Starting problems

[FrkyMnky]

Swapped my 38s for a set of VM34. Everything was running before, however I was running VERY rich with the 38s. 34s are setup as such:

159p6 needle jet
6f9 needle 3rd clip
25 pilot
180 main
.905"/23mm float level
5/32" slide level

I cannot get the bike to start now. I haven't checked the ignition side yet as I didn't mess with that, but that will be coming if it turns out not to be the carbs. Ive tried choke, no choke, turned the idle a turn in, and messed with the mixture from 3/4-1 3/4 turns. After trying to kick it a handful of times, there is a pool of fuel in the intake boots. Any idea why it isn't starting? The only thing that I can figure would cause this is the float level, unless something is wrong on the ignition side.

 

[Kathos]

Space throttle valve with a drill bit to about 7/32 on both throttles. Turn mixture screws 3/4 turn from all the way in.
If you don't see any improvement. Check your spark.
You have fuel. You need air, spark, and timing.

 

[FrkyMnky]

Ill try that today with the slide level. Im going to check the coils as well to see if anything happened to them. Im assuming I can still check timing rotating it by hand and using a timing light? Or would it be easier to just hook a multimeter up to the coil leads and watching for the voltage change?

 

[Kathos]

Timing light for timing. Look at the plug for spark. Then if no spark check power to coils. Then go from there. Yes. You can turn it by hand. Ccw on the timing rotor.

 

[5twins]

When you check timing by rotating the engine by hand, that's called a static timing check. You don't use a regular timing light that clamps on the plug wire but rather a small 12V bulb clipped to the points set (and ground) that you're checking.

 

[FrkyMnky]

Tried the 7/32" this morning and it started up first kick. Trying to get the idle down though is proving pretty difficult. At least I know I can get it started and have a base point to work on jets. I can also check timing now. For the static timing, can I just use a test light or does it need to be a specific light? I am running PMA/Pamco w/ Dyna coils and no electric start.

 

[5twins]

I'm not sure you can static time a Pamco, but since it's running, there's no need to. Just use the regular timing light.

 

[FrkyMnky]

Holy crap, what a difference properly tuned carbs makes. While I still need to do some fine tuning, the jetting is pretty close; even for my 700cc ported beast. Looks like I may need to step up to a 27.5 pilot and maybe increase the main, but it runs pretty damn well.

I did have some problems trying to check the timing though. Ive got a craftsman pro light and with it hooked up to a aux battery and a jumper to the engine, I am not getting a consistent light. Its reading RPMs just fine, but the light is jumping around all over the place.

 

[ippytattoo]

Try using the other spark plug wire or flip the clamp over. Some timing lights are real picky about the spark polarity.

 

[Kathos]

There is a really good vm34 tuning manual somewhere on here for setting it up on the xs650. He says recommends starting at 5/32" throttle sliders but I've never has success with that. If your having trouble idling, you can use the pilot screw to adjust the idle richness. You can also play with the needle position to adjust as well. I recommend finding the manual and memorizing it.

 

[FrkyMnky]

Yea I have it printed out for quick reference as well as the Sudco tuning manual. Its going to take quite a bit of time to tune this as its already pretty damn close. I was able to get the idle down to 1100, but it required me to turn the mix screw to 1/2 turn out. Ended up setting the slides at 3/16". Cant wait to start doing some hard running on this and tuning it. Gives me a great excuse to ride.

As for the timing light, I tried both plugs. I didn't flip the clamp over and will try that tomorrow. Didn't know if I needed to do something special with the Pamco and 277.

 

[ippytattoo]

With a rephase you will only be able to use one side (usually the left side) plug to set the timing. I have a cheap timing light from harbor freight that is real sensitive to polarity (it would jump around like a drop of water in a hot frying pan) and found that I could flip the clamp over (completely by accident I may add) and it worked much better. You may also be able to swap the primary wires on your coils to change the polarity of the spark.

 

[FrkyMnky]

I put marks for TDC on both cylinders so I can check timing on either, unless there is something else that would prevent that.

 

[FrkyMnky]

So I was able to do some pretty hard runs on the carbs today and noticed a pretty common problem. Under light to medium throttle I was getting very very slight misfiring/backfiring. I can't find any reference about having this problem and what needs to be changed to fix it. Also, when starting the bike, it starts on the first kick w/o the starter circuit, however I must give it slight throttle for about 2 minutes. If I try the starter circuit it will kill it. If my thinking is correct, then if I increase the pilot and turn out the mix screw that should increase air and allow the starter circuit to be used to warm up the bike.

Plugs look pretty good, although around the threads there is a buildup of soot. The insulator looks good though.