I have a 408 with alum heads made by blueprint engines in my 73 satellite and Iam running a holley 750 vac.carb. It gets way too much fuel at idle and low speed how can I clean it up so it runs better.
Thanks in advance.
Rich

I can not clean up the idle or low speed running. It smells so bad behind the car it makes your eyes water in no time, It does not drip fuel or anything else. I put all new parts in it and reset the float levels and still the same. It works great when you run it hard but you can"t drive that way all the time. Cam is 241 247 @ .050 545 lift.

What you are smelling may not be from too rich. It is high hydracarbons (spelling) or unburned gas. It can be caused by several things. high compression, big cams with allot of overlap, timing not set right, even too lean. You may never get it to go away. Just make it some better. most motors that are built up from stock have this problem.

So many things can effect this, and you didn't put much info in your question, however, check these. What vacuum are you pulling at idle. What is your powervalve? Make sure the powervalve is above the idle vacuum. What is the timing at idle? If it is retarded to much the lack of advance can cause a very rich condition (this is the main argument for keeping vacuum advance in your car). Who set the carb up? You should be idling on the idle circuit and not into the transition circuit of the carb. Hope this helps. The 750 carb is a pretty good carb setup proberly so keep working on that tune. You can get the rich condition down to a livable level, may it ain't never going to be like mom's buick.

Pull the carb, flip it over and check how far open the throttle blades are set at idle. If your exposing the transition slot at idle the idle screws won't have much effect, so you may need to drill the throttle blades. That should fix the idle mixture.
The only way the power valve would effect this condition is if the diaphram is blown and leaking fuel into the power valves vacuum port, so make sure the PV is a known good one. If you have a mighty-vac vacuum tester it should have a large rubber disk attachment that you can test the power valves diaphram.
If the transition is still too rich (low speed driving, not acceleration) you can lean out the idle bleed (bottom hole in the metering block.)

It has 10" of vacuum at idle. Has 6.5 power valve in it. Timimg is at 13 degrees at idle. I can bump up the timing some. I was just thinking I could clean it up some.
Thanks Rich

That timing doesn't sound right. I'm thinking you do not have vacuum advance. What is the idle speed? If it has vacuum advance the timing should be about 20 degrees are more at idle, so the vacuum diaphram may be shot or most likely 10inches is not enogh vacuum to advance it, you can test it by hooking a vacuum pump (like the ones used to bleed brakes) to the diaphram and apply about 20 or so inches of vacuum. The Idle should increase significantly. If you can handle a timing light at the same time or have a friend check the timing you should see it increase. If you do not have aa vacuum diaphram consider lighter springs to bring the advance in sooner. I have 10degrees set in to ease starting and a total of 34 degrees all in by 1.5k. But each engine is different. Then you can start tinkering with thw carb, as already been said you may be running on the transition circuit of the carb.

The idle is 900 rpms. I do have vacuum advance it is hooked up to a ported vacuum fitting on the carb.It is a mopar performance dis. With a msd 6al box.

Be careful about doing what Cudajon is telling you to do. You have your vacuum hooked to ported which in my world is how it should be done. He is telling you run vacuum straight to the diaphram which will pull vacuum at idle.

I would say start with the carb, make sure the transition slots are good and try to get 20 degrees of initial timing. As long as your starter can handle it you are good to go and you can keep your advance ported. Check the floats.

Don't have a clue what 68 is talking about, what I gave you was a test of the diaphram. Ok now that we know you have vacuum advance do the test I gave you. If the timing advances with the vacuum pump you can adjust your diafram with an allen wrench by inserting it in the vacuum line hole. Adjust it to come in earlier. I'm sure if you do a search on this site you can find what size allen wrench and which way to turn it to come in earlier. Be careful about drilling holes in your plates. It's not easy to undo and in all the engines I've built I've never had to do that.

Will check out the vacuum advance and see what I can find.
Thanks for the info.

Rich

Holley? Problems? That's different from.......
run a Carter or an Edelbrock.. my exp w/ Holley carbs is that they make great paperweights. or door stops.

Holley's are one of the easiest to tune so take your Carterbrocks and chuckem in the trash.

Now now now this wasn't a Carter vs Holley issue. I think when he gets his advance up in the 30 or so at idle with the vacuum it'll cure his problem. (Oh I like two carbs, carters on a dual plane and holleys on a TR)