07 m8 BD Turbo Bog

[Jred]

I have a strange mid range bog in one cylinder I can't clear up. I have a 07 or 08 bd race gas kit however I run it pump gas with the pump gas acutator and run it around 6 pounds of boost.
When I get on it it bogs like one cylinder has a fouled plug. Clutch side cylinder had wet plugs/ pto side ok.... clutch side temps 670F max/ pto side 880F Max after getting on it... checked spark and both sides good output... compression both around 100 psi... reeds looked ok...replaced and calibrated both exhaust valve cables... clutches in good condition... fuel was 47/85 on the boon docker... replaced ccu last year, the lights and reverse work good... the speedometer stopped working with the ccu last year so i don't know if it has any codes I have not replaced that yet... I'm stumped but suspisious of electrical.
Anyone have any ideas or experiance with some freak things happening I could check.

 

[bparks]

compression both around 100 psi that is real low should be around 125 any lower time for rebuild

 

[m8matt]

compression both around 100 psi that is real low should be around 125 any lower time for rebuild

Not true. 07 M8 stock compression is around 120. 100 is low.

 

[bparks]

i have an 07 m8 with 2000 miles and at 7300 feet it has 130 on one side and 133 in the other so i dont see how could come from cat at 120 but anyway i would recheck you compression and take a look at the pistons sounds like low compression not burning all fuel and loading up

 

[Jred]

After a lot of troubleshooting I finally found my problem. My instincts were right from the start my exhaust valves were not opening that was caused by a connection from the boondocker box to the servo motor that runs the exhaust valves. My boondocker kit is one of the early ones designed back around 07, but theres a yellow wire that connects so the boondocker box can manipulate the stock settings if needed. I talked to a boondocker tech and as i understood it with my setup the exhaust valves do not need manipulation from stock so I was directed to just unhook the yellow wire and as far as I can tell its back to normal. I'm not sure what was happing with this yellow wire to cause the problem.

While troubleshooting I disconnected all the boondocker box wiring at the injectors and I hooked it up back to stock. We found the engine ran crisp and we noticed the servo motor was working pulling the exhaust valve cables open, as we reved it up and down. Once we hooked up the boondocker box wiring, the servo motor didn't budge as we reved the motor.

I included a picture of the cables I replaced. They were rusty and messed up, especially where it turned into the engine. Its crazy how they didn't put more heat shield between the cable and the exhaust pipe. Theres only an inch of seperation. Looks to me like the heat on that cable is bad news. So i wrapped it with fiberglass heat wrap to add an extra layer of heat barrier on the new cables. They were calibrated to the 1.370" inch spec.

 

[Jred]

Not true. 07 M8 stock compression is around 120. 100 is low.

I'm not too concerned with the compression numbers I got because I don't know how accurate that tester I used is. I replaced the pistons last year so it has new rings. Being a high boost diesel owner I run a twin turbo setup that put out 100 psi of boost on my pickup, that had special pistons that lowered the compression so that the rods on the engine could survive better. I know my sled is different than a diesel but I was curious if guys modify the head to lower the compression a little on a turbo two stroke. I know I don't run that high of boost to require lowered compression but just a thought I had. I'm planning on riding it some more before I head up to the mountains.

To all M8 owners check your exhaust valves if you develop a bog. Apparently they are a problem, either from carbon build up sticking them or the cable curoding. $100 to replace both cables. My old 07 M1000 had cable problems too. Thanks guys.

 

[bigdogsummit800]

I'm not too concerned with the compression numbers I got because I don't know how accurate that tester I used is. I replaced the pistons last year so it has new rings. Being a high boost diesel owner I run a twin turbo setup that put out 100 psi of boost on my pickup, that had special pistons that lowered the compression so that the rods on the engine could survive better. I know my sled is different than a diesel but I was curious if guys modify the head to lower the compression a little on a turbo two stroke. I know I don't run that high of boost to require lowered compression but just a thought I had. I'm planning on riding it some more before I head up to the mountains.

To all M8 owners check your exhaust valves if you develop a bog. Apparently they are a problem, either from carbon build up sticking them or the cable curoding. $100 to replace both cables. My old 07 M1000 had cable problems too. Thanks guys.

Thanks for sharing your discovery.