Engine hesitates at mid RPMs, can I still ride it?

[volks28]

1983 850 GS no mods except K&N filter

I'm at a loss trying to fight an engine hestiation at mid RPMs. I just did a carb sync and I got it really close (all 4 in the same cm) at 3500rpm. Compression is 150 each cyl. new petcock (doesn't leak). K&N filters are clean and lightly oiled. Spark plugs are new, gapped, getting nice blue spark on all cyl. Just replaced the intake O rings and now the engine doesn't sputter if I spray carb cleaner/wd40 .

Other than that, the bike starts up real nice (within first second of cranking). It doesn't smoke much at startup, maybe a tiny bit, noting major.

After a short 5 mile run, pulled the spark plugs and cyl 1 through 3 are nice and brown/tan. Cyl #4 spark plus was a tad black. I did notice cyl #4 doesn't warm up as quick as #1-3

Question is, can I run the bike and try to live with it? Any risks of damaging the engine/valves?

[gspaul]

Should be OK, check your valve clearance when you can,if they are out you will have to rebalance the carb's after adjustment.
On number 4 cylinder swap the plug lead's on that coil around to the other spark plug, see if it's a plug lead/spark plug cap prob.
But odd's on carby prob.
You did not say , have you changed the jetting/ needle setting's.
A bit of smoke on startup is no big deal.

[volks28]

Thanks for your suggestions!

Haven't "cracked open" the carbs yet to jet. As it is getting close to "high season" here in Canada, I rather try and enjoy a few rides this summer instead of tinkering / destroying a carb. I'm a very impatiant mechanic ha ha! :twisted:

So back to my original question, can I ride it anyways or am I taking a big risk?

But odd's on carby prob.
You did not say , have you changed the jetting/ needle setting's.
A bit of smoke on startup is no big deal.

[gspaul]

That point when you have the hesitation, find a good road and run it at this point for about a mile if you can, hit the kill switch and the clutch at the same time,coast to a stop.
Pull out a spark plug , not No4,if the colour is not white you will be OK.
If it is , you run the risk of valve/piston damage.

[earlfor]

Re: Engine hesitates at mid RPMs, can I still ride it?

If 1 through 3 are tan/brown and 4 is darker, I dont see any risk of damaging anything. You cant burn a valve or cook a piston with a rich or unburned mixture. If 3 is horribly sooty, you could foul that plug but thats about the worst I see that could happen.

Earl

1983 850 GS no mods except K&N filter

After a short 5 mile run, pulled the spark plugs and cyl 1 through 3 are nice and brown/tan. Cyl #4 spark plus was a tad black. I did notice cyl #4 doesn't warm up as quick as #1-3

Question is, can I run the bike and try to live with it? Any risks of damaging the engine/valves?

[volks28]

Re: Engine hesitates at mid RPMs, can I still ride it?

I think that it's probably what's happening. #4 is getting "fouled" so it's not always firing. Does that cause a problem in the long run (for valves) because the engine is sorta "unbalanced" for short bursts of time?

Thanks

If 1 through 3 are tan/brown and 4 is darker, I dont see any risk of damaging anything. You cant burn a valve or cook a piston with a rich or unburned mixture. If 3 is horribly sooty, you could foul that plug but thats about the worst I see that could happen.

Earl

[earlfor]

Re: Engine hesitates at mid RPMs, can I still ride it?

With one cylinder burning differently from the other 3, it will increase your vibration levels somewhat. Depends on how far off it is. :-) Mechanically, it will not destroy anything. Its possible to accumulate enough carbon to cause a valve to be unable to seat and close properly. In that event, you would need to remove the head and decarbon it. (not a difficult task)
Before I replaced the engine in my 750, the old engine was just about done for and it would run black plugs no matter what I did. In the last 15K miles of sooty running before swapping out the engine, it never carboned enough to stop a valve from seating although it was fouling a set of plugs in a thousand miles. If your #4 is sooty and you have already done a carb synch, I would check the resistance on the #4 plug/resistor cap. It may be nothing more than need a new plug cap.

Earl




[quote="volks28"]I think that it's probably what's happening. #4 is getting "fouled" so it's not always firing. Does that cause a problem in the long run (for valves) because the engine is sorta "unbalanced" for short bursts of time?

Thanks