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Bad hesitation when cruising--whats going on?

  • Thread starter Thread starter GSstiny
  • Start date Start date
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GSstiny

Guest
I took my 79 750 for my first fairly long backroad run this weekend, about 175 mi one way. Im having a bad hesitation problem when cruising above 50mph for more than 2 or 3 miles. The bike starts up easy, idles perfect, around town its fine, doesnt flood out or anything. It doesnt have any trouble getting up to cruising speed and will maintain it once you get there. The problem is, when you roll on the throttle, nothing happens. Downshifting doesnt help, and the clutch isnt slipping because the RPM doesnt increase. Light to light or around town acceleration is fine, it only happens on long cruises.

I recently re-added the carb vent hoses because the #2 carb dumps a little fuel occasionaly, so my first thought was to pull those back off, but it doesnt help. The most likely culprit is fuel. I had always run 89 octane before, but I accidentally put 87 octane in it a couple weeks ago and didnt have any problem, so I put some more in on the way out of town. Ive since added some 93 to try to even it out and once it got down to 1/2 tank Added 89. I would think that if it was a spark or carb mixture problem it would happen all the time, not just in specific circumstances. The headers arent bluing, so it isnt running lean, and there isnt any black smoke to indicate a rich condition. Heck, I got almost 60mpg, so i doubt its a carb problem.

Does it sound like bad fuel to you all??
 
question

question

do you have the stock air box and stock jetting?
 
I'd also check the petcock to make sure it is flowing sufficiently.

Kim
 
It has stock airbox, filter, jets, and exhaust


Dr Shifty, you might be on to something, I checked it on prime, its ok, then I put it back to run and went for a ride and I couldnt get it to hesitate, maybe the petcock was in between positions or something.
 
Just curious, but do you have an in-line fuel filter? I've heard both positive and negative things about them. If you do, you may want to remove it and replace it with straight fuel line and see if it helps.

Brad tt
 
Ok, thought I had it fixed but Im still having trouble.

I dont have a fuel filter of any sort. I checked the petcock, all is well. Ive run 2 tanks of 89 octane through it so all traces of 87 are gone. I pulled the plugs and they look great, no fouling to speak of. The only thing I can think of is dirty carbs, but I still dont understand why it has trouble cruising and not around town, unless a main jet is gunked up or something. Any more opinions?
 
Sounds like it's probably a fuel problem to me. 90% of the time these things are fuel problems, I reckon. You should only go barking up the electrical tree as a last resort... a common heartbreak is forking out for new coils etc. only to find that the problem persists. :oops:

Key Question: What happens if you pull some choke on while it's doing its hesitating trick? If that momentarily fixes the problem, then you surely have some form of fuel starvation.

In which case,
1. Check your fuel tap and its nylon gauze filter is operating fine, and not chokked up with crud from the tank.
2. If you have the original fuel tap with its diaphragm, check that the diaphragm is not holed, and that it's indeed turning on properly with the vacuum from #2 inlet manifold.
3. If you have an inline filter, throw it away (in my opinion, that is -- we don't want to get too controversial around here!).
4. Check the air venting at your fuel cap. These small vents can get blocked and when the demand for fuel is there (eg. good thrashing at highway speed) a vacuum develops in the tank and the gravity feed to the carbies is stuffed. To see if this is the issue, go for a ride with your fuel cap partially open, and see if that eliminates the problem or not.

Happy sleuthing,
Mike.
 
Thanks guys, Ill try it out as soon as I get the wheels back on. Ill post back with the findings.
 
response

response

If the previously listed ideas do not work, I had good luck with some carb cleaner at Walmart- (seriously) under a buck, add it to the gas, it helped my 850 alot.
i do not know if this is a permanent fix but for under a buck I can fill the tank and add it 5 times. Cheaper than a carb cleaning!
 
It was fuel starvation. I rerouted the hose using gentler bends and it didnt do it when I rode tonight. Hope fully that fixed it. If not, back to the drawing board.

Thanks again all.
 
Looks like it was bubbles in the fuel line, trapped at the higher points of the fuel line, then. Good job you seem to have it sorted.

Mike.
 
In your first post you mentioned that your carb spills gas every now and then. That's not right. You should fix that before trouble shooting anything else...
 
I had the same problem. I took the o-ring off the vacuum petcock needle on the tank and added an inline fuel shut off valve. Which also increased the length of the fuel line and it's path to the carbs. Nothing but trouble. Has anyone had any luck with inline shut off valves? there is very little room to get one in without running the fuel line horizontal for a short length.
 
Jethro said:
In your first post you mentioned that your carb spills gas every now and then. That's not right. You should fix that before trouble shooting anything else...
Click to expand...

Yeah, I know I need to. I think its just dirty because its just once in a while. My temporary fix is the drain hoses, but as soon as finals are done and things settle back down Im going to get a set of robert barr's orings and clean/reseal all 4.
 
Similar problem with an 81 GS 450

Similar problem with an 81 GS 450

Hi,

Did any of these suggestions address your problem? I have a similar hesitation problem with my 81 GS 450. It is intermittent, and seems to show up when I'm cruising at low-mid RPMs (around 4 or 5,000).

I suspected some of the same things; some sort of clog in the petcock assembly, or some problem with the fuel mixture. I'm not a mechanic, just a recreational rider, so I'm not sure and don't want to start pulling stuff apart. I also don't want to take it to my mechanic with a vague description.

Thanks,
Matt
 
First thing I thought of when I read the complaint was that it was sporadically not pulling gas. Couple of reasons this can happen... the gas cap vents plugged as already mentioned. Also, you probably have a vent or vents on your carburetors. If these are obstructed in any way, the float system doesn't work well. There are OTHER possible reasons as this seems to be related to a specific engine speed. I am guessing there is also a possibility that the mechanical ignition advance on your bike is not able to rotate freely and thus, the ignition curve is not advanced as it should be. You need to remove the part that goes over the crank and on the end of the advance and clean it and the advance and then lubricate it as part of your normal maintenance routine.
 
Matt, my problem was that the bends in the fuel hose werent allowing it to flow like it should. I rerouted and shortened the hose and was trouble free unitl my latest saga. Make sure fuel is flowing through the petcock, and to the carbs, then go from there.

also, make sure your petcock isnt on prime. I did that once too. :oops:
 
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