jetting question?

[cajun31]

Yes I have read the tech tips. As my signature states I have the 80 LG and everything on it is stock other the exhaust. I have a set of Kerker 4 into 1 on it. I know that the main jets are 110s on 1 & 4 and 120s on 2 & 3. I am running lean as the pipes have turned a nice bluish black on the headers. I have fully synced them and colortuned the bike as best I could. It starts right up and idles well and has good midrange and top end power. I do notice some popping during decal... nothing extreme just some. I am interested in hearing what others would suggest for the ideal jetting for my setup. I am interested in both power and fuel economy if there is such a setup. I am also worried about being too lean and running hot. With the Kerkers I had to remove my oil cooler system because the oil filter sits too low with the addition of the oil cooler fitting down there. I also always wondered why the main jets were so much smaller on the specials starting in 80. From what I have researched they were 137.5 mains on all carbs prior to 80. Anyway .... any ideas or has someone out there already made changes to theirs configured like mine? Looking a main jet replacements on ebay now.

[DGXSER]

The reason the main jetting changed to 110 or 120 in 1980 was a change in the crab design. The earlier crabs fed the pilot jet through the main jet. That changed in 1980 to the pilot drawing straight from the bowl. So all of the 1980 and later bikes got the smaller jets.

If your top end is good, you can give it full throttle and it pulls to red line nice and hard, then your main jet size is fine.

Check float height setting, should be 23 mm +/- .5mm from crab gasket surface with no gasket in place to the highest point on the float.

With stock airbox, and a Kerker with the proper baffling and wrap inside in place, you might, I say might, need to go up to 45 pilot jets.

Try tuning the idle mix. You should be able to turn the mix screw out enough to cause the cylinder to stumble a touch. If your 6 or more full turns from seated and still not there, you may want to increase the pilot size.

[jetmechmarty]

The reason the main jetting changed to 110 or 120 in 1980 was a change in the crab design. The earlier crabs fed the pilot jet through the main jet. That changed in 1980 to the pilot drawing straight from the bowl. So all of the 1980 and later bikes got the smaller jets.

I don't know why I find that so funny, but I do.

After research here and double checking factory literature, my SG was jetted 110, 110, 110, 110 across from the factory. I found mine was jetted 110, 120, 120, 110. I am suspicious that maybe the folks who wrote the Clymer manual had a good reason to recommend this as proper jetting. 110 across for me didn't work to my satisfaction. I am now jetted 115 on 2 & 3. I may consider going back to 120. My plug read looks slightly lean in the middle. (I have stock airbox and 4 into one header)

Anyway, I strongly suggest you follow the advice in DGXSER's post. Your jetting is likely fine.

[DGXSER]

Dyslexic fingers. If you can't give intelligent answers they should at least be funny.

[D0wn5h1ft]

I would check for vacuum leaks as that is most often the culprit at small throttle openings. Also, buy/rent a timing light and take a look at what your advance looks like at different RPMs. That was my problem.

[Buckmaster79]

Popping

You might check your exhaust gasket rings, I have a 79SF with a
Kerker and that is what fixed mine.

[BA80]

The popping on decel will be in the idle mixture. It's too lean. The pipes bluing is because the aftermarket exhaust is single wall and the OEM exhaust is double walled.

Don, my bike doesn't have crabs, does yours?....

[cajun31]

Thanks guys

I will check all of this as I do my spring cleaning on the bike. Brakes, tires and now exhaust gaskets and carb float check. Hopefully once I am done all that will remain are the cosmetics.

[GLoweVA]

The reason the main jetting changed to 110 or 120 in 1980 was a change in the crab design. The earlier crabs fed the pilot jet through the main jet. That changed in 1980 to the pilot drawing straight from the bowl. So all of the 1980 and later bikes got the smaller jets.

Don, I have to ask this question, and I know I'm going to open up a huge discussion about what Mother Yammie was thinking in 1980, but I've got to know.

So, why in the early '80 carbs, some have the crossover joint/hole from the main jet to the pilot jet and the pilot hole plugged, but still have the 110-120 jet sizes.

I've got two 80's (SG and G) and one has the crossover with plugs and the other does not.

These early 80 carbs (with the crossover) seem to be a little on the rarer side, seeing as they only put them out for about 1/2 year or so.

[jetmechmarty]

George,

I have a few XS650 motorcycles. The ones with BS34 carburetors all have the crossover and rubber plug. I haven't a clue why both types of carburetor were in use at the same time. My XS650 bikes are 81 and 83 models. My 80 XS1100 has the no-crossover carbs.

[DGXSER]

George, the short answer is I do not know. . I only ever saw one set of the 80s with the crossover. We got the bike running decently, but never got it quite right. The owner suffered a massive fire that burnt the bike up before we got it properly sorted.

So, I do not understand the crossover 80s using the smaller main jets. Just like I will never understand how Jello is a liquid till you chill it in the fridge, but take it out and let it sit for hours and it is STILL Jello!! One of the many wonders of the world I will die never fully understanding.