4to1, pods & rejetting...

[Scudder]

Modifications
1. 4 to 1 pipes
2. air pods
3. main jets 127.5
4. Needle clip on 4th groove from the top

Got the 750 running pretty well. Driven it around ,and the acceleration is good, yet still a bit sketchy. I'm getting a little smoke/fumes from the exhaust. Smells like gas. Does that mean I'm running too rich??? I'm guessing yes. I have the main jets at 127.5. Everything else is adjusted as directed by the guys on this site. Shall I try 125s. Will that do anything to get rid of the exhaust smoke/fumes,and maybe smooth things out a bit. It is not a lot of smoke. When I have it idling and twist the throttle, some exhaust smoke comes out, and then stops when it returns to idle.

Scudder

 

[rustybronco]

Based on my personal experiences, I would have started with with 125's.

you may want to pickup some 122.5's also.

my previous post in regards to your inquiry...
http://www.thegsresources.com/_forum/showpost.php?p=1090789&postcount=8

start with 125's, then read the plugs via plug chops. don't hesitate to post DETAILED plug pictures when you do the plug chops.

this should keep you busy for a few days.

http://www.dragstuff.com/techarticles/reading-spark-plugs.html

Reading For Air Fuel Mixture

The porcelain around the plug’s center electrode can be divided into three areas for reading. The area that is closest to the tip is affected by the idle and transition circuits carburetor circuits and is of no real concern to a racer. If this area is gray then you drove the car back to the pits and you cannot correctly read the plugs. The middle area is only colored when you drive down the road at around a steady 30-40 mph and is normally affected by the primary circuit jetting with the power valve closed and this is really of no concern to the racer. The area you are interested in is that third that is all the way up inside the plug where the sun don't shine. This area is colored when all is wide open under full power because the combustion chamber heat totally cleans off the other two areas. It will take a special plug reading flashlight with the magnifying glass to view it correctly. Plugs cannot be correctly read by just quickly looking at them with the naked eye. You see people doing it all the time because they do not know how to read plugs.

http://www.strappe.com/plugs.html

But the insulator is much cooler deep inside the plug body, and coolest where it contacts the metal shell, which is precisely where you "read" mixture strength.

http://verrill.com/moto/sellingguide/sparkplugs/plugcolorchart.htm
http://faq.f650.com/FAQs/SparkPlugFAQ.htm
http://www.ngksparkplugs.com/tech_support/spark_plugs/faqs/faqread.asp

***what are your external carb fuel levels?, if they are to high, it will run rich***
(the how-to is in the shop manual I linked to you previously, a cheep and easy way to double check your float settings)

 

[Rudeman]

Modifications
1. 4 to 1 pipes
2. air pods
3. main jets 127.5
4. Needle clip on 4th groove from the top

Got the 750 running pretty well. Driven it around ,and the acceleration is good, yet still a bit sketchy. I'm getting a little smoke/fumes from the exhaust. Smells like gas. Does that mean I'm running too rich??? I'm guessing yes. I have the main jets at 127.5. Everything else is adjusted as directed by the guys on this site. Shall I try 125s. Will that do anything to get rid of the exhaust smoke/fumes,and maybe smooth things out a bit. It is not a lot of smoke. When I have it idling and twist the throttle, some exhaust smoke comes out, and then stops when it returns to idle.

Scudder

I had a similar set-up on my 77 GS750 and I ran 120 on the mains and one up from the stock setting on the needles. It ran great. I would say 127.5 is too fat.

 

[posplayr]

Based on my personal experiences, I would have started with with 125's.

you may want to pickup some 122.5's also.

my previous post in regards to your inquiry...
http://www.thegsresources.com/_forum/showpost.php?p=1090789&postcount=8

start with 125's, then read the plugs via plug chops. don't hesitate to post DETAILED plug pictures when you do the plug chops.

this should keep you busy for a few days.

http://www.dragstuff.com/techarticles/reading-spark-plugs.html

http://www.strappe.com/plugs.html

http://verrill.com/moto/sellingguide/sparkplugs/plugcolorchart.htm
http://faq.f650.com/FAQs/SparkPlugFAQ.htm
http://www.ngksparkplugs.com/tech_support/spark_plugs/faqs/faqread.asp

***what are your external carb fuel levels?, if they are to high, it will run rich***
(the how-to is in the shop manual I linked to you previously, a cheep and easy way to double check your float settings)

Rusty there is some great info in there:

http://www.strappe.com/plugs.html

Platinum and gold-palladium alloys can survive the combustion chamber environment as very small wires, and in that rests their great advantage. Electrons leap away from the tip of a small-diameter, sharp-edged wire far more willingly than from one that's fatter and rounded. So the fine-wire plug requires less voltage to form a spark than one with conventional electrodes, and the difference becomes increasingly biased in the former's favor as hours in service accumulate and erosion blunts the iron-alloy electrodes. There are, of course, drawbacks with precious-metal plugs: they are more expensive, and they are very sensitive to excessive ignition advance. The overheating you get with too much spark lead effects plugs' center electrodes before it can be detected elsewhere in an engine, and when subjected to this kind of mistreatment fine-wire electrodes simply melt. In one sense this is a disadvantage, as it means the ruination of expensive spark plugs. Seen in another way it's a bonus feature: it is better to melt a plug electrode than an engine

 

[rustybronco]

Oh Bill....

Your engine's spark plug doesn't cause detonation but it can tell you when and why the phenomenon has occurred. Moreover, the spark plug can tell you with remarkable precision how much spark advance and what jetting your engine needs. Those are things you can "read" in a spark plug, and all that is written there will be revealed very clearly when the heat range is right.

Never try to jet too close to a best-power mixture until after you've taken care of spark advance. As previously noted, the air/fuel ratio that yields maximum power is only a shade richer than the one that is most detonation-prone; fortunately, the plug will tell you when there has been even slight detonation inside your engine. The signs to look for are pepper-like black specks on the insulator nose, and tiny balls of aluminum concentrated mostly around the center electrode's tip. Severe detonation will blast a lot of aluminum off the piston crown, and give the plug a gray coating-which is a portent of death for the engine. A few engines will show just a trace of detonation when jetted and sparked for maximum power, but that never produces anything more than a few miniscule spots of aluminum gathered on the center electrode's sharp edges. If you see more aluminum and an extensive peppering evident on your plug, you're in trouble.

(no Jose Cuervo used in making this quote... j/k!)

Jim, there's enough info in the first two links to make your head explode!

 

[jimb12]

Fuel smoke is black, and oil smoke is blue. Is this smoke black?

 

[Scudder]

Yes. It is black. Too rich I assume? I adjusted the float in one of the carbs, and I think this might be a problem. Also, I have the needle clip set on 4 down. That is another adjustment I'll be taking a look at. Thanks.

Scudder

 

[jabberjoe87]

I have the same 750 with pods and a 4-1 and i have 120 mains as well