engine and drivetrain Timing...something Doesn't Make Sense Here

[peterschop]

The car has a pertronix unit.  - Do I measure the gap the same way as points?

 

Ordered a dwell meter - should have soon.

 

The pertronix has a preset gap. Once set up, there is no need to change the gap.

['76mintgrün'02]

The gap between the Ignitor module and the ring is supposed to be set to .030"

[kbmb02]

I've got some fiddling to do, but currently I can't get the idle to decrease below 1500 RPM (and the car is pretty rough below 1500rpm). 

 

A few thoughts: If, as it appears, you're running a BIG duration, self-oiling type* Schrick camshaft (*they were - I believe - in the 316 degree range or higher), then you may find it rather difficult to achieve a decent / satisfactory running condition at idle. You can set 'all-in' max ignition timing upwards of 36 degrees if the available fuel octane rating is up to the compression ratio of the engine build. -KB

[bruno615]

A few thoughts: If, as it appears, you're running a BIG duration, self-oiling type* Schrick camshaft (*they were - I believe - in the 316 degree range or higher), then you may find it rather difficult to achieve a decent / satisfactory running condition at idle. You can set 'all-in' max ignition timing upwards of 36 degrees if the available fuel octane rating is up to the compression ratio of the engine build. -KB

 

Solid point.  I guess, I'm just unsure whether the no-so-great-idle is as good as it can be, or if I have room for improvement.  I get some fairly drastic shaking and the like with RPMs below 1500rpm.  Sounds like I'll go for that timing strategy and see what that corresponds to at idle.  

 

I'm thinking I should adjust for optimal high RPM, and then for idle.  I should then get a pretty solid idea if it's my distributer curve/range or cam related.

Edited October 14, 2014 by bruno615

[bruno615]

Looks to me like the notch is not lined up at TDC. When I twist the orange bit with my finger, movement stops at the TDC mark (exactly). Overall, I can twist is approximately 15-20 degrees.

My assumption is that this is wrong?

[Hans]

which orange bit are we talking about here? The rotor?

[bruno615]

Yes, sorry, the orange bit = the rotor I thought that was the name of it, but wasn't sure.  I imagine this rotor wiggle is the advance mechanism.

 

Side note.  I further retarded the timing to 31 degrees at 3k rpm.  Car does not seem to like it at all.  Lots of spitting, even while driving below 2.5k rpm.

Edited October 20, 2014 by bruno615

[Hans]

the rotor should turn a bit and then snap back. That is the advance function. How did you set at 31?

Maybe try a bit more  if your motor is modded: I've heard 36 for race motor .

 

Or perhaps you've got an air leak/carb adjustment issue.

[zinz]

Is this poor running a new problem? Your 1st post is still lacking in a few details...

 

Is this a dual carb'd engine?  If so, are they properly synched? Improperly synched carbs will never idle well.  Have you confirmed there are no air leaks? (spray carb cleaner around the carb bases and throttle shafts while the engine is idling.  Any change in idle speed will indicate a leak).

 

My 40mm Solexes with a 292 cam and an IE dizzy runs best at around 33-34 degrees at 2000rpm. I have poor idling and low speed transition at anything less than 30 degrees at 2000rpm.  I was running an original Ti dizzy at one point (came to find out it needed to be rebuilt)  and it didn't use this much advance, so you're mileage will vary... Every modified engine will need it's own particular tune.

 

Spitting carbs sounds like a lean condition, non-synched carbs, or not enough advance, or a combination of each.

 

Ed

[Hans]

AS I recall the original ti was set at 39 deg total advance, but that may have been with fuel of the day. I spent a lot of time fiddling with twin webers chasing similar problem only to find that my problem was not enough advance (thanks to Jeff Ireland). Did the total advance setting - about 33 deg all in - and things improved immediately. In this case, maybe the  advance is close enough, and real problem lies with air leak or carb adjustment. That said, I can't imagine how the car would run on 65 deg advance.

[bruno615]

Is this poor running a new problem? Your 1st post is still lacking in a few details...

 

Is this a dual carb'd engine?  If so, are they properly synched? Improperly synched carbs will never idle well.  Have you confirmed there are no air leaks? (spray carb cleaner around the carb bases and throttle shafts while the engine is idling.  Any change in idle speed will indicate a leak).

 

My 40mm Solexes with a 292 cam and an IE dizzy runs best at around 33-34 degrees at 2000rpm. I have poor idling and low speed transition at anything less than 30 degrees at 2000rpm.  I was running an original Ti dizzy at one point (came to find out it needed to be rebuilt)  and it didn't use this much advance, so you're mileage will vary... Every modified engine will need it's own particular tune.

 

Spitting carbs sounds like a lean condition, non-synched carbs, or not enough advance, or a combination of each.

 

Ed

 

I swapped in a motor that I purchased here on the forums.  As stated previously, the motor is on the aggressive side, it was done to Korman stage 3 specs, including a 316 cam, ported and polished valves, and dual DCOE 45 sidedrafts (38mm choke).  It was inherently rich from the moment I started it up, and I have been tuning it to follow a better AFR curve.  I had a mechanic do a "quick tune" on it when I first got started, as at that point, it was on a much smaller exhaust.  At that time, it was quite rough and spit quite a bit.

 

I found that more advance caused the engine to run significantly better, cutting down on spitting, and causing the engine to run smoother.  When I dial back the advance, it starts to get rough below 1500rpm.  My AFR lambda at idle is 13-14. 

 

Compression is good, 195 PSI on all 4 cylinders.

 

My next moves:  

• Check for air leaks
• Map the distributer advance curve (I have a feeling it might be off)
• Regardless, set it back to more advance than I currently have.=

[Guest_anonymous]

Your engine was built to run, not idle

[bruno615]

Your engine was built to run, not idle

 

Haha, yep, that it does.  Just trying to see if it's possible to be more happy at idle/down low in the RPM range.

[Hans]

perhaps Mr. K might have a suggested target for total advance. The other thing I discovered on my set-up was a bad plug wire, which caused intermittent misfire which I blamed on the carbs. As others have said, most of your carb problems are electrical.

[bruno615]

I added 1 degree to total advance (from 34 to 35 degrees), which I found resulted in having 11 degrees at 1k rpm vs 6.  The car idles much more smoothly, with minimal to no spitting with the extra advance at idle.  Looks like either I keep this setting or I switch my distributer curve.  I do not remember off of the top of my head which distributer I have (I want to say it's a 003).