Topic: Degree Cam, How to Get +3 Degrees of Ignition Timing?

[willbird]

Finished putting together my high-ish performance motor and degree'd my Yoshi Daytona cam according to the specifications in the literature.  Lobe centers are set exactly as they should (105 degrees).  According to the parts catalogue this cam should have 3 degrees of advanced ignition timing.  Since I can't go off the standard plate markings where 'F' is marked, how do I dial in the additional 3 degrees?

Thanks in advance

What is your compression ratio in your “High-ish Performance engine”..?

With higher than stock compression and 87 octane,  1 -2 degrees of ignition advance can be the difference from destructive detonation or not when on the ragged edge.. Especially with an air cooled engine..

Your compression ratio and fuel will determine your best advance or the maximum allowable ignition..It is good you know where your cam and TDC is…

Timing is everything in high performance.

Like Scambler found what was best in his application. I’ve seen the same best ignition lead results with the old RC 836 12:1 kits using the old 95/96 octane leaded gasoline.. I like the new unleaded all gasoline better but may error too by using higher than actual needed octane….I’ve tried VP leaded gasoline but never really felt “butt dyno” a difference other than a much lighter wallet..

             If you get the chance try the VP non-ethanol small engine fuel with 94 octane....my bikes love it and it smells like the old Testor's model cement from the 60's. unfortunately the price for a 5 gallon pail has gone through the roof. Lucky for me there is a gas station 3 miles down the road from my new house in NH that sells non ethanol out of the pump.
             

There is a no ethyl 90 station in my town but it is on a shared hose with the other grades. Been meaning to buy two of the "ermergerd don't use these for gasoline" jugs and then take them up and run 1 gallon into the truck and then fill them. There are a bunch out there that the makers say to "use only with race gas, methanol, etc" I think to get around the EPA BS. The only semi local "dedicated hose" non ethyl is "rec90", Philips 66 has that. Kind of hard to find non ethyl at a random station when the odo hits 125.

https://www.ruralking.com/_next/image?url=https%3A%2F%2Fd2dz5gposoi2o6.cloudfront.net%2Fecom%2Fprod%2Fitem_images%2F7%2F0%2Fc%2F4%2F70c49a6729afb8c358ab10c6f6af069f534832ee_21636003_21636003_image_21636003.jpg&w=640&q=75

Long link but it should work.

This is not a portable fuel container as described by ASTM, EPA, ARB and other official agencies. For Racing Fuel only, such as Nitromethane or Methanol, used in sanctioned motorsports. NOT for fuel used on highways. Also for storage and transport of feed, water, attractants, fluids and other outdoor products.

$20 at Rural King.

[Tracksnblades1]

He’s in California…He’s f*#&ed. I’ve never heard of anything good at their pumps, unless something for vintage is available..maybe the airport still has real gasoline..

Our VP station has most of the unleaded blends available at one pump.. It’s 1/3 of the price of a 5 gallon of the same but still high..
I spy the 116 octane and wonder whether 40psig of boost is the same as 17 to 18:1…🤔

[NitroHunter]

I plan to use pump gas, we have 91 octane here in CA.  I never found my compression ratio as I have a slightly modified head and Yoshi 823 pistons.  Don't suppose there's a way to find out based on compression test?

Cylinder cranking pressure is the important thing to know here. Cam profile opening / closing numbers can drastically alter this. There's some really great online calculators to show you this. My old 836 had 240 lbs cranking pressure reading on my brand new Snap-on compression tester. As pump gas got worse my ignition timing kept being backed off, and I don't remember the butt dyno ever confirming the power gains claimed by the 108 octain boosters of the day. I seriously doubt you'll be anywhere near that stupid pressure but it is attainable and can be carefully streetable.

[Finnigan]

Today I pulled out the degree wheel and confirmed TDC with a piston stop.  It landed surprisingly close to the T mark on the cylinder I was using but decided to set the ignition timing to +3 degrees BTDC according to the degree wheel.  Both cylinders are bang on now.  I used 6 degrees BTDC per the manual as my reference.

