Is this idle OK?

The forum for all of your technical questions on your classic FIAT autos
User avatar
miker
quattromila club
Posts: 4007
Joined: Sun Jan 24, 2016 7:55 pm
Last Name: Richmond
First Name: Mike

Is this idle OK?

Post by miker » Thu May 16, 2019 7:08 pm

My car has idled like this for years, but I'm wondering if it could be better. Every two years I have to pass smog here in Oregon, which entails limits for unburned hydrocarbons (300ppm) and a 2.5% limit on CO. I usually can't pass that test with the car as you hear it in the video. But they let me get away with coming in with an idle as fast as 1200RPM, and when I do that and lean out the idle mixture, I can get it to pass. Obviously, with the occasional miss you hear, the unburned HC is what causes it to fail. Every once in awhile, I'll replace plugs, etc. with no change.

Specs: 9.8:1 pistons, stock cams, electronic ignition from 1980+, 36ADL carb.

https://vimeo.com/336698051
MikeR (mirafiori.com since 1995)


1977 Fiat 124 Spider
Previously owned:
2012 Fiat 500 Prima Edizione #236 (now owned by my son David)
'86 Bertone X1/9
'81 Fiat Spider 2000 #236
'78 Fiat 131 four door
'76 Fiat 128 4 door
'74 Fiat 128 4 door
User avatar
bartigue
seimila club
Posts: 6015
Joined: Sat Jan 23, 2016 11:49 pm
Last Name: Artigue
First Name: Bradley
Contact:

Re: Is this idle OK?

Post by bartigue » Thu May 16, 2019 7:51 pm

The speed masks any issues but it seems to me it has a slight miss. Probably something correctable with a minor adjustment, what plugs are you running? If you say platinum then I'd start with a set of non-platinum plugs and a coil test.
-----------------------------------------------------------
Brad Artigue
1969, 1969, 1970, 1979, 1980, 1981, 1982, and 1982 124 Spiders
1969, 1970 850 Spiders
77 X1/9
http://fiat.artigue.com
User avatar
18Fiatsandcounting
Posts: 20
Joined: Tue Apr 16, 2019 8:47 pm
Last Name: Balazs
First Name: Bryan

Re: Is this idle OK?

Post by 18Fiatsandcounting » Fri May 17, 2019 12:36 am

I think the electric fan was running when you shot your video, and so it's hard for me to hear the engine itself. However, the engine does appear to shake a bit more than I would expect for stock cams. Could be a plug issue as Brad notes, or a bad plug wire, mixture too lean, engine running too cool, valve clearance(s) wrong, low compression in a cylinder, etc.

After the engine has idled for a while like this, pull the plugs and see if one of them looks any different.

-Bryan
User avatar
miker
quattromila club
Posts: 4007
Joined: Sun Jan 24, 2016 7:55 pm
Last Name: Richmond
First Name: Mike

Re: Is this idle OK?

Post by miker » Fri May 17, 2019 12:21 pm

Sorry about the fan. Yes, it is definitely an engine miss at idle. I'm running NGK BP6ES plugs. Engine temp is fine (see fan running). Engine runs smoothly except for this miss at idle. Good suggestion to look at the plugs after idling.
MikeR (mirafiori.com since 1995)


1977 Fiat 124 Spider
Previously owned:
2012 Fiat 500 Prima Edizione #236 (now owned by my son David)
'86 Bertone X1/9
'81 Fiat Spider 2000 #236
'78 Fiat 131 four door
'76 Fiat 128 4 door
'74 Fiat 128 4 door
User avatar
18Fiatsandcounting
Posts: 20
Joined: Tue Apr 16, 2019 8:47 pm
Last Name: Balazs
First Name: Bryan

Re: Is this idle OK?

Post by 18Fiatsandcounting » Fri May 17, 2019 4:11 pm

Sounds like a plan! A trick I have used to find a particular cylinder that is misfiring is to disconnect the plug wires one at a time. The misfiring cylinder is the plug wire removal that results in three smoothly running cylinders. Well, as smooth as three cylinders on a Fiat would be expected to run... The verification test is that, when the other three plug wires are disconnected each in turn but with the suspect cylinder plug wire always connected, the engine speed will drop but the misfire will still be there.

