Topic: Spark Plugs and fuel issues

[Mark K]

I posted this the other day, but I think it may have gotten buried. If anyone has any suggestions, I really appreciate any and all help!

Pulled #3 carb pilot jet, completely clogged, unable to get it opened up. Replaced pilot jet w/same size from rebuild kit. Replacing the pilot jet fixed the cold #3 cylinder issue.

New problem, #2 carb overflow pouring fuel, just like #3 carb did, will reinstall old float, that fixed the same issue on #3 carb.

Ran the bike for about 15 minutes (w/2 fans blowing on the engine), engine idling between 1100-1300rpm. Used an IR thermometer to 'read' the pipe temps, 2-3" from the exhaust port.

Exhaust pipe temps
#1 - 182*F
#2 - 179*F
#3 - 177*F
#4 - 108*F
Checked each one numerous times and kept getting 108*F on #4 pipe.

Pulled the plugs, gap still set at .026" All plugs looked black and sooty. I cleaned the plugs after pictures and reinstalled. Plugs are basically brand new NGK D8EA, engine has only run for about an hour total time since rebuild, have gas tank issue trying to work thru, as well as the other issues.

Link to original post - http://forums.sohc4.net/index.php/topic,193060.0.html

Pictures of the plugs

[HondaMan]

I'd suggest cleaning the [probably over-oiled] K&N air filter.
Reason: K&N's instructions are poor about 'how to oil' these filters, particularly when new (and confusing at best after a cleaning!). It takes very, very little oil to make them work, and they almost always get over-oiled by newbies trying to use them.

So, try this:
Wash the filter with soapy, warm water, then let it dry at least overnight. This will make the gauze a very slight pink color. The pink is telling you that it is still oiled: it takes 3 washings to actually get all the oil out. Now, put it back into the airbox and try your experiments over again.

Another thought: a CB750K3 idling for 15 minutes WILL foul a set of D8EA sparkplugs. These plugs are too cold for the engine. They were originally the type D8ES plugs until the EPA and Nippon Denso (who makes NGK plugs) got into a fight around 2002 or so, and the EPA forced Denso to alter the plugs to a non-superwide heatrange type in the end of that battle. The original D8ES plugs in these engines fouled quickly in city traffic in the 1970s, and Honda deemed the D7ES to be a poor substitute (despite using them in the CB500/550, and all other 4-cylinder non-Honda Japanese bikes) so they asked ND to create an in-between heatrange plug, which became the D8ES-L. This plug isn't made today except in the resistor version (DR8ES-L), which you can use, or you can get it in the ND version as X24ES-U from Nippon Denso. This is the same plug as the D8ES-L in heatrange, but has a smaller tip so it ignites fuel a little better, especially when wet in slow-speed running.

Now, a basic rule about the CB750 (and other SOHC4 engines) is: don't idle them for long periods of time. They will foul the sparkplugs, all of them, when this is done, with the possible exception of the 750K7/8 engines, which which have smog-controlled carbs called "PD" type that run leaner and hotter below 2500 RPM by design.

Next: turn your air screws on the carbs inward a bit, like to 7/8 turn instead of 1.0 turn out. The bodies of the carbs have now eroded away a bit, from both MTBE gasolines in the 1980s-1990s era and previous too-tight adjustment cycles by previous owners. In other terms: the 7/8 turn opening now is likely equal to the old 1.0 turn opening when the carbs were both new and un-abused. This will lean out the idle mixture slightly and help balance the vacuum a little better between cylinders.

Make sure your ignition timing is dead-on the "T" marks at idle, and not advanced beyond them. If the timing advances too soon it makes the engine spit back at the carbs, which causes the incoming mixture to become too rich below about 3000 RPM. This contributes quickly to wet plugs, which then foul.

[Scootch]

I looked this and the other post but I couldn't find what size jets are used...

[scottly]

 All plugs looked black and sooty. I cleaned the plugs after pictures and reinstalled.

How did you clean the plugs? The best way I know of is to burn the black off the center electrode with a propane torch.

[Shtonecb500]

 All plugs looked black and sooty. I cleaned the plugs after pictures and reinstalled.

How did you clean the plugs? The best way I know of is to burn the black off the center electrode with a propane torch.

why cant u use a wire brush or something?

[scottly]

 All plugs looked black and sooty. I cleaned the plugs after pictures and reinstalled.

How did you clean the plugs? The best way I know of is to burn the black off the center electrode with a propane torch.

why cant u use a wire brush or something?

