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Old 08-09-2017, 08:11 AM   #1
Bricktothefuture
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Join Date: Aug 2015
Location: Central NH
Default First start concerns

Ok, I've been working on this car for a year and it's a few weeks away from completion. Former Kjet '79 245 now with the following -

Rebuilt NA B21F engine and head
New RSI Stage II NA cam (one of the last!)
.040 off head per recommendation from RSI and a few other folks
1st oversize flat top pistons direct from KG
Cometic head gasket
Dual Weber 45 DCOE, stock jets
Deleted A/C & P/S w/manual rack installed
Waiting on my STS Kjet injector plugs

Mechanic friend who's done this before is concerned about starting the rebuilt engine for the first time with the Webers, thinking if we're lean we could toast things quickly. So many new things going on... Aside from maybe setting the FPR on the higher side initially I'm not sure what else we can do to help. Any thoughts?
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Old 08-09-2017, 09:27 AM   #2
EivlEvo
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Isn't this why people hit them with starting fluid and then adjust the mixture screws right after it fires?
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Old 08-09-2017, 09:54 AM   #3
Janspeed
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On a carbed engine FPR is not part of the AFR equasion. It plays no role in the actual fuel metering, it only has to ensure that the floatbowls are kept full. That's it!
BTW, on a carbed engine you can't use a FPR and fuelpump from an injected engine, that pressure is way to high. (3bar?) You need something like a Facet pump specifically for carbs. Or a mechanical engine driven pump that is mounted on the block. (i seem to remember that early carbed 240's use those, driven by an excenter on the auxilary shaft)


about starting: once you have the fuel delivery sorted (full but not overflowing carbs!) i see no problem why you shouldn't be able to start the engine , just keep it at idle or light throttle.
Once warmed up, adjust the idle mixture screws to make the engine idle at the correct AFR. (set throttle at a fixed opening, say 1100 rpm. Then adjust mixture screws to achieve max rpm at that fixed throttle opening.don't forget to synchronise the carbs (using vacume gauges). Bring the idle speed back down to the desired level (900rpm?)

Once that's done do not try to drive it yet. Remember, only idle AFR's are OK, all other power levels still need dailing in.
You (or a professional tuner) can work from there to get the proper jetting for power, midrange and cruise. preferably on a dyno while measuring lambda /emissions.
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Old 08-09-2017, 12:07 PM   #4
Bricktothefuture
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Excellent. Going to order this FPR/filter combo once I can find one stateside - http://qedmotorsport.co.uk/qed-shop/...s-bowl-67/85mm

Also running only via the in-tank pump. Will run new fuel lines direct from FPR to tank inlet to make things clean and easy...
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Old 08-09-2017, 12:16 PM   #5
JohnMc
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As far as I know, it's pretty much impossible to fry an engine while it's idling with a lean mixture. Maybe if you run it lean at WOT for 10 minutes straight you'll burn some valves.

You say the DCOE's have 'stock' jets - what does that mean? A cookbook jet recommendation for a motor of that size? For a Volvo motor of that size? You should be able to get pretty close before the first start.

Past the first start, the bad news is there are practically no adjustments on a DCOE other than idle mixture and idle speed. Everything else involves swapping idle jets, main jets, emulsifier tubes, air jets, pump jets, venturis. All in sets of 4. It's not an easy process unless you're a real guru at tuning them, and even then it's best to have a big box of jets and tubes and stuff, otherwise, it gets pricey buying parts that might not work (they're not returnable).

But an engine will happily run on a fairly wide range of mixtures without hurting anything (other than emissions and MPG, heh), and carbs are never going to do as good of a job as fuel injection (should) does, I used a wideband when setting up mine and I noticed all sorts of weird behavior out driving around. Go over bumps and they'll spike rich (fuel splashing in the air corrector jets?). Go around a corner one way and they'll go lean, go around the other way and they go rich (likely due to the slanted install on a pushrod motor?).
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