General Category > General Discussion
850 T3 Cali rough between 2000-3500
Adv_hoon:
I recently bought a 1977 850 T3 California which runs really rough between around 2000-3500 rpm. If I crank open the throttle completely in that rpm range then it bogs down until i turn the throttle back and it slowly picks up. Once it is past 3500-4000 it pulls fine with wide open throttle although I think it may be slightly rich there as it pops on overrun. But that is the least of the worries.
I had a theory that it might have something to do with it being bored or fitted with 950 barrels, as it came with some documents that could point in that direction. And hence the carburators perhaps not being properly jetted. I abandoned this theory somewhat for being the full cause of the issue as from what I could read it might not need the biggest of change in jetting, even if it was 950. I pulled the slides out and found V9 needles in the lowest setting (meaning richest - as far as I know) so seems like something else is wrong. The slides did appear very worn though, so perhaps that is part of the issue?
Recently it started dropping one cylinder and had a hard time idling. I have synchronized the carbs and with some more adjustment of the idle mixture screws (only like a quarter turn) I could get it to idle properly although it seems like it very, very slowly dropped the idle. After this I went for a test-ride and when I accelerated then one cylinder would drop and then come back. This let me to believe that perhaps it has to do with ignition and low voltage instead? Perhaps the spark is weak and when the mixture is absolutely perfect at idle, then both cylinders can run, otherwise not. I have never before experienced that a quarter turn on the idle mixture screw could have the cylinder drop off?
Another reason for suspecting low voltage is that the PO just replaced the battery and starter before I bought it. The charging light also comes on at low rpm when you start it and actually only turns of once you go above 2500-300 rpm or something like that.
It will be a couple of days before I have time to work on the bike again. But how much voltage should I expect at the battery at around 1000, 2000, 3000 etc? As far as I have read it should be around 14 volt from 3500 and above?
One little side note which may point to the fact that I have more than one issue, is that it has really bad gas mileage. Just driving around country lanes I have gotten like 13 km/l (around 30mpg) and from what I have read here on the forum and elsewhere that is very low. So perhaps it is a combination of ignition and carbs.
So any thoughts on what might cause it to run very badly in roughly the 2000-3500 range and not allow full throttle is highly appreciated. Can it really be that WOT "blows out" the spark because of low voltage? My initial thoughts would be some acceleration circuit not working, but with all the other issues I at least think spark/ignition has something to do with it. As I said it will be a few days before I can work on it again so just collecting things to try and test for when I will work on it again. And sorry for the wall of text, just wanted to give some context and share my thoughts to make it easier to form an opinion.
chuck peterson:
As TOMB told me over
And over..
And over…
And over again…
Change one thing at a time…I think I’d try lowering (less fuel) the needle a notch or two, and ride it to test the effect
But the rest is Gap? Timing? Tappets? Tune up?
Good luck! Let us know
moto:
Changing things one at a time is the right way to go of course.
But before that, does the motor have good compression? Do a test.
Check the mixture at 2500 rpm by pulling the enrichener lever(s) on the carbs while riding down the road. If the motor runs stronger, the mixture was too weak. If it bogs or quits, that is a sign it was either okay or too rich.
Are the openings in the mufflers covered in carbon?
What do the spark plugs look like when you do a plug chop?
Sorry to have hit the post button too soon, earlier.
Adv_hoon:
--- Quote from: chuck peterson on May 24, 2022, 06:32:32 AM ---As TOMB told me over
And over..
And over…
And over again…
Change one thing at a time…I think I’d try lowering (less fuel) the needle a notch or two, and ride it to test the effect
But the rest is Gap? Timing? Tappets? Tune up?
Good luck! Let us know
--- End quote ---
Yes. Could not agree more. That is also why I think I will start by checking the charging as that is what the "dropping" of one cylinder points to in my head.
As with regards to the needle I actually tried all three settings and raising it made it worse, which I also expected. I am pretty sure that either the spark is too weak or else it gets too little fuel in the initial phase of WOT. If it was too much fuel, then keeping the throttle open should have it initially keep up and accelerating. But if I keep it open, then it dies down. Unless it is above 3500 then it just accelerates.
--- Quote from: moto on May 24, 2022, 06:50:00 AM ---Changing things one at a time is the right way to go of course.
But before that, does the motor have good compression? Do a test.
--- End quote ---
Hmm interesting. I have not tested that, as I do not own a compression tester, but I will look and see how expensive they are and perhaps then do a compression test.
Dave Swanson:
I agree with the prior posts. Take your time and do a proper tune up and carb balance. I would also recommend replacement of the distributor springs. Your old ones are most likely stretched out.
Navigation
[0] Message Index
[#] Next page
Go to full version