290H Cam vacuum

Yes, I saw there was a lot of implied questions about it, but no one came right out and asked those questions specifically or gave an example.

Just for some conjecture:
If he had the initial set at 14* with ported or no vacuum advance and that was the most it will start up on, then simply moving to manifold vacuum with an adjustable canister locked out to 10* could potentially allow idle advance to be in the 20-24* range with 10-14* initial. It might be enough to get the carb off the main circuit and let the idle mixture screws work.

It's just a hypothetical scenario, but sometimes that's what's needed to help visualize the cause and effect, as well as the importance of giving specific running conditions for the ones helping out.

 

True enough, it's not that radical of a cam, there must be something else causing it. I would like to see timing ruled out before looking elsewhere or buying more parts but there's not enough info to move on.

He also mentioned that the carb was heavily worked over, if it has enlarged air bleed holes or small holes drilled in throttle blades that can easily cause the problem.

 

Well this is where things are getting woefully interesting. In my haste to get this thing together due to a number of reasons, I did not degree the cam. (Yeah..I know)
- I timed it by vacuum, but the marks with the light are reading off the scale advance
- Strangely it runs well (other than the low vacuum) Goes like hellseems like it should other than the bad brakes
- Way back when on initial startup it wouldnt go until I really tweaked the distributor to a bunch of advance
I really think I have to get back in there and tear it apart and degree the cam.
Mike at T/A said to stick it in 6* advanced, which I did with the use of the Billet roller set.
I checked the new balancer and timing cover TDC alignmentits all fine.
I am a bit flummoxed at this point. How could an off the scale reading of advance be true if the car starts fine, runs fine, and just has low vacuum.

 

Dial back lights can be goofy. I support marking the dampner, although I use 36* (10% of the circumference).

You don't have to tear it down to degree it.
(If you feel you need to...)
If you remove the rockers and put an indicator on the pushrod, you can mark on the dampner (look at the cam card for an event that is near the range of the factory timing mark).
Remember to back out the rocker ratio.
I use mm's from a flexible tape, such as your wife's sewing tape :laugh: (well, not YOUR wife...she just bakes me cookies).
If you are close, it might not be worth the work to only move it a little bit.
Checking all lobes can reveal interesting results as well as understanding that cam cards might be off a bit as well.

 

whoa. This is when running and starting fine. past my 34* mark. what the heck.

This is with a non-dial back light and the tape correctly measured. ...and if I try to rotate the distributor to get it closer to where it's supposed to be, it will not run.

 

from a qjet point of view you need really big idle air bypass to keep the throttle blades closed at idle as much as possible.

This requires you to have large mix screw holes, idle tubes and idle channel for fuel at idle and in the transition slot.

 

You're positive the dampner hasn't slipped and everything is verified correctly?

 

Yup...I checked it earlier with a piston stop and it was dead on. The carb was an Osborne-modified 800 which worked nice with the 290-08H cam.....I went to a slightly smaller cam because of the brakes. Something is making absolutely NO sense with this.

 

I just skimmed comments. You have bad brakes? Possibility of a vacuum leak in the booster?

 

I'm running the 290h cam in a stage 2 465. Plenty of vacuum to run the brakes. all sorts of power. I'm running a Q-jet modded by yours truly reading the book by cliff ruggles.

 

Wow...I'll definitely try that. I haven't tested the booster for a leak because it was new...but y'know how that goes.

By the way, thanks for all your time and help guys. This issue has been kicking my ass.

 

Did the test...removed/capped all the vacuum parasites... looks to be a slight pressure coming out of the oil cap.
Also hit it with some starting fluid around the intake and other areas...nothing.

 

Last question...I hope. The cam card from T/A says " Degree intake lobe to 108* for 4* advance" Got it...but is it ground into the cam, putting it in straight up does this, or do I need to go the the proper keyway on the timing set to achieve this?