Weak Enrichment Circuit After Oil+Filter Change

Evening,

I recently performed an oil and filter change on my '81 XJ650. Was my first time doing so on this bike, and I found it fairly easy. Because the manual's recommended 20W40 is pretty much unobtainable in my area, I used 15W40, which I've heard is fine.

Weird thing though, after the oil change, my fuel enrichment circuit isn't nearly as effective as it was before. Previously, full choke would cause the RPMs to climb to about 2500 right after starting up. Now, they barely get to 1500. I can still raise the RPMs manually by opening the throttle, which I sometimes do if I need to get the bike warmed up faster. At 1500 RPM, it warms up insanely slowly, so it's kind of annoying. Once it warms up, everything is fine, and I have the idle screw adjusted to maintain idle at about 1250 RPM when it's good and warm. The bike runs beautifully when I'm riding too.

Is this something that could be due to the oil viscosity? Or could I have mucked something else up while doing the oil change? It's maybe a little colder out than it was before the oil change, but I'd be surprised if that caused the problem. My bike lives in a garage anyway, so the temperature of the bike when I go to start it will be fairly constant.

For reference, I cleaned, colortuned, and synched the carbs about two months ago. It was my first time doing so, so it's possible I missed something or made a mistake.

 

That is odd.
I wonder if the fuel enrichment cable has slipped in its holder and your not actually opening all the valves much.
I know mine floods the engine if I leave it on for more that 5 or 10 seconds on full and the engine definitely revs higher that 3k.

 

Mine has never revved past 2.5k. I found this forum thanks to a video from Melnic, where he showed off his Maxim, and I noticed at the time that his bike revved a lot higher than mine with the choke on. My bike is a non-YICS model, so I chalked it up to that. Maybe something else is up.

Here are some pics of my enrichment valves. First pic is full closed, second is full open.

If it helps to narrow it down, I also noticed that, even though the valves appear to move, I get almost no difference between full choke and half choke. I crudely marked up an image to show the approximate range.

 

Well they definitely look fully open.
All of this, btw, has no bearing on the oil change.
Just to be clear!

So... The one big thing with these carbs is the fuel bowl which has this tiny embedded jet, that the fuel enrichment circuit uses, that gets blocked as it sits in the bowels of the bowl.

Also one of the big things is squirting carby cleaner through this jet to make sure it is fully open and the whatever you do warning... Wear eye protection!

Because carby cleaner in your eye will definitely make you weep and curse a bit.

Yes I have had carby cleaner in my eye. I did tear up... No one saw me.

 

I cleaned the float bowl jets on my 900f what a difference it made. Eye protection is vital.

 

It's very possible the PO put 5W40 oil in it. Yes, the 15W will have an effect in the cold, due to drag.
If I'm running a 15w40 and put a 5w in, it's definitely noticeable.

 

I’m fairly certain they did something like this. I had to adjust the idle screw to bring the idle RPMs up after the oil change, so it does seem like they used less-viscous oil.

I will try blowing out that area in the bowls with carb cleaner. I did a decently thorough carb clean earlier this year, but it was my first time ever doing so. Wouldn’t be surprised if I missed a spot.

 

Make sure that this is very clean and that you do wear eye protecting using the compressed air and carb cleaner. I know our carb bowls are a little different, but ours do have the enriching tube or jet in the bottom of the bowls.
carbs_floatbowl_choke by Tim Brown, on Flickr