'81 CB750k Tracker - Build #3

ncologerojr

Coast to Coast
DTT BOTM WINNER
Hoosier Daddy said:
xb may have come across a little harsh but his heart is in the right place. Some here have a hard time with settling for looks over performance.

I agree, I'm sure he was trying to help. I also understand his stance in not compromising any performance for looks, on his personal bike.
I have read all of the pods threads over the past few years, and I understand the issues. What I don't understand is people getting angry, and feeling a need to write rude responses over what others are doing to their bikes. I see a lot of things on here that I don't agree with, but it's not my bike so why go put people down? I am trying to build a comfortable, reliable and stylish bike. I'm not after track ready performance here.

Now back to motorcycle talk:

I upgraded carbs to a set known to work better with pod filters, and actually went a bit bigger than optimum (36mm). After some testing, I found the bike to be running lean (even with 120 main jets) and breaking up a bit due to slide flutter on hard acceleration. So, I built the air box in an attempt to slow/smooth out the airflow coming through the pods. If I slowed airflow a bit my fuel ratio would be better, and if it flowed smoother acceleration should be smoother. So far it seems to have worked.
It has always been my understanding that cheap pods allowed a bunch of turbulent air to flood into the carbs causing the slide to move erratically, causing both rich and lean conditions during acceleration. They are also affected by crosswinds funneling into the carbs. From what I've read, I was under the impression that a k&n pod filtered more evenly through a thicker/denser filter causing less turbulent airflow. Therefor "restricting" airflow just a bit. I guess I was wrong. I also thought the large stock air box functioned by stopping turbulent air from rushing into the carbs, letting the carbs pull smooth air in. Again, restricting airflow just a bit. Neither the k&n's or stock box allow crosswinds to blast into the carb, I thought that counted as restricting airflow (in a good way).

So maybe my understanding was off a bit. I don't claim to be a cv carb expert. I diagnosed the problems the bike was having (lean and slide flutter) and came up with a solution (maybe). If I lose a few hp, so be it. The bike is still plenty fast. I didn't mean to bring the stupid.

Sorry for the rant. ;)
 

Hoosier Daddy

Earache my eye...
I noticed your carbs weren't the factory Keihins so was holding out to see if the Pods worked on the Mikuni's, even though they are still a CV style. I know others have swapped out a rack from a GSX and saw where you used the boots from a GS1000..... but didn't see what donor bike these come off from?


483C465A-EDE2-47F7-B617-5ED1FF7B1291_zpseygz40mu.jpg
 

ncologerojr

Coast to Coast
DTT BOTM WINNER
Hoosier Daddy said:
I noticed your carbs weren't the factory Keihins so was holding out to see if the Pods worked on the Mikuni's, even though they are still a CV style. I know others have swapped out a rack from a GSX and saw where you used the boots from a GS1000..... but didn't see what donor bike these come off

These are bst36ss' from a '93 Katana 750 with a jet kit so they have adjustable needles. They are "acceptable" with just the pods. Defiantly a huge improvement over previous bikes I've tuned with pods, but not quite perfect. They are smooth if your easy on the throttle, but if your riding aggressively they act up. Perhaps a better quality pod would fix it. However, if I'm not satisfied with my air box attempt I think I may take a different route all together.
I've been intrigued by a company making aluminum manifolds to run dual mikuni vm34's. I could easily make the manifolds, and probably sell my stock carbs and the katana carbs to cover the cost of the two vm34's... I may end up giving it a try eventually just for kicks.
 

Dave.R

New Member
The engine provides the vacuum, the air box causes it to even out between strokes. The design he did will surely do that. The problem with pods is they are too individual. The outer cylinders run lean, and the slides have trouble being smooth. This fabbed air box will eliminate cross wind and outside lean, and normalize the vacuum between the carbs.

Because they all pull from the "box", the intake pulses will be evened out.

I don't think this is form over function, it is function finding form.

Great work Nick.
 

dualero

Been Around the Block
Where's the intake for that box? Ncologerojr would you mind to take a pic? Or the air just passes through the cracks left in the upper cap, the one that has bolts. Great build!

DH900sl
 

ncologerojr

Coast to Coast
DTT BOTM WINNER
Dave.R said:
The engine provides the vacuum, the air box causes it to even out between strokes. The design he did will surely do that. The problem with pods is they are too individual. The outer cylinders run lean, and the slides have trouble being smooth. This fabbed air box will eliminate cross wind and outside lean, and normalize the vacuum between the carbs.

Because they all pull from the "box", the intake pulses will be evened out.

I don't think this is form over function, it is function finding form.

Great work Nick.

Thanks Dave!
 

ncologerojr

Coast to Coast
DTT BOTM WINNER
dualero said:
Where's the intake for that box? Ncologerojr would you mind to take a pic? Or the air just passes through the cracks left in the upper cap, the one that has bolts. Great build!

DH900sl

Thanks!

