I just built a 421 banshee for a friend, serval cub cylinders, trinity cool head 21cc domes, pro circuit pipes, he got 34mm mikuni round slide carbs which i think are too big, theres just no room, the pipes are hitting the cap on the left side. it wont idle at all it boggs really bad smokes horrible on the left sides, the oil is just running out of the pipe. i started with 340 mains then 310s then 300s we rode it 30 mins and both end bearings on the crank are fried. the entire engine was rebuilt and now i have it tore back apart waiting on new bearings. somebody help me out.
421 banshee help
- Thread starter Reaper26
- Start date
Sounds Like a leaky oil seal creating a lean mixture.
Did you leak test the engine before starting it.
What oil ratio do you use? 32:1 I hope.
Did you leak test the engine before starting it.
What oil ratio do you use? 32:1 I hope.
Was this a new crank? Trinity domes? Sure domes are correct angle for type of piston? Blaster and Banshee style pistons use different dome angles, wrong angle could be giving you detonation.
Unless you were using way cheap oil or extremely lean oil mix, I would think you'd have melted a piston before you'd have damaged the crank.
Anything special with clutch? Straight cut gears but no Maxiload bearings?
Unless you were using way cheap oil or extremely lean oil mix, I would think you'd have melted a piston before you'd have damaged the crank.
Anything special with clutch? Straight cut gears but no Maxiload bearings?
my first thought was the right seal leaking but if the right seal was leaking then the right cylinder would be smoking and blowing out all the oil correct? its the left side that is filling the pipe up with oil, it had to be sucking it out of the tranny between the cases cuz it was pretty low. after i pulled the cylinders back off the bottom of the cases were also COMPLETELY full of gas, mine has never been that way.
I put the stock carbs back on with 340 mains, leak tested and 20 mins per 3 lbs. Put it all back together warmed it up rode it down the rode about three miles to a long straight away to do a plug chop and half way down it it locked up, the right plug was almost out and both were really whit, burnt. Shouldn't it have been a little toward the rich side?
yes i did three heat cycles at the shop before i brought it home, we re torqued everything, warmed it up before we rode it. last summer i built it for him it was a 396 we used 310 mains with stock carbs and a stock style cool head, stock cylinders, it ran great. then someone stole it and blew it up and he found it and wanted to do the 421 so i did some reading and found similar setups with stock carbs and 340 mains so i started there.
