Cam chain timing?

[Robert Dell Aquila]

Hi yall, hopefully you guys can help me finally get my bike running.I have a 78' 650-E 277 rephased. I believe that my camchain timing is off. I put the timing marks at TDC and looked behind the advanced unit and the dowel pin in the cam. It seems to be off not by too much but enough. I also have not timed my new pamco because I could not get the engine to run long enoigh to time it. However, the engine would start up and idle for a few minutes then die then would not start back up again. I switched coils and new plugs caps and wire. Compression is around 120-130 both sides, I have spark and fuel flowing through the carbs with the mix screw set 2-1/2 truns out. My question is how would my bike even run with the timing that much off and if the problem is cam timing would it cause the bike to just sputter out after a little while running? As always any help is very much appreciated.

 

[Jim]

I'm not familiar with the 277, but if you got it to run... even for a short time, I'd guess your cam timing is pretty close.

 

[Robert Dell Aquila]

I'm not familiar with the 277, but if you got it to run... even for a short time, I'd guess your cam timing is pretty close.

Yea it'll start up and idle (or atleast it used to) but would the bike just sputter out if it was a timing problem? I thought it was carbs but I put some gas into the spark plug holes and it just back fired really loud so that made me think it was timing. And if its not starting at all now then my timing might be way off. Just wanted to get some insight before I'd have to go into the engine. Never done it before, might be fun.

 

[Robert Dell Aquila]

By the way running pamco ignition.

 

[gggGary]

You bought it like this? Cheap, from a PO that said it just needs tuning? Yeah that sure looks and sounds like cam timing off. That would drop you compression also, 120 on an accurate gauge is low.

 

[TwoManyXS1Bs]

Your TDC marking at the alternator is for the left cylinder.
The camshaft pin under the advancer should be pointing straight up (or down) when the right cylinder is at its TDC.
The right cylinder leads the left cylinder by 83°. The cam runs at 1/2 speed from the crank. If you put the left rotor at TDC, then reverse-rotate it by 83°, then the camshaft pin should be up (or down). This would reverse-rotate the cam by 41.5°.

So far, your advancer pic looks right (about 41° past top), it has compression, and has successfully fired.

Pull the plugs, leave the fuel off, fully open the throttle, kick it thru a buncha times to clear out any residual fuel. Put it back together, try again...

 

[Robert Dell Aquila]

You bought it like this? Cheap, from a PO that said it just needs tuning? Yeah that sure looks and sounds like cam timing off. That would drop you compression also, 120 on an accurate gauge is low.

Nah the PO was actually a motorcycle mechanic however he was like 85 years old and not all that together. That dude was a legend. However, he did tell me I just needed to tweak it a little. And "a little" ended up being a lot of work. You think I should pull the engine and adjust the cam? Im down to get my hands dirty.

 

[Robert Dell Aquila]

You bought it like this? Cheap, from a PO that said it just needs tuning? Yeah that sure looks and sounds like cam timing off. That would drop you compression also, 120 on an accurate gauge is low.

I diden't buy it cheap. He through in a whole other 650 motor and a bunch of extra parts. He was such a nice dude. I rode the bike up and down the block and it seemed fine, it idled real strong so I went with it.

 

[gggGary]

Follow 2M's advice and get to the bottom of the timing. Find out for SURE where everything is at. A degree wheel, BOTH side's TDC marks and valve opening closing will pinpoint the cam AND ignition timing. Yes lots of "could be's" that need to be explored, and go no go confirmed for each. Just the nature of working on "someone else's" custom.
Yes it could easily be carb issues leaking float valves can act this way, will start, idle but floods when throttle opens. Check your oil, does it smell like gas?

 

[Robert Dell Aquila]

Follow 2M's advice and get to the bottom of the timing. Find out for SURE where everything is at. A degree wheel, BOTH side's TDC marks and valve opening closing will pinpoint the cam AND ignition timing. Yes lots of "could be's" that need to be explored, and go no go confirmed for each. Just the nature of working on "someone else's" custom.
Yes it could easily be carb issues leaking float valves can act this way, will start, idle but floods when throttle opens. Check your oil, does it smell like gas?

Havent checked the oil smell. This means that gas would be leaking into the oil? How would that happen? I have an set of extra carbs I've been working on that I cleaned out and have a step up on main and pilot jets from the stock 78 BS38's. Still wouldnt start. I'm leaning torwards timing. I also read that I should check if the plugs are wet after kicking to see if gas is going into the cylinder correct? I have not done this yet.

 

[gggGary]

Yep a full round of troubleshooting 101 to start. Leaky petcocks and float valves allow fuel to slowly leak into the cylinders and dilute the oil. Quite common on many bikes. How does the tank look inside? Fine rust particles prevent valves from sealing properly. Everyone wants to "fix the problem" but that's the long way around, a full wake up maintenance is the short way to a good running bike. Spent decades learning that. See Milwaukee Iron.

 

[Robert Dell Aquila]

Yep a full round of troubleshooting 101 to start. Leaky petcocks and float valves allow fuel to slowly leak into the cylinders and dilute the oil. Quite common on many bikes. How does the tank look inside? Fine rust particles prevent valves from sealing properly. Everyone wants to "fix the problem" but that's the long way around, a full wake up maintenance is the short way to a good running bike. Spent decades learning that. See Milwaukee Iron.

