OK I have an issue with my engine and I'm not sure where to go next so I defer to you, the experts. It is a 1.8L (probably a bus engine) with Dellorto 40s. It has a very recent unkown rebuild by the PO.

Symptoms:
-Won't rev above 5K rpms
-Feels underpowered at all rpms
-Below around 1700 rpms both cylinders on the left side do nothing (I can remove both spark plug wires at idle with no effect) After 1700 rpms all four cylinders come to life.
-At idle I can hear a slight knock sound coming from the front center of the engine in an irregular pattern. Seems to go away under load.

What I've done:
-Swapped carbs from side to side, problem stays on the left bank.
-Replaced the Dizzy twice, it is now a stock 1.8 dizzy with a pertronix, new cap, wires, rotor, and plugs. all stock.
-I have fantastic spark to all four cylinders (fat blue spark).
-I pulled the lifters/pushrods and everything looks to be in good shape with no abnormal wear.
-Valves have been adjusted 3 times and adjustments seem normal valves seem to operate correctly when turning by hand
-All intake and exhaust gaskets have been replaced.
-Compression is 105#-120# (The low # IS on the left bank) The car doesn't burn or use any noticable oil.
- Oil pressure is 15psi at idle hot and 50psi at speed
-Oil temp stays ~180 degrees.
-Timing is set to about 34 degrees and seems to be spot on.



I'm guessing at this point it is some type of valve train issue, but I thought I'd see if you guys had any guesses. I planning on tearing the engine down this winter.

Thanks for any input you have!

If you have adjusted the valves three times and the compression #'s you posted

are holding, I doubt it is your valves. Are you sure that there is no rev limiter.

No rev limiter. It is just your basic run of the mill rotor button, cap, etc. (I basically replaced the whole ignition system twice.)

what color are the plugs?

I haven't looked at them since I put the new plugs in a few months ago, but the ones I removed then looked like they had a good burn. Comparing them, the non firing side had more carbon build up than the good running side.

You could have an intake leak. I have had LOTS of intake issues. If you look at the 2 o'clock and 10 o'clock positions of the intake ports on the head, they are thinner there where the cooling tin has rubbed. I get lost of leaks there. Nothing at idle but when you get the rpms up (opened throttles, less vacume) the carbs can flow fuel. Try removing that side intake and use some copper rtv in addition to the gaskets. If you have the spacers check that they are also sealing well. The lower compression on that side could be due to running lean for some time and damaging those cylinders / heads. A leak down test can tell you more. Good luck.
Nick

Hmm, I'll take a closer look at that. I did replace all the intake gaskets a few months ago. I used RTV blue for the intake manifold to head gaskets.

RTV blue is bad! BTDT. it melts and flows out making one HELL of a intake leak.

b

It could also be fuel supply to left carby,you did say the left bank were malfunctioning?The black sooty bit sounds like rich running on that side.Your mixture adjustment may eliminate that.A tacho and dwell gauge will help to correct mixture.A leakdown will pinpoint whether its a valve or rings prob!

OK, I messed around with this for a while this weekend and I beleive I have solved the mystery.

The Head bolts were slightly loose on the left bank. I torqued them back down and it has resolved about 80% of my issues. Idle still isn't perfect and it still feels a little underpowered.

I'm thinking the head bolts loosened up enough to allow a combustion leak on the left side mainly from the front cylinder. There could possibly be some damage to the head on that side, so it still leaks a little.

I'll drive it for a while and probably tear it down over the winter.

How long did you drive it with this problem?

If it was for any significant time the exhaust leak you described will erode away material from the head and/or case and will not seal properly.

BTDT!!!!

The car hasn't ever ran 100% since I've owned it (2yrs). But it really got bad in the last month or so.

I think it will probably require some head work. Oh well, I'll just have to upgrade to a six!

Hi

Quick note....have you checked to make sure the carbs are syncronized? I mean, when it comes off idle, make sure both carbs are opening evenly. I battled with a serious off idle wobble with my Dells, which ended up needing my linkages adjusted. You need a syncro tool for this. Don't overlook this, Dells are great carbs, but the T4 is sensitive to this

Later