Topic: Sup ya'll. Got some carb questions. Where do I start?

[liaudio]

Firstly, thanks for checking out the post.

I recently got a '75 750 k5.  It has Emgo filter pods, 4-2 exhaust, (which I'm told is called a 'California Header,' It looks like two mini baffles on the end of the headers.) 

It was running like crap so I put in 120 main's, air screw's like 1 1/4 turns out, and the jet needle clip in the middle.  This is the best I could get it so far.

This is the first time I've actually had to fiddle with any carb adjustments on any of my CB's. Currently rocking a 70 CB450 Cafe, and just sold my '76 750F Cafe.  Both of them ran mint.

This bike just doesn't seem to run right.  I've had the carbs off twice, cleaned everything out w/ carb cleaner and checked everything out.

Timing is spot on and I just adjusted the valve lash.  Point and plug gaps are spot on.

It idles a little rough, and the air screws don't seem to effect idle speed very much.

From a rolling start, if I crack the throttle wide open, it bogs down and dies until I let off the throttle.  If I gradually roll on the throttle and then floor it, It seems to go ok.

It's a little flat in the low/midrange and when it's wide open.  At a little closed from wide open, it seems to take off the best.

I just bought a Carb Syncronizer on Ebay and I'm hoping that Syncing the carbs might help the idle problem. 



Any advice?

Is it easy to sync carbs?

Should I ditch the Pod Air filters? (which I love the look of!)

Thanks everyone!  Long time member, first time poster!

[Jugghead]

Boy, where is TwoTired when we need him?  He was/is the master of online diagnosis!
I don't think I can help much, but my first suggestion would be to look at the spark plugs to determine either rich or lean conditions.
There are great posts regarding reading a spark plug, and from there you can diagnose if you need to lean out or enrichen your mixture.

I know someone with a lot more knowledge than I will post more specific information, but that is a starting point.
good luck, and keep us posted on your progress.

[Jonesy]

Carb sync could be part of the problem. My stock 750 did this too untill the carbs were back in balance.

[liaudio]

you guys respond quick.  That's awesome!

[jdpas29]

ditch the pods.

pods are the devil, bobby.   

[scondon]

ditch the pods.

pods are the devil, bobby.

"Pods cause cancer"(sniff, miss ya TT )

     With pods and what I'm guessing is an open exhaust I would think your running lean on idle and possibly at WOT. I ran the air screws at 1/2 turn out(richer) before finally getting larger pilot jets(45). A plug chop will tell you what's happening at mid range and WOT, but your description sounds close to what I was experiencing with main jets that were too small. I've got an 836 with a 4-1 so don't take this as anything more than a educated guess.

    If you like the smooth, all around throttle response of your other bikes AND you don't want to pull your carbs once a month until you get them tuned to your set-up then the easy route is to revert to stock airbox and possibly a more restrictive exhaust.

[liaudio]

No Pods! No open exhaust?!?     

I was afraid of that.

[Bodi]

Check the FAQs, there's a lot on carb jetting. Pods make a big difference, and if you're not ready to do a lot of fiddling with the carbs you should probably get a stock airbox and intake boot. Baiscally you have to follow the logical procedure: floats set correctly before anything else, main jet first, needle clip second, pilot jet and mixture screw last. You may have to reshape the needles, raise or lower the float setting, or even modify the slide cutout if you want "perfect" operation.

[eldar]

The exhaust is fine. Rarely do you have to do anything with jetting cause of exhaust.

Your throttle ussue can happen either running lean or rich. I get it and run slightly rich in the mid-range.

When you do a chop, make sure your plugs are clean to start with.  I would say to also do a chop at 3 different rpm ranges.

Start with idle or just above idle, then move on to mid-range about 4000 rpm or so, then do one around 7000 rpm.

My reasoning is this, Each speed is using different jets. The idle will show if your low speed is lean or rich.
The mid-range shows the mix between the 2. Going at 7000 or above and you are on the mains only.

doing it this way can tell you more than just a WOT chop ever could.  PLus with the mid-range, if you are lean, but your idle is good, then you can raise the needle one notch then.

Maybe this sounds goofy but I would be willing to bet it probably works.

[nickjtc]

Are you sure all of the jets are absolutely cleaned out? As in, poke a fine wire up them to be sure.

[scondon]

The exhaust is fine. Rarely do you have to do anything with jetting cause of exhaust.

   Gotta disagree with ya Eldar. Try removing your muffler from your header and see how well your bike runs. It's my experience that going from a restrictive muffler to an open exhaust requires carb adjusting/jetting change.

[eldar]

Straight pipe yes but as old fart has seaid before, he could count on his hands the number of exhausts that require rejetting.

A simple 4 - 2 with baffles, probably does not need it. If they are baffles.

[Jugghead]

When you do a chop, make sure your plugs are clean to start with.  I would say to also do a chop at 3 different rpm ranges.

Start with idle or just above idle, then move on to mid-range about 4000 rpm or so, then do one around 7000 rpm.

My reasoning is this, Each speed is using different jets. The idle will show if your low speed is lean or rich.
The mid-range shows the mix between the 2. Going at 7000 or above and you are on the mains only.

From what I have read by Two Tired, this is a commonly held misconception.  RPMS are not what determines what jets are being used, it is throttle position.  People say to mark your throttle at 1/4 throttle, 1/2 throttle, and 3/4 throttle, and THAT is how to do a plug chop.
While RPMs are loosely tied to throttle position, they are not in direct linkage.
Chops are based on throttle opening measurements, not RPMs.
 Not trying to shoot you down eldar, just bringing up a differing opinion I read here.  (I am by no means any type of master, and have not yet done a plug chop on my bike)  That said, it is just based on what I have read, not actual experience.

Start with idle or just above idle, then move on to mid-range about 4000 rpm or so, then do one around 7000 rpm.

My reasoning is this, Each speed is using different jets. The idle will show if your low speed is lean or rich.
The mid-range shows the mix between the 2. Going at 7000 or above and you are on the mains only.

doing it this way can tell you more than just a WOT chop ever could.

I guess I would recommend doing a chop at idle or 1/4 throttle., 1/2 throttle, and either 3/4 or WOT (wide open throttle) instead of idle, 4ooo and 7ooo RPM.  Each speed is not using different jets, each throttle position uses different jets,
If we take the throttle position vs jets used graph as true.
Doing multiple THROTTLE position chops WILL tell you more about what jets are too rich vs too lean.
Peace,
jugghead

[Jugghead]

See this post for everything explained in detail by our guru, TwoTired
http://www.sohc4.us/forums/index.php?topic=9817.0

[nickjtc]

See this post for everything explained in detail by our guru, TwoTired
http://www.sohc4.us/forums/index.php?topic=9817.0

Thanks for finding that. All very interesting! Makes you want to go out and do a plug chop just for the hell of it.