car stumbles on take off.

I need some c arb help. I am running a 2.3 .030 ford with 5.7 rods and weisco pistons. in my pro4 truck. I am running a holley 500 with a 30cc pump, 28 squirter, pink throttle cam, powervalve block off, have a 2.14 tranny with a 4.10 gear and 15 hoosier tires on a 1/4 dirt track. Engine is very strong accept just off idle. It stumbles and will almost die unless I hold the rpm higher as we come to the green and then when I hit it, it will stumble and finally catch byt by then everyone has a big jump on me. Most of the time I can catch them but it takes a long time to get there. It just will not pull off the corners without that stumble. It is not a blubber like pull over, it just hesitates. When it gets going it is very fast. Have a crane192261 310 2r 8, roller with 189 valves, com cut to the bolt holes. No other engine issues. lift is 535/510 310-300 dur. Adjust able gear is at 3 adv and timing is at 37ish. does not over heat, plugs are not lean might have a bit of rich, but I dont think that is the issue. I need help. If more info is needed ask I will try to supply...Thanks, Dan

Has the problem always been there or just started?

Check your pump arm adjustment make sure it it not too slacked and doesn't over extend. Make sure your Low speed idle adjustment is correct on the sides of your metering block 1- 1 3/4 turns out and your idle is as low as possible without cutting off, and that your throttle plates arent covering up the vertical transfer slots you should have around a 1/8" hole in both throttle plates. Around 72-75 jets. That sounds like not enough fuel if it clears up then takes off thats a normally indicating a lean stumble so you can try going up on squirters. When you run the block off plate you normally have to up Jet sizes because your not getting the extra fuel the Power Valve would deliver. OR you can go to a 3.5 Power valve and see if it goes away if your running as is

Thanks, Good minds run together, one of my racing friends just told me what you told me. I had not read your post yet. I will do what you guys suggested. I was also told to stay with the 30cc pump and make sure I was not bumping up againts the arm with vibration. Like about .010 clearance. should I run the larger jets. 69 might be too little. certainly do not want to lean out and mess this engine up. It is a rocket when it hooks up. Thanks again, I will post my results. Dan

i ran 72 jets on a 350 Holley with the 30cc.... you might be too lean. Hard to say and the longer rods like the higher timing 38-40 according to Esslinger and thats where I ran Mine about 39*. The biggest thing I found too if you don't run your distributor locked out you need at least 18* of base timing. I'd start around 72 on the Jets Maybe up the squirter to 31* It won't kill you if its wrong and the smaller pump cam one you get it right you won't need alot at one time but it will give you a little for longer. I don't like to PV block off deal, but to each their own. If you need any further help inbox me and I'll send you my number if you need help at the track!

I run the TFI distributor at 38, I am going to take out the block and use a 3.5 or 4.5 and see what it does. I will start with a 72 with the P V in. might even go to a 73. jThanks...

hey danny, how's it going? does your truck only stumble on the start or coming out of 2&4 every lap? like stated by others the 69 jets and no power valve will be too lean in a 500. what is the cam duration at 0.050 and what rpm are you running at the start and end of the straight? depending on your rpm and pump setting you may not have any pump discharge left to eleminate the bog when you go full throttle. is everyone else there running 500s?

olin

I have changed the jets to 72 and have installed a 4/5 powervalve. I have 5 psi fuel pressure. I have a pink accel cam, and a 21 squirter with the 30cc pump I am going to try the 50cc pump, and go to a 25 squirter. It will not accel from just off idle when I stab it without stumbling and almost dieing. as soon as I back off it will pick back up but by that time I am behind. With the 69s I was way too lean especially without a power valve. we have almost a month off so I have time to play with it.

Have you looked down in the carb while stabbing the gas? If it puts a good stream of gas out as soon as you hit the hrottle then the squirters might just be too small.

when I stab the throttle, sit will give a squirt then just blahs out, If I let up on it, it will come back to idle. this is sitting in the shop. On the track I cant stab it off the corner or it will just not pick it up. You guys who have had this problem know kinda what I am talking about. then it will go ahead and accelerate. Too late. Got more things to try this week end.

If it's squirting as soon as you open it up but still bogs, I would say the squirter is just too small. Those big butterflies in a 500 let a ton of air in the engine when they open quick. I would put at least a 31 squirter in it. My 350 has a 28 and is just right. When I put the 500 on it I had a 25 on it and it would do what you're saying. Went to a 31 and fixed most of it. Still needed more. I've seen people mash the end of the tubes almost flat to get the fuel busted up better before it gets to the boosters. I hope you can get it, nothing more aggrevating than a bucking carb.

thanks, I am going to change squirters, I have both numbers. How about the throttle cam, Is the pink one ok. I have not found out what the colors mean as to which one to use. Maybe it is just trial and error.

thanks, I am going to change squirters, I have both numbers. How about the throttle cam, Is the pink one ok. I have not found out what the colors mean as to which one to use. Maybe it is just trial and error. what power valve did you run.

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Originally Posted by dannyracer6

thanks, I am going to change squirters, I have both numbers. How about the throttle cam, Is the pink one ok. I have not found out what the colors mean as to which one to use. Maybe it is just trial and error. what power valve did you run.

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You can use the GREEN pump cam if you're looking for more fuel. Using a larger squirter will only allow the same amount of fuel in FASTER... Maybe that's what you need, but I would get all the main jet stuff squared away on a chassis dyno BEFORE you start trying to tune the accelerator pump stuff, it is inter-related...

On another note, why are you worried about how it responds off idle? You should only care about how it works at your pace vehicle speed and up!!! And that's also under a load...

I use a white cam. I thought using a bigger squirter put more volume of fuel in and the cams are what controls the timing of the shot. Oh well...

I am going to try some stuff today. Big E, My cam card tells me my rpm range is from 42 to 82. It is a solid roller crane 300/310 with a lift of 535. It is an iron head with a very nicely done efi intake. Not just a big hole. I don't have the money or access to a dyno or I would get it done that way. I will not try too many things at once so as to not know what is theproblem. we will see.

I put in the 4.5 power valve, I checked my vacuum and it is a 9ish, 1/2 of that is 4.5 so I used the 4.5. I have 5# of fuel pressure using 3/8 solid alum fuel line accept to the carb and it is same size flex hose. I stayed with the pink cam and installed a 28 squirter that I modified ala dave Carpenter. He knows what I mean. It is 80% better with the 30cc accel pump. No pull over to speak of, and from 3500 or so, when I accel it will rev without any problems all the way to 8000 and I only did that once, It is crisp and will come right back down to idle at around 1200 and it seems to like it there. I have 71 jets. thinking of going up one step just so it will not lean out. I am happy with it mostly. Still has a bit of stutter just off idle when I hit throttle. but I am not driving it just off idle, as Big E mentioned. I think I will try this. thanks for all of your help. I used a little bit of everything. I love 4m net.

Double check your transfer slot placement and make sure you don't have the butterflies open too far at idle. The butterfly should make the slot square..........not a rectangle *about. .030 down on slot*This picture illustrates a transfer slot exposed too far:http://i890.photobucket.com/albums/a...ps47b54c16.jpg

If you need to open the throttle blades that far to get the engine to idle then you need to drill the throttle plate hole a little larger to allow the butterfly to close some.

thanks, I will check that.