3310 carb problem

[coppergmc]

I have a 750 vacuum carb on an engine I threw together. The combo has a decked block and ported vortec heads to give me 10.2:1 compression. I am using a custom ground solid flat tappet cam with 240/250 duration @.050 and .520 lift on intake and exhauste. I had the cam ground with a 108 LDA and an intake centerline of 104 degrees. The carb sits on a performer RPM air gap intake. The timing is set a 21 degrees at idle and 34 total.



The engine is on a test stand and runs great except for a hesitation when I try to rev the engine hard and fast. I have installed a 40 squirter and a pink pump cam in the #2 position and the problem got a little better but is still there. I was wondering if someone might have some advice. Keep in mind that the engine is in a no load situation and the problem will get worse when installed in the vehicle.

[ZR1BLAZER]

i wish i could help. that is the same problem i have been dealing with for 3 years. i have swapped cams 3 times i have used about 10 different carbs and i have even tried 2 different sets of heads. i payed some one else to tune the motor for me and it runs real good. but still has the same hesitation your talking about. i am running on the rich side already. if i go any richer the motor wont run?? if you figure it out please let me know.

[ChevyKiD_69]

most trucks i have seen have this little hesitation except efi models. my truck has it i dont even bother with it. if it gets worse then i will worry about it but again most rigs that have carbs i notice has it.nick

[oncearacer52]

Sometimes switching to a dual plane intake will solve that problem. If you already have one then you can tune it out with changing air bleeds. In this case I would think you would need bigger high speed bleeds to help with the transition. If you are having trouble idleing then go smaller with the idle bleeds.

With a 40 squirter you will probably need the hollow squirter screws.

[Scotty_S-15]

CooperGMC, I presume you\'ve tried disconnecting the link to the secondaries? (just in case they\'re trying to creep open prematurely)

....... What\'s the RPMs at when you mash it? Bringing it up a hundred or two can sometimes help (crutch) these problems. Your lower vacuum at idle (because of the cam) sure ain\'t helping.http://www.s10v8.com/images/smilies/icon_wink.gif

........ My 750 HP double pumper, same problem. I played with pumps, squirters, cams, no help. But if I just bring it to about 1400 before I stomp on it, nooo problem.

......... With my old vac. sec. 750, never a problem, even from a low idle, and with all the old factory squirters & setup.

[ZR1BLAZER]

air bleeds? where is that on the holley? i have a 670 avenger.

[Scotty_S-15]

On 2007-01-15 12:19, oncearacer52 wrote:.................. If you already have one then you can tune it out with changing air bleeds.

I don\'t think Copper\'s carb has air bleeds. But, if you spring for a Pro-Form replacement body, then you\'ve got \'em! And, the air-gap intake is a dual plane manifold, isn\'t it?

........... Sometimes cheating the floats up a little higher helps this stuff too.

[coppergmc]

The 3310 has air bleeds but I am not really into drilling them out. Not to mention, I don\'t even know where to get the pin drill bits to do it.



I thought I might try an old 650 double pumper that I have had for quite a while. I have the primary metering block and can\'t seem to find the secondary. I do have a secondary block from an old 780 vac carb that might work. I have to drill out the passage for the squirter. I actually know where and what size I need to drill for this one. I figure drill it out and use epoxy to fill in the holes.



I have had this problem before on other vehicles. Usually going bigger on the squirter took care of it. I can tell you this. This remanned carb from holley is missing some parts. It didn\'t have a accel pump spring nor a weighted pin that goes under the squirter. You\'d think they would do better than that.



Let me know what you think.

[knudsonm]

What does your timing curve look like? If you are running a bigger cam you usually need to run more inital timing. Try 15-20 degrees at idle and then limit the mechanical advance to give you 36 degrees all in by 2500 or so. Remember to disconnect the vacuum advance when setting your timing.

[gdmclnh]

Is 21 deg at idle a lot?

[s10carguy]

I agree. hesitations off idle are often timing related. try lighter advance springs or an adjustable vacuum advance. may just need quicker advance off idle. I don\'t even check idle timing with a decent cam. set total timing to 35-40 at 3000.

also be sure you have the right power valve for your idle vacuum reading. and if the diaphragm is wet that means the valve is blown out. holley dropped the ball with their power valve crap.

sometimes I\'ve had to back out the idle mixture screws one turn as well to fatten the transition (usually run 1.5 to 2.5 turns from closed).

the vacuum secondaries shouldn\'t open at all under no load. if all else fails I use the bigger volume pump shot.

