670 Issue - Need Help

[Snoman69]

Looking for 670 motor help...

Took my sled on its maiden voyage on 12/22... Built a new chassis, and had the motor over hauled (rebuilt with port and polish)....

Sled started fine.. Little low on the idle, but understandable since I am double oil right now... It would take 4-5 min of feathering the throttle to get above 2K rpm.... Then it would climb to ~6200 and runnin ok... After ~ 3miles it went down hill.... Featehring to get rpm's up took longer, once above 2000, then it would climb to ~4500 rpm and struggle to move..... Ended up having to be towed out, as we dropped down some hills to play, dumb I know with it being the first time out and wasn't running right...

EGT's were identical at ~620......

Seems like the carbs were operating correctly, float, needles seets (sp), etc..... Carbs were just boiled.... Jetted down on the hill, as well as lowered the needle.

What else could cause this? Seems like it is loading up... Could it eb the rotoary valve? Mis-aligned - Would it have the same symptoms?

Thanks in advance for your help

 

[Zachmandu]

Sent you a PM

 

[winter brew]

Rotary valve timing.

 

[DWHalverson]

Air box or filters?

 

[Pastor]

Those are low exhaust numbers, if you were above idle.

 

[Snoman69]

I'm running filters, green UNI's....

The EGT #s at idle at ~320*.

The 620* 3s were at ~4500 rpm.....

I am going to check the carbs today, make sure the needles and seets are ok... The only other thing I can think of is if the RV is off.

 

[DWHalverson]

I'm thinking out loud here, but something tells me you have twin pipes also.

My experience has been that if the Rotary valve is installed and the sled starts, it will make rpm. Maybe not peak hp but it shouldn't limit the rpm of the engine. Have you ran the green UNI filters in the past with good results? Either way I would pull them off and see how the engine reacts to no filters.

 

[sledsrock]

Loaded or unloaded?

Pull the pod filters and try it unloaded on a track stand................

 

[Snoman69]

Would POD filters make that big of difference? This is the first year running PODS.. Can't run airbox, as it will not fit...

It does fine with no load, but still doesn't pull all RPM, upt to ~6400

I am replacing the needle and seets, as well as making sure everything else is fine.. While I have the carbs off, will check the RV as well.

Just trying to get some ideas...

And yes, I am running SLP twins.

 

[DWHalverson]

The foam filters can cause a huge bog off the bottom on the Rotary Valved engines. Seen it on two different twin piped engines. Mine was so bad the sled wouldn't even move when the clutch engaged. The other one would have a ferocious pop through the intake. Ditched the filters and problem solved.

Would POD filters make that big of difference? This is the first year running PODS.. Can't run airbox, as it will not fit...

It does fine with no load, but still doesn't pull all RPM, upt to ~6400

I am replacing the needle and seets, as well as making sure everything else is fine.. While I have the carbs off, will check the RV as well.

Just trying to get some ideas...

And yes, I am running SLP twins.