Because it don't work worth a #$%*.

[dave500]

wire wheeling or brush leaves metallic deposits on plugs especially the insulator nose,that is supposed to insulate.

[Mark K]

I'd suggest cleaning the [probably over-oiled] K&N air filter.
Reason: K&N's instructions are poor about 'how to oil' these filters, particularly when new (and confusing at best after a cleaning!). It takes very, very little oil to make them work, and they almost always get over-oiled by newbies trying to use them.

So, try this:
Wash the filter with soapy, warm water, then let it dry at least overnight. This will make the gauze a very slight pink color. The pink is telling you that it is still oiled: it takes 3 washings to actually get all the oil out. Now, put it back into the airbox and try your experiments over again.

Another thought: a CB750K3 idling for 15 minutes WILL foul a set of D8EA sparkplugs. These plugs are too cold for the engine. They were originally the type D8ES plugs until the EPA and Nippon Denso (who makes NGK plugs) got into a fight around 2002 or so, and the EPA forced Denso to alter the plugs to a non-superwide heatrange type in the end of that battle. The original D8ES plugs in these engines fouled quickly in city traffic in the 1970s, and Honda deemed the D7ES to be a poor substitute (despite using them in the CB500/550, and all other 4-cylinder non-Honda Japanese bikes) so they asked ND to create an in-between heatrange plug, which became the D8ES-L. This plug isn't made today except in the resistor version (DR8ES-L), which you can use, or you can get it in the ND version as X24ES-U from Nippon Denso. This is the same plug as the D8ES-L in heatrange, but has a smaller tip so it ignites fuel a little better, especially when wet in slow-speed running.

Now, a basic rule about the CB750 (and other SOHC4 engines) is: don't idle them for long periods of time. They will foul the sparkplugs, all of them, when this is done, with the possible exception of the 750K7/8 engines, which which have smog-controlled carbs called "PD" type that run leaner and hotter below 2500 RPM by design.

Next: turn your air screws on the carbs inward a bit, like to 7/8 turn instead of 1.0 turn out. The bodies of the carbs have now eroded away a bit, from both MTBE gasolines in the 1980s-1990s era and previous too-tight adjustment cycles by previous owners. In other terms: the 7/8 turn opening now is likely equal to the old 1.0 turn opening when the carbs were both new and un-abused. This will lean out the idle mixture slightly and help balance the vacuum a little better between cylinders.

Make sure your ignition timing is dead-on the "T" marks at idle, and not advanced beyond them. If the timing advances too soon it makes the engine spit back at the carbs, which causes the incoming mixture to become too rich below about 3000 RPM. This contributes quickly to wet plugs, which then foul.

As ALWAYS Mark, thank you for your time and knowledge. It is/will be extremely helpful, thank you for taking the time to post it.

I will clean the air filter and adjust the air screws to make them 7/8 turn per your suggestion. And probably pick up a set of the spark plugs you mentioned to have on hand, in case the other suggestions don't fix the issue.

I will need to buy a timing gun, any suggestions from anyone as to brand/model that won't break the bank would be appreciated??

Thanks.

[Mark K]

I looked this and the other post but I couldn't find what size jets are used...

Sorry Scootch, that has been bothering me too. I had to go back in my posts to find the main jets I'm using, which is just sad that I couldn't remember the main jet number. I remembered the pilot jet because I just pulled one the other day. The carbs had 130 main jets and 40 pilot jets, previous owner had a big bore kit, since removed, too long of a story for this answer. I had to install the 110 main jets from the rebuild kit and the 40 pilot jets, per suggestion from someone here. Freshly rebuilt stock engine, except bored .50 over (I'm probably not saying that quite right), stock airbox w/K&N oiled air filter and a Delkevic 4 into 1 exhaust.

[Mark K]

 All plugs looked black and sooty. I cleaned the plugs after pictures and reinstalled.

How did you clean the plugs? The best way I know of is to burn the black off the center electrode with a propane torch.

Scottly, I used a small wire brush to clean the soot off of the plugs. I remember when I was growing up, my dad had a plug cleaner that used some kind of sand or something, filled it with the cleaning material, plugged it in, put the plug in and turned it on. A few seconds later, the plug came out clean. Anyway, I guess I used the cave man method and used a wire brush. I have a propane torch I could use next time...

[Deltarider]

Rub it over a doormat. Your neighbour's.

