single carb conversion

[gray]

Hi does anybody know anyone or anything about converting the twin su's to a single su ?? im thinking of making something, just to see if it runs smother, more economical ?, and hopefully more reliable.. thank you il let you all know how things get on

[Cobber]

The number of carbs has nothing to do with reliability, and it's doubtful it would do anything for economy either.
Californian versions had a single ZS carb, to comply with the strict emissions regulations in that state, by most accounts they were slower that a wet week at Port Welshpool!
The buggerising about you'd need to do inorder find which metering needle and jet required to get a single SU to run properly will make you want to crush the car! You'll only be able to get it to run properly on a dyno, you may as well pay a carbie expert to do the carbies for you it would be cheaper than all the stuffing about, only to end up with a sportscar with no sport in it

[FI Spyder]

The single carb CA version only had 76 hp. Shouldn't run any smoother but will be more economical and with less ooomph. Not what you want. Back in 1968 I bought an new early '68 Triumph Trophy which was exactly right down to the cam the same as a Bonneville except it had one carb. It ran out of steam at around 80 mph but did get very good gas mileage. The reason I didn't spring the extra $75 for the Bonneville is I liked the blue of the Trophy better than the red Bonneville. Not many sold I expect as they are rare as hens teeth while Bonnevilles are all over the place. It's also very confusing as they kept changing the names around back then although the Bonneville remained the flagship.

[Hasbeen]

My twin SU 7 runs as smooth as a sewing machine. There is absolutely no reason why a twin carb system will not run smoothly, except perhaps they have slightly more gaskets that could leak air into the inlet system after the carbs.

I did a minor adjustment to the throttle stops on my twin SUs on the 7 recently. I was only lowering the idle a little, as I won't be using the air conditioning much for the next 5 months or so.

When I entered the job in my service log I was only mildly surprised to notice that it is over 2 & 1/2 years since I touched the carbs, apart from filling dashpots with oil when I do an engine oil change. Do it right the first time, & SUs really are set & forget carbs.

Hasbeen

[kstrutt1]

The su's have a balance tube and shoud be no problem, most running issues in my experince are down to worn jets or the overun valves in the butterflies leaking.

[gray]

Thank you all for your thorts on this subject i have finished making the converion and will be fireing her up tomorrow, pics and results to follow

[john 215]

Hi,

Be interested to see pictures and how you get on, afraid I have to agree with my learned friends above though BUT if you don't try you will never know. What are using for a carb ? 1 and 3/4 " HS or HIF I guess ?

Cheers John

[busheytrader]

In the classic mini world there's lots of guys who prefer to go down the large single carb route instead of twin carbs. They claim the Same power, same torque but with the simplicity of just one carb. Tuned engines with non standard manifolds though.....

[sonscar]

From my own experience of standalone EFI systems I wonder how many carburettors,and distributors,are anywhere near correctly tuned for the engines whole range?I soon realised that a mostly worn carb and an almost totally worn out distributor worked relatively well.Without serious dyno and road testing the seat of pants dyno is very subjective I found.Good luck with your project,Steve

[FI Spyder]

In the classic mini world there's lots of guys who prefer to go down the large single carb route instead of twin carbs. They claim the Same power, same torque but with the simplicity of just one carb. Tuned engines with non standard manifolds though.....

This in part makes sense. Twin carbs effect the higher rpm. Down at low rpm there is little difference. Low(er) rpm is where the torque is made (and by seat-of the-pants feels like power). Horse power is made at higher rpm (until frictional forces start to overcome it as rpm rises and you start to see it diminish). If you improve the flow through characteristics of the engine (with air filters, intakes, port & polish, and tuned exhaust) it will give more horse power, even with a single carb. Why don't all manufacturers do this as a matter of course? Because of costs which is always a major deciding factor.