Compression Question

[Cali]

Ok should I have 180 pounds of compression on cool head with 20 doms?Just did a top end rebuild.Went out & broke the engine over the weekend.Did comprerssion test and its 180 on both cylinders.I know my gage is correct cause I use it ll the time on other motorcycles.It has the check valve right in the end & its about the same lenth as my spark plug.Beofre rebuild Ihad 150 per cylinder.Can I run pump gas?Seems to run awsome but I dont want to blow this thing up.Or should I mix 110 with 91?I read that 20s were ok to run pump gas on?

[firebanshee]

Ok should I have 180 pounds of compression on cool head with 20 doms?Just did a top end rebuild.Went out & broke the engine over the weekend.Did comprerssion test and its 180 on both cylinders.I know my gage is correct cause I use it ll the time on other motorcycles.It has the check valve right in the end & its about the same lenth as my spark plug.Beofre rebuild Ihad 150 per cylinder.Can I run pump gas?Seems to run awsome but I dont want to blow this thing up.Or should I mix 110 with 91?I read that 20s were ok to run pump gas on?

How far are you bored over? 21s are ok for pump gas at sea level not 20s. If you run pump gas with 180 psi you will melt that motor down. At 180 you should be close to staight race fuel.

[vulvafan537240]

180 seems real high fro 20cc domes. whats your elevation? why did you rebuild when you had 150psi?

[bansheesandrider]

When my topend was fresh I had 185 and it currently has 175, my timing is set at +4 and I run 2 gallons of 108 or 110 octane race gas mixed with 3 gallons of 93 octane premium pump gas, mixed 40:1 with Klotz R50 at sea level. I never have any problems with detonation or preignition.I have a cut and chambered stock head by Twister and I don't remember what the chamber size is.

[papa_smurf49319]

110 octane here 185psi compression and plus seven on the timing, 850 ft. Was running 102 octante and it seemed fine, just wanted to be safe so switched to straight 110 mixed with castor 927 of course!

[Cali]

Im 040 on the bore.Im at sea leve.Will ride 90% of the time at Pismo Dunes..I had to rebuild cause LF Piston broke at bottom skirt.I figured it broke b/c it was ready for bore job..But maybe it was b/c of the pump fuel?

[Cali]

My local airport sells 100LL to the public.Is that safe to run?Or should I just buy 110 from a local bike shop?Thanks alot for all the advice.

[AKheathen]

make sure you check your squish clearance first thing. 180 is pretty high for 20's. i ran 90 oct. with 20's and stock porting for a long time no problems at all, but my jetting was always spot on, and my squish is on the conservative side @.052"~ o run a 50/50 mix of 100LL and 90 with +5.5 timing asl. strait 100LL will be fine. and, no, the low oct. did not break the skirt. that is almost always from excessive piston-bore clearance. check to see if you have a spacer plate under your cylinders where they match to the cases, or try and remember how deep the domes were when you had it off. it really sounds like a stroker, which should net you about 185 with a mild or simple stroker porting @ 1mm over

[sleeper06]

180 is not high for 20s on a stock build at sea level,and run 108 and above anytime i get that high I like to stay over 108 with the octane