Vomiting Carbs

Dorny119

Dorny119

Location
Connecticut
DylanS said:
Recently had a similar issue where small bits of plastic from a new gas tank were making their way past brand new inline filters and into the carbs. Too big to flow thru the incarb filter but occasionally a large piece would make it thru and clog my inline restrictor. Ski would start and idle great out of water but in you’d get about 15 seconds of response then that piece of debris would lodge itself into the return jet and the ski would get super rich. Would behave very similar to how a ski with exhaust leak does if you’ve experienced it.

When running my 927’s I would always use two check valves and gp800 kidney blocks to combat the fuel dribble. You can also cut your own valves out of a thicker fuel resistant plastic. Tried and true methods to combat that dribble.
Glad you got it figured out!
Click to expand...
Thanks for all the tips. I have seen your responses on other forums as well saying the same thing, which is what has me looking for the gp800 kidney plate, or looking into modifying myself. Some how, even after clearing the blockage in the restrictors, my rear carb still leak out of the venturi while idling on the stand. I have not seen any come out of the front venturi after clearing the blockage. Perhaps since there was some ethonal crud in there that i was cleaning while clearing the clogg, it may have RE-clogged. But it looks like the return flow out of each line is the same (i understand my eyes cannot accurately measure flow rate lol).

So, i am back to suggesting the vibration is throwing that needle open, and i need a modified kidney plate (or gp800 plate) in each carb. I did double up on those anti-siphon tabs. I suppose i could try 3! They are SUPER thin!

Regarding the vibration, keep in mind that i did not have this problem before i switched to the Wax manifold and VF3 reeds. I am sure the reeds are giving me a much stronger pulse than before. I am also not hating on Wax's manifold at all. But the manifold puts the carbs further away from the case, which could have amplified the vibrations. Heck, new motor mounts might even fix this lol.
 
Last edited:
DylanS

DylanS

Gorilla Smasher
Location
Lebanon Pa
Dorny119 said:
Thanks for all the tips. I have seen your responses on other forums as well saying the same thing, which is what has me looking for the gp800 kidney plate, or looking into modifying myself. Some how, even after clearing the blockage in the restrictors, my rear carb still leak out of the venturi while idling on the stand. I have not seen any come out of the front venturi after clearing the blockage. Perhaps since there was some ethonal crud in there that i was cleaning while clearing the clogg, it may have RE-clogged. But it looks like the return flow out of each line is the same (i understand my eyes cannot accurately measure flow rate lol).

So, i am back to suggesting the vibration is throwing that needle open, and i need a modified kidney plate (or gp800 plate) in each carb. I did double up on those anti-siphon tabs. I suppose i could try 3! They are SUPER thin!

Regarding the vibration, keep in mind that i did not have this problem before i switched to the Wax manifold and VF3 reeds. I am sure the reeds are giving me a much stronger pulse than before. I am also not hating on Wax's manifold at all. But the manifold puts the carbs further away from the case, which could have amplified the vibrations. Heck, new motor mounts might even fix this lol.
Click to expand...
if you do decide to drill out those restrictors you can play with your fuel pressure to try to fight that dribble a little too. Bumping that pop off up a little and fattening up your low speed jet to compensate can also help.
The dribble contributes to that rough idle and the rough idle shakes that fuel out.
 
Dorny119

Dorny119

Location
Connecticut
Hi all. I have solved my Vomiting carb issue. The OP was regarding fuel spitting back out of the top of the carb, and the ski not idling at all. What I am about to say is extremely embarrassing, but I am going to post anyway in order to follow through with this posting, and hopefully be educational.

My pistons were installed backwards...

Typically I build on a bench with the Ex ports always facing away from me (arrow on piston away from me). But this time i was seeing if i could get the job done with the case/crank still mounted in the ski. I was building from the ex port side without thinking about it, and naturally faced the arrows away from me. Just a straight up dumb mistake. After many hours/days of trying to solve the problem with carb adjustments, i put my bore camera into the holes and noticed the mistake.

Some may find the results of backwards pistons interesting, so i will post a full story.

