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Vacuum prob? Only runs on prime..

  • Thread starter Thread starter skubasteve!
  • Start date Start date
S

skubasteve!

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Hey guys. Got her all put back together, and it fired right up when I had it on prime. Once fired it put it to ON and a little later it will die.. I have the hose from the small port on the petcock running to the connection on the third carb. Is it a vaccuum problem? What am I doing wrong? Is it OK to leave it on Prime while its running, as long as I remember to switch it off when I shut her down?

Here are all the things i recently did..
*New Intake Boots and O-rings
*Carbs cleaned by Chef
*New airbox boots
*New air filter (UNI)
*Weatherstripped airbox side covers
*New OEM petcock
*Clean tank
*New plugs
*Fresh oil/filter

Thanks in advance
 
Make sure you have plenty of fuel in the tank. I would say at least a gallon and a half.
 
I'll just say the little I know of, hope it helps. The petcock I'll assume is a vacuum operated one. You have a fuel line then a vacuum line. The vacuum line goes inbetween the #2 and #3 carbs on the nipple and you don't need the prime on to start it if it's primed. You just hit the starter and the vacuum pull from the carbs/cylinders opens the petcock and allows fuel to flow. Good luck, I had to post that one also. The other two between 1 and 2 and 3 and 4 nipples are vent lines that should run over the top area of the airbox. Good luck, oh yea to follow what octain said plenty of fuel, I did this one also.
 
Octain said:
Make sure you have plenty of fuel in the tank. I would say at least a gallon and a half.
Click to expand...

That could definitely be my problem! I only put a little bit in because I figured Id have to remove the tank and whatnot to get them all synced up. I shall give that a try.. Wish me luck!

Thanks!
 
If it runs on Pri and Res but not On, it's time to hit the gas station.
Ask me how I know...

:o
 
Good for you, glad Octain had the right answer, thats why I like this place so much.
 
skubasteve! said:
That could definitely be my problem! I only put a little bit in because I figured Id have to remove the tank and whatnot to get them all synced up. I shall give that a try.. Wish me luck!

Thanks!
Click to expand...


Been there done that.
Keep an eye on the petcock anyway. Ya dont want it dumping fuel into your crankcase contaminating the oil.
Been there too..
 
Perfect guys. That seemed to be the problem, ran just fine and dandy after I filled her up some more.

I do however have two more problems to address. Hopefully they can be answered here instead of making a new thread.

1.) When I moved the throttle, it seemed to stick a little bit until I moved it back into position. Did I hook the cables up wrong, or route them wrong?

2.) After it ran for a little while it started to have a slight burn smell and I noticed some white smoke coming from what seemed to be the area where the gear oil goes... Do I just need to change out the gear oil? I assume I may have gotten some fuel in there from before when my tank/carbs/petcock were all messed up.

Thanks again for all the help everyone. I would be nowhere without this site. Once I get some extra cash I will be donating.
 
Gear oil?

I'm assuming you mean the engine oil

Just ride it about 50 miles and see what it does
 
Im not too sure about the burning/smell from the gear oil area. Perhaps just some residual oil or something burning off from the heat of the motor.
The sticky throttle could be a number of things, cables carb linkage... Just follow the cable from one end to the other.. Most likely you'll find a worn area in the throttle tube or the housing where to tube and the cable come together.


Keep us posted!
 
Its an air cooled engine..if its gonna sit in the drive or gargae for any length of time running have a fan on high speed bowing into the front of the engine..one on each side is better..it needs to be cooled to prevent an overhaet situation...
 
The cables may be a bit rusty in the sleeves..run some light oil down them and work them a bit..see if that loosenes them a bit.
 
Thanks everyone.. after lots of searching. Im waiting for the manual to download as I probably routed them wrong.. that might be my problemo
 
Well.. I really couldnt find any pictures of the throttle routing, but I did find some from searching the site and from what I can tell I have them routed correctly.

It seems as if when I twist the grip when the bike is off, it returns normally. But when the bike is running, it seems to stick and stay until I return it manually?

Im lost? Did I tighten them wrong to the carbs?
 
Have you oiled the cable yet? Take the twist grip apart and oil it formt eh top down. If you pull the cable in an out while dripping the oil it will go faster. Use a light oil. You may want to use some wd40 first as it will run through quite quickly. Use sparingly of course. I have never had a problem doing this and never bought one of those natty cable lubers.

Got any pics of this?
 
The pictures your linking to shows a shaft drive. If your bike is chain drive, it doesn't use gear oil (and it most likely is, because i have never heard off a shaft driven 750). The smoke you are reffering too, is probably some oil on cases being burn off as the engine gets warm.
 
Kjeldsen01 said:
The pictures your linking to shows a shaft drive. If your bike is chain drive, it doesn't use gear oil (and it most likely is, because i have never heard off a shaft driven 750). The smoke you are reffering too, is probably some oil on cases being burn off as the engine gets warm.
Click to expand...

Thats kinda what I thought thanks!

I made a quick video, hopefully showing how my throttle cables are run. Could someone verify that I have these ran correctly? Im having sticky throttle problems, only when the bike is running. It springs back normally when its off. Sorry, cell phone vid.
 
Give me a few minutes and I will go out and make a short video of the cable routing on a '79 750. ;)

Daniel
 
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