "sputtering"; clean running return, or random fire transition.

Cheers,

Electric ignition. Dyna Coil 5 ohm. NGK 8mm wires and caps. Provided pics if that would help. I could measure the voltage on the wires as soon as I get home.

The engine really doesn't recover. It sputters as I continue to ride continuously and rapidly and it gets worse and worse until the point of riding with wot and no power and then eventually stalling out on the side of the road. Even with the choke on it still sputters but has a bit more power. When I put the bike back together I can take a video of it if it's still doing the same thing.

I took the carbs off today. Took out the plugs (attached pics). I think 2/3 look richer then 1/4. I also noticed some gas in POD 1. Took out the jets to make sure they were all the same size (just double checking here). I'm going to check the needle height as well. I read a post where Hondaman said that the needle position with 105's should be 4th from the top or 3rd from the top for 110's. I just wanted to make sure they are in the right position. Is there anything else I should check with the Carbs off?

Thanks! I'm obviously still learning. This site is awesome.

[zerodaydave]

Ignition pics.

[flybox1]

Yes, plugs are very rich, but unless you did a  plug chop at a specific throttle position, they dont tell you WHERE you are rich...
Could be pilot, needle clip or main.

Do a proper plug chop with NEW plugs, starting with idle, and dial in your IMS.

[TwoTired]

The spark plugs are carbon fouling.  The center electrode insulator is getting coated with conductive carbon and shunting spark energy away from the electrode gap.
This is why it is sputtering. You are hearing misfires.  New or cleaned spark plug insulators will make it run better until they too carbon foul.

You need to find out why the cylinders are getting way too much fuel to burn cleanly.  (Besides too much choke operation.)

1.  get the fuel level in the bowls at correct depth/height.

2. Check pilot jet and main jets for size and ensure they haven't been drilled larger than the markings indicate.

3. Check the slide needles for clip position, wear, and check the needle jets for size of orifice and wear.

4. Check emulsion tubes holes for clean and clear.

5. Check that both air jets are clear as well as their passageways.

6. Make sure the air filter is clear to flow.

[zerodaydave]

The spark plugs are carbon fouling.  The center electrode insulator is getting coated with conductive carbon and shunting spark energy away from the electrode gap.
This is why it is sputtering. You are hearing misfires.  New or cleaned spark plug insulators will make it run better until they too carbon foul.

You need to find out why the cylinders are getting way too much fuel to burn cleanly.  (Besides too much choke operation.)

1.  get the fuel level in the bowls at correct depth/height.

2. Check pilot jet and main jets for size and ensure they haven't been drilled larger than the markings indicate.

3. Check the slide needles for clip position, wear, and check the needle jets for size of orifice and wear.

4. Check emulsion tubes holes for clean and clear.

5. Check that both air jets are clear as well as their passageways.

6. Make sure the air filter is clear to flow.

Thanks TwoTired and Flybox1.

They are new plugs. They have about two miles around the house on them. They mostly have sat at idle during the carb sync.

1. I'm afraid to ask this but I've read conflicting information on this forum. I've measured the depth/height of the float bowls at 26mm. Should I also do the clear tube test? If so can anyone provide a good link on how to do this?

2. Both main (105) and pilot (40) jets are new Kehnin jets (stamped).

3. I haven't checked the slide needles. That's my next thing to do.

4. I did clean the emulsion tubes and they are clear.

5. I did clean the mixture screws (air jets?) and they are clear.

6. The pods are new and clear.

[TwoTired]

They are new plugs. They have about two miles around the house on them. They mostly have sat at idle during the carb sync.

They aren't new plugs anymore, and they are fouled and effectively inoperative.  Unless, you clean them, they may as well have been hit with a sledge hammer.

1. I'm afraid to ask this but I've read conflicting information on this forum. I've measured the depth/height of the float bowls at 26mm. Should I also do the clear tube test? If so can anyone provide a good link on how to do this?

I like to deal with knowns as a foundation.  Used to be, a bowl measurement was enough.  But, with today's part variations, one can't be certain without a clear tube test.  Flybox will likely show his nice pictures of how to perform the clear tube test to verify fuel level in the bowls at correct level.


