Topic: Help : popping around 6000+ RPM 3/4-WOT : 73 CB500

[DSPRW]

73 CB500
MAC 4-1 Exhaust
105 mains
40 slows
needle clip unknown (carbs were cleaned right before I picked the bike up, so I've only been in the bowls)
floats at 22mm
fuel flows well
no vacuum leaks
questionable exhaust seals

Been digging through these forums for months getting the help I've needed, but now I think I need some specific help. So thanks for all the good info in the forums. Here's my problem.

After syncing my carbs I'm getting a popping and backfires at higher rpms from 3/4 open throttle and up. My intuition from what I've read on here is that she's leaning out at that point. I put the 105's in and the problem persists. I should check the needle clip, yes???

As well I'm going to go a size up on the slows because she has some stuttering in the lower rpm range on take off.

Please advise.

[dave500]

has it got pods?you didnt mention the intake, go right over your ignition first though

[Stev-o]

Do you have a baffle in the Mac? Is it popping on decel??

[dave500]

popping under load?

[DSPRW]

• Stock air box ( pods waiting, wanna rule out everything else before changing up the carbs )
• Baffle is still in the MAC.
• Ignition, from what I can tell, seems fine. Timing was on, point gap is good, sparks are purple-blue. ( Opinions on the electronic ignition?? Replacing coils etc? )
• Definitely popping under load, and gets some real power in 1st starting at 4000 then at 6000 w WOT she cuts out ( dudududududududududu sound, power flattens ). If I reduce throttle under 3/4 we're back in business, all the way up to 10000+. This makes me think its not the ignition.
• No pops on deceleration, I think it sounds nice on deceleration but I'm no expert.

When I purchased the bike, the carbs were so out of sync (among other oversights) I couldn't believe the shop left it like that. ( Probably expected me to bring it back for service

I'm getting much better mid-range power with the 105's, so I think I'm headed in the right direction, really wanna solve that WOT issue.

Thanks for the timely responses!

[Vinhead1957]

Sounds like the main jets are too big

[DSPRW]

So I should go back to the 100's and adjust the needle to be more lean? (even with the 4-1?)
or add air?

Thanks Vinhead

[Vinhead1957]

I'm not sure I think you will need to experiment to find the right mixture.  Move the needles all the way down highest setting. Then all the way up lowest setting.  There is no expense there!

Document your step and results. 

[dave500]

yeah put the 100s back in,you dont need to rejet for just a 4-1 pipe,the needle dosent even need to altered from the standard setting,itll work ok in the middle setting,once youve got it going well then decide to use pods your on your own,check the advancer is not stuck.

[DSPRW]

So checking back in.

I decided to go with Pods anyway and figured if I'm going to do any tuning I wanted to do it based on those.

So I put em on...with the 105 mains and a 42 slow
Way too lean, touch the throttle and die...but idled very nicely.

Went to my largest set of 120's, needle clip at leanest marking.
Still lean, hunting/surging. Terrible off the start.

120s with needle clipped at richest position.
Getting really close now...

So now she's running pretty well, need to take tomorrow and do a range of plug readings to figure out if I need to go up or down on the main in 1 increment. No more "dudududududu" at 6000 rpms, but still cracking with WOT around 8-9000 RPMs.

Going to follow the general advice of plug reading at this point.  Main, needle, then slow. I'm loving the extra oomph I got out of the pods.

Thanks again