Diagnose symptoms

[vmf1200]

I would like some advice for a few symptoms that i have on my 88 vmax. The bike starts great when cold (new AGM battery) and (new stator) linstalled last year. But after its hot it doesn't want to start or stay running. After hard starting it then sputters and backfires mostly through the front cylinder and carbs. I also noticed that my front spark plug boot is coated with antifreeze possibly? and the bottom of the boot looks burnt or coroded a little. 1 could be my front coils? 2 maybe a leak from above the plug like the water jacket ? There doesn't appear to be antifreeze in my oil (head gasket)?
Thanks in advance for your opinions before i dig in.

 

[Pighuntingpuppy]

If you are using green coolant, make sure it is coolant by tasting it. Green coolant tastes sweet. The newer coolants have bittering agents in them.

Sputtering, sounds like out of sync carbs. But if there are coolant leaks into the cylinders or misfires, this will cause issues too. But I would start simple and sweet, what do your spark plugs look like? The boots....are they dryrotted? Cracked?

To test your coils, you will need a KV spark tester to see what the actual spark is. I tend to start simple. This is where I would start.

 

[MaxMidnight]

I would start by:
a) Eliminate the coolant leak.
From what you describe this would appear to have allowed the cap to short and arc which would account for the burning.
This issue needs to be resolved first.
b) Replace the plug cap and if not done in living memory the leads and rest of the caps.
c) Replace the plugs if that hasn't been done recently.
d) Synchronise the carbs.
e) If you have never done it, why not give the bike a full service?

 

[vmf1200]

Thanks for your advice. I am going to check if there is a leak first for sure. I read a post where someone had a similar leak from the water jacket outlet in the head above the plug, is this common? I would like to get new plug wires but wouldn't it be better to upgrade to COP's instead while im at it? I have yet to have the carbs synched, i don't have the gauges but i am looking to borrow them from a friend. But the bike runs nice and smooth when cold, its when it gets hot that it runs like crap and has no power and wants to stall. So that tells me that usually is an electrical problem like the coils, im suspecting the front coils and or wires are having resistance problems. I have tested the rear coils because they're right there, and i took Sean's advice to cut a little wire off the end of the plug wires to make better contact with the coils and that helped it run better. But i have not checked or serviced the front coils/wires yet since they're tougher to get too. But i am ready to do that, but it looks like COP's are the way to go?

 

[Fire-medic]

You have the old, analog ignition system. Do not buy COP's without resistors, as the 1985-'89 bikes with the 4-pickup ignition have been shown to be sensitive to that modification causing the CDI to fail prematurely. Yes, you will see some people on-here who say, "mine hasn't failed!" and who don't have resistors on their COP's.

Ask Sean Morley, as he's the sales person for Gannon's COPs sets, now, I believe.

 

[MaxMidnight]

IMO COP's are worthwhile only if you need to replace coils.
Whilst you may notice an initial improvement this is possibly not because they are better than the OE system but because the OE system wasn't performing well.
I have fitted COP's but didn't notice any significant improvement thus my conclusion above.

The cross over pipe in the head does occasionally leak but this is quite a rare occurrence. I would have thought it more likely to be a hose.

Fix that first before thinking about doing any other work.

 

[vmf1200]

Update today I finally had time to really diagnose my bike. It started up fine but then it just died by itself while idling, so I did a few things to it to make it run a lot better. First off, I didn't notice it before but one of the rear coils was unplugged,,,, my bad,, so i plugged that in and I noticed that the Vboost servo was stuck in the open position. I moved a few resistors, capacitors on the Vboost control unit board and it is now cycling on when I press the run switch. Could this have been open or partly open which would have made my bike run rich and like crap?? Second, I turned all the air/fuel mixture screws 2 1/2 turns out and the bike now runs smooth and crisp, no more stuttering or back firing. I could not replicate the leak which was seeping on the front left spark plug boot, I thought it must be leaking from that heater hose which is right behind the plug but it never leaked after letting it idle for 30 min. and I have not lost any antifreeze from the overflow tank. I let the bike idle off and on for 30-40 min or so and it never stalled out and seemed to idle and run great but I could not get the electric fan to turn on at all this whole time. I've tested the fan by running the wires directly to 12v and it spins but it does not come on while plugged in and I've replaced both the thermo switch and the thermo unit. My question is....how friggin hot does the bike have to get in order for the fan to kick on?? I have never heard the fan come on by itself and I know it works.

