Author Topic: intermittent loss of power?! (Read 6667 times)

tom_eaton · « **on:** September 05, 2006, 08:33:15 AM »

hi all,

i was riding along the other day, when the power seemed to drop all of a sudden. more riding revealed that power seemed to go on and off, as well as a different sound from the exhaust, when the power dropped the exhaust sounded more 'aggressive'.

sorry if this sounds vague but its the best way i can describe it.

any questions/ideas?

stormi · « **Reply #1 on:** September 05, 2006, 01:17:14 PM »

Are you firing on all 4?

The B4 did something like that on the last trip up to the mountains. Turned out that her 3rd cylinder wasn't firing consistently. (After a plug change prior to the trip) The plug wire wasn't 100% on, and we found that the #3 carb seemed to have more fuel in it than it should. So, cleaned the carbs,... again. Then trimmed the #3 plug wire,... she seems immensely happier now.

StangMATA · « **Reply #2 on:** September 05, 2006, 01:22:51 PM »

1) Check for consistent spark to all cylinders

2) Check plugs. They can tell the story as to which cylinder is having the issue and sometimes even what is causing it

3) I know this sounds stupid, but check the petcock to make sure it is locked in the "on" position..also, another dumb one, you have enough fuel?

4) You like yams?

tom_eaton · « **Reply #3 on:** September 05, 2006, 01:28:24 PM »

ok i'll check out the plugs. what am i supposed to be looking for if there's anything wrong?

stormi · « **Reply #4 on:** September 05, 2006, 01:45:33 PM »

Quote

ok i'll check out the plugs. what am i supposed to be looking for if there's anything wrong?

If the plug is wet, it means that there's fuel in the cylinder, but no spark. That's the easiest thing to identify.

The rest of these, I'm going on memory from my Firebird days:

A tan ceramic piece ( right under the electrode) will indicate that the fuel mixture is right on.
Black (carbon) means rich or too cool. (or weak spark)
Oily ( not to be mistaken for carbon, which can be similar looking, or a wet plug) is BAD. Rings? valves? ( I don't recall off the top of my head)
White, means that the mixture is lean, or too hot.
Part of the plug missing ( don't laugh, it happens

) means that there's a foreign object in the cylinder, and impact damage has occurred. May also be from preignition, or plugs that are too long.

The other thing you can do, is if the problem is consistent enough, fire the bike up for about 30 secs, and then turn it off. You should be able to put a hand near or on each of the pipes -very- briefly, and see if they're all hot. If not, the non-hot one will point you to your problem cylinder/carb.

StangMATA · « **Reply #5 on:** September 05, 2006, 01:48:29 PM »

Quote from: tom_eaton

ok i'll check out the plugs. what am i supposed to be looking for if there's anything wrong?

Well, if one plug is different than the other three, then that indicates the bad cylinder. From there you are looking mainly for color or any pitting.

tom_eaton · « **Reply #6 on:** September 11, 2006, 11:32:44 AM »

right then, riding and general spannering have led me to believe the #4 cylinder isnt right. ive done a complete plug change, but the problem isnt much better. the bike does seem to run better when its hot. i thought it might be a problem with the coils.

any suggestions?

solman · « **Reply #7 on:** September 11, 2006, 12:57:36 PM »

If you install the same plugs and still having problems, buy a new set and install them. I've had a few spark issues on the B12 and replacing them fixed it on one occasion.

tom_eaton · « **Reply #8 on:** September 11, 2006, 01:21:24 PM »

what i meant was i bought a new set of plugs and put them in!

stormi · « **Reply #9 on:** September 11, 2006, 02:16:44 PM »

Quote

right then, riding and general spannering have led me to believe the #4 cylinder isnt right. ive done a complete plug change, but the problem isnt much better. the bike does seem to run better when its hot. i thought it might be a problem with the coils.

any suggestions?

If it was a coil, both your #1 and #4 cylinders would be manifesting problems.

Are you sure you have spark? Did you test when the plug was out? Also, Check the plug wire, perhaps even trim off 1/4" and reseat it into the boot.

The plugs are an indicator of what's wrong with your cylinder. That's why two of us told you to check the plugs when you pulled them out, not just change them. I noticed you didn't say. What did the #4 plug look like when you pulled it out? Wet? Carbonned up? Dry? That will lead you/us to the problem.

tom_eaton · « **Reply #10 on:** September 11, 2006, 02:25:01 PM »

all the plugs looked the same. i checked them when i took them out. every plug was carbonned up.

stormi · « **Reply #11 on:** September 11, 2006, 02:36:37 PM »

Quote

all the plugs looked the same. i checked them when i took them out. every plug was carbonned up.

That's very strange to have them all look the same, but the cylinders behaving differently, but I'll take your word for it.

And the answers to all of the rest of my questions? Believe me, they're valid, I'm going through the same thing right now.

tom_eaton · « **Reply #12 on:** September 11, 2006, 02:54:32 PM »

i didnt test for a spark, ill have a look tomorrow, and will trim off the plug wire asap.

the plug was dry and carbonned up, the same as the others

solman · « **Reply #13 on:** September 11, 2006, 04:22:07 PM »

Lets go back to the basics, what kind of setup do you have? Aftermarket exhaust, jet kit, advancer, etc?

tom_eaton · « **Reply #14 on:** September 11, 2006, 04:29:34 PM »

right, aftermarket exhaust, engine is completely stock exept for 33bhp restrictor kit in the carbs. spark plugs are manual recommended ngk's. the carbs were tuned not more than 4 months ago. the problem first appeared while going about 90mph on the motorway.