Topic: Air screw to reduce decel popping?

[Bigmant]

  So, to sum it up, the answer is a definite maybe, one or the other unless it's either the intake or exhaust leaking.
  The copper washers can also be leaking air if the exhaust flanges have been off, and they weren't replaced.

Copper gaskets were all new when I put on the 4:1 exhaust. BUT today I was able to get maybe a half turn to a full turn on the exhaust flange bolts, so maybe it was leaking air… I plan to take a ride tomorrow and bring a screw driver with me to test some things out. More to follow!

[Bigmant]

Ok, update. The mixture screw seems to make no difference going counterclockwise. The bike will start to stumble, I’ll increase the idle screw so it doesn’t die and the popping will continue. The only thing that seems to make a difference is the mixture screws ALL the way in… the bike has less popping then,  but not eliminated. That leads me to believe that perhaps there is an air leak at the intake boots that connect the carbs to the heads. Thoughts?

Unless going counterclockwise is cutting off air… in which case my logic is all messed up haha

[Medyo Bastos]

Try ~> http://www.hondachopper.com/garage/carb_info/idle_screw_mod/idle_screw_mod.html


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[Bigmant]

Try ~> http://www.hondachopper.com/garage/carb_info/idle_screw_mod/idle_screw_mod.html


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Medyo, that is AWESOME info. Have you tried this before to success? Interesting that this confirms my suspicion that the bike runs better with the screws all the way in but still not perfect.

[Medyo Bastos]

Yes, thats why i linked it for you! doggy has more useful carb info if you follow the links on top


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[newday777]

Ok, update. The mixture screw seems to make no difference going counterclockwise. The bike will start to stumble, I’ll increase the idle screw so it doesn’t die and the popping will continue. The only thing that seems to make a difference is the mixture screws ALL the way in… the bike has less popping then,  but not eliminated. That leads me to believe that perhaps there is an air leak at the intake boots that connect the carbs to the heads. Thoughts?

Unless going counterclockwise is cutting off air… in which case my logic is all messed up haha

Go back to Hondaman's reply, #12. Wasn't your reply that you have aftermarket intake boots? Did you get stock boots from Honda yet?
To test for leaks, use an unlit propane torch on very low gas flow, unlit, so as you pass over a leak the rpms will rise. Report back what you find.

[M 750K6]

Definitely worth another check through that there are no leaks, exhaust headers too. There are thin rubber gaskets in the top of the carb (in the roundtop, above the needle) that can harden.

You may have to live with it. If it's not too bad, it won't do any harm if you're not too lean on throttle openings.

[tctreppin]

i love this page ,the experience hereis phenomenal,i ve been doing this for 20 yrs with a clymers guide then i found this forum and i have learned so much,thank u all


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[PeWe]

My K2 had loud bubbling sound at throttle roll offs with my old K6 carbs. Like a huge loud popcorn machine.

It did not matter how I adjusted the air screws or other settings. I could change richer and leaner which was visible on the spark plugs.

Same carbs did not cause that sound back in the 80's with loud 4-1 and pods

It had some bubbling sound with stock HM341 4-4 and stock airbox the years before.

2019-2023-06 a rather loud 4-4 and air box.

I think a deep clean in an ultrasonic cleaner should help. Can be the small holes Mark mentioned.  Vent holes to float chambers.  All small passages might need a clean too.

The bike does not pop that hard and much with the 064A carbs I bought in pieces the seller claimed was cleaned.

[RAFster122s]

If there is corrosion in the carb bodies like Mark mentioned, then the ultrasonic cleaner usually won't help them enough. You either have to reem the passage way clear, slowly digging out the corrosion or replace the carbs with good ones.

[Medyo Bastos]

If there is corrosion in the carb bodies like Mark mentioned, then the ultrasonic cleaner usually won't help them enough. You either have to reem the passage way clear, slowly digging out the corrosion or replace the carbs with good ones.

