Timing problems on 1981 GS750

[themax]

I can't get the bike to run, but it backfires and sputters out of the carb. I checked all of the cam timing marks and they seem to line up. I changed the jetting on the carb from a 112 to a 120 and added a Vans+Hines header. The previous owner changed the head on it, is there a possibility that I can change the Advance/Retard settings, overriding the sensor that comes standard on the bike?
:?

Any help would be appreciated

[rphillips]

Have you disasembled any of the ign. parts? I think if the spark advancer thing is installed backwards, 1&3 will fire when 2&4 should fire & 2&4 will fire when 1&3 should fire. Happened to me on a GS1100 in 1982, but I can't remember all the details of how it happened.

[themax]

Hey there I just went out and took each spark plug out and put my finger over the spark plug hole and turn the bike over there wasn't enough to push my finger of the hole on all four cylinders.This can't be a good sign.

[rphillips]

Possible valves way too tight, or cams out of time.

[themax]

Good point about the valve's too tight. Can the crank be a 180 DEG out? The bottom end pointer lines up to the "T" 1&4 and the 1 arrow is at the joint where the valve cover meets the head. There is 20 cam chain pins between the 2 and 3 arrow indicators located on the cam gears as per indicated out of the book.

[Nessism]

Can the crank be a 180 DEG out?

Yes! (don't ask how I know).

[chef1366]

With the timing mark at TDC 1&4 and the cams are where you mentioned earlier check and see if the #1 piston is all the way up. Use a screwdriver. Move the crank and see if the screwdriver is on the way up while reaching the 1&4 mark. You should also see the top of the piston through the spark plug hole. If the piston isn't all the way up the setting is 180 off.

[themax]

Hi there every one thanks for the help it is very much appreciated.The number one piston is to the top and the "T" 1&4 is indicated by the pointer and the timing marks on the cam are good.Maybe the valves are to tight?

[chef1366]

Do a compression test. If it's good try swapping the coils.
With the timing marks as I stated earlier see if the #1 valves are closed.

[txironhead]

Wouldn't too-tight valves throw off a compression test? Might as well check the valve adjustments first.

[chef1366]

Wouldn't too-tight valves throw off a compression test? Might as well check the valve adjustments first.

You're right.:-D

[themax]

Hi there I checked the exhaust and intake valve clearances and found them very tight.Reset the clearances to .004 for all.But unfortunately I did not get to the changing of the coil wires and compression test perhaps this evening.

[themax]

Hi there everyone Well I Did a compression check and found 30 LBs 1st cyl 0 in the 2nd 20LBs in the 3rd 30 in the 4th added oil to all the cylinders.1st jumps to 60 LBs the 2nd at 80 Lbs 3rd at 40 and 4th at 90 lbs.I guess the cylinders need honing.My cams are in bad shape dose anyone where I can get the the cams ground under size and then built up again???I also need a top end gasket kit.