Starved for fuel

[suzukigs1000]

I have a 79 GS1000 with Mikuni VM29 carbs. My problem is that I doesn't seem to be getting any fuel to the motor, the float bowl's are getting fuel to them, but nothing to the motor. I've been having this problem for a while so I did some work to the bike.

Dyna 3 Ignition
New coils
New orings on intake boots
Carb Rebuild /w bench sync(waiting on vacum sync tool to arrive)
bypassed vacum line for the petcock(took spring out to make fuel flow freely)

The bike started fine after I got it back together, ran great on the test ride. Went back out a couple of hours later to ride again, got down the road and it started running like crap(not running on all cylinders) and getting hot. Made it back to the house and did a chop test to find the plugs dry and clean. Removed plug wires and turned the motor over a few time, pulled plugs and still no fuel. Compression is #1: 82 #2: 91 #3: 90 #4: 92. At this point I'm stumped and have taken the carbs back off, cleaned the starter jet with a small wire to clean any obstructions and reset the float's to allow more fuel into the bowls just incase I got this part wrong.

Any ideas on why there is no fuel getting to the cylinders. Heard somewhere on here that I can blow into the bowl vent lines and this will help?

 

[SPARKSS]

Sure sounds like something is missing from the history you've related. Was the test ride where it ran great, after having done the ignition and intake work? How long a ride was it and did it cover most of the range of operation as well as from cold to warmed up?

Was anything added to the fuel tank besides gasoline?

If all bowls have fuel in them, it's unlikely that you wouldn't run somewhat, based on just a couple of hours shutdown from a normal running condition. I don't quite understand why you'd mod the petcock though, if you suspected this to be a cause of no fuel, merely rotate it into the prime position which bypasses the vacuum operated valve inside. What did you do with the now unused vacuum line?

If that was mine, based on what you wrote, if I suspected a massive fuel failure, I'd want to attempt to run the engine on propane (flowed into the airbox, if this is still used)....which will rule out basic engine and ignition integrity issues as other possibilities.
For example, in a post earlier this summer, one rider trying to understand why he'd lost all compression, initially didn't see that his engine wasn't cranking although the starter was (starter clutch problem).....I know it sounds basic.

.02 worth (Canadian or American!)

 

[suzukigs1000]

It did run great on the test ride. Rode for around twenty minutes with no problem, taking the bike from just crusing at 40 to almost 100 with no problems. The petcock doesn't have a prime position, that why I had to bypass. Nothing was added to the tank other then gas, is clean as well.

I left the vacum line pluged into the petcock, just took the spring out of the petcock to allow fuel to flow freely. When I rebuilt the carbs, first soaked them for a few days, I used a small wire to clean all passages and also used an air compressor to clear out anything left behind.

Still when I crank the motor over a few times there is no fuel on the plugs(done with the plug wires off).

This has been a reaccuring problem. It will run great then after sitting for an hour or two, will start but doesn't seem to run on all cylinders and then gets hot, thus the coil change. Don't know what I am missing.

 

[Steve]

First of all, welcome to the board.

Next, while the compression numbers are wonderfully consistent, they are below the service limit of 100. Have you adjusted the valves recently? Tight valves can affect the compression numbers and how the bike runs, in general.

Why did it run for a while, then quit? Need more diagnostic time with that one.

I just went back and re-read what you did to the bike. Why remove the spring and vacuum line from the petcock? It won't flow any more fuel while in operation, and there is now no way to shut the fuel off to be able to remove the tank. With no vacuum line to assure that the diaphragm is pulled into the ON position, it might have closed itself, even though there is no spring pushing it. For every person on the board that has had "problems" with their petcock and replaced it with a manual unit, there are hundreds of us using stock petcocks with no problems. Unless you are running a drag bike that requires a couple of gallons of fuel in a few seconds, there is enough flow rate for any situation you are likely to encounter on the street.

How could you do a chop test when the engine is not running well? To do a chop test properly, you need to run the engine at a particular throttle setting under load for a while, then pull the plugs to read them. If the engine is not running well, the results are basically meaningless.

Resetting the floats to "allow more fuel into the bowls just incase I got this part wrong" does not make sense, either. Since you were adjusting, why not just adjust them correctly? If the floats are too high, it will affect mixtures throughout the engine operating range. Please set everything you can to the recommended settings. Believe it or not, that is where the engine will run quite well. That will also give a baseline from which we can suggest changes.

Just saw your reply before posting this, and now have to ask...when you soaked your carbs, were they completely torn apart? All the o-rings and gaskets removed? Did you replace all the o-rings when re-assembling? It's possible that if you did not get them completely apart, an old o-ring swelled and is blocking a passage somewhere.


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[suzukigs1000]

Thanks for the welcome. I have not adjusted the valves, this was going to be the next step. I took the spring out of the petcock to elminate this as being the problem for no fuel. As for the chop test I did this at the end of my ride yesterday when it was running good riding about 40mph in 3rd gear is what I've read to do. #1 and #3 were a little lean #2 and #4 looked good. As for the floats, I did this last night in frustration and have not yet put the carbs back on the bike, guess I will set them back to the correct hight after work today. I left the vacum line on the petcock to make sure it would pull open, had just taken the spring out just incase there wasn't enough vacum to pull it open.

