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Newbie needs help with "surging" at crusing speed...

  • Thread starter Thread starter scharfg
  • Start date Start date
S

scharfg

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Hi there I went on my first long ride (~1700km in 2.5 days) with a new to me '83 gs750ES. I think the bike had been sitting for a while (writen off and re-built) and I did notice this same sensation at the tail end of my test ride but chalked it up to the fact that I have never riden this type of bike before and my new found fever.

When I am at cruising speed and hold a constant throttle setting (ie: 120km/hr at ~4000rpm) the bike will "surge" like it is running out of gas. I can stop the issue by accellerating. I don't have any problems when I accellerate up to speed from a stop or when I crack the throttle from cruising speed.

On the advice of another bike owner I put a container of carb cleaner through the tank at about 2x the recommended concentration but there was zero difference. It really makes the bike not nice to ride.

Do I need my carbs "synced" or.......?

I hope it's not a bit issue as I live in a remote town (ie: limited repair/fix options) and I want to have fun with the bike!!

I had it checked out when I purchased it and put new spark plugs in, had the tank/fuel strainers checked and it seemed fine.

It definitely seems like a fuel delivery problem.

Thanks indvance eh!
 
Sounds like it could be running rich or lean.... What pipe is on it? What filter?
Is the filter clean?
Has it had any carb work?? They might need cleaning out.

When were valves last adjusted?

You could try a high concentration of "seafoam" in one tank to see if that clears it through....

Dan :)
 
Could be your bowl vent breather tubes catching wind currents. Happened to me on the 750. Stopped, tucked 'em away better, problem solved.
 
t3rmin said:
Could be your bowl vent breather tubes catching wind currents. Happened to me on the 750. Stopped, tucked 'em away better, problem solved.
Click to expand...

I agree with this, check those hoses and make sure they are out of the slipstream. Do you have both side covers on? I've had a similar problem that I think was due to taking a run with only one side cover leading to pressure changes in the airbox at some speeds.

-/\/\ac
 
Could be the vent lines. Also check the venting on the fuel cap, petcock and for kinked fuel line.
 
Hey folks thanks for the tips.

I thought the fuel filter was in the gas tank (ie: small screens over the tank inlet tubes). Help me out here.

I don't know when the valves were done (bike came with no mechanical history).

It has the stock black pipes.

I played with the petcock when riding it in different positions but it made no difference.

It seems strange that it would be the gas cap as it only happens at cruising speed, when I need more fuel (ie: at take off or accelleration) it is fine.

I'll check my vent hosing, hopefully that is all it is.

I have both side covers on.

What's a good price for sea foam as I will have to order it via the mail.

Thanks eh!
 
scharfg said:
Hey folks thanks for the tips.

I thought the fuel filter was in the gas tank (ie: small screens over the tank inlet tubes). Help me out here.

I don't know when the valves were done (bike came with no mechanical history).

It has the stock black pipes.

I played with the petcock when riding it in different positions but it made no difference.

It seems strange that it would be the gas cap as it only happens at cruising speed, when I need more fuel (ie: at take off or accelleration) it is fine.

I'll check my vent hosing, hopefully that is all it is.

I have both side covers on.

What's a good price for sea foam as I will have to order it via the mail.

Thanks eh!
Click to expand...

If you have a yamaha dealer close by they have a liquid carb cleaner that you just put in the bowls and let it sit for a while and it is suppose to clean the carbs without taking them apart.I have never tried it but it is worth looking up.
 
Ah so where are the bowls....? (see I told ya I was a newbie!).

Also which side of the bike are those breather hoses on that I should tuck out of the way? I had a look last night but I could not see them obviously.

Tanks!
 
I would order a clymers manual to work on your bike.You can get them at e-bay or www.motorbookstore.com Then get to know your bike well and you can work on it easier.The bowls are the underside of you carbs.Go to the home page on this forum and look up the carb cleaning series and you can see what parts are what.
 
Surging

Surging

I had same problem with my 850 years ago & it was carb vent lines hanging in the wind between airbox & crankcase.If I raised them up behind airbox or lowered them behind crankcase-problem solved!If your 750 is like my 850,the 2 vent lines should be sticking up from between carbs 1&2 & between carbs 3&4.They run over the top of airbox & hang down behind crankcase.If you can't see them maybe the previous owner removed them.If thats the case I'll bet thats your problem!I hope this helps(took me forever to solve).
 
We had one at the shop I worked at that when the owner rode it the seat would flex and create a gap at the rear of the fuel tank. (There was a seat recall on them in '83, the replacment had more rubber cushions on the bottom to support it better.) The airbox inlet would get too much of a crosswind from air rushing in the gap and lean it out slightly causing some surging. Side winds would do it to mine on occaisions, after I put my Yosh pipe and k/n pods on it I never had it happen again.
 
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