I finally have my coupe up and running and everything broken in but have a few questions. For reference new cam is 460 lift, 280 duration with 104 degree lobe separation. Above 4000 RPMs the motor runs cleanly at any throttle setting, idle is rough but it will idle. Most noticeable change is between 2 and 4 K, under very light load it will pull OK but not totally clean, just before 4k the motor cleans out and runs great....................basically just like a 2 stroke coming on the pipe.

Undoubtedly some of this will be sorted with jetting ( I changed the mains but have not changed the pilot jet or needles yet) the biggest issue at the moment is loading it on my tilt trailer is a bit of a bear..............either slip the clutch or get a run at it.

Oddly enough I've never really tuned 4 stroke motors much, hence my question is the 2k to 4K bog under load pretty much standard? Mainly I'm asking as to get what's reasonable to expect off-cam.

Tom

calling BigE ... he'll have some answers... :)

looking at the cam specs you put up,i would think that, that cam would work around 4500rpm towards to maybe 7500/8000rpm,it has a very close lobe sep(104). what mods has the engine got. (comp ratio /head work/carbys/exhaust etc)what engine a12/14/15. i fill this cam would need high comp(11:1+)good head/pipes/carbs/ignition/good fuel 98+) . to make it work well.
(is it a speedway grind cam)what are you using to for.
"was the cam dialed/degree in when you fitted it" cheers

A12 10-1 ported GX head fcr flat slide carbs header

Cam degreed.........er sort of, no way to adjust.

i guess you could tune some of that out. my worked a12 was like that to, was really hard to get up ramps/stands. I believe thats a trade off for top end power.

I did some more fettling and it's waaaaaaaay rich at idle and just above. Going to have to adjust the mixtures screws and possible change to smaller pilot jets. The reversion is very visible..............you can see the fuel vapor spit out the velocity stacks.......yikes. Also when it stalls you need to hold the throttle open to restart.


Tom

Hi Tom
I recently built a 1300cc A12 with similar cam specs,real good power from 3800rpm to 9000rpm but even after being on the dyno half a day jetting and tinkering the car is still hard to get on the trailer. It is a trade off for good top HP.you should be able to jet some of the low revs problems out.I am real glad i got rid of my A14 and built the 1300,produces more HP and is not so hard on the gearbox(less touqe)Much better for the race tracks i run at.GREG
Now i need to put the 13x7 wheels on and some new rubber.

Hey Tom, what carb are you running - DCOE?

I'm working out the jetting on my A15, heres the cam specs, not as aggressive as yours but a few notches above stock....




my engine -
A15, .030 over, Canon intake, sidedraught Weber DCOE & the cam above, electronic ign. - stock dist.

Weber jetting:
Idle jet 50F8
Emulsion tube F7
Air corrector jet 150
Main jet 155
Pump jet 60

I got this worked out yesterday & I was running F11 E tubes, ended up at the F7 & finally changed the pump jet from the stock 35 to a 60 & wow, what a difference. when I first started jetting I wasn't sure if it was a timing issue or fuel starvation.

Hope this helps, let us know how it works out.

Evan

Evan I'm running Keihin FCR Carbs;

155 Main
190 main-air
50 Pilot
90 slow air
needles 3rd clip from bottom
mixtures screws 2 turns out (before last night

Right not it's about as torquey as my 77 Elsinore, I now have the mixture screws 1/2 turn out and that is helping but it's not night and day.

Thanks guys for the posts................it pretty much sounds like my experience is the norm. I'll fettle it some more but I'm not going to go crazy trying to get it to do something that isn't going to be possible with this cam.

Evan for my A/E motor I will be getting the regrind from Delta and not going quite as radical.


Tom

totally different animal then my DCOE obviously. Delta's "KC" grind I got isn't bad but it's definitely a bit lumpy but I've got it to idle now at about 1K pretty smoothly although my 11 yr. old thought it was funny to see the shifter vibrating.

good luck.