What are the early signs of low compression? I seem to have a lot of power fade from about 4500 rpm and on up. Fine below. Is that low compression, or could I be looking at a weak fuel pump?

 

Low compression will cause hard starting, rough idle.
I doubt your problem is compression.
Could be a lot of things, fuel filter, state of tune etc.
hanman

 

You mention hard starting. I've been told that with low compression, starting becomes harder, if not impossible when the engine is warm. Does that match your understanding?

I've got an engine that will not start unassisted. If I add ether to the carb, it starts right up. After the car is warm, it will start on its own. I'm suspecting a carb problem rather than compression. What do you think?

 

When my 85 went bad, it would start no matter what, seemed to run fine. Never would idle below 1200 or so RPM. Even changed carbs I knew both were OK when i swapped from one carb to another.. Compression was always low in the front, so when driving one day POW no more running car, guess which rotor went bad...

 

i have the same problem, low power at 4k rpm and cant start it without assistance whether it is cold or not, and idles very roughly, sometimes sounds like it will stall by itself. Atm it is at rotomotion getting looked at, I will find out if it is the carby or compression or whatever then!!

*Prays that carby jst needs to be tuned and choke wired up, and its not low compression*

 

Good luck. Let me know what you find out.

The amazing thing with mine is that it idles fine. It starts fine when its warm. I just started noticing the power fade at higher rpm.

 

I had the same problem about 2 weeks ago. At first I though I was having a timing problem, as the distributer looked like it had slipped. But it turns out my 1st pre-cat had blown apart into the 2nd, which got cloged, and in turn sent a bunch of crap into the main cat. I had to strait pipe the main cat, and I gutted the 2nd. Problem solved

 

I got it back today and it was not the compression Bascially carby just needed tuning badly and i think the choke will help in the cold mornings. The car was running very rich (fuel wise). I still have not got all my power back though, Graham Stones at rotomotion took it for a spin thoughand said it ran perfectly, he said that the next thing to do would stick it on the dyno and check actual figures, but i dont have the money at the moment and it wont solve the problem. So what ever the previous owner had done to give it all the power is lost.

I found the power comes more gradually starting at appox 4000rpm and grows whereas before it litually snapped in at 3750rpm almost as if you pressed the NOS button. This was enough to start spinning the tyres again on a gry smooth bitumen road, i have 185/70/13 Yoko tryes with plenty of trend. Is this strange??

 

At around 3300-3700 RPM the secondaries on your carb drop open (3rd and 4th barrels on your 4-barrel carb), and start doing the great toilet-bowl effect with your fuel. You get more power, but your fuel economy plummets... The power surge isn't unusual. You can keep the secondaries from opening simply by not putting your gas pedal to the floor all the time (hard, isn't it ).

Jeff

 

Before the power came through always at that rpm even when i wasnt accelerating hard, normallly i would wait for the power to kick at 3750rpm then change gear at 4000rpm. So does that mean the secondaries are not opening up? Is there an easy way to check??

 

hmmm.... secondaries are only supposed to open under load at 3500 rpm or so, I'm pretty sure... but I think you can check by putting a twist-tie on the linkages... not exactly sure where though... Maybe someone else does...

Jeff