Alfa Romeo Forums banner
1 - 12 of 12 Posts

·
Registered
Joined
·
30 Posts
Discussion Starter · #1 ·
Background: uncontrolled engine rev increase in a 1972 GTV 2000, Weber conversion from Spica.

Anyone seen this before? Recently I've had a two instances of "runaway" revving of my engine upon upshifting - depress clutch to change gears, engine revs increase uncontrollably. Tapping throttle doesn't help. I have to turn off the ignition - fortunately, in both cases I've had a place to coast into, out of traffic. In the first instance, I waited for a few minutes, restarted the car and everything was normal again. Once home, I checked the mechanical linkage, lubricated a few pivot points here and there, but couldn't find anything amiss. The second time, each time I restarted, the engine would rev up until I turned off the ignition. This time I opened the hood and wiggled the linkage at the carburettors, and that seemed to "fix" the problem. Logic tells me I must have a linkage binding problem somewhere, but so far I haven't been able to find it. Is there anything internal to the carburettors that could be causing this? They are Weber 40DCOEs.


Any ideas?
Thanks.
Pete
1972 GTV 2000
 

·
Registered
Joined
·
462 Posts
heart attack revs

For what it's worth.... I was adjusting the tension of the cam chain. Thought I had it... phone rang, went inside, and in ten seconds the engine took-off in revs. I could not get out there in time, by milleseconds... the engine shut down. I thought it was blown... but the bolt worked loose on the tensionor. It was a 1750 cc engine.

Check that bolt is all I can offer.
 

·
Super Moderator
Joined
·
12,255 Posts
ar105gt:

Boy, it sounds like linkage to me. No, there is nothing internal to the carb that would admit lots of fuel/air into the intake. Unless the butterflies are open, there just isn't any way to admit air & fuel to the engine.

When you say it is a "Spica conversion" my antennae go up. So, you don't have factory-made linkage, right? Those conversion kits include an odd, kinked rod that connects the circular bellcrank at the top of the Spica manifold with the lever on the Weber - might that thing be hanging up somewhere/somehow? To me, that's the klugiest part of the Spica --> Weber conversion kits.
 

·
Premium Member
Joined
·
23,890 Posts
Or, if the return spring setup isn't working, I think the Spica/Weber conversion that uses the original Spica bellcrank will fall farther open just through gravity. Definitely needs some investigating. Pretty much only an open throttle will let the engine rev like that. Runaway ignition advance will rev the engine some, but I wouldn't think that much.

Andrew
 

·
Registered
Joined
·
30 Posts
Discussion Starter · #5 ·
Thanks

The bell crank area is definitely the place to look. I'll have to remove the air filter housing (It's a Euro version) to get a good view of the area. Unfortunately I won't have time to get to it until the weekend. the mechanism in that area looks a bit flimsy - not the heavy pivot bracket that Centerline sells with their Weber conversion kit.
 

·
Registered
Joined
·
283 Posts
check the condition of your motor mounts - not just by eyeballing. get a pry bar in there and see if the motor moves (more than it should). had a similar situation in my GTV due to a blown mount.
 

·
Registered
Joined
·
1,875 Posts
Could be that you just need a stronger return spring. I had a similar problem with my Fiat when I converted it to twin carbs but the cause in this case was that the standard return spring was on the throttle pedal arm but I'd converted the rest of it to run from a cable...

I engineered something like this-



but obviously because I made mine out of lumps of rusty metal I found in the garage it doesn't look so nice!
 

·
Registered
Joined
·
11 Posts
FOR WHAT ITS WORTH
When my '71 GTV1750 was a few days old I had a runaway on HWY400 north of Toronto when I shifted into 5th gear and had to shut down and pull over to the shoulder. An Ontario Provincial Police Constable pulled over to check out the new Alfa after I was stopped. When I restarted the engine it started to rev high immediately. Together we poked around the throttle cable area and when I restarted again the revs were in the normal range. It's never happened since.
 

·
Registered
Joined
·
30 Posts
Discussion Starter · #9 ·
Removed the linkage and bellcrank today - unfortunately I found no clear cause of the problem. Although there does not seem to be excessive radial looseness of the bell crank on its shaft, there is significant end-to-end movement. The bellcrank had two washers on the outside and was secured to the shaft by a simple cotter key. On the inside there was no washer. This seems a bit "jack-legged" to me, but I was still not able to determine how it was causing the runaway acceleration problem. Maybe I'll try tightening the longitudinal play (add another washer) and add a return spring somewhere, as Mound Dawg has suggested above.
 

·
Registered
Joined
·
9 Posts
Check your engine mounts, especially on the intake side. Check the carb support rod bushings. Then you need to check for air leaking in between the carbs and the intake manifold.
 

·
Registered
Joined
·
1,466 Posts
Boy, it sounds like linkage to me. No, there is nothing internal to the carb that would admit lots of fuel/air into the intake. Unless the butterflies are open, there just isn't any way to admit air & fuel to the engine.
When this happened to me, the carburetor balance was so far out of adjustment, the carburetors were allowed to move independently from each other. Then the front carburetor (IIRC) was allowed to stay cracked open a bit more than the rear carburetor, for me it caused the engine to rev uncontrollably. Advice: Check the balance screw.

Those conversion kits include an odd, kinked rod that connects the circular bellcrank at the top of the Spica manifold with the lever on the Weber - might that thing be hanging up somewhere/somehow?
I hate that bloody thing with a passion.
 

·
Registered
Joined
·
1,119 Posts
i had this happening to me ...i had the linkage too "tight" so when the engine moved on acceleration or breaking mostly it pulled the throttle...riddles
 
1 - 12 of 12 Posts
Top