My XS is a dog

[yamahammer]

Hey folks, I'm a new guy.

My 76 650 is rephased with Hugh's crank/cam, Mikes 750 kit sans base gasket, modified points with TFI modules/coils, BS38 carbs with pods (25 pilot, stock needles-middle clip, 130 main), classic hooker 2-1 exhaust.

All of the above parts were assembled by me, and I've got it tuned to the best of my abilities. The problem is that it's slow, and it vibrates worse than a 360 above 4 grand. Below that, it hardly vibrates at all.

The clutch doesn't even slip, it can't be putting out what it's capable of. The timing is spot on, the carbs are bench synched and dead cylinder sychronized at idle. Why won't this sucker rev out?

My gut's telling me that the cam isn't appropriate for the increase in displacement and static compression. Maybe I need a cam that bleeds off a little compression, lowering the dynamic compression ration and letting waves fill/evacuate the cylinders?

Thanks for any suggestions, I've bounced this off of all my local sounding boards.

 

[FB71]

to me, it sounds like the cam is out of time with the crank.

 

[yamahammer]

Perhaps very slightly. It was perfectly in time with a new endless cam chain. It's been adjusted twice, not very far either time.

 

[jd750ace]

You are not giving it any fuel! Free flowing exhaust, intake, and a 750 kit? you need to seriously rejet.

 

[yamahammer]

The plugs have definitely never showed signs of richness. I'll get some bigger mains and give it a try, I've raised the needle and it killed the fuel mileage.

 

[yamahammer]

I found some tiny drill bits and opened er up to a 150 main. I like it, nice and smooth. It makes sense now that I think of it. The pods don't allow for the same velocity/signal that the stock intakes do. I'll be interested to track the fuel mileage.

thanks for the suggestions!

 

[jd750ace]

Although I know the earlier BS38s were jetted differently than my 79, I'd be checking it out for signs of lean running down low on the pilot circuit as well. The carb guide is a wonderful document. A 14% increase in potential volume of air (650-750 CC increase) will want that kind of increase across the board in fuel, all things being equal (which they seldom actually are!) That's why we tune.

 

[650Skull]

Have to identify your carbs and make sure the jetting is for your set. Carbs changed every 2 years, Different BS 38 settings for 74/75, 76/77, 78/79 and BS34's for 80 and later.

750 kits on Standard running 650's don't need the carbs changed much, if at all. most running pods and free flow pipes still don't jet much bigger. To large jets will wash the bores.

Identify your carbs, go back to original jetting and work from there. As JD says read the carb guide. Change one thing, then test and then another and test.

 

[DIRTY DOG]

did you degree the cam in with a degree wheel sounds like the cam is off.

 

[yamahammer]

It's running really well. As far as the pilot mixture screws are turned in I imagine the pilot jets are plenty big.
I might richen it up this winter but for now, 150 seems to be the way to go. I would like to check cam timing with a degree wheel when the snow flys. Going by the cam dot and tdc it's close enough to leave it alone until the next leak or breakage

 

[yamahammer]

Thought I'd give you an update, I've tried soooo many things. I'm now running .006 intake clearance, .012 exhaust clearance for starters. I know it's noisier but the degree to which it effected runnability and power was surprising. The other thing I just did was pull the muffler off and left open headers for a quick rip, much less vibration at highway speed. The waves in the exhaust must have been producing some negative feedback through the frame. It's far too loud to ride like this for any length of time, but damn if it doesn't work well for the time being.

Does anyone know of a good flowing/sounding minimalist baffle for 1.5" headers?

 

[JP50515]

What did you have on before? Just so we don't send you in circles.

 

[yamahammer]

It was an old 2-1 hooker system. I just took the muffler off. The headers are parallel at their outlet so I'm thinking I might get an x-pipe and try a few of those homemade emt baffles I've seen here. Maybe Mike Morse's inserts at both ends.