Weber 36 IDF Rebuild and Balancing/Idle Adjustment

[Spacenut]

Hi guys - after my successful reintroduction to the world of motoring last week, I have just finished changing the camshaft belts and idler pulleys (even with the improved accessibility in the Nova that still took 3 hours), and while I was at it I removed the carbs to give them a clean and replace the gaskets and seals etc.

To this end I have bought two rebuild kits from UK Classic Carbs, they are the same as the Eurocarb kit, i.e. each kit contains the following parts:

1 x top cover gasket
1 x needle valve and metal washer
1 x inlet filter and fibre washer
2 x inlet manifold gaskets
1 x air horn gasket (note that I don't use this as I have thick cork gaskets to space the K&Ns away from the balance bar)
5 x O-rings

Its the last part that has got me confused - two of the O-rings are large, one is medium sized and the remaining two are small. The large ones just about fitted the acceleration pump nozzles, but were they for that purpose? Or should I have fitted them to the idle screws (similar size)? More to the point, what are the other teeny-tiny ones for???

OK, so carbs are back together, float levels set etc. The Weber tuning guide says the idle mixture screws are out from fully home by 1 full turn and the idle screw is in half a turn from first contact. The air bypass screws are covered by tamper proof plugs which I haven't removed.

The engine won't idle for peanuts in this state of tune. Am I doing it right so far? Is there any sage advice for getting the tuning and balance spot-on? I have got a synchrometer to measure airflow...

Any help would be greatly appreciated!

Thanks everyone,

Lauren

[Alfastrut]

Look at twin carbs by alfadave. May be helpful

[LooLooSud33Spider]

Hi Lauren
The first thing to do is to get the thing to idle long enough to actually set it up. I usually start by disconnecting the linkage from one carb . This allows you to tweek each carb without affecting the other
Firstly open the idle screws a little more until the engine idles and check the synch with your meter. I’d aim for an idle speed of 700-850 then with a short dumpy screwy wind each mixture screw in until the engine just starts to “go off” or sounds like it’s dropped one. Then turn the mixture screw back out till the engine smooths out again . Do this one at a time And recheck and adjust your idle speed and synch afterwards
Once you’ve got a decent idle and your happy with the response of the mixture screws then reattach the linkage to the carb you removed it from being careful not to affect the idle setting as you’ll no doubt know the little links are adjustable so just set it so it pops on nicely. Then just set the other screws in the linkage so that both carbs open simultaneously
It can take a bit of time and patience to
get it right .

[Spacenut]

Thanks Lou - that is very helpful. I have also read through Alfadave's twin carb thread too. Looking forward to having a decent crack at getting the tuning right this time - I can't believe I have been driving around for years with the same initial setting (all idle mixture screws two turns out from fully home). Hopefully the synchrometer will help bring some science to the occasion!

Lauren

[LooLooSud33Spider]

Hi Lauren a lot of the setting up of the carbs includes listening to the engine it’s actually talking to you and the trick is understanding what they’re saying.

[Oggie]

http://www.redlineweber.com/html/Tech/i ... ntrols.htm

Hi Lauren, I use this guide for the 33, its worth printing off a copy and marking off the steps as you adjust.

[Spacenut]

Thanks for all the helpful advice, which is much appreciated. Unfortunately I can't start the "engine whispering" until I can get the engine to idle and right now it doesn't

I think I must have got some crud in the jets while I was scraping off the old top gasket. Carb cleaning kit, carb cleaner and compressed air aerosol on order...

Lauren

[Spacenut]

On my continuing carburettor tuning odyssey, can anyone tell me what would be the baseline adjustment for the accelerator pump on the Weber 36 IDF? Also, I have two holes in the bellcrank that operates the accelerator pump lever - the rod is currently in the hole closest to the throttle butterfly shaft, so provides a shorter stroke. Is there a baseline position for this rod as well?

I have read that there should be no more than 0.5" of thread protruding from the adjustment screw on the accelerator pump rod. Is this a good starting point?

The reason I am asking all these questions is because both my carbs have been apart at one time or another, and I don't have an initial set of starting conditions. Any help would be greatly appreciated!

Thanks guys,

Lauren

[alfadave]

Regarding idling......

remove and clean all 4 idle jets....

But what caught me out, there is a small air hole in the top cover next to each idle jet.....make sure these are clear.
i used a bike pump, with a tapered football inflator as my source of compressed air

[Kegsti66]

Thanks guys, really useful tips here.
I need to sort my set soon and assemble all my parts and build my engine up.

[Spacenut]

Regarding idling......

remove and clean all 4 idle jets....

But what caught me out, there is a small air hole in the top cover next to each idle jet.....make sure these are clear.
i used a bike pump, with a tapered football inflator as my source of compressed air

Thanks Dave - it's good to know that others have succeeded in cleaning out their carbs with the same tools that I have

I have ordered some compressed air cans to blow out the crud and a set of pipe cleaners designed specifically for cleaning out carbs. This morning (before the temperature rose to 32C) I took the carbs off again ready for the clean up.

Also noticed that the accelerator pump bellcrank has one one hole, so I don't know what I was thinking there. Maybe I was remembering my old 32 DIR...

[Spacenut]

Hi everyone - so I've cleaned and re-fitted my carbs and I thought I was getting somewhere as they seemed to balance up alright and the RH carb idle mixture adjustment went OK, but on the LH bank I couldn't get the idle mixture screws to do anything.

The engine idles OK but revs very poorly and occasionally the revs won't die when the throttle is released.

As I have just refitted the carbs, and both idle mixture screws on the LH carb are not doing anything, do I have a vacuum leak somewhere?

I was hoping to go to Brooklands on Sunday for the Supercar show, so I need to fix this issue ASAP. Any suggestions/diagnostic advice gratefully received!

Lauren

[Alfastrut]

What happens to the idle when you pull the plug leads one at a time on the LH carb? A colour tune would help you to see what's happening in the piston.

[KevJTD]

I'd be suspect of the little vac pipes that go near the base of the carb Lauren, a small split in one of them will allow air to be drawn in engine side of the butterfly which will give you grief..

[Spacenut]

Thanks guys - it was an air leak, but not from the myriad small bore vacuum hoses (the originals were literally falling apart so I replaced them all with silicone hoses) - the leak was actually at the base of the LH carb., probably from the replacement gaskets that came with the rebuild kit. I couldn't be more specific, because my "steth-o-hose" (patent pending) could not pinpoint the exact source, but the air leak was massive and on the inboard side of the carb.

So today I removed the LH carb. and applied a smear of Wellseal (non-hardening gasket sealant) around the inlet manifold gaskets, phenolic spacer and carb. base gaskets. After I had cured a fuel leak from the inlet filter housing (the 19mm brass plug needed a tweak) I was able to confirm that the air leak is gone, and I can now adjust the idle on the LH carb. although pick-up is still a bit rough, so there is some more work to do...

Nevertheless, a quick run round the block showed no other anomalies, so I should be able to get to Brooklands tomorrow. Fingers crossed!

Lauren

[Alfastrut]

Glad to hear you sorted it

[alfadave]

For what its worth, I bin all the small bore vacuum hoses, and put 4 blanking plugs on the carbs.
Then run the breather outlet on the oil filler pipe to ground.
Saves a load of hassle!

[Kegsti66]

Glad to hear you sorted it

Ditto Lauren, pleased to here you are back on the road.