Carb Balancing Woes...

[eeyoreish]

Having read lots about it here on the forum and got myself a copy of the Lotus service manual instructions on the subject I set about balancing my carbs today...

Having previously balanced the airflow using a borrowed 'snail' manometer in each trumpet I thought I'd spend half an hour checking and rebalancing them properly via the air ports using my new 4 way carb balancer before checking the mixtures with a colourtune.

Having actually spent all afternoon on it I'm at my wits end as no matter what I do I can't seem to get a consistent balance between all 4 barrels. I followed the manual instructions and balanced lowest reading across both carbs first, then adjusted the remaining 2 barrels to match, adjusting the throttle linkage a touch where necessary.

The problem is, each time I get the readings close enough to think 'that'll do' after a blip of the throttle they settle back down into different positions! I've tried several times from scratch and keep getting the same problem.

The other issue I have is that each time on the back carb I seem to end up with one air screw fully in and one fully out just to get them the same.

All vac hoses are new and there are no air leaks that I can hear.

Am I doing something wrong???

[jonwat]

This sounds like symptoms of well worn carbs, what's the mileage, have they ever been refurbished?

[eeyoreish]

This sounds like symptoms of well worn carbs, what's the mileage, have they ever been refurbished?

 

Mileage is just over 80k on a 1990 car. Both carbs have just been refurbed with genuine Dellorto kits and remounted on new O rings plus new vac hoses all round.

 

What could be worn that would cause this problem?

[jonwat]

Might have been worth mentioning the refurb when you asked the question.

 

Sounds like worn butterfly shaft bearings, were they replaced?

[eeyoreish]

Sounds like worn butterfly shaft bearings, were they replaced?

 

The bearings weren't part of the refurb kit so they weren't replaced. Plus until now I hadn't suspected a problem with them. 

 

Are they easy to change?

[jonwat]

Others have done it, Giorgio has a good post with pics in the Giugiaro thread, search for butterfly bearings & you should find it. Sorry can't paste.

 

You'll probably also get more help on the Giugiaro thread as they all use carbs.

Edited July 20, 2015 by jonwat

[eeyoreish]

Others have done it, Giorgio has a good post with pics in the Giugiaro thread, search for butterfly bearings & you should find it. Sorry can't paste.

 

OK, cheers John. 

 

I already managed to find some posts from Giorgio and some from Buddsy on a similar subject. Seems it's not the easiest job but possible if it's necessary.

 

I'll have a good look at the spindle action and bearings and see if that's where the problem lies. Everything seemed to be moving fine when I had them off the car for cleaning/refurb, hence I didn't change any bearings then...

[rogerch]

Couple things you might check, the linkage between the 2 spindles is critical. Also is your return spring shutting both carbs down equally and quickly?

I used a double redundancy on the throttle return, so it had the 2 spindle springs, useless, and 2 exterior springs, mainly safety, but a good shut down response as well.

[eeyoreish]

I'll be checking the spindles at the next opportunity.

 

All seemed fine when the carbs were off the car but I'll have a closer look and see if I can identify what the problem is now.