Carb guide jetting specs chart for 70-73?

[drdano]

I have a question about the jetting chart in the carb guide. The section for '70-73 shows two different pilot and mix settings. Am I reading this correctly that there were the settings specific for 70/71 (45P and 1 mix) and then 72/73 (42.5P and 3/4 mix)? Why the difference if so? Attached is the chart for reference.

 

[5twins]

Yes, there were small changes in the pilot jet size and mix screw setting. The mix screw setting may be partly related to the jet size but could also have something to do with possible changes made to some of the internal passageway sizes. The carbs were tweaked and refined over the years, as you can see by all the differences in that chart. Keep in mind that the mix screw spec is only a suggested starting point. You should adjust it in and out from there to find where the bike runs best. It should be close to the spec, maybe within a half turn either way, but may not end up being exactly at the given spec. If I had those carbs, I would probably try both pilot jet sizes too and use what worked best.

 

[drdano]

Thanks for the reply 5twins. I know the outsides of the XS2 carbs are different, wasn't sure if the internals changed. Likely they did, hence the jetting change. I've seen the float spec as 24mm for the early XS1 carbs (which is what I'm currently dialing in), but the chart mentions 25mm. I'd assume 25 is the number to go with? Thanks again.

 

[grizld1]

From the start to the present, Mikuni float levels have always been specified +/-1 mm. (that's a tuning range, not a tolerance). Mama Yama had an endearing way of exercising her right to change her mind on a number of specifications over the years, sometimes for reasons that remain shrouded in Japanese inscrutability. You should be alright with either setting.

 

[TwoManyXS1Bs]

Do you have 70-71 carbs?
If so, there's 3 variants of those early carbs.
Info in my albums...

 

[drdano]

Yes, they are 1970 OEM carbs on this bike. The jetting appears to be stock, but with a 42.5 pilot, which may or may not have been OEM. Nothing inside of them made me think they had ever been touched...or ever cleaned for that matter.

 

[TwoManyXS1Bs]

Ok, next is to determine which variant, W1, E2, or E3.

 

[drdano]

I'm reasonably confident it's an E3 based on the serial number of the bike, but will definitely double check. That chart jives with the 42.5 pilot I feel is likely OEM in the carbs. Very interesting, thanks for that info!

 

[drdano]

Confirmed they are marked with the E3 stampings last night. I'll run the 42.5's as a start and when my 5.5mm fuel line arrives today I should have it back together. The 1/4" fuel line worked, but came off the fittings with the oem clamps a bit too easily. I'm hoping the 5.5mm line will snug it up a bit.

 

[TwoManyXS1Bs]

I used 3/16" (4.5mm) Tygon line.

http://www.xs650.com/threads/quick-question-fuel-hose-id.48985/#post-499719