Carbs... Damn Things!

Diaphragms arrived yesterday so I dug in last night... finished a bit before 9pm so a quick fire to make sure she actually started was all I could really do, could make for an interesting commute this morning...



You can see one of the tears quite obviously, and yeah you gotta cut the plastic bits off, no going back once you start!



I had to use a bit of super glue as they weren't quite a perfect fit unlike every other model I could see guides/youtube videos for... the 450 always has to be an odd one out!



See how she goes on the way to work but hopefully that gets me out to Power O this Saturday...
 
Well... she starts, she runs, and cracking that throttle feels great... but idling is another story all together. I battled stalling out and chugging all the way in to work and back home with a closed throttle or close to it despite the mixture screws going in a total of 3/4 of a turn.

Checked the plugs last night and black as the ace of spades, so the mixture screws are in to 1 turn out now but I suspect I will need to drop the needle even further.

I think all my jetting changes in recent times has actually been working around buggered diaphragms...
 
Yes indeed Rusty! Haha

I dropped the needles one notch last night and cleaned the plugs up again but I also noticed the gasket under the screw for the balancing nipples on the right cylinder is split, so that may have been letting some air in too. I've stuck some Threebond on it until I can get a new one.

When cleaning the plugs I did notice the right one looked a little lighter than the left, so either there is air coming in there or I need to balance them which I have yet to do after the diaphragm replacements.
 
Sounds like a step in the right direction there mate - Good luck Dr Pete! That 450 may just be running better than ever shortly!
 
Fingers crossed Rusty! I'll see how she goes at Power O this morning... got home yesterday avo with her wanting to rev like crazy coming to a stop then drop to idle nicely... plugs were black when I checked last night. Still a bit rich! Mixture screws in another half turn but might have to drop the needle back to stock. Hopefully I can do some full throttle checks today...
 
Power O was an eye opener... and an ear drum tester for anyone behind me... hold part throttle for a while, open her up and pop bang pop bang yeah ok... still too rich! Just kept fouling the plugs all morning.

Needles back to stock yesterday morning and plugs cleaned up again so we shall see...

There was also some discussion of velocity stacks vs. pods to get some nicely formed air flow into the carbs which may also help things.

I found this formula, no idea how good it is though:

http://www.ehow.com/info_10074561_motorcycle-velocity-stacks-long-vs-short.html

Best measurement of back of intake valve to the mouth of the carb is 6.5 inches, so for 6500 RPM I get about 3 inches for velocity stack length. According to Google my intake valve duration is 280 degrees but it's not in the factory manual so I'm not sure if that's 100% accurate or not.
 
Felt good on the way to work except possibly a little lean at no throttle so I've taken the mixture screws out a quarter turn.

However... a couple of times I got to open the throttle and I swear it was starting to misfire and pop again like the plugs were fouling... I'm thinking my Power O full throttle tests were inaccurate... starting to think that maybe I'm hitting the main jet earlier than full throttle due to the lighter spring/larger vacuum port and therefore when I back off at around 3/4 quarter throttle and it clears up then maybe that's actually the main jet...

Pretty sure I have some 137.5's at home so I might chuck them in tonight and drop from the 142.5's...
 
Checked the plugs last night, definitely lean on the mixture screws! The elements were a bit on the white side however she's still too rich with an open throttle and the outside of the plugs were still black from that.

I've taken the mains from 142.5 down to 137.5, set the mixture screws back to 2.5 turns out, and cleaned up the plugs so I'll see how she goes today.

The mains are still 8 sizes richer than stock (117.5) so I won't be surprised if I have to drop more sizes yet. I have a few smaller sizes here fortunately...
 
Good on you Pete and keep on top of it and when we last spoke did you call Old Gold as they had two 750 Kats for sale. Also will you be at S.O.O. in March, as Nambucca is a great place for an overnight stop, food and a couple of drinks, not to mention the ride there and the return home.
Nick
 
Thanks for keeping the info coming Pete, these sorts of threads are always going to help someone else out one day (not to mention keeping a log of what you have done)!!

Cheers
Rusty
 
No worries guys, happy to share my pain :D

Nick, I would love to get to SoO but the way things are it's not gonna be easy, so I'll hold off on the overnighter until I actually get a Kat of my own, however in the meantime I will continue to join the boys for most of the run south for the day at least.

The Kat fund is still quite sad but we've made a lot of progress on the back balcony so I should be able to get back on the shed soon... too many things on the go!

As for the jetting... still bad yesterday, checked the plugs and gave Todd a laugh at lunch time... black and sooty!

