Carb tuning a 40 yr journey

[8541Hawk]

Thanks for the info on the slide holes. I never thought of them as a fine adjustment to the needle circuit like the fuel screws to the pilot circuit. That makes perfect sense, though harder to tune. Unlike the fuel screws which fine tune mainly the pilot circuit and a little to the lower end needle circuit as they cross paths. With the needle circuit being in the middle any adjustment affects both the pilot circuit and the mains. This is why I guess it is best to start one end or the other and not try to tune from the middle. Either start at the mains and work your way down like in the FP CV carb tuning instructions or start the other end at the pilot.
(:-})

Well to add even a bit more on the lift hole subject.....
I'll use the single hole mod as an example but using multiple holes has the same effect, just faster instead of slower slide speed

The effect of the single lift hole is exponential not linear. What that means is when the slide is fully closed it will move slower as the air is drawn out due to a single hole. As the slide rises and the pressure inside the slide drops, it reaches a point where the single hole will have the same flow rate as the two holes.

So the slide moves slower initially then the farther it is open the closer it moves to the same speed as the slide with 2 lift holes.

That is why you use the lift holes (and the slide cut out) to tune the low mid-range

And yes it was "standard" tuning procedure to start at one end and work your way to the other.
With most bikes it was personal preference whether you started with the mains or pilots.

On this bike, as the jets are so large, you really need to start at the pilot as it flows enough to make the mains go rich if you try to tune from the mains down.

[bigtwinthing]

after reading all that, Iam glad i have Fuel Injection. Glad to see your committed Guys.

[VTRDark]

Thanks for that some interesting info there especially the following:

On this bike, as the jets are so large, you really need to start at the pilot as it flows enough to make the mains go rich if you try to tune from the mains down.

Well, today I have been doing a bit of tinkering and have gone back to 2 lift holes in each slide. I was kinda pushed into it as these slides are the slides that come with carbs I fitted. They have been ultrasonically cleaned. Not the slides the carbs bodies that is. Totally stripped and dismantled them. I'm sticking with the rear needle having the 1mm shim more than the front. What I have noticed is that the midrange is little more lively but I am requiring more turns on my fuel screws with the 48's. I'm going to see how it goes but I may very well try the 50s again with this new setup. A bit of a waste of time really considering the state of my link pipes and cans But I couldn't resist a tinker while I was in there.

Last time I ran 50's it was temperamental at idle and cold starting and a little jittery at low revs, but I am more experienced at getting my fuel screws set by ear more accurately these days. At the moment the rev needle spins up nice and crisp and falls back down to 1000rpm with no stumbles. Yeh I know it should idle at 1200 but I have mine set at 1000. I will start my fuel screw adjustment at around 1200 which gets me roughly there, then 1000 and eventually I will fine tune it so if I wished, the bike will idle at around 300. I obviously never take it below 1000 under normal circumstances. It;s knowing which carb to adjusts which I find tricky so I tend to do a bit on each one jumping back from one to the other if that makes sense. It took me a total of 3 little rides around the block with a hot engine to get my mixture and idle right or should I say to my liking Lets see how things go over the next few days. I will most likely have another tweak after getting back from a proper run.

(:-})

[bigtwinthing]

"but I am more experienced at getting my fuel screws set by ear more accurately these days"

Carl you are amazing, i struggle to hold a screwdriver with my fingers these days as getting on a bit! and your using your ears!!!. lets have a u tube clip please!

[8541Hawk]

Thanks for that some interesting info there especially the following:

On this bike, as the jets are so large, you really need to start at the pilot as it flows enough to make the mains go rich if you try to tune from the mains down.

Well, today I have been doing a bit of tinkering and have gone back to 2 lift holes in each slide. I was kinda pushed into it as these slides are the slides that come with carbs I fitted. They have been ultrasonically cleaned. Not the slides the carbs bodies that is. Totally stripped and dismantled them. I'm sticking with the rear needle having the 1mm shim more than the front. What I have noticed is that the midrange is little more lively but I am requiring more turns on my fuel screws with the 48's. I'm going to see how it goes but I may very well try the 50s again with this new setup. A bit of a waste of time really considering the state of my link pipes and cans But I couldn't resist a tinker while I was in there.

