Carb Bog

[Boone83K10]

I went back and read your first post, do you have cats? Second, when your neighbor rebuilt carb..did he touch the intake manifold at all?

 

[John81287]

No cats. Also the intake I had was stock so I purchased a new edelbrock intake. It was rebuilt and tuned to the old one. Hasn't been right since I got the new intake and dizzy


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[John81287]

In answer he didn't touch the intake


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[Boone83K10]

Intake leak. Spray some carb starter or wd40 around entire intake, under carb, around dizzy, along china walls. Any change in rpm indicates vacuum leak.

 

[John81287]

I'll have to try again. I tried it earlier and didn't notice anything but I will try that again tomorrow after work


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[hirschdalechevy]

A lot of carb problems are misdiagnosed ignition issue's , are you sure your vacuum adv. is working properly , as well as having your base timing at the right setting ? Lopey cams sometimes cause the metering rods in an eddie not to seat properly and you have to get a calibration kit to get stiffer spring tension's to compensate for different cam durations. Can be a vacuum leak or a leaking pvc valve , will give you a low vacuum reading at idle , (7 is way low). Personally that is not what I would call a big cam . I have built a lot of 350's back in the day with the 327 , 350hp cams in them , ( 222 at .050 and 447 lift ) and they were not lopey and had really good vacuum at idle , but of coarse they would be a little more choppy in a 305 , but not that bad . Check everything else first and then go to the carb , you may have other issuue's , just saying.

 

[John81287]

A lot of carb problems are misdiagnosed ignition issue's , are you sure your vacuum adv. is working properly , as well as having your base timing at the right setting ? Lopey cams sometimes cause the metering rods in an eddie not to seat properly and you have to get a calibration kit to get stiffer spring tension's to compensate for different cam durations. Can be a vacuum leak or a leaking pvc valve , will give you a low vacuum reading at idle , (7 is way low). Personally that is not what I would call a big cam . I have built a lot of 350's back in the day with the 327 , 350hp cams in them , ( 222 at .050 and 447 lift ) and they were not lopey and had really good vacuum at idle , but of coarse they would be a little more choppy in a 305 , but not that bad . Check everything else first and then go to the carb , you may have other issuue's , just saying.

It is entirely possible there is some other issue. I believe the vac advance is working properly due to when I disconnect it the motor runs a little rougher. This is where I have been hooking up the vac gauge. The timing is set at 8* before tdc, which is from what I understand the best place to start with SBC motors. I also checked the pressure with Pcv port blocked off and power brakes port block with only vac gauge on and there really wasn't much change at all. So I don't know if that eliminates a leaking Pcv or not. I'll have some time again tonight to monkey with it so I'll post again later with findings. Thanks for the input guys


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[hirschdalechevy]

It is entirely possible there is some other issue. I believe the vac advance is working properly due to when I disconnect it the motor runs a little rougher. This is where I have been hooking up the vac gauge. The timing is set at 8* before tdc, which is from what I understand the best place to start with SBC motors. I also checked the pressure with Pcv port blocked off and power brakes port block with only vac gauge on and there really wasn't much change at all. So I don't know if that eliminates a leaking Pcv or not. I'll have some time again tonight to monkey with it so I'll post again later with findings. Thanks for the input guys


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Hang on a minute!!!!!!! You need to hook your gauge to full manifold vacuum not timed vacuum , (for your dist.) and the port you are using for your dist. should not have vacuum at idle , (or at least very little to none). then as you adjust the idle mixture screws you may have your rpm come up , you need to turn it down and keep it at 850rpm as you adjust. You can use manifold , power brakes , or pcv port , not the vacuum adv. for the dist. port. but I would still check everything else first before messing with the carb.

 

[John81287]

Hang on a minute!!!!!!! You need to hook your gauge to full manifold vacuum not timed vacuum , (for your dist.) and the port you are using for your dist. should not have vacuum at idle , (or at least very little to none). then as you adjust the idle mixture screws you may have your rpm come up , you need to turn it down and keep it at 850rpm as you adjust. You can use manifold , power brakes , or pcv port , not the vacuum adv. for the dist. port. but I would still check everything else first before messing with the carb.

Got it! I will have to try that tomorrow evening. I'm also going to pull my spark plugs and make sure they are gapped properly! Glad I said what I said so you could tell me I was doing it wrong. I will have to let you know once I get a chance to check it out, hopefully after work tomorrow. Might have some different numbers to talk about.


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[Boone83K10]

I just assumed you were reading manifold vacuum, not ported!

 

[John81287]

Rookie error lets call it!


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[John81287]

Well numbers are for sure different still not great but better. I'm getting 15 with idle rpm set to 850


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[Jims86]

Idle in D was 500-550 from the factory(With timing set at 4*B tDC.)close the blades a little, and re adjust the idle mix screws to see if it gains a few Hg.
I like to open both screws evenly, just a tad past the smoothest point, then run it back in a 1/4 turn.
I wouldnt think the bog is comming from the idle circuit though...I think there may be some junk still in your carb.

 

[John81287]

Idle in D was 500-550 from the factory(With timing set at 4*B tDC.)close the blades a little, and re adjust the idle mix screws to see if it gains a few Hg.

I like to open both screws evenly, just a tad past the smoothest point, then run it back in a 1/4 turn.

I wouldnt think the bog is comming from the idle circuit though...I think there may be some junk still in your carb.

It sits at about 550 when idling in drive. In park it's around 800. Maybe a little more. I'm afraid my neighbor did a half ass job on the rebuild. Thinkin it's gonna get replaced am with a qjet probably, looking at a 750cfm electric choke remanufactured from summit. Any input Jim?


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[Boone83K10]

15 is in gear or in park? You always do it in gear. Turn screws in all the way then back out 2 full turns. Adjust evenly until best vacuum. If still bogging, look at metering rods. 800 is a little high for idling.