Can't get over 80 mph

[gcraig]

I have a 83 GS1100L I got it up to 80 miles an hour and the engine acted like it ran out of gas. I started to slow down when I got to about 55 mph it started to run fine. I have changed out the stator and rectifier, spark plugs. I know I need to change out coils because the number 4 wire has a couple of small cracks. I can run the engine through 1st to 4th gears to about 7,000 7,500 rpms and seams to have power does not miss. But when I get to 5th gear and up to 80 mph it startes to shut down. I was told when I bought the bike about month ago the carbs where rebuilt with in the last year. Any suggestions thanks.

[bwringer]

Let's see, how we do we count the ways you can get fuel starvation?

Fuel tank venting (clean air passages in cap) To diagnose, find a way to loosen the cap a bit and carefully go for a ride. Or

Clogged petcock (usually rust scale from tank)

Clogged fuel filter or filter screens (on petcock or in carbs)

Collapsed, kinked, incorrect, or clogged fuel line

I'm sure there are more...

[Anonymous]

Let's see, how we do we count the ways you can get fuel starvation?

Fuel tank venting (clean air passages in cap) To diagnose, find a way to loosen the cap a bit and carefully go for a ride. Or

Clogged petcock (usually rust scale from tank)

Clogged fuel filter or filter screens (on petcock or in carbs)

Collapsed, kinked, incorrect, or clogged fuel line

I'm sure there are more...

That's a good start. Sounds like fuel starvation to me also.

Get those plug wires replaced also, cracks aren't good.

[scotty]

ill go with fuel also

[gcraig]

Ok I'll give it a try its raining here today so it might be Sunday before I can try it. I also use the highest octane gas should I use regular gas since they did not have the this high octane gas back in the 80's

[Anonymous]

Actually high octane has been available since the early 1900's, avgas is 100 octane IIRC. But there's no need to buy premium if it doesn't ping on regular.

Like the others said, sounds like fuel starvation.

[Sandy]

Check for a rotted, cracked, or leaking petcock vacuum line. Bike will accelerate great but gradually at high throttle load will just run the carbs out of gas. If you have a prime setting try it there and see if the problem goes away.

[redliner1973]

Try draining the gas from the tank, removing the petcock. there are 2 tubular 'screens' ( one for main, the smaller for reserve). may try to clean those up with carb cleaner, and any rust you may find in the tank. pull it out and see what it looks like.

[Don Lobacz]

Do you have the stock airbox installed? Are the boots intact and sealing completely? Is there a good airfilter installed and is it sealing against the top of it's chamber?

[earlfor]

Fix what Don suggested first. There could be additional problems, but without those things fixed, nothing you can do will make it run right.

Earl

Do you have the stock airbox installed? Are the boots intact and sealing completely? Is there a good airfilter installed and is it sealing against the top of it's chamber?

[KEITH KRAUSE]

Also make sure the two floatbowl vent tubes are clear and not kinked.

[gcraig]

Sorry for taking so long to get back on this but work has taken first place. Ok I checked the gas tank cap and the vent hole is clear. So now I have removed the pet cock off the tank. The filter tub is clear and clean (no rust). With it set to ON and RES; I can blow through the big outlet but can not suck air. When I suck and blow on the smaller tub I can here the diaphragm moving and no air leaking. When I set it to PRI I can blow and suck air. So is the pet cock ok or do I need to rebuild it.

[Anonymous]

Sounds like the petcock is working properly, but try what sandy suggested. Run it on pri & see if the problem goes away. Did you check to see there were no vacum leaks between the carb & the petcock?

[gcraig]

I have not looked for the vents between carb. Ok I know this is going to sound like I do not know what I'm doing but how do I check the tubes between the carb. Other then looking for cracks is there something eles I need to do. Is the smaller tube on the petcock a vacum line.

[KEITH KRAUSE]

Some good advice above. Yes, your petcock sounds fine. Your description/symptom is a little odd.
You say the bike will run good in 1st through 4th gear up to 7,500 rpm's. 4th gear at 7,500 rpm's is 100+mph. But if you shift into 5th gear and reach 80 it will start shutting down? Seems like the engine would be demanding more fuel in 4th @ 7,500 than in 5th going 80. I think the throttle would actually be a little more open in the 4th gear situation?
Since you've checked the tank venting and petcock, do the easiest things next. Make sure the air box sealing is GOOD and the airbox boot clamps are tight. REPLACE the vacuum line with the correct size and be sure the fuel line is 5/16". Test and go from there. Hopefully your carbs were rebuilt right.