S1 Fulvia Zagato
Engine: 8181402239540.
My mechanic is unfamiliar with Fulvias & Solex carbs and asked me to find out on: HOW TO TUNE SOLEX 35mm CARBURETTORS?
I haven't checked the top of the carbs to check if they are 35mm but assume they are, according to the engine no..
Car was fully restored 26 years ago, driven into a garage and never used.
Engine fires up easily but idle is very high.
I cleaned the 4 jets per carburettor and the mechanic tried adjusting the idle screw but no luck.
Points / distributor / spark plugs (new) Air filter is off, exposing the 4 trumpets.
SHOULD THE VALVES BE ADJUSTED, BEFORE ANYTHING ELSE?
Any assistance would be most grateful.
Many thanks.
'68 Fulvia Solex tuning / adjustment?
Re: '68 Fulvia Solex tuning / adjustment?
Hi. That's a pretty hard question to answer. First: it is almost pointless to tune the carbs it the valve and ignition timing aren't set correctly, and the ignition is not in perfect condition. That said, the tuning of the carbs is pretty complicated. In all, there are 10 setting screws. But assuming the small air bypass screws are set correctly or absent in earlier carbs, still leaves 6 screws. They are: one idle set screw (in between the two carbs, the rear set screw), the balance screw that balances the two carb blocks (also in between the two blocks, the front set screw) and four mixture screws.
First, the balance between the two blocks need to be set correctly. For that, you need to have an instrument that can compare the vacuum between #2 and #3 cylinders. To connect the instrument, there are two blank-off bolts on the inlet manifold, that need to be replaced with blots that contain a connection pipe for the instrument. With the balance screw, the carbs need to be set so that the suction on #2 and #3 are the same.
Next is the mixture screws. Turn the mixture screws about half to 3/4 turn out to start. Set the idle to around 800-900 RPM (the mechanical RPM instrument of the car is far from reliable, use an electronic RPM counter). Now, turn each screw in very slowly, watching the RPM. The RPM will slowly start to rise, till it reaches a peak with the mixture screw about 1/3 to 1/4 of a turn out. Set the mixture screw to the lean side of the peak (the peak is rather flat). This will increase the RPM, as the engine now burns better on that cylinder. Turn down the idle again to about 800-900 RPM. Start on the next idle screw, doing the same, and turning the RPM down again, and so on till the last.
Now... the setting of the later mixture screws will have upset the setting of the first mixture screws, they will have to be done again. Turn out the mixture screw slightly to enrich some and repeat the procedure finding the peak and setting to lean side of peak, and then next cylinder, and so.. Each time adjusting idle as necessary, and keeping an eye on the balance, which may go off slightly too.
But...
This is the procedure when the carbs are in good order. From what you write, that you can't get the idle down, they probably are NOT in good order. There are a number of possible reasons why you can't get the idle down. One is that the balance is not set correctly (which would be the best you can hope for). But it is more than likely there is quite some air likely. The sources for air leak are numerous. Can be the rubber interconnection part between inlet manifold and carbs. Can be the flanges of the carbs that are warped. Can be that the butterflies have been scraping out the throttle openings of the carbs (a particular problem of the C.32-35 PHH Solex carbs). The bushings for the spindle may have worn out letting air through (another typical problem of the S1 Solex carbs. Another source of air leak that is often overlooked is the choke disc valve not closing off anymore due to wear. It is almost impossible to say what it is without looking at them physically.
The Solex C.35 PHH have a bad reputation. It is true they don't stand wear very well, but when in good order they are really good. It does sound to me they are due for a complete overhaul, but I can't be sure of course. By some specialist that knows these carbs well and knows all the weaknesses they have. It is not easy to find a specialist that knows these carbs inside out I am afraid. I often get carbs in that have been "overhauled"... I usually have to spend additional work on top of restoring them to correct all the bad work that was been done to them. They are really tricky carbs. And it is not worth doing half work on them, because if they aren't perfect, they simply never will work well.
Good luck!
First, the balance between the two blocks need to be set correctly. For that, you need to have an instrument that can compare the vacuum between #2 and #3 cylinders. To connect the instrument, there are two blank-off bolts on the inlet manifold, that need to be replaced with blots that contain a connection pipe for the instrument. With the balance screw, the carbs need to be set so that the suction on #2 and #3 are the same.
