Flat-spot

[Guest Gizmo]

Hi,

I have a really bad flat-spot, apparently on the cut-over between venturi 1 & 2, and usually under hard(ish) acceleration.

Accelarator pump appears to work, and can't find an air-leak, but it does smooth out while on-choke.

 

I have rebuilt the carb, don't think I have introduced a blockage (anyway, it was a problem before I rebuilt it), and fitted a manual choke conversion (auto-choke had corroded badly and U/S).

The car runs ok, plugs are "mushroom" in colour, and the idle settings and timing are right (independently checked). I use a PiperX filter.

 

I am prepared to believe that I have not been thorough enough in my search for an air leak, but before I strip everything (again) can anyone tell me if I have missed anything or if there is some big secret that I don't know about ?

Many thanks

[Guest Ianz]

Try blanking off the connection on the manifold,which goes to the servo,,,,,,,

assuming you are using servo.

 

The car runs ok, plugs are "mushroom" in colour

 

I think your mixture sounds a bit weak!!!

 

Should be brown ....ish.

 

 

To check for air leaks try brushing paraffin/diesel around the carb,

If you got any leaks it will show by turning your exhaust white!!!!

 

Cheers Ian

[Guest Gizmo]

Yeah, I though so too. I used WD40 around the carb while running, but nowt !

I haven't taken all the hoses off yet, or checked the dizzie, so there's still scope. I got the exhaust checked on an anlayser though, and that showed the mixture was ok. Of course that doesn't match what happens on the roads, but still, it must be close as theres not a lot of adjustment in a DGV.

The flat-spot is a bitch ; it actually dies for a second, right after you plant your right foot, then it coughs (loudly) and then goes like a train. I keep getting beaten away from the lights by BMW's - its so embarrasing !

Thanks for you advice though, I will have to try the air leak tests again.

Cheers

[Longboarder]

Sound as if its going weak when you floor it. Recheck low vacuum and accelerator pump diaphragms carefully and the float chamber level?

 

Nigel

[Guest Ianz]

Having read Nigels reply,I think its probably the idle mixture thats tooo weak!!!

The engine cannot cope with the transition from idling to full throttle without a delay,hence the flat spot.

 

Hope that tit bit helps

 

Cheers Ian

[Big Jim]

on the carb manifold, there's a wax stat sensor underneath into the manifold with all the small vac pipes going to it. take off all the pipes and just run one from dizzy to carb (with the smoother valve in line) you don't need or want that stat, it causes problems.

[Guest Tony Tank]

Me 2 got the exact same problem cruise along , decide to give it some and pop pop and away.

The wife goes mad :gdit: cos when it comes back in she's thrown back in to the seat.

 

Will watch this thread with interest

 

Tony

[Bob Tucker]

Try blocking off the crankcase breather connection on the manifold. The clack valve can get blocked or worn out. If that solves it, replace the breather valve.

Bob.

[Guest Gizmo]

Hi All,

Just to say thanks for all the advice, and to let Tony the Tank (a fan of Rev W Awdry ?) know what I have found so far.

 

I Bought a can of Wynn's carb & injector cleaner (Easy Start is cheaper but Wynn's is bigger and has the added advantage of actually cleaning as well) to use as the leak tester.

 

Tightened the carb mounting nuts (a tad loose ? may have leaked but I did this before I bought thw Wynn's so i'll never know now). Couldn't find any other leaks.

Replaced carb-to-dizzie tube... no change.

 

Wax-stat was decommisioned back at the build and all the pipes trashed. I read up on the pipework and basically it was all there to cover up the fact that Ford never really managed to solve the idle problems ! I blanked off the carb to air-can pipe way back too, so the only external connections I have are to the dizzie, and the crankcase valve.

The crankcase breather was replaced about a year back so that should not be blocked either (and it "clacks" nicely !).

 

Accelerator pump ok (visual check shows a good "squirt" as the throttle opens) due to the Weber repair kit I applied last winter. Pump diaphram was part of the kit.

 

So, in the end I have found nothing yet ??

 

I will try it after all the "poking around" when I go to the Uxbridge show on Sunday.... if anyone else is going, i'll see you there ! ... and post a futher update next week. Any other suggestions gratefully received !

 

Cheers.

[Peter Bell]

You say it is as the second choke opens, what size idle jet have you got on the secondary? if it is a 45 try going up a couple of sizes, the cortina used to have a 60.

Peter.

[Guest Gizmo]

OK here's the deal ............... I screwed up somewhere !

Must have been my fault as I was the last one to touch the carb.

 

As I said, I did a number of things all at once, so I am not sure what finally did the trick, but coming back from Uxbridge (damn good show by the way ! I will definitely be going next year) I gave it some wellie on the M40 and it cleared !!!

 

Since I rebuilt the carb over the winter, I think it most likely that I had some contamination in there that the Wynn's shifted ........ or it just could have been those mounting studs ?

Whatever, it's hugely improved.

 

Tony, I hope yours is gets fixed as easily !

 

 

BTW - how the hell do you get those mounting nuts done up .. is there a special spanner for them ? or are you meant to leave bits of knuckle all over the manifold ??

[Les Welsher]

Had a problem on the wifes car about a month ago. She said it wasn't running right and ticking over at 1500 rpm, got a bit worse and would tick over at 2000 rpm.

I thought this is going to cost me, all electronic and all, but before I took it to a garage to have it checked out on their computer thingies I chucked a bottle of Wynns cleaner in the tank. After driving it around for about 75 miles it started running fine and tick over back down to 850 rpm.

 

Les

[Guest rizla]

wot ever happend to that good old redex

[Swan Jnr]

redex is great. not sure it solved the problems we had at one time with an old metro (in the latter stages of terminal decline) but pouring redex straight into the carb while on the night shift and watching the flames leap up into the night in the works car park was very entertaining!

 

paul

[Guest rizla]

used to make good smoke signals to