I threw a vacuum gauge on the carb to see how much vacuum i have at idle and it was fluctuating between 5-6 at idle does that sound right? Thanks
Unless your running a huge cam it seems low to me. My 455 with a moderate cam (power to about 6K) pulls about 20 inches of vacuum. Possible vacuum leak somewhere? Also carb and timing settings can cause low vacuum as well.
In a word, "No" are you 100% sure you placed the gauge on the full vacuum port? What type of carb? I use a Performer 455 intake and luckily I had an extra port on the intake, so i stuck a fitting in there and capped it off with a vacuum cap, so I have no guesswork about ports on the carb. A pic of the gauge hooked up to your engine would be oh-so-helpful to determine if it's hooked up right In general, 15-22" Hg is what you would see on a stock type engine, depending on what altitude your locality is. The larger the cam, the less vacuum, but I'm assuming that this is a failry stock type engine. If you're only reading 5" Hg (Mercury) at idle (in park at about 800 rpm) , you might have a huge vacuum leak, poor compression, an incredibly poorly tuned carb, a cracked head/manifold or worn idle circuit in the carb (and any combination of the above) My very slightly hotter than stock cam pulls 19" Hg. the old Chiltons manuals sometimes used a range of "17 to 22 inches" as a rough guide. How's this engine run? I'm going to guess that it was running less than perfectly and this is why you stuck the gauge on it...
i have TA`s 290-08H cam,with TA Sp-1 intake and Holley double pumper,my total timing is at about 32-33. Thanks
no engine has about 1000 miles on it,its not a stock motor,reason i stuck the guage was to adjust the carb alittle. Thanks
Oh, I forgot to ask, George: do you have power brakes? How are they? if the power brakes are working fine, you've GOT to have more than 5" Hg. maybe the low reading is a combination of bad carb adjustment and the big cam...is that Holley a four corner idle unit?
290-08H Intake Exhaust Lift 525 520 Advertised Duration 290 308 duration @ 50 238 248 Lobe seperation 112
Put the vacuum guage on the engine while tuning the carb at idle, it may come up a touch. I've got a similar cam(slightly smaller) and mine has between 7-8" of vacuum.
With a cam that size and a single plane intake your not gonna have much vacuum at idle (5 does seem particularly low) maybe 8 or 9, I suppose if you had it (cam) degreed just right and ran a bunch of intial/static advance (20 degrees or so)you could bring it up some. The problem is that they can be a bear to start like that, especially when they're hot. What rpm are you idling at? My TA290-94 cam will hold 15" vacuum at 725rpm @12-13 degrees of advance. Of course I'm also running a performer intake and a spreadbore carb.
Len cam was degreed by Scotty from Pee Gee perf. off the carb i was getting at idle between 5-6 closer to 6" of vacuum,as for starting it when hot i never have a problem,the motor runs like a charm,reason i took the vacuum gauge was to adjust the carb thats all,and i`m idling at like 800 rpm`s,plus its a stick car.i`ll try to get a reading off the manifold and see what it reads tomorrow. Thanks
George, I ran the 290-08 HL last year in a 462/4 speed. Using a performer and Qjet I saw 6 to 6.5 " vacuum at 850 ish. That was with 14* initial advance. Jim Weise posted a thread on that particular cam and the timing needed to "idle it down". He stated 25* degrees of intial advance. That was an interesting read for sure. I made the adjustment on my car and two things happened, Vacuum increased to 9.5-10" and it would idle rock steady at 750 rpm after warming up. My vacuum gauge is plumbed to the manifold and I verify the dash gauge with a certified unit I use at work. Play with the timing and see what you come up with. George
What did you do exactly?if i increase the initial timing to 25 what would the total be?too high i assume?where is Jim Wiesses post about this cam maybe i can read up on it and see what i can do. Thank you
I hard copied that thread.This is what got me going on this cam.Jim had said you could get it to idle with a properly sealed motor with a lot of timing.I'm following his recipe and hoping it will work.
the other thing is i dont have problems with the car idling and the car runs well,in the beginning when i first installed the cam it would`nt idle so i call Scotty at Pee Gee cause he did the engine asked me if i had an MSD distibutor and i told him i did,so he told me a trick to remove a bushing that it comes with and replace it with another thicker one which comes with the distributor as extra parts,so i replaced it and it idled ever since no problem,i didnt want to lock my timing.
George, If you go with the higher initial vacuum then you'll have to recurve your distributor, probably only need about 10degrees of advance in the distributor if you set your initial in the 23-25 range. You definately need to search up that post mentioned above, Jim covered it real well. Len
I used a dial back timing light to set initial (static) advance at 25*. My engine has a MSD pro billet distributor therefore no vacuum advance unit. I used a stop bushing to limit total advance to 34*. Total advance is all in by 2500 rpm or so. I will be playing with timing when the car is back on the road with a different motor (same cam though). My car situation may be different than yours as I never intended for the vehicle to be anything other than a toy. So I was never concerned about driveability issues such as long cruises and what not. For the braking I use a vacuum reserve canister to help actuate the power brakes. I do not know how to put a link to the thread in question but if you do a search in this forum (290-08HL cam) you find it. Good luck. George
