Freshly rebuilt carb, cobra 6x6 pipes, popping, sputtering, mixture screws

[rafalc]

After reading through many many threads and attempting to make numerous adjustments, being ready to give up and just deal with the occasional popping, I want to give this one last chance and see if anyone has any other suggestions.

Freshly rebuilt/cleaned carburetor, all new hoses, slow 38 and 105 mains, stock needle with washer, cobra 6x6, K&N filter with no pre-filter, carbs synched nearly perfect, new exhaust gasket rings, checked all hoses and airbox-carb boots as much as I could and everything is tight.

Started with 2.25 turns out but was getting a lot of sputtering and popping, kept going up in turns and the other day ended up at 3.25 out and retightened the exhaust nuts. Less sputtering/popping but still some after bike is fully warmed up and I'm around 1900 RPM cruising or let off the throttle some. Do I keep turning the screws out more? At what point are they out too much and at what point will they negatively affect the Honda recommended mixture screw setting/highest idle procedure?

Is it safe to assume that when the exhaust noises stop, one has achieved the correct lean/rich condition or are the 2 not directly related? I assume they are not and I'm afraid that if I keep turning the screw out, I'll be running way too rich.

Let's be honest, the mixture screw adjustments are nearly impossible with the bike running. I tried the stubby tool, I tried numerous 90 degree tools but there just isn't enough room for the 90 tools, and too hot to work the stubby. Also even with the DigiSynch, the RPM readings are never steady and always bounce 20-30 RPM so the Honda recommended "50RPM increase" is just too difficult to dial in.

I also read some threads when people with a similar setup to mine ended up at 1.5 turns out which got rid of the exhaust noises ... 1.5 seems VERY lean.

Any recommendations would are welcomed...

[Bagger John - #3785]

Do you have baffles installed in the pipes?

[Foozle]

I wonder if using adjustable Cobra needles (rather than OEM) might allow you to run a little richer without backing the pilot screws out so far.  3.25 turns out with 38 slow jets seems incredibly rich.

I run Viking exhaust and went to 2.25 turns out to minimize the popping on deceleration.  It worked, but resulted in a thin layer of black soot in my exhaust pipes.  I went back to 1.75, and it cured the soot problem.  I've learned to just live with the popping.

Terry

P.S.  I also run Viking titanium needles - not OEM.

[Bagger John - #3785]

I wonder if using adjustable Cobra needles (rather than OEM) might allow you to run a little richer without backing the pilot screws out so far.  3.25 turns out with 38 slow jets seems incredibly rich.

When I got my '99 Tourer it had a set of 6x6s on it. Those were removed and an OEM exhaust installed in their place. FWIW, no decel popping was noticed and the plugs were all colored in the middle of the "ideal mixture" range.

Carbs were checked. They had had the Cobra jet kit installed (needles, slow jets, etc.) installed. I left the needles in place (clips in second notch from top) and with the stock exhaust, the slow jet circuit required the air screws to be 2 1/2 turns out for ideal coloration. I'd started with them at 2 turns out - which was where they were with the Cobra exhaust - but the bike was running lean enough to have a flat spot around 1700-2000RPM, so a bit of tuning was in order.

[rafalc]

Do you have baffles installed in the pipes?

yes, baffles are in

[yrunvs]

My $5 is on the exhaust headers have not been seated entirely on the new exhaust gaskets. I installed new header gaskets and was getting medium popping and after every ride I would retorque the exhaust nuts and each time I got less popping. Now after numerous retorqueing's I  have a very mild burble on decel. Also heavy doses of Berrymans and Mechanic in a Bottle.

[sandy]

Our performance sponsor reported to me in Taos, that 38 jets are running WAY too rich when opened 1/8 of a turn out. Return to the 35’s and set the pilots at 2 turns out.

[shadowmagic]

I just finished chasing popping sounds on my valkyrie for a few weeks. I tried everything and rebuilding and upping my jets seemed to take care of the problem. I also found a spring on one of the adjustment screws was twisted sideways and wasnt allowing movement when you turn the screw. I set mine at 1.75 turns, 38s, and 105s. After doing all of this along with replacing vaccuming lines, checking for leaks, replacing orings, tightening exhaust, etc that finally took care of the problem. It can definately get frustrating but if you keep at it you'll find whats causing the problem. Good luck.

[rafalc]

Thanks everyone for your suggestions on the popping issue, I'll do some more troubleshooting.

How about performing the mixture screw procedure per Honda? Any of you ever been successful at performing it on a running bike and actually be able to hear/see the ~50RPM changes as the manual instructs? If so....what sort of magic did you use????   

[Jersey]

Thanks everyone for your suggestions on the popping issue, I'll do some more troubleshooting.

How about performing the mixture screw procedure per Honda? Any of you ever been successful at performing it on a running bike and actually be able to hear/see the ~50RPM changes as the manual instructs? If so....what sort of magic did you use????   

