Chevy Cate motor question? I know, chevy...

[Yedi]

I hace a new 350 HO in my regal, it came with the Holley 4160 600cfm carb, intake and everything else. After alot of messing with the carb w/ my buddy, it runs pretty good. when the car first gets started, and up to 165 degrees it will pop out the exhaust, when you drive it when the secondaries open the first time it pops real bad, then it seems like it cleans it self out and runs perfect from that point on? What is set wrong here? Timing is at 13 advanced, running 93octane. Vacuum is good, car does smoke a bit and seems like it might be rich......If you can help me I would really appreciate it!

[441120]

Sounds like secondaries opening too early, or/and too lean.
This is just a band-aid though....you need a LC2...Ha Ha.
Just kidding...no really..

[CTX-SLPR]

Mechanical or vacuum secondary carb?

[Turbo6inKY]

If it's popping and then smoothing out, you're fat on throttle tip in, or possibly just at idle. Fuel loads up in the runners, you mash the gas and the unburnt stuff ignites in the exhaust manifolds.

How are you adjusting the carb? Using a vacuum gauge? Know anybody with a four-gas analyzer you can use to set the thing?

The carb is also a bit big for a regular crate 350. At 5300rpm assuming a conservative 83% VE, a 350 Chevy only needs ~460CFM to feed it. Even at 100% VE you still only need 550. You may need to do some tinkering to trim that 600 down.

[gofstbuick]

Dual plane intake? Vacuum secondaries or mechanical? Single plane intakes tend to puddle on the floor of the with vacuum secondary carbs. A one inch spacer helps, but a mechanical secondary carb is what you need. What jets are installed, primary and secondary. Start with 68s in front and 72s in the rear. It sounds like it's a little rich. Does the secondary metering block have an idle circuit? If so, adjust idle mixture on the secondary meterin block first then move to the primary metering block. How is the float setting? You should be using a blue pump cam on that carb. That timing seems a little retarded, are you using vacuum advance. If you are, review the Chevy power manual and lock out your vacuum advance and set base timing to 20 degrees BTDC. Total advacne of 38 degrees should be in before 3600 rpms. I have an 830cfm carb on my 383 and it works great with a victor jr intake (and 1 inch spacer). But when I had a dual plane intake, you can't beat the 780 vacuum secondary GM replacement carb.

[gofstbuick]

You have a metering plate for the secondaries? Get rid of that metering plate and convert to metering block for the secondairies. And switch to center hung bowls. Then it will be eaiser to tune that carb. Or sell that carb and buy a 4053 holley carb (780 cfm vacuum secondairies). If money is an issue, buy a 3310.

[Yedi]

thanks for all the replies. The Carb has Vacuum Secondaries, the GM Dual Plane intake, Floats are right on (right below the sight glass) The pump cam is the red one ( me and my buddy changed that when we were tuning, along with a softer spring for the secondaries) it's a crate motor, all this stuff was supposed to be perfectly matched to the motor. The Vaccum on the motor seems a little low, accoring to the gauge it says around 11-13 which is in the late ignition timing zone).

Well tonight I went out for a ride and it's running real bad. Poped out the carb twice and popped out the exhaust numerous times. I was told the Vacuum advance should be on the timed port on the carb vs. the full vacuum port. I've tried it both ways and it runs better when on the full vacuum port. I tried bumping up the timing and no help, the plugs are black. The idle mixture screws were 3 turns out, I put those back to 3/4 of a turn out, helped a little.

My next step is to try my Edelbrock 500cfm Carb from the 305 and see what happens. I am still open to suggestions/tips.

[RobsIron]

Replace the Power Valve in the Carb with a Blowproof one and Advance the Timing some. ReTweak.

[gofstbuick]

Plug that vacuum advance port at the carb and put a cap on the vacuum advance unit and bump the base timing to 20 BTDC. Install the Blue pump cam. This gives you a heavy dose of fuel at the beginning of the pumpshot. Did you mess with the accelerator pump adjustment? If so, did you know the pump adjustment is set with the engine off and the throttle at full throttle position? What is the list number on the carb? You should be able to find it on the right top corner of the air horn. Have you messed with the jets? If so, what jets are installed in the primary and did you change the metering plate? If so, what metering plate part number metering plate is installed. If you email me, I'll give you a phone number and we can talk.

