Engine loses power under load. WTF??

[Warren]

Try the simple things first.

The fact that you say it idles fine but as soon as you put load on it it barely makes it up a hill, and that you have changed coils and plugs leaves either points or timing.

My guess is timing, I use a very finely tuned device (my ear) and a 9/16th spanner to do my timing.

Use the spanner to loosen just slightly the bolt that holds down the base of the dizzy.

with the engine running on a fast idle twist the dizzy one way until the motor starts to falter, then twist it back the other way it will idle smoothley again, keep twisting and it will start to falter again. From memory twisting clockwise retards and counter clockwise to advance - could be vice vesa.

Now set it in the middle of those two extremes.

Lower the idle speed and repeat. Rev the engine and listen to how easily it revs.   

If you take the engine cover off you can actually drive along and udjust the timing as you drive - do this on quiet straitght roads though.

I try and get the motor to ping under load and then back it off a bit, that should have it set pretty well right.

Works for me anyway.

Warren

[MaTTe]

hey mate, you've said it idles, and dies under load..
Does it die when given some revs while parked? or only when driving?

What was done when the head was pulled off?
Did you touch the dizzy or anything else?

The compression on the various cylinders is worrying, however, the motor should still run fine, just not as well as it would if they were all higher.

With the head, what did they actually do to it? How did you test that the seats were fine?
If they have only ground the valve seats with a stone, they are likely to be out of true, if you've tested this by filling the combustion chamber with petrol and lost none, they are a good seal.

There are a number of things it could be, but before i write an essay of possibilities, i'd appreciate some more info.

Cheers

PS. there are some good tips above, i advise taking note.

[Rothu]

Ok, further information: The battery has slid forwards earthing out the live connector onto the wall. but has slid back, but shows some 5mm of arcing, actually removing brass to that extense.
The fuses are all okay. What else could it spike? the HEI?

The head had a full regrind, was a Repco recoed head, needed valve stem regrinds to naturally fall, and all valves and seats reground for proper fit. Do not by any old Repco recoed heads, they will cost you $285 for total rebuild.
The head was tested by vacuum, all sealed well. I did my own tests with metho into each chamber to see leakage. None.

it does not die revving in idle.

[Marishka]

ive got a small block of wood stopping mine from doin that.
if u suspect the hei bein damaged thus causing ur lacking power try a points dissy n see if it works better.

p.s. try running a single wire from ur power side of battery straight to the power side of ur coil 2 just in case there is some fried wires causing the power lack.

pp.s. i run a elec disy 2 but always carry a recond points disy under the passanger seat just in case the hei one fries 1 day while im traveling or even just drivin local.

[MaTTe]

Ok, good stuff. So the engine will rev while parked? can you rev it right up to 6000rpm or so?

If the motor is revving freely as you please while parked thats as much of a good thing as a bad thing..

A quick question, on your coil it should say 12V use with resistor, or use without resistor.. Are you using a resistor?

Is the car an auto or a manual?

Did the motor ever run well after the head went back on? or did the battery hit the body and arc pretty much straight away?

The main things you'll want to start looking for are burnt wires, if it's done damage to the terminal, you want to check the cable attached and consider a new fitting if need be. you want to have a look at the power wire going to your coil from both ends if accessable.

If the car is an auto, have a look at any electrical cables attached to the box, as the fact it'll rev when parked leads me to believe it will be transmission related..

If you can get a good photo of the wiring around the motor, and under the dash and bonnet this may give us a better idea also.

Also, when you said you checked the fuses, was that just under the dash or under the bonnet too?

[Rothu]

12volt coil, no resistor, direct line from battery. All fuses good.
5 speed supra gearbox.
Will try a points dizzy today.
Don't know when the battery arced but it would have been after head got recoed.
It runs the same as when the head gasket blew out between 5 and 6. Replaced it of course!
Can rev it to 6000 no problems. Just dies under load.

[Marishka]

Compression on cylinders are 110,120,110,80,150,95 = those compression readings are a big worry especially 4 and 5 .
thats 70psi difference, could u have made a mistake with the readings?

[Rothu]

tried points dizzy, even worse than before! Put HEI back in, smooth as.
Also noticed a couple of bent pusher rods, replaced those, still the same.

A friend mentioned the timing gears might be worn. anyone?

[Marishka]

bent push rods means their too tight, are the rockers adjustable?
sounds like the valves arnt closing up, thats prob why there is low compression in some cylinders.( would make it run but no power under load)
if their unadjustable rockers like on the 202 maybe the head being shaved itsnt giving enough clearance on the rockers where they touch the valve stem ends?

even moreso when ur lifters pump up with oil there would be no clearance at all thus valves not closing and would bend pushrods. and bugger all power a result.

marty

[Rothu]

The pushrods were out of another engine (same length), but I didn't check them properly, obviously.
Bled the lifters so they're fine and there is clearance on all the rods when valves are at rest, ie: you can easily twist them, that's how I found the bent ones.
It's a 173 head so it a matter of simply bolting down the rockers to 40nm.