QuestionHi,79 honda cb400t I was crusing up to an intersection when it just quit.plenty of fresh fuel,new oil/filter. I had been riding for about 1 hour when this happened.no warning signs at all.it's getting fuel,but no spark.turns over fast,had no problem starting it before I headed out.and the battery is new and so are the plugs.
many thanks for any help.
AnswerHi Gary,
There was no email address as requested to forward information to. Hope this works for you.
Respectfully,
Mark Shively
Question? If answer is NO then check for: Problem area: Suggestions:
Is fuel getting to the carb?
YES
If
NO
then check
A. for a blocked, or broken fuel line.
B. for blockage in the fuel valve.
C. for blockage in the needle and seat, or failure needle and seat.
D. improper fuel tank ventilation
E. fuel filter plugged
F. failed impulse line
G. incorrect fuel pump installation
H. defective fuel pump Repair or replace.
Is fuel reaching engine?
YES
If
NO
then check
A. plugged main jet
B. plugged low speed jet
C. throttle valve not opening
D. rotary valve gear not turning
E. for blockage in the needle and seat, or failure needle and seat. A. clean main jet
B. clean low speed jet
C. replace throttle cable free up slide
D. repair rotary valve gear
Is fuel running out overflow tubes on side of carbs?
NO
If
YES
then check
A. needle valve for sticking
B. floats for damage or leaking
C. float arms for proper level Repair or replace.
Is engine flooding?
NO
If
YES
then check
A. check to see if you have spark
B. check to see if choke is on
C. check to see if primer is working properly Replace plugs
Turn choke off
Repair or replace primer
Is spark present at spark plug cap?
YES
If
NO
then check
A. check coil wire connections for proper fit or damage.
B. check spark plug cap for continuity and damage.
C. check for faulty ignition switches
D. check for faulty ignition coil.
E. check for faulty ignition Pickups First NEVER check for spark without the spark plugs installed in their caps! Start testing the easiest things first. Like a poor connection, then the spark plug leads, cap and spark plug. When checking plug USE a NEW plug not one you have had laying around!
Is spark present at the Spark Plug?
YES
If
NO
then check
A. spark plug fouled
B. spark plug flooded
C. spark plug broken
D. incorrect spark plug gap Replace spark plugs in all instances.
Is engine difficult to start?
NO
If
YES
then check
A. air cleaner blocked
B. engine flooded
C. throttle valve open too far
D. water in the fuel
E. poor ignition timing
F. no compression
G. enricher valve closed
H. intake leak
I. improper fuel mixture
J. blown head gasket
K. faulty spark plugs
L. gear box improperly loaded Clean filter
Drain fuel, clean tank, and carb, replace with new fuel
Repair engine
Repair gear drive
Does engine backfire or kick back?
NO
If
YES
then check
A. dampening box faulty or disconnected
B. ignition wires reversed
C. ignition timing out of adjustment
D. flywheel key missing or sheared
E. faulty ignition switch
F. failed crankshaft bearing on PTO end.
G. failed MAG seal oil has contaminated condenser/points
H. gear box needs update/reconditioning Repair or replace.
Does engine run on one cylinder despite good spark in both plugs?
NO
If
YES
then check
A. improper plug gap
B. fouled spark plugs
C. spark plug cap defective
D. no crankcase pressure
E. blown or leaking head gasket
F. cracked cylinder
G. poor ignition timing
H. crankcase air leak
I. needle clip has failed on one carb Repair or replace.
Does engine cranks without resistance?
NO
If
YES
then check
A. stuck rings
B. broken rings
C. excessive piston to wall clearance
D. burnt, broken or scored piston
E. piston dome penetrated by pre-ignition
F. blown head gasket
G. spark plug is loose
H. head bolts need torqued
Repair or replace.
Engine will not rotate- lower end frozen?
NO
If
YES
then check
A. debris in crankcase
B. crank baring frozen
C. broken connecting rod
D. piston seized in cylinder
E. badly rusted crankshaft
F. foreign material has enter intake on liquid cooled engines locking rotary valve gear Repair or replace.
Does engine start but will not idle or misses just above idle?
NO
If
YES
then check
A. spark plug gap incorrect
B. worn piston and rings causing low compression
C. Carb idle circuit plugged
D. too much oil in gas
E. plugged carb jets
F. air regulating screw out of adjustment
G. stuck rings
H. poor ignition timing Repair or replace.
Does engine die when throttle is open?
NO
If
YES
then check
A. jet needle E clip installed above spring cup
B. improper carb slide used, newer models have cutout in slide
C. incorrect spark plug gap
D. excessive prop load
E. fuel pump defective
F. float level too low
G. vacuum line leak Repair or replace.
Is engine slow to accelerate or does not reach full throttle?
NO
If
YES
then check
A. fuel mixture to lean
B. fuel mixture to rich
C. poor compression due to broken, stuck or worn rings
D. float level to high
E. too much prop load
F. too much prop mass weight inertia Repair or replace.
Doe engine run rough, smoke or vibrate excessively?
NO
If
YES
then check
A. enricher valve open
B. water in fuel
C. prop out of balance
D. fuel mixture too rich
E. gear box needs update and or service
F. air in fuel lines
G. fuel pump defective
H. intake leak
I. engine mount broken or loose Repair or replace.
Does engine run poorly at higher throttle settings?
NO
If
YES
then check
A. Engine misses at higher RPM
1. incorrect spark plug heat range
2. incorrect fuel mixture (too rich or too lean)
3. spark plug fouled or defective
4. poor ignition timing
5. ignition cables arching
6. ignition coils defective
7. dampening box defective
B. Engine "loads up"
1. jet needle position to rich
2. main jet too rich
3. dirty air cleaner
4. poor ignition timing
5. too much oil in fuel
6. worn carb tuning components
C. Engine emits "knocking"
1. timing too far advanced
2. piston to wall clearance excessive
3. crank bearing burned, failed or grinding
4. excessive wrist pin play
5. circlip missing from piston
6. excessive carbon deposits
Repair or replace.
Does engine overheat?
NO
If
YES
then check
A. fuel octane too low
B. fuel mixture too lean
C. ignition timing too far advanced
D. prop load excessive
E. cooling duct blocked
F. carb out of adjustment
G. instruments or sender defective
H. low coolant or incorrect anti-freeze to water ratio
I. poor cooling system installation
J. failed water pump impeller Repair or replace.
Engine rpm surges or won't hold steady?
NO
If
YES
then check
A. exhaust back pressure tuning incorrect
B. exhaust system improperly modified
C. engine requires modified jets in mid range
D. needle and clip located above white plastic retainer
E. on 532 Rotax ignition coils and or dampening box wired wrong
F. intake socket failure Repair or replace.
Does engine lose power after standard warm up or will not reach full throttle?
NO
If
YES
then check
A. piston seizure
B. stuck rings
C. prop load excessive
D. main jet to rich
Repair or replace.
Does engine show high CHT temps?
NO
If
YES
then check
A. poor ignition timing
B. loose or slipping fan belt
C. prop load excessive
D. fuel mixture to lean
E. obstructed cooling ducts
F. poor engine design installation
G. defective gauge or sender
H. lack of oil in fuel
I. poor piston to wall clearance
J. damaged fan
K. failed fan bearing Repair or replace.
Does engine show excessive EGT temps?
NO
If
YES
then check
A. air intake leak
B. air/fuel mixture to lean
C. changes in density altitude
D. changes in humidity
E. changes in air temp
F. timing too far advanced Repair or replace.
Go Fly