[TwoTired]

The center electrode insulator is rather coarse porcelain, as abrasive as sand paper.  This takes metal off a wire brush and embeds it on the surface of the porcelain.  Adding metal to an insulator gives spark a channel to travel that is not across the gap.  Replacing carbon soot with a metal deposit rather defeats the effort of cleaning them.

Media blast them, torch, or run them in a very lean engine to burn off the soot.

[HondaMan]

 All plugs looked black and sooty. I cleaned the plugs after pictures and reinstalled.

How did you clean the plugs? The best way I know of is to burn the black off the center electrode with a propane torch.

Scottly, I used a small wire brush to clean the soot off of the plugs. I remember when I was growing up, my dad had a plug cleaner that used some kind of sand or something, filled it with the cleaning material, plugged it in, put the plug in and turned it on. A few seconds later, the plug came out clean. Anyway, I guess I used the cave man method and used a wire brush. I have a propane torch I could use next time...

I had one of those sandblast plug cleaners for decades, hooked to the 12volt battery in the car/bike. It was truly excellent.
When it finally died I discovered that no one else makes anything like it now!

[newday777]

I had one of those sandblast plug cleaners for decades, hooked to the 12volt battery in the car/bike. It was truly excellent.
When it finally died I discovered that no one else makes anything like it now! 😞

I remember using the air powered plug cleaners at the shop in the 70s. Interesting that there was 12 volt version.

[bryanj]

Back in the 70's in the trade we had a Champion air powered plug cleaner with an air pressured spark testing point so you could see what the spark did under pressure.
Used to have to take it apart regularly to rescure the rubber pressur tip knocked off when rotating plug being cleaned, when rescued there were 8 lined up on the shelf, every new bag of grit had 2 new nozzles

[dave500]

we had that same champion unit early 70s when i was an apprentice,the spark would go inches through free air,any coachroach or grass hopper we found didnt stand a chance!

[Deltarider]

[...]
Now, a basic rule about the CB750 (and other SOHC4 engines) is: don't idle them for long periods of time. They will foul the sparkplugs, all of them, [...]

This ^!! Realise that nowadays our bikes idle much more then back then.
1. There's much more traffic.
2. Members here tend to do a lot more 'maintenance' than then, which can include idling for long periods of time. For instance: unneeded syncs.
3. Realise that sparkplugs in our engines with these oldstyle carbs have to cope with an almost impossible task: stay healthy from 1000 - 10.000 rpm.
4. I recommend: idle as little as possible and treat your bike to an 'Italian tuning' every now and then.

[BenelliSEI]

Back in the 70's in the trade we had a Champion air powered plug cleaner with an air pressured spark testing point so you could see what the spark did under pressure.
Used to have to take it apart regularly to rescure the rubber pressur tip knocked off when rotating plug being cleaned, when rescued there were 8 lined up on the shelf, every new bag of grit had 2 new nozzles

We had a Champion Spark Plug cleaner and a Bosch Distributor tester too. I recently saw a guy pay $800 for a Champion unit in absolutely perfect condition. Must be some “man cave”!

[Floshenbarnical]

[...]
Now, a basic rule about the CB750 (and other SOHC4 engines) is: don't idle them for long periods of time. They will foul the sparkplugs, all of them, [...]

This ^!! Realise that nowadays our bikes idle much more then back then.
1. There's much more traffic.
2. Members here tend to do a lot more 'maintenance' than then, which can include idling for long periods of time. For instance: unneeded syncs.
3. Realise that sparkplugs in our engines with these oldstyle carbs have to cope with an almost impossible task: stay healthy from 1000 - 10.000 rpm.
4. I recommend: idle as little as possible and treat your bike to an 'Italian tuning' every now and then.

I italian tune mine almost every day, there's a stretch of highway between my exit and my work exit where there isn't an inch for a cop to post up so if the coast is clear behind me it's a straight 3-mile drag on fresh asphalt. I call it the cannonball run

[grcamna2]

I'd suggest cleaning the [probably over-oiled] K&N air filter.
Reason: K&N's instructions are poor about 'how to oil' these filters, particularly when new (and confusing at best after a cleaning!). It takes very, very little oil to make them work, and they almost always get over-oiled by newbies trying to use them.

So, try this:
Wash the filter with soapy, warm water, then let it dry at least overnight. This will make the gauze a very slight pink color. The pink is telling you that it is still oiled: it takes 3 washings to actually get all the oil out. Now, put it back into the airbox and try your experiments over again.

