.png "Powered by vBulletin")
I recently finally built a fresh GS750 engine with a set of NOS MTC Engineering 72mm 920cc 10:1 pistons, GS850 cylinders bored +3mm, and a performance Serdi radiused-inner-cut valve job. Valves adjusted. new carb o-rings, intake boots, intake boot o-rings and swapped to GS1000 spec VM26 carbs (the 750 carbs ran waaayyy too rich in the low-mid throttle range due to pilot air jet (fixed orifice) and needle jet (hard to find o-4 style 250 needle jets used). Vance and Hines upswept 4:1, and two K&N RC-2222 dual-carb-plenum oval open element filters (better than pods as the inner and outer carb share the same filter and plenum space).
I have installed an AEM universal exhaust gas oxygen (wideband o2) sensor and air fuel ratio gauge for tuning ease.
NOW... My problem all along has been the idle. with all fuel screws at slightly over 1 turn, using my timing light to spot misfires, my inner two cylinders were misfiring intermittently and often seemed like they would only fire every other cycle, causing a rough idle - and the air screws could not tune this out.
Funny thing is, when I would rev it up in neutral, or decelerate to a stop sign and pull in the clutch at higher rpm's and close the throttle, it would seem as if the higher rpm's and hotter temps of cruising had cleaned the plugs off a bit, and I would be idling at 2000 rpm's for a while. Eventually it would sputter back down to about 1050 all of the sudden, or if I would decelerate in gear down to 1000 rpm's it would just stay there and idle slightly rough.
Today, I tried about 7/8+ on the cylinder 1 and 4 fuel screws, and 13/16 turns out on the inner two cylinder's pilot fuel screws. I was able to get a better idle, but still a slight bit uneven at times. Playing with the air screws, 1-1/6 to 1-1/4 seemed to be the happiest spot, but I still wasn't terribly happy, AND - I still get the high idle after revving the engine or coasting to a stop sign in neutral!!!
Idle AFR's in the lower mid 12's now.
All of these settings outlined, I have noticed the bike is hard to kick start when the engine is hot, but cracking the throttle open a slight bit when kicking will fire it instantly with a very quick rev up and instant return to idle.
Previously I believe I had set all the pilot fuel screws at 3/4, and I was getting a slight popping on deceleration with closed throttle (typical of a lean pilot so I have read many times on here). I don't recall the difficulty starting, and I can't remember if I had the high idle after higher rpm's back then. That was also with the 0-3 (leaner) needle jets, although not sure if they have much affect on idle.
The bike sounds different on decel than it did in previous incarnations, and reminded me slightly of when I am running out of fuel and need to flip to reserve, but I am not getting the lean popping on decel now. Could be still too rich and it is sounding kind of boggy due to that. With the warm starting symptoms of having to crack the throttle to start, and lack of decel popping, I am thinking I am still on the rich side, and that the high idle is due to clean plugs, and the 1050 rpm choppy idle thereafter happens once the plugs get a little sooted up. I am running out to pull the plugs now after messing with the pilot screws. I may throw a gunson colortune on it in a day or two and check the idle flame color for proper richness.
I recall before that when warmed up with 0-3 needle jets (probably out of the picture) and 3/4 turns on the fuel screws, the air screws seemed to change the rpm's much more readily, where as with 7/8 or 1+ turns, I had a less than perfect idle no matter where the air screws were set, and the air screws never really changed the rpm's much. Again, I was getting slight closed throttle exhaust popping at 3/4 out on the fuel screws and o-3 needle jets, however.
Am I way over analyzing things here, or can someone tell me "YES, YOU ARE ON THE RIGHT TRACK." ???? I didn't have much luck with a vacuum synch yet because I did not have a solid, consistent idle (gauges would fluctuate a lot and I was afraid air screw settings and misfiring cylinders would throw off the synch), so I was saving that for after I get my pilot screw settings where they need to be. I am thinking 3/4 out or slightly slightly less on the middle cylinders, and slightly over 3/4 turns out on the outer cylinders for the pilot fuel screw settings may be where it is best, but the high idle then rough idle thing is really making me scratch my head.
Thanks!
I have installed an AEM universal exhaust gas oxygen (wideband o2) sensor and air fuel ratio gauge for tuning ease.
NOW... My problem all along has been the idle. with all fuel screws at slightly over 1 turn, using my timing light to spot misfires, my inner two cylinders were misfiring intermittently and often seemed like they would only fire every other cycle, causing a rough idle - and the air screws could not tune this out.
Funny thing is, when I would rev it up in neutral, or decelerate to a stop sign and pull in the clutch at higher rpm's and close the throttle, it would seem as if the higher rpm's and hotter temps of cruising had cleaned the plugs off a bit, and I would be idling at 2000 rpm's for a while. Eventually it would sputter back down to about 1050 all of the sudden, or if I would decelerate in gear down to 1000 rpm's it would just stay there and idle slightly rough.
Today, I tried about 7/8+ on the cylinder 1 and 4 fuel screws, and 13/16 turns out on the inner two cylinder's pilot fuel screws. I was able to get a better idle, but still a slight bit uneven at times. Playing with the air screws, 1-1/6 to 1-1/4 seemed to be the happiest spot, but I still wasn't terribly happy, AND - I still get the high idle after revving the engine or coasting to a stop sign in neutral!!!
Idle AFR's in the lower mid 12's now.
All of these settings outlined, I have noticed the bike is hard to kick start when the engine is hot, but cracking the throttle open a slight bit when kicking will fire it instantly with a very quick rev up and instant return to idle.
Previously I believe I had set all the pilot fuel screws at 3/4, and I was getting a slight popping on deceleration with closed throttle (typical of a lean pilot so I have read many times on here). I don't recall the difficulty starting, and I can't remember if I had the high idle after higher rpm's back then. That was also with the 0-3 (leaner) needle jets, although not sure if they have much affect on idle.
The bike sounds different on decel than it did in previous incarnations, and reminded me slightly of when I am running out of fuel and need to flip to reserve, but I am not getting the lean popping on decel now. Could be still too rich and it is sounding kind of boggy due to that. With the warm starting symptoms of having to crack the throttle to start, and lack of decel popping, I am thinking I am still on the rich side, and that the high idle is due to clean plugs, and the 1050 rpm choppy idle thereafter happens once the plugs get a little sooted up. I am running out to pull the plugs now after messing with the pilot screws. I may throw a gunson colortune on it in a day or two and check the idle flame color for proper richness.
I recall before that when warmed up with 0-3 needle jets (probably out of the picture) and 3/4 turns on the fuel screws, the air screws seemed to change the rpm's much more readily, where as with 7/8 or 1+ turns, I had a less than perfect idle no matter where the air screws were set, and the air screws never really changed the rpm's much. Again, I was getting slight closed throttle exhaust popping at 3/4 out on the fuel screws and o-3 needle jets, however.
Am I way over analyzing things here, or can someone tell me "YES, YOU ARE ON THE RIGHT TRACK." ???? I didn't have much luck with a vacuum synch yet because I did not have a solid, consistent idle (gauges would fluctuate a lot and I was afraid air screw settings and misfiring cylinders would throw off the synch), so I was saving that for after I get my pilot screw settings where they need to be. I am thinking 3/4 out or slightly slightly less on the middle cylinders, and slightly over 3/4 turns out on the outer cylinders for the pilot fuel screw settings may be where it is best, but the high idle then rough idle thing is really making me scratch my head.
Thanks!
Comment