Bog std 1600tp.
Idle set up ok as per manual
Once up to temp, the idle speed doubles or triples intermittently. I can sometimes bring it back down by engaging gear & letting the clutch out ie almost stalling temporarily then it reverts to normal speed.

As these carbs perversely vary the idle speed by the amt of air they suck cf the amt of petrol that goes in then it seems that too much air gets in intermittently???

No it's not a throttle stop prob- it stops where it should & the throttle spindle seems OK- anyway that would lean out the mix & cause stalling.

Anyone been down this road B4?

could be the timing is wrong, advance weights sticking, vacuum leak.

Original dizzy or 009?

The fact that it plays up once the choke comes off suggests air leak

Once it is up to temp and idling is flucuating Get a can of WD 40 and soak the inlet manifolds. It the revs come back down - there is your leak
Also inspect the manifold boots. Bit hard to pray and soak these - but give it a go

KKK I thought about that!
Stock dizzy.
Gawd these things r getting near 40yo! The idle speed does change as you change the timing so I wonder if the timing is changing intermittently? At idle, it's all vacuum so if it leaked then the timing would retard which would slow it down. But if the centrifugal plate with the weights was wobbling around & rotating backwards & forwards(at idle no tension) that could cause a momentary advance which would increase the idle speed. Then when I nearly "stall" it may re-set back to where it should be!

Geez! I haven't had a dizzy apart in years but I'd better have a look!
Thnx for the insight.
I'll look for suck leaks, but they would lean out the mix & cause stalling. But it's easy enought to eliminate with WD40!

Don't pull it apart, just spay good penetrating fluid down it, the top plates are often dry and resist turning and returning. Check the vacuum can is working and the hose ok. They run off ported vacuum so the vacuum levels rise as the throttle plate opens to give more advance on part throttle. If it advances then doesnt return properly it will run higher on idle. The air leak will increase revs if your idle mix is rich. Hence the running well on choke.

If you are using a 34 pict type carby you should be using a svda dizzy. Weight driven advance and a vacuum can.

Was it running well then started lifting revs? When did it start?

Yes idles perfectly at traffic lights & it just suddenly increases without any prompting or blipping. Then I put in top gear, let the clutch out & the idle revs drop to normal & stay down, usually. Started happening after last point change.
My SC has a 1600SP with a 009. I am going to swap distribs over to see if the idle improves. Don't like 009's due the dreaded flat spotting on TP's but the SC runs real well using a 28PCI with about a 130 main jet & slightly bored out venturi. The MPG is dismal, however.

Finally got around to do the swap!

Results are a great & stable idle but, you guessed it, an annoying flat spot.

Has anyone tried this??

http://www.aircooledtech.com/34pict3_modification/ 


Or is it viable to repair/replace the stock dizzy?

OK, I've just done the mod as described in the link on the prev post.

1st impressions r good. Full bore = no flat spots but part throttle gave a bit of hesitancy. I then slightly enriched the idle mix & advanced the ign timing to just before the ping-point.

EUREKA!! Excellent acceleration full or part throttle!

THIS IS A GOOD MOD.

Some notes on the job:
The screws that hold the throttle disc in are peened over (so that they don't fall in!) so the threads may get chewed out when u extract them. U may need a tap & die to clean up- 4mmx0.75.
I was concerned that as I decommissioned my oxy, I may not have enough heat to solder. The kitchen blow torch I use for creme brulee's worked fine. U need flux (Baker's Soldering Liquid) or resin cored solder. I used both. Make sure u countersink the hole first & have the disc on a flat surface or the solder will run & stick underneath giving you a bigger filing job.
When re-assembling, use loc-tite on the threads & re-peen the ends of the screws. I used a blunt screwdriver & some blunt force trauma- ie a hammer. Blow it out well with comp air- there WILL be filings.

Hi

You need to set your total timing with the 009 to 32 degrees total maximum on a stock motor, your motor is probably pinking now, but you cant hear it, but a long hill on a warm day might show it up. Excess timing is like heroin, feels good until your bodies F%&#@, the air-cooled motor makes more power with timing notched up, but for how long until the heads lift off or you bearings are screwed.

So how does the air bypass work now that the hole is soldered up?

Steve

Good point! In the absence of a dial, wot's the distance along the rim of the pulley from the notch for 32 degrees?

I'm not talking bucketloads of advance. I twisted the dist abt 2mm off the static setting!

Doesn't the premixed idle mixture exit UNDER the throttle disc?? It must or it wouldn't be idling at all! I don't have a manual here to check.

I'm guessing the idle mix is quite a bit richer but it wasn't sooting & I'll keep an eye on the plugs over the next week or so. That should also show up any pre-ignition too I guess.

I'm tolld 009's are made in China now. I'm buying another for the SC but 2nd hand due to quality worries (?).

Hi

I read that other page and he was talking about timing at 5 AFTC, our local cars with a single vacuum dizzy were set at 7.5 BTDC, our 71 Supers had dual vacuum advance unit and were set at 5 ATDC.

As far as the distance goes you can measure the circumference of your pulley then divide it by 360 the x by 32 to give you right total figure using a timing light.

The idle air on 34 Pict 3 goes via the idle cutoff valve and idle screw, I guess that if your car is idleing now OK you must have had to wind air speed screw out a bit to compensate for the hole being closed of, interestingly the early dual vacumm cars had a much larger hole in the butterfly, they were pigs and many were converted to single vacum, Ive seen lots that were converted but left at 5 ATDC.

Steve

Have you replaced the 2 small O rings in the idle and fule mixture screws on the side of the carby I thing there may be air suckin through there as well also check the rubber mainifold boots for leaks as they expand when hot

Pulley is 170mm diam. Circumference is DxPi ie 170x3.14 which is 534mm.
Then 360deg is 534mm so 32deg is 47.5mm. So to time the 009 put a blob of liquid paper 47.5mm away from TDC & hook up the strobe & line up the blob with the crankcase seam at full bore by twisting the dist. Well, t'would appear I needed a bit more advance! It's running real good now!

BTW, just a thought on audible pings. I've owned a heap of old Jags (but I don't miss'em) & the XK eng had a Lucas dist with a screw vernier to make small timing adjustments "on the road". The factory advice was to chose a long slow incline & plant the foot at 30MPH in top gear. If it didn't ping, advance 1-2 clicks on the vernier until it started to ping, then 1-2clicks retard.

Not applicable to VW?

Hi

Good figuring.

The back it off after the ping is OK on watercooled car, air coolers are littel more sensitive and with the mechanical noise that they make it can hard to pick.

I saw an intersting feature on an old Jag once, the oil light was hooked up to the - side of the coil, no oil pressure, no ignition.

Arrr, Lucas the prince of darkness, now owned by Bosch, scary thought.

Humour, do you know why poms drink warm beer? Lucas make fridges.

Steve

Steve, guess wot's makin da sparks on my MGA 1500???

A Bosch Dist.!!! TA DA!

[ Edited on 3-6-2007 by geodon ]

Go and see Hank in vines road and tell him Doc sent ya:thumb if something like this happens again

[ Edited on 3-6-2007 by beerdoc ]