OKay- 70' 1.8L, with dueling Dellorto's 40mm.
Car runs sweeeet, perfect.
Then starts running crappy. Hmph, thinks I.
Pointless ign, I check the rotor anyhow, and swap it.
Test Drive, LOTS of pinging, and at 1/3 throttle or less the car just LUGS does not even try to accelerate below 2500RPM. get the RPM's up and it starts pulling.
Smells funny.. ..weird oilt smell. ..not burning. Just oily.
Any guesses.. .?
Not *quite* sure I understand it yet.
But I found what seemed to be the problem.
-Bob O

The problem is, it has Carbs :finger2:

Oh....THATS ORIGINAL.

jeez... okay, since you give up.
One hose to my breather box had cracked.. venting fumes into the engine compartment.
My guess is the fumes were causing a very bad mixture into the carb?
The oil vapor is very hot (right out of head) so the mixture was hot causing detonation / pre-ignition?
But dont most applications say to vent the breather to the carb anyhow?
I dunno, but as soon as I replaced the hose it was fixed.
hmm.

Man, that sounds a lot like way advanced timing to me...have you checked the timing with the engine at idle? Not sure which dizzy you're using (stock,009,050...) but something might have run amok with the advance.

more evidence of a dizzy problem perhaps

Nope-
checked, and checked again.
Problem SOLVED when I replaced the hose to the breather.
Like I said...not quite sure I understand it.

Hmm hope it stays fixed. But I bet there was some gunk in a idle jet anyway. 2500 RPM is about where the mains start to kick in.

I was venting each head to a Carb. Worked fine.

Gunked up idle jets.

Sounds a lot like sticking mechanical advance. That would explain why it runs great above 2500 rpm. Maybe only sticking after it gets warmed up? I had my advance jam up (c-clip holding dizzy shaft together came off) and this is exactly what it did. Full advance all the time. Below 2500 it would buck and knock, smoke and smell bad. At 2500 rpm it took off like a rocket (well, the 1.7 liter version of a rocket, which would be an Estes A or B size rocket).

-Ben M.