pitz0022
New member
I just rebuilt the engine on my viper from the crank up. I siphoned as much fuel as I could from the tank, added 2 gallons of ethonol free fresh fuel mixed 50:1. I got it started and ran it through a couple heat cycles. When I blip the throttle full open for a half a second, the engine bogs - if I hold it I can actually get the engine to stall. From what I have read here, it is indicative of a lean condition.
I knew better than to post this without checking my pilots again, so I pulled the carbs and cleaned them again (I did it once already a few weeks ago but better safe than sorry). One of the pilot jets was partially plugged again. I checked that everything else was up to snuff (I didn't pull the needles or touch the floats). and reassembled everything and opened the fuel screws to 2 turns. It still had a slight bog. I opened them to 2 -1/2 turns and the bog is almost not noticeable.
I have a couple questions.
Is 2-1/2 too far (spec is 1-7/8 )? Am I merely covering up some other issue by compensating with the Fuel screw?
Could it be running lean because of the 50:1 fuel mixed in the tank in addition to the oil introduced by the oil pump? I'm confident my oil pump is working and has been bled successfully. Should I dilute with good fresh ethonol free fuel? I really don't want a full tank sitting in it until we get snow, but I also want to make sure I address all the issues and don't have to wrench much more and wait for parts, etc once we get snow.
Thanks for your help.
I knew better than to post this without checking my pilots again, so I pulled the carbs and cleaned them again (I did it once already a few weeks ago but better safe than sorry). One of the pilot jets was partially plugged again. I checked that everything else was up to snuff (I didn't pull the needles or touch the floats). and reassembled everything and opened the fuel screws to 2 turns. It still had a slight bog. I opened them to 2 -1/2 turns and the bog is almost not noticeable.
I have a couple questions.
Is 2-1/2 too far (spec is 1-7/8 )? Am I merely covering up some other issue by compensating with the Fuel screw?
Could it be running lean because of the 50:1 fuel mixed in the tank in addition to the oil introduced by the oil pump? I'm confident my oil pump is working and has been bled successfully. Should I dilute with good fresh ethonol free fuel? I really don't want a full tank sitting in it until we get snow, but I also want to make sure I address all the issues and don't have to wrench much more and wait for parts, etc once we get snow.
Thanks for your help.
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mod-it
Member
Most will tell you that after 2-1/2 turns you should go up to the next jet size. That being said, mine are set at 3 turns to get no bog and I don't have any issues with it. I would try 3 turns, and if the bog is still there then go up one size and start over. Be aware to watch for an idle hang. You may get rid of the bog, but if the idle hangs after coming back down it may still be a little lean.
I wouldn't worry about the mixed fuel, most do this when breaking in a new motor. Once you get to go ride it, plan on doing several plug checks to make sure it's good. Depending on how you like to break in the motor, it may take a few rides before you're ready to do a full throttle check.
I wouldn't worry about the mixed fuel, most do this when breaking in a new motor. Once you get to go ride it, plan on doing several plug checks to make sure it's good. Depending on how you like to break in the motor, it may take a few rides before you're ready to do a full throttle check.
The 50 to 1 will lean you out slightly, although shouldn't cause a lean bog. Make sure the boots frim the carbs and airbox are properly secured. Also, I wouldn't worry to much on dialing it in yet. Not until your area starts hitting winter temps. No sense in tuning it to 40 degree weather.
Macheater
New member
I'm gonna make a couple of assumptions here since you weren't as specific as you could have been. I'm assuming that you have the track off of the ground and the engine is idiling when you "blip" the throttle. Does that mean your going from idle to full throttle instantly? If so, in all likely hood you are gonna have a bog. That is a huge amount of instant airflow and the gasoline being heavier can't keep up. I would be more concerned about how it accepts full throttle when your actually launching from a complete stop. If it launches hard and clean, that would be a far better indicator of how you're jetted than just stabbing the throttle. Back in my racing days, we use to call the guys who just like to sit there and rev there engines as "throttle tuners". That gives very little indication of how your jetted.
pitz0022
New member
Macheater said:
Sorry, I thought I had most of the variables covered. Track is off the ground. Engine is idling at 1800 rpms when I stab it. either way though you shouldn't be able to kill the engine by stabbing it right? I just want to make sure everything is set up right after I put all this time into rebuilding the engine.
