Frustrated, changing parts, doing tests, same results.

[MadRat 88]

I'm having trouble getting my 81' dialed in. I'm running open pipes, 45 pilot, 142.5 mains, new XS performance ignition coil and stock TCI. I have adjusted valves, checked timing, changed TCIs, switched plug wires and I keep getting the same response out of my rig. I don't have any guages on the bike so I'm not sure at what rpm the problem occurs, but my problem is somewhere above mid range and into upper/high rpms the bike starts to shake and jerk and will not get over 55-60 mph.
I thought it was an ignition issue and have been testing/replacing parts with no luck.
When I read the plugs, the right side is a light brown and the left is black and sooty with a hint of oil. I haven't done a compression check since the day I brought this basket case home but I'll be heading to Sears this morning when they open. I have been on the forum since 4am reading about testing compression and trying to isolate the problem.
I seem to run fine all the way up to about 3/4 throttle, the bike then starts bucking and I have to let off the throttle and find a "happy" spot where the bike is not shanking, unfortunately a top speed of 60mph isn't all the "happy" to me.
Sorry for the long wind, just trying to put out as much as I can and get this thing ripping!

 

[pamcopete]

Mad...,

Did I already post this list for high speed problems?

Bike acts up > 50MPH
1. Low battery / charging system. A low battery will produce a low ignition voltage at the plugs which is most evident at higher RPM's.
2. Timing. Did you use a timing light to set the timing?
3. Stuck or no advance. When checking the timing with the timing light, did you check for maximum advance at 3,000 RPM.
4. Binding advance rod. Check out this video:

5. Fouled plugs. Did you install new plugs? Check them after you got it running?
6. Plug wire not making contact in the coil. Measure the resistance from plug cap to plug cap to ensure that both plug wires are making contact in the coil.
7. Brakes dragging.
8. Speedo out of calibration. You are actually going faster than 60 MPH! Use your GPS to check the speedo.
9. Tire pressure. Pump up to 32 PSI for high speed.
10. Drive chain too tight. That will rob you of power to the wheels.
11. Enricher plunger stuck partially on.
12. Enricher (choke) left on or partially on.
13. Weak or loose advance springs. Weak or loose advance springs cause the advance to use up some of the available movement because you have to essentially retard the advance to get it on the idle advance mark, so there is less movement available at higher RPM's.
14. Timing chain needs adjustment.
15. Cheap or bad gas.
16. Low octane gas.
17. Water in the gas.
18. Partially blocked pet cock or fuel filter.
19. Paper filter that has low flow when the tank is not full.
20. Try a run with a full tank of high octane, fresh, expensive gas.
21. Blocked fuel cap vent.
22. Incorrect sprockets. What RPM are you getting at 60 MPH.
23. Rear tire rubbing on brake rod or swing arm.
24. High wind resistance. Are you a large person?
25. Throttle cable not fully opening the throttles.
26. Blockage in the muffler(s)
27. Dirty or blocked air filters
28. High altitude
29. Very hot air, like 95+F
30. Very cold air, like 32F
31. Low oil
32. Really dirty oil
33. Gas in the oil
34. Weak TCI magnet in rotor. Unplug Reg/Rect to test

 

[Kingwj]

I run stock carbs, stock exhaust and stock ignition on my stock bike. I don't seem to have this many problems. I guess I'm just lucky.

 

[MadRat 88]

Thanks Pete, yeah I've seen that list before and I'm going down it eliminating one at a time. About to go check the compression, battery and TCI magnet. The timing is real close and advances, the video with the advance rod isn't what I have, there's nothing under my covers, it's an 81'. Installed new coil and plugs last night, right side plug is light to tan brown and left side is black and sooty with a hint of oil.

 

[MadRat 88]

Compression test reads 100psi on both sides, cold and warm. If nothing else I think at least now I have a clue.

 

[pamcopete]

MadRat,

Did you hold the throttle wide open when you did the compression test?

 

[scabber]

The compression is low but the same both cylnders. The 142.5 main jet seems to be too big the reason for the high end problems. Too much fuel will hurt your engine washing cylinder walls with fuel ring failure piston scuffing ect. When my bike was stock I changed exhaust 1 and 1/2 od pipes shorty emglo short reverse cone mufflers I went up on the main jet 135 main jet. Years later 750 big bore headwork shell cam. With the same carb set up I had a little surging at cruse. I went to the 45 piolet jet 140 main jet too ritch I'm running a 137.5 now better gas milage. It doesn't seem to me that straight pipes on a stock bike would require that big of a main jet. I would look at the carbs again the left for sure check the float levels again.

 

[pa23driver]

MadRat,

Did you hold the throttle wide open when you did the compression test?

x2 on this

i just ran a compression check on my girlfriends '81 650. with the throttle closed it topped out at 110 psi, opened the throttle and imagine my surprise when she jumped up to 150 psi

 

[MadRat 88]

Thanks for the response guys, actually I started another thread about the compression and didn't come back to this one. I picked up another guage from a buddy and that one tested 150 psi on both sides cold, with the throttle wide open.
The real problem was in the oil bag where I have my electronics stashed, wires were rubbing on the hole I cut out of it and dancing on the inside of the bag causing a short every time it hit metal. I have isolated the problem and now I am going through the wires to make sure all are secure and covered. I guess the hardtail bounces a lot and hot wires vs a less than smooth edge opening is causing my problems.
I read both plugs last night with 142.5 mains in after going WFO, they were short of perfect but not over rich, I may back out the idle screw a 1/4 - 1/2 turn just to get the plugs a little better.
Thanks again for all your insight! I'm riding today!

 

[MadRat 88]

Oh, scabber I'm running open pipes with a 45 pilot and 142.5 mains. I've heard most people with a similar set up are running 145 mains. I'll just keep adjusting until I find my rigs happy place!

 

[XSLeo]

Just because others run to big a main jet don't mean it's right for thier bike or yours.
The cv carbs are an easy carb to over jet. The carbs will only give what the engine can use. If jetted to big the slide just won't open as far.
You need to do testing with several jet sizes to find what works.
The carb guide will help on that.
Leo

 

[scabber]

Thank you Leo Listen straight pipe people just because one of you jump off a bridge don't all of you jump yet. Just because you may have cured your midrange stumble with main jet blead thrue from a larger main jet doesn't mean you are not over jetting your bike. I,m just trying to show you a better solution that won't destroy your bike. I've read the carb guide more than once I understand the BS 34 carb pretty well. From talking and listening to to XS JOHN the 137.5 the largest jet he would recommend for straight pipe 135 the smallest. john spent alot of time developing his needles. Since john is no longer with us and us and his needles are no longer an option his wisdom still is. The canadian needle looks to be the best option the length appears to be the same from the comparison pictures in a thread below.Thank You kev. 49 piolet jet John and I didn't always agree on everything I run lean for horsepower but the 45 piolet seems like it will work since the the information obtained so far says it won't. I don't run straight pipes most of the real carb tuners don't on the street. xsleo real biker carb tuner 5 twins griz1 xsjohn to name a few. Most would't touch this with a 10' pole and haven't as far as I know. So here we are the end of road