Next is the mixture screws. Turn the mixture screws about half to 3/4 turn out to start. Set the idle to around 800-900 RPM (the mechanical RPM instrument of the car is far from reliable, use an electronic RPM counter). Now, turn each screw in very slowly, watching the RPM. The RPM will slowly start to rise, till it reaches a peak with the mixture screw about 1/3 to 1/4 of a turn out. Set the mixture screw to the lean side of the peak (the peak is rather flat). This will increase the RPM, as the engine now burns better on that cylinder. Turn down the idle again to about 800-900 RPM. Start on the next idle screw, doing the same, and turning the RPM down again, and so on till the last.
Now... the setting of the later mixture screws will have upset the setting of the first mixture screws, they will have to be done again. Turn out the mixture screw slightly to enrich some and repeat the procedure finding the peak and setting to lean side of peak, and then next cylinder, and so.. Each time adjusting idle as necessary, and keeping an eye on the balance, which may go off slightly too.
But...
This is the procedure when the carbs are in good order. From what you write, that you can't get the idle down, they probably are NOT in good order. There are a number of possible reasons why you can't get the idle down. One is that the balance is not set correctly (which would be the best you can hope for). But it is more than likely there is quite some air likely. The sources for air leak are numerous. Can be the rubber interconnection part between inlet manifold and carbs. Can be the flanges of the carbs that are warped. Can be that the butterflies have been scraping out the throttle openings of the carbs (a particular problem of the C.32-35 PHH Solex carbs). The bushings for the spindle may have worn out letting air through (another typical problem of the S1 Solex carbs. Another source of air leak that is often overlooked is the choke disc valve not closing off anymore due to wear. It is almost impossible to say what it is without looking at them physically.
The Solex C.35 PHH have a bad reputation. It is true they don't stand wear very well, but when in good order they are really good. It does sound to me they are due for a complete overhaul, but I can't be sure of course. By some specialist that knows these carbs well and knows all the weaknesses they have. It is not easy to find a specialist that knows these carbs inside out I am afraid. I often get carbs in that have been "overhauled"... I usually have to spend additional work on top of restoring them to correct all the bad work that was been done to them. They are really tricky carbs. And it is not worth doing half work on them, because if they aren't perfect, they simply never will work well.
Good luck!
Re: '68 Fulvia Solex tuning / adjustment?
oh, I forget. It is much harder to tune the C.35 carbs with the air filter off. The air filter is made to be in tune with the carbs. Put the air filter on when trying to tune the carbs.
Re: '68 Fulvia Solex tuning / adjustment?
Small correction in the long first message: "Start on the next idle screw, doing the same, and turning the RPM down again, and so on till the last." should read : Start on the next MIXTURE screw, doing the same, and turning the RPM down again, and so on till the last.
Re: '68 Fulvia Solex tuning / adjustment?
Thanks Marnix.
And make sure the support under the air filter is there and the rubber at the bottom end is in top condition.
Under no circumstance should the carbs hang on the rubber between carbs and manifold.
Test by lifting the air filter by its inlet tube. It should move the engine without any slack.
And make sure the support under the air filter is there and the rubber at the bottom end is in top condition.
Under no circumstance should the carbs hang on the rubber between carbs and manifold.
Test by lifting the air filter by its inlet tube. It should move the engine without any slack.
Re: '68 Fulvia Solex tuning / adjustment?
H Marnix,
Thank you so much for taking the time to explain the Solex set up. You certainly seem to know your stuff!
I shall copy / paste your reply and give it to my mechanic. Hopefully, it will work out. If not, I'll remove the carbs and find an expert to set them.
If you recall, back in 2015, I dropped in on route from Sweden - UK in my Swedish reg. '71 S2 coupe. You kindly helped me with a small problem.
Next time I drive up to Sweden, I will contact you.
Keep well
I
Thank you so much for taking the time to explain the Solex set up. You certainly seem to know your stuff!
I shall copy / paste your reply and give it to my mechanic. Hopefully, it will work out. If not, I'll remove the carbs and find an expert to set them.
If you recall, back in 2015, I dropped in on route from Sweden - UK in my Swedish reg. '71 S2 coupe. You kindly helped me with a small problem.
Next time I drive up to Sweden, I will contact you.
Keep well
I