alfisti

continuation of https://www.rx7club.com/1st-gen-gene.../#post12415569

Having a strange problem with a recently acquired car. It seems to run very well with the exception of random stalling at idle. It idles at roughly 1100 RPM, smoothly - but out on the road, in warm weather, sometimes when shifting or coming to a stop, it will inexplicably stall. Ideas? Any professionals who can tune the carb/troubleshoot, in the NJ/Easton PA area? Thanks!

j9fd3s

iTrader: (3)

kind of from the other thread, a lean mixture will tend to make a weak idle. i'm not sure where the idle mixture adjustments are on the holley, but i would try that first. as you're doing this i would also lower the idle speed, 1100rpm is high

alfisti

Thanks. So when you say "weak idle", you mean, could stall? It idles smoothly otherwise... if a bit high. Just want to make sure I understand the term. Thanks

j9fd3s

iTrader: (3)

yes, it'll idle, but easy to stall

alfisti

ugh. The process I see for tuning the idle mixture requires a port in the manifold for measuring pressure. Mine does not have a port :-(

Is there any other recommended process for setting idle mixture? There is a bung for wideband sensor (which I have), and the car is equipped wtih an exhaust temp gauge.

Thanks

j9fd3s

iTrader: (3)

turn the mixture screw until it idles the best. try a half turn out, and see what it does.

alfisti

thanks. Given than it's idling fine right now (while warmed up), albeit a high RPM - should I lower the idle speed first, and then adjsut the mixture screws to stabilize it?

j9fd3s

iTrader: (3)

try it! i'm not sure it matters which one you do first, just go slaw and make small changes

Maxwedge

iTrader: (1)

Before adjusting Id start by seeing exactly where the PO set the screws. With the motor off turn them in counting by 1/2 (or 1/4) turns, until they bottom out gently. Write it down. Last guy prolly spent some time getting it just right so be careful you don't get things all messed up.
I think Holley recommends starting at 1.5 turns out (from closed). I think my 12A/Holley likes 2 to 2.25 turns out to idle decent around 800. Lower the engine idle speed until the idle gets shakey. Richen the idle slowly in 1/4 or 1/2 turns until it's smooth again. Do this until it has a reasonable idle and takes off from a stop okay.
Of course this all assumes everything else is working and adjusted properly, and the carb is jetted/tuned decently. But it's a start.

Maxwedge

iTrader: (1)

Nice car, by the way.

alfisti

Thanks! Is that yours?

alfisti

I called Racing Beat - and they recommended a 1200-1300 RPM idle. The guy I spoke to knew the Holley carbs inside and out. Opinions?

Maxwedge

iTrader: (1)

No no no. But I looked up Locost 7 to see what it was, and then posted the pic to show others. Show us yours.

Maxwedge

iTrader: (1)

More info? Does the motor have a large port job? For a tame 13B 1100rpm is a high idle, but if it has a bridge port maybe 1200 is right (I dont know). My bro's turbo P-port idles around 2000 but it's a bracket racer.

alfisti

It's a street port, 6-port 13B.

j9fd3s

iTrader: (3)

i don't really see why you'd need to idle that high, my P port will idle at 950, i could go lower but the carb runs out of resolution.

alfisti

@Maxwedge - should I do all this while the engine is running, and warmed up? thanks

Maxwedge

iTrader: (1)

Turn idle mix screws in with engine off, just to see what the current baseline is. Return them to that point (1.5 turns, or whatever it is/was)
Then start up motor and adjust when warm. Choke & high idle setting is different so get it warmed up and take care of that normal operation first.

alfisti

Thanks. Just a reminder, there is no choke at all on this carb. I assume that does not change anything about the process you said.

LongDuck

One reason to keep a higher idle is to compensate for a light flywheel; the added rotational energy of a higher idle speed will help smooth idle and help with off-idle acceleration. My RB lightweight aluminum flywheel idles best on a stock -SE 13b at about 1k RPM. Any lower and the idle quality suffers and it's lumpy and erratic. That's part of the trade off for going with a 12lb flywheel.

OP may have a lighter rotating assembly than stock.

Maxwedge

iTrader: (1)

Excellent point Longduck, I didnt know about that.

alfisti

Thanks. I don't have anything in my pile of receipts for the car that mentions the flywheel - just the street porting. So it's POSSIBLE, but I doubt it. But who knows?

LongDuck

Easiest way to look for a light flywheel is eyes-on. Pull the metal inspection cover at the top of the transmission where it mates to the engine (2x 14mm bolts), and look down in there. If it has an auto trans counter-balance weight and the flywheel is bolted to that, then it's not stock. A stock flywheel will have sections of thick metal around the edge which serve this purpose. The other easy way is to drive a stock Rx7 and compare how the engine revs; a lightweight flywheel has a markedly different speed to rev when you step on it with the clutch in.

I would be hesitant to change a steady and consistent idle on an -SE; it's hard enough to get them there when stock what with fiddling with the bypass air control screw, the Throttle Stop screw and the TPS (*much less the Idle Mixture rheostat which is hidden for a very good reason...). Entire tutorials have been dedicated to getting an -SE to idle well with worn intake parts...

Chimby

Hi. Im curious if you got your holley issue figured out. Hopefully you did.