coughing and sputtering

[rcb]

i'm having some coughing and sputtering issues. i haven't changed the fuel filter. it seems to only be happening at around half throttle, but when i pull the choke a little over half it seems to smooth out.

the carb is stock aisen. never been rebuilt to my knowledge. it idles fine.

i'm gonna change the filter and check the line into the carb for dirt. but any ideas other than that and ultimately a carb rebuild?


btw 73 stock 40, F- engine.

 

[Romer]

Fuel filter is a good thing to try and something that should be done if you don't know how long it's been. Mine acted similar driving home on the highway. All of a sudden it started sputtering and I had to get off the highway. Worked OK under 40. Changed the filter and the problem went away.

 

[rcb]

i'll change it tomorrow

 

[Romer]

Still could be other things, but that's the best place to start.

 

[rcb]

so i changed the fuel filter, air filter, and i've got a new pcv valve. and checked the filter screen at the carb. so could an adjustment screw be out of whack? a carb rebuild is my next plan

 

[theo]

fuel pump not putting out? rust particles from the tank got into the pump maybe? pump diaphragm starting to go?

Not sure how to check a pump output other than at cranking speed.

 

[Poser]

I would bet if you take the top off the carb, and look into the float bowl, that you will find all sorts of trash in there, just waiting to cause even more problems then are occuring already.


Good luck!


-Steve

 

[rcb]

shall i just get a carb kit and replace evrything while i'm in there or am i able to take the top off and clean anything out.

 

[Magoo]

pull your fuel pump,and put it in 5 gallon bucket like half full of water and pump that little fawker like you hate it,and see what comes out.rust,crap,whatever it will also kinda tell you if its working or not.
shawn

 

[Magoo]

shall i just get a carb kit and replace evrything while i'm in there or am i able to take the top off and clean anything out.

if you take it apart you WILL need to have gaskets to put it back together.no reason not to have the gaskets handy.but it really kinda sounds like a stuck jet or possibly accelerator pump to me.

 

[Poser]

How do jets get stuck?

 

[captahab18]

Maybe he meant clogged or that something was stuck in them.

Definitely do the carb rebuild as its great fun and good way to figure out all the ins and outs of it. Soak in some thinner also be sure to get some compressed air and blow the crap out of all the little fuel channels and holes.

 

[IDave]

What's yer dwell angle?

 

[65swb45]

What's yer dwell angle?

Someone else thinking 'outside the box.'

Before you start tearing into the carb, try and duplicate the stumble in your driveway by throttling the carb manually while you watch the sight glass. If the fuel level doesn't drop, you've eliminated the fuel pump and fuel delivery system.

On the other hand, the fact that the choke helps could be a sign that the richened air-fuel mixture is compensating for an underperforming power valve in the carb.

I'd still check the dwell.

 

[lunap]

have you guys been able to get fuel filters at the local Autozone or Napa?

 

[IDave]

If you want a nonOEM filter, just get a clear inline cylinder type. They are rather generic and work well. You can get them about anywhere.

I use OEM Toyota fuel filters, but that's just me.

 

[Pighead]

If it smooths out with half the choke, first thing I think is vacuum leak. How many vacuum lines do you have? Smog stuff? Got a vacuum gauge handy? I found the vacuum gauge in my toolbox was so useful that I installed one in my dash.
A bad distributor diaphragm could give you the cough and sputters too.
Rebuilding carbs is good fun. If you find a good kit, buy a few of them. They're not getting any cheaper or easier to find.

 

[rcb]

for vacuum lines i have the following: two small lines from carb going to distributor. one for brake booster and one to the pcv. the smog stuff has been removed by po. so i'm not sure 100% that everything is routed correctly w/o the smog stuff. i'l have to find my dwell meter. and i'm gonna go pick up a vac. guage today. i've got new dist., rotor, and points

any suggestions on where to get a carb kit ?

thanks y'all

 

[Pin_Head]

Sounds like a lean condition at half throttle caused by something like a cloged jet on non-functioning "power valve" (axuiliary main jet).

It can't be a vacuum leak below the throttle plate or it wouldn't idle. There aren't any places for a vacuum leak above the throttle plate before 1975 (the EGR valve).

All this points to try rebuilding your carb. You can get a kit at NAPA or any online vendor for about $20-30. You might as well get a new secondary diaphragm too for about $15 from you local dealer or Jim Chenoweth.

Clean the carb in Berrymans Chemtool dip in the gallon jug (or its equivalent). After cleaning, was twice in clean acetone or paint thinner and blow out all the tiny holes with compressed air or spray type carb cleaner. Don't fool with anything else. Do not remove the butterflies from their shafts. Videotape the disassembly process and take extensive notes writing down jet numbers and which holes they go in so that you can get it back together properly.

 

[rcb]

got a vacuum guage and connected to the brake booster line and i get a reading right around 16 inches Hg.