Hey guys,...

Me and my dad just took the Vette out for its first run this year after completing a transmission swap, converter, and gears among other things. But the car just hasn't been running right. I noticed it last year and "hoped it would go away" lol. But thats not going to happen obviously. First let me give you some specs....

HEI Distributor
MSD 6A Ignition
144 Blower
600 CFM Edelbrock Carb jetted to 750 - Manual Secondaries
2800 Stall TCI converter
700R4 Performance Transmission
3.73 Gears
28IN Tires
93 Octane Sunoco Gas
Bosch Plugs
350 CI GM Crate Engine.... Pretty much bone stock
Noisy Gear Drive

Ok,... Now heres the problem.... In Neutral or Park you can rev the engine, and it revvs up nice... no sputtering, stumbling, or hesitation. When in gear its a different story... from a dead stop, if you put the pedal on the floor, the car just bogs (hesitates) before it sputters up to about 2500-3000 RPM and then it takes off hard like it should. I can't figure it out. Thought it was ignition timing, but then wouldn't it do that all the time. Only when it’s under a load does it seem to do that.... hummmm???

Any of you guys want to take a shot??

Dan

 

BOg is sometimes a lean condition,,maybe you need a bigger carb with that blower or jet up some more

 

What do you mean by a 650 EDL carb with "manual secondaries"? Have you inactivated the airvalve..? That won't work... If you alter the secondary airvalve system, you will get a massive lean bog condition.

 

Hey Motorhead -
Isn't it past your bedtime...?

 

How hard is it to replace the valve and float in a holley 4150?

 

Ok,... You know, I should probably take a moment and look this up in the edelbrock book but I want to respond to you first. I think the secondaries on the 600 are mechanical (did I say manual?). Now if I remember correctly there is a pickup for Vacuum Secondaries on an edelbrock carb but if you don't hook it up it runs as if it had mechanical secondaries. I'm thinking the same thing you guys are thinking. Lean condition. Now supposedly he re-jetted the carb - all jets - and what he jetted it to equals 750. But heres the thing. The car had a 750 to begin with. It ran really well, and really fast, but also really really rich. Your eyes would burn while driving it and it would leave black smoke at WOT. Now it appears to be running in the right range... plugs are in good shape, no black smoke. So I don't really know what to think.

Also, I read somewhere that blowers prefer mechanical secondaries??? What direction should my tuning be going in?

Dan

 

Anything in a 4150 can be replaced in less than 10 minutes. The floats are usually brass, and do not need to be replaced uness you ran over the carb with your truck. Needle and seat can be replaced from the outside, and the Power Valve comes right out the back side of the metering block after pulling the 4 bowl screws.

 

Thanks for the info Lars! Someone suggest that perhaps my float "sunk" after sitting all winter, in addition to the needle.

 

Dan -
You have something messed up here....
The Edelbrock 650 is a re-pop of the old Carter AFB carb. This carb is a mechanical carb with a weighted airvalve to control secondary activation & air/fuel flow. It cannot be converted to a vacuum secondary carb, and the airvalve cannot be eliminated to make it a non-airvalve carb (straight mechanical). Many people think the carb is a vacuum secondary due to the airvalve system (similar to a Q-Jet). If you have made any mod that alters the secondary airvalve system, that carb will not work, because it will not get a fuel shot on the secondary side when the throttle blades open.

You cannot take the jetting from one model carb and utilize it in another. You need to establish the baseline on your carb and jet from that point, regardless of the jetting configuration of other carbs. The jetting setup of a 750 has nothing to do with your 650. Start with the stock 650 jet/rod combo and go from that point in your tuning. The 750 jet/rod combo is irrelevant. But fix your secondary airvalve and bring it back to its stock configuration first.

Most people running blowers on the street run vacuum secondary carbs. Nothing wrong with that. But they also run boost-referenced power valves to assure that the system does not see a lean-out condition under power. If you have an Edelbrock carb, your power pistons may not be sensing boost conditions, causing the pistons to stay seated (full lean) when the engine is under boost.

 

Pretty unlikely on a Holley... Just pop the bowls off it and clean it up. Set your float levels once you get it re-assembled and started back up.

 

 

Lars,

Thanks for the help,... to be totally honest I haven't touched a carb in a while and I was never really any good with working on them to begin with. To my knowledge, I did not touch the air valve at all. For some reason I was confused about whether the carb could be vacuum or not. Now I know its not even a possiblity

As for the jetting.... O BOY .... did we screw that up. My thinking was that if I took the jets from the 750 and put them into the 650 I have, that would make a 750. Now after I start by re-installing the 650 Jet and metering combo, what do i do next... how do I "properly" tune this thing to the car.

I was never a Holley guy but I understand the power valve theory... I don't know how to relate this to Edelbrock

Also.... can you give me a little more insight on this "power piston sensing boost condition?" Like I said, I really know very little about these carbs or how they work.

Thanks,

Dan

 

Dan,
If you don't have the Edelbrock manual for the carb, I'd suggest contacting them and get a copy. It's pretty good. It covers the general operation & theory behind your carb and it has a really handy jetting chart that makes life a lot easier. Read the manual front to back ... it will help you out a lot in understanding the tuning process. I use to have a Edelbrock and they are great street carbs.

 

You may want to get rid of those Bosch plugs. Working as a service manager in a shop I see nothing but problems with them. Unless you have a german or japenese car they do not seem to work well.

 

Dan,
Good luck with your carb problem. How are you coming on the T5 you are considering?
Bernie

 

Can't the brass floats collapse from super chargers or blowers?

 

Very strange, but my experience has been the same. These plugs seem to work great for a very short time. Then they foul.

My Toyota loved them, but the vette and my various Saturns seem to hate them.

 

Not too well unfortunately, but the next swap meet is in about 3 weeks so I'm going to make a 10th attempt there. I haven't really been able to find what I want.... Part of the problem is that I spent way too much on the rear of the car. Give me some time and I will send pictures. Its all nice and painted; every single bushing is brand new and has been changed to polygraphite. I bought a new set of GR2 Shocks (until I can get money for the Billsteins). New Shock mounts, Shim Kit From Ecklers, and of course the 3.70 Posi Rear.

So I am hoping that will give me enough performance for the time being until I can find the right T5....

In the mean time I'll just play with my dad's vette... LOL

Dan

 

I can agree with you guys on this one. My dad sticks with them because he's been told they are the best, and I use them too from time to time, but I have experienced the same thing with the Bosch plugs... car seems to run great for about 5,000-10000 miles and then its no longer as smooth as it once was. Change the plugs and it always seems to run a little better.. Maybe its psychological because we see most of these plugs in Imports, and I can imagine our cars came with AC Delco's too.

What type of plugs are you guys using?

 

Only on a blow-through application where the whole carb is in the pressure box. This is a pretty uncommon setup.