Hey Ding, thanks for all the great tips and areas to check. So I've been insanely busy the last 2 months (Christmas/Wedding/First nephew) but I finally had time to try and breath some life in the old girl. Especially since the Viper has been nothing but a peach this season. (Thanks to Ding and MrViper) So I fixed the air pocket problem in the fuel line by priming the sled multiple times until the pocket entered the bowl and now I have great fuel pressure from the pump.
As Ding suggested i cleaned the carbs again and yes it's a Mikuni VM30. Now I have one last fuel related problem. The sled only runs when at half or full choke. As soon as I pull the throttle it bogs and wants to die. I know that the obvious problem is that the main jet is clogged but I swear I saw light through it before installing. Should I play with the air screw and see if that helps. It revs very high at half choke aswell. I have a video and picture I'll try and post in the next post.
Thanks again for all the help.
As Ding suggested i cleaned the carbs again and yes it's a Mikuni VM30. Now I have one last fuel related problem. The sled only runs when at half or full choke. As soon as I pull the throttle it bogs and wants to die. I know that the obvious problem is that the main jet is clogged but I swear I saw light through it before installing. Should I play with the air screw and see if that helps. It revs very high at half choke aswell. I have a video and picture I'll try and post in the next post.
Thanks again for all the help.
Check your air jet passages (all of them). Just because your fuel jet is clear doesn't mean it can flow fuel because it also needs air to flow in the air jets in order to work.
Also the pilot circuit has 2 fuel openings in the venturi. One under the slide and one after the slide. If the one under the slide is plugged it will stumble as you thottle it off idle because the first rush of air will be starved for fuel (not rich enough to accelerate).
So to check the air passages . . .
When you look at the air horn (where the air goes in the carb) from the front you should see multiple holes at the bottom. The one that is centered should be the main air passage and may or may not have an air jet in it (many manufacturers realized it didn't really help). The main air passage goes directly to the nozzle (the long brass tube that the main jet screws into). You may want to pull your slide out, remove the main jet, and pull the nozzle to make sure it is good and aligned right. It will also let you know which one you have (with good eyes or a magnifying glass).
One of the other holes may appear to have what looks like a brass ball in it. This is a plug and that hole was just used for drilling a internal passage. Just ignore this hole.
The other smaller hole should be your pilot circuit air passage which also may or may not have a jet in it. This passage is small and usually the first to plug. It leads directly to the air screw (which regulates the mixture) and then to the mixing chamber above the pilot jet where it also joins with the 2 pilot fuel passages that go to the venturi (mentioned earlier).
The hole that is recessed and quite a bit higher is the starter circuit air passage. This rarely gets plugged, and your indications suggest that yours is fine.
Anyway knowing where the holes lead can help you in determining whether or not you can get a good flow of carb cleaner through the passage. A lack of good flow indicates a plugged passage. You need to see cleaner flowing out each of the connected orifices for each circuit or something is wrong.
One other thing to check is your fuel level. Note the height of the pickup points for each circuit (Starter, pilot, and main) they are usually not all at the same level. If you look at them you can see where one circuit can pickup fuel where another circuit might get air if the fuel level was between the 2 pickup points.
Also the pilot circuit has 2 fuel openings in the venturi. One under the slide and one after the slide. If the one under the slide is plugged it will stumble as you thottle it off idle because the first rush of air will be starved for fuel (not rich enough to accelerate).
So to check the air passages . . .
When you look at the air horn (where the air goes in the carb) from the front you should see multiple holes at the bottom. The one that is centered should be the main air passage and may or may not have an air jet in it (many manufacturers realized it didn't really help). The main air passage goes directly to the nozzle (the long brass tube that the main jet screws into). You may want to pull your slide out, remove the main jet, and pull the nozzle to make sure it is good and aligned right. It will also let you know which one you have (with good eyes or a magnifying glass).
