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Engine break-in
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tidybol
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PostPosted: Sat Dec 26, 2020 6:16 pm    Post subject: Re: Engine break-in Reply with quote

Just took it for a drive to break in the rings. Brakes are EXTREMELY sketchy so it was difficult to get up to decent speed. More importantly though, still having issues with the carb and a nasty flat spot. Adjusting the accelerator pump seemed to help a bit. Pertronix SVDA distributor and Bocar Pict34 carb. Carb was adjusted 2 1/2 back from bottom out(mixture and volume control). Seems to run best at 33 total advance(around 10-12 idle).
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tidybol
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PostPosted: Fri Jan 15, 2021 1:53 pm    Post subject: Re: Engine break-in Reply with quote

So we're going to try and get it running right since I'm pretty sure the rings didn't seat last time because of the rough running/flat spot. Since my last post my dad bought a pic34 replacement carb from jBugs
https://www.jbugs.com/product/113129031KJB.html and tried to get it running but it wasn't all that different. Makes me think the Bocar was just fine. Also, I picked up a tri-mil exhaust to replace the bugpack: https://socalautoparts.com/product/satin-black-cer...at-risers/

Anyhow, I'm pretty sure our timing is right, the vacuum advance is working properly so I'm thinking the jetting is off or possibly there's a vacuum leak somewhere(new intake rubbers btw)
Based off the carb and exhaust I'm running can anyone recommend a good starting place to tune the carb as far as jet size?
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tidybol
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PostPosted: Sat Jan 16, 2021 10:49 am    Post subject: Re: Engine break-in Reply with quote

Got it running yesterday! We put in larger jets. 137 main and 60 on the airbleed. Still some low speed hesitation and it wants to stall if revs come down too quickly. We were able to do a couple runs to try and seat the rings better. Afterwards we pulled the plugs and found one of them way too hot/lean and the rest maybe a touch too rich? Is the lean one indicative of an incorrect valve setting? Also, it seems to run much better with the timing set to 38 degrees total advance. I'm wary of running it like that long term though. I'm going to double check the valve tolerances again(last set at .006 IN and .008 EX).


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airschooled Premium Member
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PostPosted: Sat Jan 16, 2021 12:28 pm    Post subject: Re: Engine break-in Reply with quote

tidybol wrote:
it seems to run much better with the timing set to 38 degrees total advance.


Is this with the hose on or off? 28-32btdc is our safe max with the hose OFF, around 40 is normal with the nose on.

Something I find helpful on fresh builds is an exhaust system retorque on a stone cold engine. Hit every manifold and flange nut with a wrench, don't skip any. Sometimes intake manifolds enjoy a torque check too.

Robbie
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bsairhead
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PostPosted: Sat Jan 16, 2021 4:15 pm    Post subject: Re: Engine break-in Reply with quote

On a cold engine valves lash should be set to .006 for both intake and exhaust. Unless you have chromoly pushrods - loose "0". Recheck timing, it is critical.
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tidybol
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PostPosted: Sat Jan 16, 2021 7:45 pm    Post subject: Re: Engine break-in Reply with quote

bsairhead wrote:
On a cold engine valves lash should be set to .006 for both intake and exhaust. Unless you have chromoly pushrods - loose "0". Recheck timing, it is critical.


I have the CB performance Cheater cam in there and they recommended .004 IN and .006 EX. Should I ignore that and go .006 for both?
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tidybol
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PostPosted: Sat Jan 16, 2021 7:48 pm    Post subject: Re: Engine break-in Reply with quote

airschooled wrote:
tidybol wrote:
it seems to run much better with the timing set to 38 degrees total advance.


Is this with the hose on or off? 28-32btdc is our safe max with the hose OFF, around 40 is normal with the nose on.

Something I find helpful on fresh builds is an exhaust system retorque on a stone cold engine. Hit every manifold and flange nut with a wrench, don't skip any. Sometimes intake manifolds enjoy a torque check too.

Robbie


Hose off and holding a finger over the vacuum port its about 7.5 to 8. With the hose on and the engine revved up a bit it's about 38-40. Am I in the ballpark?
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bsairhead
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PostPosted: Sat Jan 16, 2021 8:26 pm    Post subject: Re: Engine break-in Reply with quote

Revved up with hose off is what is important.
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