  1. Pistons installed backwards
  2. Break in day went just fine, EXCEPT for very poor peak RPM after break in. I had seen 7350rpm in the past, but was only getting 6800rpm now. The ski would not idle in the water, but really wasn't that awful. It felt like your typical over rich low speed or low pop off situation. It DID idle out of the water. In my notes from that day i wrote "After breaking in, the ski felt a little weird off the bottom end. It also wouldn't idle. It wasn't hesitation like a lean hesitation. It just felt different, not right".
    • My Jetting here was Dual 46, Low 130, High 132.5, NS 2.3, pop off 18psi, spring unkown. (Yes i know that is super rich, but understand i was coming from an earlier situation where i thought i was lean seizing, so i enriched it way up to verify or disprove this)
  3. On break in day i saw plumes of smoke coming from my carbs. I figured the only way this was possible is if my reeds are not sealing. So, i pulled the reeds and sure enough some of the pedals had out of spec gaps. one as bad as 0.025", when 0.005" can cause issues?
    • At this point, i thought certainly this was my problem found in note #2 above.
  4. I install new VF3 reeds and new WAX intake
  5. Upon first start up, the ski sounded worse than any engine i have ever heard. I had to turn my idle screw probably 3 or 4 full turns to allow the ski to just barely idle on the stand. I also observed fuel spitting upwards out of my carbs. That is when i posted this forum.
    • In retrospect, perhaps the reason the ski was able to idle on the stand on break in day was due to the motor having less negative affect from the backwards pistons due to the poorly sealing reads?
  6. I find that fuel is dripping out of the venturi at idle. Therefore i raise my pop off to 21psi. This did not fix my leaking venturi, or my idle issue.
  7. I then raise my low jet to 135, and lower my high jet to 125. I also installed an extra anti siphon tab on the kidney plate. This did nothing for either issue
  8. I then changed my NS to 2.0 and put in a 95g spring for a pop off of 19psi. I also lowered my high jet to 122.5. The results of this were a slightly better idle, but still very bad. My venturi leak still not solved.
  9. I then changed to a 115g spring. The results were no different. Same idle as in note #8 above.
  10. I then put the 95g spring in again, but changed the low jet to 125. The result was worse.
  11. I then found that my return orifices in the carbs were clogged in both carbs! One was 100% clogged, and the other was probably 20% of it's designed flow. I cleared the clogs with a bit of compressed air, and a wire that i yanked out of a wire brush.
  12. After clearing the clog, I changed my low jet back to 135. The ski still idled poorly but did improve, and the rear carb still leaked out of the venturi. At least the front carb stopped leaking from venturi.
  13. I opened the low speed adjusters by 0.5 turns and that improved things. This was odd because I know i am already very rich? I thought... "How could this be better?"
    • To recap, my settings are now Dual 46, Low 135, High 122.5, NS 2.0, 95g spring, pop off 19psi
  14. I finally took the ski to the water since it was at least able to run on its own now. It did start and idle in the water, granted an unusually high idle screw setting. Maybe 2.5 turns? However, if i even breathed on the throttle... it died. So, i pulled it back up on the stand, started it, revved it, put it back in the water, and now some how i could blip the throttle in the water. But it was still pretty awful sounding and feeling. Upon riding it, the throttle response was the same as note #2 above. Not snappy, but not hesitating or loading up. Just plain not good. When i went WOT, i achieved 7080rpm. That's 250rpm better than break in day! I only rode for a few minutes until i made my way back to the launch. As i was going back to the launch i was going from idle to WOT at a low speed to feel the bottom end response. After about 4 of these braps, the ski died. It struggled to turn over for a second, then fired back up. I slowly rode back to the launch. Over all, the ski was rideable, and pretty quick. But was just awful when it cam to idle. In fact, when the ski was dying as described in the beginning of this paragraph, i had to use engine start spray to start it again..
    • In retrospect, the event that happened when going WOT back to the launch was probably when the front piston blew up (you will see this later in the story).
  15. I changed the NS back to 2.3. I also removed one of the anti siphon tabs, so i was back to the single tab on the kidney plate. I did a compression test, and the cylinders are dead even.
    • to recap, my carb settings are now Dual 46, Low 135, High 122.5, NS 2.3, Spring 95, pop off unkown
  16. I took the ski to the water, and rode long and hard. It felt pretty good, but i could tell it was loading up on the bottom end. My max RPM was now 6950rpm. Obviously the idle situation was still garbage.
  17. I then changed the low speed to 130.
  18. I took the ski to the water and it was excellent across the whole rev range. I achieved 7080rpm. The idle situation still bad.
  19. Since i still felt that something was off, i popped my bore camera in there and of course found my backwards pistons... and a blown up front piston. Since the pistons were backwards, the ring ends had grabbed the exhaust port and pulled the top of the piston off. Yes my compression was even in both cylinders... So this thing was blown up, but making even compression, and actually running decent minus the idle
  20. I honed, replaced pistons/rings, broke in the ski... Like magic my idle and starting problems were solved. So, 100% the backwards pistons were affecting my idle/starting and low end response.
    • as a side note, the exhaust ports now have an EXTREME chamfer on them courtesy of the ring ends digging in. This of course raises my port timing on an already raised port job, and decreases my trapped volume even more. I was making about 170psi prior to this with 37cc domes (should make 185psi with stock port timing) and now with the chamfer, i was making 155psi.
  21. I took the ski to the water, and it idled and started in the water very well. The bottom end response was crispy. However, my max RPMs were the same! 7080rpm...
  22. I then changed my high jets to 115. I am now achieving 7220rpm max. The entire rev range is fantastic and the ski rips.
    • recap, Dual 46, Low 130, High 115, NS 2.3, 95g spring, pop off unkown.
  23. I think i could even drop down to 110 high jet because the ski gets to 7100 rpm quickly, then slowly creeps to around 7220rpm. I will continue to work on this ski of course.
Anyway... that's all of it if anyone cared to read. The problem of the OP is solved. Now to keep making this ski faster.
 
