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Engine will only start on prime

  • Thread starter Thread starter Anonymous
  • Start date Start date
A

Anonymous

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Okay, just to let those of you know who have been keeping up my 450A rebuild project the engine is all together and running, as of today (had to replace a crankshaft bearing). I have a small issue with it though, when I go to start the bike it will only start when the petcock is on prime. After I get the bike started I can switch the petcock to run and it will stay running for a good 1-2min then die. One cylinder appears to run lean and the other one appears to run rich.
 
In the run position the petcock requires vacuum to open. You have a bad petcock or you didn't hook up the vacuum line to the carbs. Since one cylinder is running lean I'll bet that's the one with the open vacuum port.
 
Exactly what Swanny said.

Also maybe a bad crack in the vacuum line between carb and petcock.
 
carb

carb

Exactly what they both said but my vote is for the line hooked up wrong
 
I bought a rebuild kit for my petcock off Ebay and redid it today. I didnt realize that my bike was starving for fuel, but after changing the diaphram and the gaskets on the petcock, the bike runs so much better. It is a whole lot faster and there is no hesitation when i really get on it. I had to run mine on prime for a couple of weeks, cause it just wouldnt run right on the "on" position, so you may need to look into the rebuild or replacment of the petcock.
 
what would be the effect of having a crack in the vacuum line from the petcock to carbs?

I took my petcock off and cleaned it. .. . the diaphragm still seemed to be in pretty good shape, and things were clean for the most part.

one thing though, on my petcock, the allen-slot to adjust the setting (prime, run) just keeps turning in any direction.

I'm thinking this might cut off my fuel supply and be the reason my bikes not starting after this winter?

In that case, would the whole piece need to be replaced, or just the very bottom end of the petcock?


poot
 
The slotted part that is under the actual lever is what i assume you are talking about. If so, it is supposed to turn. The problem i had yesterday is that it wouldnt turn, it had gotten pushed doen too far and was stuck. i had to tap it out through the other end and then just set it back in there. I dont know how the other board members will like this suggestion, but if you think your bike isnt getting any fuel, take off the air box and spray starting fluid in the carbs. If the bike starts, you will know that fuel is your problem, even though the bike will only run until it burns up the starting fluid. If it doesnt run then you know you have another problem.
 
Avoid starting fluid or spray it is tough on motors.........just pour some gas in a windex bottle and spray that in the carbs. Thats how I revive bikes and snowmobiles after long storages.

Dr. Dre
 
motorcyclemodeller said:
Avoid starting fluid or spray it is tough on motors.........just pour some gas in a windex bottle and spray that in the carbs. Thats how I revive bikes and snowmobiles after long storages.

Dr. Dre
Click to expand...

I have to agree with that. Good advice.

I still recall an incident from years ago: I used starting fluid to get a car engine going, but the battery didn't havee enough left to do the job. With the aid of a boost from someone else, the car fired right up....and the collected (unburned) starting fluid that had made it through to the mufflers, and took up residence there, ignited. And exploded. 8O 8O

Blew open the entire side of the muffler!
8O 8O

Be sure that you dispose of the spray bottle after use. Do NOT keep it in the garage or house.
 
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