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-   -   No change when adjusting air/fuel screws?? (http://www.hotrodders.com/forum/no-change-when-adjusting-air-fuel-screws-214618.html)

jjack010 02-13-2012 06:49 PM

No change when adjusting air/fuel screws??
 
Working on my 88 Chevy C1500 stepside, sbc 383. I recently rebuilt the Edelbrock 1407, 750cfm carb. I'm not getting any change in idle when adjusting the air/fuel screws. I took it back apart and double checked all the gaskets and blew out everything again. No change. When I punch it, she screams. At part throttle driving, it's a little rough. Idle is fine. Spark plugs indicate rich. Also, the truck has a big cam so there is low vacuum at idle. The calibration on the carb is stock. Bad accelerator pump? Need different step up springs because of the low vacuum at idle? I want to make sure this carb is right before I get a calibration kit and start changing settings, unless of course this is for sure my problem. Any help is appreciated.

jjack010 02-13-2012 07:07 PM

FYI, I'm pulling 8" of vacuum at idle. Fuel pressure is roughly 8lbs. I have a fuel pressure regulator that I will be installing soon to get it at about 5.

DoubleVision 02-14-2012 02:17 AM

Thanks for the info. THe issue is obvious. You don't have enough base timing.
When you have low base timing and a big cam, what issue might that cause?
The cause would be the carb's idle speed is so far opened to make it idle properly it's off the idle circuits of the carb so it has no choice but to pull from the main boosters. And when the carb is pulling off the main boosters at idle would the idle screws have a effect? Nope.
Try this. With the vacuum advance disconnected and plugged, move the base timing to 12 degrees before top dead center. Lock down distributor.
Now connect the vacuum advance to a full time manifold vacuum source.
This is any source that pulls vacuum full time, including idle. On a Eddy carb it will be the port on the drivers side front. When you connect it, the idle goes up right away,, that's a good sign. When the idle goes up, idle it down on the idle speed adjustment to the given cam, likely around 700 rpm. Now the butterflies are back on the idle adjustment of the carb. now you can set the idle air fuel mixture. However as you said, you've got too much fuel pressure which can cause the same problem as Eddy carbs don't like anything over 5 psi.

jjack010 02-14-2012 07:18 AM

I'll get some work done this afternoon. I should be able to get the regulator plumbed and set. I haven't had the truck long so I've been trying to work these bugs out. I'll get a timing light on it as well. I have no clue what the timing is at now. I would like to know the cam specs. I guess I'll get around to pulling the timing cover one day. The previous owner had nothing documented, so I'm playing catch up to find out whats in it! I'll post results later today.

jjack010 02-14-2012 03:55 PM

Update.......so I put a timing light on it. There is a cheap timing tab on there that reads 8 degrees retarded and advanced with 0 in the middle. Advanced is on the right side, correct? When I started the balancer mark was way off, to the left, about 12 o clock position. I slowly rotated the dizzy clockwise and after several attempts got it to 8 deg advanced (right of 0 on the timing tab. By this time the temp was starting to get up there, I had the idle screw on the carb maxed out and the idle was at about 600 rpm's. I decided something wasn't right and shut her down. I heard a little detonation before shutting it off. After shutting it down I got a tremendous backfire. Hopefully i didn't do any damage to the piston!? So what now folks. Cam timing off or am I goofing up here. I also had the vac advance disconnected from the carb and the carb vac capped off.

jjack010 02-14-2012 04:23 PM

OK, so I don't think I blew a hole in a piston. :) I went back out, turned the distributor counterclockwise until it was maxed out against the intake. Starts and idles fine. I put a light on it and there's possibly a mark at roughly 12 degrees. So if I'm thinking correctly, I need to verify #1 tdc and see if that mark is lined up with the zero on the timing tab. Right? If not make a new mark and get rid of the old sh*tty markings.

dogwater 02-15-2012 06:26 AM

Pass. side port for full vaccum on Eddy Carb. That's how my 1406 is.

jjack010 02-15-2012 07:20 AM

I'm starting over on the timing since I'm not sure the balancer mark was right for #1 tdc. I fought with getting the dizzy lined up with the oil pump shaft last night for over an hour. I'll continue tonight. I couldn't find any timing tape locally so I'll use an advanced timing light. My vac. advance is connected to the passenger side of my carb (even though that seems to be a matter of opinion unless it's for emmission reasons). More to follow....

