Valve Clearance Vs Idle

[johnnyboy666 195 1 Cars]

Hello,

 

I need a bit of help, having exhausted all avenues I can think of. I have a TU3S engine which is fitted with a Piper Rally camshaft, and I cant get it to idle. When I first fitted the camshaft, I fired it up to run the shaft in, and it started up first flick of the key and ran fine to get it run in, and I took it for a few short drives up and down the road to make sure it was running properly.

A few months later (house move got in the way) I get back to working on the car and realise that I didn't set the valve clearances after fitting the shaft, which was causing some clickety-clackety noises. So I whipped out the haynes manual and set the valve clearances, and hey presto, no clickety-clackety, but also, no idle, I had to wind the screw out on the carb so it runs on the main jet at idle (not ideal!), I then realised that Piper specify different clearances on their website, so I re-did them to that spec. Still having no luck getting an idle. I then thought I must've cocked something up, or something must've died from being sat for a while. I changed the plugs, leads, ignition amp, dizzy cap and rotor arm, swapped carb for a known working one, checked, double checked and triple checked the cam timing.

 

So all I keep coming back to is the valve clearances, seeing as they were the only thing to change before the idle issues. Does anybody know if they can have such an effect? And what would I do to resolve it? Is there a different clearance I should use instead of the Piper specified ones?

 

If it makes a difference, it runs absolutely beautifully when you you get above 3k rpm, but low revs/part throttle is very rough below that.

Plugs are showing overfueling on idle, but after cleaning them, popping them back in and having a proper thrash, they are showing the nice beige kind of colour, which would indicate to me that the fueling is ok at the top end.

 

To be honest, I could live with a rough idle, but i'm concerned it wont get through the mot emissions if I'm running it on the main jet on idle.

 

Any help will be much appreciated, I was hoping to have this back on the road about 3 months ago

[RossD 43]

What is the spec of the cam? How far out where the valve clearances? Remember, the wider the valve clearance, you are effectively retarding the valve timing.

Have you tried playing with the cam timing (presume you have a vernier pulley?) to see if you can get the idle back? Remember the piper timing spec will be a starting point, not a definitive setting. Once you played with the cam timing, you'll also have to check the ignition timing with a strobe light.

[johnnyboy666 195 1 Cars]

Its a piper Rally cam 300 duration.

The clearances were more than my thickest feeler blade - not good I know, rookie mistake not checking them before initial startup!

Yeah I've got a vernier pulley so I could try taking it back a degree and see how that goes.

Checking the ignition timing so far has been a bit tricky due to the lack of idle!

[RossD 43]

You will never get a very good idle with a 300 degree cam with a single carb unfortunately.

[johnnyboy666 195 1 Cars]

Yeah I knew that would be the case anyway, it's just that it idled so perfectly before I did the clearances, now its rough as hell

[welshpug 1,627]

you need more throttles, and compression possibly.

[johnnyboy666 195 1 Cars]

I'm already on the case, just saving up for mapable ignition. Just want to get it on the road so I can iron out any niggles first.

Regarding compression, i decided against a heavy skim because I want to swap the 1400 block for a 1600 block at some point later down the line, which should result in a high CR as I understand it.

[johnnyboy666 195 1 Cars]

I had the emissions checked yesterday, CO was 1.54% which is within limits, Hydrocarbons were waaaay up at 2242ppm (out of permitted 1200).

 

Was looking at it again today, and it turns out the head gasket is toast. That would probably explain the rough idle. Not sure if it explains the hydrocarbons, but pretty irrelevant for the time being.

 

Going to take the opportunity to stick the 1600 iron block in, that should bring the compression way up. Will get the head checked over and whatnot at the same time.

 

So much for getting it on the road before xmas :/