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Louie, Technician
Category: Motorcycle
Satisfied Customers: 12139
Experience:  25+ yrs. experience
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2003 Honda vt750dcb it misses and pops and runs like ,it has

Customer Question

2003 Honda vt750dcb it misses and pops and runs like crap,it has been to the bike shop five times they have tuned it abjusted the carbs,the plugs are sooty and it runs perfect after a plug change but that lasts about 100 miles and then back to square one,please help!
Submitted: 8 months ago.
Category: Motorcycle
Expert:  Louie replied 8 months ago.

Hi John, I’m Louie. Sorry you had to wait awhile but I’ll do my best to help.

Initially, is the idle high / uncontrollable when the Honda "...misses and pops..." ?

Still, have you tried:

  • • drain-clean tank and replace with fresh fuel (even if just to eliminate as a suspect);
  • • check the charging system particularly if the voltage exceeds 15 Volts @ 4,000 RPM;
  • • re-inspect the battery, its ground lines and/or re-check and re-clean the battery cables + terminals, connectors and wiring;
  • • then have the battery externally charged.

The above post on the electrical/battery is an alternative suspect to a fuel issue.

Customer: replied 8 months ago.
Tank was drained,new filter in the tank and also the inline filter,the carbs were rebuilt and sinkronized
Customer: replied 8 months ago.
It runs perfect after new plugs and then when you try to ride at a steady speed it skips and bucks
Customer: replied 8 months ago.
I will try a meter on it
Expert:  Louie replied 8 months ago.

Yes please; an over (charging) voltage would mess the electronics,

Customer: replied 8 months ago.
The plugs are sooty
Expert:  Louie replied 8 months ago.

Replace the plugs.

Other than a fuel mix issue, it is possible also for a developing vacuum leak.

The above voltage check would be the easiest to do hence the first to try.

Customer: replied 8 months ago.
I replaced the plugs and it runs perfect for about 100 miles then it runs shitty and the plugs are not wet but are black and sooty
Expert:  Louie replied 8 months ago.

When the symptom comes up again, check the charging voltage. If it is higher than 15 Volts @ 4,000 RPM, then the ignition system woulkd be constantly kicking in auto-protect and the spark would be erratic.

As posted above, this would be the easiest to check hecne should be considered and tried first.

The other possibility is a developing vacuum leak which by its very nature more difficult to trace.

Customer: replied 8 months ago.
Ok I will check that,thank you
Expert:  Louie replied 8 months ago.

Good luck and thank you too for the opportunity to be able to share the information.

Customer: replied 8 months ago.
Voltage is ok,but I checked the spark and at least one cylinder looses it spark at higher rims,would that be coils.
Expert:  Louie replied 8 months ago.

Hi again John,

Possibly but if it were an ignition coil issue, then the no-spark would be exhibited on two (2) spark plugs as each coil is commonly powering 2 spark plugs.

It may more be the spark plug wire from the coil and/or the cap of that particular spark plug that misses.

Customer: replied 8 months ago.
if I check the plug on the same side that should tell me if it's the coil?
Expert:  Louie replied 8 months ago.

The same coil powers the two (2) front spark plugs and same coil for the 2 rear.

Customer: replied 8 months ago.
It is the left rear cyl,only what should I change
Expert:  Louie replied 8 months ago.

Left rear; check the high voltage wire from the ignition coil to the spark plug cap and/or even the cap itself.

Depending on the type of coil used, it may be removable hence can be replaced.

If not, then the rear ignition coil should be replaced.

Customer: replied 8 months ago.
Check with lemon meter?
Customer: replied 8 months ago.
Can it be the coil if it's only one cyl
Expert:  Louie replied 8 months ago.

Yes; it can still be the coil even if just 1 cylinder has no-spark.

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