Topic: Yet another pod filter question....

[flyingwolf]

I have a 1977 cb750k. This is also my first rebuild so be patient if this is a dumb question. I have the stock 4-4 exhaust which I love, however when I got the bike the airbox was basically junk (plus I like the look of pods). I have some good quality foam air pods and I'm wondering if I'd be able to run them with the 4-4 if I put in some bigger jets (Right now I have some 115's and some 130's). I really don't want to buy a 4-1 exhaust but is this really the best way to run pods?
thanks

[spyug]

I wouldn't worry so much about the exhaust as long as it is in good shape with no leaks. If there are leaks, even pin holes, it can cause issues like severe backfiring on deceleration or hesitation in acceleration at certain speeds.

The main issue is to get the filters/jets sorted out. You have not identified the type of foam filter you are using, but generally, they should be a bit more air restrictive than say a metal screen type like an Emgo. Emgo and that sort don't really do much filtering and the air flows relatively freely. That requires an upgrade in jet sizes to compensate. However, you may not need to do that with a foam filter when it is correctly oiled. Or if you do, the jet sizes might only go up say one step.

 Before getting to this, you should ensure the carbs are clean and balanced with the stock jets or you could be chasing your tail trying to get it to respond properly when the filters are installed. It will be trial and error to find what works best after that.

While pods look cool just be aware that they don't all do the job you might be hoping for. Cheap filters can be a royal pain to make work and there is a reason K&N filters are so pricey.

Good luck and have fun.

[Davez134]

Easy answer, yes you can make pod filters "work" with the 4-4 exhaust. You will just have to mess with the jetting quite a bit (and understand what jet effects what throttle position) My opinion, which is not from an elitist "stock is the only way to go" viewpoint, is if you ride the bike alot go find a good condition airbox and be done with it.

I've ran both. My last cb750 had pod filters on it, from cheap to k&N. I understand the jetting, I tested and tested some more and got it to run good. But results were still inconsistent, wind, weather whatever. My current cb750 has factory airbox with k&N filter. Yes, It does not have to look of pods, but for a daily ridden bike I cannot tell you how much better it feels. Easy startup, consistent idle, no really unexpected "dead" spots through acceleration.

Choice is yours, and if only a part time ride and you are more concerned with looks you can get it to run ok with pods and help from some people on here.

[flyingwolf]

Thanks for the replies! I have well oiled UNI foam filters. The exhaust is in great condition, no rust (another reason why I don't want to get rid of them). I completely took the carbs apart (including the pilot jets) and cleaned them with carb clear, compressed air, and guitar strings. I have 130 jets in there right now, it starts up cold after about 3 or 4 kicks, but idles at a high RPM. The lowest I could get it down to with a bit of tuning had it idling at about 2500-3000.

I wanted to test everything before trial and error with jet sizes, so I sprayed some carb cleaner on the intake boots and it roared like I was giving it full throttle. Took the boots off and turns out they were in worse shape than I though. Cracks everywhere so it was getting a lot of extra air from the worn boots I assume. . So I order a new set (which sucks because they cost $100 new).

Am I nieve in hoping that with these new boots will bring the idle to where it needs to be?

[RAFster122s]

Going with pod you might need to go down a jet rather than up...Pods will theoretically have less velocity into the carbs and that will drop your fuel draw because the jet is no longer sized for the air velocity caused by the restriction of the stock air box and filters. Honda worked hard to get the jetting right out of the "box" with the stock system and for a stock bike it really is hard to beat overall. Function really trumps form often, and this is one of those cases that is true on the CB750, CB650, and CB500/CB550.   Modified motors it becomes less of an issue. But, yes...all the things that Dave mentions plus in heavy rain you really run the risk of sucking in water which the motor definitely will not like and some guys cannot run them in the rain as a result without some kind of shield to protect them from the rainwater.  Definitely use real carb parts...no aftermarket or you will be chasing your tail and often never can get it tuned properly as a result. So, don't waste your money on those carb rebuild kits with new brass, totally not worth the money.  Stock gaskets from Honda or direct from a Keihin source is the way to go...

[RAFster122s]

Uni filters can actually run richer...gauze type pods can be leaner...K&N being a better example of the gauze type pod...at least when the oiling and cleaning is done frequently enough and not overdone.
Same with the Uni can be over oiled.

David

[spyug]

I have had more success with Uni filters than any other. As I mentioned, they are a bit more restrictive than gauze type 'cones" so are easier to match to stock jetting. They don't seem to be as affected by crosswind or rain either in my experience.

As RAF did say, the engineers did spend a lot of time designing the airboxes for best overall performance so stock components and jetting are hard to improve on. Cosmetically, pod filters do look sexy, especially on a café, tracker or brat build but for an everyday dependable ride you would have less issues with a stock airbox.


The cracked intake boots will definitely be another source of problems as you note so new ones should definitely sort that idle issue. But don't forget to balance the carbs before and after the filter change up. A Morgan Carbtune or other vacuum gauge tool is indispensable for getting your setup to run right IMHO.

Good luck on the project.

[flyingwolf]

Thanks so much for the responses! I have a carb sync kit and I synced the carbs with the bad boots, but I'll do it again once I put the new ones on. I have the stock jets still luckily so if my bigger ones seem to be too rich I'll just swap them out. Here's hoping once I get the new boots I'll be able to just do a little tuning and she'll be able to ride!
Thanks for the responses you've all been helpful!

[PetesPonies]

How about the aftermarket air boxes? I little pricey, but look great. Perhaps they are easier to dial in?

[flyingwolf]

Well I got the new shiny boots. Put them on and started it up, but it will only run at the lowest of 2000 rpm but as soon as I give it throttle it either delays or dies. Also I have to start it with the choke on, but once it starts it revs up to 4000 rpm. I've blessed with the throttle adjuster quite a bit, I know the carbs  and jets are clean. I sprayed carb cleaner on the boots again and nothing happened so that problem is fixed. I don't know what else to do now though. Very frustrating.

[flybox1]

What pilot jets size are you running, and what are your IMS set at?

[flyingwolf]

I got it to steadily idle at 2000-2500. My idle jets are stock and the ims are out 2.5 turns. I'm going to mess with the ims and main jets next. Going to switch back to the stock jets and see what happens.

[flybox1]

Ok.  lets back up for a sec and get some vital info.
What is your carb model?
What # is stamped on your pilot jets?  you say stock, but that doesnt mean you or the PO swapped out for larger or aftermarket jets....
Are all your jets OEM Keihin jets, or aftermarket?   We need to know the size and the brand.
What type of pods are you using.  Emgo?  K&N?
Are your 4:4 pipes the stock pipes?

[flybox1]

Have you done all the suggested maintenance items for your K7?  (Valve adjustment, timing & advance, cam chain adjustment...etc.)
Did you verify all carb float heights are stock (14.5mm)?  Bench sync'd the carbs?
Verified your fast idle cam and accel pump are functional?