.292 Cam Idle ?

[rcf925]

I'm running .292 cam and was wondering if it's normal to have slight engine shake at idle due to not stock cam. It idles at 900 and runs great with the dual 45's other than shaky idle. All mounts everywhere are new

[Markster]

I also run a .292 on my  Dellorto '40s and I do have a bit of a shake at idle.  I think it is normal?   I also have 1mm oversized pistons.  I am in the midst of doing the interior now so I won't be turning the key any-time soon.  otherwise I would love to compare notes.

 

I got an application on my iphone (simply called "vibration") -- I have been wanting to see what is normal...  You just rest the phone on the engine and you can record.   My concern is with the higher RPM - I feel like I have a bit too much vibration.  Could be my crank shaft- long story - but gonna tackle that next.

[coloincaalpine RIP 2021]

There should be little if any "lope" using a 292.  More likely carb sync.

dq

[rcf925]

I'm using Racetek forged 9:8 CR Pistons, Balanced and blueprinted motor, Nice and smooth all the way past 7500 rpm. Just slight shaking at idle which I've tried tuning out to no avail, But can live with if normal

[zinz]

292 shouldn't make your engine idle lumpy. Check sync as suggested, but also check your ignition timing... you'd be surprised how much advance sidedrafts need, especially at low rpms.  Ignition advance tables in the Haynes and the blue binders show 18-22 degrees at 1000rpm for the Ti engine (sidedraft Solex 40PHHs and 9.3:1 compression).

 

Ed

Edited February 24, 2020 by zinz

[rcf925]

1 hour ago, zinz said:

292 shouldn't make your engine idle lumpy. Check sync as suggested, but also check your ignition timing... you'd be surprised how much advance sidedrafts need, especially at low rpms.  Ignition advance tables in the Haynes and the blue binders show 18-22 degrees at 1000rpm for the Ti engine (sidedraft Solex 40PHHs and 9.3:1 compression).

 

Ed

I think I have my timing set @ 12 degrees at idle, Maybe I'll advance some

[zinz]

Does the timing mark jump around in the timing light strobe? A worn distributor will certainly give you a poor idle. 

[coloincaalpine RIP 2021]

On timing for you people of altitude,    rule of thumb is 1 degree of advance per 1000' of altitude

[gary32]

23 hours ago, rcf925 said:

I'm running .292 cam and was wondering if it's normal to have slight engine shake at idle due to not stock cam. It idles at 900 and runs great with the dual 45's other than shaky idle. All mounts everywhere are new

Lots of questions about tuning here. Per zinz, sounds like a worn distributor.

My last stage 2 M10 was a 2.0, 1 over with 10.25 to 1 compression some porting and cc'd chamber work with a Schrick 292 cam. My timing was always around 12 degrees @ idle adding advance did not help power I was @ sea level. I think my 40 dcoe's were more focused on the 292 power band, anyway she idled smooth at 850-875 depending on temp. The only mod I made that I have yet to read about here was slightly larger than ideal idle jets with a small bleed hole in the butterflies to really dial in drivability and get the idle just right. When you open the throttle plate even a small amount the hole is no longer relevant due to air angle. My drivability and mileage was excellent.

I still have my old weber jet drill set and some solder.

[rcf925]

Finally got around to putting timing light on. Timing was at 8 btdc, Moved to 12 at idle which  smoothed idle out a bit at 900rpm. I think it's about as good as it's gunna get. My distributor is also good as I checked out before complete rebuild 1500 miles ago 

[Preyupy]

If you are at 12 deg BTDC at idle where are you at 3500 rpm?  This should be at full mechanical advance and you should be somewhere around 32-35 deg.  

[rcf925]

Just found another problem, I think idle jet on #4 is plugged. I have carb off now. On another note Starter decided to  die so now have to pull that too

[Slavs]

Higher duration cams = rough idle. The higher the duration, the lumpier it gets. Not fun for everyday driving. But, most 02s these days are not everyday drivers. The factory used the stock cam on the Ti and Tii for a reason; to keep it smooth and yield acceptable MPG.

[rcf925]

I plan on pulling carb off car today and going through it. I'm pretty sure idle circuit has a blockage somewhere on it cause cyl #4 Idle air screw does nothing when turning and I can even take it out when car is running, No change. Other 3 idle air screws work fine. Car does idle at 900 rpm and doesn't shake too much at idle but I'm pretty sure when I figure blockage out it will smooth out, Other than the idle issue car runs awesome

[2002Scoob]

#4 eh? ya check for vacuum leak or brake-booster issues?