Total advance

[BA80]

What is total advance? I'm thinking it's like 50ºor 52º. Base, centrifugal, and vacuum combined.

[dbeardslee]

What is total advance? I'm thinking it's like 50ºor 52º. Base, centrifugal, and vacuum combined.

According to the manual it should be 36 degrees BTDC with the vacuum hose disconnected at 5200 rpms. 31 degrees on SF's at 5400 rpms. Only the UK G model is listed in my manual, and it shows 36 degrees at 5400 rpms for that one.

[BA80]

I know that part, what I'm looking for is TOTAL advance.

[IanDMacDonald]

Just like he said Greg, 36°.

[BA80]

That is with the vacuum advance pod disconnected. With it connected it will be more.

[IanDMacDonald]

Just going off Steve's post's, I know the vacuum advance at WOT is not operating, so I'm not really sure what it is other than 35° @ (specific year) rpm's.

[3Phase]

Greg,

By the numbers in the book, it depends on the year/model but the early ones are supposed to be 52* with the later ones having a range of 50* to 53* with everything all-in.

Use one of those hand-held vacuum pumps with a gauge to work the vacuum advance so you'll know when and how much advance it adds.

My '80G had 53* all in with the stock advance pot but that changed to 52* with a different load curve when I used the one from the '79SF and it didn't ping as much.

I still dunno about the XJ11 past the 36* electronic RPM advance but with the vacuum/boost sensor should be able to make 50* to 53* possible too.

.

[BA80]

Base timing set on the "F" I'm getting about 38º at 5500 with no vacuum and about 55º with vacuum.

I have a 79 engine and I've put a NOS 2H7-11/AD131-01 mechanical advance unit on.

[crazy steve]

That's a stock advance unit for the '79. It's interesting to note that Yamaha didn't list the '78 mechanical advance as a separate part, but showed the same for both the '78 and '79. They didn't list the '78 vacuum canister separately either, only as part of the complete timing plate assembly.

Given production tolerances and fit of the various parts, I'd say you're pretty close.

[3Phase]

Base timing set on the "F" I'm getting about 38º at 5500 with no vacuum and about 55º with vacuum.

I have a 79 engine and I've put a NOS 2H7-11/AD131-01 mechanical advance unit on.

New mech advance, huh... the new mechanical advance is out of spec or the timing pointer is bent or it was removed and then put back on using the old pencil trick to find TDC.

The vacuum advance internal stop is hopelessly worn or it's from the wrong year/model if it's high by a whole degree for an extra 3* with the +2* mechanical timing error.

You can do several things:
Use a degree wheel and dial indicator to find TDC, then find out what's giving it the third degree.
Loosen the timing pointer or bend it to point to the F mark at 1,100 RPM and 36* @ speed.
Ignore it, just go for a ride and see if it pings.

.

[BA80]

I've been getting terrible mileage if I run over 65 70 mph and Having to shift down to 4th to go over 100 with the 850FD. trbig has no issue with that and I can't have his XJ running better than my XS.

I've swapped carbs and gone up 2 sizes on mains, replaced ALL ignition parts and adjusted valves.

The timing was about 5º retarded at base. We'll see if bumping that up helps.

[3Phase]

It sounds like you need to find TDC so you can work out what's going on with the fire and the fuel after you know the timing pointer and the marks aren't lying to you.

.

[BA80]

Checked TDC today. The pointer is about 5º off.

[3Phase]

Checked TDC today. The pointer is about 5º off.

Was it 5 degrees Gifted or Short Bus?

Set the timing with the vacuum gauges when you synchronize the carburetors: max vacuum then back off a few degrees. Take it out for a check ride to get it hot. If it pings, move the timing a few short seats or a backrest or two.

.

[CaptonZap]

Was it 5 degrees Gifted or Short Bus?

If it pings, move the timing a few short seats or a backrest or two.

.

Scott, you must have had a tough childhood.
Which bus did they make you ride?

CZ