Topic: Cb650, Carbs Blowing out Air, Exhaust sucking in air

[dave500]

dont tamper with the advancer!!you cant install it wrong against the crank because of that pin,,dont dissemble the advancer!,just recheck your cam timing with it bolted up to the crank,you might be one or two teeth out maybe from the old one having slipped perhaps from the missing in action locating pin?

[trueblue]

If I recall correctly there are two little dots on it that line up when they are assembled correctly.

[goldarrow]

Sorry guys. I thought 650 were much the same to 550.  I take everything I said back. 

[trueblue]

The Cam spins two revolutions for every one of the crank

Why is the cam sprocket bigger than the one attached to the crank?

Who said that the cam spins once for every two turns of the crank.  The gear on the crank is exactly half the size of that on the cam to achieve this .

[dave500]

The Cam spins two revolutions for every one of the crank

Why is the cam sprocket bigger than the one attached to the crank?

Q..why is a girrafes neck so long? A...because its head is so far away from its body.

[Bailgang]

that note in red is just the way they like to do it so everyone conforms mate,,you can #$%*ing not for the last #$%*ing time have the cam 180 #$%*ing degrees out!

Well actually you can. The manual describes positioning the cam assuming the 1-4 pistons are at TDC however if you position the cam that way but are using the "T" timing mark for the 2-3 cyls on the advancer instead to determine TDC then you're timing the cam with the 1-4 cyls at BDC when they should be a TDC thus making valve timing completely the opposite of what it should be.

[dave500]

well actualy you cant!!then it will be 90 out,anyone whos thinks the cam can be 180 out is a total moron.

[Bailgang]

Okay here is the info from the manual and a couple of pics from the bike. As you can see from the live pics there are two timing marks on the timing wheel in my pics it is hard to see but they both say T F I || S so my understanding is either should work

Dave , 90 OR even 270 at the cam depending on how you want to look at it but the diff at the crank between tdc and bdc is 180 but that isn't the point either because this is how a newb  screws it up. Our man curemode here seems to think it doesn't matter which "T" mark to use whether its the "T" on the 1-4 or 2-3 which you and I of course know it does matter. If he's positioning the cam as if 1-4 were at tdc but he's using the "T" mark for 2-3 to find tdc then he's starting his cam timing with 1-4 at bdc  (crank 180 off where it should be) and he can spin that crank from now to infinity and he'll never get the cam marks to align with tdc and in the mean time the exhaust will suck air while the carbs push it out because of it. I'm not trying to dis you Dave, I totally understand what you're saying about the cam marks being 180 off and just having to turn the crank 360 and all will be well but that only applies if you started with 1-4 at tdc in the first place. We're talking about some newbs that don't understand that.

[Bailgang]

If someone had said the crankshaft was out 180 to the cam marks then I'd say it's AFU, but that was not the technical term used. Spin it later as you will but Dave is still absolutely correct.

Setting cam on 2/3 deserves what it reaps for not reading up on the process basics. To bend or not to bend, that is the question

rt

rt

I didn't mean to make it seem as though Dave was wrong, just the opposite because I agree with what he's saying it's just that the confusion is where are you taking your degrees from. Are you taking it with the cams position in relation to where it's supposed to be or are you taking the cams position in relation to the crank? If the cam is 180 off with it's own position then it's 360 off to the crank which as Dave said doesn't amount to a hill of beans and I absolutely agree because all it means is that instead of #1 being at tdc at the end of it's comp stroke, it's at tdc at the end of it's exh stroke however if the cam is 90 out of its position then its 180 off from the crank and now you have problems. The confusion here is that Dave is looking at the degrees from the cams point of view in which 90 out of time is correct, I on the other hand am looking at it from the cranks point of view in which 180 out of time is correct which basically means we're both right but as I said before that's not the point because your still screwed. So if you're reading this Dave please understand I wasn't trying to dis you at all. I was just simply pointing how newbs get this confused.

[Vinhead1957]

We have ascertained the cam was off due to the alignment mark being off at the points in the start. The cam alignment is critical to the 1/4 T (TDC) mark go there check the valves and verify everything break out the manual pull the plugs and turn everything over by hand gently! Both 1 and 4 fire at the same time. One is wasted ignition timing may be too far off. Or in worst case you bent some valves. Dave I think we all know you can't have a cam 180 out. Lets be constructive and solve the riddle.

[dave500]

phew,thanks goodness for that,this now belongs in the same league as an oil bloody thread,i might get T shirts made that read  "the 180 cam benders"?

[wdmcdonald]

Ok it runs finally!! Not very well... but still. Idles perfectly but as soon as I give it gas it wants to backfire and die. Cant even rev past 1/4 throttle. I do have a 4-1 exhaust and pods... so I think I will need to up the jets. But will more fine tuning on the timing and a carb tune/sync help this issue?

[DH]

Ok it runs finally!! Not very well... but still. Idles perfectly but as soon as I give it gas it wants to backfire and die. Cant even rev past 1/4 throttle. I do have a 4-1 exhaust and pods... so I think I will need to up the jets. But will more fine tuning on the timing and a carb tune/sync help this issue?

What did you to get it started since your last post?
jmo...if it ran good before, something has changed since you first worked
on it. Jets and sync never changed. Now that you have a known good advancer, do the marks
ACCURATELY INDICATE "TRUE" T.D.C.? If so, are you absolutely certain that
the camshaft sprocket marks line up like they are supposed to? Might be a
good idea to remove the valve cover to physically VERIFY cam position when cyl#1 is at true tdc. ("T" 1-4) mark.

