Desmogged 74 struggles on cold starts (2 Viewers)

[Matt1260]

just sulking and drinking at this point

 

[Vintij74]

Maybe you would like a double IPA at this point? Knee Deep Brewery is a fav.....Breaking Bud lifts the spirits

 

[Matt1260]

Just found a test from more dizzy educational sites to test resistance between the wire on the side of the distributor and the engine block/points.
Performed the test and discovered the POINTS have no continuity when CLOSED unless I press them together real hard.

The POINTS are CURSED.

No wonder there's no spark.

 

[C6H12O6]

ALL POINTS are CURSED.

Fixed it for you.

 

[Matt1260]

Apparently the .016 gap was not allowing the points to close perfectly even though they looked closed. Wish someone noted that among the bazillion posts about points issues on this forum

 

[Matt1260]

DAY 7:

Fixed the points, double checked gap and that they closed properly. This time the engine fired up properly on cold start. However, vacuum weirdness remains and the timing once again has to be at ~30° btdc @ 650 RPM

How can the combustion be so slow or the flame front take so long that the ignition has to be so far in advance? Still trying to sort this out.

I will be taking it to a specialist once I get the chance. Hopefully next week.

 

[JohnnyC]

Again... are you running vac retard dizzy or vac advance?

 

[Solace in Solitude]

Again... are you running vac retard dizzy or vac advance?

It’s in his video Johnny... “aftermarket vacuum advance”

 

[JohnnyC]

Are you timing it with the vac plugged?

 

[Matt1260]

Are you timing it with the vac plugged?

As in capping the port? No. I read from some instructions from MAF i think to "unplug" vac hoses while setting the timing... which I've done.

 

[thebigredrocker]

Have you re-tightened your intake manifold and carb base nuts?

Did you have your manifolds planed together before installation?

Did you use a Fel-Pro manifold gasket or copper coat?

Does the bottom of your intake manifold have a heat provision?

 

[Matt1260]

Have you re-tightened your intake manifold and carb base nuts?

Did you have your manifolds planed together before installation?

Did you use a Fel-Pro manifold gasket or copper coat?

Does the bottom of your intake manifold have a heat provision?

Manifolds were re done at a shop and powder coated. I'm using the thick gasket from SOR.
The exhaust manifold has the heat flap removed and a gasket. I know some have blocked it off. the intake provisions I am not aware of.

 

[Solace in Solitude]

As in capping the port? No. I read from some instructions from MAF i think to "unplug" vac hoses while setting the timing... which I've done.

Unplug the vacuum advance hose from the vacuum advance module... But, plug the hose (pencil works well), or you have a vacuum leak.

 

[thebigredrocker]

Matt I wonder if a small part of your issue is poor fuel atomization. Following are quotes from two legit cruiserheads.

My guess is that you do not have a manifold "heating plate" installed. This is a plate that covers up the concavity where the exhaust manifold originally connected to the intake. In the OEM configuration, the exhaust warmed the intake manifold. This is important in cold weather. The fuel needs to be warm to properly atomize. That's why you have to choke a cold engine. Since the fuel does not completely vaporize when it is cold, but tends to remain in small droplets, you have to put more fuel in to get enough to burn.

The heat of the exhaust manifold warms the intake tract so that very shortly after start up you no longer have this problem. But since you have a header instead of the OEM mani, you don't have this heat source.

Back to the plate... This plate is bolted on to turn the concave area into a shallow chamber. There are a pair of fitting in the plate. These connect to yout heater hose which leaves the engine at the back/top of the head. The warm coolant form the engine is routed through the chamber. This warms the intake and solve the poor cold weather performance.

The coolant does not warm the intake as rapidly as the exhaust would. But it is pretty darm quick.

In addition to poor warm up times, without any source of heat to the intake manifold, you can experience continued poor performance. In some situations you wil never attain optmum conditions for fuel atomization. In fact under some conditions you can actually experience carburetor icing

Air expands when it enters the intake tract (lower pressure). expanding air cools. The fuel cools as it vaporizes (just like sweat evaporating off your skin). Some heat source is normally needed to counteract this. On a straight six engine, with the intake having minimal contact with the warmer sections of the motor this heat source has to be specifically provided.


Anyway, if you don't have this plate in place, this is your problem. Check the MAF and SOR catalogs. It is only about a $35 kit IIRC



Mark...

F engines don't make much power, so don't make much heat. With no heat to the intake manifold and the AC expansion valve vaporizing liquid into the manifold, it's gonna be cold.

Wait, did he say AC expansion valve? Yes, a carburetor is an AC expansion valve that is vaporizing gasoline instead of freon and does it across a pressure drop, pulling heat of the surroundings to accomplish that.

Install the Hot water heat riser

and let us know how much better it works then.

So you removed the heat flapper. Did you block off the heat riser passage?
You did start this thread off stating fuel isn’t reaching the cylinders when cold. At some point you might consider reinstalling a flapper.

 

[C6H12O6]

Current link: Man-A-Fre Fluid Heat Riser Kit F and 2F Engines

Not that you need it, as you don't have headers, but thought others might benefit having this part of the thread. Like me.

Along these lines, though, is the flapper working on your air cleaner for the hot air intake?

 

[Matt1260]

The flapper was removed by a PO. There is nothing blocking the heat riser passage. My research into that while assembling seemed to reveal that it was ok without it....

Matt I wonder if a small part of your issue is poor fuel atomization.

My friend, the aircraft mechanic, immediately noticed the fuel "not atomizing" when he was looking into the carb and watching it.
How does one rectify that?

Along these lines, though, is the flapper working on your air cleaner for the hot air intake?

no air cleaner flappers... curious about what might be missing.. you have a picture of yours to compare it with?

 

[thebigredrocker]

Do you recall if your aircraft mechanic was seeing fuel at idle? If so, that’s an indication your idle circuit isn’t working as designed. At idle the carb should appear dry. Idle fuel shouldn’t be visable.

As for your no flapper setup, I would think you may consider adding one. At startup the bimetal spring positions the flapper so it shoots hot exhaust to the intake. The spring eventually gets so hot it expands and moves the flapper to block off the intake so it doesn’t get too hot.

In reading Mark W’s explanation, I’m guessing your setup is taking way to long to heat the intake but eventually overheats the intake due to constant exposure to exhaust gasses.

 

[thebigredrocker]

The major head scratcher is why is the vac gauge needle jumping. If you get to a point where you suspect an intake gasket leak, you might want to have both manifolds planed by a machine shop while bolted together.

I've never had a problem with any brand of head gasket. I've installed a lot of them. For manifold gaskets I won't use anything but Felpro.


Mark...

Not sure why Mark W is so adamant on Fel-pro only. My research led me to believe his advice is worthy of following so that’s the route I went.

 

[Matt1260]

Do you recall if your aircraft mechanic was seeing fuel at idle? If so, that’s an indication your idle circuit isn’t working as designed. At idle the carb should appear dry. Idle fuel shouldn’t be visable.

He said it looked like this at idle:


I just looked at it again myself it looks like its atomizing now...20171127_221024000_iOS.MOV

 

[Matt1260]

Finally solved the advanced timing problem. FINALLY. And it's actually quite stupid.
Turns out that setting the timing at 650 RPM, which is what various instructions say to do, is incorrect. The FSM says to set idle to 500 and to 650 for USA models. I decided to try things at 500 RPM. Bingo. Running real nice at 10 btdc. The timing was basically correct the whole time.
So I guess the F-engine is not a USA version or something? Whatever.

So now its just down to the vacuum problem. Found out the brake booster does have a little bit of a leak there. But the lack of steadiness is still due to something else.