Engine started to sputter in gear

So after weeks of working on the carbs and even fine-tuning it using a mercury based vacuum gauge, I took it out for a test ride this morning. Things were fine for the first couple of rounds around the neighborhood. And then all of a sudden, it started to sputter like crazy in any gear. I'm not able to get good RPM's. Got it back into the garage and verified that the petcock was working fine. I think I hear a little sputtering on idle(very little, not noticeable at all) but when I rev the engine in neutral, everything sounds just fine. When I'm not revving though, I did notice that the RED OIL light comes on and off. Idle holds fine though. What could be going on here?

Background: When I was setting the fuel level on the carbs, I noticed one of the brass overflow tubes had a crack. I used epoxy to seal it up and verified that the leak stopped and also that the overflow mechanism itself was working and the tube wasn't blocked or anything.. I then reset the fuel level correctly.

This morning, before the test ride, I noticed that one of the overflow carbs(not the one with the crack) was leaking full on PRIME. I hit the carb bowl with a screwdriver suspecting a stuck float and that stopped the leak. Not sure if I'm still having problems with the float on this carb. Just surprised that everything was fine for a while before things slowly went bad.

I suggest you find and correct the oil problem before worrying about the carbs. It could be anything from loss of oil pressure to a simple loose wire on the pressure sensor. Also, revving the engine to high rpm with no load is not good for it. Ed

Any suggestions on where I start and what I look for?

Bunty27 wrote: Any suggestions on where I start and what I look for?

I would start with the oil pressure switch. Make sure the connector and wiring are in good shape and not grounding against anything when the engine vibrates. Also make sure your oil level is correct. If that is all good you may need to hook up an oil pressure gauge to test the pressure. If the pressure is good but the light still flickers the oil pressure switch may need to be replaced (no biggy). If the pressure is not good you may have a clogged screen on the oil pump, or worse case but less likely a bad pump. Ed

Update from this morning.

It was bit chilly this morning but the bike did start up with the choke enabled. However, I noticed that it was struggling to idle and I had to help by giving some throttle. But when I tried to get it moving in gear, I noticed that there was very little power and it was struggling to go. After a couple of seconds and going a few meters, it completely stalled. I pushed it back in the garage and now it won't even start though the engine turns fine. The fuel switch was on prime and I verified again that the fuel is flowing out of the petcock.

I quickly did a compression check and the numbers haven't changed since I checked them last (150 - 170 psi). I then did a spark check and though everything seemed to look good, I'm concerned about the spark on plug #2. I did install new plugs and recently cut a 1/4" off the ignition cable.

I did not see the oil light come on this morning during the test. The bike went from riding just fine to sputtering and power loss to more power loss to complete death. I was soo excited that I was ready to ride just in time for the fall weather but it looks bad this time. What should I be looking for? Thanks for all your help.

Fuel filter --
Has an in-line fuel filter been fitted continuously since the carbs were reassembled?

Advancer --
Has correct operation of the ignition timing advancer been verified by observing it with a strobe type timing light to see it quickly moving back and forth as rpm is varied by blipping the throttle?

If the engine won't crank and run, would lube the advancer pivot points anyway, and attempt to manually move the weight arms in an effort to assure they aren't stuck. Access may be gained through the timing inspection window.

If the advancer looks rusted or seems tight, would remove it for clean-up and lubing.

Spark --
What's the apparent issue with spark on plug #2?

Good Fortune!

Thanks Patton.

Yes, I did install a in-line fuel filter since the carbs were re-assembled.

I did lube the advancer and verified that the springs were good (by moving it by hand). I have a transistorised ignition so timing shouldn't be the issue. The engine does crank just fine but doesn't fire up and run anymore.

Not sure about the Spark plug but I don't see a nice big blue spark but a mixed blue and yellow spark on each of the plugs that kinds looks weak. I will try and test the coils as explained in the manual later this evening but could this be the issue?

Bunty27 wrote: ...The engine does crank just fine but doesn't fire up and run anymore.

Not sure about the Spark plug but I don't see a nice big blue spark but a mixed blue and yellow spark on each of the plugs that kinds looks weak. I will try and test the coils as explained in the manual later this evening but could this be the issue?

Where the starter motor spins over the engine just fine, it indicates that the battery is okay and sufficiently charged.

Less than perfect spark at the plugs is sometimes due to inadequate voltage at the ignition coils' primary terminals, often due to corroded wiring connections somewhere along the line between the battery and the coil.

Ideally, voltage actually received at the coil primary terminal should match battery voltage measured across the battery posts. Look for 12+ volts at each coil primary terminal with the ignition ON and engine not running.

If voltage at the coils is lower than battery voltage, here are some places to check for voltage loss:



Ohm checking the primary and secondary coil windings is okay, but usually both coils don't fail simultaneously. Would ohm-check the secondary loop both ways, being from plug cap to plug cap, and also with the plug caps removed (from core to core).

Are the original spark plug wires still in service?


Good Fortune!

Thanks again.

Thinking more about this, the sparks that I noticed earlier this morning didn't look way different from when I checked them just recently before I put the carbs back on. The fuel seems to be moving through the carbs fine since I loosened the overflow screw on the carbs and noticed the fuel flow freely when the fuel switch was on prime. Also, with the overflow screw turned in, I don't see any overflow which would suggest that the float valves are working well too (the float valves are brand new).

So if the sparks are ok and the fuel is flowing through the carbs and the cylinder compression is fine, what else could slowly kill power and turn off idle start? I could easily start the engine with the choke engaged without any problems for many months until this morning when it stalled. Hmmm......

Bunty27 wrote: ...So if the sparks are ok and the fuel is flowing through the carbs and the cylinder compression is fine, what else could slowly kill power and turn off idle start?....

One possible reason could be too tight valve clearances.

Good Fortune!

But could that happen all of a sudden like that?

My model has air suction system and I was reading in the manual that problems with this valve could result in sudden power loss. I'll take a look at it this evening and see how it's doing.

I'm stumped!!

I just verified that both the coils are fine and all the wires have a nice blue spark on them. I then verified that all the plugs have a nice good spark on them too. I have the fuel tank off but there is still some gas in them from before. I was able to crank up the engine and it started to run and idle just fine. I was able to crank up the rpm's just fine on idle. Since the bike is on center-stand, I put it in gear and rev it up a bit but it wouldn't move up much and started to stall again. It almost felt like the mixture was getting too lean. The clutch does engage and wheel does turn but the rpm's just aren't there. I will try putting the gas tank back on in the morning and see what it does.

Any more ideas on what may be happening? Thanks for all your help as always.