Engine Not Getting Fuel After VM Rebuild

[slaveforthewave]

After dipping and rebuilding my VM carbs on my 78 GS1000 engine I can no longer get the engine to crank reliably. After an hour of tinkering with the choke, starting fluid and throttle position i can usually get it to fire erratically for a minute or two before it dies; but before the carb rebuild it would start pretty reliably. I have no tank and just funnel gas into the float bowls so it isn't a petcock issue. And I used all the jets that were in the running bike before disassembly so it everything should be close original. Plugs are all firing so I am a little confused where to go next.

Any ideas on what I could be doing wrong? I know the pilot fuel screws were bottomed out so hard before I got this bike that they were flattened on the tips, but I cannot find replacements anywhere. Could this have to do with my problem?!

Thanks.

 

[dr_fosg8]

Did you bench synchronized the carburetors? Also have the valves been adjusted? May set a remote fuel tank like from a lawn mower to get consistent fuel delivery. I am not familiar with point but are those adjusted properly? Is the clutch safety switch still functioning?

 

[Agemax]

if you are fuelling via funnel, have you blocked up the vacuum hose that goes to the pet cock? could be sucking in too much air

 

[Big T]

You cleaned the carbs per the tutorial?

It should start better than before, fuel needle problems or not

Where did you set the fuel and air screws?

Plus, vacuum port noted above capped?

Did you check to confirm there's gas in the float bowls?

 

[Rover]

Agemax may be on to something.
Fuel delivery problem?

 

[tkent02]

Did you put it on PRI for a little bit before trying to start it up?

 

[Adler]

Which screws are flattened??? Theones on the bottoms of the carbs or the one on the side? the ones on the sides aren't supposed to be sharp and the ones on the bottoms have a tendancy to break off in the carb body and cause serious issues... make sure that you can see light through the hole on the bottom.

Did you put it on PRI for a little bit before trying to start it up?

He isnt using a petcock... no PRI.

 

[Agemax]

Did you put it on PRI for a little bit before trying to start it up?

hes using a funnel, not his gas tank. can you switch a funnel to prime?

 

[2BRacing]

I encountered a similar situation last week on my son's 400. After setting valves and cleaning carbs, I set up a funnel with fuel so that I could synch the carbs. However, not even a burp when trying to start. Spark was good. Eventually I blew into the fuel line to "force" some fuel into the float bowls, because there was no fuel in the bowls, as tested by removing a drain screw.

I think the funnel setup did not cause enough fuel "pressure" to open the fuel inlet needles.

 

[Adler]

I encountered a similar situation last week on my son's 400. After setting valves and cleaning carbs, I set up a funnel with fuel so that I could synch the carbs. However, not even a burp when trying to start. Spark was good. Eventually I blew into the fuel line to "force" some fuel into the float bowls, because there was no fuel in the bowls, as tested by removing a drain screw.

I think the funnel setup did not cause enough fuel "pressure" to open the fuel inlet needles.

The fuel doesnt have to overcome the inlet needles. They are open unless they are stuck.

 

[2BRacing]

Good point, just realized that! Mine must have hung up somehow, as there was no fuel in bowls originally, but only came through after blowing on fuel line.

 

[slaveforthewave]

okay, so the needles that are flattened are on the bottom side of the carbs on the side closest to the motor. the vm rebuild pdf on the basscliff site calls them the pilot fuel screws. i took everything apart, dipped the carbs, pumped compressed air into every nook and cranny, bought the rebuild kit, and put everything together the way i found it. pilot screws are at about 1 1/4 turns from bottom, pilot air screws are about 3/4 turn from being flush with top of carb body, took bowls off and they were full of fuel but not leaking from the overflow tubes on bottom of bowls. i fill the funnel up until no more fuel is going into the carbs and hang it from a nail with about 4 feet of hose. i did not block off any of the vacuum lines, but i will try that next. if i squirt a bit of starting fluid in the carbs and choke it at about half the bike will run for about 30 seconds at somewhere around 1500-2000 rpm. after that you can here it pop a few times and then the motor dies a few seconds after. there are no points on the motor because i took the stock electronic ignition, igniter box, and coils off my 82 GS850 motor and made a custom harness for it all.

kind of a bummer that the thing ran just fine before but the carbs leaked gas like crazy, so i rebuilt them and now nothing but problems!