[soopertruper]

Read this , I have a similar problem maybe it will help you as well. Good luck. I swaped over to the quickfeul metering block and put in the .031 air bleeds. Seems better, but I haven\'t had a chance to completely finish tuning. Good luck <a href="http://www.s10v8.com/viewtopic.php?topic=14233&amp;forum=4&amp;37" target="_blank" target="_new">http://www.s10v8.com/viewtopic.php?topic=14233&amp;forum=4&amp;37</a>

[Scotty_S-15]

On 2007-01-15 13:31, coppergmc wrote:

The 3310 has air bleeds but I am not really into drilling them out....................................



I don\'t think you do have air bleeds, maybe you\'re referring to idle feed restrictors, etc.

......... The air bleeds are the 8 removeable \"jets\" that you are looking at when you pull the air cleaner, 4 lined up near each squirter. Of course with a vac. secondary carb has no secondary squirter, but in that vicinity. I\'ve never seen air bleeds in a stock vacuum secondary Holley.

........... Regarding the problem, I\'m wondering how the engine starts hot with 20+ degrees of initial. Like others have said, try even more advance. Don\'t worry about total timing for the moment. If the engine responds, there\'s a good chance TDC is wrong, and you don\'t really have that much advance.

[mzoomora]

They all have air bleeds, but most are not changeable.



I would try backing off od the 40 squirter to maybe a 36 and see if it improves. Make sure the pump arm is right, etc. Sounds like you hav ethe timing close enough and that shouldnt be your problem.

[bowtie316]

I had the same problem with a very similar combo, acted lean when I mashed it. I went to a 650 DP with a plug and 50 squirters front and rear, no change, I decided that wasn\'t the problem. Timing is at about 19-21 at idle and 34 total. I ended up going to a hotter spark plug and the problem went completely away.

[soopertruper]

oh yeah, sorry about that .031 idle feed restrictors.

[Scotty_S-15]

On 2007-01-15 20:28, bowtie316 wrote:

I had the same problem with a very similar combo, acted lean when I mashed it. ............................................

I ended up going to a hotter spark plug and the problem went completely away.





hmmm. Can\'t argue with success, right? http://www.s10v8.com/images/smilies/icon_biggrin.gif We\'ll have to remember that one.... http://www.s10v8.com/images/smilies/icon_wink.gif

[ZR1BLAZER]

how do you get a hotter plug? you go to the local autozone and those guys dont know there ass from a hole in the ground!! i have 97 vortec heads with the factory plugs. so i just ask for a hotter plug?

[Scotty_S-15]

ZR1BLAZER wrote:

...................... you go to the local autozone and those guys dont know there ass from a hole in the ground!! ......................



I\'m so surprised! http://www.s10v8.com/images/smilies/icon_razz.gif Yeah, they\'re trained that way. Clueless.

........... First, you\'ve got to know what plug you have now, and if it\'s \"in the ballpark\". Then find some heat range charts, and/or cross reference charts. Here\'s a link to Champion technical page, scroll down to the bottom and click \"Manufacturers numbering system, CHAMPION\".



CHAMPION PAGE (http://www.championsparkplugs.com/sparkplug411.asp)



OK, so that link isn\'t what I thought....http://www.s10v8.com/images/smilies/icon_confused.gif Looks like NGK is the only mfg. that seems to list any sort of cross reference chart, and heat ranges charts apparently aren\'t that easy to come by either.

.......... But rule of thumb in both Champion and AC Delco is that a lower number means a colder heat range. AC Example, R45s is hot, R44s is mid range, R43s is colder. Champ example, RC12YC is mid range, RC9YC is colder.

[knudsonm]

On 2007-01-15 16:09, gdmclnh wrote:

Is 21 deg at idle a lot?





no. I have my BBC running 20 initial and 36 total. I ran it locked out for a while even.

[coppergmc]

I talked to a holley tech guy today. He really didn\'t give me any help. He did say that if I sent him the carb, he would go through it and see if he can find the problem. He thinks I am changing things on the carb to cover up a real problem.



I am starting to think maybe I should take a look at the power valve. I can\'t believe it but I didn\'t check engine vacuum. I will take a reading tonight and make sure I have the right valve.



I will keep you posted.