One rich one lean

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Fentible

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AS an addendum to my previous post 'misfire above 400rpm' I've just taken the plugs out to find that one side is running rich and the other lean. I'm unable to make any adjustments on the pilot jets as both are seized and the heads have been butchered (not by me!!). Advice greatly appreciated

Fent
 
I'm guessing you mean your idle mixture screws are butchered, right? The ones accessible from the outside of the carb, not the pilot jets inside the carbs?
If it's the idle mixture screws, soak them in penetrating lube and try to get them out one way or another, possibly drill them. Get some new ones online and stick those in, you'll never be able to fix your mixture issues otherwise.

If you are talking about your pilot jets, leave those in and adjust your idle mixture screws.

good luck
 
Hey Willem

Yes you are absolutely right its the externally adjustable idle mixture screws not the pilot jet :doh:.
Now then I don't know what availability of these screws is like in the states but I can't find these listed separately on any web site or ebay this side of the pond. Struggling to even find a decent set of used carbs :banghead:
 
yep, you can try ebay germany as well, they have a lot there

yambits.co.uk
cmsnl.com
japparts.nl
 
CSMNL was my first port of call but they don't identify the part separately on the diagrams. Unless its simply not an OEM part.

Incidentally, whilst it no doubt affects the Idling, Is it within the idle mixture screws adjustment range to cause the higher rev band misfire??
 
I would say that 4000 - 7000 rpms would be mid range actually, and then yes, the idle mixture screws would still cause misfires if not set correctly.

btw, it never hurts to check for air leaks on your lean side. Spray some brake cleaner or deodorant around that side
 
Sesty thanks for links but not sure about XS 360 carbs. Just emailed Mikes to see if he will ship to the UK.

Willem yes I tried the spray approach but no change to revs.
 
could be the right part, if fentible has an 77 xs400d? What's your exact model? UK custom 1980 doesn't say much :shrug:
 
4k-7k is your needle and needle jet. Pilot jet and mix screws are 1k-4k. I would look to make sure the needle jets are clean and all the holes are open. Also make sure the carbs are synced proper out of sync carb's will pop or miss at higher rpm's. If you idle mix screws are messed up bad you might want to start looking for another set. The xs360 pilot mix screws will not work on any xs400 carb.
 

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That's the model...a UK spec 1980 'US Custom'..at least that's what the badges (Yamaha original) on the side panel say :shrug:. However looking through the manual (Haynes) and extrapolating that into model codes reveals that its a1980 XS400SE 4G5 (UK spec) and you are right Willem perhaps using that designation would have been more helpful

Lucky8 that looks exactly like the part, I had checked the 1980 SE carb diagram and it doesn't show that as a separate part, yet clearly they are the same (visually) carb Mikuni BS34. However CSMNL are almost twice the cost of Mikes XS who has confirmed that they do ship to the UK.


Thanks for input guys, this is really helpful.
 
xschris said:
4k-7k is your needle and needle jet. Pilot jet and mix screws are 1k-4k. I would look to make sure the needle jets are clean and all the holes are open. Also make sure the carbs are synced proper out of sync carb's will pop or miss at higher rpm's. If you idle mix screws are messed up bad you might want to start looking for another set. The xs360 pilot mix screws will not work on any xs400 carb.
Click to expand...

Hmm.. you have thrown another possible into the mix XS Chris. I did remove the needle jets and ultrasonically cleaned them after a soak in carb cleaner so I'm fairly confident that they are sparkly clean, the carbs were also sync'd to within a whisker of each other courtesy of vacuum gauges. When removed, the plugs were at opposite ends of the spectrum in terms of one rich and one weak, sooty black to hard white

Interestingly my manual states that both the XS360 and XS400 use the Mikuni BS34 with different jets, so you are right about the fact that the pilot jets cannot be transposed but the idle air screws should be identical? As a matter of interest with the idle air screws does turning out richen or weaken??
 
The 76-77 xs360 carbs are bs34's but not like the 77-82 models. They are more like the 76-77 bs38's there are no interchangeable parts between them. They where pre-emissions standard carbs and run/tune much better that the later ones it's what I run on my 80.
 

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xschris said:
The 76-77 xs360 carbs are bs34's but not like the 77-82 models. They are more like the 76-77 bs38's there are no interchangeable parts between them. They where pre-emissions standard carbs and run/tune much better that the later ones it's what I run on my 80.
Click to expand...

:yikes: Wish you'd posted that sooner, I've just bough the two items linked in Sestys's post..oh well live and learn.
 
xschris said:
If you idle mix screws are messed up bad you might want to start looking for another set. The xs360 pilot mix screws will not work on any xs400 carb.
Click to expand...

:doh: shit sorry to lead you the wrong way, try to contact the seller for refund.
 

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