[scottly]

I used 6 degrees BTDC per the manual as my reference.

That version of the manual is WRONG!

[Finnigan]

I just read your post again on the F position being 10deg BTDC

Looking up the topic in my cb750 book the K1's had 6 degrees while the later models had 10.  Looks like I'm aiming for 13 instead of 9...3rd times a charm.

[scottly]

My K1 advancer has the F mark at 10* BTDC.

[Tracksnblades1]

I plan to use pump gas, we have 91 octane here in CA.  I never found my compression ratio as I have a slightly modified head and Yoshi 823 pistons.  Don't suppose there's a way to find out based on compression test?

Engine:
Line bored cases and coated bearings
Balanced stock weight crank
Yoshi SuperRods
Coated rod bearings
Yoshi 823 NOS kit
Daytona Cam
HD cam chain and MessnerMoto tensioner
Ported 71 head (Jerry Branch)
Valve job by Kurt and HD APE springs

Read on Yoshimura’s web site that Pop’s original 823 pistons were borrowed from (and later based off of) Honda’s 350 twin 64.5mm os…

If yours we’re not high domes I’m guessing you might have up to 9.8:1 compression..
Probably less if your chambers have been reworked, valves sunk, OEM deck clearance, and gaskets...?
Do you have any info in the piston boxes..

[Finnigan]

That's interesting, hope mine are higher compression than that but is what it is.

I have an original article that says the rings from a 350 will work (can't remember if they need to be 1 size over) but that pistons from the 350 will absolutely not work in a 750.

Pics of the boxes, unfortunately no literature to go with.

[willbird]

That's interesting, hope mine are higher compression than that but is what it is.

I have an original article that says the rings from a 350 will work (can't remember if they need to be 1 size over) but that pistons from the 350 will absolutely not work in a 750.

Pics of the boxes, unfortunately no literature to go with.

I have seen mention of using 350 pistons ?? Quick google gave me this

When the big bore kits first came out they used cb350 pistons but they did need modifying. The Wiseco kits are 65mm which is a 836cc, this is the best option as the pistons are far superior to the 350 pistons. The 350 do need modifying as the dome is to tall and doesn't have correct valve reliefs.

Some mention of early 811 kits using heavily modified 350 twin pistons.

350 twin stock bore might be 64mm, 4th over is maybe 65mm ??

[Finnigan]

The pistons themselves look a LOT like the Honda ones except the ART and HONDA casting marks are replaced with 812 and Yoshi logo.

I wouldn't be surprised if these are made by ART in Japan since Yoshimura and Honda had the relationship they did, maybe even helped continue development.

[Tracksnblades1]

Looks pretty and flat on top..😇

What exhaust valve to piston clearance did you end up with your big cam..?
Intake..?

[MRieck]

The pistons themselves look a LOT like the Honda ones except the ART and HONDA casting marks are replaced with 812 and Yoshi logo.

I wouldn't be surprised if these are made by ART in Japan since Yoshimura and Honda had the relationship they did, maybe even helped continue development.

What kind of gloves are you wearing....they look nice.

[Finnigan]

Just amazon disposables, they tear more than I'd like but have great grip

[MRieck]

Thanks. The texture does look good. Chemicals F all of them up unless you are using gloves designed for nuclear waste.

[Finnigan]

These aren't bad in terms of chemical resistance, they eventually break down but you can go through just a few pair of these where the cheap nitrile from Costco last a few minutes whenever I put them on.

Really though, hardest part is putting them on because they are a little thicker than normal and they tend to tear

[HondaMan]

Thanks. The texture does look good. Chemicals F all of them up unless you are using gloves designed for nuclear waste.

Boy, if THAT isn't the statement of this decade, I don't know what is!?
As near as I can figure, most of these gloves are made of oil so it also dissolves them on contact.