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.

 

[KEITH KRAUSE]

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.

If you mean the two floatbowl vent lines, just make sure they are clear and not kinked. You should be able to blow into them. Cracking won't stop the venting ability but water may seep in if you wash the bike.
The smaller nipple/line on the petcock is for the vacuum. It goes to carb #2.

 

[gcraig]

It's been raining here so I have not been able to work on the bike (no garage). I had to order an o-ring for the petcock it should be here by Friday or maybe Thursday. Planning to ride to the Woodland north of Houston this weekend. I did pull the air filter box and when I looked in the connection to the carb. there was a lot of gas on the air box connector to the carb. Any ideal how the gas could accumulate there. I have had the gas tank off the bike for about a week but before that it sat for about week with the tank on the bike. All of the connector look good and the clamps where all tight. I did find out that I have a K&N filter# G-103A4 or SU-120. I have read about having to re-jet the carb. if you put a K&N filter. If this is true then how do I make sure the carb. are jetted correctly. Sure hope I do not have to take the carb's apart for this I sure hate to have to buy a carb. kit.

 

[KEITH KRAUSE]

I don't think you need to re-jet for the K&N filter.
When the bike is running right, take some plug reads to be sure. If the plugs look lean, we'll help you with the jetting. I doubt it would involve more than a step up on the mains and a little richer on the mixture screw settings.
If you've got gas in the airbox, it would be the petcock, or a leaking float needle valve, or an o-ring/gasket for the float needle valve seat, or a float not operating correctly or the float level needs adjusting.
Your previous test of the petcock sounded like it was good. To be sure, take the fuel line off and vacuum line off the carbs and plug/pinch them closed. Let the bike sit as it did and check to see if ANY gas collects. If it's easier to do, leave the lines connected at the carbs and get some extra lines and hook them up to the petcock.
If it's the carbs, you may be lucky and just find some dirt interfering with the float needle. If there's a deep enough groove worn around the tip of the valve, or the spring is weak, replace the valve. Also check the o-ring or gasket for the valve seat. The floats should move smoothly and float in a bowl of gas. After being held under they should still float and not have any gas inside them when you shake them. If all this checks OK and the petcock is not leaking, you would need to check the float height. This would require taking the carbs off.

 

[gcraig]

I checked the vacuum and fuel hose there ok. I have not done the bowl check yet. I think I?ll wait until the middle of winter to do the bowl check. Well I have the air cleaner and petcock back together. Who ever had it be for me took a hose and cut it in half and screwed it to the top of the air cleaner to seal it to the air box. I cleaned the K&N filter and replace the rubber hose with weather strip and put the air cleaner back on the bike. Made sure it sealed. I got to ride to work this morning and go up to 80 ? 85 and held it there for a short time short road, it kind of missed fire about 75 and then got to 80. It did not shut down it kept going Maybe this weekend if its not to cold I will test it more. I think the next thing is to replace the coils to make sure the plugs are firing well.

 

[duaneage]

test

test

try this

Take it up to around 70 for a minute or so, then crank it up until you have your acceleration problem. As soon as it begins to miss or bog or whatever, kill the engine and coast to a stop .

Pull a plug and see what they look like. Fouled plugs indicate a coil problem, white plugs indicate a lean condition. Does the engine ping if you accelerate from 45 - 60 in 5th gear? Fuel delivery problems will cause pinging at low manifold vacuum, not just high speed.

Do the plug test on a clear road and make sure you can safely pull over and check the plugs. I did this for Holley carbs to get the jetting and secondary opening right, also power valve testing.

These things are nothing more than overgrown lawnmower engines on two wheels after all.