Twin SU’s full throttle
 

Good evening all,

I have had my car for nearly two years and only just realised I’m not able achieve full throttle when pressing the accelerator pedal, no matter what I do with the linkage!
Does anyone have any tips for getting it set up to achieve full throttle?
Thanks in advance,

Doug.

Are the butterflies opening fully?


https://sucarb.co.uk/technical-h-typ...retter-diagram

Doug;

"not able achieve full throttle" could be interpreted multiple ways, with multiple causes, just one of which has been pointed out and asked about by WS! Throttles should open completely, that is, give minimum restriction to carb throat when Throttle Pedal is "floored". Does a carpet prevent fully flooring it? ...otherwise, you may be loosing linkage movement elsewhere along the way...study the linkages and adjustable ballends (which are separable by removing the little springclip!)...when you have sorted it, give a good lube to all pivots and ballends!

Good Hunting!

Cheers Ron and WS,

I’ve adjusted all of the linkage as much as I can and yes Ron you are correct the carpet and sound deadening were causing part of the issue and I’ve sorted that out now but I can’t be 100% sure the butterflies are or aren’t fully open or not so I’ll check tomorrow, but I can move the linkage about a further 10-15% towards fully open with my hand when the pedal is pressed hard on the floor!

Doug.

Hi Doug,

On GAM the nylon bushes that hold the mechanism in place had worn away:

https://i.imgur.com/PiuZCvL.jpg

... I replaced then (either 2 or 3, I forget) and the throttle action has much improved.

Alan

Hi all,

I have just spent the last hour attempting to resize photos taken on my iPhone to be able to upload to the forum to show the difference between pedal full throttle and direct on engine linkage but have failed so until I can get to a computer it’ll have to wait! 😡

Doug.

On a different note, I've learned from experience that the original gas pedal on all 1800 series cars, as they age, can prevent you from being able to fully open the throttle.

This pedal is made up of rubber bonded to two pieces of steel; one part is horizontal under the screws that fasten it to the floor, and the second piece is used under the rest of the vertical length of the pedal. The pedal pushes against a roller on a steel lever that is a part of the accelerator linkage.

The hinge is the section of rubber between the two pieces of steel and after 50-plus years, the rubber hardens, and the hinge section stiffens. When you think the pedal is at wide open throttle, it isn't but is only about 75% open.

I discovered this issue a few years ago after the screws that fasten the pedal to the floor loosened up, and one fell off while making a competition run up Mt Equinox in Vermont at the VSCCA.org Hill Climb. The pedal was left off for the next 5.5-mile run up the Mountain, which was noticeably faster, and the clock showed that the run was 25 seconds faster than before with no other changes to the car. Following that times remained consistent on the rest of the runs over the two days of competition.

A few weeks later the next VSCCA race meet at the Lime Rock Park track lap times around the road course droped by about 8 seconds.

If you have an 1800 with an original pedal, a new one should give at least a 10% or more performance improvement.

Good morning all,

I've finally managed to attach some photos of the butterfly positions when operated from the pedal compared to directly at the carburettors, photo 1 is pedal and photo 2 is direct.

Doug.

Have you got some photos of the linkage? Have you set it up so at idle it's sitting just proud of the stop on the manifold?

Hi Mitch,

No photos of the linkage sorry I'll get some tonight and I'm not sure on the set-up with reference to the stop, I will also check that!

Doug.