[curemode2002]

That is awesome news wdmcdonald but I agree with DH was it running before all this just fine or is this all new to the bike?

Bailgang if those two marks on the timing wheel are indeed for different cylinders do you know how I can tell which is which? If you look closely at my higher res picks both marks on my 650 say the same thing.

[Bailgang]

That is awesome news wdmcdonald but I agree with DH was it running before all this just fine or is this all new to the bike?

Bailgang if those two marks on the timing wheel are indeed for different cylinders do you know how I can tell which is which? If you look closely at my higher res picks both marks on my 650 say the same thing.

I have a couple of advancers, 1 from a 550 and the other a 750 (same advancers really) and they both have 2-3 or 1-4 stamped right after the "TF" stamp. I looked up a 650 advancer on ebay but couldn't find a good enough pic of one for me to take a close look. If your advancer isn't specifically saying what cyls the "TF" marks represent then you can try simply pulling the spark plug from either the #1 or 4 piston and dropping a straw down the cyl bore so the bottom of the straw rests on the piston. VERY slowly turn the engine over by hand and the very moment the straw stops coming up and starts to go down STOP turning the engine over and take a quick look at your advancer to see which "TF" marks are closest to the timing mark on the block. The marks on the advancer for the 1-4 and 2-3 cyls are 180 apart from each other so the one you're looking for should be real close to the timing mark on the block provided you weren't turning the engine over too fast and stopped quick enough. You might want to spin the engine around again just to confirm the same marks on the advancer line up or are close to the mark on the block when the straw stops coming out any farther. Once you're satisfied that you have the right "T" mark, then go ahead and mark it some how so you'll know which one is which.

What ever you do try not to be tempted turning the engine over with a wrench on the nut or bolt that holds the advancer to the crank, you can easily bend that bolt and or snap the pin off the end of the advancer which is what happened to the OP's advancer. I know it's a pain but the safest way is to pull the stator cover off and turning the engine over with a socket and ratchet on the balancer bolt.

[scottly]

The 650 advance plate is marked differently than a 750. The 1 and 2 are under the T, and the 3 and 4 are under the F.

T F
1-4

The 3 and 4 are mostly hidden by the spring, even with the advancer off the bike, and only the top of the 1 and 2 may be visible through the window when installed on the bike. One of the units I looked at had a dab of green paint on the 1-4 position.

[Bailgang]

I have a couple of advancers, 1 from a 550 and the other a 750 (same advancers really)

I think I should clarify that a bit. What I meant is that the 550 and 750 advancers are pretty much the same from a visual point of view to each other though I don't know if they share the same part #. I didn't mean to imply they were the same as a 650 advancer.

[curemode2002]

Thanks tons Bailgang and scottly that is very helpful I will update my earlier post to reflect that. What I did the first time I put everything back together was to hold my finger in the spark plug hole for cylinder one and found it that way. I will also look closer at my timing plate to see the 1-4 and 2-3 marks.

[wdmcdonald]

Sorry for the late response. I know the cam is set correctly and the 1.4T marks on the advancer are positioned correctly. Valves are all adjusted as well. However I still could not get the bike to start... So I started rotating the ignition plate to try and see if I could find a spot where it would work. I rotated it about 45 degrees (Which there is no notches lined up with the screws so I had to grind one.), it literally started right up in under a second. What would cause this? I've never had to put the plate in such a weird position. So the bike idles great now but I think I need to rejet the carbs and sync them. It actually didnt run perfectly before, it had this same problem I just never got around to fixing it.

So now the issue is... idles great. As soon as I try to rev it up it hesitates, backfires and wants to die. I think with the pods and open exhaust its just getting way too much air and not enough gas. Im gonna start with bigger jets and go from there.

[trueblue]

If the marks are synchronized correctly mess with the point gap so the points open at the F marks.

No points in the 650 .  It does sound to me like there is something up with the advancer, either it is off something other than a 650, but more than likely it has been reassembled incorrectly at some point.

[wdmcdonald]

I'll post a picture of what I have going on. But if the advancer was disassembled and reassembled incorrectly then how would the bike even start with where I have everything set?

[jamesbekman]

Hi, I breezed through this posting.  Double check you dont have your coils reversed.  Left side coils from drivers view to 2-3 and right side to 1-4.  I had that happen.  Fired right up!

[jamesbekman]

If you have them reversed that would mimic the 180 "camshaft out" brainwave someone was having.

If its the case and the coil spark plug wires are reversed, do the test light static timing for the points all over again and then give her a go.  Im thinking the reason you got the bike to fire up with the points plate so out of whack is due to it technically being 180 out and getting it to run from turning the plate so far out of spec that it makes it catch some spark to get it to idle enough but when you rev it the advancer takes the timing way out again.

-James

[scottly]

if the advancer was disassembled and reassembled incorrectly then how would the bike even start with where I have everything set?

To check the assembly of the advancer, there is a small circle stamped on the base plate. The "lobe" should point to the circle.

Edit to add picture.

[wdmcdonald]

Ok... so the advancer is assembled correctly. So i have no idea what the heck is going on. Bike starts and runs a little better with some carb adjustments but still wont rev. Its backfires and pops at 1/4 throttle but I can work it up to WOT where is just sounds like its hitting a wall at about 5k rpm. Where do I go from here? Still the only way it will start is when the ignition plate is in the random position.

Dillon