engine misfire
 

Hi all im new to this and could really do with some advice.:confused:My VTR is missing like hell at 7000 rpm ive had new spark plugs/coil leads and carbs balanced but still the same,would really appreciate any help or advice....thank you..

Hook up a timing light and check if you loose spark, then check them to see if the carbon is white.

Cleaning the fuel system is a good idea as well. I usually do this job first as it is easy for the home mechanic to do.

misfire
 

thanks all for the quick reply
ill check them all to day and keep you posted

vtr missfire
 

hi mine did the same closed the plug gap very small works fine now

Does it misfire @ 7000 rpm but no load (clutch pulled in)? If so the problem is more than likely spark related not fuel related. If it misfires with the clutch pulled in do the following

warm up the bike, then run the bike to the stumble point (with clutch pulled in).As soon as the misfires happen(give it 2-5 seconds of stumble), kill the engine (switch) and close the throtle. Quickly pull the plugs and examine them. If ONE is wet and the other dry, you found your bad cylinder. If BOTH are wet, check your plug gaps, coils, and ignitor box. If both are DRY...then the problem is fueling.

If it only misfires under load, check the fuel system/carbs.
Do you have a inline fuel filter? If so check it for flow/clogs.
Check your fuel lines for kinks/flow.
Pull the petcock off the bottom of the fuel tank, and clean the screen. You'll be amazed how dirty it gets.
If the basic's of the fuel system are good, and the bike runs fine with no load, then you've got to look into your carbs.
Are they seated properly? If you idle the bike and spray starter fluid/wd40 around the seals does the idle speed change? If so, you've got airleaks. If not, it's inside the carbs.
Check your floats (more than likely fine, as it idles fine, but never hurts), then check your needles and shims, and jets.
Record the settings here and folks can give you an idea if they are way off.

oh, and the plugs... are they black with carbon or white from heat? Are both plugs the same color? maybe one cylinder is rich, or lean compared to the other?

as a last attempt warm up the bike, then run the bike in 1st gear up to the stumble point (underload) very close to your house/driveway/garage. As soon as the misfires happen, kill the engine (switch) and close the throtle and coast to your driveway/garage. as described above Quickly pull the plugs and examine them. If ONE is wet and the other dry, you found your bad cylinder. If BOTH are wet, and you verified the ignition system, your carbs are way outta wack. If both are DRY...then the problem is fueling.

misfire vtr1000
 

Hi thanks for all that info,its actually missing underload at 7000rpms ive checked all that info you have given me all looks as it should do.Ive had the carbs balanced but the bloke did not give me any readings because he said they were fine.What it actually does is gets to 7000 then its as if a limiter is coming in and then goes in and off in and off continuously in every gear,but with no load it runs perfect.Any more ideas would be appreciated thanks in advanced.

Ady

If you checked all I stated, what were the results?

Were plugs wet? (both or just one?)
What color were the plugs, Black or White or Grey or ???
Did you do spray test around carbs? Did idle speed change?

Did the bike run fine when you bought it, and this problem just popped up? Or has this been a problem since you bought the bike?

Do you have a factory service manual? If not, get one, and test the entire ignition system. You said you replaced the coils and wires, why? Did they test bad? OR were you just guessing?
Have you tested the CDI box per the Factory Maual?

Torn Diaphram?
 

Sounds like a problem someone else had on here. It turned out to be a torn petcock diaphram. Not enough vaccuum under load at 7K rpm to the diaphram to get fuel. Ran great at everything else though. Worth a check.