[Alizard]

If I am cruising and let the throttle close and hear the "rap rap rap" exhaust sound, is that running too rich or too lean?

Still trying to dial in the MAC headers. Pilot jet headaches.

#40 (stock) runs too lean. Balky throttle response, TERRIBLE when cold. Best setting for mixture screw is backed way out to get very rich.

#45. Great throttle response but runs too rich. Has "surging" at light throttle openings in the 2k to 3k RPM range. Best screw setting is cranked way in to get it lean enough.


WENT TO #42.5:

Throttle response is fairly good, best screw setting is about in the right place. PROBLEM: I hear lots ot "rap rap rap" when I let off the gas. Did not hear that with the other jets.

 

[Alizard]

HMMMM.... just tried applying a bit of choke and it ran better so it sounds like it is running too lean still. What a PITA.

 

[JimmyD]

Yeah, I think this is why some remove the exhaust recirculating systems, i.e. marbling of their bikes.

It's supposed to help stop popping. I'm assuming a 70s twin doesn't have much of that on it though.

 

[Alizard]

Yeah, I think this is why some remove the exhaust recirculating systems, i.e. marbling of their bikes.

It's supposed to help stop popping. I'm assuming a 70s twin doesn't have much of that on it though.

Doesn't have anything like that. Just a stupid MAC 2-1 header with unequal length down pipes which were probably designed by Satan to make men crazy. I don't think they are ever going to run right. I guess I will have to put the #45 jets back on and live with the surging.

 

[elr658]

BH don't you know that MAC stands for Make Another Choice? Intake leak.

 

[Alizard]

BH don't you know that MAC stands for Make Another Choice?

I know it now.

The MAC header doesn't block the oil drain plug or the center stand like the high performance header did. It's also a lot quiter and doesn't make my ears ring.... or my neighbor complain.

Intake leak.

Nope, already checked that. It "went lean" going from a #45 jet down to the #42.5 jet..... makes me wonder about the jet. I didn't change anything except drop the bowls, screw in the jet, fire it up... and it is running LEAN!

Someday they will invent something adjustable to dial in the richness..... oh, wait.... they call that the choke.:mrgreen: I'll be using that driving home tonight....

 

[JimmyD]

Well.. Are you sure it's actually too lean? My EX pops like mad on deceleration and it came stock without the air switch. And I know it's running well, even a little rich at idle. Stock cans.

I dunno, I dont mind the sound and my plugs have told me the bike is running alright at mid range.

 

[StarGate]

Mine use to pop bad like that and only 2 things I found that helped other than changing jets to make it richer was to idle it up about 200 rpm and tighten the nuts that held the header to the head. I think I had a slight leak on 1 or 2 of the pipes letting it draw air in on decel.

 

[Alizard]

Well.. Are you sure it's actually too lean?

Yep, and last night at about 10PM I found out why:

The new BS30/96 pilot jets which fit my Mikuni carburetors (mechanically fit) do not use the same sizing pattern. The "new" 42.5 I just bought has a much smaller hole than my stock 40 jet, hence the bike running so much leaner than it did with the 40.

And, the new #45 pilot jets that came in the rebuild kit I recently purchased are also smaller than the stock 40 jets, but they are slightly bigger than the new 42.5.

At least I know I'm not crazy......

The stock 40's still run too lean and the "stock 45's" I bought way back in 1982 run a bit too rich, because they are bigger than the stock 40's.

I will have to buy a bunch of new BS30/96 jets in the size steps up and use my sizing gauge to pick the one that falls between my old 40 and old 45. My guess is it will be about 50 - 52.5.

 

[Alizard]

Mine use to pop bad like that and only 2 things I found that helped other than changing jets to make it richer was to idle it up about 200 rpm and tighten the nuts that held the header to the head. I think I had a slight leak on 1 or 2 of the pipes letting it draw air in on decel.

My head gasket is dead tight, I will going for richer jets as soon as I order a bunch more.

 

[JimmyD]

At least I know I'm not crazy......

Glad your sanity is intact :smile: