feels like it's "missing" sometimes

[skreemer]

While I'm on the throttle everything seems fine. She pulls way from stoplights and pulls through all the gears wonderfully. The problem comes in when I'm just cruising down the street. Pick any gear and hold it at any MPH and it feels like I'm running out of gas. The hesitation, the pulsing in power. As soon as I get back on the trottle though it all goes away.

The first thought was that I was way lean on the bottom end because at one time I was. Now I have the screws out 5 and a half turns and it's still giving me the problem.

Could this be a timing issue? Not too long ago I had a problem with my signal generator going out and I put a new one in. I know for a fact that it moved a few degrees when I put it in but I didn't pay much attention to it at the time as I was running so lean i couldn't get the bike below 7K RPMs... Now that I am closer, or at least feel like I'm closer to getting the carbs dialed in this crops up.

Is there an easy way to check/reset the timing? Could I be thinking the wrong thing and it is a carb issue and I just need to go up one pilot jet size?

Any help greatly appreciated.

(Also what's the common agreement on when valve clearances should be checked?)

 

[TheBigRed]

Do you have the vent tubes connected?

At least with my 650 with only a drop in K&N replacement filter, I can't run with the vent tubes connected or I get symptoms almost exactly like you are describing.

This posed a problem as I had to blow in the vent tubes in order to "choke" the bike to start it. So I lived with the hessitation, sort of. Got to the point I'd yank the vent tube off after I knew the bike was running for the day, but then I'd have to put it back on for the next day and repeat.

However, my choke is now working right and I've got the tubes removed.

Just something to try.

Amos

 

[duaneage]

Check for leaks at the intake boots. At cruise the vacuum goes up in the intake runner. If there are any vacuum leaks from the o-rings or cracked boots the carb will "think" you are still running wide open and this will lean out the mixture.

Carbs are like computers, the vacuum created by a partially closed throttle is a signal that is used to meter fuel from the bowls. The vacuum "tells" the carb how much demand the engine has. At wide open throttle there is little or no vacuum so air rushing through the carb picks up a great deal of fuel and all is well. At part throttle different circuits meter the fuel to maintain 14.7 to 1 air to fuel ratio. At Wide Open Throttle (WOT) it is more like 8:1. Some of the metering circuits could be dirty inside the carb as well, meaning only the high speed main jets are feeding the engine.

This is a very simple explanation of how it works, in practice quite a bit of science goes into carbueration. I would look for a simple explanation first and the intake boots are a big problem on these old bikes.

 

[Joe Nardy]

Re: feels like it's "missing" sometimes

While I'm on the throttle everything seems fine. She pulls way from stoplights and pulls through all the gears wonderfully. The problem comes in when I'm just cruising down the street. Pick any gear and hold it at any MPH and it feels like I'm running out of gas. The hesitation, the pulsing in power. As soon as I get back on the trottle though it all goes away.

The first thought was that I was way lean on the bottom end because at one time I was. Now I have the screws out 5 and a half turns and it's still giving me the problem.

Could this be a timing issue? Not too long ago I had a problem with my signal generator going out and I put a new one in. I know for a fact that it moved a few degrees when I put it in but I didn't pay much attention to it at the time as I was running so lean i couldn't get the bike below 7K RPMs... Now that I am closer, or at least feel like I'm closer to getting the carbs dialed in this crops up.

Is there an easy way to check/reset the timing? Could I be thinking the wrong thing and it is a carb issue and I just need to go up one pilot jet size?

Any help greatly appreciated.

(Also what's the common agreement on when valve clearances should be checked?)

Steve,

Would you describe this as 'Surging'? If so it sounds very much like my bike ran when I installed the jet kit and was setting it up. Raising the needles a step at a time gradually improved the symptom until it was finally gone. You can also troubleshoot by covering 1/2 of the pods with duct tape to restrict the intake. If it runs better you have a lean condition.

I'm not familiar with your engine but if you have screw and locknut valve adjusters it is pretty easy to do and IMO would be worthwhile to do just for peace of mind. If it has shims that's another story and I'd be reluctant to dig into it for no reason. Do you know when they were checked last?

Joe

 

[skreemer]

yes it does feel like a surging. I've already shimmed the needles from the reccomended setting. I'll bring em up another notch and see what happens...

as for the valves I'll have to look in the manual to find out what kind they are.

I'm not sure they were ever done or looked at... the previous owner did nothing in the way of maintenance and only paid for service that would keep the bike on the road... anything else wasn't needed according to him... I'm glad the owner before him too such loving care of the bike and the guy I bought it from only had it for a short time. The reason I'm wondering is that there's a little over 24K miles on the bike and if I was going to do some hefty maitenance/checkup on it(I need to redo the forks too) I'd do it all at once..

 

[Joe Nardy]

Steve,

With jet kit needles there are grooves that an e-ring snaps into to adjust the needle height. Each groove is probably 1/16" or more above the other. If you're shimming with washers you may need quite a few to make a significant difference. My GS1100 has pods and a pipe, like your 750, and the needles are at their highest position. Then again, the jet kit needles are noticeably different in shape than the the stockers so maybe the stockers need to be raised less to make a difference.

If you're planning on doing any maintenance other that what is absolutely necessary, do it during the week so we can ride on the weekends! If you want to wait until winter we can do it up at my house in the heated garage if you'd like.

Joe

 

[skreemer]

I'll definitely take you up on that this coming winter... I'll see if I can get the surges figured out this week...

I wish I had a 750.. mine's just a light and fun 550 though...

 

[Joe Nardy]

I wish I had a 750.. mine's just a light and fun 550 though...

I knew that....................

 

[first timer]

raise it up joe? i was having the same problem and i droped the needle a 1/2 step with the shims that came with the kit. i thought it was a to rich condition so i droped it a 1/2 step down and it went a way, but at the same time my plugs still read white..... so i don't know what exactly to tell you. maybe i'll get bored and try goign up a half step. from where it was before.

-ryan

 

[Joe Nardy]

raise it up joe? i was having the same problem and i droped the needle a 1/2 step with the shims that came with the kit. i thought it was a to rich condition so i droped it a 1/2 step down and it went a way, but at the same time my plugs still read white..... so i don't know what exactly to tell you. maybe i'll get bored and try goign up a half step. from where it was before.

-ryan

Yep, raise it up. This pulls the needle up higher in the needle jet for a given throttle position and allows more fuel to flow making the mixture richer.

Joe

 

[first timer]

yeah i know that but i what i was getting was if i ran it at 5k for a while then hit the gas it feel lik it was clearing extra fuel outta the way like extra fuel was collecting, thats why i lowered it. make sence?

-ryan

 

[Joe Nardy]

yeah i know that but i what i was getting was if i ran it at 5k for a while then hit the gas it feel lik it was clearing extra fuel outta the way like extra fuel was collecting, thats why i lowered it. make sence?

-ryan

Yes, that makes sense. How was it running while on steady throttle at 5k? If it was surging then that usually indicates a lean condition. You're right that if it seems to stumble it may be rich. Sometimes with CV carbs it is hard to eliminate the stumble. It can be caused by the slide raising too quickly when the throttle is whacked wide open. The jet kit for my Hurricane included stiffer slide springs to help that symptom by slowing down the rise of the slide. If I used the stock springs it would stumble every time unless the throttle was rolled on rather than cracked suddenly.