Carb tuning questions??

[want-a-be]

If this is race only i would get rid of the power valves all together and jet accordingly

I agree with this.

Don

[Gus68]

Ok, I was kinda thinkin that the 80s in the primarys might be a little much, so maybe I will go back to the 77s, this thing did work really good, when it was warmed up with out the spacer, I just thought I should richen it up a little with the spacer. I am not sure what the NASCAR linkage is but I might have it on this one cause I have never seen another holley like this, the linkage for the secondarys is kind of a big triangle shape with a slot cut into it, and a roller that is attached to the secondarys rides in this slot. (if that makes any sence) This carb also has a choke horn but there is no holes in either side for the shaft for a choke. There is also no ports for any vacume lines. I do know that it is an 830, I have checked the numbers on the choke horn. Anyway.... I bracket race this car, but only about 2 or 3 weekends in the year, I can say that it is a street car, I drive it around on the weekends in the summer. So what are the pros and cons of blocking off the power valves? Is it just because it makes it easier to tune? Does blocking it cause milage to suffer? I didnt build this car for milage so I could care less. Want a be, I would like to talk to you, Im also kinda computer stupid as well, how do I PM?

[grandville455]

Gus
Do U race at BIR? Ever come to the rock in eau claire?.When u add a spacer u add to the plenum and it will require more of a pump shot. Have that same carb on my car, Its A annular carb correct? That is the linkage I was talking about. I just bought a billet QF 1 3/4 baseplate with the much better linkage. and it loved it! Ran its best mph yet in worse air!!. I run a drilled 37 shooter in front with a 50 c.c pump and in back i use the pink cam in hole 1 and a 37 shooter in back, I also use a velocity stack and I stage at 2000 and it rips!.. on the steet it had a slight stumble when cruising at 2000 and punching it that is why i went to a bigger shooter in back now its right there!. I also run 75 jet in front with a 4.5 power valve and 86's in back with none, and jet extensions..

[want-a-be]

Gus,

At the top of the screen next to your name is a place where you can go to read messages sent to you. I think it will say you have 2 messages. Unless someone else has sent you a pm. Click on it and you should be able to figure it out from there.

To send me a PM,...look at one of my posts. At the bottom on my post you will see the letters PM in a tab near the bottom. Click that and you should be able to type a message and press send at the bottom. That is how you send me, or any one a PM.
Don

[Gus68]

So here's my latest update. I spent most of the day screwing with this dam carb . I started with 42 squirters in front and rear and the "stock"? white primary cam, same thing, warm or cold if you stomp on it, big BLA waaaaaaa. tryied all kinds of different color cams, big bla waaaaa. I thought maybe the secondarys have too much squirt, so I went extreme and put in a 21 in the rear. Still not much of a difference. went to a 37 in the rear... same thing. Put the 42 back in the rear and stared at it for a while. My assortment of cams came with this big ugly kinda brown cam, I thought what the hell, none of the others I tryied made much of a noticable difference, I at least wanted to make it way worse so I knew if I was going in the wrong direction, (does that make sence?) so I put it in. Well it didn't cure it compleatly but it made it WAY better. So I thought it must want a BIG shot, so I put in this AED 50cc pump kit I bought, it came with the diaphram, cover, arm, and a black cam. I removed the big brown cam and used the black one that came in the kit. It was better but still there, so I put the big brown cam back in and it is about 95% better!!! Now I am VERY happy that it is better and I might just go with it, but it is just alittle bit there. I was wondering if messing with the rear cam would help? Do you usually have to mess with the rear cam? I think my carb has the nascar style secondary linkage and the secondarys do not open with the front, but when it does, the rear squirter sprays instantly. Would jetting help this last little bit? Any advice on what I did? Sorry this is such a long post!

[jmarkaudio]

I can see how timing could cause this problem, and it could be, but why does it get better once the car is warmed up?

Timing can be a huge factor. If you have anything much more than a street cam you need a fair amount of initial timing, in some cases locked timing will run best. How much timing any engine needs is a result of how well the fuel is burned in the combustion chamber. That is a combination of the plugs heat range, compression ratio, combustion chamber design, dome shape if a dome, air velocity of the intake runner, camshaft design, THE AMOUNT OF HEAT IN THE ENGINE, fuel type, the carbs ability to properly atomize the fuel... as you see everything will affect it. A cold engine will make the most power if everything is optimized for it, in your case adding heat to the engine allows the fuel to burn more completely with the combination of parts you have AND the way it is tuned. My 23˚ 427 SBC ran best with about 41˚ of timing, both the 447 and 461 SB2 head engines we put together in the last couple years run best with only 29˚, so you can see how the combination of components can make a difference (and why my 427 will have some mods made to it when it gets freshened).

