Bowl vent pipe

[Gumpster]

Drove my 1978 GS1000 to work on Saturday and it ran real well but the return home was another story. 3 weeks had passed since I rode it last so carbs were suspected to be the culprit. The bike stalled a couple of times and was very sluggish of idle. At half throttle it would eventually wake up and function as normal. The carbs were removed and the bowls. I had a problem years ago with the vent pipe inside one of the bowls. It had a crack and would drip fuel from the vent hose. I patched it with some epoxy and it worked okay. I noticed that the epoxy was soft so i decided to remove it, clean it and properly rectify it. I eventually managed to break it off. Not the end of the world but here is my question: Can I block off this one hole where the vent pipe used to be and still have enough bowl vent from the other vent hose on the side of the carb. K & N pods, V & H pipe, Dyna S, coil mod, progressive springs, 530 chain.....

[Gumpster]

Fuel bowl

Well, not a lot of responses. I have determined that the pipe is probably more for overflow than bowl venting so blocking it off would be a temporary fix. This should not affect operation but could expose me to filling the engine with fuel if the needle and seat fail. Anybody have a mikuni bowl (VM)? left side preferably...

[BassCliff]

Hi,

What part are you talking about? Got a picture? All of those carb parts are pretty important.


Thank you for your indulgence,

BassCliff

[Gumpster]

Picture attached VM fuel bowl

BassCliff,

Thanks for replying and for all the help and information you provide through your site. I am a big Fan!!!

The fuel bowl on the left is good. The one on the right had a broken bowl vent/overflow pipe so i sealed it as a temporary fix. Will it be okay?

Thanks

[BassCliff]

Hi,

I guess that will be OK temporarily. Just know that if it does overflow, now it will go into the cylinder, past the rings, and into the crankcase. Keep an eye on your oil level. If it goes up inexplicably then it may have been diluted by gasoline. Make sure the float height is set properly.


Thank you for your indulgence,

BassCliff

[KEITH KRAUSE]

That's not a vent tube, it's an overflow tube. If your float level is too high or the float needle valve allows excess fuel into the bowl the excess fuel will spill out through the tune and overflow line routed safely to the ground.
As Cliff said, with the tube missing you can get fuel into the motor.
Wondering what your final jetting adjustments are.
Be sure to remove the two float bowl vent lines to avoid fuel starvation at various levels. Stronger crosswinds often cause starvation when running pods with stock vent lines. I have the same bike and removing the lines really helped. It's also recommended by Dynojet in their stage 3 kits.

[Gumpster]

Keith,

I did remove the the vent hoses after reading some of your other post with regards to the fuel starvation concerns. The bike seems to be running okay now but am still a bit concerned if the needle and seat fail or if i forget to cut the fuel as a manual valve is installed. Didnt receive any respose when posting in the parts needed section for a bowl but accidently stated VM29 when it is actually VM26 bowl needed. Might need to repost correctly....

The needles on these carbs have 5 positions. I think not all 1978 bikes have this but mine is an early version built in December of 77. It even has a switch to kill the headlight. Anyway, I installed mikuni 120 mains, needle clip on the lowest position (richest), pilot screws out 2 to 2.5 turns, and the air screws out 1-1.5 turns. The needle clip was 4th from the top and probably would be best at 4.5.... Will do some plug chops later this week and see if the clip needs to be reset or shimmed.

[KEITH KRAUSE]

Keith,

I did remove the the vent hoses after reading some of your other post with regards to the fuel starvation concerns. The bike seems to be running okay now but am still a bit concerned if the needle and seat fail or if i forget to cut the fuel as a manual valve is installed.

The needles on these carbs have 5 positions. I think not all 1978 bikes have this but mine is an early version built in December of 77. It even has a switch to kill the headlight. Anyway, I installed mikuni 120 mains, needle clip on the lowest position (richest), pilot screws out 2 to 2.5 turns, and the air screws out 1-1.5 turns. The needle clip was 4th from the top and probably would be best at 4.5.... Will do some plug chops later this week and see if the clip needs to be reset or shimmed.

