Manky throttle housing from a 2.5/3.0 Carlton down scrap yard. Costing a grand total of £6. Bargain.
After cleaning the oily mess out of the housing with degreaser and carb cleaner I set to with the
angle grinder. The 3.0 housing has many connections to it that the 2.0 engine doesn't use. So
I ground all of these away. I also removed the water heating connection.
Because the mounting holes are closer together on the 2.0 unit I had to file the 3.0 holes
into slots so that it would fit. Only 3 out of the four holes match up to the 2.0 manifold. The
4th is dealt with later.
In order to deal with the 4th hole I had an adapter plate made by a local engineering sub contractor.
It has 6mm clearance holes for 3/4 of the studs and moves the 4th hole to the position
required by the 3.0 housing.
The superfluous holes in the throttle housing were filled with quick setting epoxy. Also clear in this
picture is the adaptor plate for the throttle position sensor. I found that the 3.0 and 2.0
spindles are identical except that the holes are in the wrong place on the 3.0 unit.
The alignment of the throttle pot relative to the spindle is important. I found this out a few months later when I change it and the car felt a lot faster. Adjust the pot so that when the throttle is fully open the pot is at its end stop. ie: leave any slack at the closed end of the range.
Custom gasket cut out of gasket material with knife.
This picture shows how much larger the 3.0 throttle is. It's 10mm bigger on diameter which
is a 40% area increase. No need to "flow" the large plate or housing.
The throttle return spring was fitted with a handy extension made from a piece of coat hanger.
Finished job. Carlton 3.0 throttle plate matched to Irmscher inlet manifold. The inlet to the
manifold was filed and ground out by about 3mm on radius so that it matched the 3.0 throttle
plate outlet.
Before and after! I spent a few hours cleaning up the shape with a file, Proxon (hand held drill thing) and Emery paper.
I then had the throttle polished at a local place.
The 3.0 housing and spindle were given the same treatment as the previous 2.0 unit. The
spindle was cut in half and the screws were partially countersunk. The steps in the wall of the housing
were smoothed out using a sanding drum on a high speed hobby drill.
I decided to have the manifold polished also. These two images show the before and after. The assembly
still wasn't finished in the right hand image - all fasteners were replaced with Stainless Steel
items.
After a while I found the jerkiness round town annoying. Trying to slowly speed up in slow moving traffic was most difficult. I'd gently press the throttle and nothing would happen, more, more, more and then suddenly the engine would pick up with a big jerk. I decided that a way round this would be to make a progressive mechanism so that at first the throttle opening is geared down and it then gears up as it opens.
I discovered an easier way to cure the problem. I noticed a spring on the end of the throttle cable between the cable and the accelerator pedal. When the pedal is pressed a little then this spring takes up some of the slack. Fine on a standard car. However, in my case, it was introducing and unknown into the system when it was at its most sensitive. So I removed this spring (by unwinding it with a pair of pliers). This made the car much more drivable. Satisfyingly difficult rather than annoyingly difficult.
Sadly,
the throttle spindle snapped a few months later. I was very lucky - no parts
were sucked into the engine. I decided that maybe it was a better idea to leave
the spindle alone.
When I was fitting a replacement spindle I adjusted the throttle pot. I arranged it so that the pot was at its end stop when the throttle was fully open. I left the "slack" at the closed end. The car was noticeably quicker after this. I suspect that the ECU wasn't getting the WOT (wide open throttle) signal and hence wasn't in max power mode.