Advice. Revs not dropping down during gear changes

Guys, looking for some pointers to a little carb problem. When running (once my bike is warmed up) I have an issue where the revs are not dropping right down so when I pull in the clutch during gear changes the revs are a bit high. When I stop the bike will usually tick over ok. Just looking for the thought of some of the very clever, experienced and knowledgeable people on this forum to give me some pointers.

The bike details. 1980 Xj650 built from a mix of parts from a UK and a Canadian bike. Engine completely stripped and rebuilt by a competent mechanic. Carbs stripped, cleaned and rebuilt by myself. New diaphragms professionally installed in carbs. Bike is running pod filters and a straight through exhaust (I know this will make it difficult to get the bike running perfectly but apart from above problem seems not too bad!). Main fuel jet is 118 (112 standard), pilot jet is 48 (standard 43).

Haven’t done too many miles since rebuild and will check plugs in a few miles time to see if she’s showing signs of being too rich or too lean but appreciate any advice or suggestions to help me with troubleshooting. Wondering if float height could be cause or pilot mixture screw setting as this is the two things I’m not confident are 100% correct.

Thanks in advance.

 

Are you rolling off the throttle when you make gear changes? Is the throttle snapping back into idle position when you release your grip?

 

Yes rolling off the throttle and as far as I can tell throttle is snapping back. When sitting ticking over I can blip the throttle and revs drop back down ok. Then I go out for a run and revs are definitely not dropping down during gear changes? Sometimes I’ll stop and put it in neutral and revs drop down normally and sometimes not. If I switch off and then restart it, then it ticks over ok and revs drop down after revving the bike. That’s why I wondered if it could be float height??

 

Check for any vacuum leaks around the intake and throttle shafts.

 

Thanks, new intake rubbers and new throttle shaft v rings when carbs were rebuilt. Pretty confident this isn't the issue but thanks for the suggestion.

 

My bike was running lean, causing the rpms to not drop immediately. Vacuum leaks will cause leanness, hence the earlier suggestion. One of the issues with pods is you might not be running lean at idle rpm, so no hangup, but due to the restriction of a carb, might run lean at 4000rpm, or 6000rpm, ect. What you can do is run the bike at speed at those rpms, and while running, shut the bike off and pull the clutch. coast to a stop, and at the side of the road check the plugs. From What I remember from a different post, the only way to remedy this with pods is to change out the needle in the carb to one with a different taper. Also, you can disconnect the throttle cable from the carbs to make sure it is sliding smoothly, probably not it, but still....

 

Thanks Bryce,
Interesting theory about running lean at higher revs. Getting a needle with a different taper might be difficult but I do have a set of even larger main jets (122). Would this be worth a try or more likely to cause her to run too rich at lower revs?

 

Someone more knowledgeable about jets would have to chime in, but if you have too big main jets, that can also cause issues. The thing about it comes down to, are you sure the main jet you have in there is the right size? If they are too small, and you are running lean everywhere but at idle, then upgrading them could work. However, if they are sized correctly, and you are running perfect at the top end, but not in the middle, you'd have to look towards different tapering needles. I know you get get them from Chacal in the fuel section of XJ4ever, at "https://xjbikes.com/forums/threads/xj-parts-catalog-section-c-fuel-system.44642/" . At any rate, if leanness is your issue, then you'll have to do a lot of runs checking spark plugs to see where you are running lean at. Like I said though, it COULD be even still be something else entirely....

 

Thanks Bryce, all comments appreciated.

 

You can use small washers as shims to raise the needle and get to the tapered area sooner when the plunger rises.

 

Thanks, i'll try and confirm if she is lean and then shim the needles

 

No one has mentioned anything about do a carb sync.

 

If possible, I would replace the pods with a stock air filter. It would make it much easier to get right. Mine had a standare intake box but with a foam filter, and I never got it right until I replace the foam filter with a stock paper filter.

 

I just read my post! I must have been preoccupied because I generally don't slaughter the King's English like that. If I were a drinking man, I could claim one to many.