84 gs400 limited run time

[atrent]

I have an 1984 GS400 that I saved from the junk yard. It was rather a sad looking case. Installed new o rings, washers and springs on idle air screws (they were missing). Did a fast clean up of the carbs and the bike has been cleaned up and was running reasonable well. Very easy starting etc. Started to run a bit rough so took off the carbs and cleaned them in carb cleaner. replaced the boot o rings, new plugs, reinstalled carbs and now it will only run for a few seconds maybe a minute and it slowly dies. Will not start again. Leave it for a few minutes, 2 or 3, and it will start and run for a short time again. Good fuel flow to the carbs so the fuel supply doesn't seem to be a problem. Spark is not the greatest but there is spark. My daughters GS250 has a fatter spark. Coil primary ohms approx 4, secondary 22k on one and 21k on the other. 12.5 volts at coil primary and the igniter pulses can be observed with the multimeter. Considered swapping igniters with the 250 but they are not the same. The tank is off and a temp fuel tank consisting on a one gallon can is being used so no petcock to cause concern. I have about come to the end of my ideas and am looking for some more experienced help.
alex

 

[trippivot]

well you might not have an ignition problem

well you might not have an ignition problem

clean up main ground at both ends, check all grounding connections for corrosion-- FIRST

next as it IS running what it the dynamic running voltage at the battery terminals? NEXT TEST

get a booster battery hooked in parrallel to primary battery. Does it run better and longer?


TPI systems make spark or they do not... so the intensity of the spark is source related or resistance inhibited.

pulser sine wave ac signal range is .2~3 ACV. USE 320 grit sand paper on the metal pick up and reluctor so there is fresh metal for fresh induction. ( air gap smaller 0.030")

the secondary resistance is a little high but in operating range.
primary resistance is also bit high but you have spark.

you do have old resistor caps I bet they are over 8K each.
if they ARE OVER 8K do not use resistor type spark plugs.

I'd also take the caps off of the wires , trim 0.250" off of the wires and replace resistor caps.-- if you have the length for them to still reach the plugs.

advise us of any changes.

 

[atrent]

clean up main ground at both ends, check all grounding connections for corrosion-- FIRST

next as it IS running what it the dynamic running voltage at the battery terminals? NEXT TEST

get a booster battery hooked in parrallel to primary battery. Does it run better and longer?

TPI systems make spark or they do not... so the intensity of the spark is source related or resistance inhibited.

pulser sine wave ac signal range is .2~3 ACV. USE 320 grit sand paper on the metal pick up and reluctor so there is fresh metal for fresh induction. ( air gap smaller 0.030")

the secondary resistance is a little high but in operating range.
primary resistance is also bit high but you have spark.

you do have old resistor caps I bet they are over 8K each.
if they ARE OVER 8K do not use resistor type spark plugs.

I'd also take the caps off of the wires , trim 0.250" off of the wires and replace resistor caps.-- if you have the length for them to still reach the plugs.

advise us of any changes.

Approx 13 volts at 2k R.P.M. stable at 15 volts above 4k R.P.M.
Already using booster batt with headlight off. makes no difference.
Tomorrow will be a busy day
Thanks for the tips.
alex

 

[tom203]

I couldn't fine this model in my listings, But............ My first thought is that a coil is heating up in a few minutes, but this could be caused by bad ignitor. Swapping ignitors was good thought, but like you said, maybe they aren't the same. Are some of this era's ignition systems true CDI ? Maybe Mr. Blowerbike will chime in, since he seems to like these things!

 

[atrent]

clean up main ground at both ends, check all grounding connections for corrosion-- FIRST

next as it IS running what it the dynamic running voltage at the battery terminals? NEXT TEST

get a booster battery hooked in parrallel to primary battery. Does it run better and longer?


TPI systems make spark or they do not... so the intensity of the spark is source related or resistance inhibited.

pulser sine wave ac signal range is .2~3 ACV. USE 320 grit sand paper on the metal pick up and reluctor so there is fresh metal for fresh induction. ( air gap smaller 0.030")

the secondary resistance is a little high but in operating range.
primary resistance is also bit high but you have spark.

you do have old resistor caps I bet they are over 8K each.
if they ARE OVER 8K do not use resistor type spark plugs.

I'd also take the caps off of the wires , trim 0.250" off of the wires and replace resistor caps.-- if you have the length for them to still reach the plugs.

advise us of any changes.

