Hey Guys,

First post on the forums, hopefully I can get some help. My wife just surprised me with my 69 camaro project for christmas. I've had the car for 10 years but never had put it all together, now its a driver, best wife ever.

Anyway, it's got a 350 with roller rockers, camel hump heads, edelbrock intake, mallory ignition system and distributor, headers, and a speed demon 750 carb (#1402010V).

I had my uncle who's a very experienced mechanic set the timing for me which he did slightly advanced as its a high performance engine.

The problem I'm having is it seems like its dumping too much fuel in or something. I'll be cruising along in 2nd gear about 15-20 mph and then I'll jam on the gas and the engine will bog down like crazy then rev up. Or when I'm going about 30-40 in 3rd gear and I put it to the floor I can feel it hesitate. It idles great and doesnt have a miss or anything, revs up super strong, just has those two issues which dont seem normal. The car is very driveable and runs strong but just doesnt feel like its at peak performance.

The float levels check out fine, fuel about halfway up and its a new carb. Nearly everything on the engine is new except for the block and heads.

Any help would be appreciated, thanks!

 

I'm not much on fine tuning carbs, but I'd be interested in hearing if you find out.

 

Found this and thought it might help.

Holley carburetor specifications, list numbers, jetting and tuning tips.

ACCELERATOR PUMP CAMS AND SHOOTERS

Accelerator pump cams come in various sizes and are color coded and number coded by Holley. The cams have different shaped ramps that the arm from the accelerator pump rides on. By changing the size and shape of the arc on the cam, the pump shot can be tailored to start early or later as you go from off idle to full throttle. Changing the cams can have an effect on the way a vehicle leaves the start line in a drag race. If you leave the line off idle or at a higher RPM (while foot braking or when using a trannie brake or when using a clutch with a manual transmission) experimenting with the pump cams can help. There is no set rule for use, you just have to experiment with the different cams and the different cam positioning holes in the throttle linkage of the carb. Holley sells individual cams or you can buy their kit which includes an assortment of cams to choose from.
Pump shooters are another area of experimentation. Holley carbs come with a standard shooter size which differs by carb list#. If you are experiencing a bog or hesitation off idle, you can try a larger, higher # shooter size. The bog or hesitation may be caused by a momentary lean condition when the carb goes from the idle throttle postion to the main metering system. The shooters help richen this momentary condition and eliminate the stumble. Keep going up in shooter size until a puff of black smoke comes out the exhaust, then go back one or two sizes. Playing with the shooter sizes is particularly helpful, when you have an intake with a large plenum area, such as a large open plenum or a tunnel ram. Keep in mind that as you increase the shooter size, you may also need a "hollow" screw to hold the shooters in the carb. At shooter sizes over .039, Holley recommends that you use the "hollow" screw (PN-26-12) which allows more fuel to flow to the shooters.

 

This is also a great site that may help detirmin why your car hesitates. check out the 2nd video.

www.V8TVshow.com - Tips for tuning your Holley Carb

I know that you have a demon, but I'm pretty sure that the demon and Holly are very simalar.

BTW, drove my Camaro for the first time yesterday and I've got some carb tuning to do as well. I've got a punched out 850 and only really need a 700....

 

great resource! thanks for sharing. I was speaking to a guy yesterday and he said that the stumble may also be caused by the bottom of the carb being warped and thus causing a leak. This was commonplace in demons due to over-tightening. It would need to be re-milled to fix it.

just a thought

 

wow, that's also good to know.

According to Holly, and I'm assuming Deamon is the same???? But is your power valve 2 lbs lower than manifold vacume at idle (neutral on stick, drive w/ automatic). that might be your stumble while your already going. Or, the "Squirters" could be too big / small causing the stumble off idle.

Seems like it's pretty straight forward. I know I'm going to check this on mine this weekend for sure.

Keep me posted at what you find. hey, I'm learning too.

 

Hey, after all the research and learning over the past week to attempt to get my bog and off idle stumble gone, I made some significant progress this weekend. I wanted to share my journey.
1. started researching how carbs work in general. I made sure to get to about 80% retention with the different components and how they work.
2. I started asking for advice from experienced people who knew way more about it than I did. The advice I got ranged from: "buy a holley or quick fuel carb and dump the demon" to "i can tune it for you but I charge $100/hr" to "try the accelerator pump, bigger squirter etc"
3. To recap my issue, my timing was set correctly, the car would start hot, revved fine under no load but had a significant bog/stumble under hard acceleration in any gear.
4. MY PROGRESS:
4.a. I looked at the BG website and they said to "readjust my butterfly position". So i learned at what it should be set as which is turning the idle speed screws (the two on each side for primary and secondary NOTES:not to be confused with the idle mixture screws) to have a nice little square showing in the slot in the side of the carb for both primary and secondary. I left this as a baseline and put the carb back on.
4.b. I went up from a #31 to a #35 squirter. Super easy to change out, takes 2 min.
4.c started the engine, let it warm up to operating temp (about 160 on my car) it ran great but was idling at about 1200 RPM now up from 1000 previously. I left the idle mixture screws where they were from the previous tune job my uncle did. My plugs were nice marshmellow color so I knew my mixture was okay.
4.d I turned the idle speed screws evenly to get my idle down to about 950.
4.e. I drove the car around the block to see where I was at. The bog was totally gone but there was still a little bit of a stumble.
4.f I turned the car off and reset all of my idle mixture screws. I turned them all the way in and then backed them out 1.5 turns.
4.g I started the car again and the engine was idling okay but didnt seem super strong (im a newbie remember). I then plugged the vacuum guage into the manifold port and was reading 12.5 vacuum.
4.h I turned the idle mixture screws evenly until my vacuum read a solid 15.
4.i. I drove the car again and the bog and the stumble were completely gone. HOWEVER, it still seems that at wide open throttle that something was still holding the engine back from letting loose.

MY NEW QUESTION
Now that my off idle stumble is gone, what could be causing the engine at WOT to not be getting total power?

Thanks for your continued help and I hope what I've found so far can help someone else in my situation. So when you say you've got a Demon and someone tells you to scrap it, I only put a little time and energy and at $13 squirter into mine and got it running much much better. Hopefully I'm not too far away from getting it at top performance.

 

Thanks for the update! Good stuff man!

I would think two things.

1. Is your gas pedal opening the throttle wide open? Check to make sure and adjust linkage accordingly. Note" if you're using a cable, make sure the cable is adjusted to WOT and not more or you'll stretch the cable out.

2. Jets. Try going two sizes up :-) Check plugs for correct color after doing a WOT pass. You can play around with your jets until the plugs show they're running rich, and then just back it down a set.

Keep me updated!

 

Hey, thanks for the reply. How do I know if the throttle linkage is getting it to wide open? I dont think I have a cable, I have a rod that connects to the carb and has a little nut on the other side, not sure if its distinguishable from my pic.

 

Hi James,
It's actually pretty easy. Take off the air cleaner so you can look straight down into the carb. Have your wife, kid or friend go mash the gas pedal all the way to the floor and hold it. When you look inside the carb, the butterfly's should be straight up.

If you need a base point for reference, take the rod off the carb and manually open the carb all the way. Adjust the rod accordingly.

One of the problems I had with my 68 was with the old carb linkage. Because I was running a taller pair of motor mounts, and my heads were taller than stock, and I'm running a high rise manifold.... The old linkage just wouldn't accomodate and I ended up dropping about 150 into a cable system.

Good luck!