Engine Timing and Back Fire

Fergie · Posted: May 7, 2009, 11:39 pm Post subject: Engine Timing and Back Fire

Hey guys, I haven't posted in a while. This winter I decided to rebuild my engine. It was leaking oil every where, hard to start, and just didn't feel like it was delivering the 48 bhp it should be. I bought all my goodies through Mike's XS, and took pictures of the whole process. It's been a little slow going mainly because I broke my right carb taking the float pin guide out, and then broke 2 of the bosses in the clutch basket trying to tighten down the nut. $100 later on eBay, I'm back in business!

I finally got the bike to fire the other day, but it's very sick. I have to crank my choke to full ON, and if I adjust it back at all it won't run or start. I also have to adjust the idle screw all the way out to get it to maintain idle. I'm getting good spark from both plugs, but my right cylinder is not firing at all. I have the exhaust off, and I can feel that the exhaust coming out of the port is cold. I'm also getting backfires and occasional flames coming from the left cylinder. I just put a timing light on the engine (digital with +/- timing capability), and I am all the way on the far advance mark. I adjusted my strobe to 28 deg. advanced to bring the timing mark back to the "F" position.

y bike is a 1982, it does not have points ignition, and is not equipped with a timing advance. I don't know how to adjust the timing other than trying to rotate the stator and physically adjust the static timing. This sounds like a lot of work.

Does any one know how to adjust the timing on my engine?

Here is a picture of my alternator and trigger:

jayel · Posted: May 8, 2009, 12:11 am Post subject: Re: Engine Timing and Back Fire

sounds like either you've sheared the rotor key or your cam timing is off, line everything up and double check it, pistons at TDC timing marks lined up, all that good stuff

Retiredgentleman · Posted: May 8, 2009, 1:35 am Post subject: Re: Engine Timing and Back Fire

You said you re-built the engine. Are you confident that you lined up the timing marks on the camshaft, index mark on left side at 12:00, and divot on right side at 09:00 even with top surface of the head?

Are the pilot circuits in the carbs clean?

nj1639 · Posted: May 8, 2009, 5:39 am Post subject: Re: Engine Timing and Back Fire

Where's BFE in Indiana? North, Central, South?

Fergie · Posted: May 8, 2009, 9:10 pm Post subject: Re: Engine Timing and Back Fire

BFE Indiana is in the southern part by Seymour.

I haven't looked at the carb jets, I just gave them a quick look over. The eBay seller said they came off a running bike, but I should check them up a little more.

When I put the cam back in, I followed the manual, but was worried that I didn't take all the slack up in the front of the chain. It's probably worth checking.

nj1639 · Posted: May 9, 2009, 8:54 am Post subject: Re: Engine Timing and Back Fire

I thought that's where I lived.
I'm about 15 miles east of old downtown Madison. Now there's a bike friendly town as long as you're not an a$$.
Yeah, timing is fixed on the E.I. bikes. No adjustments needed if everything is lined up and the slack on the cam chain is taken out as the manual says.
New cam chain?

Fergie · Posted: May 9, 2009, 11:35 am Post subject: Re: Engine Timing and Back Fire

It's not a new cam chain, but I did use a new master link. I'm going to go eat lunch, and then start tearing into my bike again. Hopefully I find the problem.

Fergie · Posted: May 10, 2009, 1:02 am Post subject: Re: Engine Timing and Back Fire

I took the engine out, checked the cam timing, and I was three teeth off. I re timed the cam, and put the engine back in. I then took the carbs off and cleaned the jets. I cranked the engine over, and I'm getting good spark, but it still won't start. I opened the drain ports in the float bowls, and I'm not getting any fuel coming out, so I don't think I'm getting fuel to it. It's late, and I have a head ache so I'll give it another shot tomorrow.

Retiredgentleman · Posted: May 10, 2009, 1:09 am Post subject: Re: Engine Timing and Back Fire

Try using the PRI position on the petcock to initially fill the bowls.

Fergie · Posted: May 10, 2009, 11:30 pm Post subject: Re: Engine Timing and Back Fire

Well the reason the fuel bowls weren't filling, is because my fuel line was dry rotted, and sent large chunks of rubber into the float needle assembly. I've cleaned it all up, and the bowls are filling on their own Wink

y next problem deals with tuning the carbs. I can get the engine to start,but it only runs on the right cylinder (hot exhaust vs. cold exhaust). I covered my hand over the intake of the left carb, and the cylinder started firing. Since this is not a practical solution while riding the bike, I need to find out how to make it fire on its own.

Unfortunately this shows my ignorance of carburetors, which is partly due to growing up in the fuel injection era. I have capped off the breather tubes that use to go into the air box. Instead I am running K&N style air filters that I purchased from Mike's XS. I'm guessing I can either capped the breather tubes, or let them flow to the atmosphere. There is also a small adjustment screw on top of the carb, just before it bolts to the engine. I'm guessing I have to tune these so that the engine will run properly. Is there a procedure for that?

pumps · Posted: May 11, 2009, 12:01 am Post subject: Re: Engine Timing and Back Fire

Do you not have a manual? Maybe this will help.
www.knucklebusterinc.c.../XS650.pdf

What Happened to 650rider.com?

Yamaha xs650