This is on a sb 400, everything practically new.

I recently changed plug wires, plugs, and intake gasket. I wasn't sure the intake gasket actually needed to be changed, but I wanted to see if it would have any effect on the vacuum at idle, and it didn't.

The problem is that it won't return to idle after the engine is revved slightly. I can get it to idle OK just sitting there, but it'll die when I go to drive it. It's kinda like the idle circuit isn't working at all on the carb after the engine is revved. I double checked the transfer slot setting and it's OK.

I didn't have this problem before the intake gasket and plugs were changed....but my vacuum at idle is the same as before. At 22 degrees initial, I have 12.5 - 13.5 inches of vacuum at 850 rpms. If I retard the timing from there, vacuum gets worse, along with idle quality.

I couldn't find the same spark plugs that I took out of it because none of the stores carried them. They were NGK "V-Power" racing plugs, and were colder than stock. I have stock AC's in it now.

I've tried tweaking the carb every way I know how, but doesn't seem to matter. Any ideas?

 

Was there anything wrong with your previous set of plugs and wires? Or did you just change them because they were getting old? I'd start by taking off the new set of plug wires and replacing them with the old set. If that doesn't do anything, go back to the old plugs.

 

I changed the plugs because I had fouled them numerous times while trying to get the carb adjusted. They were all pretty black, plus I broke one while snaking it out past the headers. The wires are Taylor spiro pro, and are much better than the cheap ones I had on it before.

But- I have gotten past the no idle....I tinkered once again (for the hundreth time) with the a/f screws and the butterfly position, and it's returning to idle now.

I think my electric fan is really messing up my tuning attempts....

Every time it starts, it puts a load on the electrical system and the idle gets too low. I now have the idle set at 1000 rpms with the fan off, and they'll decrease to around 750-800 when it's running. Funny thing is, even with the Griffin 1" aluminum radiator and high flow pump I just installed, the temps still creep up to 220 before they drop back down.

Guess it's better than the 230 degrees is was running at with the stock radiator though... Except for the tuning at idle issues I continue to have, it runs great off-idle!! Only thing I lack is any decent traction!! I don't get it....I'm seriously considering re-adjusting valve lash to see if it improves anything - do you think it's worth a shot??