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MG Midget and Sprite Technical - carsbs adjusted much better now but throttle not q

73 midget:
Had much better success adjusting the carbs this time. Now that understand what needs to be done I think that the entire process could have been described in a much more straight forward way. It is really not very hard to do but the books sure describe it as something more complicated than it is.

Anyway, the only anomaly that remains is that the throttle won't open all the way before the pedal runs out of travel. We adjusted it as much as possible but it is not enough. Then we disconnected the springs (because we wanted to play with it). We noticed that then the throttle could open all the way. It appears that the shaft of the bolt that the cable threads through (and a nut secures the throttle cable) is worn such that it has a lot of slop in the throttle belcrank that it is bolted through. I am sure that if I eliminate all that extra play that the throttle will open all the way (we proved this). This still leaves me with the remaining question of why was the throw on the pedal so close to being not enough. Is there something else that I can do to adjust the throw of the pedal? Right now it bottoms out on the floor when it is pushed down all the way and when my foot is not on the pedal it looks like it is at 90 deg (straight up). so, I don't see where I can get anymore throw. Fixing the extra play mentioned above will fix it but it is hard to believe that there is no extra room other than that.

Am I missing something?

Rebecca
R Harvey

if the throttle lever on your carb shaft is longer than stock, that would increase the needed pedal travel to stroke it over the same angle as a shorter one would.

Mathematically, that would happen, though, I am not familiar enough with the various parts used over the years by SU to know if it is likely.




Norm
Norm Kerr

I dont think so - it is quite marginal on the standard setup and for those that have changed to the single HIF carbs its not sufficient at all and needs tweaking in other ways. On mine I found even the thickness of carpet in the footwell was making a difference.

The 1500 throttle pedal is a different design and gives more movement. Presumably the 1275 setup didn't give enough movement for the 1500 carbs.
Dean Smith ('73 RWA)

The shaft of the screw that the cable is bolted to is very worn (you can see that it is no longer round). When you pull up on the cable you can see that the screw does not stay at right angles with the belcrank on the carb shaft. At first glance you might not think that there is a problem. If I am right about what is wrong, I would be willing to be that there are a lot of people out there that are not able to get full throttle and they are not aware of it (because they did not look to see how far it can open when they push the pedal). In my opinion, lots of tiny bits of wear from end to end can add up to enough slop to keep the throttle from opening all the way (it is closed at least 25% at full throttle).
Rebecca
R Harvey

reb.


you may have to bite the bulit and call joe curto and get a new part and do it the right way esp if the holes are worn out of round for the throttle linkage

or you can do like I did, and get one of these new more modern cable fittings and rig it up.

http://www.pegasusautoracing.com/group.asp?GroupID=ENDFITTINGS

I also used a bicycle brake adjuster in the hole at the top of the heat sheild to adjust the tension on the throttle cable and remove all the slop so throttle response was greatly increased

Prop

Here is a photo of the general concept of the bycycle barrel adjuster, You can see the direction Im going with the 2 phootos

Prop

Prop

I ordered a new throttle linkage and a new shaft (that the cable is bolted town to. That should eliminate all of the extra play.

However, the design is not great and I am also open to changing it. thanks for the suggestions and photos.
Rebecca
R Harvey

This thread was discussed between 13/07/2010 and 14/07/2010

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