One of the other holes may appear to have what looks like a brass ball in it. This is a plug and that hole was just used for drilling a internal passage. Just ignore this hole.
The other smaller hole should be your pilot circuit air passage which also may or may not have a jet in it. This passage is small and usually the first to plug. It leads directly to the air screw (which regulates the mixture) and then to the mixing chamber above the pilot jet where it also joins with the 2 pilot fuel passages that go to the venturi (mentioned earlier).
The hole that is recessed and quite a bit higher is the starter circuit air passage. This rarely gets plugged, and your indications suggest that yours is fine.
Anyway knowing where the holes lead can help you in determining whether or not you can get a good flow of carb cleaner through the passage. A lack of good flow indicates a plugged passage. You need to see cleaner flowing out each of the connected orifices for each circuit or something is wrong.
One other thing to check is your fuel level. Note the height of the pickup points for each circuit (Starter, pilot, and main) they are usually not all at the same level. If you look at them you can see where one circuit can pickup fuel where another circuit might get air if the fuel level was between the 2 pickup points.
Just another suggestion . . .
If you can take a bunch of pictures and post them, sometimes we can see things that we don't realize in the ongoing discussion.
If you can take a bunch of pictures and post them, sometimes we can see things that we don't realize in the ongoing discussion.
This is what the carbs. (Not mine but exact model)
Sounds like plugged circuits, I would pull the carb and go back through it. Carefully check and adjust everything, check and note all the tuning parts. Pics while you do it will help. We have to be missing something.
Be sure to check the following . . .
One thing I don't like is the way the air bleeds back into the fuel supply line. Not sure what to make of that yet.
Sure wish I could see this thing in person.
Yes, that is the stock carb. I have one sitting here in front of me. Maybe I'll go through it in case I forgot something.
Be sure to check the following . . .
- Needle
- Needle position
- Slide
- Slide height adjustment
- Nozzle
- Nozzle aligned (it shouldn't drop into place unless aligned, but check anyway)
- Main jet size
- Pilot Jet size
- Air screw condition & number of turns out
One thing I don't like is the way the air bleeds back into the fuel supply line. Not sure what to make of that yet.
Sure wish I could see this thing in person.
Yes, that is the stock carb. I have one sitting here in front of me. Maybe I'll go through it in case I forgot something.
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So the air doesn't bleed into the fuel supply line anymore. I had to keep pulling the sled over until the entire carb was full (No air pockets).
Also before i pull it again tonight I want to clarify some terms:
slide - (carb piston valve)
nozzle - (Needle Jet)
As per attached drawing.
Also before i pull it again tonight I want to clarify some terms:
slide - (carb piston valve)
nozzle - (Needle Jet)
As per attached drawing.
Yes
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Hey Ding,
For some reason I totally forgot to update this thread after I found the true cause. The one thing i hate about forums is finding a "whats my problem" thread which doesn't have any closure so here it is.
I did as you said and cleaned the carb till I and a new born baby could eat off of it. The thing was immaculate. Put it back in the sled and she ran. I was extremely happy..... until i saw a massive spew of oil coming from the crankcase and spitting onto the exhaust. Come to find out that the crankcase was not creating enough vacuum to actuate the fuel pump and push fuel into the carb. Now I'm currently sourcing a new... to me.... crankcase so that I can breath some more life into it. Thanks again for all the info.
For some reason I totally forgot to update this thread after I found the true cause. The one thing i hate about forums is finding a "whats my problem" thread which doesn't have any closure so here it is.
I did as you said and cleaned the carb till I and a new born baby could eat off of it. The thing was immaculate. Put it back in the sled and she ran. I was extremely happy..... until i saw a massive spew of oil coming from the crankcase and spitting onto the exhaust. Come to find out that the crankcase was not creating enough vacuum to actuate the fuel pump and push fuel into the carb. Now I'm currently sourcing a new... to me.... crankcase so that I can breath some more life into it. Thanks again for all the info.