Holley 650 double pumper help

[jgrewe]

I've been handed the keys to a Miata with a 13B in it. It has the Holley carb from the title on top of it, and I've been asked to make it run better. Its been about 15 years since I've touched a Holly carb and I've gone over the basics of float level and Idle etc but I'm looking for somebody who knows if this is too much carb for a stock port engine? When pushed to a carb I'm a Weber guy.

Any help with jetting or power valve mods would be great. The car has a pretty free flowing exhaust for the engine the exhale through so its not plugged up on that end.

[FC Zach]

I don't think it's too much. I'm still stock ports and basically drive my car daily. I did have to make a few modifications though. I went down a few sizes on the primaries. If I remember correctly the size that comes in the carb. from RB is 61 or 62, and I moved down to a 59 or 60. The carb. also comes from RB with a solid power valve. (depending on what type of driving the car is used for determines whether or not this is suitable for the guys car) A solid power valve is not a good choice if the the car is going to be driven on the street, it's not very forgiving. I swapped mine out (I'll get back to you on the size I swapped it out with). The last thing I did was make sure the ignition was up to par. A powerful ignition is almost a requirement. There are so many options to choose from that it's basically going to be personal preference.

[jgrewe]

The car has dual MSD's and FC coils running through a 1st gen dizzy so spark is good and at the right time.

The car will be on the street 99% of the time with an occasional track day. So the power valves will help if I can get everything else dialed in.

I think I'm going to punch a hole in the exhaust and hook up my wideband this week then I can see what is going on with my laptop.

(did I mention I hate carbs?):banghead:

[FC Zach]

Yeah there a pain in the ass but when dialed in the work is worth it, well at leastto me.

[FC Zach]

Alright, I made a phone call to confirm the size power valve we used and 6.5 is it. There is one other modification I may do to the metering plate but im a little unsure of attempting it since its not reversible (drilling requiring).

[BigTeddy]

no the carb is not too much...

And don't drill the meterin plate...Usually something like is only required when he/she is needing more fuel flow on a huge ported, bridge ported, or pp ported motor...

[BigTeddy]

what is the car doing now or how is it running now?

[jgrewe]

I spent a little time on it today. I got it to run pretty good through the RPM range, just a few little burps here and there.

It pulls about 10.5Hg at idle so I'm going to get a 9Hg power valve for it and try that. It has a slight stumble when you first tip into the throttle while rolling and it seems to clear up when it reaches 6.5Hg(that is what the PV is right now). I'm going to grab a few different squirter cams as well.

The next issue is at the highest RPM. I can't tell if its the FB dizzy that is causing trouble, I know they get a little "iffy" above 7500RPM. If going a couple jets higher doesn't help out I may throw a modified CAS in between the engine and MSD boxes and see if that helps.

Over all it is night and day from how I got the car with just making sure the details are correct. I have made huge improvements with a vaccuum guage, timing light, screw driver and a couple wrenches.

I'll post all the specifics when I'm happy with the whole RPM range and drivability with my wideband checking my work.

[Sterling]

The carb is too much.

[StumpDrummer]

The carb is too much.

You guys need to trust Sterling on this one Ive had an eb 650cfm on mine before it took about 3 months of continous tuning before I got I half way right
feel free to ask sterling some tuning questions hes always glad to help peeps out....better yet buy his modified nikki hes got a hell of a reputation so far

[jgrewe]

I ended up making it idle well and run like a raped ape on the top end. Midrange driving is so-so and it stumbles on throttle tip in just a little. Over all I told him to drive it like he stole it until we can find another carb or go EFI. I have a couple Megasquirts laying around and some stock S4 manifolds. I'm trying to push him that way. If he blows the engine up I'll port it and make the carb work that way.