Long story short ---- I've been building my 1934 Buick street rod for 12 years and finally got to give it a proper road test. It's a fully re-built stock engine and fitted with a later model 800 CFM Quadrajet 17080212. Behind is a 700r4 and it drives through the gears OK, but once into overdrive on the open road the engine starts to falter and lose power with a slight depress of the pedal. Almost like it's not getting enough fuel. I have the idle timing set at 10-12 degrees with the vacuum advance disconnected. Have 15 hg of vaccum at carb, 20 hg at around 2500 rpm. It just seems to not idle smooth. Stock distributor with Crane XR-i ignition. The distributor has not been re-curved or had springs / weights changed. I'm starting to lose confidence / interest because of all the work put in over the years ( did it all myself ) and just need some advice here please on where to start ???
I am considering swapping out the coil, have an Accel Super coil somewhere. Isn't idle timing set with the vacuum advance disconnected ?
What RPM is it in OD when you experience the problem? Does it do the same thing with gently stepping on the pedal and heavy stepping on the pedal in OD at that same speed? Yes, timing initial timing is set with vacuum advance disconnected and the line to the carb/manifold plugged. Take a look at Larry's "power timing" thread. https://www.v8buick.com/index.php?threads/power-timing-your-buick-v8.63475/ And be certain mechanical and vacuum advance works correctly. Nailhead distributor sometimes have bushing for the advance arm that controls amount of movement to base plate missing or worn and that can result in too much or erratic advance. Having the correct distributor as well, some nailheads started with 2* and others with 12*, but the curve has to be correct for the distributor to be set at 12*. If you have one curved for 2* and set initial to 12* your going to have incorrect advance functions.
Do you have access to another Q-Jet, to swap and see if it's the carb or the car (truck)? Can you drive through it, and does it run better at higher RPM's?
Trunk monkey --- I don't have a tach set up in the car. It goes in to 4th / OD at about 45- 50 mph -- I still haven't set up the electronic speedo to read correct ( too many things going on ) had a back up vehicle following sending speed reading. If I stomp on the gas pedal it falters then changes down to 3rd. The distributor is 1959 model so don't know settings ? Bigpig --- I do have another 750 CFM Quadrajet off 1973 Chev truck just in case. Want to change coil first and see. Only got car to 55 mph because of highway restrictions. Starc Trax --- axle ratio is 3.08 which doesn't help with the taller tyres 235/70/15 Tyres from original passenger car the trans came out of were 205/65/15 But even with the tall ratio the car should not falter / miss but just have less power.
With 3.08 and overdrive at 50 mph and 26 inch tires your lugging a nailhead. You are probably about 1300 RPM and that can cause it to really fall on its face when you step on it in OD at 45-50 MPH. But ignition timing and carb issues contributing. Nothing that can't be figured out. (a cheap tach would help)
That's what I'm sort of thinking. You are probably on the money with 1300 RPM, it does sound like the engine is just ticking over. Will get a tach somewhere. But it's going to be the most expensive and pain the arse option because the whole rear has to come out and taken to expert workshop to have new gears installed. I would like to nail ( no pun intended ) any carb / timing issues first, if any. Once I get all that confirmed and it's still misbehaving then I will have no choice. But I can still drive it held in 3rd. If it eventuates I will have to go to a 3.55 or 3.9 set of gears. Which one would you recommend ?
I have 3.55 gears and . 68 OD with 3200 lb '64 Skylark with 2x4 nailhead. Pulling from 65 MPH in Overdrive is not a problem, but if I tried to pull from 45, the pistons would be rocking and the engine would be knocking like an Outback Rockabilly band. Either set of gears would be great for your truck. Given the ratios of the transmission.
Fortunately I have a set of used 3.9 gears here. The 3.55 are very sought after and hard to find and $$$$ My friend gave me an idea. I also have a set of wheels, same diameter and bolt pattern here with the smaller tyres that I used as a workshop roller. I will change them and take car out and will tell me for sure if there is an improvement. On another matter for you fellas ------ what would be the best new aftermarket out of the box carb for stock 401 ?
3.9 gears with .64- .68 OD will be great. Nailhead on the highway between 2200-2800 is very happy. The Edelbrock 1413 800CFM is a good carb for the nailhead if you have a square bore manifold. If you have a spread bore, the Q-Jet is fine, just have it properly built and adjusted. If you can, tell us what distributor (part number) you have. Having a good re-curved, or properly built distributor is key to power. 61-63 distributors as well as those used on the 64-66 2x4 engines are 12* initial and best curve. Other units are typically 2.5*, and will work, but provide less power overall ranges (and if set to 12* initial, can cause issues with timing, ping/overheating or other trouble) And over 60 years of engines and parts changing hands, no telling what you might have without verifying.
I have been thru crap like this many times when I have helped out other folks and here's what to start with. Get the motor up to temp and then take the car out for a full throttle blast up thru first and second gear, if there are no issues with that then the ignition system is not at fault, but the Carb likely is. If it pulls good thru first gear but falls flat in second then you have a fuel delivery issue to chase down.
Thankyou everybody so far. I can't feel any issues 1st > 2nd > 3rd But I did think of something else. If the engine is only spinning around 1300 in OD / 50 mph then it's probably still operating on the Quadrajet primaries and the engine is struggling to get the fuel / air required for a gentle acceleration ? What do you think of that theory ? The major issue , it's not just like I've made changes from a well running driving car. It's all a blank canvas scenario.
You need at least 3.73 gears. You've got to give the engine a chance to breathe. It's basically at fast idle. You can't get the transmission to downshift fast enough to increase rpms before it coughs and sputters. Also, as previously mentioned, recurve your distributor and hook up the vacuum advance to the ported connection. Cool truck!
Trying to accelerate .6x overdrive with a 3.08 and 26 inch tires, is killing a nailhead. You would be crusing at 100 MPH. at 2800, where peak torque is. That alone would put you in a stumbling mess as low vacuum signal to the carb, and bog, bucking and backfire. (And likely, detonations)
" That alone would put you in a stumbling mess as low vacuum signal to the carb, and bog, bucking and backfire " --- it certainly does not like it I think we're all singing from the same songbook here. So I'll swap to the smaller tyres and let you all know any difference. That might take 1-2 weeks, got too much other stuff happening. I doubt there are any places locally that would re-curve the distributor. Will have to research that one. These are the numbers off the distributor Delco Remy 9 A 30 1110956