W

waxhead

wannabe backflipper
Location
gold coast
Dorny119 said:
Hi all. I have solved my Vomiting carb issue. The OP was regarding fuel spitting back out of the top of the carb, and the ski not idling at all. What I am about to say is extremely embarrassing, but I am going to post anyway in order to follow through with this posting, and hopefully be educational.

My pistons were installed backwards...

Typically I build on a bench with the Ex ports always facing away from me (arrow on piston away from me). But this time i was seeing if i could get the job done with the case/crank still mounted in the ski. I was building from the ex port side without thinking about it, and naturally faced the arrows away from me. Just a straight up dumb mistake. After many hours/days of trying to solve the problem with carb adjustments, i put my bore camera into the holes and noticed the mistake.

Some may find the results of backwards pistons interesting, so i will post a full story.

  1. Pistons installed backwards
  2. Break in day went just fine, EXCEPT for very poor peak RPM after break in. I had seen 7350rpm in the past, but was only getting 6800rpm now. The ski would not idle in the water, but really wasn't that awful. It felt like your typical over rich low speed or low pop off situation. It DID idle out of the water. In my notes from that day i wrote "After breaking in, the ski felt a little weird off the bottom end. It also wouldn't idle. It wasn't hesitation like a lean hesitation. It just felt different, not right".
    • My Jetting here was Dual 46, Low 130, High 132.5, NS 2.3, pop off 18psi, spring unkown. (Yes i know that is super rich, but understand i was coming from an earlier situation where i thought i was lean seizing, so i enriched it way up to verify or disprove this)
  3. On break in day i saw plumes of smoke coming from my carbs. I figured the only way this was possible is if my reeds are not sealing. So, i pulled the reeds and sure enough some of the pedals had out of spec gaps. one as bad as 0.025", when 0.005" can cause issues?
    • At this point, i thought certainly this was my problem found in note #2 above.
  4. I install new VF3 reeds and new WAX intake
  5. Upon first start up, the ski sounded worse than any engine i have ever heard. I had to turn my idle screw probably 3 or 4 full turns to allow the ski to just barely idle on the stand. I also observed fuel spitting upwards out of my carbs. That is when i posted this forum.
    • In retrospect, perhaps the reason the ski was able to idle on the stand on break in day was due to the motor having less negative affect from the backwards pistons due to the poorly sealing reads?
  6. I find that fuel is dripping out of the venturi at idle. Therefore i raise my pop off to 21psi. This did not fix my leaking venturi, or my idle issue.
  7. I then raise my low jet to 135, and lower my high jet to 125. I also installed an extra anti siphon tab on the kidney plate. This did nothing for either issue
  8. I then changed my NS to 2.0 and put in a 95g spring for a pop off of 19psi. I also lowered my high jet to 122.5. The results of this were a slightly better idle, but still very bad. My venturi leak still not solved.
  9. I then changed to a 115g spring. The results were no different. Same idle as in note #8 above.
  10. I then put the 95g spring in again, but changed the low jet to 125. The result was worse.
  11. I then found that my return orifices in the carbs were clogged in both carbs! One was 100% clogged, and the other was probably 20% of it's designed flow. I cleared the clogs with a bit of compressed air, and a wire that i yanked out of a wire brush.
  12. After clearing the clog, I changed my low jet back to 135. The ski still idled poorly but did improve, and the rear carb still leaked out of the venturi. At least the front carb stopped leaking from venturi.
  13. I opened the low speed adjusters by 0.5 turns and that improved things. This was odd because I know i am already very rich? I thought... "How could this be better?"
    • To recap, my settings are now Dual 46, Low 135, High 122.5, NS 2.0, 95g spring, pop off 19psi