In my opinion carbs require a combination of science and art.  I have followed the Honda procedures and was able to 'mostly' tell the difference of 50+-RPMs... it's a slow tedious process, but it did result in a well tuned engine.  I used a separate shop tachometer and followed the procedures slowly to allow ample time for the engine to respond to the slight changes.

[rafalc]

Thanks everyone for your suggestions on the popping issue, I'll do some more troubleshooting.

How about performing the mixture screw procedure per Honda? Any of you ever been successful at performing it on a running bike and actually be able to hear/see the ~50RPM changes as the manual instructs? If so....what sort of magic did you use????   

In my opinion carbs require a combination of science and art.  I have followed the Honda procedures and was able to 'mostly' tell the difference of 50+-RPMs... it's a slow tedious process, but it did result in a well tuned engine.  I used a separate shop tachometer and followed the procedures slowly to allow ample time for the engine to respond to the slight changes.

What tool did you end up using? No matter what I try I either burn myself, the tool is too bulky, or just plain garbage that doesn't work.

Thanks

[-mike-]

This works for me:


You'd need a stubby D-insert for US carbs, though.

-mike-

[Jersey]

Thanks everyone for your suggestions on the popping issue, I'll do some more troubleshooting.

How about performing the mixture screw procedure per Honda? Any of you ever been successful at performing it on a running bike and actually be able to hear/see the ~50RPM changes as the manual instructs? If so....what sort of magic did you use????  

In my opinion carbs require a combination of science and art.  I have followed the Honda procedures and was able to 'mostly' tell the difference of 50+-RPMs... it's a slow tedious process, but it did result in a well tuned engine.  I used a separate shop tachometer and followed the procedures slowly to allow ample time for the engine to respond to the slight changes.

What tool did you end up using? No matter what I try I either burn myself, the tool is too bulky, or just plain garbage that doesn't work.

Thanks

Motion pro makes one, as well as, a few others.

https://www.amazon.com/Pit-Posse-Motorcycle-Carburetor-Adjusting/dp/B004N0EX7Y

https://www.motionpro.com/product/08-0229

[rafalc]

Thanks everyone for your suggestions on the popping issue, I'll do some more troubleshooting.

How about performing the mixture screw procedure per Honda? Any of you ever been successful at performing it on a running bike and actually be able to hear/see the ~50RPM changes as the manual instructs? If so....what sort of magic did you use????  

In my opinion carbs require a combination of science and art.  I have followed the Honda procedures and was able to 'mostly' tell the difference of 50+-RPMs... it's a slow tedious process, but it did result in a well tuned engine.  I used a separate shop tachometer and followed the procedures slowly to allow ample time for the engine to respond to the slight changes.

What tool did you end up using? No matter what I try I either burn myself, the tool is too bulky, or just plain garbage that doesn't work.

Thanks

Motion pro makes one, as well as, a few others.

https://www.amazon.com/Pit-Posse-Motorcycle-Carburetor-Adjusting/dp/B004N0EX7Y

https://www.motionpro.com/product/08-0229

Thanks, I tried that exact Pit Posse last week and the head was too bulky and would not fit/align. Maybe I'll try the Motion Pro next

[-mike-]

The pit posse one you mentioned is the very same as mine. Only the stubby blade gear box (in the box pic upper left corner) works. The screw adapter is a tad too long to fit - that's right.

I have am European Carb, so the mixture screws are slotted, no D-shape.

[rafalc]

The pit posse one you mentioned is the very same as mine. Only the stubby blade gear box (in the box pic upper left corner) works. The screw adapter is a tad too long to fit - that's right.

I have am European Carb, so the mixture screws are slotted, no D-shape.

I guess I should have slotted the screw heads while I had the carb out, now I have to deal with the "D" bit.....

[98valk]

The pit posse one you mentioned is the very same as mine. Only the stubby blade gear box (in the box pic upper left corner) works. The screw adapter is a tad too long to fit - that's right.

I have am European Carb, so the mixture screws are slotted, no D-shape.

I guess I should have slotted the screw heads while I had the carb out, now I have to deal with the "D" bit.....

this is the best honda tool to get, it was org listed for the cbr900.

it has a flexible spring head. been using it for yrs.

07MMA-MT3010B WRENCH PILOT SCREW

[rafalc]

The pit posse one you mentioned is the very same as mine. Only the stubby blade gear box (in the box pic upper left corner) works. The screw adapter is a tad too long to fit - that's right.

I have am European Carb, so the mixture screws are slotted, no D-shape.

I guess I should have slotted the screw heads while I had the carb out, now I have to deal with the "D" bit.....

this is the best honda tool to get, it was org listed for the cbr900.

it has a flexible spring head. been using it for yrs.

07MMA-MT3010B WRENCH PILOT SCREW

Thanks, maybe I'll give it a try. I tried some of the other generic flex/spring tools but they just did not have enough of a flex to make that tight turn.