Tank looks pretty good on the inside, no leaky petcock. I also have a rock filter from the petcock to carbs to filter out debris. I'm going to go home and take 2M's advice. Do you know if having a rephase would alter his input about when the right cylinder is at TDC and the cam pin is up or down? Anyways thanks for reaching out. I appreciate all the people that respond on this forum. Much love.

 

[5twins]

He was explaining how it should be WITH a rephase. Stock, both pistons rise and fall together. Both are at TDC at the same time.

Carbs older than '78 have an overflow pipe in them. If the fuel level gets too high, the excess drains out the overflow tube and out a nipple on the bottom of the float bowl. The overflow tube and that nipple were eliminated on the '78 and newer carbs. If the fuel level gets too high in them, the excess gas has no where to go except into the main carb bore. From there, it runs either back into the air filter or forward into the motor, or a little bit of both.

 

[Robert Dell Aquila]

He was explaining how it should be WITH a rephase. Stock, both pistons rise and fall together. Both are at TDC at the same time.

Carbs older than '78 have an overflow pipe in them. If the fuel level gets too high, the excess drains out the overflow tube and out a nipple on the bottom of the float bowl. The overflow tube and that nipple were eliminated on the '78 and newer carbs. If the fuel level gets too high in them, the excess gas has no where to go except into the main carb bore. From there, it runs either back into the air filter or forward into the motor, or a little bit of both.

Thanks man. Im going to kick the bike over a few times to try and clear out some fuel. I have a question however regarding 277 valve clearance. I used OEM spec for the valves is there a specific valve clearnace for 277? When I set it to spec with the right cylinder at TDC I can get the correct feeler gauge width under the tappets. However when I rotate the alternator 1 full revolution back to TDC on right cylinder there is no clearnace uner tappets. Seems like every other revolution it will have clearance do you know if this is normal??

 

[5twins]

Yes, that sounds normal. A 4 stroke motor, in the course of going through it's 4 strokes, will reach TDC twice during the process. Going through the 4 strokes takes 2 complete revolutions of the motor. The first time is TDC on the compression stroke, when the spark plug fires. There will be valve clearance then. The 2nd time however, is TDC on the exhaust stroke. The exhaust valve will be just closing and the intake will be about to start opening. There will be no valve clearances at that TDC. If you were to set the valves at this 2nd TDC, the gaps would probably be too big.

So, it seems you have set the valves on the right TDC stroke (compression) but then one full revolution is bringing you to the TDC exhaust stroke where there are no clearances. Give the motor another full turn to TDC and the clearances you set should be there again.

 

[Robert Dell Aquila]

Yes, that sounds normal. A 4 stroke motor, in the course of going through it's 4 strokes, will reach TDC twice during the process. Going through the 4 strokes takes 2 complete revolutions of the motor. The first time is TDC on the compression stroke, when the spark plug fires. There will be valve clearance then. The 2nd time however, is TDC on the exhaust stroke. The exhaust valve will be just closing and the intake will be about to start opening. There will be no valve clearances at that TDC. If you were to set the valves at this 2nd TDC, the gaps would probably be too big.

So, it seems you have set the valves on the right TDC stroke (compression) but then one full revolution is bringing you to the TDC exhaust stroke where there are no clearances. Give the motor another full turn to TDC and the clearances you set should be there again.

Thanks very informative. Appreciate it. I kicked over the bike with plugs off and tried to start it after and just get back fire through the carbs. Pulled the plugs and they did not seem wet with fuel. Not really sure what else to do. I put some fuel into the spark plug holes and tried to kick over. Just loud backfire which lead me to believe its timing but my cam chain pin faces up when right cylinder is at TDC. Which is why I created this post initially. I'm leaning torwards a combination of carb/timing troubles.

 

[Robert Dell Aquila]

Follow 2M's advice and get to the bottom of the timing. Find out for SURE where everything is at. A degree wheel, BOTH side's TDC marks and valve opening closing will pinpoint the cam AND ignition timing. Yes lots of "could be's" that need to be explored, and go no go confirmed for each. Just the nature of working on "someone else's" custom.
Yes it could easily be carb issues leaking float valves can act this way, will start, idle but floods when throttle opens. Check your oil, does it smell like gas?

Honestly my entire garage smells like gas ahaha so I pulled the bike outside and gave the oil a wiff. No gas smell to me. It seems like I'm getting a ton of fuel in the float bowl but none in the cylinders because when I kick it over a bunch and check the plugs theyre dry. And when I put some gas directly in the spark plug hole it just backfires real loud. I confirmed 2M's degrees and mine match up. The cam dowel pin on the right cylinder at TDC faces up or down (depending on exhaust/compression stroke).

 

[gggGary]

Any chance you swapped coil wires while working on it?

 

[Robert Dell Aquila]

Any chance you swapped coil wires while working on it?

Already checked em. The thing that I'm wondering is why it started before and won't now. Timing doesnt just go away does it? I set up pamco for intial firing.

 

[Robert Dell Aquila]

Any chance you swapped coil wires while working on it?

I tested that the cam pins infact point straight up or down when my right cylinder is at TDC. I used a degree wheel, thanks @TwoManyXS1Bs. I discovered that the issue I'm having is most likely carbs. I put my spare carb set on my bike (78bs38's), floats adjusted to spec. Needle and jets all stock. I sprayed some starter fluid into the carbs and got the craziest kickback. I used the electric start and the bike started right up. However, it was reving real high. I backed out the idle scew all the way and it still was reving real high. I turned off the bike and saw white smoke coming out of my left carb. Any thoughts?