I'm wondering if you still have the slide needle jet in the carbs.  The symptoms do match carbs assembled without them.

Do check the slide needles.

Cheers,

[zerodaydave]

I'm wondering if you still have the slide needle jet in the carbs.  The symptoms do match carbs assembled without them.

Do check the slide needles.
 

Can you explain this? I was just going to check the needle position since I have the carbs off. Is that what you mean?

[TwoTired]

I'm wondering if you still have the slide needle jet in the carbs.  The symptoms do match carbs assembled without them.

Do check the slide needles.
 

Can you explain this? I was just going to check the needle position since I have the carbs off. Is that what you mean?

Yes, to the needle position.  But, the slide needles poke into the Slide needle jets located at the end of the mains emulsion tube.
I'm not intimate with the CB750 carb prior to the PDs.  But, I understand that the slide needle jet can separate from the mains emulsion tube.  I've seen pictures where they were missing and definitely caused problems.

Someone unfamiliar may not notice they are missing.  I'm asking you to check they are present in your carbs, and to find out if they are worn.   Missing needle jets will cause rich run issues as will jets that have worn.  Same for worn slide needles.  Yes check position, also check for wear damage.

Cheers,

[flybox1]

1. I'm afraid to ask this but I've read conflicting information on this forum. I've measured the depth/height of the float bowls at 26mm. Should I also do the clear tube test? If so can anyone provide a good link on how to do this?

Here's that picture 
The proper procedure is to verify/adjust your floats to factory setting, and then use the clear tube test to verify your floats give the carbs the proper fuel level.  Any aftermarket float valve and or seat will dramatically change the bowl fuel level. 

[zerodaydave]

1. I'm afraid to ask this but I've read conflicting information on this forum. I've measured the depth/height of the float bowls at 26mm. Should I also do the clear tube test? If so can anyone provide a good link on how to do this?

Here's that picture 
The proper procedure is to verify/adjust your floats to factory setting, and then use the clear tube test to verify your floats give the carbs the proper fuel level.  Any aftermarket float valve and or seat will dramatically change the bowl fuel level. 

Thanks for the pictures. Just to verify. Check the factory settings of 26mm and then the fuel level with the fuel level being the priority if I have to make an adjustment correct?

[PeWe]

My CB750-K6 had 105 mains, 40 pilots. With 4-1 mains jumped up to 115. Pods upon that should need even more, maybe 120-125, pilots still 40.
Higher living less fuel when air is less by the altitude.
- Ignition OK?"

[zerodaydave]

Yes, to the needle position.  But, the slide needles poke into the Slide needle jets located at the end of the mains emulsion tube.
I'm not intimate with the CB750 carb prior to the PDs.  But, I understand that the slide needle jet can separate from the mains emulsion tube.  I've seen pictures where they were missing and definitely caused problems.

Someone unfamiliar may not notice they are missing.  I'm asking you to check they are present in your carbs, and to find out if they are worn.   Missing needle jets will cause rich run issues as will jets that have worn.  Same for worn slide needles.  Yes check position, also check for wear damage.

Cheers,

I'll check the needles today and report back. I have suspicion that the original guy that I bought the bike from changed the needle position to compensate for the 102 main jets. When looking at the needles is there something else I should be looking at for damage other than the needle being bent or rounded?
 

[zerodaydave]

My CB750-K6 had 105 mains, 40 pilots. With 4-1 mains jumped up to 115. Pods upon that should need even more, maybe 120-125, pilots still 40.
Higher living less fuel when air is less by the altitude.
- Ignition OK?"

I was thinking about going just 1 size bigger to 110's from stock to compensate for the pods and exhaust but I'm already running too rich. I may reevaluate jet size once I figure out why I'm currently running so rich. But for now I'm just trying to get the bike back to stock with a good mixture so that I can decide if that's appropriate. I think 115 would be to much for my altitude but then again what do I know haha .. at least right now 115 would be way to much.