QuestionHi Bill, This problem is driving me nuts. About a year and a half ago while
driving my bike in the city it began to backfire bad. No problem I thought,
popped a new round of plugs in and off I went. I did notice the idle was not
perfect, but what the heck, seemed to run pretty good. 1000 miles or less the
plugs went again (rear), all carboned up especially the right rear. So off to the
dealer for the 16,000 mile maintenance. The mechanic informed me that the
valves were nearly perfectly adjusted and everything else looked excellent. So
off I went again, threw the rear plugs after about 800 miles. Changed the oil,
put a new round of plugs, air filter, and off again. Threw another set of rear
plugs. So that led me to an article on the Internet about a grounding problem
with the 2002's coils and battery connections. I very meticulously took the
coils off the frame, exposed the bare metal, slopped on some dielectric
goop and reassembled and of course popped a new set of plugs in. Still had
the problem, so I replaced the rear coil, raced down the highway a couple
hundred miles to blow out the buggers and all seemed well. Popped the plugs
to have a look, a little dark but both the front and rear plugs looked about
the same for once (the rear plugs were always darker). I thought I had fixed
the problem. Just to make sure I went through the manual, and checked the
cylinder compression, to my astonishment I had 120 psi per cylinder (the
manual specified 95psi per cylinder). Only one explanation for this problem,
carbon buildup in the combustion area. Called the mechanic, told me this
motor is a bugger to remove and to run it down the highway hard (no
problem with that) so i blasted down the highway one afternoon @ 300 miles,
added a bit of Lucas fuel additive to clean the injectors and carbon buildup
and all seemed to be well. Driving around the city for a month, and threw the
plugs again (front and rear). Replaced the plugs took it around the block,
started to backfire, and stall when off the throttle. When on the throttle it rips
hard, but at a non accelerating throttle jerks misses a bit, when I let up
totally on the throttle it barely stays running if not stalls. I don't know what
to do, I love my bike, but she is seriously ill. Any help is very appreciated.
AnswerTed, I really don't have any experience dealing with newer FI Honda models. However, when engines backfire and run poorly, it is often something to do with the intake system. I don't know if Honda has a diagnostic tool for these models or not, but I would see if that is a possibility.
If you look here:
http://houseofmotorcycles.bikebandit.com/parts/Honda/VTX1800C/2002/380550
There is a MAP sensor, TPS and fuel regulator, any of which could cause running problems, in my opinion.
I don't know the specs on these engines but I would have been more surprised at a 95psi rating than 120, which is what you generally see on most Honda motorcycles. A Honda 305 twin from the 1960s has 175 psi, with an 8.5:1 compression engine.
Basically, you have a fuel injected engine, like most any modern car, so the same rules apply. If diagnostic analysis is available, it should be the first step. If you have a manual, look at the troubleshooting steps for erratic idle and backfiring symptoms.
That's about all I can say about this issue.....
Bill Silver
