No start with backfire

Polishmafiaboss

Polishmafiaboss

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Aug 30, 2020
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Location
Michigan
New issue that is driving me nuts:

Reassembled a Viper top end mated to a SRX bottom end. Lots of new parts to avoid issues later. Specifically all new gaskets from the cylinders up and a Super-cool head gasket (Hauk), new ring sets on all 3 cylinders (OEM cylinders/pistons/rings) cylinders lightly honed using ball hone.

Replaced stator (old one proved defective) w/another Viper stator. Cleaned carbs (multiple times now thru all of this) and made sure floats were set at 14.3mm on all 3).

There is good spark being produced at the plugs. (Nice bright and steady blue on all 3 plugs.). Using brand new plugs. All old fuel was drained from the tank and fresh put in.

Fuel pump checked. All lines providing a good supply of pulsed fuel when engine is spun over. (Hopefully eliminating a fuel pump issue.)

Checked compression for giggles. (Keep in mind, engine has NOT been ran to seat rings yet.). PTO: 105-108 (just under 110). #2/3: 120

When trying to start it, first couple pulls produce an attempt to start. (It spins over and sounds like it WANTS to start for about a second.). 2nd & 3rd pulls produce the same. 4th or 5th pull will usually produces a backfire from PTO cylinder.

The questions:
1) Will a leaky case (bottom end not sealed anymore) cause this?
2) Will leaky crank seals (either PTO, MAG side or both) cause this.

What could I possibly be missing?

TIA (sorry for the length)
 
Is this sled an SX Viper?
If so the 2000 and up SRXs, and the 700SX Vipers have a digital ignition that fires each plug individually.
If you have the coil wires mixed up both the wires to the coils or the actual spark plug wires it would create an issue like you have.
Check all the wires to the stator, ignition switch, and kill switch ect.
Try a little fuel down each cylinder, replace the plugs and try to start it again...maybe its too much or too little fuel.
 
sideshowBob said:
Is this sled an SX Viper?
If so the 2000 and up SRXs, and the 700SX Vipers have a digital ignition that fires each plug individually.
If you have the coil wires mixed up both the wires to the coils or the actual spark plug wires it would create an issue like you have.
Check all the wires to the stator, ignition switch, and kill switch ect.
Try a little fuel down each cylinder, replace the plugs and try to start it again...maybe its too much or too little fuel.
Click to expand...
Bob, good ideas.

Lower end is a 99 SRX, rest of engine and sled is a 2003. The rotor/flywheel for a 99 is the only non-Viper item being used, and that is to get (hopefully) correct gap between pickup coil and flywheel.

Coils were not taken apart when I tore down the engine last year. Left the wire spreaders on the coil wires. The ‘03’s have a plug to connect coils to rest of chassis, so I am pretty sure everything is wired / connected correctly.

I’ve checked and re-checked everything about 8 times now in between scratching my head. I could understand it if it would start and STAY running but run like crap or something. At least there you have things to troubleshoot😂
 
Now there's the issue....using a pre 2000 SRX crankcase creates issues as the stator and flywheel were different then the 2000 up and Viper crankcases.
You will have to use a Viper or newer SRX flywheel with your Viper stator as the flywheel is required to properly fire the plugs.
People have used the older cases on Vipers by modifying the pickup mount....I have never done it.
If you search the forum you should be able to find info on this.
 
sideshowBob said:
Now there's the issue....using a pre 2000 SRX crankcase creates issues as the stator and flywheel were different then the 2000 up and Viper crankcases.
You will have to use a Viper or newer SRX flywheel with your Viper stator as the flywheel is required to properly fire the plugs.
People have used the older cases on Vipers by modifying the pickup mount....I have never done it.
If you search the forum you should be able to find info on this.
Click to expand...
The flywheel is off the same 99 engine. Was “hoping” that would fix the issue of spacing for the pickup. I’ll do some more checking on here and see if I can find info on what it should be.
 
The Vipers ignition system triggers the plugs individually and the 1998/99 SRXs trigger all three plugs at the same time....the ignition components can't be mixed and matched. You have to somehow use the Viper flywheel in those cases as well.
 
Some info:

02 viper 700 Spark Issue

Hey guys. bought a 2002 viper 700 triple with electric start and reverse. Worked great most of the day til the battery lost juice. Found out the voltage output at the battery was only around 10 volts while running at any speed. Everything seemed to operate just fine for 150 miles except the...
totallyamaha.net totallyamaha.net
 
sideshowBob said:
The Vipers ignition system triggers the plugs individually and the 1998/99 SRXs trigger all three plugs at the same time....the ignition components can't be mixed and matched. You have to somehow use the Viper flywheel in those cases as well.
Click to expand...
So if the following components are ALL Viper parts, would that still present an issue? : Stator, CDI, Coils, all engine wiring.