Agreed!


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[HondaMan]

One of the REAL hard-to-find corrosion spots in the roundtop carbs occurs in the air-vent port that runs from the tiny brass disc (with tiny hole in it) all the way up to the mainjet's emulsifier. To clean it (and push any debris out) you first remove the emulsifer (that's the part the the mainjet screws into) and then the needle jet (that's the part where the slide's needle slips in-out). This air passage goes right into the hole in the crab's throat where those parts reside. A soft mechanic's wire can be pushed around the slight bends enroute to the hole from the back of the carb, in that tiny brass hole. Then 'saw' it back-and-forth a few times if you get ANY crumbs from this passage, to push them out toward the needlejet's hole. If there are crumbs in one, they are likely in all of them.

This blockage, when it happens, makes it almost impossible to prevent sparkplug fouling and rich-running mixtures through the whole RPM range. I find it in about every 10th set of roundtop carbs I've cleaned. In my own 750 when it sat for almost 6 years when I couldn't ride it for a while, 3 of the carbs had this blockage and I could not ride 5 miles without fouling 2 or 3 sparkplugs. It also sputtered and popped, backfiring when slowing from high RPM.

[newday777]

One of the REAL hard-to-find corrosion spots in the roundtop carbs occurs in the air-vent port that runs from the tiny brass disc (with tiny hole in it) all the way up to the mainjet's emulsifier. To clean it (and push any debris out) you first remove the emulsifer (that's the part the the mainjet screws into) and then the needle jet (that's the part where the slide's needle slips in-out). This air passage goes right into the hole in the crab's throat where those parts reside. A soft mechanic's wire can be pushed around the slight bends enroute to the hole from the back of the carb, in that tiny brass hole. Then 'saw' it back-and-forth a few times if you get ANY crumbs from this passage, to push them out toward the needlejet's hole. If there are crumbs in one, they are likely in all of them.

This blockage, when it happens, makes it almost impossible to prevent sparkplug fouling and rich-running mixtures through the whole RPM range. I find it in about every 10th set of roundtop carbs I've cleaned. In my own 750 when it sat for almost 6 years when I couldn't ride it for a while, 3 of the carbs had this blockage and I could not ride 5 miles without fouling 2 or 3 sparkplugs. It also sputtered and popped, backfiring when slowing from high RPM.

Mark
What size soft mechanic's wire?

[PeWe]

If that tiny hole is clogged by dried fuel, it must be possible to get it cleaned by fuel additives.

I used an additive in my K6 with Mikuni TMR carbs last September that made a huge difference after ca 150 km ride.

I had to stop and reduce fuel screws by 1/4 turn when I noticed it ran rich at throttle roll offs in low speed (legal speed) maybe a little more, 1/3 turn less

I had used that additive before without that effect. I read the instructions on the bottle more careful. The dosage lines on the bottle was for daily use.
Cleaning was almost triple which I added,  4 times more.

That made it.
I found that I will use an additive every year at the first longer ride. I usually stop for a refuel after ca 220-230km when I had ridden it on reserve for maybe 10-30km.
Cruise in legal speed important so mostly the pilot circuit is used.

[Bigmant]

One of the REAL hard-to-find corrosion spots in the roundtop carbs occurs in the air-vent port that runs from the tiny brass disc (with tiny hole in it) all the way up to the mainjet's emulsifier. To clean it (and push any debris out) you first remove the emulsifer (that's the part the the mainjet screws into) and then the needle jet (that's the part where the slide's needle slips in-out). This air passage goes right into the hole in the crab's throat where those parts reside. A soft mechanic's wire can be pushed around the slight bends enroute to the hole from the back of the carb, in that tiny brass hole. Then 'saw' it back-and-forth a few times if you get ANY crumbs from this passage, to push them out toward the needlejet's hole. If there are crumbs in one, they are likely in all of them.

