Topic: Pods off, airbox on = instant smoooooth!!

[traveler]

come on, guys.....let it go.

~Joe

[Stogie1020]

I am dangerous with tools.  As in, more likely than not to break things and lose skin...

Perhaps you are placing too much reliance on the force?  Are your thoughts betraying you?


 

OK, that cracked me up!

[Gordon]

come on, guys.....let it go.

~Joe

That's like trying to politely request of a pit bull to let go of your mangled appendage.

[Terry in Australia]

My gold K2 was built by Ken Piper, one of Australia's premier race bike builders from "back in the day". His race expertise was with Yamaha's, so when he decided to build a CB750 for the first time, he looked at it with a new "unbiased" set of eyes. He bored an F2 engine out to 836cc with the correct Wiseco kit, but otherwise left the engine stock.

He didn't like the standard carbs at all, so tried a few different variations on the theme, and with the aid of an exhaust gas analyser, decided that stock carbs were not the way to go, so modded some 32mm CV carbs from a later model Honda, and adapted a stock airbox to suit. This bike has the sweetest CB750 engine that I've ever owned, and it's a credit to his attention to detail and engineering skills.

I'm sure that if he thought there was any real advantage in fitting pods over many hours reworking a stock airbox to suit entirely different carbs, he would have done it in a heartbeat, but he didn't, so I'm happy to keep it "as is". Cheers, Terry.

 

[traveler]

how about no air cleaner....just open carb?

[754]

The 78F rider was about 70 lbs lighter than I was (someone asked), and had ridden it to Texas and back from Canada, so I would say he was used to the bike.

 Ofreen, let me say this.. there is running good, and running even better.
 My first 750, header and K&N seperate filters.. used to run just a wee bit behind my buddies, who had a 74 with Jardine 4-1. One day I upped the jets, and suddenly it was quicker, could actually pull a bit on him! 3 days later we wrecked both bikes..

 My next 750, I was ready, ran the same cleaners, header, & jets.. upped the needles, it ran great..

 Then I ran Webers, tuned them one day up at out track, ran fine before I left. Now we live at 1300 ft, track is at 4000ft. I fidlree with the jets made a lot of runs... got some nice gains.. dropped 3 tenths in the 1/8. But it still felt fine, even with that jetting down low. The point is, I cant always tell by feel, need a control.. either a time slip, or another consistent bike. Sometimes the change is subtle, but more than you think..

 The strip or a dyno can tell you things that you may not be able to measure..

[scottly]

I am dangerous with tools.  As in, more likely than not to break things and lose skin...

Then leave your bike alone. Chances are the PO never re-jetted, unless he actually gave you the old jets. Even then, is your bike running OK, at least as far as your noob experience can tell? If you really think something is wrong, and you do have all the parts to re-install the stock air-box, then do so. You may want to put a bit of time on the bike, and learn about it first, before jumping in and fixing something that isn't broke, or worse, breaking something is isn't broke.

[ofreen]

 Ofreen, let me say this.. there is running good, and running even better.
 (snip)
 The strip or a dyno can tell you things that you may not be able to measure..

Your point is well taken.  But I'd submit that if the difference is so subtle that it takes a run at the strip or on the dyno to tell the difference, then those are the only places it matters.  On the road, maybe not so much.  I get around enough that I ride anywhere from sea level up to 10,000 ft or more, from temps in the single digits to 100+.  Real world jetting is pretty much a compromise.  The main consideration in a street bike is ridability, not a tenth of a second at the drag strip.  But like I said, I understand what you are saying.

[Frostyboy]

However, if it's really more noise you are after, loud pipes and pods sure make it "sound" like there is more power from the engine, even if "performance" has actually diminished. 

I'm going back in years here, but from 1978 to 1988 I spent 10 years working on a chassis dyno tuning cars. I lost count of the number of V8 owners who presented their standard vehicles with the lid on the air cleaner inverted. They truly believed their cars had more performance since they "let more air in."
In fact, and we tested this countless times, it made not 1 kw of difference at the back wheels. The only difference it made was to the induction noise. They obviously felt it sounded faster but in fact it make not one iota of difference to performance. 

[edbikerii]

Yeah, that's what I though when I was running my UNI in-airbox filter and MAC 4-1 without re-jetting, until I measured my cylinder head temps at ~50% higher than normal.  I guess I could have gone ahead and rode around that way indefinitely, or I could have blown a hole in my piston the very next day.  The world will never know, as I installed pods, then re-jetted properly, and got the temps down to normal (see thread in my sig).

I'd estimate that I picked up about 10% more power.  Could have been from getting the mixture right alone, or it could have had something to do with the pods.  My belief is that it was a little bit of both.

 Ofreen, let me say this.. there is running good, and running even better.
 (snip)
 The strip or a dyno can tell you things that you may not be able to measure..

Your point is well taken.  But I'd submit that if the difference is so subtle that it takes a run at the strip or on the dyno to tell the difference, then those are the only places it matters.  On the road, maybe not so much.  I get around enough that I ride anywhere from sea level up to 10,000 ft or more, from temps in the single digits to 100+.  Real world jetting is pretty much a compromise.  The main consideration in a street bike is ridability, not a tenth of a second at the drag strip.  But like I said, I understand what you are saying.

[754]

Ofreen, not sure about Boise, but I am guessing at 300ft or higher?