 

[Big T]

Well, the starter spray indicates a carb problem

So, don't use it anymore

Your screws are messed up. They should be

1. Fuel -7/8 from seated
2. Air - 1 1/2 to 2 from seated

You did get the broken tips of the fuel screws out of the carbs??

Cap the vacuum port (adjacent to the fuel T) on #3 carb

Keep plugging away, it's something small

 

[slaveforthewave]

okay, just went back out to the bike, filled up the funnel just a bit and blew into it. a little bit of fuel came out of the pod filter side of the carbs, but the drain tubes stayed dry from what i can tell. either way, i fired the bike back up and idle was still high even though the idle adjust strew isn't even touching the throttle/slide mechanism.

BUTTT the interesting part is when the 'popping' started which seems to be a gas/air mixture blowing back out the carbs pod filter side, i blew into the funnel again and the bike stayed alive for a few more seconds, popped again, i blew into the funnel again, etc. it kept the bike alive. what could this mean?!

 

[Adler]

okay, so the needles that are flattened are on the bottom side of the carbs on the side closest to the motor. the vm rebuild pdf on the basscliff site calls them the pilot fuel screws. i took everything apart, dipped the carbs, pumped compressed air into every nook and cranny, bought the rebuild kit, and put everything together the way i found it. pilot screws are at about 1 1/4 turns from bottom, pilot air screws are about 3/4 turn from being flush with top of carb body, took bowls off and they were full of fuel but not leaking from the overflow tubes on bottom of bowls. i fill the funnel up until no more fuel is going into the carbs and hang it from a nail with about 4 feet of hose. i did not block off any of the vacuum lines, but i will try that next. if i squirt a bit of starting fluid in the carbs and choke it at about half the bike will run for about 30 seconds at somewhere around 1500-2000 rpm. after that you can here it pop a few times and then the motor dies a few seconds after. there are no points on the motor because i took the stock electronic ignition, igniter box, and coils off my 82 GS850 motor and made a custom harness for it all.

kind of a bummer that the thing ran just fine before but the carbs leaked gas like crazy, so i rebuilt them and now nothing but problems!

Those needles don't "flatten" they break. The little piece that breaks off blocks the air flow and the carbs don't work. You need to clear the tiny holes behind those screws.

As for the "flat" screw. You may be able to sharpen them... Otherwise they will need to be replaced.

 

[Big T]

Those needles don't "flatten" they break. The little piece that breaks off blocks the air flow and the carbs don't work. You need to clear the tiny holes behind those screws.

As for the "flat" screw. You may be able to sharpen them... Otherwise they will need to be replaced.

I believe they block off the fuel flow, not the air

 

[slaveforthewave]

since the bike ran before i disassembled the carbs is it possible when i pulled the screws out they broke? the bike was jetted with an 4-1 exhaust before i got it. points were shot so i switched to electronic and the bike fired right up no problem and idled fine. now the bike will only run if i'm blowing into the funnel lightly...

i've got no problem pulling the carbs again and trying to locate some missing screw tips, but if it sounds like a tuning problem i'd rather go that route.

thanks for all the responses btw, it's much appreciated.

 

[Big T]

Check my post above about your screw settings

BTW, did you use some kind of rebuild kit?

 

[slaveforthewave]

i put the screws exactly where you said and it's still acting the same. pressure in the fuel line makes her run, but idle is extremely high and popping out of the carbs is still there.

i used the Z1 rebuild kit here http://www.z1enterprises.com/detail.aspx?ID=502 just kept and cleaned both jets that were used after PO jetted bike.

 

[rustybronco]

I know the pilot fuel screws were bottomed out so hard before I got this bike that they were flattened on the tips, but I cannot find replacements anywhere. Could this have to do with my problem?!

Thanks.

At what point did adjust the pilot (fuel mixture) screws to get the bike to run correctly before you started doing the carb rebuild?

okay, so the needles that are flattened are on the bottom side of the carbs on the side closest to the motor. the vm rebuild pdf on the basscliff site calls them the pilot fuel screws. i took everything apart, dipped the carbs, pumped compressed air into every nook and cranny, bought the rebuild kit, and put everything together the way i found it.

kind of a bummer that the thing ran just fine before but the carbs leaked gas like crazy, so i rebuilt them and now nothing but problems!

Considering the excess amount of fuel being supplied to the carbs, you probably didn't need the fuel from the pilot screws to get it to run. AND with damaged pilot screws and the carbs overflowing there's no way it ran correctly. ran yes but not correctly.

remove one of the damaged pilot screws and take a GOOD picture of it- then post it up.