This blockage, when it happens, makes it almost impossible to prevent sparkplug fouling and rich-running mixtures through the whole RPM range. I find it in about every 10th set of roundtop carbs I've cleaned. In my own 750 when it sat for almost 6 years when I couldn't ride it for a while, 3 of the carbs had this blockage and I could not ride 5 miles without fouling 2 or 3 sparkplugs. It also sputtered and popped, backfiring when slowing from high RPM.

Good stuff everyone! Everything on the bike has been gone through and replaced at this point. Carbs included. I ultrasonic cleaned every piece but did NOT go through that fuel hole with mechanics wire. Before rebuilding the bike it sat in my parents garage for about 30 years, so it wouldn’t surprise me if that line is blocked up.

I’d also love to know what gauge mechanic wire to use!

[PeWe]

I guess that hole is a vent for air, balance pressure in bowls

[Finnigan]

I have a cheap set of guitar strings that I use to push the crud in carbs out, nice to be able to pick what size diameter is best for each passage.  Also found they are fairly stiff for the diameter which is great for pushing through a clog.

[HondaMan]

I have 2 mechainc's wires:
One is 0.028" and stiffer than the larger one, which is 0.042" and dead soft. I use the smaller one to do those passages. I put a slight, gentle bend on the end of the smaller wire, about 1/8" or so from the end, to let me turn it this way and that to make it snake thru the hole. Then I push the debris out with multiple strokes toward the needle jet's hole in the center of the throat.

I suspect that the debris in mine came from having parked it in 2001 with MTBE-laced gas in it when I had the big cancer operation that kept me out of the saddle for almost 6 years (I couldn't manage the bike's weight for a while). When I started back up with it, I couldn't ride to work (4 miles) without having to replace the plugs when I got home: 3 of the 4 would be fouled black each time. I did this for a week before deciding it wasn't going to "clear itself out" and then it started snowing again (this was in March) so I took off the carbs to find out. I had never cleaned that passage before, but the carbs were sparkly clean [from sometime during the sojourn when I cleaned them], yet they fouled plugs immediately, with any gas. Jerry (RXman) was convinced I needed to rejet and he even found me some leaner #100 and #95 mainjets, but that had zero improved effect: the problem was coming from the lack of atomization of the mainjet. If I rode at 2000 RPM I could ride for 10 miles and the plugs would just be starting to have darkness, but as soon as I revved toward my normal RPM (3k-6k mostly) it would smell of fuel, blow blue smoke, and foul 3 sparkplugs immediately.

When I found this stiffer wire I used it to fight my way thru those passages (5th time the carbs were off, argh...) and all this white powder started showing up: it was by then the only spot I hadn't hand-cleaned (ultrasonics did zero for it). One of them was REAL hard to clear out, it seemed to have really packed itself in, hard. So, it takes patience if you find it in yours.

After that I started doing it with the many carb sets I was getting from others for cleaning: I found it in about 10% of the carb sets, and like mine, not in all of them in that set. Then I did some research to find out 'why' this would happen and came across several reports of 'results of MTBE in fuels' that were done by the EPA and DOT, and some others by people who had left them under protest, and did their own reports. ALL of those documents pointed toward how MTBE had been selected to "...damage zinc-aluminum alloys in the fuel atomization devices..." of the cars' carburetors, intentionally done to get old carb'd cars off the road slowly, but permanently. The last straw (for me) was when the famous reports showed up here and in other States where the government would buy your car ("Cash for Clunkers" program) and then immediately take the ones that ran and would pour "acid mixed with fine sand" into the carbs while running the engine at high speed, until it stopped. Then they were hauled off to crushers. The "acid" was MTBE.

[HondaMan]

I guess that hole is a vent for air, balance pressure in bowls

No, this is the hole that is in the back of the carb's bells that has a little brass port staked into it. It runs forward to the side of the needle's jet position (you have to remove the needlejet to let the wire through).

