642b rough idle

[duhop]

new to the forum. lots of good info. My brother and I have a 1989 642b . the idle is rough (up and down) but when it is choked it runs just fine. I was told not to run it like that as I could blow it up. We have changed the fuel line and filter and the fuel pump is working good too. open for any suggestions. thanks in advance.

 

[Fishfiles]

runs good choked , would guess it's a gas motor and I would say your carb is clogged up in one of the jets or passages and needs to be cleaned out

 

[Tazza]

runs good choked , would guess it's a gas motor and I would say your carb is clogged up in one of the jets or passages and needs to be cleaned out

I agree, sounds like a blocked jet in the carb. If its not blocked your air/fuel mix is not rite.
Have you changed the plugs too?

 

[duhop]

I agree, sounds like a blocked jet in the carb. If its not blocked your air/fuel mix is not rite.
Have you changed the plugs too?

yes, its a gas motor, haven't changed the plugs although pulled the wires one at a time while it was running to see if it would have any effect and it did so we didn't change them. we were thinking plugs, cap and rotor could probably be changed out. pulling the carb looks to be little tough. thanks a bunch for the quick replys!!!! duane

 

[duhop]

yes, its a gas motor, haven't changed the plugs although pulled the wires one at a time while it was running to see if it would have any effect and it did so we didn't change them. we were thinking plugs, cap and rotor could probably be changed out. pulling the carb looks to be little tough. thanks a bunch for the quick replys!!!! duane

well we pulled the carb off and we are going have a look inside tonight. also going to replace all the vacuum lines while we are in the area.

 

[duhop]

well we pulled the carb off and we are going have a look inside tonight. also going to replace all the vacuum lines while we are in the area.

well the carb looked very clean and we hope it is cleaner now. going to put it back on and put some new vacuum lines on.

 

[Tazza]

well the carb looked very clean and we hope it is cleaner now. going to put it back on and put some new vacuum lines on.

Hopefully that will do the job!

 

[duhop]

Hopefully that will do the job!

well it is still the same. doesn't make any sense that it could be the points but they look pretty worn so that's on the list.

 

[Tazza]

well it is still the same. doesn't make any sense that it could be the points but they look pretty worn so that's on the list.

If you have done any of the following just ignore it.
Plugs, leads, coil, points, rotor, cap, capacitor that is usually on the side of the distributor. Thats just about all the ignition components i can think of. I'd check the vacuum advance is working and the hoses are good.
I'm not sure how you tune it, could it be as simple as your mix is too lean?

 

[jerry]

be sure to check the mechanical advance in the distributor under the point mounting plate also, if it has rusted or a spring broken it would throw the timing off. And take a look at the governor too for broken springs or loose parts.

 

[jerry]

be sure to check the mechanical advance in the distributor under the point mounting plate also, if it has rusted or a spring broken it would throw the timing off. And take a look at the governor too for broken springs or loose parts.

If the carb is set right and all else looks good take a look at the intake manifold, bolts may be loose or gasket shot. put a gauge on the vacuum port for the vacuum advance to see if it is sucking air somewhere causing the lean mixture.

 

[jerry]

If the carb is set right and all else looks good take a look at the intake manifold, bolts may be loose or gasket shot. put a gauge on the vacuum port for the vacuum advance to see if it is sucking air somewhere causing the lean mixture.

Another thought on this, if you squirt wd 40 or light oil around the intake manifold where it fastens to the block a leak will draw it in and change the engine rpm or make it smoke out of the exhaust. be very careful of fire though and do not do it on a hot engine.

 

[duhop]

Another thought on this, if you squirt wd 40 or light oil around the intake manifold where it fastens to the block a leak will draw it in and change the engine rpm or make it smoke out of the exhaust. be very careful of fire though and do not do it on a hot engine.

WOW thanks for all the replys and info !!! We have the cap, rotor, plugs and points so we are going to do them one at a time tonight. also we were told to check the oil in the governer...never heard of that before.

 

[duhop]

WOW thanks for all the replys and info !!! We have the cap, rotor, plugs and points so we are going to do them one at a time tonight. also we were told to check the oil in the governer...never heard of that before.

Ok, well... we put all the new parts on and guess what....yep...still the same. Soooo after a lot of head scratching and thinking "vacuum leak" we took a look at a some sort of cylnoid up just right of the carb. It has 2 good size vacuum lines and a hot and ground wire going to it from a ballas resistor. So we pulled the vacuum line closed to the back of the carb and plugged it with his thumb and waalaa, it ran like new. So what is this thing? I have been searching but nothing yet. Maybe something to do with pollution ?? What ever it is it ain't working. thanks again for all info guys. we are almost there.......pics...... http://i208.photobucket.com/albums/bb56/duhop/bobcat.jpg http://i208.photobucket.com/albums/bb56/duhop/bobcat1.jpg http://i208.photobucket.com/albums/bb56/duhop/bobcat2.jpg http://i208.photobucket.com/albums/bb56/duhop/bobcat3.jpg

 

[mllud]

Ok, well... we put all the new parts on and guess what....yep...still the same. Soooo after a lot of head scratching and thinking "vacuum leak" we took a look at a some sort of cylnoid up just right of the carb. It has 2 good size vacuum lines and a hot and ground wire going to it from a ballas resistor. So we pulled the vacuum line closed to the back of the carb and plugged it with his thumb and waalaa, it ran like new. So what is this thing? I have been searching but nothing yet. Maybe something to do with pollution ?? What ever it is it ain't working. thanks again for all info guys. we are almost there.......pics...... http://i208.photobucket.com/albums/bb56/duhop/bobcat.jpg http://i208.photobucket.com/albums/bb56/duhop/bobcat1.jpg http://i208.photobucket.com/albums/bb56/duhop/bobcat2.jpg http://i208.photobucket.com/albums/bb56/duhop/bobcat3.jpg

http://i208.photobucket.com/albums/bb56/duhop/bobcat3.jpg
http://i208.photobucket.com/albums/bb56/duhop/bobcat2.jpg
http://i208.photobucket.com/albums/bb56/duhop/bobcat1.jpg
http://i208.photobucket.com/albums/bb56/duhop/bobcat.jpg


You have to put a space before and after each link
Mike


http://i208.photobucket.com/albums/bb56/duhop/bobcat1.jpg

 

[duhop]

http://i208.photobucket.com/albums/bb56/duhop/bobcat3.jpg
http://i208.photobucket.com/albums/bb56/duhop/bobcat2.jpg
http://i208.photobucket.com/albums/bb56/duhop/bobcat1.jpg
http://i208.photobucket.com/albums/bb56/duhop/bobcat.jpg


You have to put a space before and after each link
Mike


http://i208.photobucket.com/albums/bb56/duhop/bobcat1.jpg

Hey, thanks Mike !!! I was wondering why they stacked up.

 

[mllud]

Hey, thanks Mike !!! I was wondering why they stacked up.

I may be mistaken but I believe that part is to assist in controlling vacime during warm up. ?? Emmision control.? Someone here will know.
Your links will hilight if they are going to work before you post. Mike

 

[OldMachinist]

I may be mistaken but I believe that part is to assist in controlling vacime during warm up. ?? Emmision control.? Someone here will know.
Your links will hilight if they are going to work before you post. Mike

You said one line went to the back of the carb where does the other vacuum line go?

 

[duhop]

You said one line went to the back of the carb where does the other vacuum line go?

One vacuum hose comes from the piece of cast is on top of the carb, then goes to this valve/cylanoid and then a vacuum hose goes from this part to the intake manifold.