Hahaha. This is exactly what I told steve today. Just a little ball bustin, nothing personal, derogatory or demeaning, however maybe an element of truth in there haha. Makes you think, evokes a sense of humor, nothing serious. can't take yourself too serious huh.

Spent a couple hours changing mains and syncing. Everything done ready to go, but suddenly decided to straighten out the sync adjuster plate which i inadvertently bent with a snake tool several syncs ago. AhOh! Should have left well enough alone. Couldn't get the the idle down and it was running on one cylinder. Steves havin the big one by now.hahaha. Took everythin apart again, changing throttle and return cables to get the idle to go down. Now we get it to sync, sucked the fluid up the line faster than an addict on withdrawalsnortin up lines of crystal. Took the front plug out because steve said maybe it's fouled/running on one cylinder, thus one carb overwhelming the other in terms of the sync tool. Front plug black and oily and the rear white/gray lean. I had a new set we threw in and got it running, but to get the idle down we had to screw in the sync adjuster almost the whole way. Didn't get into the sync part cause steve had to leave the bike in my garage and get to work. Hopefully we will get it sorted out tomorrow.

I think I'm starting to get little OCD via osmosis, tearing his carbs apart on a daily basis. My ocd question of the day is this: if you have a 175 in the front and a 180 in the rear, shouldn't the air mixture screw be a little different to account for the extra fuel? For example, 175:2.25 turns out; 180:2.32 turns out. how's that for OCD? hahaha

Also, how do you get that freakin left hand breather hose hooked up under the airbox? After steve left, I ended up taking it loose underneath on the eng cover, hooking it up under the air box, put the airbox on and then hooking it up on the engine cover last. At least i could assure that it was hooked on the airbox securely.PIA

 

I'd just like to clear up one point. A lean condition does not cause backfire on deceleration.

Decel backfire is caused by the rich condition that results when the throttle is closed suddenly. Normal intake manifold vacuum tops out at 21" hg. When the throttle is closed suddenly from moderate to high rpm, the piston speed temporarily creates intake man vacuum up to 25" hg. This higher vacuum draws more fuel through the carbs, which causes an overly rich mixture. The richer mixture doesn't burn completely, leaving unburned hydrocarbons (HC) to exit with the exhaust. If the excess HC in the exhaust is still hot enough when it hits the atmosphere (outside air at your exhaust tip) it combusts...Boom!

This is why the "anti-backfire" valve used on older cars with air injection systems (AIR) was triggered to operate at 22" hg or higher. This would be the vacuum operated bypass, diverter or gulp valve used on cars equipped with AIR, prior to computer controls. The bypass and diverter valve prevented the backfire by diverting the air from the "smog pump" to the atmosphere, rather than to the exhaust manifold. The gulp valve sent the pump air to the intake manifold to lean out the rich mixture. Both systems worked equally well.

The shorter or less restrictive the exhaust, the more prone to decel backfire. An exhaust leak can also suck in outside air, causing the HC in the exhaust to explode.

A lean condition can, however, cause an intake backfire...aka: "carb fart".

 

Not a problem. I suppose I read into that a little more than I should have. Kinda hard to tell if someone is serious or not over a computer. Anyway, I appreciate all the advice I've gotten along the way. I just want it to run right, and as noted in nath981's previous post, **** really took a turn for the worse during the sync today. It's not a great feeling to see the slide on your rear carb opening and closing rapidly at idle and flames coming out the top while the front carb does nothing (we had the airbox off at that point). I did take the mains down to 175/180, but until I figure out the issue I encountered during the sync, I won't know if this will be the answer. I hope it is. As tweety said earlier, that should cure the slight lean spot at the begining of the dyno run. Anyway, no hard feelings.

 

I totally get your point. I read into that too much. I'll be the first to admit that I am mostly clueless on this jetting process. The main reason I was convinced that it was lean stumbling was because it would only occur during cruise speed between 3/4k rpm. I could feel a thud under the tank. Also, this would only occur after a drop in needle position. I also found that my rear plug was white today. Thinking about it, I suppose it is unfair to keep asking questions without any real direction. I just kinda ask things as I think of them. If i had a more of an idea of what I'm doing, the questions would probably be more focused. I'll try to be more concise from here on. Anyway, I think if I can get the carbs synced, which turned into a nightmare today, (see nath981's previous post), my setup I 'm at now should work with some tweaking. Really don't have anywhere else to go with it. And thank you for the dyno chart. It gives me a little clarity.

 

remove the hose from the front valve cover first to get some slack. Then attach it to the airbox, install the airbox, reattach the hose to the valve cover.

 

Actually if you start with that hose, tilt the airbox up & forward you can put it on first and then push the airbox down on the two short hoses and manouver the rear one...

 

that is too easy

 

that's what I did because I got frustrated with trying to put objects in under to push it on and because of difficulty seeing. I'll try Tweetys method next time because the last time we thought it was on, i could feel the air blowing up along side fo the airbox once we started it up, Thanks both of you.

But what about my OCD question of the day? if you have a 175 in the front and a 180 in the rear, shouldn't the air mixture screw be a little different to account for the extra fuel? For example, 175:2.25 turns out; 180:2.32 turns out. We used to set one carb by turning in to stumble and then reversing to smooth it out, but with 2 carbs and the inaccessible air screws, forget it.

 

I have not done this myself, but I have read that you first set the front cylinder, then the rear using your method. If you really want to know how I do it - I guess, based on how things are running.

Also, these are pilots, the mains have little effect down there, .05mm difference in mains will become indistinguishable to the pilot circuits. Other factors have more of an affect. There is a degree of tolerance, so my OCD stops at the pilots screws - others may differ.

