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1977 GS-750 re-jet. Here is where I am at.

  • Thread starter Thread starter TBC
  • Start date Start date
Except they don't all do it.
Are you talking whacky whacky from idle or from some realistic RPM?
Sounds from his post, hes going WOT from a standstill...Not going to work, no matter what you have on there. From realistic RPM, you should be able to whack the throttle open, or more precisely, roll it on QUICKLY and feel little or no effect, if jetted right. But WoT from low rpms or dead is not going to do anything but bog.
 
Sounds from his post, hes going WOT from a standstill...Not going to work, no matter what you have on there. From realistic RPM, you should be able to whack the throttle open, or more precisely, roll it on QUICKLY and feel little or no effect, if jetted right. But WoT from low rpms or dead is not going to do anything but bog.


Couldn't get back at it this afternoon due to rain. Hopefully tomorrow or Sunday but weather is not suppose to cooperate. If you go back through my posts I have been going to WOT from around 2500 to 3000 RPM, not idle and not from a standstill. It has been as I pull away from being stopped. I believe my "off the line" comment leaves everyone with the impression that I have been at a standstill and at idle, and understandably so. My error in wording.

Cafe Kid. I am ready to go with your most recent advice ( as a result of my 135 main's adventures ) but the rain beat me to testing it out. Hopefully this weekend, but as I mention above, weather isn't suppose to be anyone's friend this weekend.

Tom
 
Couldn't get back at it this afternoon due to rain. Hopefully tomorrow or Sunday but weather is not suppose to cooperate. If you go back through my posts I have been going to WOT from around 2500 to 3000 RPM, not idle and not from a standstill. It has been as I pull away from being stopped. I believe my "off the line" comment leaves everyone with the impression that I have been at a standstill and at idle, and understandably so. My error in wording.

Cafe Kid. I am ready to go with your most recent advice ( as a result of my 135 main's adventures ) but the rain beat me to testing it out. Hopefully this weekend, but as I mention above, weather isn't suppose to be anyone's friend this weekend.

Tom

Ok tom, but thats STILL pretty low RPM to be going straight to WOT. Try to roll it on rather quickly, but not jerk the throttle all the way open instantly. Again, I still say 135s are a bit big, and im going off of info ive gathered from those MORE knowlegeable than I on this particular subject. As I said, based on YOUR findings, i went ahead and ordered 130s and 132.5s just in case.
 
Ok tom, but thats STILL pretty low RPM to be going straight to WOT. Try to roll it on rather quickly, but not jerk the throttle all the way open instantly. Again, I still say 135s are a bit big, and im going off of info ive gathered from those MORE knowlegeable than I on this particular subject. As I said, based on YOUR findings, i went ahead and ordered 130s and 132.5s just in case.

That's cool. I am going to take your advice, back up a bit, and try again. I thought it was a little lean with WOT with 127.5's and clip in 4th position. Maybe going to 5th position will work for my bike. Hey, it's all grist for the mill, isn't it? I'm a newbie at re-jetting, so a big learning curve for moi.

Thanks,
Tom
 
Cafe Kid, I have a question for you. When you go to fine tune your pilot circuit ( small throttle openings ), are you going to preset your fuel screws and then adjust air screws or vice versa?

Thanks,
Tom
 
Cafe Kid, I have a question for you. When you go to fine tune your pilot circuit ( small throttle openings ), are you going to preset your fuel screws and then adjust air screws or vice versa?

Thanks,
Tom
You really *shouldnt* have to mess with the fuel screws nearly as much as the air. Use the air for FINE tuning, the fuel, once you decide you are getting enough fuel to the pilot circuit and what not, you shouldnt have to move them. I would start at 1.5 to two turns out on those, and leave it. If you're rich, back off a bit, but i doubt that you'll be lean on those at that large an opening. Stock i believe is only ONE turn out. Air screws play with to fine tune highest idle...
 
If your problem is at full throttle, then it's the mains that need changing, not the jet needles. Simple 1/3 to 1/2 throttle tests/plug reads would verify if the jet needle is right to begin with.
Your bench synch could be off significantly, adding to the problem. A vacuum tool synch is a basic part of any re-jet.
Are you sure the jet needle assembly was correct? Thicker factory jet needle plastic spacer on top the e-clip and thinner under the clip?
Did you verify the ignition advancer is operating smoothly and the advance timing is spot on?
 
If your problem is at full throttle, then it's the mains that need changing, not the jet needles. Simple 1/3 to 1/2 throttle tests/plug reads would verify if the jet needle is right to begin with.
Your bench synch could be off significantly, adding to the problem. A vacuum tool synch is a basic part of any re-jet.
Are you sure the jet needle assembly was correct? Thicker factory jet needle plastic spacer on top the e-clip and thinner under the clip?
Did you verify the ignition advancer is operating smoothly and the advance timing is spot on?


Just a little update, but not much because I have not been able to spend much time at it.

Hi Keith,

To answer your questions. Bike bench and vac synced. There are no spacers on my jet needles. As I purchased this bike stock from original owner with stock jetting, I can only assume there never were. Verified timing is correct and spot on with timing light. BTW compression with hot motor is 110, 110, 115, 115 for cylinders 1 to 4 respectively. Bike has 76K on it. It was re-ringed by me at 50K and also valve job which was done by shop. I am hoping to sort myself out jetting wise later this week.

Tom
 
Just a little update, but not much because I have not been able to spend much time at it.

Hi Keith,

To answer your questions. Bike bench and vac synced. There are no spacers on my jet needles. As I purchased this bike stock from original owner with stock jetting, I can only assume there never were. Verified timing is correct and spot on with timing light. BTW compression with hot motor is 110, 110, 115, 115 for cylinders 1 to 4 respectively. Bike has 76K on it. It was re-ringed by me at 50K and also valve job which was done by shop. I am hoping to sort myself out jetting wise later this week.

Tom
Correct he is Keith. The 77 VM26SS set up had NO spacers on the needle. Only the clip. I wonder if one were to add some spacers, if any advantage, or ease in jetting would be gained.
 
I'd leave the needle where it was if the bike was running ok off full throttle. Concentrate on getting the mains right first, sort everything else later.
 
I'd leave the needle where it was if the bike was running ok off full throttle. Concentrate on getting the mains right first, sort everything else later.

A local shop where I get jets has told me that the Emgo's do not flow well, as compared to K & N's and, as such, said it would be trickier to jet the bike. Not impossible though.

Tom
 
I've never tried Emgos but have used cheaper 'K&N copies' (which look similar to Emgos) and whether they flow as well as K&Ns I've no idea. I've also used K&Ns, foam filters and bellmouths (I think you call them velocity stacks) on various bikes.

I can't see why the shop thinks jetting will be more difficult - you have to re-jet for changes to the air intake and both Emgo and K&N are significant changes. It'll probably be different, just as different bike wearing the same set up can be different, but not trickier.

The crack is to break your carb tuning into stages and master each stage independently. You may have to fine tune at the end to match the different stages but you're gonna be pretty close by then.
 
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