slow Engine decelaration

[fgc]

My 1750 has weber carbs. Would like opinion and advise on why the engine seems to take quite a few seconds for the rev to come down as if there is a massive flywheel causing it to keep spining.

By the way, when the trottle is lifted, is there anything to cut the fuel supply to the engine? I have checked my butterfly valves and they do snap close when the throttle is released... but yet, I seem to get the impression that fuel, plenty of it, is continually being fed to the engine.

any idea why?

thanks
fgc
67 spider veloce

[John M]

Hey FGC:

Check your synchronization and your mixture. I have seen this happen whenever initially tuning. I cannot remember for sure which caused it, but I believe its most likely related to synchronization on the forward carb. On the mixture, lightly seat each of the four mixture screws. Then turn all four out two complete revolutions. 720 degrees. That will give you a good starting point.

Best Regards,
John M

[djone101]

Not much help but I've had the same problem - It's very slow to come down to idle and often hangs up. I can bring the idle speed down by loading the engine - let up the clutch slightly with the brakes on - and it stays down at a sensible idle. I suspect the carbs need cleaning - hasn't been done for several years... have you checked out your throttle linkage for a stiff/sticky joint?

[papajam]

Two things come to mind; improper throttle plate closure and/or distributor advance is hanging up. My thought in Dave's case, since the idle stays down after the engine is loaded, is that the problem is distributor related and has nothing to do with the carbs.

fgc,
As John M suggests, ensure that the carbs are synced and adjusted properly. If the problem is still there, look at the dist.
The fuel supplied by the Webers on closed throttle decel is only what's required to idle the engine - no more, no less. There is no fuel cutoff device.

[djone101]

Good call Jim - It has been running on a bit recently too - could be that the distributor is finally giving up after 115,000miles.... hadn't thought about the distributor. Thanks for the tip.

[papajam]

Running on, or 'dieseling' as it's called here in the States (I think because that's what the engine sounds like when it's doing it), can have many causes including carbon build up in the chambers, sparkplug heat range too hot, engine overheated, low octane fuel and in particular (for this thread anyway), high idle speed and over advanced ignition timing. What might be happening Dave is the dist advance might be hanging up (or the static timing is too far advanced to begin with) which causes the idle to hang up and this results in run on. Does the car run on if you shut it off when the engine idling at the proper speed? Are the dwell and timing set to specs? I'm assuming your Mk2 (1750 is it?) has a Bosch 044 or 045 dist.

[fgc]

Thanks Jim and John for your advise.

I have forgotten about the distributor. When I first got the car, I relied on the PO mechanic to look after it while I spent time reading and learning about my first Alfa. I remembered that the mechanic took out the distributor and packed heavy grease on the advance weight bec the advance mechanism appeared to be rather dry and devoid of oil! I told him not to but heck he insisted asnd was alittle too late when I realised what he was doing. Since then I remembered that the car was driving a little strange as I think the advance would sticks initially and then creep up when the rmp increase but would retract slowly when rmp falls.... looks like I'll have to take the distributor out and washout all the grease. Anyway gotten so used to it that I totally forgot about it.

As for dieseling, my car starts first crank and dies immediately when ignition is switched off. I had thought about the synchronisation between the 2 carbs (need to get a carb flow meter to check that out?) By the way, how do I remove the carbs without distrubing the sync? I would suppose the answer is to remove it very carefully? Any trick or technic while removing it to ensure that they stay sync?

This is my opinion after 1 year of alfa ownership and having finally coming to the end of the restoration job (only left the engine and gearbox overhaul to do.) that is if you dont have a good mechanic, then it certainly pays to learn about the car and do it yourself and so far I'm glad to say that I dont think I've fared too badly in the DIY stake... at the least I follow factory specs and I'm a little more careful if not anal about doing it right.

Thanks a lot, I will look into the advance and sychonising the carbs when I get the time.

By the way, my distributor is a bosch 0 231 178 006 model... Was thinking of changing the distributor since I think there is some shaft wobble, but what should I change to to ensure that the advance curve is similar?

Cheers
fgc
67 1750 spider veloce

[John M]

Hey FGC:

Here are some handy tools for carb synchronization and setting the appropriate mixture.

First a colortune kit to appropriately adjust your mixture. Really handy for a performance tune. But for most you can get away with the two full turns out on the mixture. The colortune kit allows you to visualize the combustion chamber through the spark plug hole while at the same time acting as the spark plug. You can see the color of the fire. It also comes with a nice guide to tell you what to look for.



Next for synchronization, you can do it via visualization of the throttle plates within each carb and set them equally. Perhaps Papa will explain this as I just use a unisyn synchrometer. I know that there are other types of synchrometers out there that may be more accurate. Here is a pic of that:



Basically the ball within the unisyn travels with suction. You just adjust your sync screw at the linkage on the front carb until the ball travel is matched between the two carbs. I wouldn't worry too much about the synch screws if you are removing the carbs. Synchronizing will become very familiar to you especially after you rebuild your motor. And trust me, its not a big deal at all.

The screw on the rear carb at the linkage adjusts your idle.

Here is a link that sells both if interested.

RD Enterprises

For the distributor, you have a lot of options out there from Centerline, to IAP, and RML just depending what you may be considering. You can stay totally stock, go Pertronix, or use one of the optical distributors with the crane boxes marketed by IAP and RML. If funds are not plentiful, you probably can turn up a good used one on ebay or one of the dismantlers. I can also add that the RML setups are very nice and those guys are extremely knowledgeable. However, be prepared to lay down some green backs.

BTW, why are you having to remove the carbs?

Best Regards,
John M

[papajam]

Quote:

Originally posted by fgc ...By the way, how do I remove the carbs without distrubing the sync? I would suppose the answer is to remove it very carefully? Any trick or technic while removing it to ensure that they stay sync?...

[120]

might be worth a try, seems to me I had a car that was slow to drop rpms, I believe it had an air leak. Either a vacuum tube or bad mount. I couldn't get the carbs to work so I changed carbs.

You can check how close the sync. is (roughly) by opening the progression caps and seeing where the throttle plates are in relation to each other i.e. from carb to carb. Adjust the idle speed high so that the throttles are in progression.
The plate edge can be barely visible through the progression holes, use good light and rotate the throttle via the screw. you should notice the plate then. Adjust the sync screw till both carb's throttle plates match. Decrease the idle screw
All this does is, is get the two throttle plates mechanicly the same
it may take the meter to fine tune.