Question about cylinder base gasket.

[Skyhawk66]

Has anyone tried running a 66cc grubee without the base gasket? I'm wondering what it would do to the port timing. I am curious if it would help or hurt the low-mid range pull? Maybe affect the top speed or top end pull? I would imagine it would raise compression as well since the jug would sit lower.

 

[butre]

Thinner or no base gasket will improve low end and hurt max rpm. Plenty of people do it with 2 stroke engines of all sorts, it's an easy and cost effective way to alter port timing. Lots of people go the other way too, thicker base gasket means improved top end power

It does change compression as well, but that change is fairly minimal. You won't need race gas or anything if you ditch the base gasket.

 

[Skyhawk66]

Thanks for the reply! I seem to have decent low end, I may have to try and raise my jug for better top end performance.

My only issue so far is my bike 4 strokes a lot during riding. I have a 66cc grubee on a schwinn beach cruiser with a 32t on it. I have a later CNS carb on a offset extended intake. I've smoothed out the intake, gasket matched both intake and exhaust, gutted the cat from the factory muffler, reduced the main jet size in the carb, sanded the head smooth and run no head gasket, and I've made a homemade boost bottle.

I can pass cars in a 35 mph zone, it bogs on hills, and when rolling back into the throttle after making a turn, then it starts pulling hard again till it 4 strokes. While cruising it'll 4 stroke, then pull for ten seconds, then 4 stroke, then pull again. It keeps doing that the whole time you ride. Any suggestions??

 

[butre]

the only one I've got is to replace the carb. CNS carbs aren't too great. the popular opinion is to go for a mikuni vm18, but those can get a little pricey.

I personally use a PZ19 carb, but the catch with those is that you need to make your own intake plenum. Mine is just some copper plumbing bits soldered together, you don't need anything fancy.

 

[Skyhawk66]

I really don't want to completely give up on the CNS yet. The throttle response is decent, and the low to mid range feels strong. It just keeps 4 stroking while cruising. I'm going to attempt making a expansion chamber exhaust for it to see if I feel any gains from that. Maybe it'll help with the 4 stroking.

 

[undercover bluebird]

i had a cns carb and it did the same. I went back to the nt carb and never looked back

 

[Deleted member 12676]

http://www.dragonfly75.com/motorbike/4stroking.html

 

[sbest]

<SNIPPED> I've smoothed out the intake, gasket matched both intake and exhaust, gutted the cat from the factory muffler, reduced the main jet size in the carb, sanded the head smooth and run no head gasket, and I've made a homemade boost bottle.

I can pass cars in a 35 mph zone, it bogs on hills, and when rolling back into the throttle after making a turn, then it starts pulling hard again till it 4 strokes. While cruising it'll 4 stroke, then pull for ten seconds, then 4 stroke, then pull again. It keeps doing that the whole time you ride. Any suggestions??

I found the same problem when I port matched (smoothed out) the stock offset intake. I am better off with a stock one. I suspect the port mismatch helps fight reversion.

I've run many 2 strokes with no base gasket, just 3Bond sealer. My KTM has the squish gap set with select fit base gaskets.
The problem with the two HT engines I have is that the piston will hit the head if you leave out the base gasket.
Lowering the cylinder will lower the rpm powerband and typically lowers the power and top speed, all other things being equal (they never are!)

Steve