Another thought: a CB750K3 idling for 15 minutes WILL foul a set of D8EA sparkplugs. These plugs are too cold for the engine. They were originally the type D8ES plugs until the EPA and Nippon Denso (who makes NGK plugs) got into a fight around 2002 or so, and the EPA forced Denso to alter the plugs to a non-superwide heatrange type in the end of that battle. The original D8ES plugs in these engines fouled quickly in city traffic in the 1970s, and Honda deemed the D7ES to be a poor substitute (despite using them in the CB500/550, and all other 4-cylinder non-Honda Japanese bikes) so they asked ND to create an in-between heatrange plug, which became the D8ES-L. This plug isn't made today except in the resistor version (DR8ES-L), which you can use, or you can get it in the ND version as X24ES-U from Nippon Denso. This is the same plug as the D8ES-L in heatrange, but has a smaller tip so it ignites fuel a little better, especially when wet in slow-speed running.

Now, a basic rule about the CB750 (and other SOHC4 engines) is: don't idle them for long periods of time. They will foul the sparkplugs, all of them, when this is done, with the possible exception of the 750K7/8 engines, which which have smog-controlled carbs called "PD" type that run leaner and hotter below 2500 RPM by design.

Next: turn your air screws on the carbs inward a bit, like to 7/8 turn instead of 1.0 turn out. The bodies of the carbs have now eroded away a bit, from both MTBE gasolines in the 1980s-1990s era and previous too-tight adjustment cycles by previous owners. In other terms: the 7/8 turn opening now is likely equal to the old 1.0 turn opening when the carbs were both new and un-abused. This will lean out the idle mixture slightly and help balance the vacuum a little better between cylinders.

Make sure your ignition timing is dead-on the "T" marks at idle, and not advanced beyond them. If the timing advances too soon it makes the engine spit back at the carbs, which causes the incoming mixture to become too rich below about 3000 RPM. This contributes quickly to wet plugs, which then foul.

Mark,you say the Nippon Denso X24ES-U is very similar to the original NGK D8ES-L,I understand that.
The company name of ND has been changed to just Denso:does this info also apply to the Denso X24ES-U in the same way ?

[HondaMan]

I'd suggest cleaning the [probably over-oiled] K&N air filter.
Reason: K&N's instructions are poor about 'how to oil' these filters, particularly when new (and confusing at best after a cleaning!). It takes very, very little oil to make them work, and they almost always get over-oiled by newbies trying to use them.

So, try this:
Wash the filter with soapy, warm water, then let it dry at least overnight. This will make the gauze a very slight pink color. The pink is telling you that it is still oiled: it takes 3 washings to actually get all the oil out. Now, put it back into the airbox and try your experiments over again.

Another thought: a CB750K3 idling for 15 minutes WILL foul a set of D8EA sparkplugs. These plugs are too cold for the engine. They were originally the type D8ES plugs until the EPA and Nippon Denso (who makes NGK plugs) got into a fight around 2002 or so, and the EPA forced Denso to alter the plugs to a non-superwide heatrange type in the end of that battle. The original D8ES plugs in these engines fouled quickly in city traffic in the 1970s, and Honda deemed the D7ES to be a poor substitute (despite using them in the CB500/550, and all other 4-cylinder non-Honda Japanese bikes) so they asked ND to create an in-between heatrange plug, which became the D8ES-L. This plug isn't made today except in the resistor version (DR8ES-L), which you can use, or you can get it in the ND version as X24ES-U from Nippon Denso. This is the same plug as the D8ES-L in heatrange, but has a smaller tip so it ignites fuel a little better, especially when wet in slow-speed running.

Now, a basic rule about the CB750 (and other SOHC4 engines) is: don't idle them for long periods of time. They will foul the sparkplugs, all of them, when this is done, with the possible exception of the 750K7/8 engines, which which have smog-controlled carbs called "PD" type that run leaner and hotter below 2500 RPM by design.

Next: turn your air screws on the carbs inward a bit, like to 7/8 turn instead of 1.0 turn out. The bodies of the carbs have now eroded away a bit, from both MTBE gasolines in the 1980s-1990s era and previous too-tight adjustment cycles by previous owners. In other terms: the 7/8 turn opening now is likely equal to the old 1.0 turn opening when the carbs were both new and un-abused. This will lean out the idle mixture slightly and help balance the vacuum a little better between cylinders.

Make sure your ignition timing is dead-on the "T" marks at idle, and not advanced beyond them. If the timing advances too soon it makes the engine spit back at the carbs, which causes the incoming mixture to become too rich below about 3000 RPM. This contributes quickly to wet plugs, which then foul.

