MG-Cars.net

Welcome to our resource for MG Car Information.

Recommendations

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG Midget and Sprite Technical - Su HS2 carb idle ....Mystery ???

Here lately in the last several weeks my idle has decided to go it own direction.

When I start the car and get it warmed up and take the choke off....it idles where I want about 1000 to 1200 rpm....(yeah I know it should be around 800rpm...but I like 1000 rpm myself).......

But after a half hour of driving at normal conditions it decides it wants to Idle at around 2200-2500rpm

So any ideas why it has became self aware, and devoloped A.I. ,,,will it now call itself skynet, and destroy all mankind????

Anyway....the linkage is in good condition,(not overly tight and not loose) accel cable is fairly new and dosnt appear to be binding, as is the same for the choke cable....

I dont have the air filters on it,(time lacking) and Im currently running 10W40 in the dashpots, as of late december, when the 20w50 turned into a thick, slimey, honey goo....Hmmmm maybe I should go back to 20w50, and try that know that the weather is alot warmer.

Anyway, as usaual, any thoughts ideas or suggestions are always welcome

Thanks guys
prop
Prop

oh BTW...No smog attachments, basic set-up, no modification (yet) 71 1275...twin Su HS2

prop
Prop

... high idle normally airleaks into the manifold... search with a spray, e.g. WD-40.

A
anthony

I think the oil you are using is way too thick. Per the factory provided owner's manual regarding the carburettor dampers: "Under no circumstances should heavy bodied lubricant be used". Keep in mind that once the engine is up to temperature & heat begins to soak into the carbs, the oil will take on the higher viscosity rating. I have always used automatic transmission fluid & have no problems with sticking. I find the carbs to be very responsive to tuning changes & hold those settings consistantly. The oil is for damping purposes but it doesn't need to be super thick since the movement of the damper is caused by changes in port versus carb vacuum and these are very small forces relatively speaking.
Mike G

A worn throttle spindle could cause this, the throttle disc does not come back. Is it over when you blip the accelerator?

Flip
Flip Brühl 948 frog 59

hey flip,

It does it continously, after about a 1/2 hour of driving.

hey Mike,

the 20w50 is what is recommended according to the haynes manual....the reason I changed it, I was thinking due to the sever cold it changed the chimistry of the 20w50, so I cleaned it out and added a lighter wieght oil....the 10w40.....

I should be working on that, But Im exhausted after washing, vac. and polishing all day on the car, I cant belive how dirty it got over the winter months, just sitting there in the shop.....


prop
Prop

The dashpot oil should have NO effect on the speed of the idle. Its purpose is to smooth the pulses a bit and to effect the "accelerator pump" function. Air leaks into the manifold as indicated by Ant, mixture a bit rich, linkage not moving smoothly, weak throttle return springs, butterflies not properly centered in the bores, weak poppet valves on the butterflies...
David "the options just keep going on" Lieb
David Lieb

Nope!!!

None of the above..."skynet" just needed lots of driving, Drove to the lake ozark, and around and back...and agian that seemed to fix the problem.....I cant get over how just driving the car will cure problems....not sure what the problem was....but now its idling at 1100 rpms....im wondering if there was some varnish build up in the carbs


On a sad note, I think I toasted my radio amp, it got sorta wet when I was washing down the car....and now I anit got no tunes, the radio works...just no sound, must be teddy bear revenge for using its carcass to was my car

prop
Prop

>>> ...must be teddy bear revenge for using its carcass to was my car. <<<

Ha! I KNEW that teddy bear would come back to bite you! So to speak...

I agree with the suggestions above, regarding an intake air leak somewhere.

Good luck,

-:G:-
Gryf Ketcherside

Well,

I had another look this morning, and it did it agian, So spayed it down with w40 and nothing, gave it a good grab and a manly tugg, and felt solid, so I put a wrench to it...and turned a couple of flats, on 3 of the studs, not awhole lot...so hopefully, that will fix it

Ill know tomarrow...

prop
Prop

Overly optimistic, Prop. Tomorrow you will have more data...

You are halfway to the REAL solution, which is: NEVER STOP driving the car.
David "I never practice what I preach" Lieb
David Lieb

Hey David,

With the car running so good, I really am an optimist these days....Icant belive what I got done this last weekend, got the front U-joint changed out, got the car washed, polished, and vac. figured out how to make those maniflow intake manifolds, bouaght a new mig welder, and got to drive the midget about 200 miles.

Hey Gryf, LOL.

I was wondering if anyone would remember my idea of using the teddy bear to wash the car...Hey, it may be sick, esp. cutting out the eyes and other hard parts but it works really well...lol


prop
Prop

This thread was discussed between 06/04/2008 and 08/04/2008

MG Midget and Sprite Technical index

This thread is from the archive. The Live MG Midget and Sprite Technical BBS is active now.