When I started her up after months in a rented garage to rebuild the transmission, it was like music to my ears. A minor setback with a recalcitrant starter motor aside, she started up willingly on the very first attempt, no coaxing was needed.
It’s hard to describe the throaty growl the Maserati tipo 107 creates, it’s got a great low rumble with an urgency to it at idle, with increasing midrange bark as the revs increase. It’s one of Maserati’s longest running engine series. You can read a little bit more about it here: http://www.maserati-alfieri.co.uk/menotti12.htm
Getting the car back on the road was great, and the engine sounded smooooth as could be when I rolled out of the garage a few months ago. She’s been running great since, up until about a week ago, when things started getting rough.
I haven’t done anything at all to the car or motor (well, I removed the rear seats in order to clean and provide better access to the rear parcel shelf, of which I’m trying to restore the leather covering), and am at a loss to understand why it’s running so poorly.
It usually idles ok, but at lower than normal revs (4-600 instead of 8-900). Today it actually died while idling, which is new. While out on a trip yesterday it would sputter and die when accelerating from a standstill, but would idle fine. If I managed to coax it past the stumbling, it would accelerate fine, and seemed smoother the higher I rev’ed the engine. The problem seemed to lessen after driving for 30 minutes or more on the highway (I always warm up the car – water & oil temp to at least 50C – before driving, what I’m describing happens after the car is warmed up), although today accelerating from a standstill seemed to work ok. The engine was running rough all along today, at slow or highway speeds.
Another symptom is backfiring – with occasional flames coming out the exhaust (as entertaining to passerby’s as it is disconcerting to me), at all speeds, but especially prominent when decelerating.
Pondering the cause and possible solution, several lines of thought emerge.
1. Perhaps something is clogging the fuel line, or the carburetor jets are dirty? I found the fuel pressure gauge had stopped working two days ago, and removed it and replaced it with a plug. I had used Teflon tape on the threads, bits of which seemed to be disintigrating. Finally I pulled it out, cleaned up the threads and used Locktite white thread sealant (e.g. Stag) on it. Maybe some bits ended up in the carbs?
2. Vacuum leak somewhere? Seems to be a common cause of backfiring and acceleration problems. Not sure if it’s mine, though, and even less sure as to where to begin looking.
3. Exhaust leak? I’ve noticed a faint whiff of exhaust in the car on occasion, especially when the windows are rolled down. Due to the missing grommet and bushing around the steering column through the firewall, i’ve previously thought that the open windows create a vacuum that sucks in fumes from the engine bay while driving, but lately I’m not so sure, and suspect there may be a leak between the headers and exhaust underneath the car.
4. Condensation in the distributor? The weather has been wildly (and typically) unpredictable, changing from sunny almost warm days to hail and prodigious downpours only a few degrees above freezing.
Today I checked all fuel input filters on the carburetors, hoping to find scads of miniature teflon spaghetti remains clogging them up, but was disappointed (and a little bit relieved) to find them clean and clear. So barring some larger debris in the fuel line between the fuel filter and carburetors (where the pressure gauge was installed), I can cross suspect number 1 off the list.
I recall that when I got the car, it was running a bit rough initially as well. It turned out to be the battery. When I replaced it, the car ran perfectly and has since. Since the battery is only a year old (and a high output AGM type), and measures ok, it’s not the problem.
Next up will be to spray the distributor cap with moisture repellant and see that everything inside looks ok.
Since the PO (previous owner) had the heads, manifolds, and carbs all cleaned, refaced, rebuilt and tuned (and it has run perfectly before), I’ve ruled out carburetor adjustment for the time being, choosing instead to focus on the points listed above.
Fired her up last weekend when I needed to pick up a friend at the airport, ran smoothly without the slightest hiccup. When the engine and fluids were warmed up, I rev’ed up the motor on some long open road stretches, with nary a hitch. The engine pulled strongly, ran exceptionally smoothly and with no hesitation, backfiring or other problems I had noticed.
My best guess is that there must have been moisture under the distributor cap, or maybe some sediment in the carburetor or gas tank, because now everything is back to normal smooth running. If it were a bad spark plug, valve, vacuum leak or similar I would expect to notice it all the time, not just intermittently. We have had some very cold and wet weather lately, so next time I’ll pull the distributor cap to see if there is indeed a bit of condensation inside.
Same thing today – ran like a fine swiss watch, from when I started her up until the end of the afternoon run.