ap72 02-15-2012 07:47 AM

Quote:

Originally Posted by jjack010
I'm starting over on the timing since I'm not sure the balancer mark was right for #1 tdc. I fought with getting the dizzy lined up with the oil pump shaft last night for over an hour. I'll continue tonight. I couldn't find any timing tape locally so I'll use an advanced timing light. My vac. advance is connected to the passenger side of my carb (even though that seems to be a matter of opinion unless it's for emmission reasons). More to follow....


fought for an hour lining up the dizzy? It should drop right in, take a whole 3 seconds.

Find TDC on #1 cylinder and mark your balancer, you don't need an advanced timing light a simple one will work fine. Your distributor should go to manifold vacuum.

You're making this a LOT harder than it needs to be. Set your timing at 14 degrees and go from there. ALSO turn your idle screws all the way in and back them out 1 1/2 turns to get started.

After you get it running you need to get your carb "right" and there is no way to do that without either buying a tuning kit for it OR drilling out your own jets, turning down your own rods, and somehow making your own springs (so get the damn kit). You'll also need a distributor tuning kit, eventually you'll need to run more initial advance BUT keep your total to around 34-36. You can (and should) also tune your vacuum advance.

It sounds like you have no clue on what you're doing and either need to spend a lot of time reading and learning OR need to pay someone to fix this for you. The first time I had to tune timing and a carb it took me the majority of a saturday, and still required a little tweaking after that. Now it takes me about an hour.

jjack010 02-15-2012 08:53 AM

In the perfect world, it should take 3 seconds to seat the dizzy. But, the oil pump shaft wasn't lined up with the dizzy shaft and because of clearance problems from removing and installing the dizzy, it was eating up time.

I'm in the process of locating #1 TDC and marking the balancer. I can use my simple timing light to get my initial timing, but after that, I have no way to determine total timing unless I have timing tape or an advanced timing light. I got an advanced timing light.

I'm not opposed to buying a calibration kit for my carb. I started the post because I want to make sure everything else is in order before I randomly start changing out jets, metering rods and step up springs. Once I determine that everything else is correct, I will calibrate it and make it "right." I understand that 1.5 turns out is a good starting point for the mixture screws. However, if I start from fully seated or 5 turns out, there is no change in vacuum or idle, which is why I started this thread.

I do have plans on dialing in my vacuum advance and springs within the dizzy.

I wouldn't say that I have no clue as to what I'm doing. I appreciate your word of inspiration though. This is a hobby and I enjoy it. I have a full time job that typically takes me to a foreign land 12 months out of every 24 months. So yeah, I'm rusty. But thats why I'm on this forum. Sorry to inconcenience you Mister. Oh, and congratulations on the record breaking time for dizzy installation. I bet that was your first time too. :thumbup:

2old2fast 02-15-2012 09:04 AM

jjack , fyi , next time , drop your dist. in , does not matter if it doesn't line up w/ the oil pump, just bump the starter over till it falls in , then proceed, might take a few tries to get it in the right spot, but you'll get there , patience....

dave

jjack010 02-15-2012 09:46 AM

Patience, yes. :)

DoubleVision 02-15-2012 02:09 PM

http://www.edelbrock.com/automotive_.../1000/1406.pdf

jjack010 02-15-2012 04:02 PM

update....

So I tried numerous times to seat the dizzy. I tried manually rotating the oil pump shaft with a large screw driver. I tried rotating the rotor to various positions. I tried bumping it over with the key. It still wouldn't seat. Well I just got it seated and it was a little snug so I had to apply some light presssure to get it to seat fully. There's a few hrs I'll never get back. Anyway, I'm moving forward.

jjack010 02-15-2012 06:05 PM

Alright, I'm back on track. Timing is good. And I have eliminated that as my problem. Still no adjustment from the mixture screws. I still have to adjust the vacuum advance and check the springs on the dizzy. That will come later. Tomorrow I'll get the fuel pressure regulator installed and get the carb calibration kit ordered. I'm thinking the step up springs may be the answer because of the big cam and low vacuum at idle.


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