  14. I finally took the ski to the water since it was at least able to run on its own now. It did start and idle in the water, granted an unusually high idle screw setting. Maybe 2.5 turns? However, if i even breathed on the throttle... it died. So, i pulled it back up on the stand, started it, revved it, put it back in the water, and now some how i could blip the throttle in the water. But it was still pretty awful sounding and feeling. Upon riding it, the throttle response was the same as note #2 above. Not snappy, but not hesitating or loading up. Just plain not good. When i went WOT, i achieved 7080rpm. That's 250rpm better than break in day! I only rode for a few minutes until i made my way back to the launch. As i was going back to the launch i was going from idle to WOT at a low speed to feel the bottom end response. After about 4 of these braps, the ski died. It struggled to turn over for a second, then fired back up. I slowly rode back to the launch. Over all, the ski was rideable, and pretty quick. But was just awful when it cam to idle. In fact, when the ski was dying as described in the beginning of this paragraph, i had to use engine start spray to start it again..
    • In retrospect, the event that happened when going WOT back to the launch was probably when the front piston blew up (you will see this later in the story).
  15. I changed the NS back to 2.3. I also removed one of the anti siphon tabs, so i was back to the single tab on the kidney plate. I did a compression test, and the cylinders are dead even.
    • to recap, my carb settings are now Dual 46, Low 135, High 122.5, NS 2.3, Spring 95, pop off unkown
  16. I took the ski to the water, and rode long and hard. It felt pretty good, but i could tell it was loading up on the bottom end. My max RPM was now 6950rpm. Obviously the idle situation was still garbage.
  17. I then changed the low speed to 130.
  18. I took the ski to the water and it was excellent across the whole rev range. I achieved 7080rpm. The idle situation still bad.
  19. Since i still felt that something was off, i popped my bore camera in there and of course found my backwards pistons... and a blown up front piston. Since the pistons were backwards, the ring ends had grabbed the exhaust port and pulled the top of the piston off. Yes my compression was even in both cylinders... So this thing was blown up, but making even compression, and actually running decent minus the idle
  20. I honed, replaced pistons/rings, broke in the ski... Like magic my idle and starting problems were solved. So, 100% the backwards pistons were affecting my idle/starting and low end response.
    • as a side note, the exhaust ports now have an EXTREME chamfer on them courtesy of the ring ends digging in. This of course raises my port timing on an already raised port job, and decreases my trapped volume even more. I was making about 170psi prior to this with 37cc domes (should make 185psi with stock port timing) and now with the chamfer, i was making 155psi.
  21. I took the ski to the water, and it idled and started in the water very well. The bottom end response was crispy. However, my max RPMs were the same! 7080rpm...
  22. I then changed my high jets to 115. I am now achieving 7220rpm max. The entire rev range is fantastic and the ski rips.
    • recap, Dual 46, Low 130, High 115, NS 2.3, 95g spring, pop off unkown.
  23. I think i could even drop down to 110 high jet because the ski gets to 7100 rpm quickly, then slowly creeps to around 7220rpm. I will continue to work on this ski of course.
Anyway... that's all of it if anyone cared to read. The problem of the OP is solved. Now to keep making this ski faster.
Click to expand...
This is a fantastic write-up, and I love seeing the honesty here. So often, people avoid showing the truth to dodge blame, but I really applaud you for telling it like it is. They say the difference between an expert and a beginner is that the beginner hasn’t blown up enough engines. Congrats—you’re well on your way to expert level!
 
Flash-FX

Flash-FX

No Square..No Round..FX-1
Location
South Jersey Shore
Glad you figured that out.

looking at the first pic that you posted of the carburetor, it appears that the butterfly might be worn along the shaft axis (ends). look a little closer at that. Worn butterflies that slide back and forth let air in the wrong place at idle.
 
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