Engine tuning

[TGGodfrey]

Good Morning Guys

Factory 340 AAR should be around 10-15 inches of vacuum correct?  I am at 5" at 850rpm.  I didn't build the motor so it has me wondering if he put a cam in it.  Idle screw should be pretty good.  I have them 1 turn out from killing the rpms.  Turning them in doesn't improve vacuum.  Power valve is good. I have base timing set at 5 degrees BTDC.

Another question.  Will the secondaries open free revving.

Thanks

Terry

[Cratos]

check for missing or unhooked vacuum line

[Cudajason]

check for missing or unhooked vacuum line

your initial timing seems pretty low.

I would try increasing that.  Increasing it should increase the RPMs...keep going until the rpms  stop increasing then back it down a bit.

You may need to adjust the carb as you go to get the idle speed back down.

That should increase your vacuum.

Jason

[TGGodfrey]

I can increase it, i was just setting at what the manual called for.  Total timing at 2500 is 32 without the vacuum advance hooked up.

[Chryco Psycho]

You will need to limit the mechanical advance  slots in the dist but for sure advance the timing at idle to at least 12* probably more .
No the secondaries will not open without a load on the engine free revving is too fast to allow time for the vacuum to open the seconadries .
The power valve needs to be at least 1.5 inches lower rating than the vacuum you get at idle in gear so at 5" you need 3.5 or lower rated power valve to stay closed at idle

[TGGodfrey]

I do appreciate the help.  I am familiar with the power valve setting and found a 3.5 in the carb so it's good there.  It's also got 55 jets in the center which is kinda lean.  Factory had 61 if i recall.  It does fall on its face if you slowly rev up to 3000 so i am going to have to pull the center again.  If you blip the throttle to engage the accelerator pump it will rev up just fine.

Floats are set just perfect at this point. 

[TGGodfrey]

I take it back, i found a 6.5 Pv in it.  I miss read it when i changed out the gaskets.  E3 on one side and a very faint 6 by the 5 on the other side.  Off to get parts.

[TGGodfrey]

Ok, got the PV sorted out and 62 jets in it.  Richened it up at idle about 1/4 turn.  Total is 1 1/4 turns out.  Base timing is 10 degrees.  Took it all the way out to 15degrees.  5 hg is top vacuum at 850rpm.  I'll have to take it out tomorrow and see how it feels but i think that is the best it is going to be.

This winter when the motor comes out for paint and cleanup, i will degree the cam and see what the lift and duration is.  I have a feeling it isn't stock. 

Thanks for the help

Terry

[Chryco Psycho]

No way it is a stock cam with that low vacuum or it is installed way out but it would not start or run well , 62 is correct for stock jetting .
As long as you use a limiter plate no reason not to run the timing up to 16* at idle if it likes it .

[TGGodfrey]

Sorry to update so late.  Cam has factory lift.  It's not an OEM cam as there are numbers stamped in the end of it.  Cam itself was 3 teeth advanced (crank was retarded).  Every valve grooved the pistons, all intake pushrods bent or bowed to some degree.  Stock cast pistons has .007 clearance.  Engine still full of breakin grease and rings not yet sealed.  Needless to say i was appalled and i got it all torn down.  I am going to bore it, sink new slugs in it, cut the crank 10/10 to clean up some of the marks.  Polishing won't take them all the way out.  Still debating on forged rods and balence out the front new in the motor.  There were 5 rods replaced from a later 340 but all the rods are 803-811 grams so balencing may not be bad depending on what the small ends measure.  Going to try stall hardened seats.

The previous owner claimed his friend was an engine builder and did the work.  This was a half added attempt at a rering.  A high school kid wouldn't do this.  He is no engine builder.  Those pistons wouldn't have made it past 20 miles.

[Chryco Psycho]

Hmmm that might explain the low vacuum !
Sounds like the cam was liked up with the crank key not the timing mark , not the first time I have seen that . if the block is decent I would not bore it far , maybe just .010 & get some Diamond pistons , used forged what ever you do

[Cudajason]

ouch man...that sucks.

If the block is good, I have a set up standard bore 340 pistons and rods that I am looking to sell.  Shipping might suck, but...

[Scooter]

Geesus that sucks... but at least you won't be fighting a mystery any more one you get it back together.

[TGGodfrey]

The timing set use was a three keyway set and yes, he lined up the timing on the mark and f the keyway.  Complete install error.

Factory pistons won't work, thank you for the offer though.

The issue on rehire right now is getting the pistons.  Speed pro is the only one i see making 20 over off the shelf.  Problem is no one has them so far.  Any special Order is a minimum of a month out.  The machine shop i use is trying a few different warehouses to find them.  If they can't then i am stuck with 30 over.  Pretty much all manufacturers are backed up due to this Covid bullshit.  I'll know more end of the week.

Right now i am trying to see what options i have for cut to fit pushrods.  I only see Hughes and Mancini.  The ones in the motor appear to be the factory 7.2 pushrods and 8 are not useable.  I don't mind cutting and building them but I need to buy an adjustable checker to make so i correct any geometry issues it may have.

Just a lot more work that i didn't plan to do.  As said before..... i will know 100% every detail of this motor.  I have the machine shop do their work and i do all final
Measurements and assy. 

The best part.... although expensive..... all the little things that just didn't quite look right..... are explained.

[Chryco Psycho]

Smith Brothers Pushrods , Bend Oregon , great service & 2 day turn around , they are the only place I use
Check with Diamond for pistons