Aprilia Top speed

[DavidHill]

Morning All,

Finally on the road, taking my Aprilia down the by pass with a GPS speedometer I can only register a maximum speed of 65-67 MPH flat out with the throttle wide open.  I am running the standard Zenith carb, with a standard exhaust.  The motoring reports describe an easy 70mph with an 80mph maximum...should I be able to achieve that?? 

[lancialulu]

is it a 1500?

[GG]

Have you checked the hole in the main carb jet? We rebored one in a vintage Appia to original specs, and found another 10+ mph.

[ColinMarr]

Remembering former times when Aprilias were less precious than they are now, I recall 80 mph was quite realistic. Flickering speedo needles were not reliable, but by the late 1960s electronic rev-counters were available and I remember putting one to the test. On my car, which had a Series 1, 1352cc engine, fitted with a “big Weber” and straight-through exhaust, it would readily pull 4000 rpm and cruise at 3500. At the time, we thought 1000 rpm in top gear equated to 20 mph and it seemed reasonable to claim 80 mph.
The attached photo from 1969 is a ‘still’ from an 8mm cine camera filming while driving a Morris Minor in pursuit. At times, its speedo read over 80 … and I burnt out its exhaust valves, but that’s another story.

[DavidHill]

Thanks for the thoughts re carb jets etc...any information on what the bore size is on the main jet for my Zenith carb?  (it looks clean and unaltered so am fairly sure it is ok).  My engine is a 1500cc and has recently been rebuilt. (last 500 miles).

[Spider2]

with a rebuilt engine is it wise to attempt top speed? Not familiar with the Aprilia engine but would not a more gentle approach to running it in be quite a good idea?

[Kari]

The main jet size on the Zenith 32 VIM and the VIML 3 is 110.
Recent engine rebuilt: The rings have seated properly? Valve timing on the spot? Just a thought.

Karl

[Sliding Pillar]

I think you really need this.....
https://www.rubinoclassiccars.com/it/ricambi/ricambi-lancia/kit-nardi-lancia-aprilia-detail

[davidwheeler]

Mine is also (almost) 1500 cc and has a twin carb Nardi setup.    After having run it in over some 2000 miles! I find it easy to cruise on the motorway at 70mph with quite a bit in hand so it should attain 80mph.   Remember Vincenzo when taken for a ride in the first Aprilia said nothing until the end of the test when he said "Magnificent motorcar" (or something of the sort, in Italian) but also said it was too fast so the top speed was reduced to 80mph.

[LatheJon]

Hi David, If your Valve and Ignition Timing is ok, it may be Fuel. If you have a standard Fuel Pump it may not be getting enough. I think I remember Harry saying "using a thick gasket on the fuel pump, the car wont go above 50"
A thick gasket and a worn actuator rod may not help top speed.

[davidwheeler]

Part of the reason I use an electric one!

[DavidHill]

Some progress to report...i have checked the main jet size - and it is 1.1mm, so the jet is fine.  Interested in the report that it could be a too thick gasket on the fuel pump.  How much is too thick? My fuel pump is mechanical - but has new parts in it so should be ok...but could be the issue.  On a drive down the duel carriageway this afternoon it was very happy at 50 mph, but i have decided to properly run it in first before trying for higher speeds...so far 400km in from the engine rebuild...

[peterblenk]

David, I saw you yesterday at Brooklands. In thinking about this, I would suspect fuel starvation. If all the other good ideas from those cleverer and more experienced than I am do not solve the problem, you might try testing how much fuel your pump is delivering. My car suffered fuel starvation, even though I had fitted an auxiliary electric pump in the fuel line near the tank, but the pushrod of the mechanical pump was too short and was therefore impeding flow.

[davidwheeler]

Also, modern fuel has a different viscocity from the original, hence the need to incresase the size of Fulvia intermediate jets to get decent slow running and acceleration.   But I agree, sounds like fuel starvation.   Fit an electric pump and pressure controller in the boot and bypass the mechanical one.

[DavidHill]

Thanks for your comments Peter and David, they reminded me I promised an update on the trip to the rolling road...it was v good and I would recommend Jamie and the Race team, they were very helpful and knowledgeable. (https://www.raceltd.com/).  Jamie stated that the exhaust gas analysis showed that there was no fuel starvation. He set the timing to be spot on (mine was a bit out) and opened up the main jet 0.05mm so that it was the correct diameter, and that added 5hp...the car now runs much more smoothly, starts first time, idles smoothly and has more umph from lower speeds. The Rolling road read outs show i now have approx 40hp, but Jamie stated that it may be reading low at the lower HP range.  Overall i now have the car running well and just need to run it in (only 600miles so far after the rebuild.) so well worth the trip