Carburetor jet sizes...

If it's mechanical, electrical or just downright confusing, this is the place to find and share answers.
User avatar
ssava
Registered Member
Posts: 514
Joined: 22 Sep 2017, 13:13
Location: Franklin, TN
Contact:

Re: Carburetor jet sizes...

#51

Post by ssava »

Smilodon wrote:
12 Jan 2020, 19:09
If the elastomer on your damper has failed, the ring can turn, relative to the crank. That means the timing marks won't line up any more, but it also means the counterweight on the damper is not in the right place, and can snap your crank.

Best to find TDC on your #1 piston and verify your timing marks, then set things correctly. Dealing with a bad damper, or misadjusted timing can both destroy your engine very quickly. Timing is not about guesswork, and this isn't something that 'no one's figured out'. Better to just make sure things are right, so you can enjoy your car for many years to come! =)
Thank you. We did find it (with my cousin Chris who's an amazing mechanic) via the first piston. We're sure of it.
The problem, in my opinion, is the timing curve of the distributor.
But my son is having too much fun "tinkering" and... well... that's the point of us getting the car. So I'm going to let him keep playing.
"Esmerelda"
'67 Cougar XR7 purchased September, 2017 to work on with my twin (14) year old boys
Franklin, TN

User avatar
xr7g428
Site Admin
Site Admin
Posts: 4852
Joined: 23 Dec 2010, 21:02
Location: Cave Creek, AZ
Contact:

Re: Carburetor jet sizes...

#52

Post by xr7g428 »

Okay so you have verified that at TDC on cylinder 1 (front cylinder on passenger side) the timing pointer is aligned with the 0 line one the damper. Next disconnect and plug the vacuum line going to the distributor. Loosen the hold down clamp, and rote the distributor so you have 6 degrees advance at another 650 RPM. This is the factory spec. Anything less will make it run like crap and overheat. Then connect the vacuum line. The timing should not change. If it does you have the vacuum line connected at the wrong place. This verifies that initial timing is working properly.

Next, disconnect and plug the vacuum line again. Now it’s time to verify mechanical centrifugal advance. The idea is to observe the change in timing as RPMs increase. As you increase RPM note the change in advance. Some where around 2800 RPM it should stop advancing. You will probably see something like 32 to 38 degrees. If so, your distributors mechanical advance is working properly.

The vacuum advance should be connected to the ported vacuum port on the carb. It is on the passenger side of a Holley or the upper of the two on the front of an Edelbrock . your first driving test is with it disconnected and plugged.
Bill Basore, Editor / Publisher
Legendary Cougar Magazine
Currently in the Cat House
'67 XR7 GT 390 4 speed, AC, AM FM, Lime Frost Green
'68 XR7-G 428CJ C6, Tilt-Away, AM, Black Cherry
'68 XR7-G 390 4 speed, Sunroof, Cardinal Red
'68 XR7 GT-E 427 C6 AM Cardinal Red
'68 XR7 resto mod 351W, soon to be AOD, Black Cherry

User avatar
xr7g428
Site Admin
Site Admin
Posts: 4852
Joined: 23 Dec 2010, 21:02
Location: Cave Creek, AZ
Contact:

Re: Carburetor jet sizes...

#53

Post by xr7g428 »

Time for road tests. The engine needs to be fully warmed up. Hopefully you won’t have any pinging. Then you can try advancing initial or base timing by 2 degrees (8). Keep advancing the timing in two degrees increments. Most likely it will start pinging again at about 15 degrees or less. Once you find the threshold, adjust back by a degree or two.

Vacuum advance is only intended to fine tune efficiency at part throttle cruise. Reconnect the vacuum line and road test. If you get pinging when you go up a slight grade or tip on the throttle it means you are getting too much advance. Tighten the spring by adjusting the screw inside the vacuum canister.
Bill Basore, Editor / Publisher
Legendary Cougar Magazine
Currently in the Cat House
'67 XR7 GT 390 4 speed, AC, AM FM, Lime Frost Green
'68 XR7-G 428CJ C6, Tilt-Away, AM, Black Cherry
'68 XR7-G 390 4 speed, Sunroof, Cardinal Red
'68 XR7 GT-E 427 C6 AM Cardinal Red
'68 XR7 resto mod 351W, soon to be AOD, Black Cherry

User avatar
ssava
Registered Member
Posts: 514
Joined: 22 Sep 2017, 13:13
Location: Franklin, TN
Contact:

Re: Carburetor jet sizes...

#54

Post by ssava »

Thank you Bill. This is really helpful.
We have done the timing with the engine warm. Here's what we got.
image01.jpg
image01.jpg (68.8 KiB) Viewed 95 times
This was with an initial advance of 10 degrees and NO vacuum advance.

She drove fine during normal driving, but knocked and pinged on load and on highway.
So, we retarded it and added the vacuum advance.
After some tweaking (-10 degrees retarded and vacuum advance), we had a great run. She had tons of power and did NOT knock and ping.

I thought it was fixed, until I started her up the next day. She couldn't make it up the driveway.

Thinking it was just that she wasn't warm enough, we let her warm up the next day and tried again. But she still barely ran. Kept sputtering and dying.

