Hey everyone, I have been reading for weeks but not able to post till now. I have an 88 4cyl that has good compression and timing is set correctly but still have performance issues. I think a weber is the way to go here with no smog testing but I am considering rebuilding it but unsure of the probability of ending up with a good carb. I know they are a pain to rebuild but I have had one apart years ago in college.
The thing that has me really scratching my head at the moment is I have little or no vacuum at the accessory vacuum control box on the fender well. When I pull the main hose off that goes directly to the intake I can see fuel vapor and feel a slight pulsating vaccum/pressure. My parents had an 87 ram 50 with the same engine and I thought there was a strong vacuum signal on that line. I was wondering why because I had the head off and had a bad exhaust seat fixed and have 150lbs of compression across the board.

I am unsure if backpressure from the converter could be causing the no vacuum on that line issue because I had the air pipe unhooked at the valve on the exhaust manifold and didn't have anything but noise from it but again I am unsure how it is set up at the exhaust manifold because I figured i would have a lot of noise and straight exhaust coming out of it.

Please give me some tips on where to go from here.

Hows your vacuum at the brake booster ...?... You really need to put a vacuum gauge on your motor .. And see how good the vacuum is and if the gauge is really moving a round .. If the gauge is really moving a round you have a bad hole ( cylinder ) ...The motor has a 150 compression right now ?..Or it did last time you looked ?.. Make sure thats still true ... I'm dealing with someone right now that was just sure one part of there cars was new and fixed ... Come to see the new work had and parts had died .. Its sad how Mitsu trucks are hated over there goofy carb .. Mitsu really killed there sells by not making the carb alittle easyer to deal with ... But most carbs of the time are a pain ... Car makers tryed to keep the carb and pass smog ..And not go to EFI is why theres so much junk on a Mitsu carb ..

Sorry on your troubles

David

Hazardous Toys inc

I still have the compression and I had the same thing when #2 had 25lbs of compression. I fixed the head and thought 'wow it will sure help the carb to have good vacuum. The other lines I have pulled have good vacuum and none pulse except that one. In the garage the engine is smooth as can be and revs nicely but after a 1/2 mile of driving it starts acting like its running out of fuel and then it will start to run fine for a bit and then back to gagging and choking. I know its a major carb issue but I would like to know about that one single line before I jump on the carb.

Is it supposed to have a good strong vacuum signal like manifold vacuum should be?

On the end of the box there are two lines there that one has good vacuum at idle and the other must be port vacuum because it is rather weak.

You can spend a lifetime thinking about that carb. The answer for me and others was FCproducts.com. Your carb is 22 years old !

The weber is a valid option and will get you down to one vac line for dizzy advance.

You should have good vac at the reed valve. If not your issue may be leaking intake gasket. Will the truck run? Have you checked every vac line for cracks? You have to pull each line, sometimes they are just hardened and are leaking without the cracking. I would nip off the ends to get back to a tight fit.

<img src="/forums/images/graemlins/patriot.gif" alt="" />

It runs and idles fine and has a new intake gasket and I just put the head back on after fixing a valve seat issue. I have good vacuum everywhere else but that port on the intake. Weird.

Maybe the vacuum source is clogged or otherwise gummed up?

If its full vacuum your looking for...??????????

Vacuums is vacuum....... (full vacuum that is) ...

Try getting it ware ever you can with a (T) in another vacuum line and see ware that gets you ....

Good news... I sprayed that port with carb cleaner and got much better vacuum. I unplugged the computer and plugged it back in after a few minutes and it still bogged and had hesitation but not as bad. I later drove it 5-7 miles and it ran like a top so I decided hey lets hit the highway. I made it about 200 feet down the ramp and it started gagging and bucking. BLAH at least its intermittent which tells me after running 4k miles in the past 5 years it probably has something stopping up a port in the carb every now and then.

There you go. <img src="/forums/images/graemlins/zombie.gif" alt="" />

I have an FSM for the Feedback Carb. You can pull it from the link in my sig.