I have posted about this motor a few times in the past, I get great suggestions, have made quite a few changes and each time I tell myself the motor is running better, but I still feel like there's got to be one underlying issue remaining. I'm turning back to the board to try to finally get this thing buckled down so I can drive and enjoy the car for the first time since before the rebuild. Here are all the details: 1970 Buick 350 Block, rebuilt in 2016. Heads are 1968 350 heads that had been reconditioned ( I bought them used). Had my engine builder go through them, they're ported and polished, oversized valves ( not 100% sure what size). TA 284 Cam, degreed and timed 4 degrees advanced. Sealed power cast 340P pistons .30 over. TA stage one intake. Hooker headers. Large cap HEI distributor, 14 degrees initial, 36 total, all in around 2600 RPM. High flow water pump, 7 fin fan with new clutch and yes it has a fan shroud installed. 185 degree stat. Radiator was recored last year 102 cores, increase from factory. 2400 stall converter. 3.42 rear gear. TH 350 trans. Quadrajet carb. idle in gear 750 rpm. leak down test 5-7% per cylinder. Compression test 154psi +-3 psi Here are the issues: Very hard to start: I have to keep feathering the gas pedal to keep the engine running until it gets warm enough after a minute or two I can finally let off of it. Idle is rough in/out of gear. The whole car has a good shake to it almost like its missing at idle. But seems to run good wide open. I have tried running the motor with the converter disconnected with no difference. I have tried plugging every vacuum port to eliminate any potential vacuum leaks and no difference. I have also checked the old fashion way with a can of starter fluid sprayed around the intake with no intake leaks found. The intake additionally has been removed and reinstalled in the past with a new valley pan gasket to try to eliminate intake vacuum leaks. In addition to the quadrajet on it now, I have also tried a QFT Slayer with no significant improvement over the Qjet. Even after adjusting the mixture screws and idle screw there's only so much improvement to be had. The motor tends to run hot. Temperature slowly climbs even on light cruises around town. seems to regulate itself for about 20 minutes then slowly starts climbing. Ive had to pull over in the past and let it cool off to keep it from getting too hot. Havent let it get past 220 but seems like it would just keep going if I let it. Also worth noting the vacuum is relatively low, I've never seen better than 13-14 inches at idle. At this point I don't know what else to try with the motor. I just want to be able to enjoy all the work I've put into the car and I feel like I'm almost at a dead end. I did recently see a video of "Nicks Garage" on youtube where he was workng on a 455 buick with an internal vacuum leak coming from the intake manifold. He fixed it by using a composite gasket with the valley pan gasket. Could this be a possibility even after changing my gasket? I'm open to anything at this point. Even getting to the point of considering going back to my stock heads. I'm out of ideas as to where to turn. Any input would be appreciated.
Remove thermostat, if it still heats up, you need a new, not recored, radiator. Especially if you have a high flow pump. Losing any coolant?
Not losing any coolant, I could remove the stat but I'm starting to think its getting hot due to what ever is causing the other idle running conditions.
I currently do not have a functional choke. but it did behave similar even when using the QFT with an electric choke. And the qft also didnt help the running conditions. The only thing I could try to do at this point would be to maybe send the carb out to have it built for my combination? maybe that would help?
I would, but there are guys on here that know a lot more than me. Is strange that is ran the same w/the QFT. PM sent.
Actually ran better with the Q jet than with the Qft which is why the qft is now sitting in a box on the shelf and the quadrajet is back in the car, but now that does leave me without the choke
There wasn't much difference which is why I am still concerned, but it did seem to run better with the Q jet. Like I said in the original post part of me feels like its an intake vacuum leak or or something of the sort, even tho the intake gasket has been replaced.
I would definitely start with the carb and choke, since it's a street car you want that all to work well. I agree with above regarding the radiator as well, but the rough running I wouldn't worry about until the carbs righteously setup and the timing is also.
This... Disconnect the booster vacuum line and plug it and see how it runs. Edit...could possibly be bad check valve in booster.
Easy way to sanity check for a vacuum leak is completely the carb with your hand while the engine is running. If it doesn't immediately die, then air is coming in from somewhere else!
You got to plug the vents on top, not the carb, that will choke it and flood it, this will only check carb for internal leak. Turn that timing back down to 32-34 to stop the hard starting which i think now you meant it will not keep running I would still go with 34 total. Is the fan clutch good? I see it is new put a vac gauge on it and set those jet screws to get your highest idle and turn the idle screw down at the same time to stay at the 650rpm in drive. Use a rpm gauge at the same time so you can monitor both. You got 284 cam, it is going to run on the rougher side, lope as we say. I see you have new clutch fan so ditch what I said there. The vac gauge should tell you some of what is going on I have a 510 lift cam with a 230-245 dur @.050 My vac at idle is 13 in park and 10 in drive You should be there or higher I have no choke and once I get the car started and idle up to 1000rpm for 30 seconds the car will sit there and idle on its own and the vac gauge is at 10 or 9 in park till it gets warmer then climbs up Too bad you did not get the SP3 intake mine idles a lot better with this intake and personally I would put a 750 Holley DP with 4 corner idle screws on it unless you are worried about gas mileage and like the Q-jet. Do not use the bottom part of the valley pan gasket with composite gaskets the gasket gets pinched on the bottom from the valley pan. I had AM&P make me a valley pan gasket after I gave him the dimensions from my engine so this is available if you want to use the composite gaskets which work good.
I have the same camshaft. I've tried 3 carburetors with my setup. The 284 likes alot of idle fuel. I have a fairly smooth idle when I have the mixture rich and I can idle in gear at 650 rpm. Vacuum is 13-14 in park at around 800 rpm. I'm actually running a 600 cfm double pumper with an sp3 intake and the car runs good and responds well to the throttle. Cold starts are fantastic. but I'm like you and want more out of it. I'm planning on a new converter, gearing, and 2004r transmission. Give it more idle fuel. it may require playing with the idle jets in that Holley/qft
