Topic: 20R sputter

[yota pu/runner]

Alright here is my problem I just noticed yesterday and more today.  I have an 80 20R that has a rebuilt carb as of maybe 6 or 8 months ago.  I was running a header to a muffler and just recently removed the the header and put the stock manifold and cat on and I am now experiencing problems.

I also had an issue about a month ago when on my way up to go wheelin we had to make a fix to seal off the air cleaner to the top of the carb and it seems to have been running better until I put the manifold and cat on it. 

Could that be my problem?  Could it be something else?  I am really not sure what to do and it is my daily driver.
Thanks for any help.

[79coyotefrg]

the 20R exhaust manifold is EXTREMELY restrictive, put the header back on

[yota pu/runner [OP]]

Ok so i am taking your advice coyote and i will put my header back on.

Now this maybe a dumb question but if i put the header back on do i need to pull off the cat?  Running the header it would produce more heat coming out of the exhaust wich in turn could damage the cat, or I could very well be wrong.

[Marlin]

The 20R engine is a cross flow design and does not preform well without back pressure.

Back pressure is needed to slow the air flow and produce more power.

I recall removing the factory cat and driving my '80 with the open exhaust. It had no power.

Marlin

[yota pu/runner [OP]]

So I should leave the stock manifold and cat on?

Although its not an arguing point but i feel that when I was running the header on my truck as to compared with the manifold i had more power, but it also could of just been the fact that it was louder.

Last night replaced almost all of my vacum hoses i still have a little more to do just need to stop by and pick some up, but it didn't seem to do anything different on my way to work this morning.

So do I leave the stock manifold on or bolt up my header?

[wakkjobb]

+1 /\ get the header back on. Better low-end torque and all that goodness. Stock stuff is no fun; made for 'the masses'=no fun. Put your header and exhaust on and see what happens. Trouble shoot as beat you can/cheapest way possible. Hell, maybe you left a vacuum line open?

 
Dan

[yota pu/runner [OP]]

alright so I started putting the header back on I will finish it up tomorrow. 

I went ahead and replaced almost all of my vacum lines still have a handfull of them left but it hasn't seemed to change it but will find out tomorrow after i can get it all buttoned up.  Will let you know how it turns out.

[yota pu/runner [OP]]

ok here it is a week later and I now have the header back on and have replaced the plugs and cables since I was right there and couldn't remeber the last time I did them.
Anyways it has been running fine up to this morning, on my way to work I got off the freeway and as I took off it began to sputter just like it was doing when the manifold was on it.
I have checked all my fluids and everything is good other than needing an oil change, the fuel filter is new and almost all of my vacum hoses have been replaced.  And I went back over them a few days later just to make sure they are all tight. 

Please help I do not know what to do at this point or what to even look at. 
Thanks

[kneedownnate]

The 20R engine is a cross flow design and does not preform well without back pressure.

Back pressure is needed to slow the air flow and produce more power.

I recall removing the factory cat and driving my '80 with the open exhaust. It had no power.

Marlin

Wierd    My 80 came with no cat (alaska truck) and small exhaust tubing.  I replaced the stock manifold with a long tube 4 to 1 header, glasspack and 2.5" tubing, and it really woke the truck up!  It even had very nice low end response, which actually went away when I stuck a 2.25" glasspack in the system to quiet it down for deer season.

[yota pu/runner [OP]]

Alright so this is a dumb question but can you melt the inside of a cat with the heat from your header?

[kneedownnate]

Not necessarily.  A header shouldn't run hotter than a factory exhaust system, and the cat will probably be the hottest part of the system anyway. 

[ed lee]

sputtering? like vapor locking? if you answered yes to these questions.........it's your fuel pump.. especially if you are using the mechanical pump, and if it's new.. new doesn't mean it's any good...

[Just4Fun]

i nice had an 83. thought i would save money by using a cheeeep distributor cap during a tune up. the cap developed a crack causing the engine to sputter at different speeds.

that's my

[79coyotefrg]

i would change the fuel filter, if that still sputters  and the cat is HOT  your carb is running too lean, 

[Tim]

you said you rebuilt your carb???  sounds like you have a choke issue.  i wouldn't jump to conclusions of your exhaust system being the problem but i wouldn't say its the carb right yet, look at filters first.  i drive a 20r and rebuilt the carb too.  at first it was perfect hot, cold.  start-ups and everything had a great cold to hot kick down.  put it this way it was harmonious.  now i came back from deployment and mechanically it was a little dry and the choke works but doesn't open enough on start-ups so its spits and sputters with excessive fuel not burning from lack of air.  ya ya choke works by restricting air but this is too much restriction.  after it gets warm im fine but in your situation i am leaning towards your rebuilt carb being the problem.  when it spits look to see if the butterfly is open and you might have a jet getting clogged too.  if it spits smell your exhaust for fuel, if so check the butterfly.  might have a bad diaphram in the choke assy.  i run a stock manifold into a 2" pipe to 2" glass pack out to 2" tail pipe.  i have no issues but as marlin mentioned if you open the exhaust too much your back pressure (which helps close the valves effectively/timely) will be lost and there for reducing your performance, no engine braking, it will be too free so to speak.  it may increase your highway performance but on the trail it will be a dog.  i wouldn't go above 2" on the exhaust, if you do, have a 1 3/4" muffler to slow the gasses a bit.