2.25 w/ a 2.5 cam, how advanced?

[scott]

hello all

i heard that putting a 2.5 l cam in a 2.25 will allow for or was it require more advance timing. right now i get a pretty smooth idle but it's waaaaay advanced and the carb pops on acceleration. any thoughts?

[badvibes]

Scott-

Did you do the check for vacum leaks around the carb? Also does the pop/backfire go away or lessen if you retard the timing?

Jeff

[scott]

checked and no vacuum leaks, seams worse when retarded. could it be the gas? it's sat in the tank sincelast sept.

[Bertha]

I have that set up in my truck and run the timing associated with an 8:1 head(cant remember right now but it is in the ws manual) You shouldn't need any more advance than that. Also using champion N12yc spark plugs fwiw.

[scott]

could i have installed the diz/oil pump drive gear off by one spline? if so would it have started? would it be why it seems to idle smooth at 30 degrees before tdc? that gear has 15 splines which devided into 360 is 24.

[Bertha]

could i have installed the diz/oil pump drive gear off by one spline? if so would it have started? would it be why it seems to idle smooth at 30 degrees before tdc? that gear has 15 splines which devided into 360 is 24.

That shouldn't have any effect on your timing, only on the position in which your distributor sits.

[greenmeanie]

Its been a while but IIRC you can add about another 4° of advance to the base timing over stock by adding a 2.5L.

[scott]

Its been a while but IIRC you can add about another 4° of advance to the base timing over stock by adding a 2.5L.

so if i understand you my timing should be between 7 and 10 degrees befor tdc. and that freak'n drive gear will affect the orientation of the dizzy to the engine but shouldn't mess with the timing, i.e.: where the vacuum adv doohicky is situated now may be different than before but use the timing marks regardless of the the diz' orientation, such that i'm between 7 and 10 before tdc.

once i got an idle at say 9 degrees before tdc w/ vac adv disconnected, adjust mixture 'til the idle smooths out hoping that i'm between 1 and 2 1/2 turns out on the mix screw.

i notice that if i excel slowly no pop'n sound (backfiring thru carb). and again i think i should o get some good gas. there's no brakes or clutch master cylinders yet so no road testing for about a week.

[Bertha]

that freak'n drive gear will affect the orientation of the dizzy to the engine but shouldn't mess with the timing, i.e.: where the vacuum adv doohicky is situated now may be different than before but use the timing marks regardless of the the diz' orientation, such that i'm between 7 and 10 before tdc.

.


correct

[greenmeanie]

i notice that if i excel slowly no pop'n sound (backfiring thru carb). and again i think i should o get some good gas.

If your still running fuel from before you started the rebuild it will have gone off after a few months. Put a tank of good fuel, doesn't have to be higher octane than your normal stuff, and dilute the bad juice. That'll help her running no end.

[Jim-ME]

Ethanol blended fuel bad much sooner than regular "old" fuel. Add some fresh and try to find Stabil for ethanol. I use it all the time especially if the Rover sits for any length of time. It stops the separation of the ethanol from the gas.
Jim

[scott]

fuel issue eliminated. maybe i should check valve adj?

[badvibes]

Scott-

A source of popping thru the carb can be if the dizzy has enough advance it can send the spark to the plug before the intake valve closes fully allowing the fuel mix to ignite back thru the carb. That was why I asked if retarding the timing helped, you replied it seemed to make things worse. Sure check the valve adjustment it could be off. Do you have a live chicken you can spare?

[scott]

used up all the chickens trying to install the motor w/ the clutch slightly out of alignment.

should i be expecting a rougher idle w/ a 2.5 cam? you know kind of giving a little at low end to gain more at the top.

[Andrew IIA]

My SIIA (8:1 head, 2.5cam, 2bbl Weber), which is running well, is timed at 6 deg BTDC.

YMMV. Regards, Andrew
'63 SIIA 88" SW

[scott]

thanks, andrew. i would time it by ear and the smooth sounding idle was happenning around 15-18 btdc. set at 6 and it idle rough but accelerates nicely.

[mechman]

I'd set at 6 btdc and check for an issue in the idle circuit of your carb. Old gas (or garbage in the fuel) may have partially clogged it. Check the accelerator pump circuit while you're at it, too - a sticking ball valve can cause rough idle as well. Too much advance will burn your valves...

Mech

[scott]

found part of the problem. while testing the adv action of the dizzy deck plate i notice it moving less than smothly. pulled it off and found a scratch about 5/16" long on the undeside where the eyelet for the ground wire was rubbing. i think this was mess'n with the adv returning to 6 btdc and slowing its advancing. still have a little popping but not nearly as much. lubed up the mechanincals in there too as they were pretty dry from the thorough cleaning i did when the motor was at the machinist's.