Cascade Crew

91RSVert · Posted: Thu Dec 27, 2012 5:09 pm Post subject:

The carb is what was on it before when it did run, with all the jetting n that stuff.

Never heard of a pump shot cam.

I can move the peddle about 1/2", then it starts to stumble as I'm accellerating. Will take it for a drive this weekend and try to record it with a better video cam then a crappy cell phone.

Twilightoptics · Posted: Thu Dec 27, 2012 5:30 pm Post subject:

1/2 is about when thr mechanical secondaries are kicking in. Disconnect them and tune the primaries only. Then work the secondaries.

Pv on the secondaries? Are we s ure? If its capped the hetting needs to come up. Need to know the vac when stumble happens.

What you describe now isnt what you first stated. Still sounds light on thr timing.

izcain · Posted: Thu Dec 27, 2012 5:54 pm Post subject:

Pump shot cam is located on the side of the carb and they come in different colors (different ramp rates) and are basically a ramp for the linkage on the accelerator pump.
It allows you to give more of a shot initially or spread the shot for longer. Lots of possibilities. I would cap the PV in the sec. and up the jetting on both front and rear first though. Definitely rear at least.

chevymad · Posted: Thu Dec 27, 2012 6:10 pm Post subject:

Stock jetting on that carb appears to be 59 front 60 rear. If you block the rear power valve you'll need to up the rear jetting quite a bit to compensate. Since the carb is a spread bore the rear power valve must be adding alot of fuel since the jetting is almost square.

Looks like someone has changed the front jet and went a bit leaner.

According to holley you have the power valves in the correct locations and have the right valves.

chevymad · Posted: Thu Dec 27, 2012 6:16 pm Post subject:

Also Aaron is a little wrong on the vacuum vs ported for the vacuum advance. The right answer is.. it depends..

Ported is not only for emissions. If you have an engine that bogs down quite a bit when put into gear. Like when you have the idle set up for a bigger cam but dont have a very high stall convertor then you want to use ported.

What happens with manifold vacuum being used in that situation is that when the idle drops from being put into gear the vacuum drops off and backs the timing off as well. That either kills the motor or you can end up with a surging unstable idle.

In this situation its better to use ported vacuum and then adjust your initial timing up to compensate. After that you would need to limit the mechanical advance so that you don't end up with too much total timing.

aaron_sK · Posted: Thu Dec 27, 2012 6:42 pm Post subject:

B, I had that exact scenario when I had the cammed 390 in the Mercury with a stock converter. I still used manifold vacuum I just recurved the mechanical advance and pod. Cool

I read through this topic again and noticed this:

Twilightoptics · Posted: Thu Dec 27, 2012 7:21 pm Post subject:

I ran 29deg initial in my 350 with the big nasty cam. 26 when I had the "mild" cam.

chevymad · Posted: Thu Dec 27, 2012 7:24 pm Post subject:

Twilightoptics · Posted: Thu Dec 27, 2012 11:32 pm Post subject:

Opps. Initial was the wrong term. Idle I meant. I was busy working on mixing a song for my band.

Figure your average vacuum pot pulls 8deg so its on par.

91RSVert · Posted: Fri Dec 28, 2012 6:35 am Post subject:

izcain. I did some searching, appears it goes on the linkage where the throttle cable attaches to. None of the pictures I have show it, so I will look tonight. But I dont remember any "colors". I think everything was the gold plated steel.

ok, we will try putting more timing on it as that cost nothing and is easy to undo if it doesnt work.

91RSVert · Posted: Fri Dec 28, 2012 2:53 pm Post subject:

izcain, its white.

izcain · Posted: Fri Dec 28, 2012 8:24 pm Post subject:

This chart should be the pump shot volume in CCs for each cam in each position.

Position 1 Position 2
White 17 19.5
Blue 18 20
Red 18.5 20
Orange 19 24
Black 19 18
Green 24 30
Pink 30 37.5
Brown 36 N/A

it has the lightest shot right now

Twilightoptics · Posted: Fri Dec 28, 2012 9:07 pm Post subject:

Yeah, thought it sounded like a lean issue.

Definitely get the timing sorted out and the idle mixture set in gear. I'd go for a orange cam. That seemed to work pretty good for MOST mild applications with a SBC when I was fiddling with these things.

91RSVert · Posted: Sat Dec 29, 2012 10:31 am Post subject:

Ok, timing adjusted. About 20degs we think. Plate only goes to 16. Does anyone make plates that can bolt on to extend the stock one?

Were guessing it was around 24 from the previous owner.

Runs 1000x better. Still has a slight studder, but it may be a fowled plug from as rich as it was when we first started it. Going to let the engine cool down and clean all the plugs.

izcain · Posted: Sat Dec 29, 2012 11:27 am Post subject:

Might also want to change the pump cam to a little more aggressive cam it would cover up the stumble that much more.

chevymad · Posted: Sat Dec 29, 2012 1:29 pm Post subject:

You can put timing tape or simply mark your balancer for more advance marks.

Unless you're 100% positive the mark is correct I'd be using a piston stop to find TDC. When a 70s era balancer is used the correct timing will be with the TDC mark pretty much straight up behind the water pump.

91RSVert · Posted: Sat Dec 29, 2012 5:16 pm Post subject:

izcain, I'm going to see if its a fouled plug before I change or tweak anything else.

mad. It is almost strait up, but I have no effing clue why??

chevymad · Posted: Sat Dec 29, 2012 6:04 pm Post subject:

Through most of the 70s chevy used a balancer with tdc straight up and a timing cover with a matching scale at that location. You had to look down behind the water pump with the timing light to time it. When these motors get swapped around that balancer ends up being used with a timing cover that has the traditional drivers side tab. Then no one can figure out why the engine won't run right without appearing to be advanced to some crazy position.

Buy or build a piston stop and then mark TDC on the balancer at your tab's 0 mark.

aaron_sK · Posted: Sat Dec 29, 2012 6:37 pm Post subject:

A dead stop and a roll of timing tape can be had cheap off Summit. No reason not to.

91RSVert · Posted: Sun Dec 30, 2012 5:01 pm Post subject:

Alright, all plugs pulled. One was gapped slightly larger then the others.

btw, I have these gapped at .040, is that correct for an HEI? I think they are r44 delco plugs.

Plugs all looked lean. So I am thinking I may need to change that lobe like izcain suggested. Can you tell me which part number I need to order?