quick brain refresher question on diagnosis

[who444444]

Am I right thinking that a mild increase in idle rpm and a  occasional slight backfire during heavy deceleration might indicate a small  intake vacuum leak?
Having a slight senior moment and I'm still in my 50's 

dave

[76shuvlinoff]

It's about difficult to spray WD 40 or starting fluid or carb cleaner or just hold an unlit propane torch on the intake seals without getting some into the back of the carb air cleaner cover.

..... but that's what I would try first. 

Remove the air filter cover leave the backing plate on. I believe this stops the cover from funneling test sprays and such into the carb. With the bike idling give it a snort.

Are you running old style ignition? Might be time to pop the points plate and check the pivots and springs on the flyweights.

Mark

[Tobias]

I agree with Mark
But my money is on the flyweights

[easyricer]

That's the top two right there! 
EASY

[who444444]

Aha.  running points, and weights and springs have been in there for who knows how long. I was thinking about putting in new advance one of these days so.....
Thanks, you guys, for direction on which way to go. Will check for vacuum leak first as that is easier to do.
dave

[76shuvlinoff]

If it's been that long check the weights too.  Those are easier to change than the manifold seals.

Damned if you do, damned if you don't. 

[Old Crow]

Worst breakdown I ever had on the road on a Harley.  Broke the center bolt for the advance unit on my old Ironhead about 1800 miles from home. 
Ended  up I was 6 blocks from an Indy shop that had a couple of bolts and a set of weights.  I was able to get the stub of the screw out of the cam using the roach clip, er hemostats out of my wallet.

[76shuvlinoff]

Had my pretty chrome coil cover come loose and ground out the ignition. It took a while to find that. Cover went sailing. 

[ARBY]

Am I right thinking that a mild increase in idle rpm and a  occasional slight backfire during heavy deceleration might indicate a small  intake vacuum leak?
Having a slight senior moment and I'm still in my 50's 

dave

Not necessarily. Take a look.

http://www.hmfracing.com/forums/showthread.php?t=3927

I'd also check for a possible exhaust leak.

[HotRodShovel]

Good article, Arby.  I don't think I've ever NOT had some popping on a heavy deceleration.