Low speed "snatching"?

[Shane4371]

I've orders pilot jet,40.0 ive been told I'll need to readjust everything once again once I install them.I also orderd a fresh screws and oring kit for the carbs.ill see how that goes.no need to do anything else till thats done.it did vety well this weekend tho.

[Pat Conlon]

Hey Arnie, why would adjusting the air/fuel idle screws affect the openings on the throttle plates?

[Arnie]

Hey Arnie, why would adjusting the air/fuel idle screws affect the openings on the throttle plates?

I would expect (IOW, I could be wrong, it has happened once or twice before) that the change in density of the air/fuel mix would change the manifold vacuum some.  I'll have to check the next time I sync my carbs.

[Earl Svorks]

 Pat and Arnie,
Regarding carb synch vs mixture adjustment. Many hours spent looking at the manometer has shown that the reading on all 4 instruments will vary up or down together when a pilot screw is adjusted on any carb . The only adjustment
that will affect individual gauge readings is the throttle plate adjustment for that specific carb. 
  Otherwise on the snatching business,aside from mechanical issues in the driveline, a lean condition is a good bet. I would also put a timing light on it to verify that you do not have too much advance in low rpm  where it should be fully retarded.
   Simon

[Pat Conlon]

I would also put a timing light on it to verify that you do not have too much advance in low rpm  where it should be fully retarded.
   

Interesting Simon, a timing light on a FJ. Have you done this?

Here's the advance curve for the 1100's:

[movenon]

I am thinking the advance is in the electronics of the DCI/TCI box?  From memory I don't remember my timing rotor showing any movement with a timing light.
George

[Earl Svorks]

 George, Pat,
The FJ is no different  than any other bike using pointless ignition when it comes to checking dynamic timing.  You cannot really check the ignition timing in  static fashion , as in a unit using breaker points because at zero rpm, I don't think the electronics will open the primary circuit .  There are however timing marks on the rotor and or breaker plate that will show TDC. Usually another for timing before any advance  T and another for full advance " Their appearance can vary from one machine to another. With an inductive pickup on #1 or #4 plug wire your timing light will show you what your ignition system is doing.  If there is any doubt as to the accuracy of your timing marks, you can at least confirm TDC on either outboard cylinder easily enough. Running at base idle the mark for retarded timing should line up with the reference mark. Something around 5 degrees BTDC. When you bring the RPM up the timing should advance progressively until it reaches full advance. Something like 28 to 32 degrees BTDC. The marks that indicate full advance should line up by 4K rpm. This spec varies from bike to bike but the theory remains. The only factor that affects the advance on most FJ motors is  RPM. I say most, because the early 1100 FJ had in addition to the electronic advance ,a vacuum sensor integrated into the control module. Just like dad's Chev, the timing would advance when high vacuum is present , idle and light cruise. When you open it up, vacuum drops and the timing will retard a few degrees to prevent pinging under load.
  So George, put the timing light back on and take another look. I have seen many failures of ignition box where it will fail to advance on both or only one of it's two channels, or quit or become erratic when the temp comes up, there's lots of ways for them to screw up. Lets hope yours is OK.
   Simon

[movenon]

Thanks Simon. I will try to check mine tomorrow.  I know an initial advance of around 5 degrees is built in and I have a 4 degree V&H advancer installed. When I had my light on and playing with it was a while back and I just don't remember it advancing all that much.
George

[ribbert]

Here's the advance curve for the 1100's:

That's very interesting Pat, I have never seen the advance curve plotted before.

I had a light on mine recently, for other reasons, and as you would expect, eyeballing it, it does just as the chart shows.

It is just a 4 cylinder motor and as Simon says, with a curve like most others with perhaps the exception of the flat line up to around 2000rpm. You will notice if you increase the revs from idle very slowly in neutral, it sounds like it's labouring then hits 2k and the revs shoot right up.

I suspect this is by design to dull the throttle response at low revs. Just my theory, anyone have an opinion?

Noel

[movenon]

  So George, put the timing light back on and take another look. I have seen many failures of ignition box where it will fail to advance on both or only one of it's two channels, or quit or become erratic when the temp comes up, there's lots of ways for them to screw up. Lets hope yours is OK.
   Simon

Thanks Simon. The sun was shining a little today so I went out to do some troubleshooting and work on the FJ.

The advance on both channels works fine.  It will go to the full advance mark when spooled up as you noted.   Things are good.

In the past when I had the timing light on it was when I slotted the back pick up mount plate for more advance and was just looking at the advance at idle and probably wasn't focused on the total advance.   Since then I have replaced the back pickup mount plate with a unmodified plate and installed a V&H 4 degree advance rotor. 

It was a good exercise.  I have some electrical trouble shooting to do anyhow on the bike.  Toward the last of the season I noticed a charging problem (low voltage) and have to figure out if it is the regulator or alternator. Fun , fun..

George

[Earl Svorks]

Noel,
Concerning advance curves,, I have encountered several different motorcycles that displayed running symptoms related to ignition timing. These bike's engines had no provision to check ignition timing using a light. No external timing marks, nothing rotating outside the engine cases. The only way I could get around this dilemma was to fabricate a device with a pointer which I could fasten to the end of the crankshaft. (the makers do provide access to one end of the crankshaft) With my pointer , set to a TDC mark I had established after finding TDC, I flash him up with timing light ready. Now I can see when spark occurs and verify it's advance. Just because it's not adjustable, don't assume the timing is as it should be.( There's a couple of pictures that follow.)
The Ducati 860 I spoke of elsewhere, was an example of this sort. No timing mark or turning parts accessible. Making up a pointer to go on the end of the crank was made more difficult by the fact that the cap on the primary cover was where oil was fed to the crankshaft, under pressure. I got around that eventually and with my homemade pointer
in place running the engine, the spark occurs at 5 before, when I rev it up, no change until around 2800 and then ,,,, BANG,,, the timing shoots straight up to 30 degrees. I check it again, exactly the same. No curve, nothing progressive just, 5 or 30 depending on RPM. This is what Ducati called modern electronics in them days.
     Simon