prochaged 350 jetting help please
 

i have a 22 scarab with a 350 .30 mag carbed. it has stainless marine headers, a small cam, msd ignition and dis, single plane intake holley , holley 750 doulbe pumper mech. no power valves in prims or secondarys. procharger m1 5.5 lbs boost. currently i am running 74 prims 80 sec. the carb is not a blow through so it is in box with no flame arrestor on it. the mechanical fuel pump is ahigh flow holley thats boost referenced. 10 deg base timing with 30 total by 3000 rpms.


my question is when i start to take off its fine untill i start to add a little bit more throttle it coughs under planing conditions so there is a load on the engine after that no issues at all while driving. i am not sure if this is a lean condition or rich. or maybe i need a different squarters size or large accel pumps current size is 30 cc.

i think it coughs alittle when the secondarys start to open but not sure.

maybe some help with the jet sizes and the squarter sizes or maybe i need to add a power valve to the prims.

i just need some help

What kind of fuel pressure is it running and what is the oil temp ? As I am sure you know richer is much safer than lean. I run 7lbs. on 502's and run 88 pri and 145 secondary's and maintain 7.5 psi fuel . If it is lean the oil temp will be high . Hope this helps.

Fixx
 

carb is to big for a blow through and your motor size..

did you replace the floats? they are suppose to be the black solid floats,,you will also need rear jet extensions..(the boost pressure may be forcing the fuel to the back of the carb bowl)
you will also need a boost referenced fuel pressure regulator..example,, at idle if you have 7 psi of fuel pressure and 5.5 lbs of boost your fuel pressure needs to be 12.5 lbs @ Wot..if you have taken out the pv's then the carb will need to go up at least 5-10 jet sizes then check your afr's from their,,reading spark plugs will work to but the afr gauge and a egt gauge is the best way to play it safe with a pro charger..

fuel is boost referenced already, floats are done , jet extensions are done. i guess its back to jetting and checking plugs. i dont have a egt or a/f gauge i run and check the plugs at all the rpms ranges. if i cant fix it i will bump it back down to a 650 cfm carb.


do you think 32 deg of total timing will be ok at 5.5 lbs of boost. its currently at 30

thanks for your input guys

Fixx
 

ok one more thing to check,,did you drill the metering blocks where the power valve sits or the plugs in your case..? that area will only flow so much fuel while pressurized..

no there not drilled as far as i know i had a friend do the carb setup for me but he doesnt live near me anymore.

if they were to be drilled whats the benifits and how big do you drill it.

i went by this guys recommendations a few years ago,,his techniques work really on my set up..

http://www.hangar18fabrication.com/blowthru.html

mr fixx what size accel pumps are you using 30 cc or 50 cc. 30cc is the standard. ill prob pull the carb of my boat in the next week or so to take a look at it. and redial in the jets for testing.


thanks for the help ill let you guys know what i find.

Fixx
 

i have 502's,,use to be 600 sc's but now have prochargers on them..

750 carbs,annular boosters 30cc primary and 50cc secondarys