I'm sure someone has a bowl for you here. Just be sure to get the right bowl (ex: left to right, carb 1, 2...).
A float needle valve can fail like any other part and not seal perfectly. So with a manual fuel valve (I have one too) you just have to remember and make it part of your routine. I turn it on first, before the key and choke. At shut off I turn it off first. Works for me. Unless you think you may have a real leak problem, you should only have to turn off your valve when parked for the night or when getting to work. Stops for lunch or short stays shouldn't require shutting off but I do anyways out of habit.
The stock jet needles always have 5 grooves as far as I know.
Jetting: If your bike is in good tune, compression, valve clearances, advance timing, good spark, etc, then... a 120 main jet is too lean.
A stage 3 DJ kit which is designed for exactly your exhaust/intake mods supplies 138 and 142 main jets. You want the 138. It works well. No need to test. If it doesn't work then somethings wrong other than the jetting. If you want typically better results then order the DJ kit. It comes with better quality jet needles. If you can't spend the $ then you can try seperate jetting and your stock jet needles but be aware the results are sometimes noticably inferior.
If going with Mikuni mains, them buy 130's which are approx' the same size as 138 DJ's. Each brands sizing is determined by different methods but those two sizes are nearly identical.
If stock jet needles then the bottom (5th) position MAY work but may be too rich. You can test the needles and get accurate plug/performance reads by running the bike at 1/3 to 1/2 throttle position for a mile or so at full operating temperature. Chop off the throttle for best results. Position 4 from the top is generally too lean but you can always try. I may be wrong but if using the stock needles I'd probably try position 4 1/2 first and test. But you need jetting spacers typically found in the DJ kit that are approx' .022" thick to make the 1/2 position changes. Some members say Radio Shack, etc, has thin washers that will work. If you get them, place the jetting spacer directly on top the e-clip in the bottom position. If none of those three positions work well, then you need the DJ needles. Be sure all factory nylon spacers are re-assembled on the jet needles in exact factory order. Thicker spacer on top the e-clip, thinner under the clip. Like I said, the DJ needles are far better so if you can I suggest buying the kit.
As for the pilot circuit, if using seperate Mikuni jetting and stock needles, you'll probably want one step larger pilot jets, 17.5's. You can FIRST try using the stock 15's and richen the pilot fuel screws underneath. These screws ASSIST the pilot jet and are for fine tuning. They are generally 1/2 to 1 full turn out from LIGHTLY seated, straight from the factory. With that range as a starting point, you can try 1/2 additional turn on each and test the pilot circuit at minimal (under 1/5 throttle) throttle positions. You can richen them a little at a time as needed to get the performance you need. If you reach a point where they are about 3 full turns out and you still get lean symptoms then you've gone past their effective range and that means you need the larger pilot jets and return the screws to something close to the factory settings. Slow warm ups on colder mornings and deceleration popping are more likely with the stock pilot jets.
If you use the DJ kit then that kit is designed to use the stock #15 pilot jets and only richer pilot fuel screw adjustments may be needed. Screws are sensitive and it does take time to get them spot on.
As for the side air screws, they generally end up about 11/2 to 2 turns out BUT you always adjust these by using the highest rpm method, not just setting them to some pre-determined position. Set them initially at 1 1/2 turns and then use the method to find each screws sweet spot. The bike will run better if you're careful doing this job.
Remember you must re-synch each time you disturb/change the jet needle positions. A vacuum tool synch should follow the bench synch for best results and to more accurately test the new jetting.

[Gumpster]

Keith,

Thanks for all the valuable information and for taking the time. I will likely order a jet kit and go with the DJ 138 mains. $ is not really an issue and I spent almost as much on ordering mikuni jets as a DJ kit. I am quite sure that 120 mains was reccomended in the instructions that came with the exhaust. Cant find them now but had them in hand when ordering the mains for a set up with pods or lid removal. A kit is available for around $100 on ebay so that will be my next step. what started all this was I figured trying the clip on spot richer due to the alcohol content in fuel these days. Just experimenting.....

Thanks again....

