Crackling

As some may know, I have a somewhat modified 750. Js1 cam, BSA lifter and beehive springs, 40mm carb that we won't get into now, JoeHunt Mag, milled head RH1, 1 1/2" exhaust, blah blah blah.

My issue is when backing off the throttle a little when shifting or cruising a boulevard with little to no load while neither accelerating or de-accelerating, I get a bit of a crackling effect or a pipie kinda sound. It seems to say, "Hey, ass hole, give it some gas and lets get going here". Accelerating and at highway speed all is good.

My thinking is that
1. my cam is advanced 10 degrees to function
2. the big bore exhaust just isn't doing it for this setup.

So, for 1. perhaps a stepped cam key to bring it down to 8 degrees advanced.
and 2. Maybe a Viking 1 3/8" 2 into 1 might offer better back pressure for my fussy setup.
Or 3. this is the price I have to pay for my hot street 750.

For what it's worth I am neither lean nor rich throughout the entire range

What do you think?

Hi Pete,

My 850 isn't a million miles away from your spec, JS1, beehives, JS rods and pistons at 10.5:1 CR, 35mm FCRs, Tri Spark, etc.

When I tested 1 1/2 pipes on my 850 they produced less power, and even less torque, than 1 3/8 unbalanced pipes and peashooters.

My bike isn't 'fussy' so my thinking is that 'no' this is not 'the price you have to pay'.

Also, on the dyno, the Steve Maney system gave a huge increase in mid range and a worthwhile increase in top end. It was, by far, the best set up I tested.

So, if you have access to some stock 1 3/8 pipes, I'd suggest trying them. If you wanna get flash, you could do worse than PM Brooking 850 and buy one of his Maney replica systems that will soon be available. I'll be trying one hopefully, we could compare notes !

All IMHO of course.

pete.v said:

with little to no load while neither accelerating or de-accelerating, I get a bit of a crackling effect or a pipie kinda sound.

What do you think?

Click to expand...

I think that if you could bottle it and sell it, you could make a fortune ?

Other than that, you are so far off the page for a standard bike, it says 'ask the owner how it goes'...

Richening the (idle) mix up a shade can reduce/eliminate all sorts of noises on the over-run.
Its the lean burn in the pipe that you are hearing... (?).

Your crackling description reminds me of my 57 Ford 292 that was pumping out an estimated 300 hp at the flywheel (not too shabby for the early 60's).

When I tried to convince another gear nut that I had a stock engine with hot mufflers, he listened to my exhaust crackles, then listened to the engine idling (or rather running at 1200 rpm), and then pronounced "Dude! These shade tree hot rodders around here have only hot mufflers and lie about their engines. You have a hot engine and are lying about your mufflers"

Crackles just comes with the stage of tune .... it is raw gasoline combusting in the exhaust system. That happens with a cam.

Slick

Pete,

Just trying to get my mind around the sound to be sure I understand what you are describing. Is it a loud raspy cackling sound that is similar regardless if what constant speed you are decelerating from (40 or 70 mph), but perhaps the higher speeds equate to louder sound on deceleration? If that's what's occurring I'd probably align with Slick's camp and rationale.

Regarding altering cam timing to address the sound, just wanted to remind you that we got to the bottom of this previously, where your 10 deg advance setting resulted in an actual 2 deg advance, due to a machining error that occurred on an early lot of JS cams. So when you advanced your cam 10 deg, to achieve the result specified by JS (IN open 0.020" more than EX at TDC), the actual result was that it was advanced 2 degrees to move the IN CL from 105 deg to 103 deg. You can refresh your memory here.

http://www.accessnorton.com/radiused-cam-raced-years-bean-oil-t21574.html?hilit=pete.v JS2#p282219