Buick 455 build...last one i swear

Good lord the last hour and a half have been trying. I got a Summit 750 carb today for my daily driver carb and the install was easy but the damn rubber hose from the stock line to the carb wouldn't stop leaking. After putting a new hose and different clamps the damn thing was still leaking. Come to realize the stock hose barb fitting they give you to put in the feed line wouldn't seal. Luckily, i have tons of brass fittings and had one that fit. Now, its leak free.

I know a 750 is small for a warmed up 455 but I got this carb for two reasons: i wanted a choke to help with those early morning start ups and better economy. So far I'm impressed as hell. This thing has allowed me to get my idle down to 550-600rpm! Smooth as butter too. It's helped quiet down my exhaust tone due tot he lower idle and that's also a hidden plus. it's really rich at idle as the jetting is pretty high. The one thing i like about this version of the Holey 4010 is that i don't have to drain the carb to change the jets, just unbolt the top of the carb and wallah! I didn't get a chance to drive it yet so tomorrow morning will be an adventure.

 

Oh yeah! Between a softer spring, changing from 79 to 82 jets in the rear and adding a 50cc pump on the primary, the car runs like a beast. The addition of the 50cc pump made the biggest difference and solved the lean spot i was seeing before the secondaries opened. Now the car is in the low 12s for AFR at WOT. It's still running rich at idle even with the idle screws all the way in so I'll try smaller jets and see if that does anything. If not, ill have to dig into the air bleeds.

 

Im thinking that if your cam bearings were fine than all you had to do is use a dent puller on the pan and you would be ok. If the pan wasnt dented in, how can your crank hit it? especially with a girdle. I change the oil and filter ounce right after break in of cam, then after the first drive. then again after 500 miles.

 

Quick tuning update:

Went from 77/82 jets to 72/80 to see if i could get the cruise and wot to lean out a little bit and this carb is way more sensitive than my double pumper. I went from low 12 AFRs across the board to WAY lean. i have to be really careful loading up the engine to stay out of the 15s or higher! i didnt even try to go WOT. I'll probably go to 75/80 and see how that goes. i will say the primary jets have no effect on idle afrs at all so ill have to play around with the IABs and see if i can lean it out some.

 

Changed the jets to 76/82 and got the WOT back to 12.5 but its still lean during light acceleration (before secondaries open). I also have a lean spike if i punch it from a stop. I have the blue pump cam installed with a 50cc pump and .035 orifice shooter (these can be changed via tiny jets). I also have the lightest secondary spring installed. The hestitation during a WOT stomp from idle is probably not even a full second but it is there and the AFR jumps to 17-18 before the secondaries start to open. i don't want to go drill PVCRs just yet so i'll keep messing with the pump cams and shooter orifices.

 

yesterday's ride home from work was fun, typical gorgeous SOCAL day with an empty stretch of highway in front of me. I pop the trans down into third and roll onto the throttle. I watched as the tach climbed to 5000 (roughly 121mph) before i let off. it's crazy but the exhaust note disappeared it seemed at that speed...all i heard was this beautiful low frequency hum and the wind as i cut through the air like a razor blade. AFR stayed at 13 all the way up so i think i have the secondary jetting just right.

When i got home i decided to check the engine vacuum at idle and messed around with the idle mixture screws. Turns out i had them way too far out. After watching the vacuum and AFR, a quarter turn out on each screw gave me best vaccum of 11.5" and an AFR of 14-14.7. Bottoming out the screws, however, did NOT casue the engine to sputter, cough or die.

Later, i decided to change the primaries up again to 78's to continue looking for that sweet spot for cruise and acceleration. The cruise richened up a little bit and at part throttle the AFR's are at 13-14 but if i give it any more than partial throttle the AFR's go way lean waiting for the secondaries to open. I'm pretty sure I need a couple things: bigger shooter orifices and drill out PVCRs. After going up in jet size again, I bottomed the misture screws out and my idle AFR is now in the 12s so i've reached the working limits of my idle circuits adjustability. To me this means, my PVCR's are too small requiring huge jets to provide the flow i need at partial throttle. I'll keep going up in jet size until i get the cruise and partial throttle AFRs where i want, calculate the PVCR/jet size, then start lowering the jets and increasing the PVCRs until i get the optimal cruise and partial throttle.

I have a set of emulsion bleeds on the way so i can start messing aroud with the shooter orifices to try and get rid of then off idle lean spot too. Tuning is fun!

