Having a little trouble getting decent power out of this engine I put together. Any comments as to what timing I should be running?

455 and 4 speed trans

Low compression (71-up) pistons

E heads with big valves - all new valves, springs, seats, rockers, push rods.

W-31 (402194) cam

70 442 M/T carb newly rebuilt

72 350 4V distributor (advance is working)

Have timing now at about 14 degrees before TDC at 1100 rpm with advance disconnected. Engine starts very easily and is not dieseling, but if I advance it anymore, the engine starts to really hop around. Thanks.

 

you would need more info than this. what is the total timing and when does it come all in? you could run this piston combo with 40 degrees total with out any problems. two engines with the same compression can run two very different timing curves based on quench, flame travel, camshaft etc.
by "hop around" what exactly do you mean?

 

Yeah, with low compression and the W-31 cam you should start with 60 degrees! Just kidding. Do a compression test and get back to us with your findings. Did you degree the cam? Do you know when the intake valve closes? Has the balancer spun? Verify with #1 piston at TDC. That engine should like plenty more than 14 degrees initial. I would guess it would handle 20 easily.

 

Thanks for your response. Just did compression check tonight - cylinders ranged from 151 lbs. (#1) to 147 lbs. (#7).

I did not degree the cam, and I'll recheck to make sure the balancer has not spun. Tomorrow AM I'm going to set initial to 20 degrees and run the vacuum advance directly off the carb port (to check if the Electric vacuum switch might not be working correctly) and see what happens.

 

It just shakes a lot. It's not missing, and the engine is not backfiring or anything. It "smells" rich, but there's no black tailpipe smoke.

 

Who built the carb? Did you check to see where the throttle plate is set? The blades should be roughly in the middle of the transfer slot.

Check to see if fuel is leaking from the boosters at idle. How many turns out are the idle mixture screws?

Back to the timing. Are you running manifold vacuum for vacuum advance? If so, try disconnecting it and advancing initial to 16 degrees. If it runs smooth hook the vacuum advance to ported vacuum and see what happens. Then you can bump initial up to see what it likes. Of course you will have to lower idle every time you bump the timing. Once you get it to idle good, then you can work on total timing. Just have to play with it until you find what it likes.

The cylinder pressure is pretty low as I suspected. You should be able to run 20 initial.

 

You are on the right track. Start with the basics. Find true TDC and the make sure your balancer matches the timing marker at 0. Are you still running points? If so what what is your dwell set at?

 

Well, after the above compression test, I tried one last time getting it right before sending it to a local guy known for musclecar tuning. Did the following, still no real change to performance

Verified true TDC

Set timing to 14 deg. initial advance at 1100 rpm with vac. advance disconnected.

Idle adjustment screws 2 turns out from fully seated.

Used the "cool" timing light to verify that with vac. advance plugged into carb ported vacuum, secondary advance was 25 deg. - bringing total to 39 deg at 1800 rpm.

Check dwell - is set to 30 deg. New cap, rotor & points

Checked all plugs are firing and rechecked firing order.

Set hot idle at 750 rpm.

With all that, engine fires just by breathing on the key (it starts better/quicker than my '08 Z-06). It idles well with just a little W-31 shaking, and shuts off well, even with temp at the 1/4 mark on the rally pak with no "dieseling" No backfiring, nothing

It just has no power. I can barely get the secondaries to open up at all. I'm wondering if I might have the wrong throttle cable, or maybe the carpet is still holding the pedal off the floor too much, but still, just getting up to speed with the throttle mashed all the way down reminds me of a VW bus. No backfiring, no surging.

Any last ideas before I take it in tomorrow AM?

 

OK, so far so good. sounds like the timing issue is close enough to look at the rest. have someone sit in the car and press the gas pedal to the floor. check to make sure that the secondary blades on the base plate are opening all the way. (make sure the secondary lock on the choke is released) the blades should come up even to the vertical plate going across when you open the air valve and look down. if the secondary blades are opening correctly then it is also possible that the air valve is too tight or too loose. most 'bogging' issues with a quadrajet are from the air valve too loose and opening before the engine is capable of using the air. too tight and it usually makes moderate power and sounds like it is trying to go, just gets there very slowly.

 

X2^^^^^^^^^^ Although, I am surprised it idles good with the mixture screws only 2 turns out. Usually it should be 3-4 turns out especially with a cam like you have. But, if it works good leave it.

 

Carb. rebuilt, but any idea what Primary jetting and what Secondary rods are in it? I agree timing sounds close...now let's look at fuel.

Danny

 

2 turns out - 4 turns out - is crap!!
Set it with a vacuum guage to the highest reading is the only and correct way to do it!!
I'd also set the secondary air door a little looser -

 

39 @ 1800 sounds like its coming in too fast. I think it would be better coming all in at around 3000-3500.

X2 on setting the carb with a vacuum gauge or a tach.

 

Your right set it with a vacuum gauge but I have NEVER seen an engine that liked 2 turns out except maybe a 120 hp 4 cylinder!

 

Yes. Set Idle with a Vac. gauge and in conjunction with a Tach to watch rpm. That said, most carbs running that W-31 cam would have been about 4 turns out. IF the car is idleing at 2 turns out, then the idle speed may be set so high that the throttle plates are too far open and the carb is pulling primary fuel at idle.

A 70 MT carb re-built to stock specs would have some trouble ideling properly with that cam..and the fuel curve would be out of whack for what the engine is asking for.

Just my thoughts from some years of working with these cars.

Danny

 

Looks like carb problems are at the root if my power problems. Will give full report on when complete analysis is finished, but it did idle best at two turns out - for all the wrong reasons.