We advanced her a bit and it helped some. But not enough.

I truly believe it's the distributor that's causing these problems. And if we had one with a better curve, we could move her back to say 6 degrees as you mentioned.

When my son gets home from school today, we'll try your notes.
Thank you again
"Esmerelda"
'67 Cougar XR7 purchased September, 2017 to work on with my twin (14) year old boys
Franklin, TN

User avatar
xr7g428
Site Admin
Site Admin
Posts: 4852
Joined: 23 Dec 2010, 21:02
Location: Cave Creek, AZ
Contact:

Re: Carburetor jet sizes...

#55

Post by xr7g428 »

You have to sort out one system at a time. Disconnect and plug the vacuum advance then try it at 6 degrees. Don’t connect vacuum until mechanical is sorted.
Bill Basore, Editor / Publisher
Legendary Cougar Magazine
Currently in the Cat House
'67 XR7 GT 390 4 speed, AC, AM FM, Lime Frost Green
'68 XR7-G 428CJ C6, Tilt-Away, AM, Black Cherry
'68 XR7-G 390 4 speed, Sunroof, Cardinal Red
'68 XR7 GT-E 427 C6 AM Cardinal Red
'68 XR7 resto mod 351W, soon to be AOD, Black Cherry

User avatar
ssava
Registered Member
Posts: 514
Joined: 22 Sep 2017, 13:13
Location: Franklin, TN
Contact:

Re: Carburetor jet sizes...

#56

Post by ssava »

Okay. Last night, we set it to 6 degrees at idle and then put the vacuum advance back on.
She definitely ran better on the streets, but didn't get a chance to try her out on the highway.
Will try today.

Any advice on a new distributor?
Any recommendations?
"Esmerelda"
'67 Cougar XR7 purchased September, 2017 to work on with my twin (14) year old boys
Franklin, TN

User avatar
xr7g428
Site Admin
Site Admin
Posts: 4852
Joined: 23 Dec 2010, 21:02
Location: Cave Creek, AZ
Contact:

Re: Carburetor jet sizes...

#57

Post by xr7g428 »

Your current distributor is working properly at least as far as you pinging issue. Are there other problems with it?
Bill Basore, Editor / Publisher
Legendary Cougar Magazine
Currently in the Cat House
'67 XR7 GT 390 4 speed, AC, AM FM, Lime Frost Green
'68 XR7-G 428CJ C6, Tilt-Away, AM, Black Cherry
'68 XR7-G 390 4 speed, Sunroof, Cardinal Red
'68 XR7 GT-E 427 C6 AM Cardinal Red
'68 XR7 resto mod 351W, soon to be AOD, Black Cherry

User avatar
xr7g428
Site Admin
Site Admin
Posts: 4852
Joined: 23 Dec 2010, 21:02
Location: Cave Creek, AZ
Contact:

Re: Carburetor jet sizes...

#58

Post by xr7g428 »

Also, you need to test first with vacuum disconnected and plugged. I suspect that one problem may be that you are inadvertently running manifold vacuum instead of ported vacuum.

The factory manual has a chart with both mechanical and vacuum specs. Once you get mechanical advance dialed in you can start on vacuum advance.
Bill Basore, Editor / Publisher
Legendary Cougar Magazine
Currently in the Cat House
'67 XR7 GT 390 4 speed, AC, AM FM, Lime Frost Green
'68 XR7-G 428CJ C6, Tilt-Away, AM, Black Cherry
'68 XR7-G 390 4 speed, Sunroof, Cardinal Red
'68 XR7 GT-E 427 C6 AM Cardinal Red
'68 XR7 resto mod 351W, soon to be AOD, Black Cherry

User avatar
ssava
Registered Member
Posts: 514
Joined: 22 Sep 2017, 13:13
Location: Franklin, TN
Contact:

Re: Carburetor jet sizes...

#59

Post by ssava »

xr7g428 wrote:
14 Jan 2020, 09:29
Your current distributor is working properly at least as far as you pinging issue. Are there other problems with it?
The distributor is "frankensteined" from the original one and the new one and, honestly, I just would prefer something I know works well.
I want to stop wondering if the problem is the distributor and I'll never get rid of that doubt with this one.

Also. We've NEVER run vacuum advance. So this is our first time.
We're running it from the drivers side port off the Edlebrock carb.

We've also tuned it using the allen wrench to the best of our ability.
"Esmerelda"
'67 Cougar XR7 purchased September, 2017 to work on with my twin (14) year old boys
Franklin, TN

User avatar
ssava
Registered Member
Posts: 514
Joined: 22 Sep 2017, 13:13
Location: Franklin, TN
Contact:

Re: Carburetor jet sizes...

#60

Post by ssava »

Update:
Took her on the highway this afternoon and she did great.
The ONLY knocking we heard was at 90mph going uphill.

Idle has been up at about 1,000 rpm in park.
It goes down to about 700 rpm in drive.

What is the best for that?
"Esmerelda"
'67 Cougar XR7 purchased September, 2017 to work on with my twin (14) year old boys
Franklin, TN

Post Reply