Low speed "snatching"?

[great white]

Alright, minds out of the gutter gents!



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.

[Dads_FJ]

What do you have for your pilot jets and how many turns out are your mixture screws? 

[great white]

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.

[Pat Conlon]

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)

[FjLee]

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.

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

[great white]

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.

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.

[JPaganel]

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.

[TRoy]

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

[Rhino]

Mine had a bit of that until i balanced the carbs. Made such a difference everywhere.

[great white]

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....

[JPaganel]

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.

[Shane4371]

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.

[Arnie]

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

[Pat Conlon]

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.

[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.

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?