[Bigmant]

I guess that hole is a vent for air, balance pressure in bowls

No, this is the hole that is in the back of the carb's bells that has a little brass port staked into it. It runs forward to the side of the needle's jet position (you have to remove the needlejet to let the wire through).

Bought a small wire carb cleaning tool and some genuine Honda insulators. As it turns out I bought the 4:1 off brand kind (they were about half the price). I’ll report back if it makes any appreciable difference!

[PeWe]

I guess that hole is a vent for air, balance pressure in bowls

No, this is the hole that is in the back of the carb's bells that has a little brass port staked into it. It runs forward to the side of the needle's jet position (you have to remove the needlejet to let the wire through).

Is it the pilot air jet (PAJ)?
Or it might be called Main Air Jet (MAJ) on these carbs or equal function?
Mikuni VM29 and TMR have jets possible to change for correct amount of air here. Of just remove them for easier clean.
These carbs not, the brass is pressed into place.

[Bigmant]

I guess that hole is a vent for air, balance pressure in bowls

No, this is the hole that is in the back of the carb's bells that has a little brass port staked into it. It runs forward to the side of the needle's jet position (you have to remove the needlejet to let the wire through).

Is it the pilot air jet (PAJ)?
Or it might be called Main Air Jet (MAJ) on these carbs or equal function?
Mikuni VM29 and TMR have jets possible to change for correct amount of air here. Of just remove them for easier clean.
These carbs not, the brass is pressed into place.

Hondaman was saying it’s the channel under the main jet. The ones you pointed at I believe can be blocked by certain types of pod filters if you’re not careful.

[Tracksnblades1]

I wouldn’t go digging around in those itty bitty holes with any thing harder than the jets, nozzles, offices themselves are, if I were you..

Especially if your dad hasn’t in the past.. Virgin Honda brass is hard to come by…

Copper and bronze wires can be purchased in thousands sizes like 0.020 for a few bucks at model train suppliers..

Copper is what I prefer because it’s several times softer than brass and bronze..And Bronze is harder than Brass which is what you got unless you have them removed before digging. But look at Delta’s cutaway of a pilot jet in case yours are partially plugged or varnished up to the next smaller size..

Check your timing too.  I like somewhat  advanced initial timing and limited centrifugal max timing. Remember your ignition fires on the exhaust stroke too, so don’t blame it all on your exhaust lighting it off on the deceleration..

Advanced initial timing is a no-no with low octane fuel, but makes for a torquey just above idle launch at the stop sign with premium fuel when trying to tame the open exhaust from the local germaine..

Have you tried premium to see how it affects your deceleration popping..?

[Bigmant]

I wouldn’t go digging around in those itty bitty holes with any thing harder than the jets, nozzles, offices themselves are, if I were you..

Especially if your dad hasn’t in the past.. Virgin Honda brass is hard to come by…

Copper and bronze wires can be purchased in thousands sizes like 0.020 for a few bucks at model train suppliers..

Copper is what I prefer because it’s several times softer than brass and bronze..And Bronze is harder than Brass which is what you got unless you have them removed before digging. But look at Delta’s cutaway of a pilot jet in case yours are partially plugged or varnished up to the next smaller size..

Check your timing too.  I like somewhat  advanced initial timing and limited centrifugal max timing. Remember your ignition fires on the exhaust stroke too, so don’t blame it all on your exhaust lighting it off on the deceleration..

Advanced initial timing is a no-no with low octane fuel, but makes for a torquey just above idle launch at the stop sign with premium fuel when trying to tame the open exhaust from the local germaine..

Have you tried premium to see how it affects your deceleration popping..?

Believe it or not, I’ve been running premium since the day I put it all back together. But am now realizing the compression on these engines will never need it. I had a thought that the lower octane may actually make it run a bit better

[Tracksnblades1]

Yep, burns a little slower needs a bit more timing than 87 but is more tolerant of pre ignition and detonation..