I had this problem with getting a timing tape mouted for my LT1 motor..i got all the taken care of was timing it in
i have a vacuum advance distributor and a 650 DP...

in holleys instructions it says to use the timed vacuum port on the passenger side of the primary metering block...

i was setting base timing which i set to 10 degress...i then i "stepped on the gas" and saw that i had about 32 degress total WITHOUT the vacuum advance hooked up...i hooked up the vacuum and did it again and i had about 48 degrees

this time i changed vacuum sources from the timed port to the port right above the plates...with the vacuum hooked to it it was almost 30 degress at idle...and 48-50 "all in" (2,800)


Is there anyhting that doesnt seem normal?, and what vacuum source should i use?


thanks guys
Rob

 

Rob that sounds about exactly perfect. Keep using the timed/ported vacuum port on the carb unless you have good reason to do otherwise.

32* total w/o vacuum advance -10* initial = 22* centrifugal. Just peachy.

50* total advance WITH vacuum advance - 22* centrifugal - 10* initial = 18* vacuum advance. Again, in the bounds of sanity.

I prefer a little less vacuum advance than what you distributor is giving- usually around 12* maximum. That would give you a maximum of ~45* advance, which is what I generally try to shoot for. 50* is maybe just a smidge high, but might still be OK if you're not running high compression and pump gas.

 

well the C/R is 10.3-10.5...the heads are aluminum and i use nothing but ultra 94

i havent taken it for a drive yet (6" of snow), but tomorrow i should be able to...

 

ok i took er' for a ride today and i was ALMOST satisfied

i dont know if it was becasue the air temp was soooo cold or if the timing isnt quite right yet but i have a little issue...

the car was in a heated garage for a couple days before i drove it

i pushed it outside aand fired it up (no choke) and let it idle for a few mins...i started driveing and got to some dry pavement....the coolant temp guage was around 150 maybe? and it was idleing in 2nd gear...i went right to WOT and it stumbled and coughed a little then "caught" and proceded to anihilate the tires to about 50 mph.....now later in my drive after she was good and hot i did that same thing..idled in 2nd gear and hammerd it...it didnt stumble, but didnt break the tires loose either....all the way thorugh 2nd gear it was cougheing and popping..definetly not the 325+ ponies it should be...it kinda felt like it was intermitantly missing on a cylinder...but a differnt cylinder everytime (if that makes sense)


considering it did it when the motor cold and warm i think its still timing related...
what do you guys think?
BTW...this was all done with the vacuum advance hooked to the timed spark port not manifold vacuum...

 

Sounds like you may have 2 plug wires swapped or crossfiring. It could also be that double pumper you have on top of it. More than likely you are getting a rich bog then it acts overcarbed until you get the revs way up there. Sounds like the common mistake of using a DP with an automatic transmission. A vacuum secondary carb will give you much better performance in normal driving. Also what gears do you have 3.08's?, because tall gears only complicate the bogging problem.

 

i have a T-5 and 3.42's....thats why i went DP

when i timed it in it ran flawlessly (meaning no misfire or poping)
so i know its not a crossed wire....im almost 100 percent its timing related...when i slowly accelerate or whatever it doesnt do it...its only when i go WOT and the motor gets loaded....the carb is right out of the box new...the only adjustment i made to it was turing the idle mixture screw on both sides a half turn back in because 1 and a half out was choking the neighborhood...

the motor doesnt run rich so that goes back to timing...fuel isnt the issue...the fire is

So guys...by my above posts on my timing setting and how i described how it was running...do i have to much or not enough timing...

Thanks
Rob

 

Your timing looks great. That is the same setup I am using on my 305. It ran best on the dyno with 32* total advance. I am also running 10* vacuum advance on the Ported nipple. In conclusion unless your timing has retarded due to a loose hold-down bolt it is fine.
I think your problem is fuel/carb related. Mine was bogging when I pushed the pedal to the floor with my Q-jet (mechanical secondaries w/ air valves = same thing as vacuum secondary w/ mechanical secondary control) I set the air valve tension tighter and the bog went away. I was overcarbed until I got the revs way up there (3,500+ rpm). I would check your plugs as I bet you are running rich and overcarbed (should have light mocha coffee colored electrodes not carboned black or scorched & blistered white). I would see if you could borrow a vacuum secondary holley and see if your performance picks up. I think the DP is just too much carb for your motor and the only way you are going to get better response is with the VS. I think you have some carb tuning issues though!!!!