 

[[email protected]]

The fan comes on approximately 221 degrees F.
It kicks off when it drops down to approximately 195.

 

[vmf1200]

Well that is not helpful when the boiling point of liquid is 212° my bike must have reached 221° several times but my fan never turns on. Could it be my thermostat possibly?

 

[Edward]

Well that is not helpful when the boiling point of liquid is 212° my bike must have reached 221° several times but my fan never turns on. Could it be my thermostat possibly?

VMAX lists are replete with complaints about high temperature.

There is a thermostat that can be subbed that forces the fan on sooner. It is a Borg Warner and I can't find the number right now. It opens at 180°F. I have one on mine.

There used to be a guy posting on Paul Sayegh's VMAX list called Don "Old Man" Smith. He stated that the screw in the middle of the gauge face was 205°F. He also said that the stock fan comes on at 225°F.

The boiling point of water is for distilled water, at 1 atmosphere of pressure. These systems are pressurized and diluted with alcohol (antifreeze) so the boiling point is much higher. You must not have any traffic where you are. Even with the replacement thermostat, there's nothing like the blast of superheated air when stuck in traffic, wearing leather and being irradiated by cooking asphalt.

Try shorting across the thermostat switch (NOT the fan leads) to force the fan on and check to see if the problem is with the fan.

Having said the above and even though I have replaced mine, I question whether it's a good idea to arbitrarily alter a setup calculated by the manufacturer's engineers. There must have been a reason they wanted their engine to run at a higher temperature.

 

[vmf1200]

Thanks for your input and suggestions. I did a search and found the Borg Warner thermostat number and the thermostat switch replacements that will make the fan come on sooner. I really don't want to buy them now as I just replaced the factory ones last year the thermal switche and thermal unit. I don't remember changing the thermostat but if that wasn't working it would definitely overheat and leak which it's not. I just took it for a good ride and it's got into the middle of the temperature gauge but never in the red. I did smell antifreeze here and there while I was driving but it could have been from another vehicle in front of me when I got home I checked I didn't see anything wet or any leaks. I'm going to go back outside and check real good I know my fan is working I tested the fan but it's just not coming on thanks for your suggestions

 

[[email protected]]

Well that is not helpful when the boiling point of liquid is 212° my bike must have reached 221° several times but my fan never turns on. Could it be my thermostat possibly?

You're forgetting that the system is under pressure which raises the boiling point to well over 250 degrees.

You say the bike must have reached 221 degrees. How do you know that?

IF the coolant was that hot and the fan did not kick in, it would either be a problem with the fan, or a problem with the thermoswitch that tells the fan to turn on. The thermostat controls the flow of coolant thru the motor. It has nothing to do with fan operation.

Looking at the gauge and seeing the needle close to the top makes many folks worry. Is the needle actually up INTO the red zone? Or, is it just at the beginning of the red zone?

If its not up in there, its not overheating. Are you boiling coolant out the overflow at a stop light?

 

[vmf1200]

I've replaced the thermo switch and have tested the electric fan by passing the switch and it comes on. I just haven't heard it come on by itself yet for 4 years I owned the bike. I replaced all the antifreeze and the overflow tank doesn't leak and the gauge doesn't get in the red. But shouldn't the fan have come on by now a few times? It may not be 220° like you say but i will have to take a thermo test of the hoses and or radiator, thermostat housing and i bet it will be around 250°!

 

[vmf1200]

Update 4th of July weekend, I took the bike out a few times and it started right up, never stalled and ran the smoothest its ever run since i've owned the bike really. I couldn't find any leaks of anti-freeze or water or oil at all, that's pretty good for a 31 year old bike in my opinion. Now I just want to try and fix the intermittent on and off problem with my V-Boost controller. But I'm liking the V-Max again!