Backfire and slow RPM drop

[faber]

Yeah I'm running 2 1/4 now.

Interestingly my buddy with a 77 bonnie has the exact same problem. I saw some suggestion that there could be a problem with the jetting, and the fix might be to replace the jets (pilot and main) completely.

 

[faber]

If I can't find anything else wrong I'm going to pull the carbs and rebuild with new parts (brass). When I do I'll document it on my fmbikes site.

 

[xs400neophite]

check yer mufflers fer leaks/holes back pressure issue and runs lean...maybe

 

[faber]

They seem solid, no leaks indicated with backfire / popping. Plugs look good and don't indicate lean condition

 

[xs400neophite]

so many posts on this subject...do a search maybe type 'hanging revs' or something.
...and then there is
http://www.xs400.com/forum/showthread.php?t=4951&highlight=houghmade
Love drewps prose...poet but didnt know it

maybe hit up 'dman1049'

 

[bentwrench]

This sounds like a lean condition still. You said 82 - DOHC? Did you switch to pod filters? when you installed the carbs, did you really crank down the clamps on the boots? Does this change as the engine gets warm (indicating valve tappets are out of spec?)

It's likely not ignition - this still sounds like carbs.

 

[domains]

2 1/4 was the sweet spot for me aswell tried 2 1/2 then 2 but it was slogish... thx for tip runs great now

 

[faber]

Well a bit more work on the bike recently after a long time away from it (it's been a busy summer).

Anyways, I pulled the filters and replaced them with pods, after that rejetted to 130 on both sides. the bike seems to run very well, less the idle down issue.

After that I tried to tape up the pods to restrict air flow, this actually worked well which speaks to running in lean condition still, however once the bike warmed up again it was back to it's old tricks of idle down problems.

At this point I suspect possible ignition issue however any additional advice would be great.