1991 VFR 750 Cranks but No Start

I have a 1991 VFR 750 that I've had for 10-12 years. Sometimes it sits too long, won't hold idle so I clean out the carbs and everything is OK. I just did that this weekend and it completely refuses to start. It was running before I took the carbs off and cleaned that, just it wouldn't hold idle. It cranks fine, has spark from the coils, and I just put in new gas. It's never refused to start. Any ideas? I made sure the kill switch is OK, the gas switch on, everything obvious.

 

Have you cracked a carb drain to make sure you are getting gas to the carbs?

 

be sure the throttle plates are nearly fully closed when cranking---use no more than ab out 1/4 choke--have a look at ur sparkers

 

i have a like-new set of cleaned carbs for ur bike for sale or exchange---check classified --- guaranteed to work on ur '91 ----------------------- -----

 

I've heard about the carb drains, but I don't see them. I've tested the fuel pump per the service manual, and it pumps out plenty of fuel.
Oddly, when I check spark with a timing gun, sometimes I get spark, and sometimes not. But either way, it's not even trying to start. You would think at least one cylinder would fire from time to time. Any other ideas? Isn't the "spark unit" know to fail on these from time to time?

 

So you've cleaned your own carbs, but you don't know where the carb bowl drains are?

There are flat blade screws on the bottom of the float bowls next to the drain nipples.

Ok, so your pump works. Are you getting fuel to your carbs?

Are you sure you have the fuel lines off the pump connected to the appropriate inlet and outlet?

 

Someone posted a picture of the carbs two messages up. Could you point out where the drains are? And is it possible to access them with the carbs installed on the bike?
Yes, I only disconnected the outlet line on the fuel pump o verify that fule was coming out of it.

 

They are accessible when mounted.

See the nipples on the bottom in the first pic?

The drain screws are on the end of "tunnel" shaped feature. 2 point to the left hand side of the bike and 2 to the right.

If you look at your carbs in the V of the engine on the left, one will be staring you in the face.

 

Thanks for the help. I never noticed those. I took one out, no gas came out. I'm guessing that's a bad thing. I'll put the tank back on and try cranking it.

 

Yes, that appears to be a problem.

In the future, they don't have to come all the way out. A couple turns and fuel will come out of the drain nipple.

 

do you hear the fuel pump clicking ? if not, try bypassing the fuel pump relay

 

Yes, as I mentioned previously, I pulled the hose off of the output, bypassed the relay and got a steady stream of fuel out of it. So I'm gessing there must be a blockage in between the pump and the carbs somewhere.

 

Have you tried priming the carbs with the relay jumped? It should run and then eventually start clicking slowly and stop.

 

Yes, that didn't do anything. I've got the carbs off now and looking for a blockage in the fuel lines. Either that or maybe I mixed up the fuel and air hoses when I put it back together. That's kind of unlikely though as I have done this several times before and never had a problem.

 

Bike ran, but didn't idle. You took it apart, which you have done before, and now it doesn't even want to try to start.

Fuel line blockage in this scenario seems highly unlikely. Sounds like you didn't reassemble something properly.

 

this wanker thought he was cleaning his carbs, 2 crushed emulsion tubes the result----could have destroyed the carb-------------------------

 

My old RC24 had really soft fuel lines that kinked if you looked at them funny. Managed to cause a fuel shortage on my first reassembly which took some tracking down, I replaced them with real fuel line and the problem was resolved.
With the fuel relay jumpered, the fuel pump should go like the clappers for some time then slow and finally stall out when the float chambers are full and float valves shut the fuel flow off. If the pump just keeps clattering away, there is likely something stopping supply from the tank (or its empty) or the pump is just airlocked (and needs to be primed).

 

OK, I'm getting fuel to the #3 and #4 carbs (right side). What am I missing?

 

Sounds like you're missing fuel to the #1 and #2 carbs.

Sorry. I had to.

Did you 100% ABSOLUTELY verify that you are not pushing fuel in to the vent lines?