Press fit jets

[thwrightstuff]

All,
I have searched and searched and have yet to find any thread anywhere on press fit slow jets on an '80 CB650 Custom bike. I'm sure this has been beaten to death with discussion in the past, but I have never been able to get a clear, concise answer on this. I am about to do a carb tune overhaul this weekend and need some advice first.

My carbs, PD50, have pressed in slow jets and adjustable main jets. Based on my throttle marks, I'm having most of my performance issues at 0-1/4 and 3/4-Full throttle. I know 0-1/4 are my slow jets and I know they aren't clogged, I've cleaned them 4 or 5 times over now, I lost track, maybe more, and the lack of performance has been the same. I just bought an after market exhaust from CE and would love to put on my pods, but first I need to tune the bike's slow jets with the airbox.

Here's my question, how do I adjust my slow jets, if necessary? Do I drill them out gently? Do I dare try removing them? Or do I just buy a whole new set of carbs? Please help me come to a sure fire answer, if there is one.

Additional question, is there a thread about how to get the PD50 carbs to work nicely with pod filters? If so, please point me in the right direction.

My apologies if this thread is misplaced. I'm new to this so I have yet to fully understand forum etiquette.

 

[cxman]

to extract the slow jets i place the carb bodies in boiling water with a bit of lemon juice (3-4 oz)

and let them warm up for 10 minutes i pull them out and grab them with a oven miitt and using a number 1 irwin extractor i remove the jets

if the carbs are hot they will come out

some tap the jet (it can still be reused ) and then extract it using a nut and washer on the screw

here are some pics

http://cx500forum.com/mediawiki/index.php?title=Removing_low_speed_emulsion_tubes_with_a_4_40_bolt

 

[4eyes]

http://www.sudco.com/Carburetor01.html

Is a great resource for all things carburetor if/when you need replacement parts.
The jets can be drilled (or better yet reamed) in place:
A) If you are reasonably sure they are too small.

B) If you are very anal retentive about keeping track of your chips. (I would use a reamer coated with bearing grease.)

 

[cjdisaffected]

If you are sure you want to go with pods this might help http://www.chinonthetank.com/2010/08/cb650-pod-filters/

 

[thwrightstuff]

4eyes, if I decide i need to drill/ream, how do the sizes translate from jets to actual units? As I recall, size 40 jets doesn't exactly mean a 40mm drill bit or even 4mm for that matter.

Would you recommend drilling out the jets or just pulling them out and pressing new ones in? Or threading the hole and screwing in other jets that might fit?

 

[4eyes]

If you are sure you need to go bigger, you may as well drill/ream.
You can always pull them and replace if something goes pear-shaped.
I have seen charts for jet sizes to thousandths of an inch online, but damned if I can remember where. Maybe on on of Sudco's PDF's.

 

[thwrightstuff]

Never mind. Last night I decided to break down my extra set of carbs that I always forget I have and played around and cleaned it out. Turns out removing and reinstalling the slow jets is very very easy and they sit back in nicely every time. The only drawback is that the outside can get a little scratched from the pliers.

 

[crazypj]

Luckily, Kei-Hin 'mostly' use hole diameter as jet size -BUT- the flow rate is logarithmically connected to hole size
For example, 40 is 0.40mm and flows 'X' amount of fuel.
45 is 0.45mm but flows 'X' multiplied by 'X' multiplied by 'X' fuel not and extra 5cc (or whatever)
Some drill/reamer sizes are almost impossible to get hold of, 37.5 being one I still haven't found for less than $100.00 (number drill claiming to be 0.375mm doesn't give a hole even close to correct size)
If your used to inch sizes, you will be working with drill/reamers between 0.012" and 0.060" (around twelve to sixty thousandths of an inch) Your more likely to loose them than break them as they are so tiny (get steel not carbide, it will flex a little before snapping )