There are currently two small holes in the bottom between the 1&2 and 3&4 inlets. I also left the crack you spotted around the top panel. If more air flow is needed I plan to add some louvers to that panel.
 

brad black

Been Around the Block
while i haven't played with any 4 cylinder carbs setups, i've done quote a lot of the ducati 38mm twin mikunis with pods or open airboxes.

my experience with them is that the more you try to make them a performance carb, the more the lack of an accelerator pump shows. you end up with rich pilot jet or needle settings to get them to do everything you want them to.

saying that, you should be able to make them work. when you change the vacuum difference across the carbs markedly, as removing an airbox does, you have to go quite a bit richer on the needle side of things ime, but not always the main jet. i'd start with the main jet sizing, then go to the needle and finish with the pilot. i know a lot of people are wary of using dynos, but it can be a very quick way to sort stuff out. especially the wot bit.

i'd also second the getting bigger pods from a name brand. they really can make a difference.

if it has a jet kit fitted you could try to slow the slide down by preloading the springs or refitting the originals to get rid of the roll on miss. originals often look much heavier due to the thicker wire, but often they have more coils and are fitted with less preload, so it might not be as bad as it looks.

doug lofgren makes (used to make?) a jet kit for the ducati bdst carbs that others have told me is the most responsive setup you can get for them, and he uses std springs.

also it may be worth going down in size to a set of 32 from a 600 katana for instance. the smaller the carb the greater the suck, and that can help a lot of things. 4 x 36mm carbs sounds pretty big for the power that engine won't be making.

make the airbox bigger too. it's way too short. given your fabbing skills, you could easily make a flat panel filter holder and seal the box, allowing you to remove the pods from the carbs. maybe fit some short trumpets. or extend the box and go longer till it hurts the top end.

then put some clear sides in it for the "oooooh" and "aaaaaaah".
 

brad black

Been Around the Block
ncologerojr said:
I've been intrigued by a company making aluminum manifolds to run dual mikuni vm34's. I could easily make the manifolds, and probably sell my stock carbs and the katana carbs to cover the cost of the two vm34's... I may end up giving it a try eventually just for kicks.

given the firing order is 1 2 4 3 (from what i found) you'd be best pairing 1 and 4 and 2 and 3. might be tricky. maybe 1 and 4 on a long manifold and 2 and 3 inside the y on a short manifold. go weird.
 

ncologerojr

Coast to Coast
DTT BOTM WINNER
brad black said:
while i haven't played with any 4 cylinder carbs setups, i've done quote a lot of the ducati 38mm twin mikunis with pods or open airboxes.

my experience with them is that the more you try to make them a performance carb, the more the lack of an accelerator pump shows. you end up with rich pilot jet or needle settings to get them to do everything you want them to.

saying that, you should be able to make them work. when you change the vacuum difference across the carbs markedly, as removing an airbox does, you have to go quite a bit richer on the needle side of things ime, but not always the main jet. i'd start with the main jet sizing, then go to the needle and finish with the pilot. i know a lot of people are wary of using dynos, but it can be a very quick way to sort stuff out. especially the wot bit.

i'd also second the getting bigger pods from a name brand. they really can make a difference.

if it has a jet kit fitted you could try to slow the slide down by preloading the springs or refitting the originals to get rid of the roll on miss. originals often look much heavier due to the thicker wire, but often they have more coils and are fitted with less preload, so it might not be as bad as it looks.

doug lofgren makes (used to make?) a jet kit for the ducati bdst carbs that others have told me is the most responsive setup you can get for them, and he uses std springs.

also it may be worth going down in size to a set of 32 from a 600 katana for instance. the smaller the carb the greater the suck, and that can help a lot of things. 4 x 36mm carbs sounds pretty big for the power that engine won't be making.

make the airbox bigger too. it's way too short. given your fabbing skills, you could easily make a flat panel filter holder and seal the box, allowing you to remove the pods from the carbs. maybe fit some short trumpets. or extend the box and go longer till it hurts the top end.

then put some clear sides in it for the "oooooh" and "aaaaaaah".


Wow. Thank you, that's a lot of info. I'll have to read that a few times lol. Defiantly helpful.

I originally thought I was getting 34mm carbs, that's what they were listed as on eBay. By time I really looked at them too much time had passed to cause a stir about it. I figured I'd try to make them

This is the dual carb set up made by speedmotoco.com. I figured I could make that manifold pretty easily. There are other companies making a similar product as well. Supposedly it functions well, but I also understand the point you made about the firing order...



Before going that route I think I'll try some of the mods to my air box that both yourself and Canyoncarver suggested. I can easily remove the pods and add a flat filter to start. I would read hate to make it bigger, but I see that I may have to. Like I mentioned earlier, I'm trying to preserve the stripped style of the bike as much as possible...
 

cxman

Over 1,000 Posts
DTT SUPPORTER
that setup is made by www.murrayscarbs.com

speedmotoco.com is just a dealer for them
 

Dave.R

New Member
Did you ditch the tach, or does the one gauge have both coming into it?

