Cascade Crew

[Quasi-Traction]

be warned this is a lengthy post.

I currently have 2 double pumpers in my posession a 600cfm and a 650.

The 600 I got in pieces and rebuilt following the holley book I have. Set float level dry to where its centered in the bowl, Running 25/28 squirter nozzles (pumpshot) and went with the factory 66/72 jet combo, and a Pink pump cam in the #2 postion on the primary side, and a White pump cam in the #1 position on the secondary side. This was following what my holley book said was "factory" spec for that particular list number.

The 650 I got complete but it looks quite a bit older. I have completely dissasembled, cleaned and rebuilt with new powervalves, gaskets, accel pumps diaphrams. Rebuilt it according to the holley book spec for its list number. I've changed jets and squirter nozzles in this twice. orginally with a 69/83 jet combo, now its a 62/69 jet combo, and from 28/31 squirters down to dual 25's.

What is throwing me is how pig rich the 650 is both idling and on power enrichment. jetting down and getting smaller squirter nozzles have not improved things hardly at all. engine hardly runs.

The 600 idled okay when paul was over last week, and we tried to set timing. but seemed to be a little rich and bogged when you bliped the throttle (I assumed discharge nozzle related, and I went down one step on the secondary side)

I've messed with the curb idle and secondary idle stops on both, messed with the mixture screws, it only improves slightly (i.e. keeps it from stalling, and engine idles more evenly). checked and re-checked float level.

I'm running out of ideas. I'm almost to the point where i"m wondering if its more timing related than an issue with the carb.

Thoughts guys? I'm at the end of my rope here.

[rjmcgee]

What size power valve in there now?

Also what is your base timing set at?

Vacume advance hooked to manifold vacume?

[Quasi-Traction]

Both 65's (6.5hg vaccuum) for the power valves. Both brand new right out of the holley trick kit. I don't think I'm cammed enough to where I'd need smaller ones (218 @. 050 and .480ish lift + 1.6 rockers).

When paul was over the other night the engine seemed to run best with the 600 on it, 6-8 of base timing, 33-35 degrees of total timing. When we would hook up the vaccum advance on either port, it would start idling badly. so we just plugged both ports on the carb. I did neglect to throw the vaccum gauge on there while we were tuning. Just kind of did it by ear, and what the engine seemed to idle best at.

[chevymad]

Adding the vacuum advance on top of 6-8 degrees should not make it idle poorly. Verify your timing mark.

Changing the main jets will not change idle. Only the mixture screws, leaking power valve, transfer slot set incorrectly, idle air bleeds will change idle mix. Idle air bleeds arent changeable, so unless someone drilled them they should be fine. Set the primary throttle blades so that the right amount of transfer slot is exposed(dont remember the amount) then adjust the secondary blades for idle speed. Adjust mixture, reset idle.. go round and round til you like it.

If it's backfired at all you could have ruptured the power valve. If you take the metering block off, the hollow in the main body behind it should be dry.

Make sure its not sucking fuel through the accelerator pumps. It can happen, dont remember if you change the weight to fix or what.

The bog on tip in, can be from incorrectly set transfer slot, or wrong squirter/pump size, or cam. If you need a short quick pump shot, use a big nozzle. Long heavy shot, big pump with smaller nozzle. etc.

You did the right thing by trying to go from factory settings. They're usually pretty close. You shouldnt have to mess with the main jets, till you start tuning cruise/wot. But idle mix has to be proper first.

When the carb was apart did you lay a straight edge on all the surfaces of the main body? If a gorrilla tightened the screws last time things could be warped.

[Twilightoptics]

He's running about 22-24º base. 36º Total. I told him to leave the advance ports plugged.

[Quasi-Traction]

I laid the metering block's and fuel bowls on a granite stone. I took a carpenters square to the main body. all that seemed to be okay, and pretty true.

Been reading up on this guy's reccomendations and a couple things caught my attention:

Tip: Use a power valve that is about 2 inches of mercury below the LOWEST manifold vacuum reading you get on cruise and idle (in gear for automatics). If the power valve flutters open at idle, it can act as a pump, and push extra fuel into the main well, causing a drip from the booster venturis. If the power valve opens a lot while you're driving down the road, your gas mileage will suffer.

He also reccomended putting a plug on the secondary side where the power valve would be. This is what he says:


It is, however, recommended to plug SECONDARY power valves, due to the inconsistencies encountered with WOT, low vacuum operation, which is when the secondaries are open. Basically, the only time the secondaries are open is at Wide Open Throttle (WOT). At WOT, vacuum is very low, and the power valve is open, so it's really a waste to even run one in the secondaries. In the vast majority of cases, you will need to jet up on the secondaries when plugging a secondary power valve.

The website is this: http://www.bob2000.com/carb.htm

[Quasi-Traction]

[rjmcgee]

Your timing should be good at that. I run 24 base with the advance plugged into manifold vacume. Gives me about 40* at idle.

I'm also running a 9.5 PV

[Twilightoptics]

Thought you said you tried to check it with a straight edge, but didn't have access to a stone?

[Quasi-Traction]

[rjmcgee]