roaddogscycles

I posted this in the engine section but figured i should post it here as well just incase the issue is just the carb settings and maybe not everyone looks at the engine threads.


Heres my engine combination with a HP goal of 475-500 at the flywheel haven't dyed it yet tell i get it tuned. Due the goals seem realistic?

383 Stroker Spec.s

Eagle Billet stroker crank
Arp main studs
Eagle H-beam rods with ARP bolts
Machine Work: 350 machined 4 bolt main block .30 over balanced and blueprinted
Forged Diamond Pistons with custom thick ring glands for large nitrous shot in the future
compression ratio 10.8 to 1
clevite bearings throughout
Melling high flow oil pump
Lunati 1.7 to 1 billet rocker arms

Lunati Voodoo Cam
Cam Spec's:
Advertised Duration 294/302
duration 243/251 @ .50
.560/565 lift
LSA 110/106

195 AFR eliminator heads
ARP head Bolts
Edelbrock single plane Air gap RPM performer Intake
Quick Fuel HR-780-VS Carb
High Flow edelbrock fuel pump and regulator set to 6.5 PSI
MSD Billet Distributer 85551
MSD 6AL Ignition
NGK Plugs one plug cooler then stock have to look up the number.


So now where I'm at and what i have done. The first problem i had was the aftermarket pointer was no where close to TDC. So i found TDC and made a mark on the balancer and worked with that.

I set the initial timing at 10 BTDC 850 RPM and i get my total timing around 3800 RPM of 32 BTDC. The MSD 8551 mechanical Distributer is set up stock i haven't touched the timing curve which appears to be 22 degrees advance. Full advance @ 3800 unless I'm looking at the chart wrong. So with my initial 10 BTDC i am assuming I'm at 32 BTDC degrees total @ 3800 rpm. Im sure this is very mild for this motor, i have heard any type of audible pinging.

Engine runing at Idle only makes about 7.5 In vac and at about 2500-3000 no load i get around 10-13 in

The only adjustments i have done to the carb is the idle mixture screws on the carb. At the suggestion of a local shop i changed the power valve from the 6.5 that was in it to a 3.5 which they recommended for the vac the engine currently has at idle. All changing the power valve seemed to do was lower the upper end of the stumbling issue from 3000 RPM down to 2500 and it seemed to make the idle air mixture screws work better.

I pulled the one plug yesterday to see what them look like and the plug looked brownish black more brown then black. So A/F docent appear to be that bad overall.

Engine wants to idle around 950-1000 but diesels when shut down, but i managed to get it down to idle around 800-850 after changing the power valve and re-adjusting the idle mixture screws the dieseling affect not nearly as bad almost gone.

One issue id like to eliminate is the engine dieseling from time to time. I assume this is because the cam profile, and having the idle circuit open too far causing too much left over gas at shut down. An idea i had was to add a little more initial timing, many bump it to 13-14 degrees to make the compensate fro the big cam and bump the idle up a little more, then adjust the idle back down with the idle screw hopefully closing the butterfly enough to just be in the idle circuit. Then re adjust the advance stop to 18 degrees advance so my total would still only be around 32 degrees at full advance.

Second issue is the engine stumbles and does not run well tell 2500 RPM up. From 3000 up the car is almost underivable, the power comes in and you can physically feel the car twist and the rear end of the sink deep into the springs almost like to wants to lift the front end......, tires light up etc....to be expected with stock tires on the open dif. Cruising is poor the car runs real rich bumping the throttle lightly even causes a little visual brown/black smoke.

I spoke to quick fuel today and they recommended adjusting the primary to secondary progression which is a small allen located under the vacum secondary adjustment module on the passenger side of the carb.

I am going to try that adjustment but i am curious if my timing advance curve is also contributing to this issue, would i be better to adjust my timing curve first so that my total advance came in at say 2500- instead of 3800 where it currently comes in?

I plan to get a A/F gauge in the car just haven't tuned a performance carb engine before and want to take it slow as i figure it out, have plenty experience in EFI LS1 engines. Looking for suggestions on tuning this carb as I'm not familiar with and there are no local shops in the Vegas area id trust to tune it considering the investment i have in the engine.

midias

Timing does not have a required number where it runs good it is good.

If I build that motor I would probably guess about 36 degrees total is a good start and the base timing would be w/e you get. I would get the MSD 8464 kit and put in springs to make it advance faster and try to get total timing in by 3k RPM.

You most likely need the extra timing and seeing how you dont have a vac advance you are at even more of a loss.

pancherj

I have a slightly smaller, but similar cam in my 350 with AFR heads, Air Gap, Etc. Mine likes around 50 degrees advance at idle and 36 degrees total mechanical. Produces almost 15" at idle. You are SOL with that distributor. Get a GM Performance HEI with vacuum advance. Set it to 14 initial, 32 total and then whatever the vacuum can adds in at idle and cruise (you can then work your way up from there). Once you dial in the timing, you can then tune the carb.

bigal55

iTrader: (1)

Sounds like you're going to have a bunch of tuning to do, both carb and distributor setup. I would get a good carb book and read it through. Sounds like you have the primary open enough to uncover the idle circuit slot at idle. This is a common problem when tuning for a big cam (low idle vacuum). As for the distributor, you should get one with an adjustable vacuum advance can. Why would you run a non-vacuum distributor on the road? Without vacuum advance at idle, you will never get the motor to run reasonably. If you crank up the static advance at idle to compensate, you will create problems in higher rpm/load levels. JM2C!

midias

Without vac advance you might want to get a fast timing curve so your base can be low enough to start but you get needed timing asap