RS Motorsport :: Classic Speed Restored

After some ideas of what to look at next.

New engine - HT1E cam, big valve head, 12:1 compression
Started on the key - ran at 2000rpm+ for first 20min to run new cam in

Drove it and won't rev over 3500rpm without breaking down (sounds like a machine gun). But does rev freely unloaded

Put it on a dyno and fuelling is good - dyno operator blamed by MSD igntion. I resorted back to old GT4 coil (by passing the MSD), different leads, cap, plugs and still the same.

I then discovered the valve springs wern't the 37mm retainer gap that kent specified so pulled the head and have had then shimmed up. At the same time we checked the spring pressures (70ldb to 224lbs), and valve seats and all was good there.

Once re-assembled it was just the same - breaks down consistently at 3500rpm+ and keeps misfiring upto 5000rpm (as far I wanted to take the fresh engine).

I have now swapped to a different dizzy (thanks Avon) and have checked I have 12v to the coil (when running), and reduced the plug gaps to .2mm


So in summary I have changed every ignition component, checked cam timing, checked valve spring pressures. I also ran a compression test and have 180psi +/- 2psi across all 4 cylinders.

I normally have timing running at 12 degrees idle and max's out at 34 ish - this was checked and confirmed by dyno operator. I have tried bringing this right back to 0 degrees at idle and 20ish on advance with the same results.


Any ideas on what to do next??????

Fuel?

It started and ran (then misfired) on 3 week old 98 which I raced the old engine on. It's been topped up with another 20ltrs of fresh 98 prior to the dyno session. The dyno operator confirmed it wasn't running lean (lamba probe up tail pipe)

Bad fuel would cause det rather than misfiring wouldn't it?

On the dyno did the engine run okay under load above 3500 rpm?

Do you run airfilters?

Did you check the floatlevels of the carbs?

Fuel pump maybe.

May be OK at lower revs but may be unable to keep up supply higher up the rev range.

Matt

Fuel pump maybe.

May be OK at lower revs but may be unable to keep up supply higher up the rev range.

Matt

No airfilters fitted (yet) and fuel pressure is OK.

Carbies have been rebuilt and float levels were checked and reset then and also fitted with new needle and seat valves. It doesn't run (dyno or road) above 3500rpm under load at all, but free rev's to 6000rpm OK.

I might try to stick the old carbies off the other engine on it tomorrow just to eliminate another variable. But the dyno operator did state it wasn't a fuel issue (he's words were to the effect "it's getting plenty of fuel" at those revs).

Paul where did you stick the cam timing

I timed the cam using the full lift #1 at 104 degrees before TDC


If the cam timing was out surely it would run bad across the whole range not just "top" end?

When I pulled the head last night the pistons and combustion cambers where pretty black - the inlets were brown. On the dyno when the breakdown occurred it didn't appear to be spitting back through the intake - i.e. no fuel mist out of the weber trumpets

Try using the Esslinger bar method and tell me where in relation to straight up it is

Argh Paul this must be driving you mad

A few more 'helpful' things to check

1) Are you using the same HT lead (I've had a very similar problem to yours and it ended up being this)
2) Did you remember to connect the earth lead from the engine to chassis?
3) Did you get the valve seats cut to match the valves (just wondering if there is some weird lack of compression thing)

Thanks everyone - problem solved!


I got up early this morning and checked the cam timing again using both methods on the kent/burton sites and it's within a nats wisker. I then removed the carbies and intake manifold off the old engine and fitted to the new and went for a very fun drive in the Perth wet weather. Obviously the carbies arn't balanced or tuned for this engine/cam but it pulls hard without any hesitation or break down.

I'll now strip the "new" carbies and see if there is any obvious issues. The new ones have 38 chokes vs the old 36 chokes but I doubt that would cause an issue.


Now 3 weekends to run it in - seal the boot space (they now want us to fit a panel above the wheel arches in the quarter panel areas), and fit the nav gear, get the sump gasket to seal!

Is 98 a high enough octane rating for 12:1 compression?

I'm actually running a 20tho thicker HG so it's more like 11.5:1

I've now got the engine bay cleaned up again, got the mud flaps fitted the rear boot area sealed and the new trip meter fitted - so a good Sunday all in all

What are the jets (main jet, air jet, idle jet, emulsion tube) in the old and new carbs?

The carbies I removed had #2 main three turns off it's seat which i suspect was the issue!

I got the carbies rebuilt and fitted them as delivered to the new engine and then had the issues. Same guy dyno'd the car and pointed me towards the ignition. This lead me off on a merry path in the wrong direction, but also did highlight a few othewr issues (valve springs tensions etc.)

The real test will be to refit the new carbies and manifold and find out if 5 days of stress and several 100 dollars was all due to #2 main not being screwed in...

I feel for ya Paul
At least you found something wrong, its when you can't find something it drives you to

Clayton: I was so close to pulling the engine and poping the pistons to check the rings.

I must say i'm impressed with those cometic HG - definately live up to their re-usable claim.