Engine Tuning Help after rebuild (1 Viewer)

[phoenixrider]

OK, any advice here? 40 over motor, decked heads, Downey Torquer cam, MAF tri-y cermain headers, demogged and no cat. Stock Asian carb.

Problem: big flat spot going off idle. Like it stumbles and wants to stall, unless I rev it up and feather in the clutch. Bucks and chugs when trying to cruise in 3rd, at less than 30 mph. Big, huge backfires when decel.

Above 45 in 4th, seems to run fine, nice and smooth. The decel backfire is VERY annoying, though

Is the stock Asian carb to small for this engine now? Even if I do re-jet, will it work, or should I go with a Weber or Holley conversion? I'd much like to stay with the Asian, if I could

What is causing the backfire? any ideas?

 

[NocalFJ60]

I don't see why the stock carb will still not work. Might need to tune it but that does not sound like your problem. You check the valves after letting it run? Check the timing again. Check the check valves for the right direction going to the main diaphram on the distributor.

 

[patagonia cruiser]

hi
my experience with backfiring was points, check the gap, the 3F tends to be supersensible with the gap. I would also check the timing. The stock ausin carb should work fine but might need some tinkering.
regards

 

[phoenixrider]

ok. We cold set the valves at 15 - Downey reccomends 19 on the all valves. Haven't put enough miles on it yet to re-check valves

Set the timing to about 10 degrees advance

everything smog is off. Air injection, egr, et all. I have one vac line going to the dissy (not even using the HAC) one vacum for AC idle up, and the PVC lines and that's about it. Everything else is gone

thanks

I can post some pics later

 

[NocalFJ60]

Do you still have the vacuum switch hooked up for the deceleration fuel cut off system? It closes the fuel solenoid on deceleration.

 

[phoenixrider]

I don't think so. what does it look like and where does it go? what does it hook into?

 

[NocalFJ60]

Here is a picture and it also shows it in this desmog diagram.

 

[phoenixrider]

OIC. I do believe that is gone. In researching other posts, it seams that I can discard the 'computer', as I no longer have any smog, and ground the thingy on the carb (ICS?) permantly to make it always on, I presume.

I still wonder though, how and when this is suppose to work/come on?

 

[NocalFJ60]

When you let off the gas above 1800 rpm's the vacuum switch is off due to high vacuum from the port. This tells the computer to shut the fuel cut solenoid valve to lean it out and prevent backfiring during deceleration. I think that diagram is the one Jim C. approved and it is on it.

 

[Elbert]

I grounded one side of the fuel cut solenoid valve on my partially desmoged 60 and it made a real differnce in totally removing the decel popping and sputtering the truck use to do going down large hills etc... I don't have an air rail, smog pump, or cat on my truck. Like others have said I would make sure the valves are adjusted correctly, and your timing is right.

 

[phoenixrider]

yeah, we'll double check the timing and readjust the valves once I put a few miles on it.

But, it sounds like the decel solinoid is supposed to come 'on' via a vacum switch, but if it left on by grounding one side, that doesn't harm anything?