Try more initial, keeping the total timing where you have it, it will require modifying the mechanical advance in your distributor. I'll bet if you check, you have under 20˚ initial timing.

[grandville455]

So U put the 50 on back? I would try it on the front and keep the 30 in back with either the white cam or the pink one..Also I agree on the initial timing too. Aren't cars fun?

[Gus68]

Sorry for the confusion, I put the 50cc pump in the front with a 42 squirter. I also have a 42 squrter in the rear, I was wondering if I would notice much by messing with the cam in the rear.

[grandville455]

Np... So did u use the hollow screws too then? It makes a big difference putting that 50 up front.. alot of people don't do it it seems.

[Gus68]

Yes I did put a hollow screw in the front squirter but not in the rear, cause I only have one. I thought after all my screwing around this weekend that I had it figured out, but I took it out today after work and now I'm not so sure. First of all when I went to start it I gave it one pump like I always have, and I got a POOF and a little fire in the air cleaner. I just cranked it over and it finally started. So I took it out for a cruise. When it was cold it still had the bog bad. after i drove it for a while it did get better, I'm not happy with it but it is better. I'm going racing on memorial day weekend and I might just run it this way. Frustrating!

[grandville455]

Does this only do it when floored from idle? do u leave at idle or do u bring it up some? where is your jetting at now?

[Gus68]

It does this if I floor it off of idle or if I floor it from 2000rpm which is where I leave off of. I can be rolling down the street at about 2000-2500 and mash it and it does it. As I said earler my carb has the "nascar" secondary linkage, which opens the secondarys at about halfway through the throttle's travel, and there is no way to adjust that. I was thinking about getting a different base with the "normal" style secondary linkage. After screwing around with my carb tonight I cracked an ear on my base plate so guess I'm gonna get the new base plate!!!!!!

[grandville455]

Yea I bought the QFT baseplate its a very nice piece!Got mine on ebay from rpm limited?.If u look at your linkage it actually starts opening the sec at I think its 35 degrees of the primary opening so they open relatively quick , but i got rid of it and i think u should too!.This one opens at 40 degrees, but then keeps opening the other style follows that cam and does some weird shit.. Mine still has a small hesitation when i punch it from 2000 rolling along, but i run a velocity stack, but at the track when i am up on the conv around 2200 , it launches hard! No stumble nothing!.. Do U have a wideband to see where your at with your jetting at part throttle etc? My part throttle is still on the rich side around 12.0 -12.5. i don't have vac advance hooked up either, will be hooking it up to ported source to lean out cruise some more, but keep my 12.6 WOT! I was at 11.3 cruise with my 75 jets so i jetted down to 72 and then added 3 into the back still keeping my same WOT. They really do help in tuning.

[Gus68]

Hey guys!!!! Well I guess you could say I took the easy way out. Like I said, I needed a new base plate, so I went to c-n-c motorsports here in town (where I've been getting all my holley stuff) to get a base. of course they did not have the one that I needed!!! But I got to talking with the guys there and long story short I left with a NEW AED 750!!! I didn't want to spend that much but I got to thinkin, I've already got about 70 bucks in little stuff trying to make this old one work, a new plate would be about 110 bucks, and I'm not sure if this will help my problem. I was also wondering if maybe an 830 is alittle too big for my motor? Could it flow more air than is needed and I'm trying to compensate by dumping a bunch of fuel at it? Plus we are going racing on memorial day weekend and that doesn't leave me with much time to sort this out. Anyway, so far I am pleased with the new carb! I just hope I don't LOSE any time with the smaller carb!!! Last year by best was a 11.93 @ 111mph with a 1.62 60 ft. I guess I'll be the first to know. But I have to say thank you to all you guys for the help and advise!!!! Even though I "FAILED" and bought a new carb I have learned alot. I will up date with my results next weekend. Thanks again!!!

[grandville455]

well u will have to let us know how it performs!.. U racing at BIR?