401 nail trembles

**gforcecuda** · 12-12-2010, 05:18 AM

i have a 401 54 Wildcat engine punched to 413 cu in. all stock fresh rebuild to stock specs except bore, one off custom headers, 4L60E trannie, 9" rear...Had the stock carb rebuilt but when you are sitting at a light, and take off it goes thru a tremble as it moves off idle..It seemed to helpwhen I jacked up the accelerator pump to the highest setting but it still trembles some..any more ideas? I also have a 1964 Riviera that was frame off restored to original specs..Both cars seem to boil all the gas out of the carbs when I park them for a little while...Both are very hard to crank because I think the carbs are dry..even the 58 Caballero with the 401 which has an electric fuel pump..I let it build fuel pressure, the pump it several times and it still isn't quick to fire..We are going to build a spacer to insulate the carbs from the intake heat in hopes that will help...I have read that this new Alcohol infused gas boils at a very low temp..I have a lot of other older cars, and all of them don't exhibit this problem though...

**Dr. Frankenbuick** · 12-12-2010, 05:39 AM

Was the engine balanced when you rebuilt it? Was the flexplate put on in phase to the balance. The flexplate will fit on six ways, but is only in balance when the index hole in the flexplate is aligned with the index hole in the crank (assuming it was balanced in that position).

**gforcecuda** · 12-14-2010, 09:36 AM

Originally Posted by Dr. Frankenbuick

Was the engine balanced when you rebuilt it? Was the flexplate put on in phase to the balance. The flexplate will fit on six ways, but is only in balance when the index hole in the flexplate is aligned with the index hole in the crank (assuming it was balanced in that position).

the motor is balanced very good...doesn't tremble unless you are coming off idle and accelerating...then only for a second or so...it's going thru a lean out stage or something..making the motor not happy..I don't think it has anything to do with the 4l60E trannie or torque converter..could be though...like I said, when I jacked up the accelerator pump, it seemed to moderate the situation some..

**Bob** · 12-14-2010, 10:46 AM

A "tremble" sound like it might be a electrical firing miss? Bad plug, wire, or cross fire?

**gforcecuda** · 12-15-2010, 07:30 AM

Originally Posted by Bob

A "tremble" sound like it might be a electrical firing miss? Bad plug, wire, or cross fire?

highly unlikely...everything is new..seems like it's going thru a lean out point or something..goes out of it real quick..I think i am going to put it on a distributor machine and see just how this curve is working on the motor...if anyone knows how much initial, vacuum advance at certain RPM, and centrifugal advance is optimum, I would like to hear it...Also how much total the Buick likes at part throttle and full throttle..I'd like to post some pictures of my Caballero on here but I am not computer oriented...I had some one off brackets made for the air conditioning, power steering, and alternator..looks way cool...not that ugly *** looking Alan Grove crap...If anyone would be interested in some, they would be duplicated by my guy at waaaay less than what it cost me to get these one offed..I have him making me a bracket for my 56 Pontiac Safari Wagon with a 400 Pontiac now...The one that's on it has the compressor sticking way up in the air and it looks like crap..the other brackets look ok..

**telriv** · 12-16-2010, 04:47 PM

Cuda, the way I set-up 401/425 distributors. I build in 11* total advance (22*@crank) all in by 25-2700 engine RPM's. I like it to start advancing about 900 Engine RPM's or so & going up at 2* increments. The "Nails" mostly want 32* MAX. But this can change +or- a few degrees either way. Much depends on camshaft selection also. As an example I've found my "Nail" to run best with 36* advance up to 3800RPM's & then retard 4* to 32* above 3800. With 11* built into the distributor, for a total of 22* at the crank now gives you more of an option where you run your initial advance. Which could be anywhere between 8* initial for a total of 30* or 16* initial for a total of 38*. More initial advance gets a heavier car moving quicker on the bottom end. Less total is better for the top end. I usually set-up my the vacuum advance between 8* & 12*. The point of vacuum inches where it starts again depends on cam selection. Without a vacuum advance hooked up, the engine in my car anyway, runs hotter by about 10-12*.

**gforcecuda** · 12-19-2010, 02:13 PM

Originally Posted by telriv

Cuda, the way I set-up 401/425 distributors. I build in 11* total advance (22*@crank) all in by 25-2700 engine RPM's. I like it to start advancing about 900 Engine RPM's or so & going up at 2* increments. The "Nails" mostly want 32* MAX. But this can change +or- a few degrees either way. Much depends on camshaft selection also. As an example I've found my "Nail" to run best with 36* advance up to 3800RPM's & then retard 4* to 32* above 3800. With 11* built into the distributor, for a total of 22* at the crank now gives you more of an option where you run your initial advance. Which could be anywhere between 8* initial for a total of 30* or 16* initial for a total of 38*. More initial advance gets a heavier car moving quicker on the bottom end. Less total is better for the top end. I usually set-up my the vacuum advance between 8* & 12*. The point of vacuum inches where it starts again depends on cam selection. Without a vacuum advance hooked up, the engine in my car anyway, runs hotter by about 10-12*.

thanks..kinda weird, when you move the timing up or down on my 401 Caballero, it just didn't seem to affect the running of the car...jack it way up, it didn't ping or anything...didn't even make it idle much faster. this engine isn't nearly as responsive to timing changes as any other motor I have had..it is all stock except the over bore..

**telriv** · 12-19-2010, 03:37 PM

Somethings wrong. Put a timing light on it & see if the timing moves.

**gforcecuda** · 12-20-2010, 02:51 AM

the timing is moving fine..that's what had me puzzled....you can see the timing go over 40 degrees total, then go down to 32 degrees and it just doesn't make any discernable difference..even when driving it..car is strong, has tons of torque, pulls that big wagon very well...motor just doesn't seen real happy. There was an article in Street Rodder 2 months back that got into setting up distributors and the need to reset them for todays alcohol infused gasolines...they are supposed to follow up on that article with one for carbs and ideas for resetting them for todays fuels..

**Anomaly** · 12-25-2010, 01:24 AM

Dumb question, maybe even a dumber thought.... Can a 401 run with the distributor 180 out? I am thinking it's possible the rotor / cap may be backwards?

I had a V6 once that I crossed two cylinders when replacing plug wires, and it started and ran fine, but wouldn't pull a Radio Flyer wagon.

I have heard of engines that would run with the timing 180 degrees out, but not as they should.