I did some more putting 2 and 2 together and I think I'm getting close to 4 now...

These being CV carbs means rev's are going to have a lot to do with slides lifting rather than just throttle position... der... took me a while to get that...

Anyway, seems that when the rev's are up towards 6K RPM is when the plugs start fouling so I reckon it's still my mains, so last night I went from 137.5 down to 127.5. That's now 6 sizes up from stock as opposed to the original 10 sizes up I had in there. I realise now just how extreme I had to change things to work around dodgy diaphragms...

I've left the needle at stock and mixture screws are 2 turns out at the moment.

I don't want to go too small on the main so that if I do go the velocity stack path she doesn't become too lean... hopefully she runs better today otherwise a commute in the rain with fouled plugs is gonna be... interesting!
 
I went back to stock last night... 117.5 mains and reset the mixture screws to 2.5 turns out.

Battling fouled plugs while it's pissing down doesn't sound fun to me!
 
Pete - in a previous life - i junked the airbox - but as discussed kept the venturi's on my GSX - did a few basic mods (within the rules) and went from standard main jet size of circa 110 to 160 - bike was set up on a dyno and the jet size was based on incremental increases keeping an eye on both power and air/fuel - settled on one size bigger than most power and therefore a little safer......
 
Thanks Derek, that's good to know.

The ride in this morning was horrid, now too lean. Cold leaving home I thought I was going to have to turn around as she wanted to stall out at part throttle, not good! I decided to push a little just til she warmed up a bit and then it was nowhere near as bad. Opening the throttle and getting rev's up helped but at full throttle she felt a bit choked so the stock main is too small as well. When I got home yesterday the base of the plugs was black again but the electrode was getting to be a nice tan colour, so I think if I go only a bit richer than stock I'll be close with the pods. When there's a break in the rain I'll wind the mixture screws out a turn just to make it a little richer for the ride back home.

Tonight I'm going to shim the needle half a notch and go up to 122.5 mains which is the next size up I have at home. Power O could be interesting tomorrow...

I have a feeling going the stack path with it right now could result in way too lean a mixture so I might persist with the pods the way they are until I get what feels like a good setting, then I'll think about stacks once I know what's going on.

My biggest issue right now is that everything I thought I had right is wrong due to the diaphragms so I need to get back to a good base setting.

Of course if you have different thoughts then please feel free to pass them on! This is all a learning exercise for me...
 
No drama - the stacks are there when you are ready.

At this stage irrespective of weather - it looks like Scrapeit and I may not make the rollcall tomorrow at Power O when the bugle is sounded.....
 
I'm definitely thinking I would like to try the stacks at some point, but right now I need to keep the variables to a minimum for my poor little overutilised brain...

And not turning up at Power O?? Sacrilege! :D

At this stage I plan to be there providing the adjustments go to plan tonight, just ducked downstairs and wound the mixture screws out a turn to try to make it a little better for the trip home in the rain...
 
Rightio... I swear now that my issue is not fueling so much as a vacuum leak. I was blaming fueling on a symptom but I really don't think that's right at all...

When coming to a stop after she's nice and hot, she keeps the rev's up at a couple of grand before eventually dropping back to idle. Perfect vacuum leak symptoms! Given I haven't disturbed the pods or carbs since replacing the diaphragms the only way this can be is if the diaphragms aren't sealing against the slide correctly and given I had to use bit of glue to hold them in place I reckon that's right.

Rubber expands when hot right? So I reckon full throttle when hot when she stumbles is actually the vacuum leak also not allowing the slides to get all the way up. This would explain that after that happening today, looking at the plugs with Jesse did *not* show them as rich at all.

So I just picked up some Permatex Form-A-Gasket #2 non hardening stuff and I will run that around the top of the slide where the diaphragm attaches. It's fuel resistant and from what I can see is not silicone based which JBM explicitly say not to use, and it says you can use it on hoses so I assume it's safe for the rubber. Couldn't really find anything definitive via Google but everything else I've got here is either non fuel resistant or eats rubber.

I'll try to get that done tonight and see if I can't get a test ride in tomorrow morning.

Fingers crossed I can finally get this sorted!!!
 
Well if things keep going the way they are that'll be a big yes! Haha

I got the form-a-gasket in last night, 4 hours to use and 24 hours to full cure so hopefully I'll get a test ride this morning and see if it makes a difference.

I definitely see a way for vacuum to leak on the left carb as one of the spots of glue had started to give way, so I'm hopeful I really do have a vacuum leak and that this will solve it.

 
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