 

if its overcarbed, then its the 15 degree air its gulping thats causing it...ive seen 750 DP's on basically stock 305's...so a 650 on a 350 HP motor shouldnt be a problem of any sort....

the only thing i can think of that would cause this is this extrememly cold air....in which case its isnt "overcarbed" it just isnt jetted for 15 degree air

 

It isn't the 15* F air. It will give you even more hp and torque than a summer's day would.

On Qjets the bog is from not enough fuel on the secondary side. It could be that your Holley needs richer jets on the secondaries. Strange but possibly true

 

did a plug check today...there pretty dark...

what about if i slowed down the pump shot

 

took it for another short ride (cooling problem in another thread) adn tried a few things...it i let it idle in 2nd gear (10 mph) and mat it it wil hesitate and stumble...if i let it idle then push the clutch in and do a quick little rev to 2 grand then dump the clutch it'll get up and go like a raped ape....

i didnt do anything with the pumps today as i wanted to see what u guys thought about that...


if i let it idle in 1st gear and hammer it, it still hesitates and stumbles but it will GOOO like a MF'er.....

 

Sounds like you dont have enough pump shot, what squirters are in it? The black on the plugs is the either the jet or the idle mix screws. you need to adjust the idle mixture screws out in the cold, then take it for a drive. The Jet is seperate from the squirter. Annother thought, you could have too much squirter, can someone watch when you get on it and see if there is a puff of black smoke??

 

Having too much or too little accelerator pump shot won't make the slightest bit of difference in plug coloration. The accelerator pump only functions for that tiny split second when you open the throttle to prevent a bog (or fail to prevent a bog if it's not enough, fast enough). Plug coloration is all about the A/F mix provided by the idle circuits and primary jets/rods. In short, your carb's basic calibration.

 

Yea, but can running over advanced cause a rich condition?

 

its an out of the box holly 650 DP...i forgot the jets that are in it, but holley claims its should be very close for any 4 barrel application...i looked in my mirror when i did it and i didnt see any smoke, but that really doesnt say much

the reason i thought about slowing the shot down was becasue if for that 1 second or so the shot is deleiverd and its just alittle to much, and being that it would probly run a little rich anyway it wouldnt be able to catch up with the fuel being now being deleiverd by the carb itself, and essentially load up....becasue every time i drive it i try this so naturally the plugs would be dark...

im also curious about the timing

Thanks alot guys!!
Rob

 

I had the same problem with my 650DP when it was new and Chickenman walked me through the tuning. Here's what we did -

1. Changed the accelerator cam to blue in the #2 hole. Stumbling quit almost immediately.

2. Changed primary jets from 67 to 65. Plugs got better and stumbling was virtually eliminated.

3. Changed to 31 squirter. Absolutely no stumbling, plugs still look good and gas mileage improved to about 17mpg.

Don't know what model you have, but mine is a 4777c. These are quick, but effective, changes that made a world of difference.

At very cold temps, even now, I do get a stumble. I've been told that's inherent to the DPs in general. Of course, how cold does it really get in Tennessee?

 

First off let me put out a little "Warning"...i know what all those thinds "do" but ive never "tuned" a carb before...im sure i can handle changing the pump cam (i assume #2 hole means secondarys correct) and changing the squirters...but when it comes to taking off float bowls and changing the jets, im afraid i dont know WTF im doing....for the squirters, change them both to 31's?....i also have the 4777c....and im all to framiliar with bitterly cold air temps, (5 degress yesterday) thats kinda why im hesistant to change stuff in it, if the air was 50 degress or something i dont think it would do this
i didnt buy any parts when i bought it so i dont have any jets or cams or anything...how much does this stuff run?

Thanks a lot for your post!!!
Rob

 

Putting the cam in the second hole is pretty obvious if you have the cam in front of you. There is a number 2 stamped on the cam. That is where you would mount it to the linkage. It really is very simple.

To change the jets, just remove the front of the carb being careful not to tear the gasket. The jets are the gold colored "screws" going into the carb. I believe the carb came with 68s. I went down to a 65. It doesn't seem like much, but it did the trick.

The squirters are easy. Be sure to remove the carb before you remove the squirter. ( Sound like a bad experience here?) I changed them both to 31s.

The jets cost about $6.00US/pair. The cams are kind of expensive. About $25.00US for the set. I haven't found anyone that sells only the blue one.

I haven't done anything to the rear of the carb yet. I just wanted to get it right for the ten mile trip to work. This spring I'm going to finish the motor (roller cam/lifters), torque converter, rear gears, etc.

It takes patience and a lot of trial and error to get it right. Just stick with it. One day you'll get in, start it up, and say "Damn, that's nice".

Good luck.