Mark,you say the Nippon Denso X24ES-U is very similar to the original NGK D8ES-L,I understand that.
The company name of ND has been changed to just Denso:does this info also apply to the Denso X24ES-U in the same way ?

Yeah, I just got a new box(es) of plugs and I see their new "DENSO" logo on it. They were always known as Nippon Denso before, which I once understood to mean JAPANESE Denso, as opposed to [somewhere else] Denso. These plugs' individual boxes state they are "Designed and Engineered in Japan, made in China" now. It's the same online store I've used for years (Sparkplugs.com). The plugs don't look any different from the ones I've been getting lately, but are quite different-looking above the metal body from my 15-year-old ones in my bike.

[grcamna2]

I'd suggest cleaning the [probably over-oiled] K&N air filter.
Reason: K&N's instructions are poor about 'how to oil' these filters, particularly when new (and confusing at best after a cleaning!). It takes very, very little oil to make them work, and they almost always get over-oiled by newbies trying to use them.

So, try this:
Wash the filter with soapy, warm water, then let it dry at least overnight. This will make the gauze a very slight pink color. The pink is telling you that it is still oiled: it takes 3 washings to actually get all the oil out. Now, put it back into the airbox and try your experiments over again.

Another thought: a CB750K3 idling for 15 minutes WILL foul a set of D8EA sparkplugs. These plugs are too cold for the engine. They were originally the type D8ES plugs until the EPA and Nippon Denso (who makes NGK plugs) got into a fight around 2002 or so, and the EPA forced Denso to alter the plugs to a non-superwide heatrange type in the end of that battle. The original D8ES plugs in these engines fouled quickly in city traffic in the 1970s, and Honda deemed the D7ES to be a poor substitute (despite using them in the CB500/550, and all other 4-cylinder non-Honda Japanese bikes) so they asked ND to create an in-between heatrange plug, which became the D8ES-L. This plug isn't made today except in the resistor version (DR8ES-L), which you can use, or you can get it in the ND version as X24ES-U from Nippon Denso. This is the same plug as the D8ES-L in heatrange, but has a smaller tip so it ignites fuel a little better, especially when wet in slow-speed running.

Now, a basic rule about the CB750 (and other SOHC4 engines) is: don't idle them for long periods of time. They will foul the sparkplugs, all of them, when this is done, with the possible exception of the 750K7/8 engines, which which have smog-controlled carbs called "PD" type that run leaner and hotter below 2500 RPM by design.

Next: turn your air screws on the carbs inward a bit, like to 7/8 turn instead of 1.0 turn out. The bodies of the carbs have now eroded away a bit, from both MTBE gasolines in the 1980s-1990s era and previous too-tight adjustment cycles by previous owners. In other terms: the 7/8 turn opening now is likely equal to the old 1.0 turn opening when the carbs were both new and un-abused. This will lean out the idle mixture slightly and help balance the vacuum a little better between cylinders.

Make sure your ignition timing is dead-on the "T" marks at idle, and not advanced beyond them. If the timing advances too soon it makes the engine spit back at the carbs, which causes the incoming mixture to become too rich below about 3000 RPM. This contributes quickly to wet plugs, which then foul.

Mark,you say the Nippon Denso X24ES-U is very similar to the original NGK D8ES-L,I understand that.
The company name of ND has been changed to just Denso:does this info also apply to the Denso X24ES-U in the same way ?

Yeah, I just got a new box(es) of plugs and I see their new "DENSO" logo on it. They were always known as Nippon Denso before, which I once understood to mean JAPANESE Denso, as opposed to [somewhere else] Denso. These plugs' individual boxes state they are "Designed and Engineered in Japan,made in China" now. It's the same online store I've used for years (Sparkplugs.com). The plugs don't look any different from the ones I've been getting lately, but are quite different-looking above the metal body from my 15-year-old ones in my bike.

I hope the Chinese 'Denso' brand X24ES-U spark plugs also have the 'in between heat range' feature as you mentioned the Nippon Denso has. I like the old school Made in Japan Nippon Denso X24ES-U plugs and find that they used to last a very long time in daily use,if not fouled prematurely;I do my best to locate NOS X24ES-U Nippon Denso plugs,difficult to locate..

[RAFster122s]

Denso has a plant in Alabama that makes auto electronic stuff, my nephew whom is a mechanical engineer worked for them for a while...