I have also been "forced" to go to 2 lift holes in the slides....lol for me it is because of the Akro system.
With the Dr Honda stacks it has always been a bit of a grey area of do you run 1 or 2 lift holes.
One one hand they are "long" stacks so you want 2 lift holes, On the other hand, they flow better than the stock units so 1 lift hole should be correct.
It ends up what the bike you are tuning likes.
On mine 1 lift hole used to work but while dialing in this exhaust I have one last "issue" in that I get a lean "pop" from time to time while cruising between 3.5K & 4K or right at the top of the pilot circuit and the slides are just starting to open.
Tried raising the needles, which cleared that issue but gave a rich "cough" at little higher up.
Opened up the pilots but the bottom goes too rich before the issue clears.
That leave the option of getting the needles to pop a little quicker down low, or 2 slide holes.

Still waiting for my new slides to show up as I have the HRC slides in there and don't want to mess around with drilling them, so should know Wed if things are how I like them.

Last time I ran 50's it was temperamental at idle and cold starting and a little jittery at low revs, but I am more experienced at getting my fuel screws set by ear more accurately these days. At the moment the rev needle spins up nice and crisp and falls back down to 1000rpm with no stumbles. Yeh I know it should idle at 1200 but I have mine set at 1000. I will start my fuel screw adjustment at around 1200 which gets me roughly there, then 1000 and eventually I will fine tune it so if I wished, the bike will idle at around 300. I obviously never take it below 1000 under normal circumstances. It;s knowing which carb to adjusts which I find tricky so I tend to do a bit on each one jumping back from one to the other if that makes sense. It took me a total of 3 little rides around the block with a hot engine to get my mixture and idle right or should I say to my liking Lets see how things go over the next few days. I will most likely have another tweak after getting back from a proper run.

(:-})

While I also run my idle at between 1000 & 1100 I have never been able to get 50s to work.
Though everything else is pretty much how I set my stuff

[VTRDark]

I have also been "forced" to go to 2 lift holes in the slides....lol for me it is because of the Akro system.

How uncanny. Your not going to believe this one....freaky man I also noticed after a ride today that I have a bit of popping around the same area.

while dialing in this exhaust I have one last "issue" in that I get a lean "pop" from time to time while cruising between 3.5K & 4K

Accept mine is not while cruising and only on the over-run. It may be a small leak in my exhaust system, I have yet to check properly but it wasn't there before I changed the carbs, well....no way near as much anyway.

The thing is above those revs the bike is an animal and goes like a rocket, much better than before. Full throttle and and the torque pushes me back in the seat, so the mains (178/180) are good for full throttle and changing the slides I believe has had a good affect on this. It just goes to show how much affect the lift holes have. I'm hoping it has richened up the mains a tad as on my last dyno it was a tad lean and I'd rather be a bit richer up top.
http://www.vtr1000.org/phpBB3/viewtopic ... 19#p356138

Getting back to the pilots (48s) and the popping. I actually considered it may actually be a rich gurgle. I cant believe with the 48's that my fuel screws should be that far out and still be lean. I don't know how many turns but I can see the head of the screw sticking out below the fuel screw carb casing. The springs are good on them so hopefully they don't work loose. The bike started this morning perfectly. Full choke, hit starter and it ticked over at 1500 nice and smooth. I could even gradually push the choke back in and the bike carried on ticking over without flooding, cutting out and revs gradually decreases as I pushed the choke in.....perfect Later in the day with the bike already warmed up and parked for a few hours. It started with no choke, no throttle and only hitting the starter. I thought I would give the choke a go to test if it cut out or not as it used to do before. To my surprise, no it didn't. It simply ticked over at higher revs and gradually decreased as I released the choke. Low end and idle the bike runs perfect. If I am too be picky I would say that maybe the bottom end is a tad flat which also suggests rich, not lean. It could do with being a little perkier off the line.

So my next step as I have to give it a try is the 50's, depending on how many turns are really on my fuel screws.I shall count them properly when I lift the carbs off. The last time I ran 50's I only got about 1 to 1.5 turns on the fuel screws and the bike was jittery and temperamental to start. I've got to give it a go though. At the moment it would not surprise me if my fuel screws are more then 3 turns out but I could be wrong, we'll see. Shame there's not a 49 pilot jet

Let the games begin

(:-})