 

Getting closer. Decided to dismantle the whole carb today to measure the PVCRs and found something interesting. The power valves were in the wrong holes. All the literature said their should be a 9.5 in the front and a 6.5 in the rear...mine were opposite of that. Good quality control huh?

Anyway, the PVCRs front and rear are .070! HUGE. Put the 30cc pump back on and put the jets at 76/80. I also cracked the secondaries just enough to barely reveal the transfer slot. I'm getting really close to the tune i want. My test drive showed 13.2-13.5 at WOT so i changed the rears back to 82s and I'll see how that works tomorrow.

Of course, as soon as i get this thing perfect I'll probably get the QFI on my doorstep. I would like to drag it at least once before i make the switch just to see how this engine combo compares to my old one. LOL.

 

This carb baffles me. I decided to "square up" the jets by drilling the primary PVCRs to .086 and throwing in 74 jets. The idle is still rich and low speed/high vacuum acceleration is still lean. Take off, WOT and part throttle cruise is perfect. The idle mixture screws are all the way in and i can't lean my idle out more than 12.4. It idles at 600rpm and i have 21* of initial timing. I even lowered the float levels a little below half to see if that would help and nothing. I guess the next step is to mess with the IARs but i don't really know how that's going to help lean the idle and richen the light acceleration lean spot im experiencing.

Light throttle cruise is good but when im coasting or very low throttle cruise it richens up again. Freaking weird.

I will say; i was doing some test hits and footbraking/launching the car feels awesome. The AFR is perfect all the way through the rpm range when WOT. I even took it to 5500rpms for the first time with the 2-3 shift and holy crap it felt and sounded amazing.

 

I swear, sometimes this carb tuning thing is for the birds. LOL, i FINALLY got the fuels bowls set where the car seems to like them and the primary and secondary throttles adjusted to where the idle mixture screws actually make a difference. Got the idle around 650, with 11.5-12" vacuum and between 13.8-14.5 AFR. Now, i just need to find a flat stretch of road to tune the primaries.

Here's a question: standard practice is to set your cruise afr based on 2500 rpms, however, with the overdrive trans i usually cruise around 2000rpms in 4th. SO should i tune the primaries off the 2000 spot or 2500?

 

I'd say tune where you will be cruising.

 

Here's another thing that causing me some grief, with the weather getting warmer ive noticed that as the engine gets heat soaked the afr leans out. I understand why this is happening but it makes the tuning process impossible. Any suggestions?

 

Finally, broke down and got some headers. TA Comp headers wrapped in DEI Titanium heat wrap. The install went SUPER easy which was crazy considering all the trouble i had the last time i installed headers in this car. Only took about 2 hours. It AMAZING just how much low to mid-range torque and high rpm power was being held back by the manifolds.

I took the car for my first roadtrip today, from San Diego to Oxnard, about a 3.5 hour drive. Drive went smoothly with no issues. I will say an alarming issue has arisen the last couple days when i was testing and tuning. I had noticed at high rpms that i would sometimes stumble or shudder if that makes sense but AFRs were good. Then the other night i heard a loud BANG and thought for sure i had blown the motor but it kept running normally, no loss of oil pressure or odd noises after that. Now, it seems that when im in 3rd accelerating when i get to around 5000rpm it has this loud bang. Obviously, i stopped doing that but i also noticed when i rev in neutral it doesn't do this so I'm thing something is happening in my ignition system like im losing spark or something. Kind of a bummer cause i really want to open up then engine now that i have the headers on but i dont want to risk things going boom. Maybe a valve is floating and hitting the piston? i dont know.

 

What would cause that?

 

I would get an air fuel meter on there before you tear it apart again... Sounds like its going lean... If that checks out I would do a leak down test on each cylinder to see if there is a valve that is not sealing up.

 

Plus read #38,42,44,44,46,47

 

I have a wideband o2 and meter on there already, that's how i've been tuning. I'm fairy certain the afr was in the low 13s both times this has happened but there may have been a spike i wasn't able to catch as i watched the road.

Thanks, it was actually helpful to go back and look at that.

 

That was actually for Sean since I figured he missed all the AFR notes you've been taking.

 

Only in 3rd and 5,000rpm?

I'd be wondering about the transmission, and fluid level unless it's when you lift and then it might be over timing and arc'ing to the next cylinder.