Engine dies randomly while riding

[mcquillr]

Hi All,

I?m in the process of getting my 1977 GS400X running nicely and I think I?m close! I most recently swapped out my stock points & centrifugal advance system out for a Boyer-Brandsen EIS after I found someone had grinded down the lobes of my advance mechanism. After doing that and tuning the carbs the throttle response is good and power is strong through the power band.

However, while on a long ride the other day (after about an hour) my engine lost power and died while cruising at around 50mph. I pulled over to the side of the rode, turned the bike off, turned it back on and it kicked right over. I rode the rest of the way home with the petcock in Prime mode but the engine died a few times along the way.

Since then I checked the petcock and the screen is clean. Fuel flows freely though while in prime and when I pulled the bowls, they had plenty of fuel.

Does this problem sound electrical to you all? It happens while cruising or while moving slow. Sometimes when the bike is hot and sometimes after it has just warmed up.

Things I?ve done:

1.) I replaced my stock coils with a new 12V 4Ohm coil when I upgraded to the EIS.

2.) Rerouted all my grounds to the frame so they were not mounted to any metal that is painted.

3.) Checked neumerous connections and made sure nothing is lose or making promiscuous connections with other things.

4.) Bypassed my the Run/Off switch.

5.) Checked to make sure the battery terminals were tight.

6.) Checked my spark plugs and they look fine.

Disclaimer: I replaced my stator (I checked it and it is outputting the correct amount of AC voltage) but it looks like I do have a bad R/R. It only outputs around 12.5V even at higher RPMs. The battery is not super low though: it rests around 12.75V before starting.

I?m currently looking for an SH775, but does this sound like the problem or is there something else at play here?

 

[tom203]

I'd suspect electrical, due to your poor charging...might be giving your ignition fits when things get toasty.

"...replaced my stator (I checked it and it is outputting the correct amount of AC voltage"

did you look for possible short to ground when you checked AC?

while you wait for SH-775, consider buying a used shunt unit to test things,like a SH-232, about $20 to eliminate the r/r as culprit. Remember the SH-775 won't work without a decent stator.

 

[LAB3]

I'm with Tom on this one, if the bike just shuts down without any sign that it's low on gas then an electrical problem seems to be the most logical thing to look at first. If you've already been through the grounds and connectors my suspicion would be that something is getting hot. If it happens again pulling off a side cover to check if anything feels warm is easy enough to do. Feeling around the spark box is a bit more of a challenge but if you look into how close you can get it might be worth while.

 

[mcquillr]

Could it be the new coil I put in? I've seen cheap coils, moderately cheap coils and then pretty expensive coils. I'm not exactly sure what the difference is but I only have a moderately cheap coil in there right now. My coil did feel hot but it's also right over the engine...

 

[tom203]

Wait,I missed this..

"1.) I replaced my stock coils with a new 12V 4Ohm coil when I upgraded to the EIS. "

Did you mistype ? This bike has two coils - or did?

 

[mcquillr]

It used to, but the new EIS system fires both cylinders each time (basically it double fires) so you really only require one coil which supplies spark to each cylinder.

 

[mcquillr]

Here are the instructions that came with the kit. http://www.boyerbransden.com/pdf/KIT00091.pdf

I followed Figure 3

 

[posplayr]

It used to, but the new EIS system fires both cylinders each time (basically it double fires) so you really only require one coil which supplies spark to each cylinder.

The stock GS 4 cylinders fire twice per revolution or twice per 4 cycles on a per cylinder basis in what is called "wasted spark". It needs two coils and with two high tension wires to fire per coil.

That is that the current path from a coil for the high voltage spark goes out one high tension (HT)wire jumps the plug gap, then goes through the head to jump the other plug gap and go back on the other high tension (HT) wire to complete the circuit in the coil.

Coil 1-4 Plus==>HT_1==>Plug1 Gap ==>Head ==> Plug4 Gap ==>HT_4==>Coil 1-4 Minus

 

[mcquillr]

The stock GS 4 cylinders fire twice per revolution or twice per 4 cycles on a per cylinder basis in what is called "wasted spark". It needs two coils and with two high tension wires to fire per coil.

Interesting, but this isn't the case for the 2-cylinders right?

 

[mcquillr]

Another thought I had was the gas cap. I pulled off my gas cap and checked to see if there was a breather hole that was gunked. I did notice there is a little hole that looks like it might lead to crimped openings around the outer part of the cap but am not sure. Otherwise, the gas cap fits pretty tightly over the fuel port.

 

[posplayr]

Interesting, but this isn't the case for the 2-cylinders right?

The hosting of the pictures is gone but it looks like the 2 cycle is wasted spark as well.

https://www.thegsresources.com/_for...n-Firing-Order-Diagram&highlight=Firing+order

 

[Steve]

The hosting of the pictures is gone but it looks like the 2 cycle is wasted spark as well.

https://www.thegsresources.com/_for...n-Firing-Order-Diagram&highlight=Firing+order

Yes, they are also wasted spark, but the two-cylinder GSes that I know of have a 180? crank, which requires two coils. :-k
A 2-cylinder bike with a single coil can only work on a 360? crank.