The SRX flywheel has the same timing blocks for spark. The only difference I can tell between my Viper flywheel and the SRX flywheel is a small block that is just a small square in line with the timing blocks.

If I must use the Viper flywheel, I’ll have to make a bracket of sorts to get the pickup coil closer to the flywheel. Or…..just say f@&k it and find a Viper lower end and start over!!😂
 
sideshowBob said:
Some info:

02 viper 700 Spark Issue

Hey guys. bought a 2002 viper 700 triple with electric start and reverse. Worked great most of the day til the battery lost juice. Found out the voltage output at the battery was only around 10 volts while running at any speed. Everything seemed to operate just fine for 150 miles except the...
totallyamaha.net totallyamaha.net
Click to expand...
Wellllllll. That may just explain my issue😎

From reading that, I’m going on the assumption that the newer sleds using digital ignitions need that small block as a check block or something. I will do some figuring out on how to use my old flywheel and get the gap down to the .020-.030 referenced in the other thread.

Thanks for the link! I had not run across that one yet during any of my searches.
 
The older SRX flywheel will not work with the Viper stator and ignition system. The link I sent in a previous post says the 2001 and up twin light SXR "red head" flywheel will work in your application but I have no experience with it.
Mr Viper really knew/knows his stuff so I myself would pick up a used Twin Light SXR flywheel and try it.
 
sideshowBob said:
The older SRX flywheel will not work with the Viper stator and ignition system. The link I sent in a previous post says the 2001 and up twin light SXR "red head" flywheel will work in your application but I have no experience with it.
Mr Viper really knew/knows his stuff so I myself would pick up a used Twin Light SXR flywheel and try it.
Click to expand...
I happen to have an ‘01 SXr that runs like a champ. Maybe I’ll borrow the flywheel off that for testing and see if that works. I know a guy with a yard full of sleds he parts out. I can always get one from him if it works.

Thanks again Bob!

And absolutely!! Everything I’ve found on here that MrViper has posted seems spot in with no fluff💪
 
Bob's right.
Furthermore, even if you could get the pickup coil where you want it, the internal magnet configuration will most likely also be an issue. I've ran into enough similar situations on various machines and brands to know. I can't explain it all, because I'm not an electrical engineer. :)
 
Polishmafiaboss said:
I happen to have an ‘01 SXr that runs like a champ. Maybe I’ll borrow the flywheel off that for testing and see if that works. I know a guy with a yard full of sleds he parts out. I can always get one from him if it works.

Thanks again Bob!

And absolutely!! Everything I’ve found on here that MrViper has posted seems spot in with no fluff💪
Click to expand...
Great!
Keep us posted
 
fourbarrel said:
The '01 and up SX-R flywheel,dual headlight, is what you need.I have my '98 SRX converted to '01 SRX electronics and I got the flywheel tip from BetheViper years ago.
Click to expand...
Fourbarrel: Do you know if it’s the one with PN:8DM-81450-00-00 (listed as fitting everything redhead from 2001&up)? The other flywheel listed for those goes backwards in years, so I’m guessing that’s for the single bulb sleds. (Turns out my ‘01 SXr is a single bulb unit!)

If that’s the critter, I will get one headed my way.

Thanks for the input, since you’ve already done it😎
 
Polishmafiaboss said:
Fourbarrel: Do you know if it’s the one with PN:8DM-81450-00-00 (listed as fitting everything redhead from 2001&up)? The other flywheel listed for those goes backwards in years, so I’m guessing that’s for the single bulb sleds. (Turns out my ‘01 SXr is a single bulb unit!)

If that’s the critter, I will get one headed my way.

Thanks for the input, since you’ve already done it😎
Click to expand...
Your 2001 SXR must be a 600....they didnt go to the twin headlight until 2002
 
Update on progress:

Finally got my hands on the correct flywheel. So far, so good. After reassembling everything, the beast fired up on 3rd pull. Running thru a couple heat cycles to seat the new rings…..and wait for snow to run it in🤦‍♂️.

So in the end, if you are using a 98/99 SRX lower with the rest of the sled being ‘01 or newer (SRX or Viper), use the flywheel from an ‘01 or newer dual headlight redhead 700 and you should have success.

Thanks to all the input. I greatly appreciate the info and learning experience.
 
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