New jets

[vintageman]

I have a 351c 2v with Performer 2750 and Summit Carb 750 CFM. Stage 3 cam and recent full rebuild by myself. The plugs show it to running rich. My idle likes about 1000 rpms and my static timing is 13-14 degrees btc. I have vacuum at around 17 and does not bounce around. The currents jets in this carb are 77 primary and 79 secondary, with a 6.5 power valve. The car starts and runs like a raped ape but I want to address the rich plugs. What are your thoughts about going to 74 primary and 76 jets? Thanks and as always, I appreciate the comments.

Tom

 

[boilermaster]

Vintageman,
Just as long as you are 100% sure you know the richness is coming from ONLY the main circuit.
It would help if you would post the carb part number.
Does your carb have a single power valve or does it have both primary and secondary power valves ?.
I see in summits reviews, a few customers stated that primary and secondary power valves were reversed on a few carbs.
For the carb I specd. it showed 9.5 hg. secondary power valve.
That could make you over rich right there.
If this were a 750 vs Holley, I would say you should be around a 72 or 74 primary jet. this carb is very different from a standard Holley.
Boilermaster

 

[Sheriff41]

Here in Texas (900' elev) I'm running a 4160 Holley with 72 primaries and 6.5 power valve. This works well for my 351C 4V engine. The choke setting took a bit to get dialed in; the factory setting was too aggressive.

 

[vintageman]

Thank you boiler master and Sherrif41, I appreciate your quick responses. I will pull the carb and check the power valves over the next couple of day and see if they are reversed as well as verify the jet numbers. The part number of the carb I have is SUM-M08750VS (electric choke). This has been my third change out of this carb because the first one had a sticking throttle, the second one had a vacuum leak at the throttle butterfly and every time I would start it, would require me to to change the throttle and idle mixture screws to get it to idle correct (turned out they acknowledged the accidentally sent me one that was due for repairs but had not been repaired yet), and this one that runs and starts great other than the richness. I love the fact that I can pull the top off and do jet and other changes without having fuel spill all over but if I can't figure this richness out, I may swap over to a Holley carb since I have had zero issues with those in the past.
Either way, I am good with changing out to a Holley because each time that I warrantied these, the Summit team has started my 12 month return policy over again and if I run back down there again this weekend, they will refund and add that to the price of a Holley carb. The guys at Summit in Atlanta have been great to work with.

More to follow, I want to get it running and performing right, then add the subframe connectors and paint.

Thanks

Tom

Tom

 

[Cleveland Crush]

I have a 351c 2v with Performer 2750 and Summit Carb 750 CFM. Stage 3 cam and recent full rebuild by myself. The plugs show it to running rich. My idle likes about 1000 rpms and my static timing is 13-14 degrees btc. I have vacuum at around 17 and does not bounce around. The currents jets in this carb are 77 primary and 79 secondary, with a 6.5 power valve. The car starts and runs like a raped ape but I want to address the rich plugs. What are your thoughts about going to 74 primary and 76 jets? Thanks and as always, I appreciate the comments.

Tom

Tom, Please pull one spark plug from each bank and take a couple good photos of each tip, electrode and thread area. We'll be able to give additional feedback after we take a look. The attached illustration is a general guideline of what to look for:

 

[vintageman]

Will do Cleveland, thanks.

Tom

 

[vintageman]

Sorry to take so long to update this thread, I had a little time to pull the carb a few days ago and dropped the carb primary jets down to 74 from 77 and the secondary from 79 to 76. After doing that the car runs great. No issues with idle. I pulled the plugs and changed them (forgot to take pics though), before the jet change, they looked were black. After I changed the jets and ran the car for a couple days, I pulled a couple from each bank and they were not bad, normal looking brownish, and no blackness to them. I now start up cold at about 2000 rpms and at operating temps after the choke comes off, idle in park/neutral about 850 and in gear about 725 or so. While I had the carb off I also checked the idle circuit to verify that the slots were not too exposed (have a square showing at the butterfly slots) and turned the idle air mixture screws out to 1 1/2 turns out. Initial timing is at 14 degrees btdc, my timing light took a crap and I couldn't get the total timing yet. Need to go pick up another light this weekend. Thanks everyone for your advice and guidance.

Tom