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Question for all the Carburetor gurus here.

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Mark_M

Mark_M

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Need to pick you carburated bike experts brains with a question.
My new to me Honda 1998 VT1100C2 ace bike is starting up and running for a while while fuel is in the carbs and petcock is in the off position ONLY. when petcock is turned to the ON or RESERVE position the bike mmediately shuts off ?? and seems like the carbs get flooded ??
So far these things have been done by a trained professional with me on looking and relearning the carb system.
Petcock checked is working fine.
New battery
Carbs rebuilt oem jets replaced float height adjusted per oem manual.
Choke plunger and pin checked out and replaced.
New plugs
All electrical gone over we are getting spark.
Bike has good compression.
Fuel tank cleaned out new gas added .
Vacuum line attached to tank is free and clear.
Next step is replacing fuel pump though when testing old one it works fine.
Kinda stumped here this bike should work like new by now with all that is done.
So what in your opinion could be going on ?
Anything u can think of may help out ?
Sometimes it's the silliest little thing that throw it off....
 
Fuel pump issue is all I can think of off hand, but I am no carb expert by any means (but did have a '94 VT1100 and hung out on the Shadow forum for quite a while).
Has the fuel filter been changed (not that I see how that could cause the issue you are having).
 
no experience with fuel pump AND carb with motorcycle. I can tell you a blown fuel regulator running a Holley carb will do what you describe in a heartbeat.

Is it possible fuel pump failure mode is providing too much pressure?

After the bike died, did you confirm over fueling by pulling plug to see if it was soaked or witness carb over flowing through vent. Vent overflow could be hard to see. On my KZ, it would overflow into airbox were you couldn't see it.
 
Float needle is not seating so it works when peacock is in off postion so bike is running on residual fuel in line then may flood out when peacock is turned on
Not very familiar with the VT 1100 but why is there a fuel pump in the system, carb are usually gravity feed so if there really is a pump ln the system it may be over pressuring float needles
 
Have you checked the floats to make sure they are sealed? I've seen a cracked float that would fill with gas and not put enough pressure on the float valve to seat the needle.
Some carburetored bikes do have a fuel pump if gravity can't feed enough fuel to keep the bowl full or if the petcock sits lower than the bowl. This bike does have a fuel pump.
 
Mark_M said:
Vacuum line attached to tank is free and clear.
Click to expand...
It's been a few years since I had my VT1100, but I don't recall a vac line to the tank. There was a breather line from the tank. If that is mistakenly hooked up to engine vacuum, it would draw excess fuel into the engine.
 
dukey33 said:
It's been a few years since I had my VT1100, but I don't recall a vac line to the tank. There was a breather line from the tank. If that is mistakenly hooked up to engine vacuum, it would draw excess fuel into the engine.
Click to expand...
^^THIS. Or if not exactly, otherwise, extra fuel could be getting in through some vacuum line.

Likely a "vacuum line" running to the tank would be part of the EVAP system. It's a vent intended to vent to a purge valve which is likely vacuum operated, idea is to dump fuel vapors into the carbon canister. If you eliminated the EVAP system and hooked this line straight to the vac line then it could cause problems.
 
dukey33 said:
It's been a few years since I had my VT1100, but I don't recall a vac line to the tank. There was a breather line from the tank. If that is mistakenly hooked up to engine vacuum, it would draw excess fuel into the engine.
Click to expand...
Potentially waay better answer than mine. Look through service or parts manual to see if you can find bike vacuum line map.
 
Never mind yours has carbs. Sounds fuel pump-ish. See if it will run with an Aux fuel pump and the main disconnected? Turn on fuel pump with hose disconnected see if fuel moves? Haven't messed with one of those but there is a lot out there on the VTX.
 
Hopefully Diagnosed it today she started up without the fuel pump connected with the petcock in ON position so diagnosis most likely is bad fuel pump pumping too much fuel to the carbs.
And for those who were wondering the Honda Shadow VT1100C2 Ace is carburated but has a fuel pump. That's just Honda go figure lol
 
Update
Bike is starting and running with fuel pump disconnected and petcock in the on position keeping fingers crossed that changing out the pump will resolve this dilemma.
 
UPDATE
Ok so now we have independently connected the NEW fuel pump via hose and fuel line. SAME ISSUE bike starts without fuel pump connected with fuel in the carbs but the moment the NEW (WORKING/TESTED) FUEL PUMP is connected the bike immediately shuts off ??? At my wits end here any thoughts guys ?
I am also trying to check the fuel relay now to see if that could be faulty . Any input would help working on the bike now as we speak.

Mark_M said:
Update
Bike is starting and running with fuel pump disconnected and petcock in the on position keeping fingers crossed that changing out the pump will resolve this dilemma.
Click to expand...
 
Last edited:
Mark_M said:
UPDATE
Ok so now we have independently connected the NEW fuel pump via hose and fuel line. SAME ISSUE bike starts without fuel pump connected with fuel in the carbs but the moment the NEW (WORKING/TESTED) FUEL PUMP is connected the bike immediately shuts off ??? At my wits end here any thoughts guys ?
Click to expand...

Did you chase down that "vacuum line"? Because that was the most likely cause IMHO. Fuel pump is doing its job. Running without a fuel pump is not the correct operation.

I'd start with an accurate fuel and vacuum line diagram, a roll of new fuel hose, a roll of new vacuum hose, and a bunch of hose clamps, go through it piece by piece replacing the fuel lines and vac lines, ensuring they are exactly like the diagram. Something in there is screwed up, I can almost guarantee it. Like, a vacuum port on the carb is hooked to the fuel supply, etc.
 
My son owned an 1100 Shadow, 2006 model. His did that and we bypassed (alligator clips and wire) his fuel pump relay. Fixed it.
 
Ok done everything we possibly could so now the bike is going to the repair shop. Hands up in the air I give up. But it was fun troubleshooting and relearning many things. Ty all for your tips and help 🙏
 
mr72 said:
Did you chase down that "vacuum line"? Because that was the most likely cause IMHO. Fuel pump is doing its job. Running without a fuel pump is not the correct operation.

I'd start with an accurate fuel and vacuum line diagram, a roll of new fuel hose, a roll of new vacuum hose, and a bunch of hose clamps, go through it piece by piece replacing the fuel lines and vac lines, ensuring they are exactly like the diagram. Something in there is screwed up, I can almost guarantee it. Like, a vacuum port on the carb is hooked to the fuel supply, etc.
Click to expand...
Honestly I looked over the lines they looked ok to me and was pretty frustrated at this point after the fuel pump checked out so am sending it in to a shop I know that has fixed this type of bikes before and they will deal with it now. Ty for your advice though.
 
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