All these things done. Replaced the HT lead on one coil, a bit of a challenge. I will likely change the other simply because the wires are quit hard and stiff. Plug cap 7.5K ohms. About what it should be according to my info. Plugs have no suppressors. Cleaned up ground connections. Checked gap at reluctor it was set at .025. Still the same result. I have set the idle stop so it starts at 4.5K R.P.M. The speed drops to 4k rather quickly then holds at 4 for a few seconds then slowly drops and at or about 1.5K just quits. There is never any increase in speed. If I play with the throttle I can keep it going a bit longer but not for any significant period (a few seconds). I am at a loss and wonder if it may actually be a fuel problem after all.
alex

 

[atrent]

I couldn't fine this model in my listings, But............ My first thought is that a coil is heating up in a few minutes, but this could be caused by bad ignitor. Swapping ignitors was good thought, but like you said, maybe they aren't the same. Are some of this era's ignition systems true CDI ? Maybe Mr. Blowerbike will chime in, since he seems to like these things!

I believe this bike was only offered in Canada. I am having a hard time finding info on it
alex

 

[atrent]

clean up main ground at both ends, check all grounding connections for corrosion-- FIRST

next as it IS running what it the dynamic running voltage at the battery terminals? NEXT TEST

get a booster battery hooked in parrallel to primary battery. Does it run better and longer?


TPI systems make spark or they do not... so the intensity of the spark is source related or resistance inhibited.

pulser sine wave ac signal range is .2~3 ACV. USE 320 grit sand paper on the metal pick up and reluctor so there is fresh metal for fresh induction. ( air gap smaller 0.030")

the secondary resistance is a little high but in operating range.
primary resistance is also bit high but you have spark.

you do have old resistor caps I bet they are over 8K each.
if they ARE OVER 8K do not use resistor type spark plugs.

I'd also take the caps off of the wires , trim 0.250" off of the wires and replace resistor caps.-- if you have the length for them to still reach the plugs.

advise us of any changes.

I have done as you suggest but my problem has progessed to the point where it won't start. I am using a booster battery which has dropped to 12.25 and is presently on charge. I ran a wire directly from the booster to one coil and clipped a spark plug to the cylinder fins with an alligator clip.
The voltage at the coil dropped to 8.5 volts while cranking and the spark was red and weak. The charging system is ok it was putting out a stable 15 volts at 4k and above while it was running. I have replaced one HT wire and this is the coil I am looking at. This is a twin. Checked the coil caps and resistance is 7.5 K ohms. Wire is non resistive type as are the plugs.
alex

 

[tom203]

So you got a jumper wire direct to this coil from your weak booster ( this bypasses the ignition switch and everything )- but you'll still need to turn ignition on to power whatever ignitor or cdi you have. Yet when you crank, coil voltage drops to 8.5 ? Something is eating alot of juice.
Did you try my suggestion of manually firing coil to see if spark improved? Not while cranking - just momentarily ground negative coil after disconnecting ignitor lead (with ignition or your booster jump wire on).

 

[atrent]

So you got a jumper wire direct to this coil from your weak booster ( this bypasses the ignition switch and everything )- but you'll still need to turn ignition on to power whatever ignitor or cdi you have. Yet when you crank, coil voltage drops to 8.5 ? Something is eating alot of juice.
Did you try my suggestion of manually firing coil to see if spark improved? Not while cranking - just momentarily ground negative coil after disconnecting ignitor lead (with ignition or your booster jump wire on).

Tried that and no spark at all? I shall have to do a more thorough check of the wiring.

 

[tom203]

This bike looks hard to figure out- you probably don't have wiring diagram?
Suzuki sold gn 400 models in 1980-82- maybe the layout is the same.
Go to Alpha-Sports.com and look at electrical parts for these years- does it look similar?

 

[atrent]

This bike looks hard to figure out- you probably don't have wiring diagram?
Suzuki sold gn 400 models in 1980-82- maybe the layout is the same.
Go to Alpha-Sports.com and look at electrical parts for these years- does it look similar?

I now have good spark, solderd splices in o/w and b/w wires and cleaned up grounds. Back to my original problem of short run time. I am definitely now leaning toward bad boots but can't find replacements. Boots were my original thought but they looked fine and were fairly soft. The bike was running but was starting to idle a bit erratically. Alpha Sports doesn't list any 400's that I can find. I was told by a local dealer the boots will have to be ordered from Japan so I guess that is what I will have to do.

 

[tom203]

So you now have good spark to both cylinders, but bike has "short run time"- how short ? does it go into death spiral? or just idle erratically?