Carb rebuild and now some new problems

[sgr60]

I rebuilt my carb this past weekend, and I thought that everything went OK. No extra pieces, and everything seemed to go back on as it came off.

BUT - now I have a new problem with the carb back on the truck. It idles fine, but when I get on the throttle it shudders, and boggs down like it wants to stall and the truck also bucks pretty severely.

I'm sure that this is based on something I did with the carb, I just don't know what...

[BLT gmc]

?what carb? If there are no "extra or missing pieces", I suspect you may have a gasket flipped. This can happen in some carbs when the gasket can fit more than one way. This may cover a passage and cause problems. I am assuming the air/fuel mixture screws were put back the way they were? Did you adjust the floats or are they as they were? Good luck, Bruce

[sgr60]

Originally Posted by BLT gmc

?what carb? If there are no "extra or missing pieces", I suspect you may have a gasket flipped. This can happen in some carbs when the gasket can fit more than one way. This may cover a passage and cause problems. I am assuming the air/fuel mixture screws were put back the way they were? Did you adjust the floats or are they as they were? Good luck, Bruce

It's a Quadrajet - 17080230. I 'm pretty sure it's not the gaskets - I did try each of them both ways and they only fit one way properly. I adjusted the air/fuel screws with a vacuum gauge once I had it back on the truck. My vacuum was right around 20 inches so I left the srews alone - maybe I should try re-adjusting them?

I replaced the float, and adjusted it to the spec that I found for that carb - 7/16 in as I recall. If the float was set too low and there wasn't enough fuel in the bowl, that could do it too I guess.

[geezer#99]

Maybe your metering rod hanger is hung up on the gasket. Poke in the vent with a small pencil and you should be able to push it down and feel it pop back up. Motor shut off of course.

[sgr60]

Originally Posted by geezer#99

Maybe your metering rod hanger is hung up on the gasket. Poke in the vent with a small pencil and you should be able to push it down and feel it pop back up. Motor shut off of course.

Thanks - will give that a shot.

Also, I just went out and adjusted the idle mixture screws again. The engine seemed to be running better - still about 20-21 inches on the vacuum gauge, however I did notice that when I operated the throttle by hand that the secondary doors were not opening when I reved it. The vacuum solenoid was holding them closed. Is that right?

I took it out and drive it again. It was fine for about 5 minutes, but when I turned around to come home and got on the gas pretty good - WOW - the problem was back definitely just as bad as before. I wasn't sure I was going to make it home without a stall.

Not good...

[geezer#99]

Secondary air valve is working correctly.
Can you adjust either mix screw all the way in without the motor quitting or idling rough?

One more thought.
Did you hang the needle on the float arm correctly. Like in here.
http://www.crankshaftcoalition.com/w...4MV_carburetor

[mattybilt79]

Sounds like an accelerator pump issue. Last time I did a rebuild I noticed that the replacement cup as I call it didn't have a spring that went inside it like ones I had seen before. If its bogging right off idle that seems suspect to me as its not pushing fuel through the carb. Operating the throttle can make the plunger roll in the bore causing intermittent problems or if you put it in upside down. Did you see if your getting a good strong squirt of gas with the engine off when you checked the secondaries?

[sgr60]

The needle was hung correctly - I did make sure on that.

I didn't actually replace the accelerator pump, just reinstalled the old one.

Before the rebuild the motor would die if the idle screws were turned all the way in, but I haven't tried running them all the way in since. What would that indicate?

I will check to see if I get a good squirt of gas with the motor off.

[geezer#99]

[QUOTE=sgr60;69

Before the rebuild the motor would die if the idle screws were turned all the way in, but I haven't tried running them all the way in since. What would that indicate?

[/QUOTE]

A vacuum leak or slight flooding or lack of initial timing.

[sgr60]

Is it possible that it's not something I did on the carb and that its about timing?

[donut]

Yes, a lot of carb problems can be fixed with the distributor. In your case, start with the adjustment screws, see where your at. Adjusting the timing will not fix a vacuum leak,

[sgr60]

Originally Posted by donut

Yes, a lot of carb problems can be fixed with the distributor. In your case, start with the adjustment screws, see where your at. Adjusting the timing will not fix a vacuum leak,

Thanks. I did re adjust the mix screws and I'm reading about 21 inches vacuum, so it seems like that may be ok. Could I still have a vacuum leak with that high a reading? I do feel like I hear something right as I engage the throttle but before the accel pump goes, but I'm not sure.

[geezer#99]

Try hooking the vac pot to manifold vac port. Your idle will speed up and you'll need to slow it back down.
Have you looked inside the carb when you have the problem?
Down below the choke plate.
Look for any raw fuel.

[Gregski]

Originally Posted by mattybilt79

sounds like an accelerator pump issue.

+ 1

https://www.youtube.com/watch?v=5X26WEfR4Ek

starts @ 3:30 into the video

[sgr60]

Well, got out and did some more checking.

1. It looks like the accelerator pump is working properly - with the engine off it sounds like a good squirt of gas is getting pumped in when I operate it.

2. There was one other change I made when I rebuilt the carb - I reattached the purge vacuum hose from the charcoal tank to the carb, which was previously not connected. I disconnected that hose again and capped each end and drive the truck. It seemed like the problem was resolved by doing that - I couldn't get the truck to replicate the symptoms.

BUT - when I got back home the truck wouldn't idle once it was at operating temp - it was reving way high. I went in and turned back the idle screw (not the mix screws) and it didn't help. What could cause it to rev high like that?

I also noticed down by the fuel pump that the larger of the two hoses is pulsing with the engine running - not sure what that's about or if its related...

[donut]

Can you "kick" the idle down with a blip of the throttle?
You could still have a bad vacuum leak or the fast idle needs to be adjusted. Vacuum leaks can occur in anything vacuum related, esp hoses. My last bad vacuum leak was actually a failed brake booster.
Fast idle has an adjustment screw on the choke side of the carb, down low. If this is staying engaged it could keep the throttle blades held open.
Keep track of adjustments, I try to write everything down so I have a baseline I can go back to. To many screws, to many adjustments, real easy to get turned around. Also stick with one adjustment at a time.