-Bryan
User avatar
Jefco
Posts: 50
Joined: Fri Nov 17, 2017 12:18 am
Last Name: Aurand
First Name: Jeff

Re: Is this idle OK?

Post by Jefco » Fri May 17, 2019 11:22 pm

Mike, are you in the Portland area or Ashland? If Portland, I'd like to help with it.
Jeff
1986 Bertone X
1972 124 Sport Coupe (2L project)
1987 Maserati Biturbo i spyder 2800
1970 Volvo 145
Ex '74 X, '62 1100D, '75 124 Sport Coupe, '70? 850 spider
User avatar
vandor
quattromila club
Posts: 4449
Joined: Sun Jan 24, 2016 10:03 pm
Last Name:

Re: Is this idle OK?

Post by vandor » Fri May 17, 2019 11:30 pm

What is the ignition advance at idle? I've seen engines miss like that when they had a lot of advance at idle.
Csaba
Parts: http://www.autoricambi.us
Cars: http://italiancarclub.com/csaba/Fiat.html
'71 124 Spider, much modified
'72 124 Coupe, new project, ex-Pete, ex-Eli, ex-Jack car (all Mira members)
'73 124 Wagon, no floors
User avatar
miker
quattromila club
Posts: 4007
Joined: Sun Jan 24, 2016 7:55 pm
Last Name: Richmond
First Name: Mike

Re: Is this idle OK?

Post by miker » Sat May 18, 2019 12:15 am

I have it set for 10 degrees BTDC, but have not checked recently. I think I kind of got used to it running this way, because for awhile, I had no vac advance (back when I ran IDFs) and used to set it to more than 10.

One other thing I noticed when I went down the path that Brad suggested. I checked the coil resistance and seems to be fine. But I also took a close look at the hall effect pickup, and there is a slight skew to the gap, closer on the top than on the bottom. I think I'm going to put some brass shim stock under one side to level it out so I can get the gap a consistent .5mm.

Jeff, I'm 6 blocks north of the Raleigh Hills Fred Meyer, on Brentwood St. It would be great to have another set of ears/eyes on this!
MikeR (mirafiori.com since 1995)


1977 Fiat 124 Spider
Previously owned:
2012 Fiat 500 Prima Edizione #236 (now owned by my son David)
'86 Bertone X1/9
'81 Fiat Spider 2000 #236
'78 Fiat 131 four door
'76 Fiat 128 4 door
'74 Fiat 128 4 door
User avatar
Jefco
Posts: 50
Joined: Fri Nov 17, 2017 12:18 am
Last Name: Aurand
First Name: Jeff

Re: Is this idle OK?

Post by Jefco » Sun May 19, 2019 12:26 am

Cool Mike, I 've wanted to get over to World of Wet Pets ( near Jesuit HS) for a while now, so I'll get to stop there afterwards.
I'm near Johnson Creek Blvd, on the edge of Milwaukie.
Call me, see PM.
Jeff
1986 Bertone X
1972 124 Sport Coupe (2L project)
1987 Maserati Biturbo i spyder 2800
1970 Volvo 145
Ex '74 X, '62 1100D, '75 124 Sport Coupe, '70? 850 spider
User avatar
miker
quattromila club
Posts: 4007
Joined: Sun Jan 24, 2016 7:55 pm
Last Name: Richmond
First Name: Mike

Re: Is this idle OK?

Post by miker » Mon May 20, 2019 11:28 am

I levelled out the pickup with some brass shim stock and set the gap to .5mm. No difference. I pulled one plug wire at a time, #2 was definitely missing more than the others. Looked at the plug compared to #1 and they look the same. Nice and clean. I opened up the idle mixture screw 1/2 turn and it definitely sped up some and smoothed out some.

I wish I had access to one of those old-style oscilloscopes.
MikeR (mirafiori.com since 1995)


1977 Fiat 124 Spider
Previously owned:
2012 Fiat 500 Prima Edizione #236 (now owned by my son David)
'86 Bertone X1/9
'81 Fiat Spider 2000 #236
'78 Fiat 131 four door
'76 Fiat 128 4 door
'74 Fiat 128 4 door
Post Reply

Who is online

Users browsing this forum: No registered users and 16 guests