My carb was plugged up with old gas so I had a shop rebuild it. The guy told me I had a bad timing advance computer. and he had to set it to 30 degrees to get it to run decent. It ran fine on the way home. I pulled the MSD timing comp and sent it back for testing/replacement. It tested good, 34.00 down the drain. reinstalled it and set the timing to 36 total and 16 initial. idles like ****. I advance the timing some to get it to idle decent. Then I talk to the shop and he tells me to come by and he will look at it. show up the next morning and he says come back later. So I decide to set the idle mixture and see if I can get it to run like It did before the bad gas gummed it up.
We took it for a test drive and it ran good for 3 mi. or so then it starts to run real bad like it was running out of gas. Just like before the carb rebuild. It won't idle at stop signs or get out of its own way.
So I get it home and mess with it some and I get it to where it will idle, reset the timing to 16/36. try to set the idle a little higher and no matter how far I turn the idle screw in it just wont idle any higher. I can hear the butterflies letting more air past them as I turn the screw in but the idle speed stays the same.
What is happening here? It revs up just fine. What can be causing this?

 

What carb again?

If you can't get it to idle up turning the idle screw up, then something is majorly WRONG! Can you slowly rev it up with linkage? Or does it do the same as when you turn idle screw up?

Just to clarify...........you are adjusting the IDLE screw...NOT mixture screws when speeding the motor up? The mixture screws will not adjust speed(per say).

 

What the hell is a "timing advance computer" on a carb engine?

 

I had to go to Randy's web page to find specs:

Edelbrock Performer 750 cfm carb

MSD 6AL ignition control, MSD timing advance computer, Holley phasing kit in the Duraspark distributer.
Is there a rev limiter in all that crap? LOL

I don't know beans about the MSD stuff, but there was this guy named Murphey who said: "The more complex a system becomes, the more opportunities there are for failure". I wouldn't rule anything out at this point.

 

LOL... Yeah, it is the idle screw. The one on the linkage where the throttle cable hooks up.
The engine will rev up and return to a idle. If I turn the idle screw in to raise the idle you can hear the air as the butterflies open up, but the idle speed stays the same. If I rev it with the idle screw set to a high idle it will hi idle for a sec then slow down to the same slow idle regardless of the idle screw setting. The idle adjustment screws don't seem to have much of an effect on idle quality either.
The MSD stuff is not a factor in this, It is definitly a carb issue.
Strangest thing I ever saw.
It is going back to the shop that did the carb rebuild tomorrow. I will tell you guys what happens. I think he missed something in there and it has plugged a passage or something.

 

Yeah, 6000rpm.
The MSD stuff is as simple as it gets. a lead from the dist to the timing comp then a lead to the 6AL and then a lead to the coil. No mech. adv. to stick or adjust. 2yrs. nno failures. I will take this over recurveing a dist any day.

 

Ya, MSD is pretty simple. It either works or DON'T.

I HATE them carbs. I would think there is still something stuck in it somewhere?
Sounds like the intermediate circuit is afoul? Not letting fuel in as you advance the throttle. It will rev as you pump the accel, but when that fuel is gone it falls on it's face.

 

I agree. It is going back today. If he can't fix it for free (he did rebuild it last week) I am going to get a brand new carb. I have always heard that rebuilt carbs just aren't as good as a new one and since this one was full of that gooey varnish from sitting too long I don't have much faith in this particular carb ever working as good as it did before.
Besides the Edel carbs are supposed to be real bad for off road use. Maybe I will get a QJet.

 

I rebuilt, God only knows how many carbs but better than 2000 in my career and only had 5 that wouldn't work right. 2 actually had cracks in the carb body, two were mystery problems. But 99% of the carbs replaced don't need to be. If you know what you are doing, a rebuilt is as good as a new in almost all cases.

 

It is always nice to hear from people with real world experience.
How many of those carbs were gummed up with old gas?
I don't have the eye sight to do a carb rebuild right, too many little pieces to keep track of.
Hopefully the shop will figure it out.

 

The majority of carbs I worked on were from marine engines, both 2 and 4 stroke. Most sat a minimum of 6 monthe. some as long as 10 years. You wanna see a really gummed up carb, have 2 stroke one that sat for several years and see what the oil does along with the gas. I've soaked carbs as long as a week to get all the crap out of them. Then used a syringe with alcohol in it to make sure all the passages were clear. I think the only new carb I ever bought was a 390 CFM Holley in 1972 for a race 2.3 Ford motor, the rest have all been reborn for used or even from a collection of parts. I know about the eyesight thing, I have several magnifing tools that I use, most with extra lighting.