This may be a dumb question but would a warped base plate cause the tuning issues I'm having?

 

It certainly could cause vacuum leak issues, it's worthy to check for sure.

I myself have been victim to this. I overtightened a 2bbl Holley, which led to vacuum leaks and eventually a cracked mounting ear. Fortunately a replacement base plate was not that expensive at the time.

 

Tje confusing thing is I don't have any vacuum leaks. I checked for that very thoroughly by spraying starting fluid around the entire perimeter of the carb and manifold....

Question.....is it possible that if the base plate is warped in the center but sealed on the gasket on the perimeter would that cause the issues I'm having? It would definitely explain the wet gasket but would it cause all these issues I'm having with the stumbling and hesitation and getting it to run properly?

 

I didn't think about the possibility that he possibly had the vacuum advance hooked up to full manifold vacuum. If it was the vacuum port on the metering block, it's ported vacuum and disconnecting/reconnecting the vacuum advance at idle should make no difference. But if it's a vacuum port in the baseplate, then it'll definitely change idle since it's activating the vacuum advance at idle.

 

Yes it's possible but not very likely. Usually, when a baseplate is warped it's from tightening down one of the corners more than another, which causes a corner to curl down.

You can quickly test this by laying a straight edge across it (especially in a diagonal) and making sure it's flat.

But if what you described was the case, you could have the manifold supplying vacuum to ports/passageways that are supposed to be blocked by the gasket, and therefore screwing up the metering.


Carburetors should only be torqued down to around 5 - 8 ft/lbs and tightened in a criss-cross pattern.

1------3
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4------2

 

Yeah, that's how I tighten the carb....I'm tentatively thinking about buying a base plate and replacing the one on my carb but I don't want to blindly throw money at this and not fix the problem, especially since the base plates are about $105. That's why I'm wanting to know if a warped base plate (warped in the center) would cause my issues. But looking at the big picture, That's all that I can find that could be possibly wrong with it (as evidence of the wet gasket) so.....hmm, do I or don't I......that's a lot of money to throw away if it doesn't solve the problem....Guess I need to sleep on this.

 

The vacuum advance is plugged into the metering block.

 

I've replaced a baseplate on one of mine and it cured a lot of headaches. Some of which were caused by worn throttle shafts (which a rebuild kit does not address).
You can test both. Wobble the throttle shafts in their bores and check for play. There will always be some, but if it's excessive, it'll suck air in through those and cause issues.

The second is to slide a straight edge over it and you should be able to see that it's warped.

Ok. Then plugging/unplugging the vacuum advance at idle (unless you're idling around 1500 RPMs or more) shouldn't do a single thing to the engine.

 

With the Holley it immediately died and didn't even entertain the thought of continuing to run. With the Edelbrock, the rpm dropped 300 rpm but continued to run smooth.

I'll verify with a straight edge tonight when I get home.

 

That's strange about the vacuum advance then.

If it's idling correctly, there should be 0 vacuum coming from the vacuum port on the metering block (ported vacuum) and the vacuum advance only has any affect on the engine if there is vacuum supplied to it.

About the only way to have vacuum through the ported vacuum port that I can think of is either the wrong metering block gaskets, or if the throttle plates are open far enough at idle to expose the transfer slot. Since you adjusted the throttle plates with it off, that's unlikely.

However, that does beg the question, are you sure you have the right metering block gaskets? I accidentally put the wrong gaskets on mine once (no idea where I got them from) and it still ran, but it was really screwed up.

Can you post up a picture of your metering block and gasket?

 

Sure, I can post a picture of the gasket. I'll get the picture tonight or tomorrow night. I did buy a gasket rebuild kit specific for this carb, which has a different part number than the rebuild kit I bought for the 570 carb, so I can't imagine the gasket is wrong, but you never know. I'll even provide you with the rebuild kit part numbers also.

Something to note.... I couldn't get the carb to idle at all with the transfer slot set up as a square. I even adjusted the secondary butterflies and it still wouldn't idle. In fact, I ended up adjusting the secondary butterflies so much that it started spitting and popping through the exhaust, soninhad no choice but to open up the primaries just to get it to run. Nothing I did, per the advice everyone has given and all the info I've read, has worked at all. I'm hoping that the base plate is warped and if I replace it it fixes the problem.

 

Here are the gasket pictures you requested for both my 570 & 670 and the rebuild kit I bought that these gaskets came out of.

Also, I put a straight edge on the base plate and both of them are warped in the center. So I think I'm going to buy a base plate for the 670, install it and see what happens. If it solves my problem, then I'll buy a base plate for the 570.

 

Bummer, those are the correct gaskets. That would have been an easy fix.

Hopefully the base plate does the trick. There's a lot of stuff going on in the base plate and I know replacing them on mine has done a lot of good for them. I've replaced them on every used Holley I've purchased and they really clean things up. It's where all the moving parts are, and where your leaks are. The rest of the carb is a simple metering device with very little to go wrong.

Keep us posted.

 

I was able to buy a base plate for the 670 but apparently they don't make one for the 570 even though they still sell the 570 carb. Makes no sense to me at all. But whatever, it is what it is.

Question..... Is it possible to disassemble the base plate on the 570 and sand or plane the surface flat? Would doing this cause any problems with the way it functions? Just trying to come up with a resolution if I can't locate a base plate. What do you guys think?

 

I've run into that too. I had both a 390cfm and 465cfm Holley (which are both still sold new) and there are no baseplates to be had without simply buying a new carb. They seem to only make them for 600+cfm carbs. The 390 I lucked out on because the service guy I talked to on the phone was willing to go pull one off of a new carb and send it to me, but I've never run into that since...

You can disassemble it and resurface it as long as it isn't warped too bad. Otherwise, you run the risk of making the vacuum passages too narrow, but I think you'd have to remove a lot of material for that to happen. Just be gentle when torquing it down since it'll be even thinner.