Vmax struggles to start, spark comes out of vacuum port

[Zaos]

Hi, my 1989 vmax has been running fine until recently it’s been giving me issues to start, it’ll crank for a while and eventually make a loud bang as if all the gas just ignited, when it does turn on there’s a spark on the vacuum ports and it idles incredibly rough, I would wondering what steps I should take to diagnose this issue?I’ve included a video, you can see the spark under the right carb cover

 

[Fire-medic]

A hard to diagnose phenomenon when you give us a 1 second .mov I played that brief clip probably a dozen times and cannot see any spark.

Try draining the float bowls, into a container, one at a time, and inspect the drainings for water or impurities. You may have a bad batch of gasoline. A small funnel will help you to collect the gas, and keep it from being spilled. I suggest doing this outside, and nowhere-near any gas-fired appliance like a gas water heater, space heater, home furnace, or similar. Gasoline vapor can travel easily 30 ft to an ignition source, and ignite!

 

[Zaos]

Apologies, seems like with the compression it makes the spark pretty hard to see, Ill attempt to drain the gas and look at it The spark is coming from this port (picture attached) the one with the black cap on it, in the video there's a quick flash, it happens consistently while running.

 

[MaxMidnight]

If you are seeing a spark then that would suggest that the HT leads are finding an easier way to get to earth.

First step would be to ensure that the leads are clean and and the insulation is intact. Also check the the HT lead is fully screwed into the cap and that the caps are clean and free of cracks especially where the lead screws in. Check the ends of the leads for corrosion.
I have also head of instances where the HT lead can short onto the coolant hose retaining clip.

If the leads and caps are original then they may be trying to tell you they would like to be retired?

 

[Zaos]

The leads and caps seem to be new, no cracks and everythings clean, I put proper vacuum caps and the bike doesnt send that spark out anymore and it idles much better, the old caps had holes in them, It still struggles quite a bit to start up initially and makes a loud bang, but once its started it runs fine and i can turn it off and back on no problem. I purchased some carb clean, I plan on cleaning the carbs and swapping the plugs and see how that goes. also purchased some fuel clean because might aswell.

 

[Zaos]

A hard to diagnose phenomenon when you give us a 1 second .mov I played that brief clip probably a dozen times and cannot see any spark.

Try draining the float bowls, into a container, one at a time, and inspect the drainings for water or impurities. You may have a bad batch of gasoline. A small funnel will help you to collect the gas, and keep it from being spilled. I suggest doing this outside, and nowhere-near any gas-fired appliance like a gas water heater, space heater, home furnace, or similar. Gasoline vapor can travel easily 30 ft to an ignition source, and ignite!

View attachment 88867

Another thing I noticed was two of these drain screws are leaking, Is there a gasket involved with these?

 

[Zaos]

Posting this update for any onlookers that may be able to help, I cleaned the carbs and they looked fine, I cleaned a very dirty air filter it had, bike runs phenomenal once it’s on, it seems to be solely starting issues, it’s a new battery and R/R and it cranks fine just doesn’t turn on, any ideas ?

 

[VMAXXIMUM]

Are you using the choke to start?

 

[Zaos]

Are you using the choke to start?

Yes, choke all the way opened

 

[Zaos]

I changed the spark plugs and it’s Been turning on fine for a week or so, then the problem has come back, videos included of a cold and hot start
View attachment IMG_7275.mov
That video above is a cold start

View attachment IMG_7276.mov
The video above is a hot start,
To me the hot start sounds like a starter going bad but I am unsure why on cold starts it doesn’t run, the battery voltage reads 12.93 while the bike is off and 13.3-13.4 while running

 

[VMAXXIMUM]

For sure your turning over way to slowly. So time to diagnose why. Battery, charging, both or perhaps the starter.

 

[Fire-medic]

For sure your turning over way to slowly. So time to diagnose why. Battery, charging, both or perhaps the starter.

Numbers like that, his charging system & battery seem healthy. Maybe a current draw test? There's no 'can of rocks' sound for the starter.

 

[VMAXXIMUM]

Numbers like that, his charging system & battery seem healthy. Maybe a current draw test? There's no 'can of rocks' sound for the starter.

I stand corrected. I listened to the video but didn’t scroll all the way down to the numbers. Thanks Fire-medic

 

[MaxMidnight]

I changed the spark plugs and it’s Been turning on fine for a week or so, then the problem has come back, videos included of a cold and hot start

Do you still see the sparking that you mentioned in the first post?

That video above is a cold start

That sounds pretty normal to me. When do you get the 12.93 volt battery reading? i.e is it after the bike has stood for several hours or after it has been running?
If it is the latter then you are measuring the surface charge of the battery and not the true voltage.
You will need to dissipate the surface charge by letting the bike stand for several hours or having the headlight on for a couple of minutes.

The video above is a hot start,
To me the hot start sounds like a starter going bad but I am unsure why on cold starts it doesn’t run, the battery voltage reads 12.93 while the bike is off and 13.3-13.4 while running

When charging you should be getting between 14 and 15 volts so it may be that the battery isn't being fully charged?
First step would be to clean all connections in the charging circuit and then re-measure the charging voltage.
If not already done dot 'The Splice' - see below.

Your bike has a two brush starter which can give hot starting problems. (id - SM-13 = 4-brush starter; 93-94 on SM-229C = 2-brush starter) so that may be the issue.
You could try the fix suggested in the attachment.
You might also like to give the starter a workout.

If that doesn't help then work through this.

 

[Zaos]

Do you still see the sparking that you mentioned in the first post?

That sounds pretty normal to me. When do you get the 12.93 volt battery reading? i.e is it after the bike has stood for several hours or after it has been running?
If it is the latter then you are measuring the surface charge of the battery and not the true voltage.
You will need to dissipate the surface charge by letting the bike stand for several hours or having the headlight on for a couple of minutes.

When charging you should be getting between 14 and 15 volts so it may be that the battery isn't being fully charged?
First step would be to clean all connections in the charging circuit and then re-measure the charging voltage.
If not already done dot 'The Splice' - see below.

Your bike has a two brush starter which can give hot starting problems. (id - SM-13 = 4-brush starter; 93-94 on SM-229C = 2-brush starter) so that may be the issue.
You could try the fix suggested in the attachment.
You might also like to give the starter a workout.

If that doesn't help then work through this.

reading done after bike sits for a while, also the running temp is a low idle speed recording not sure if that’ll make a voltage difference, I’ll give the rest a try, sparking is no longer there