Carburettor tuning

[davidwheeler]

1. Fulvia.  Retarding the spark timing makes no difference at all so I have returned it to standard.  Changing the cam timing made no difference either.   Worn throttle spindles manifests as irregular tick-over and I can get a smooth tick-over at 500 rpm so it's not that. More hours on the computer convinces me that the problem lies in the accelerator pump diaphragms which are, of course, totally inaccessible on the car.  I have sent for a recon. kit and we shall see what we shall see...
2.Aprilia.  35watt is feeble at the best of times, Andy.  Yes, I have a direct earth wire to the body as also on the Lambdas and all the wiring is 2.5mm.  6 volt electrics on a dynamo cannot do much.  I wonder  if I can fit in a 2CV alternator?  (sorry Fulvisti, we'll go away now).

[roddy]

Hello David

I have been following the posts about your engine faltering on pick-up with some interest, as I experienced similar symptoms.  Having now seen that you have exhausted alternative suggestions, it is perhaps time to throw in my tuppence worth......

I am convinced that the viscosity and volatility of current petrols is so different to that of 40 years ago that the behavour of the fuel in Solex carbs is different from what the factory developed.  Admittedly both my 1600 Fulvias have altered ports and manifolds from standard, but on both cars I found idle was fine and main-jet running was good, but to get an adequate pick-up, the fast idle jet had to be significantly increased from the standard 50.  On one car I am using size 55 and the other, size 60 (states of engine tune/distributor advance curve/spindle wear etc. are different), but both now give good instantaneous pick-up. I had to do similar alterations on the 1300 engine, too.

Italian Carburetors of Corlo, Ferrara, Italy can supply new Solex jets in most sizes for a very reasonable amount, and offer a good service.  The url is :
http://stores.ebay.com/ALFA1750S-CARBURETORS-PARTS-STORE

They can also supply the diaphragms - which do seem to harden with age / degrade with modern fuels.  With the carbs off to fit the diaphragms, take the opportunity to try and adjust the drop rods to ensure the activation arm moves the same amount for each diaphragm.  Good luck.

Regards - Roddy

[davidwheeler]

Hmmmm, must look at that.
Took the car into my local wizard who reckoned that there is some air getting in somewhere - but I've just looked at the spindles and they have been recently re-bushed by Omicron and no slack there so I'll go through all the gaskets again and maybe add a bit of Wellseal or blue Hylomar.
Looked at the carburettor pumps.  When the throttle is opened they are feebly pushed by the springs and hardly move at all.  If the eccentric were mounted the other way round they would be firmly pulled by the nut at the end of the rod.   Can anybody tell me if mine are the right or wrong way round (see pics)?

[lancialulu]

David

Looks like there are new gaskets in the pump area and that Omicron must have cleaned the carbs.

Tech spec say that 30 full pump strokes should give 6-10 cc's. Happy measuring!! BTW it is not clear whether this is for 1 or 4  or 2 chokes...

I am rebuilding a Flavia Solex 32 with an even more curious pump action and a brass disc that appeared out of no where and there is no logical place for it nor it is on the detailed parts list for the carb. Having rebuilt it without that piece the pump works but it is pushed bu a spring rather than a rod action.

Cant help with lever on your carb. I went out to try to take pictures on a complete car but cant get the camera in the right place due to the drip tray (I assume you have one of these under the carbs?). However looking at the carb drawings it seems that yours are correctly assembled.

Tim

[roddy]

Hello David

From the two photos, I would confirm that the drop rods and cam arms seem to be in the correct position. Perhaps like Tim, I have never managed to devise a method of collecting and measuring the requisite number of cc's, and just rely on visual appearance and engine performance to assess if the settings are about correct.  Looking at your photos, compared to the 42s fitted to my 1600 Fulvias, there is very little of the threaded part of the drop rod visible below the nut.  In other words, the cams arms do not appear as if they will be moving very far, and in consequence moving the pump jet diaphragm.  On all my carbs, the nut is screwed much further up the rod, there is then a second 'locknut', and there is still 3 - 5mm's of thread visible. So the arms are moving considerably further arc.

The last line of my earlier post referred to ensuring that when the throttle spindles are opened, the arms are both activated from the rest position at the same point of throttle opening (ie almost the instant the spindle begins to move), and cease to move and the rod smoothly drops through the drilling, again both at the same point.  Sometimes a little grease on the curved face of the nut and on the rod will ensure nothing sticks. I know it is all a bit unscientific, but in theory if the arms are moving the same distance, the diaphragms will be moving identical amounts, and matching amounts of fuel will be pumped in.  The theory works for me in practice!

Regards - Roddy       

[lancialulu]

Re the pump I may be wrong but I think the design also only pushes a finite amount through with any potential excess bleeding back into the fuel chamber so it is self governing.

Tim

[davidwheeler]

I have  tightened up the nuts so that the pump lever actuates immediately and checked that the throttles are synchronus.  Put the carbs back on with Blue Hylomar to eliminate leaks, replaced the plug leads and redone the valve clearances (all about 2 thou tight).  She is somewhat better but still hesitant so the next thing is to try some 55 isle jets...  The other thing my wizard wondered about was a high lift cam but how could I tell?

[lancialulu]

I have a high lift cam and no hesitation. I did carefully time though (as I have said before this in my opinion is the key to hesitation in the 1600)....

[nistri]

It might well be that there is some air getting into the system as your workshop guy had suspected. In my experience, the gaskets between the carbs and the flexible support and those between the latter and the intake manifold can perish and give problems. Retightening the nuts will not help in this case. Did you fit new gaskets? Andrea

[lancialulu]

Like Andrea I had big problem in the area until I started using a very thin smear of Locktite 5920 copper loaded silcone. All air leaks banished. This was even trying new gaskets.

Tim

[chriswgawne]

Back in the 80's I used to 'paint' rubber solution from bicycle repair outfits on the outside of the rubber part of the carb mountings with good results.
Chris

[Parisien]

Theres an article or two on Fulvia carbs and tuning in The Lancia Journal, summer 1988, if you want them scanned and emailed to you let me know?


P

[davidwheeler]

Even better, scan them and post them on here?
Yes, all new gaskets and good rubber mounts.  Bigger jets on their way.

[Parisien]

Will do it later this evening


P

[Parisien]

Even after resizing, still too big, sent to Steve to see if he can help out


P