I have the same bike, and hate how huge the gauges are but would like to retain them. Also, your key placement is genius. Any pics you could show of the triple tree / gauge area would be helpful. Not saying I'll copy cat, just looking for inspiration.

Thanks Nick
 

ncologerojr

Coast to Coast
DTT BOTM WINNER
Dave.R said:
Did you ditch the tach, or does the one gauge have both coming into it?

I have the same bike, and hate how huge the gauges are but would like to retain them. Also, your key placement is genius. Any pics you could show of the triple tree / gauge area would be helpful. Not saying I'll copy cat, just looking for inspiration.

Thanks Nick

Yeah, I got rid of the tach. I'm running the 2.5" speedo with led indicators from deadbeatcustoms.com. I highly recommend ordering from him too, super nice guy with awesome customer service. I'll try to get a pic up for you tomorrow.
 

Dave.R

New Member
This might be a silly question, but I haven't gotten this far.

Doesn't the tach cable go into the engine? How did you block that hole?
 

M.B Co

Coast to Coast
xb33bsa said:
you are a great fabricator but you don't know fuck all about engine breathing ::)
the "lack of sufficient vacuum" statement really brings the stupid
the restriction of the small pods is a lot to do with the air being broken up into little streams and being too turbulant to soon before the carbs
if your lashup was better the japs would have done it stock think about it
think how the stock airbox has presicely shaped tubes running into a still air large volume box
the air needs to have a place to settle down and be smooth before it jams into the carb
all o that stock airbox design is after much power dyno testing

I'm sorry, but I don't understand how anyone can take you seriously. You have no idea of ones knowledge or skills.

I can only imagine what you do in real life if anyone challenges your opinion or "expertise". I don't care how old you are or how long you have been around motorcycles. An asshole is always an asshole.
 

ncologerojr

Coast to Coast
DTT BOTM WINNER
M.B Co said:
I'm sorry, but I don't understand how anyone can take you seriously. You have no idea of ones knowledge or skills.

I can only imagine what you do in real life if anyone challenges your opinion or "expertise". I don't care how old you are or how long you have been around motorcycles. An asshole is always an asshole.

A little more harsh than I would say, but my thoughts exactly.
 

bananas

Been Around the Block
TBH I didn't feel like XB was being much of an asshole -- It's difficult to convey tone over text. In my mind anyone willing to contribute automatically get the pass. The real assholes are the ones who see you doing something poorly/ wrong who just brush you off without making the attempt. The opposite of love isn't hate, its indifference.

The guys over at CB1100F or the other CB forums are much, much meaner when it comes to the CV carb/Pod filter debate.


NCO, Have you seen the RSC Carb modification for the DOHC bikes? Seems like this is the answer to the CV carb/ pod issue with the DOHC bikes. It might help with wanting to run pods. I myself am planning to do the mod when I have time in the future. Best part? It's DIY and probably costs about $5 in parts.

I've posted this over in 750mors thread as well:

Reference material:
http://www.cb1100f.net/modules.php?name=Forums&file=viewtopic&t=70514&postdays=0&postorder=asc&start=0

Link to PDF manual:
http://www.cb750c.com/Genesound/carbdocs/RS1000manualV1.pdf
Page 54-55
 

ncologerojr

Coast to Coast
DTT BOTM WINNER
bananas said:
TBH I didn't feel like XB was being much of an asshole -- It's difficult to convey tone over text. In my mind anyone willing to contribute automatically get the pass. The real assholes are the ones who see you doing something poorly/ wrong who just brush you off without making the attempt. The opposite of love isn't hate, its indifference.

The guys over at CB1100F or the other CB forums are much, much meaner when it comes to the CV carb/Pod filter debate.


NCO, Have you seen the RSC Carb modification for the DOHC bikes? Seems like this is the answer to the CV carb/ pod issue with the DOHC bikes. It might help with wanting to run pods. I myself am planning to do the mod when I have time in the future. Best part? It's DIY and probably costs about $5 in parts.

I've posted this over in 750mors thread as well:

Reference material:
http://www.cb1100f.net/modules.php?name=Forums&file=viewtopic&t=70514&postdays=0&postorder=asc&start=0

Link to PDF manual:
http://www.cb750c.com/Genesound/carbdocs/RS1000manualV1.pdf
Page 54-55

Thanks for the info. I am a member of 1100f.net, and I've seen the rsc info posted there. Very cool stuff. I am currently working on a custom air box idea, if that doesn't work out I'll probably considered the rsc mod.

Xb and I have some differences, but ultimately he always has good info. Check out my air box design thread in the engine forum.
 

ncologerojr

Coast to Coast
DTT BOTM WINNER
For anyone following this build, it is still very much in progress. Check my airbox design thread to see what I've been up to. The bike is running better than ever, except for a little Shorai "hiccup"... I'll have more on that soon.
 

ncologerojr

Coast to Coast
DTT BOTM WINNER
The bike was running great, until....



It's 100% my fault. I over discharged it multiple times, upon a re-charge the crack developed and it will no longer hold more than 50% charge.
 

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