Thanks to the other pieces of advice as well. I feel better about the situation. I am mainly concerned that I'm not covering up a problem by making these adjustments. Good to know that others have adjusted the fuel screw as far as I have.
Also, excellent note about not tuning at 40 degrees. Just getting excited I guess. Plenty to do until the snow flies though.
Thanks Guys!!
Macheater
New member
I forgot to mention that the temperature of your engine and carbs is gonna play a role as to how much throttle the engine will accept when you're "blipping" the throttle. A warm engine will always accept throttle more easily and cleanly, provided the jetting is close. Just like a cold engine on a cold day needs the choke to rev cleanly. Once it warms up, the choke can be turned off completely since the fuel is atomizing much better.
Siphoing fuel from the tank is NOT siphoning fuel from the carbs and the rest of the fuel system. Depending on how old/fresh the fuel was in the carbs can play a huge role as well. Old gasoline does not play well with 2-strokes. If you have fresh gas in the tank but not in the lines and carbs, its gonna take a little running time for all of the new fresh gas to make its way through the system.
As far as a bog killing the engine. It depends on how severe the bog is. If the engine bogs and you don't let off the throttle and let the engine recover, it certainly will kill the engine.
Siphoing fuel from the tank is NOT siphoning fuel from the carbs and the rest of the fuel system. Depending on how old/fresh the fuel was in the carbs can play a huge role as well. Old gasoline does not play well with 2-strokes. If you have fresh gas in the tank but not in the lines and carbs, its gonna take a little running time for all of the new fresh gas to make its way through the system.
As far as a bog killing the engine. It depends on how severe the bog is. If the engine bogs and you don't let off the throttle and let the engine recover, it certainly will kill the engine.
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akrievins
New member
I have had that problem for years. Never cleaned the carbs once in 4 or 5 years. I know, guys will kill me on here about this, but hey, it is what it is. I may try to clean them myself this season.
Anyways, from an idle at 1800, if I press the gas to the bar in a race, my engine will always bog and die. If I rev it up a little bit, and then give it all the way, I'm off like a race horse.
I posted about this some time ago, and everyone agreed I had dirty pilots...
Anyways, from an idle at 1800, if I press the gas to the bar in a race, my engine will always bog and die. If I rev it up a little bit, and then give it all the way, I'm off like a race horse.
I posted about this some time ago, and everyone agreed I had dirty pilots...
My SRX 700 also bogs from 1,800 to WOT. It doesn't die, just slight boggg. Carbs cleaned, fresh fuel, plugs gapped and changed, wires cut back, track off of ground, motor warmed up, pilots set at 1.5 turns out, etc. etc. This ONLY happens when I stab the throttle.
Mine too. A small bog is probably common and maybe a limitation of the carb. Snapping the throttle plates wide open introduces more air then the jets can handle coming from an idle. You could set your idle to about 2k and gopen up the fuel screws to compensate?
axapowell
New member
Pittz, funny! I posted this at the beginning of last year exactly what you said. I also did the top end, broken power valve bolts/threads, re-ringed too while I was in there.
Didn't notice it before the work was completed, pulled the carbs twice to be sure and it still did it. I have the fuel screws out 2 1/4 turns, but plan to increase the pilot jet one size and go 1 1/2 turns to start. That is this falls project along with the usual PV cleaning. I'll post the results when I'm done!
Dave
Didn't notice it before the work was completed, pulled the carbs twice to be sure and it still did it. I have the fuel screws out 2 1/4 turns, but plan to increase the pilot jet one size and go 1 1/2 turns to start. That is this falls project along with the usual PV cleaning. I'll post the results when I'm done!
Dave