 I think (not sure) baseline jetting would be different on a bike sold in Denver, as opposed to LA. But I dont know if this is done at dirsributor level, dealer or the factory. At any rate, there must be an elevation point that decides if they get higher altitude jetting. ( correct me if this is wrong)  So I was thinking, some locations may be jetted toward the rich side, meaning if you intalled a header, you could be closer to optimum..

 A couple tenths, in the 1/8 mile does not sound like much, but 3 tenthsin the 1/8 equals about 4.5 tenths or near a half second, in the quarter, that is quite a lot.

 The point I am making, is if you have the jets, its not really costing any money, but you can get more out of what you got.

[Stogie1020]

I am dangerous with tools.  As in, more likely than not to break things and lose skin...

Then leave your bike alone. Chances are the PO never re-jetted, unless he actually gave you the old jets. Even then, is your bike running OK, at least as far as your noob experience can tell? If you really think something is wrong, and you do have all the parts to re-install the stock air-box, then do so. You may want to put a bit of time on the bike, and learn about it first, before jumping in and fixing something that isn't broke, or worse, breaking something is isn't broke.

Point taken.  The reasoning for wanting to put the stock airbox back on was to for aesthetics and to return the bike to it's original state. 

[ofreen]

Ofreen, not sure about Boise, but I am guessing at 300ft or higher?

 I think (not sure) baseline jetting would be different on a bike sold in Denver, as opposed to LA. But I dont know if this is done at dirsributor level, dealer or the factory. At any rate, there must be an elevation point that decides if they get higher altitude jetting. ( correct me if this is wrong)  So I was thinking, some locations may be jetted toward the rich side, meaning if you intalled a header, you could be closer to optimum..

 A couple tenths, in the 1/8 mile does not sound like much, but 3 tenthsin the 1/8 equals about 4.5 tenths or near a half second, in the quarter, that is quite a lot.

 The point I am making, is if you have the jets, its not really costing any money, but you can get more out of what you got.

Boise is at a little over 2800 feet, but I bought it when I lived in western Washington back in the '70s and I know it was purchased new in Auburn.  I've heard it said that they were jetted differently depending on where they were sold, but I've never seen one of these (750F0/F1) with anything but 105 mains stock.  Maybe Jerry in Colorado can offer some insight.

The main thing I've seen with these carbs that affects carburetion is needle jet set wear.  By 35,000 miles the early to mid 70's needle jet sets (they were soft) are worn enough to throw things way out of wack.  Symptoms are not needing the choke to start cold, decreased fuel mileage, fouled plugs, etc.  I am on my third needle jet set now.  The needle develops a visible wasp-waist shape and the jet wears as well.  This causes a rich condition at cruising speed and makes throttle response very punky.  The rate of wear appears to accelerate as they rattle together more and more during intake pulses.  Anybody trying to sort out jetting with a worn needle jet set will be just chasing their tail.

[754]

I dont recall that being mentioned before..VERY good point.

 I distinctly remember my buddy with a hi-miler 71 with an 812/Yoshi cam. He said, you know its sorts strange, but I am thinking of jetting down, after I put a lot of miles on it.
 What I did realize back then, was they did not need a huge jet increase with a 836 and a cam...

 Wonder what them needles look like now... at least 150K on them carbs.. dont know if they were changed.

[ofreen]

I dont recall that being mentioned before..VERY good point.

Here's a thread I did a couple of years ago -

http://forums.sohc4.net/index.php?topic=41542.0

[TwoTired]

The main thing I've seen with these carbs that affects carburetion is needle jet set wear.  By 35,000 miles the early to mid 70's needle jet sets (they were soft) are worn enough to throw things way out of wack.  Symptoms are not needing the choke to start cold, decreased fuel mileage, fouled plugs, etc.  I am on my third needle jet set now.  The needle develops a visible wasp-waist shape and the jet wears as well.  This causes a rich condition at cruising speed and makes throttle response very punky.  The rate of wear appears to accelerate as they rattle together more and more during intake pulses.  Anybody trying to sort out jetting with a worn needle jet set will be just chasing their tail.

I have heard of this before on the early CB750 carbs.  Slide and Jet wear doesn't seem to be an issue with the PD style or the CB550 carbs.  I'm thinking that the needle is held in place on the slide better by the PDs or other model carbs.  I don't have any non-PD 750 carbs to examine.  But, might you make a shim or something that keeps the needle from flailing about adding to wear?
Just thinking out loud...
Cheers,

[ofreen]

I don't have any non-PD 750 carbs to examine.  But, might you make a shim or something that keeps the needle from flailing about adding to wear?
Just thinking out loud...
Cheers,

My understanding is that Honda began to hard anodize later needle jet sets to make them more durable.  That seems to be the case as the second set I had went about 80,000 miles compared to 35,000 for the set that came in the bike.  I still have the original set somewhere around here.  I remember the appearance was different, a different color.  The newer ones were duller.

I had the same idea as you trying to think of a way to reduce the amount of movement of the needle in the slide to reduce the slamming around in the jet.  The needle shank is a fairly close fit in its hole in the slide, but there is some slop.  The problem is that the needle is long and play is magnified toward the end.  The trick would be to reduce the slop yet allow the needle to remain centered.  The best solution would be more bearing surface in the hole through the slide combined with a closer fit, but if this new set goes another 80,000 miles, I'll be happy.