 

thanks res. There are some many mitigating factors in the real world like ambient temps, humidity, and altitude among others that it's difficult to arrive at any solid setting that satisfies all situations. I set mine one time accord to my signature below and have never touched it since. It runs pretty well with not stumbles or misses.

 

Assuming "175" and "180" represent the diameter of the orifices and you based your pilot screw adjustment calculation on that relative difference, the rear cylinder should be closer to 2.31 than 2.32!

But that doesn't work. You'd need to base your calculation on the difference between the area of the two different circles representing the two different orifices! Certainly the percentage difference in orifice area would be greater than the difference in diameter and would call for more out turning of the rear fuel screw. My OCD isn't severe enough this morning to figure out how much.

And of course all this is based on the assumption that opening the pilot screw say 5% results in a 5% increase in flow. Ha!

 

Area = Pi * R^2 where R = D/2 of MJ sizes. D of 175mj = 1.75mm...

I do not have a calculator handy

Pilot screws also have an effective range ending at ~3 turns, or less, so if you are at 2.75 out, you should consider larger pilots, likewise if you are at .5 turns out, you should consider smaller pliots

IMHO jetting is not just science, there is some art to it as well, at least that is my excuse for the guess work part of it.

 

Which it most certainly doesn't... Last I tried calculating something similar I ended up with several pages of mathematics and a bad headache... Actually doing the idle-drop procedure gives you a decent baseline to start working from... Although I agree with Hawkriders assesment that it's not an optimal setting for power, just for the best balance between power and lean enough to pass emissions... But it will give you a baseline and the difference yoju get doing that is the actual difference which will produce the best results...

 

Uh... You are neglecting the fact that the jet has a beveled edge, the needle has a taper, and throwing anything that physics teaches us about laminar flow out the window... But ok...

And that's the main reason for the guessing if you ask me... After a while the mathematics get to involved and you decide an educated guess is better than filling a whole notebook...

 

Wow...you guys are nuts.

 

Yeah. I'm not COMPLETELY sure about anyone else, but I was just goofin' on Nathan's OCD attack, which I'm 90% sure was him goofin' in the first place.

 

I was trying to keep it simple, when is that last brush stroke, one too many...

 

Ha! That would be the one following "crank 'em both out 2.5 turns"!

 

Ha. Yea he claims he's got OCD now from spending too much time around me. I tend to obsess a little when it comes to the bike. I'll try anything, then second guess my decision. It's a bit of a hinderance.

 

Thank you, I know... And I'm proud...

Yup... Goofy with a bit of thruth in there... I have once tried to calculate similar things... Flow dynamics in fluids and gasses are kind of on the curriculum in uni depending on your choice of engineering degree... If I manage to clear out the cobwebs I could probably give you a decent aproximation of the flow differences... But I'm lazy...

 

Actually though my remark about the idle-drop is the truth... Do that and note the difference... That's roughly the difference that gives you the best results from the two carburators and cylinders based on the difference in combustion...

 

To perform the idle drop procedure, you need the pilot screw wrench from honda correct?

 

Yeah. Goofy and truth aren't mutually exclusive. Maybe you're more smart than lazy. Maybe smart enough to realize that calculations applicable to winning in MotoGp or a successful mission to Mars aren't required to tune a street bike.

When you've gone past the point of wondering "how many angels can dance on the head of a pin" and want to know if they're waltzing, twisting or doing the river dance, you're way past the point of diminishing returns on the investment of your time.

 

my guess is that the 180 probably flows more than the 175; Occam's Razor

 

Ok. First, thanks to all who gave suggestions on my jetting issues. Second, I think I finally got it! Currently I'm running 175/180 mains, 48 pilots, needles 4th from top, and 2.25 on the pilots. The bike undoubtedly runs the best it ever has. Tomorrow I get put on the dyno and will post the results. However, one question remains, actually I suppose it's 2 rolled into 1. I expereinced what I have been refering to as a lean stumble or carb fart. This occurred as I first drove off after syncing the carbs, didn't happen again. Could that be due to the fact that the bike was idling at low rpm for a long time while doing the sync? The second part of the question is, am I even assigning the correct term to that? Is it really a lean stumble? My limited knowledge says yes. It happens only on the intake and can be felt under the tank. I'd like to know so in the event I am incorrect, I can start referencing it properly to eliminate future confusion if I need to do more tuning. I assume I should not concern myself with it since it only happened once. But if it were something that needs correcting, would another .25 turn out on the pilot screws be the answer? I know I can cure it by going up on the needles, but in the past that resulted in being overly rich. Or would the circumstances be different now that I have smaller mains? I'm of the mindset that I will not be replacing jets anymore. this is the closest to perfection I have been and I'm not about to screw it up. After reading this, i guess I asked more questions than I originally intended. I should probably save them for after I post the latest dyno graphs. Anyway, thanks guys.

 

If it's under the tank it's probably a "carb fart" not a "lean stumble"... Yeah, yeah not very scientific names I know... One is lean, the other rich... Basically the carbs spit back up when they get to much fuel... So try leaning it out a bit more on the mixture screws and see if it goes away...

As for idle drop, no you don't need the Honda tool... You need an angle head for a screwdriver/bits though, since I guess you have already slotted the mixture screws? It's considerably cheaper to locate that in a good hardware store than buying Honda's tools...

 

Thanks tweety. I'm glad you cleared that up for me. I've been diagnosing that wrong the entire time! No wonder I've had so much difficulty. And thanks for the info on adjusting pilots via the idle drop method. I did slot the screws so I will utilize that method.