I'm at a loss here. I'm not real familiar with the older bikes but I have a 1969 T120. 6 months ago was out riding and it was beautiful. This week, drained fuel and added fresh and she fired right up. Idles great and takes throttle great.... until you pull off. Sputters the whole time. You can whack on the throttle and it takes off hard but still rough the whole time. Plugs are good, carbs are clean, all the passages are clear, updated ignition. What the frack am I missing? Doesn't really backfire and never stalls, just falling on itself while accelerating. Any input is appreciated.
Cheers!
we need a little more information here... Why did you drain the fuel? Was it bad? What do the spark plugs look like?
the two obvious culprits for these conditions are carburetors or ignition. . It could be something as simple as a condenser going bad... There are some good mechanics here, but we need a little more from you, before trying to diagnose this
This bike has an upgraded electronic ignition. Fuel was not bad, but bike sat for six months, so clean fuel as precaution. One plug (Right side) tends to foul. We are confident that Carbs are in good shape/clean. Problem appears to be getting worse each time bike is run.
Wondering if it's a timing issue due to the worsening backfiring!
There are no moving parts to wear out like a rubbing block on a set of points that narrow the gap closed. I think that eliminates the timing once that is set.
If the bike idles, it says that both jets are open. Both feed in that blending there of. If it was hard starting and you had to rev it a lot or the choked kept it alive, then the low or idle jet is clogged.
If it won't rev, the main might be clogged. However, both low and main feed idle. It would still be hard to start and idle if the main had any contamination in it.
If you have that hesitation, could it be a weak cylinder that "Hez no power," could make you think there is a fuel problem but it is more a cylinder lagging with not too much power (compression)?
That is why the net is so tricky to diagnose from here.
It seems more like compression. Spark and fuel is present. You are saying the one side fouls plugs. That to me says check compression first. Go from there. Waste taking apart the clean carbs would be a waste to clean them and the problem is still there? No... First sign of an old bike with problems of the 3amigos? Compression first WOT ARE THE NUMBERS... Says to not chase one's tail.
Just to rule out ignition, install new plugs and swap spark plug wires. Put the right plug to the coil for the left and vice versa. Since most electronic ignitions for these are dual fire, it should run that way. Check to see if the left cylinder misfires.
I do not know of the plug fouling is gas or oil (you did not say), so let's start with the simple stuff and work up.
Swapped the coil leads and it wouldn't even start. It actually backfired out of the left exhaust pipe. (loudly) Spark seems consistent on both sides. Compression is showing 70p.s.i. both left and right cylinders, however I've been a little suspect of my Motion Pro compression tester lately.
The strangest thing is, on Wednesday the bike ran fantastic. Yesterday it ran rough and today is runs like crap! It's as if something is progressively deteriorating.
also 70 PSI is not great. was that running or just you kicking it through with a compression tester?
If one was low, I would think bad rings, but with both being equal, and you saying that the right was fouling plugs, but not the left, I am leaning back towards carbs or ignition
Not sure on the brand. Zenner is gone and replaced with the small electronic ignition box under the tank and the plate where the points were at. All the connections are clean and tight for the ignition and going to the coils. No intake leaks. The carbs are Amal 930's without chokes. I actually drilled the sides to better access the pilots for cleaning then tapped and plugged the holes.
Just had it running again. While sitting there idling you can hear the right cylinder hunting around and firing at times and when it would pop it was actually throwing flames!
for clarification...
do you mean that the rectifier/regulator and the electronic ignition box are one unit?
I do remember a unit like that back in the 80s. . They weren't so good. In fact they were prone to failure. The one I had left me walking home one day (before the time of cell phones).
gap an extra plug wide. By wide, I mean double the gap called for. If it cannot bridge that gap outside the engine, it will not do so inside, under compression
The ignition is separate from the reg/rec. It looks to be like a newer modern system. All the wiring looks new. I'll try the spark plug trick and see if it can jump the larger gap.
hey I had a similar series of problems. check all your leads to your coils. to and from the ignition and between each coil. turned out mine had a loose wire at the spade connector at the coil and a minute wear spot on one wire from the wire rubbing on the gas tank, exposing a dot of wire. fixed both wires and she fired up like a champ with no misfire for the last month. Good luck
Check your battery voltage & alternator charge rate. With electronic ignition, can cause mis firing if not correct. Charge rate 13.5v min to 14.5v @ 3000 all lights on. Static battery volts around 12.5v min.
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