desmog stumble

[brian]

weber 38, header, full desmog.
under load bad stumble, bucking, depress clutch while stumbling and it picks right up, release clutch and back to stumble.

lays down under load at rpms under 2000.
over 2000rpm it runs fine. 4th gear under load above 2000rpm you can just feel a slight hesitation.


used to be able to cruise around in 4th at 1000rpm's or less in town. not possible now.

it pulls a pretty good 19(valves need done) inches at idle, with just a slight ~1/4-1/2 inch or so flutter.
timing right at 7*
weber is 2 years old.
header install was in april. installed with $pector's super green gasket. retorqued a few times, including agian yesterday.
plugs are pretty newish.
cap&rotor replaced this morning, wires about 2 years ago.
fuel filter 2 years ago.
fuel pump with in the last year or so.(tho it's an advanced auto unit....). going to check pressure output tomorrow.
no fuel pressure regulator. i have one that i'm going to throw on, but doubt that's teh issue.

thoughts?

 

[Gabbo]

Vacume leak?

 

[Trapper50cal]

hot gas/vaporlock?

 

[mp_cude]

mabey without your airpump the cat has gone bad...if yo hollow it out

 

[jonzen1977]

Mine is doing about the same thing. Here is a thread I started the other day. Yesterday I took the carb off in my 10 degree garage, took the carb completely apart and cleaned it. still the same. Idles fine, then stumbles bad until I get to 2-2500k. Above 2500 it'll run pretty good. But not like it did before I touched the Idle mixture screw. Have you done anything to your timing or dizzy? I know I should get the dizzy re-curved, but mine was running good, just had a stumble at 2500 that I was trying to get out.

 

[Gabbo]

mabey without your airpump the cat has gone bad...if yo hollow it out

Crap, that is still on my list of things to do.

 

[brian]

mabey without your airpump the cat has gone bad...if yo hollow it out

already been taken care of.

 

[Pin_Head]

Stumble, bucking and spitting through the carb when under high load are often signs of fuel starvation or inadequate fuel delivery. Look for dirt in tank, clogged fuel filter, inadequate pump volume, kinked or collapsed rubber lines, or clogged inlet strainer. It doesn't sound like it is "desmog" related.

 

[brian]

Stumble, bucking and spitting through the carb when under high load are often signs of fuel starvation or inadequate fuel delivery. Look for dirt in tank, clogged fuel filter, inadequate pump volume, kinked or collapsed rubber lines, or clogged inlet strainer. It doesn't sound like it is "desmog" related.

that's been my though the whole while....lack of fuel.
i'm throwing a fuel pump at it.
filter is pretty new, tank was down a few years ago, and cleaned out, tho it was pretty clean.
do webers have inlet screens?
desmog was thrown in to weed out suggestions to check parts of the system i no longer have.

 

[Pin_Head]

Measure the pump output volume first. It should pump about a half cup of fuel in 15 seconds of cranking. Also make sure that the inlet line and filter is not obstructed. I don't know about Webers, but inlet screens are pretty common.

This is unlikely to have anything to do with emissions control or lack there of.

 

[brian]

looks like i'll be tearing into the carb.
fuel pump made plenty of pressure.....put the new one on just for S&G's..of course it did nothing.
the screen in the weber is a fine steel mesh. the brass nut that holds it on was full of junk that made it through the fuel filter. also looked like it had a few small holes in it.
i'm going to pull the top off it and try just hosing it down with carb cleaner.
i have another truck with the same carb, so i guess it would'nt hurt to have an over haul kit on hand. if the spray and pray does'nt work i guess i'll have to take it apart.....problem is this is my dd..as it is it runs ok, just is pretty annoying.

 

[GLTHFJ60]

I've got the same problem on my 60 with the stock carb. I was thinking it felt like there wasn't enough fuel, but wasn't sure what to do. I've replaced my filter recently, and it had no affect.

 

[brian]

well i think i got it.
don't think the spray and pray did it.
went over the intake bolts agian, they were tight, so i don't think that was it.
went around the weber agian. that lil bastard of a nut around teh back under the choke stuff...that's the one i think got me. it was'nt loose, but i got a few degrees of a turn out of it.

she'll pull 4th from 600rpm now(agian), with no burping, poping or lurching.

life is good agian.