Fuel Pump

[86MaximusPrime]

Hey, I have a question, I have an 86 Vmax that will not start...it tries to turn over or just back fire... i will hear a loud bang out of the exhaust or a small whispy pop out of the carb area...also when i turn the key the fuel pump sounds horrible...different sounds usually and goes on for about 8 seconds. I took the fuel pump out and there was fuel inside when i took the tubes off... So with what i provided, can anyone tell me what might be the cause?

 

[wishbone]

Is the fuel pump running constantly or not stopping? If so you may have a rubber valve out of place in the pump making it not build pressure. If that is the case there is thread about reparing it. Just search on fuel pump.

 

[86MaximusPrime]

well it seems to be running constantly...it does stop after about 10 seconds...i saw the thread im going to take the pump apart tomorrow to see if i can fix that

 

[MaxMidnight]

Before dismantling why not take the pipe that feeds the carbs off and see what comes out when you turn the ignition on.
Without wishing to state the obvious, you will need to be careful as you are potentially spraying fuel around - extending the pipe to discharge into a small necked container would be prudent.
If you are getting a good flow then it isn't the pump that is the issue.

The fact that you are getting a backfire suggests to me that you are getting fuel to the carbs.

Have you taken the spark plugs out to see if they are wet or dry? While the plugs are out you could also check you are getting a spark.

 

[86MaximusPrime]

You know, the whole idea with the spraying fuel into a container is what i was going to do in the morning, but yeah you are right...the backfire sounds like fuel is getting to the carbs...and its a very gassy smell after i try starting it a bit...i did not check the spark plugs but every once in a while the bike does turn over. and runs for a second...it seems like it will only run while the start button is pressed

 

[86MaximusPrime]

Just tested the fuel pump and it seems to be working fine...it shot a bit of fuel out into a gas can i have..but i dont know how much is a proper amount...it seemed to shoot off about half a cup worth...havnt measured yet...how much should it be?

 

[86MaximusPrime]

Ok so i looked at the spark plug wires and i didnt see a spark...but i dont understand how i can get backfire with no spark...also when i try to start the bike the pump will keep clicking..as if sending more and more fuel to carbs..then eventually from one of the carbs i see a mist and a whisp sound...what can that be?

 

[MaxMidnight]

You must be getting a spark(s) but perhaps not at the right time or intermittently.

Suggest that you start by checking that you are getting power to the ignition unit.

My gut feel is that it's not one of the pick-up coils as you would get ignition on two of the cylinders.

 

[86MaximusPrime]

I see..but why would the pump send more fuel to carbs if the carbs didnt use the fuel already provided to them

 

[wishbone]

Ok your pump sounds like it is good. I would at the very least put new plugs in it. I have a 85 and it does the backfire deal and won,t start when the plugs go to crap. Then like was said check for voltage at the tcu.

 

[86MaximusPrime]

Ok update: the fuel pump is not pumping anymore, i took it apart and the rubber things were in place...it clicks for about 10 seconds just like the relay tells it to do...but now it will not pump...if i put it together and blow hard on one end while plugging the other end...i can still get air through...so i dont know if that has anything to do with it...no pressure building to actually pump...who knows..any suggestions?

 

[brownrxmd]

When you took the cap off the pump there is a very very small black wire that runs from the the contacts into the part of the fuel pump you can't get to. is that melted? I went through two fuel pumps before I got one from kyle that worked. In both cases that little wire was melted and I couldn't solder it back together,,,just an idea.

 

[86MaximusPrime]

i checked it out, it didnt look melted.

 

[brownrxmd]

Mine didn't either, till I tugged on it a bit then the rubber stretched, but yours maybe ok. The book says test it by putting 12v to it, I either misread that or the book is wrong. I think the 12v motorcycle battery melted that little wire, or it was just bad when I bought em. Anyway not sure what else to tell ya. you can check the voltage at the connector and see if their is voltage, supposed to be more than 11v, if less than 11v, then check output voltage from fp relay.

 

[86MaximusPrime]

ok i will do that tomorrow...on duty today unfortunately

 

[86MaximusPrime]

UPDATE: it was the fuel pump the entire time, i bypassed the pump and had fuel enter via gravity and the bike started right up no problems, stayed at idle and everything, so the pump probably has been dying for a while now...so i need a new fuel pump.

 

[06VMAXIMUS]

Wouldn't hurt to change the filter and check the lines for cracks/rot while your in there.

 

[86MaximusPrime]

yeah, i noticed the thing wrong with the pump seems to be a rubber gasket the goes between the 2 pieces to the pump...its cracked and old and is allowing air to get by not creating a proper seal...so i wonder if i can replace that part instead of getting a new pump.

 

[86MaximusPrime]

UPDATE:

Received test kit from sean morley plus fuel pump...so lets break it down.

I havnt been able to get my vmax to run and have been trouble shooting what i can without the kit, last week i decided to bypass the fuel pump and just have fuel enter carbs via gravity, bike ran great! so hazaa!!! its the fuel pump...

Well here i am working fuel pump, i see it pump fuel to carbs via the glass fuel filter but the bike will not start...doing what it did before...but what i notice and i should have mentioned this...is i can hear a low rumble from the exhaust...but only while the start button is pressed...so ...active starter = rumble exhaust...thats why it keeps sending fuel to carbs i think..because im actually using the fuel ...just not running by itsself...so what will keep the engine firing after i stop pressing the starter?

Could this be a CDI issue?

Thanks everyone for all the help!

 

[one2dmax]

Try bypassing the pump again and make sure the pump I sent is for sure good. It could be that the pump is flooding the carbs with it's pressure vs the gravity feed too.

Sean