Alright, minds out of the gutter gents!
:sarcastic:
Is it just my bike or does anyone else experience something like a low rpm snatch when just starting off or rolling by at low speed/RPM?
I find if I'm starting off and I don't slip the clutch a fair bit and/or keep revs around 1500-2000, it will bog, snatch, chug and/or threaten to die. Same if I let the revs drop too low while rolling, even in 1st gear.
Once rolling and above 2000, there's absolutely no issue. Smooth as butter.
Now, a smaller bike I would understand this behavior. But as this is a 1200, I would expect it to be a little less sensitive to light throttle and loads.
My Venture is a 1200 (v4 though) and you can just clutch it out from idle and it will roll away, no questions asked. Pretty much the same with my 750 Interceptor (v4 again), although it's a little weaker being only a 750.
Now I know it's just a jap inline 4 and they're not exactly power houses of idle, but is the FJ12 really this dead below 1500-2000? Or is there possibly something wrong with my bike?
It did the same thing before and after I set the idle screws to factory and synched the carbs.
(http://www.fullsizebronco.com/forum/images/smilies/scratchhead.gif)
What do you have for your pilot jets and how many turns out are your mixture screws?
Quote from: Dads_FJ on September 04, 2015, 12:23:35 PM
What do you have for your pilot jets and how many turns out are your mixture screws?
Its all stock for a Canadian 89 FJ1200.
Mixture screws 2 1/2 turns as per the manual. They were set at 3 1/2 prior to my adjustments (by some PO) and it made no diff to the snatching behavior, but it did make it very hard to start.
Drive sprockets are a bit worn and could use replacement, but the chain rolls smooth and doesn't snatch.
I'm doing a 17" wheel swap this winter and it will get new sprockets/chain then.
The low speed carb issues aside, on the driveline look at a worn chain and sprockets.
Also, take your rear wheel off and pull the sprocket drive hub, and look at your cush drive rubber inserts. Over the years, they get dry and hard, perhaps some fresh ones are in order. While the hub is off look at the axle bearing in the hub (different than the wheel bearings)
Quote from: great white on September 04, 2015, 12:16:46 PM
Is it just my bike or does anyone else experience something like a low rpm snatch when just starting off or rolling by at low speed/RPM?), although it's a little weaker being only a 750.
(http://www.fullsizebronco.com/forum/images/smilies/scratchhead.gif)
I wonder why I'm having probs. "posting" a "reply"?? Lately I've been getting pissed off cuz I hafta type and "post" a reply
several times before it actually appears.
Try increasing idle rpm's in very small increments. I've experienced the approximate same condition on my 84 FJ.
FjLee 84 FJ1100 Denver CO
Quote from: FjLee on September 04, 2015, 12:59:56 PM
Quote from: great white on September 04, 2015, 12:16:46 PM
Is it just my bike or does anyone else experience something like a low rpm snatch when just starting off or rolling by at low speed/RPM?), although it's a little weaker being only a 750.
(http://www.fullsizebronco.com/forum/images/smilies/scratchhead.gif)
I wonder why I'm having probs. "posting" a "reply"?? Lately I've been getting pissed off cuz I hafta type and "post" a reply
several times before it actually appears.
Try increasing idle rpm's in very small increments. I've experienced the approximate same condition on my 84 FJ.
FjLee 84 FJ1100 Denver CO
I'm at 1050-1100 now. Not really willing to go any higher on idle speed. Higher than that seems too high.
I got a little bit of a similar thing going on. I've also had that on other bikes.
I think it's between the idle mixture and worn chain and sprockets, with the driveline being the more important part. New chain/sprocket set makes a bike buttery smooth.
Quote from: great white on September 04, 2015, 12:16:46 PM
it will bog, snatch, chug and/or threaten to die. Same if I let the revs drop too low while rolling, even in 1st gear.
Once rolling and above 2000, there's absolutely no issue. Smooth as butter.
...a lazy battery can certainly cause an ignition misfire at low rpm (low volts) ...sounds kinda like what i went thru many years ago. did all the regular go thru stuff... plugs, coils, carbs.. then later noticed it got worse especially when running aux lights, heated gear, etc... got a battery and it fixed everything. interstate AGM all the way. hopefully you will be as lucky :)
Mine had a bit of that until i balanced the carbs. Made such a difference everywhere.
Quote from: TRoy on September 04, 2015, 05:46:12 PM
Quote from: great white on September 04, 2015, 12:16:46 PM
it will bog, snatch, chug and/or threaten to die. Same if I let the revs drop too low while rolling, even in 1st gear.
Once rolling and above 2000, there's absolutely no issue. Smooth as butter.
...a lazy battery can certainly cause an ignition misfire at low rpm (low volts) ...sounds kinda like what i went thru many years ago. did all the regular go thru stuff... plugs, coils, carbs.. then later noticed it got worse especially when running aux lights, heated gear, etc... got a battery and it fixed everything. interstate AGM all the way. hopefully you will be as lucky :)
Worth a try. Battery is of unknown age and condition.
I'll have it load tested....
So, I've been working on a similar thing.
I can now say with some certainty it is the idle mixture.
When I got the bike, the pilot jets were crazy - three stock US-speck jets and one monstrously oversized one. I swapped to the Euro-spec pilots from Randy. Everything was fine above 3K and at idle, but below 3K it was jerky and weird.
I reset the pilot screws to 3 turns. It got better. Set them to 2.5 turns - better still. 2 turns - even better. Took them down another 1/4 turn. Almost there.
I may have a little bit of an electrical issue since the low RPM twitches a bit, but I'm pretty sure idle mixture was the most of it.
I hope this help.today I synched my carbs,made a huge difference,then proceeded to my idle mixture screws,with a exhaust gas analizer a Buddy brought over from work.my screws were 3 1/2 to 4 turns out just bought this bike aonth ago,we turned all screws I. Till barely touching bottoming out,then backed each screw out in 1/2 turn increments,their all at 2 1/2 turns out.it runs great now.
Shane,
Did you "sniff" the exhaust at the end of the muffler(s), or at the screw tap in each header ?
After you finished the CO sniff, did you re-sync the carbs? They will have moved a bit.
Arnie
What values did you use for the sniff test?
If it's a tail pipe sniffer syncing the carbs should have little effect....the big change will be from the air/fuel idle screws.
Quote from: Pat Conlon on December 13, 2015, 11:16:42 PM
What values did you use for the sniff test?
If it's a tail pipe sniffer syncing the carbs should have little effect....the big change will be from the air/fuel idle screws.
Pat,
If he uses (or used) a "tail pipe sniffer" to set the air/fuel idle mixture screws, which he has told us he has done, then the carb sync will be affected.
I was telling him that the sync would be affected, and (implying) that he should re-sync the carbs.
You seem to be saying that sync'ing the carbs will not affect the air/fuel mixture.
Huh?
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.
Hey Arnie, why would adjusting the air/fuel idle screws affect the openings on the throttle plates?
Quote from: Pat Conlon on December 14, 2015, 09:28:10 AM
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.
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
Quote from: Earl Svorks on January 25, 2016, 05:03:45 PM
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:
(http://i949.photobucket.com/albums/ad337/craigo987/FJ11001984ServiceManual269-1.jpg)
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
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
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
Quote from: Pat Conlon on January 25, 2016, 07:09:39 PM
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
Quote from: Earl Svorks on January 25, 2016, 10:09:15 PM
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. :hi: 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
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