Rear Cylinder Timing

[Ron99]

My Crane HI-4 recently died so I replaced it. Timed it 35 degrees at 1500 RPM. Bike rode well for several days but the last few days I got a noticable backfire and pop the first 2 miles. Been quite a bit warmer outside so I'm thinking that helped percipitate the problem. After two mile she runs great. What to do.... I sprayed WD 40 around intake manifolds with no change at idle. I did however notice that the carb to intake mating seemed a wee bit loose. I replaced gasket and to be safe while I was in there I replaced the intake to cylinder gaskets. Seems better but I still get some backfire for two miles. I'm going to retard the timing a few degrees and see what happens. So now my question. The HI-4 allows for varying the rear cylinder timing -5 to +5 degrees. What is the reccomended setting? I have it at 0 but I figure the option is there for a reason and the manual does not really describe it well. Do you use a timing light fired off the rear jug to set? Thanks

99 FSXTC
EV-27
CV carb / Thunder slide / SE intake
SE Heads
V&E Pro Pipe HD W/performance baffle
Crane Coil & HI-4
Always solo
42 & 180 jets
Low mix screw out 2.5 turns

[Dr.Hess]

Did it backfire before you replaced the ignition? Did you set the new one to the same settings as the old one? I dunno what you have going on there and why it only does it for the first 2 miles. Sounds kinda like your timing is just off or erratic, since you are confident you don't have an intake leak. Is the carb too lean?

As for the rear cylinder timing, a top fuel drag racer I met told me that 3 degrees retarded on the rear cylinder was the best setting. Take that for what you will.

[rcsoftail]

Depending which curve you selected, timing it at 1500 rpm is probably not accurate since max advanced probably hasn't happened yet. Try the static timing procedure. My experience has show this to be accurate within a degree of timing.

[Ron99]

Update: I'm sure the full advance was hit since when I gave it more throttle the mark did not move. Its my understanding that a specific RPM is not the issue; only that your at the full advance point. I retarded just a hair and also set the rear to -2.5. Runs excellent now. However I still don't understand the rear timing difference. Maybe due to the added heat on the rear jug?

[rcsoftail]

Some do retard the rear cyclinder 2-3 degrees due to the extra heat. I read the front and rear plugs to make sure the timing is the same for both. You can tell by looking at the ground strap for the change in heat color. Here's a couple links for reading the plugs
http://www.dragstuff.com/techarticle...ark-plugs.html
http://www.4secondsflat.com/Spark_plug_reading.html

The rpm for max advance will change depending on race/oem switch, the slope curve selected and if the voes is grounded or not. Sounds like you verified full advance since the timing didn't increase as the rpm's went up. Here are the crane instructions.

ADVANCE TIMING PROCEDURE - USING
STANDARD TIMING LIGHT
This timing procedure requires that a VOES switch be connected
to the HI-4E. For racing applications without a VOES
switch, you must ground the VOES input (purple/white
wire) while setting the timing. Connect a timing light to the
front cylinder. Set the HI-4E advance slope switch to 5
(midrange). Run the engine at 2,400 to 2,500 RPM. Rotate
camshaft position sensor until advance timing mark is centered
in the observation hole. Tighten the standoffs and verify that
timing has not shifted. Timing will now correspond to the curves
in Figures 5 or 6.

SETTING PRECISE ADVANCE TIMING FOR
RACING - USING DIAL BACK TIMING LIGHT
Determine the advance you want at 2,500 RPM. Use a dialback
timing light. Set the amount of advance you want, say 35
degrees, on the dial-back timing light. Connect the dial-back
timing light to the front cylinder. If the VOES is used, disconnect
the VOES input (purple/white wire) while setting the timing with
this procedure. Set the HI-4E advance slope switch to 9 for
maximum advance. Run the engine at 2,500 RPM. Rotate
camshaft position sensor until TDC timing mark is centered in
the observation hole.You will now have the amount of advance
you dialed into the timing light. Tighten the standoffs and verify
that timing has not shifted. Some dial-back timing lights are not
compatible with odd firing H-D® V twin engines. Most Sears
units are OK. Snap-On units may not function correctly.

[Ron99]

Rode the bike off and on over the past two weeks. Problem is the same as before. Backfire and popping the first 2 miles or so till the bike warms up. I think the problem was not evident after m timing check because the motor was not stone cold. I'm stymied here. Timing is dead on as described and I'm sure there is no intake leak at the carb or manifold. Could this be a small exhaust leak that seals itself when hot? Once hot the bike runs great. Also got a a fresh tank of gas so its not a fuel contamination thing. Ideas?

[AirGlider]

Ron,

Is it possible you could have a cracked exhaust? Take a towel and cover the exhaust exit when cold and listen for a leak.

AG

[Ron99]

The exhaust, a VH 2-1 Propipe, was installed this spring. I replaced the selas and was careful to secure the head flange connections before tightening the frame bracket connections. I've heard that not following this technique can induce stress at the flange. I will try your suggestion. I'm wondeing if perhaps the head exhaust has a slight leak thaqt "heals" when hot.