I did tear them all the way down before the dip and then replaced all the orings. Thinking on it I might have put the wrong size(not thick enough) on the choke plungers. Could this cause a lean condition. During the rebuild I put in bigger mains (from 95 to 102's).

What happens is after I let it sit for a while and then try to restart it, it will start on choke and seem to run fine. get a little bit down the road and it seems to not run on all cylinders, looses power(from getting hot i assume), if I give it full throttle it pulls hard but will soon start sputtering and dies. when I try to restart it will barely idle and then dies again.

About to take really big hammer to this thing after pushing it home about a mile lastnight.

 

[Steve]

I have not adjusted the valves, this was going to be the next step.

Adjusting valves should always be done before adjusting carbs. In fact, adjusting the carbs is the LAST part of the tune-up procedure.

I left the vacum line on the petcock to make sure it would pull open, had just taken the spring out just incase there wasn't enough vacum to pull it open.

Good enough thinking by leaving the vacuum line on, but it would have been better to just run in PRIME position to assure fuel flow. Inside the petcock, there is a pin in the center of the diaphragm that closes into an o-ring to close off the fuel. I have seen problems with that o-ring being stuck in the wrong place. Check that. As far as the (possible) low vacuum, adjusting the valves might take care of that. If adjusting the valves does not help your compression numbers, you will have other projects to consider before it will run right.

I did tear them all the way down before the dip and then replaced all the orings. Thinking on it I might have put the wrong size(not thick enough) on the choke plungers.

Where did you get your o-rings? Hopefully not at the corner hardware store. If you bought kits for the carbs and put the wrong ones on the choke plungers, where else did you put the wrong ones, or were there o-rings left over?

During the rebuild I put in bigger mains (from 95 to 102's).

Why? Do you have either/both header and pods? None of this was mentioned before and would make a difference on what was recommended. If everything is stock, the larger jets are not really necessary. If you have either pods or pipe, it might be close. If you have both, pods and pipe, the mains are still too small.

What happens is after I let it sit for a while and then try to restart it, it will start on choke and seem to run fine. get a little bit down the road and it seems to not run on all cylinders, looses power(from getting hot i assume), if I give it full throttle it pulls hard but will soon start sputtering and dies. when I try to restart it will barely idle and then dies again.

Sounds more like valve clearance problems here. They might be barely sealing enough to get it started, then changing as it warms up, preventing it from idling well. Get the valves set, then we will re-adress the carb issues.

About to take really big hammer to this thing after pushing it home about a mile lastnight.

Not fun, unless that mile was all down hill. When you get it all sorted out, it will be worth it. 8-[


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[SPARKSS]

Based on your last post, it sounds more like it's running out of fuel. You might check to see whether the fuel tank cap has stopped venting (was anything changed here?). This alone would cause exactly what you're looking at. You might try causing it to fail and then opening the cap and see whether you're breaking suction at this point (or just try the engine again).

You've mentioned it getting hot a couple of times.........and that you'd changed the coils because of this etc.........You might verify that the system voltage is normal when at operating RPM.......High voltage can cause the coils to overheat and will most likely hurt your electronic ignition setup in time (depending on the severity).

 

[suzukigs1000]

The bike has a 4 into 1 header (unknown brand) stock air box, thus the bigger main jets. As for the coils, I replaced them with the electronic ignition conversion. As for the valve's, I have never adjusted them and don't know where to start. I believe the motor is getting hot because of not having enough fuel getting to it, could be wrong tho.

I haven't checked the fuel cap to see if it is venting corectly, how would I go about doing this. Also what does it take to adjust the valves, should I take the head off and clean the inside(if the valves aren't seating as they should), also where do I get shims for it. I'm learning as i go here.

The PO said that he had taken the carbs apart to clean them because the bike had sat for 10 years. could he have gotten #2 and #3 carbs in the wrong position(#2 becoming #3) and would this make a difference?

The orings were puschased from Robert Barr, heard of him through this fourm. Also purchased new intake boot orings. All are in correct places via picture/instructions included with orings. The reason I think I might have the wrong ones on the choke plungers is because the kit came with two sets that were the same diameter but one set was thicker then the other, no instructions for these.

 

[robertbarr]

The reason I think I might have the wrong ones on the choke plungers is because the kit came with two sets that were the same diameter but one set was thicker then the other, no instructions for these.

Gonna have to disagree here. I include clear instructions with every kit, and just in case, it's also online. You had to see these instructions to order the kit.

http://www.cycleorings.com/VMkit.html

Each size is in its own zip-lock, marked A-F, and each letter corresponds to one clearly identified component.

The O-rings for the choke plunger are identified as 'E'. Nice big capital lettering. Hard to screw that up...

 

[Nessism]

As for the valve's, I have never adjusted them and don't know where to start.

Do you have a manual? If not, that's a good place to start. :-D Another good place is the Search function right here. Tons of information, including BassCliff's nice pictorial. You are going to need a new cam cover gasket, and a valve spring compressor ($15 at Z1). Also some different shims.