[KEITH KRAUSE]

Keith,

Thanks for all the valuable information and for taking the time. I will likely order a jet kit and go with the DJ 138 mains. $ is not really an issue and I spent almost as much on ordering mikuni jets as a DJ kit. I am quite sure that 120 mains was reccomended in the instructions that came with the exhaust. Cant find them now but had them in hand when ordering the mains for a set up with pods or lid removal. A kit is available for around $100 on ebay so that will be my next step. what started all this was I figured trying the clip on spot richer due to the alcohol content in fuel these days. Just experimenting.....

Thanks again....

OK. You'll find lots of incorrect advice around. Don't accept anything as fact unless you've tried it yourself. 120 mains are too lean. Maybe for pods alone with stock exhaust but not a quality pipe and K&N pods. I know the DJ kit works well because I've tested it. Many here use them. I've forwarded jetting advice and everyone says the suggested jetting worked as long as the bike was tuned well to begin with and ready for jetting. But even DJ can give poor advice when it comes to their "baseline" settings for the jet needle in their stage 3 info. You'll hole a piston if you follow what they suggest regarding the needles.
You'll like the kit.
138 mains, e-clip in 4th position from top with all factory spacers re-assembled in correct order, stock pilot jets with richer pilot fuel screw adjustments (will take some tinkering but about 1 to 1 1/4 turns out is a common final setting), set air screws using highest rpm method (about 1 1/2 to 1 3/4 turns out is common), remove floatbowl vent lines and leave ports open, bench synch followed by vacuum tool synch. Should run well with minor adjustments to the pilot fuel screws.
Let us know if you have issues.
PS: the Morgan carbtune vacuum tool is a very good tool to synch with. No mercury and the heat related condensation issues that mercury may have.
Motion Pro makes a good mercury tool for less than half the cost but if you take awhile synching you may get condensation mixed in with the mercury in each cylinder line and the gaps in the mercury make it more difficult to get the vacuum levels uniform.

[Gumpster]

Okay, ordered new gaskets (bowl and top) and a dynojet kit from Z1 for $95. What a bargain..... Takes all the guess work out and provides quality parts which are proven. I will report back once it is all installed and let you know how it works. Thanks for your recommendation and Suzy will have 138 DJ mains this time next week. Still need a left side bowl and will repost that in the appropriate area.

[Gumpster]

Okay, received the Dynojet kit and installed per Mr. Krause direction. I do think Keith's set up direction is great but looks like I have other problems. #2 and #3 exhaust was not getting as hot as #1 and #4. switched plug wires and output leads from the Dyna S and the problem moved. Looks like one of the coils is bad. Found some 3 ohm green dyna coils on ebay for a good deal. Does this look like it will fit my application?

http://cgi.ebay.com/ebaymotors/Dyna-DC1-1-Coil-Dual-Output-3-ohm-Kawasaki-Suzuki-_W0QQcmdZViewItemQQhashZitem484124e727QQitemZ310330582823QQptZMotorcyclesQ5fPartsQ5fAccessories

I am still glad to have done the carb upgrade, Just want to get back on the road before the cold weather arrives. That is the two weeks in Feb in south Georgia when it gets too cold to ride in shorts and flip flops.... Guess I have a little time.

[Jason the terminator]

Yes, those should be the correct coils. What voltage do you have at the coils? May want to look into doing a coil relay mod while your at it.

[Gumpster]

Installed the new coils, decided to take a look at the carbs again since the tank was already removed. Discovered that all 4 fuel mixture screws tips were broken inside the carb body. I was able to force them out with access through the slide opening. When I started the bike, it idled really high. I guess the PO just set the idle high since the pilot circuit was toast....

Since my bike developed a skip several weeks ago, I mis-diagnosed a carb problem when the fault was actually a coil; but the good news is I have 3ohm green Dyna coils, clean carbs, working pilot circuit, Stage 3 Dynajet kit, and a great idle with smooth acceleration. It is now almost too fast!!!

Clip at #4 position, fuel screws out 1 1/2 turns, air screws out 1 1/2 turns. I will be doing some fine tuning over the next couple of days but it is pretty close. The mixture screws needed a little dressing up and probably need to be turned in a bit since they lack the sharp point. Did the best I could with re-shaping.

Oh yeah, I did replace the bowl. Thanks Tom!