I'm running a carter 500cfm carb on a rb intake manifold. My problem is that whenever I open up the secondaries after about 4k-6k. The engine begins to misfire and will not rev any farther. It will rev to the redline with just the primaries. It's not fuel starvation because I cleaned out the tank, replaced the fuel line with 3/8's, got a 140 gph pump, holley regulator and a new filter. I don't think it's the ignition because I tried a different coil and it only misfires when the secondaries open. It's not the air control valve either because when I remove it, nothing different happens. My a/f meter says that it isn't leaning out but I don't know how accurate that thing is. Right now I'm running .083 in the primaries and .101 in the secondaries. I noticed the other day that the secondary ports on the intake manifold are about 5/16's lower than the ports on the block. I'm out ideas but I think I'll try cleaning out the carb again.

 

Check your ignition timing. Otherwise, how sure are you that your secondary jets are not clogged? The ignition will also demand more power at higher rpms, so you might want to go over your wiring to make sure that your coils are getting all the juice that they need. Are you using stock coils, and if not, are you sure that they are up to the task?

If you want to upgrade, check out the 2nd gen ignition mod in the FAQ section. Down the road you can add a Transistor Trick unit to that for an even bigger boost in performance.

One other possibility; how are your plugs and wires?

 

I'm assuming you have a 12A in there. It is possible that is running too rich due to sec jets being too big. .101 might just be a little too big. Compare to .063 stock. You will have simmilar symptoms than those of fuel starvation if you are running excesively rich. What is your a/f ratio when you open the secondaries?

 

Kenetsu- I replaced the wires with Jegs 8mm and we have tried a different coil. Also I have a high energy ignition unit with makes plenty of spark, and I have tested with it disable and enabled. And I have tried a couple of spark plugs.

cdrad51- I do have a 12a. My a/r fuel meter says that I'm running around 13:1. I don't think that it is to rich, if it was to rich wouldn't it just bog down. My problem feels more like you are hitting a rev limiter. I don't know if I can trust that a/f meter, because for some reason it says I'm running richer if I disconnect the trailing ignition.

 

Might look at the distributor cap. might have a small crack in it.

 

But it goes to the redline on the primaries so I really don't think its the ignition.
You guys don't think that the secondary ports on the manifold not lining up with the ports on the engine has anything to do with this? I'm thinking that the air comes down the secondaries and the hits parts of the block that is blocking it and cause all kinds of turbulence.

 

Well, 13:1 is certainly not too rich. If the meter is accurate of course. But I'm telling you, I had the same exact problem and symptoms with a modded nikki, and I was running .074s for secondaries. I also could redline without opening the secondaries. And it also felt like I was hitting a rev limiter. Went down a couple of sizes on the sec jets, and voila! problem solved. I'd give it a try.

 

I don't think that those jets are too big because I was reading a old thread by rototiller and I think he was useing bigger secondary jets that me and he had a stockport. I really think it's the manifold.

 

Trailing spark fires more of the fuel mixture, it will show richer without it due to more unburned mixture passing to the exhaust. How is yor cat? Almost sounds like the cat is plugging.

 

I don't have a cat I have have a setup very similiar to the rb streetport exhaust but my presilencers are louvered not prerforated.

 

I would not trust your A/F gauge and go with what seems logical which in my opinion is what cdrad51 is saying. Too rich when the secondaries open. Although, I had a similar problem with my 650 Edelbrock on a 351 Windsor engine and after rebuilding it and finding that every setting was wrong, from float height to accelerator pump throw to the vacuum secondary rod being out, it runs near perfect now. I'd be really checking out that carb.

Darren

 

Ok I put in the smallest jet that I had in the secondaries and now it will rev all the way to the redline but it still very low on power. Also it seems more powerful when it's running leaner but it's hard to drive when it leaner.

 

Ok I'm trying to understand what is happening now. Are the original symptoms gone, including misfiring? what size did you put in the secondaries? very low on power compared to what? And I couldn't make any sense at all of the last sentence. Please clarify.

Just so you know, you do want the engine to run lean rather than rich at high rpms.