New 502 carb woes.
 

Hey all. Just installed a new Gen6 502 in my 26ft envision purchased from a fellow member here. Excellent person to deal with. Great communication. Great motor. No problems in transaction.. Anyhow. Motor was a stock 502 with procharger installed on it. (I purchased motor without procharger though). Was previously tuned and dynoed with pro-charger a 850 nickerson carb. Prim jets were 80's... Sec 100's. No p.v in rear. 30 deg total timing. Took it for its first run saturday and it wouldnt rev past 3600. Blubbering bad. Way to rich. Returned to dock and proceeded to adjust timing to 34 degrees total. Found a set of 88's and replaced the 100's and it woke up pretty good. 4700rpm. but still has a terrible blubber right at the half throttle point.(still seems rich right there). Will continue to blubber as long as the throttle is there. anything below or above that seemed acceptable compared to the first run. Any opinions on what this carb should be jetted at without the pro-charger would be greatly appreciated... Havent run it enough to get a good plug reading yet. 45 minutes top. Also have a 750 demon that was on the previous 454 lying around that worked perfect.. Worth a try?..

you had this thing on the dyno ? tuned it and sorted it and it was fine and in the boat you have to move the timing all over the place and change the jetting 20 % ?

what exactly was it you did on the dyno ?

The previous owner had it dynoed and set up with the pro-charger installed. I bought the motor minus the pro-charger but the carb and ignition still were tuned to run with the pro-charger.. Just wondering what to re-jet to without pro-charger? First run was with carb and jetting set for pro-charger set-up as i received it.. sorry 'bout that. Thanks.

850 is too big for a blow through on a 502

ah ha... well that makes all the sense in the world. with the sc it would have wanted a lot less timing and a lot more fuel.

so the timing sounds a lot better where you have it now and might even stand a bit more but the carb sounds big and rich as you guessed . do you know if they did anything weird to the carb for extra enrichment ? at anyrate... if you have the carb off the 454 known good, thats not a bad test. it won't be wildly wrong on the jets and it will either clean up the whole mid range as you hope or not. so its more of a " big fix " test than final tune, so to speak. did you do a mechanical check of the motor before you carried it off ? a compression check/ leak down etc ? and you are certain the mechanical spec is stock ? no reduced compression ratio for big boost or something ?

Fixx
 

Stock jets on a 850 is 80 primarys an 80 on the secondarys..PV's are 6.5's.. is their still power valves in the carbs,,rear should have jet extensions also for the procharger which you can leave in with the jets.. my concern would be if they drilled the metering blocks for more fuel or left some jets out in the metering block for tuning the procharger..

Heres the motor details. (I took one of them) .2 complete GM Gen VI 502 motors. Bow tie siamese block with four bolt mains with GM aluminum intake, 1 piece rear main seal, 1053 steel Forged & Cross Drilled Crank, 4340 Forged Rods with 7/16” bolts, Rectangular Heads, forged pistons, and steel hydraulic roller camshafts, rectangular port heads with 2.19 intake valves, 1.88 exhaust valves and 118cc chamber which a 8.75 to compression ratio. Also includes 6 qt oil pan (Merc style) with windage tray.

These engines have dyno time only, was going to be used in my Cig so I installed new Inconel exhaust valves and reassembled with Cometic MLS (Multi-Layer Steel) head gaskets. These will work beautifully with mild boosted applications such as with a turbo or blower. ....
.......Putting demon on would be a breeze. Just didnt want to take the motor out and run it lean right off the shelf.

well they sound like fine motors assuming they were put together correctly. would you consider going back to the dyno and dialing it in ? i'm sure there are carb guys on here that can look at those specs and tell you jets plus or minus nothing but i'm not one of them... the dyno day might pay off in the long run.

if the carb was modified to be used as a blow through for the procharger then you may never get it to run right without it. there are several internal mods done for a blow through set up that just dont work on a naturaly aspirated setup. try the 750 and see where you get.

My 502 has a nickerson 980 with 90/98 mains. Previous setup ran about 480hp with 84/90