Then, again, there is this "1977 GS400X" bike. Yes, there was a '77 GS400, but it should be a GS400B. The X bikes came in 1981, but there was not a 400, it would have been a 450. On the other hand, there were non-US bikes that were different than what we got here, so I am going to need some more details on exactly what bike is being discussed.

.

 

[mcquillr]

Then, again, there is this "1977 GS400X" bike. Yes, there was a '77 GS400, but it should be a GS400B. The X bikes came in 1981, but there was not a 400, it would have been a 450. On the other hand, there were non-US bikes that were different than what we got here, so I am going to need some more details on exactly what bike is being discussed.

.

So my VIN number on the frame says GS400X and I think the model number is GS400XB. Check out this link and look at the GS400X 1977-1978. http://www.suzukicycles.org/GS-series
/GS400.shtml

Mine was blue when it was stock, has drum breaks on both wheels and no electric start (only kick). I think the "X" simply denotes that it didn't come with a electric start, gear indicator or front disc break.

 

[Gorminrider]

your bike has points, right? That's important per the symptoms....the Clymer manual for Suzuki_GS400-450-77-87 is on Bass cliffs site
BikeCliff's Website
You really have to run through all the basics before you start imagining complicated scripts....
Firstoff, if the bike was running well before you made changes, go back and look really hard at anything you did...sometimes is just that you forgot to retighten the battery lead while following directions to install your new coils....I have to assume it's not the coils themselves.

then, Open up the breaker points cover, check for any debris that could be intermittently floating around jamming points, or the advance mechanism... look for any broken insulation especially where the wire leaves the cover and goes to coils....often said,doesn't fix everything but change the condenser, if it's not new. A bad capacitor can cause peculiar symptoms ...sometimes visibly, with arcing at the points but sometimes symptoms aren't visible without instruments...

Your charging system questions and batteryare probably a separate issue unless the battery connections are loose or shorting intermittently. The bike won't stop weirdly as you describe... Check the ground connection is number 1 for looseness. Inspect the fuse(or swap it for a new one because just looking at it doesn't always do it...and look at wiring in general.

 

[posplayr]

your bike has points, right? That's important per the symptoms....the Clymer manual for Suzuki_GS400-450-77-87 is on Bass cliffs site
BikeCliff's Website
You really have to run through all the basics before you start imagining complicated scripts....
Firstoff, if the bike was running well before you made changes, go back and look really hard at anything you did...sometimes is just that you forgot to retighten the battery lead while following directions to install your new coils....I have to assume it's not the coils themselves.

then, Open up the breaker points cover, check for any debris that could be intermittently floating around jamming points, or the advance mechanism... look for any broken insulation especially where the wire leaves the cover and goes to coils....often said,doesn't fix everything but change the condenser, if it's not new. A bad capacitor can cause peculiar symptoms ...sometimes visibly, with arcing at the points but sometimes symptoms aren't visible without instruments...

Your charging system questions and batteryare probably a separate issue unless the battery connections are loose or shorting intermittently. The bike won't stop weirdly as you describe... Check the ground connection is number 1 for looseness. Inspect the fuse(or swap it for a new one because just looking at it doesn't always do it...and look at wiring in general.

See first post:

Hi All,

I’m in the process of getting my 1977 GS400X running nicely and I think I’m close! I most recently swapped out my stock points & centrifugal advance system out for a Boyer-Brandsen EIS after I found someone had grinded down the lobes of my advance mechanism. After doing that and tuning the carbs the throttle response is good and power is strong through the power band.

 

[mcquillr]

Inspect the fuse(or swap it for a new one because just looking at it doesn't always do it...and look at wiring in general.

This isn't a bad idea though. I don't know if the fuse has ever been changed.

 

[Brendan W]

Might be worth getting it running and then take off the side cover and start pulling at wiring, particularly the fusebox tail and anything ignition related. The coil supply plug can hide a mess of corrosion even though it looks fine on the outside.

 

[mcquillr]

Might be worth getting it running and then take off the side cover and start pulling at wiring, particularly the fusebox tail and anything ignition related. The coil supply plug can hide a mess of corrosion even though it looks fine on the outside.

Also a good idea.

So we are all pretty certain this isn't a fuel delivery issue then?

 

[Brendan W]

Also a good idea.

So we are all pretty certain this isn't a fuel delivery issue then?

Well I'm not betting my house on it.
Loss of ignition feels different to loss of fuel. I can't really explain it. Fuel starvation can gradually lose power and then finish with a flourish and maybe a lean backfire or two. Loss of spark is different,
How would you describe the power loss ?

 

[mcquillr]

I would say its a quick loss of power, maybe over the course of 3-5 seconds, no backfiring just dies.