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Discussion Starter #1
The plan is new head, warmer cams and rebuilt carbs.

Getting the carbs back from the rebuilder and just bolting them on, will they run well enough to properly break in the cams, or do I have to tune the rebuilt carbs on my old cams (and tappets) before installing the new cams?
 

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I'd do it on old setup, deal with one thing at a time. Less **** to go wrong
Sorry, I assumed only the carbs and cams were new/rebuilt. Missed the new head part.

Wait for more experienced to chime in on this. FWIW As I understood new cams usually are broken-in at steady 2000rpm for 30-40 min or so on street engine.
On a new/rebuilt engine with new piston rings, depending on the brand and type, 2000rpm steady break-in might not be the best way. You should talk to cam manufacturer, see what they have to say. If your engine has new head and old bottom end, I'd just put all new parts on the head and adjust carbs to run smoothly at 2000rpm or whatever is reccomended by manuf. There are bunch of very good guides to adj./tune webers on alfabb. Use google to search instead of internal alfabb function
 

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Two engine builders that I know and trust, Richard Jemison and Jim Steck both recommend breaking in piston rings and cams by running at about 2000 rpm for about 20 minutes and that is it for the cams. The rings have to be treated nicely for a longer period.
Richard supplies a break in lube for his cams which is sticky and Jim specifies the same lube for cylinder head nuts.
 

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Discussion Starter #6
Two engine builders that I know and trust, Richard Jemison and Jim Steck both recommend breaking in piston rings and cams by running at about 2000 rpm for about 20 minutes and that is it for the cams. The rings have to be treated nicely for a longer period.
Richard supplies a break in lube for his cams which is sticky and Jim specifies the same lube for cylinder head nuts.
Thanks, I hear that.

By my question is this:

Will fresh-from-the-rebuilder carbs run well enough right out of the box to break-in the cams properly? Or will freshly rebuilt carbs spit and stall until they're tuned, meaning I'll have to first set up the carbs on the old cams so they run properly, and only then install and break-in new cams?

My pistons, rings, etc. are not new. We're just talking about a top-end rebuild here.

Thanks!
 

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Yes or no. I do a lot of Weber restorations, both for stock and modified engines. I tell my customers that they will run as received on modified engines, but TUNING WILL BE REQUIRED for best performance. I'm not talking about balance and idle mixtures, but jetting changes. I try to set them up for performance builds so the high speed circuit will be a bit rich to overcome unknowns in the build, knowing maximum power appears just as everything goes to too lean. Idle is set up so it will idle, but maybe or maybe not transition to the high speed circuit smoothly. Pump circuits are usually very close to dead on correct (except for one of my own engines{It happens}). The only way to get jetting right on modified engines is with an A/F meter, or by trial and error. Trial and error works great for those experienced with Webers, not so well for those lacking experience.
Then there is ignition, both timing and curve location. It must somewhat match the Weber progression circuit to avoid the dreaded dead-spot on acceleration. I just explained this to a customer last night. His performance engine build has unknown cams, unknown compression, and an unknown solid state ignition curve with my restored 45DCOE Italian Webers. It idles great, and accelerates smoothly with no load (Amazing!) but bogs under acceleration under load. Probably ignition curve, but I'm amazed I got the jetting this close!
Now, YES you can break in this particular engine as is. It will run to 2,000 rpm and beyond smoothly with no load, and has no signs of lean mixture. It does need ignition curve and jetting attention for best power and performance.
Many BB readers questions are often best answered by a qualified "maybe", and lack of experience or knowledge is a learning opportunity. That IS GOOD. Experienced readers should offer opinion and direction. This is an interesting thread! Please continue with questions and answers.
 

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You should pay close attention to whatever ^ they say!!! A wealth of knowledge and experience these gents have and are generously sharing with us.

If your Weber rebuilder is anywhere as good as Gordon Raymond and you have done this before, I'd go straight with new parts. Otherwise, install old parts, get ignition and carbs close and then put new parts in. If you are not planning to have the engine tuned by a professional and want to do it yourself, install wide-band AFR meter now. It will save you headaches later.
Cheers
 

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I would udse known Webers if possible. You don't want to be screwing around with the idle mixture and throttle stop and have the motor stalling and not wanting to start while you are breaking in the motor. The motor might not be harmed but your nerves will.
 

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Discussion Starter #10
Thanks for these very helpful answers.

Having never done this before, it sounds like I'd be safest first making sure the engine runs on its new carbs before installing new cams.

When the new cams are installed and broken in, I'll take the car to a pro for carb and ignition tuning.
 

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I would udse known Webers if possible. You don't want to be screwing around with the idle mixture and throttle stop and have the motor stalling and not wanting to start while you are breaking in the motor. The motor might not be harmed but your nerves will.
Fair point, but would have to be a pretty ****** carb rebuild for them to be set that different and out of balance, plus you want it to be running around 2000 rpm so no idling.

Anybody that rebuilds a pair of carburetors should set all the adjustment screws to the same setting for the same type of adjustment (i.e. all mixture screws should be the same number of turns out from seated, all idle screws should be the same number of turns out from fully closed, etc.), so at least they are mechanically synchronised on the first start.

Anyway I will find out in a few years ...
Pete
 
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