[Yedi]

gofstbuick, got your e-mail. repiled to ya. The jets are whatver came in it. I havent touched them. As far as the accelerator pump adjustment, I dont think my buddy messed with that, he just changed that pump cam to the red one, he said this would dump more gas in. What is the easiest way to tell if a power valve is bad? I dont know, all I know is this thing is running too rich. I have a feeling it might be the valves are out of adjustment, might be too tight, this is what my dad thinks. We're gonna go through it this weekend and trouble shoot everything. Give me a few days guys and I'll update ya with what I find.. Thanks Again

[RobsIron]

Drop the front bowl and screw in a new power valve. Your symptoms are how a engine runs with a bad power valve.

I run up to 38 degrees advance on my chevy's.

Usually backfire out of the exhaust means to retarded and spittin' out the carb is to advanced.
One good 'spit' out the carb will kill the power valve.

If that doesn't fix it...you might be a tooth off on the distributor gear. Redrop the distributor and retime.

[Yedi]

RobsIron, I'll look in to that. It's a possibility, along w/ all the other crap. Will have updates Sunday for sure..

[gofstbuick]

Closest that carb matches to is an 80457. Primary jets are 69 and secondary plate is 69. Secondaries are a little lean, but that carb should idle nicely. From our conversation yesterday evening, I'm a little off in initial mixture settings. Base settings on the mixture screws are 1-1/2 turns, not 1-1/4. Make equal adjustments to each mixture screw. Start there and also set your idle speed to 750 rpm in drive.

[Yedi]

Last Night I put the edelborck 500 on from the old 305. Started right up, no smoking, and ran very smooth. No popping or back firing. Base timing set @13 with all advances hooked up and working perfect. Idle set @750 in drive. Went for a ride and it's low on power, obviously from the smaller carb. Even with this carb @ 1500rpm the car still shakes pretty descent, in gear it's worse than in park, but it still does it in park. So somthing is still not right, the vacuum is still only @15, so now I'm gonna check the valves and make sure they arent too tight, somthing is wrong with that low of vacuum. I also checked all my vacuum lines ( by plugging everything off and there is still only 15) so it's not a leak. Soooo.......now I need to exchange the Holley 600 to GM and try a different one. The right side idle mixture does not adjust, you can turn it all the way in and nothing happens, I think somthing is sticking or somthing causing there always to be too much fuel. At least I'm making headway, it's definetly the carb, but that shake at 1500rpm is a problem too. Could it be a fouled plug? I"m gonna put in some new Platinum plugs and try it when I get the carb back... later.

[Yedi]

This past weekend put on the new Carb, new platinum plugs, and got everything set up. car runs perfect, no popping, backfiring, or smoking. When I switched the plugs I noticed all of the plugs were a nice coffe brown except for the #5 plug which was totally black, must have been fouled, thus the shake at 1500rpm. Any how just wanted to let you guys know I got it after alot of messing around and taking the tranny out and putting it back in because of a leaky torq converter seal, and being told the tranny is junk only after 2 years of running it. But at least I can drive it and enjoy the old Buick again. thanks again guys

[gofstbuick]

What are you goig to do with the holley carb. I was working on a guys chevy crate engine this past weekend and he had an 850cfm on it . A touch over carbed for the street. I jetted it down and it runs well, but still needs a little smaller carb. email me, i may be interested.

[Yedi]

Actually the Crate motor is under warranty so I had to send the old carb back for an exchange for the new one. It's still a Holley 4160 600cfm, but.....this one is differnt than the one I had. This new one has a vacuum hose that runs over the choke assembly, just like the pics in Summit and Jegs, the carb that came with the motor did not have the hose or the fittings? kinda weird. All I know is it runs perfect, night and day difference.