Topic: CB650 trouble

[razor02097]

first topic in the tech forum...

My CB650 was bought with an idle problem.  Idle jets where clogged no problem... PO hollowed out the stock mufflers (just my luck ) Anywho I promptly cut off the mufflers and welded in their place some shorty slash cut mufflers with internal baffles.  The jets are probably stock at #90 for the main and unmarked for idle... I am going to go ahead and re jet the carbs richer.  I have a set of 105 jets I am wondering if that is too much for the motor.  It has a stock airbox still.

Next thing is right now with the #90 jets in and carbs clean it runs fine and accelerates to 9500 RPM no problem.  When idling it sometimes sputters and won't idle below 1500RPM  It almost sounds like preignition but it does it even when started cold...  It'll stumble and the RPMs drop for a split second then it starts idling normally or sometimes its enough to stall the motor.  This also happens if I stop at a light and lightly flick the throttle.  If I don't do a rolling acceleration the bike WILL stall.

I get around 120 miles before I hit reserve (about 2 gallon reserve so that makes 40MPG)  There is no puff out of the exhaust pipes if I whack the throttle open (running lean?)

No bad engine noises or chattering but the valves are tight, as soon as I get a chance I'm going to make a valve adjustment tool so that may be something too
For driving habits the front wheel has left the ground before (and not on the lift either )

I'm thankful for any help you guys can give me

[Ibsen]

The 650 carbs was jetted very lean from the factory with 90 jets. Increasing the main jets to 98 with stock exhaust and air filter has been recommended, so 105 might work with the modified exhaust. You wil just have to try them and check the spark plugs too see if they are to large.
For your other problem; have you checked the float hight, adjusted the idle mixture, and synched the carbs?

For adjusting the idle mixture you should get a workshop manuak (Clymer will work fine if you don't have one already), l since the procedure is a pretty long write up.

[Zeke]

As far as the jetting....

My 80650c had 95 mains.  I just installed a 4 to 1 pipe and am working on pod filters.

I got a recommendation to do 102 jets.  Haven't tried them yet.  Figured a worst case of 105 mains.

So, 105s may be a bit much for you.  The sizes after 90

95,98,100,102,105, .... 108? .... 110 can't remember.

But a jump from 90 to 105 is alot.

[Short Round]

I agree with Zeke.  The recomendation for switching over to pod filters is a 20% bigger jet due to the increase air flow into the carbs so that would but you at 105 ot 110 since it fall in the middle, so I wouldn't go with the 105 unless you switch to the pods filters.

[Ibsen]

I don't diasgree with you guys, you just have to try it out till you get the jetting right. There are so many factors that has to be taken into consideration in addition to the air filtering and exhaust, like altitude and air humidity, so there is no way to tell what size will work best before you can test ride the actual bike.
You just have to have in mind that the 650 carbs was originally jetted very lean from the factory. With the stock jetting they had a slight stumble in the 5000 rpm area, and if you snapped the trottle wide open, there was a flat spot. This is mentioned in several test reports from the periode. And the recommened cure for this problem, at least in England, was to go up on the main jets from 90 to 98, with the stock exhaust and air filter. Then add pod filters and a 4-1 exhaust, and it is impossible to tell in advance what main jet size that will work best. But by putting on pod filters you can also face other problems, like a leaned out mid range and idle mixture. And if you have the CV carbs, they don't always work to well with pod filters at all.

[Zeke]

What Ibsen said.

You can't know what'll happen until you try.  I bought a few different sizes just so that I would have a few different sizes to try.

Due to a fitment snafu with K&N on my bike, I still don't have filters other than stock.  I'm hoping to ditch the stock box just because I hate it and the way it busticated my choke arm which has led to alot of heartache.  I realize I'll have to do some tuning to make them work, but at least removing them will be a snap!!

 

Zeke

[cb650]

Carb removal is the best thing for pods.  My 80 after a long rest went vroom vroom today!!!
Still needs some work.  Nothing important just front brake and rear tire!  Think might have to take carbs back off for a little tweaking. 



                           Terry

[razor02097]

did some work today

adjusted valves
rebuilt and jetted carbs to 105 mains
replaced airbox boots
replaced air filter (old one looked OEM?)
replaced spark plugs
changed oil and filter


All finds as follows...

2 idle jets where plugged
air filter quite old and dirty
air box boots turned plastic
valves >.0015" clearance adjusted to .004"
spark plugs worn
1 mixture screw broken off all mixture screws where taken out and cut for a flat head screwdriver, set mixture screws to 1.5 turns out may have to adjust later.



I'm hoping all the discrepancies listed above will solve my problem

Thank you to who has posted help I appreciate it

[razor02097]

problem solved it runs and sounds better then ever!

now for that damn oil leak

[JSGAuto]

This can't be the same Razor as the CB-F club could it?


Jim

[Pinhead]

So 105 mains work well with the stock airbox and slightly less restrictive exhaust, huh? Do you think 102's would be too much for stock airbox and exhaust?

[razor02097]

This can't be the same Razor as the CB-F club could it?


Jim

Yup sure is

So 105 mains work well with the stock airbox and slightly less restrictive exhaust, huh? Do you think 102's would be too much for stock airbox and exhaust?

as Ibsen said above 98 mains would be good for a stock setup but if you have 102 jets just laying around you would probably be ok