Custom/Hybrid Backfire during 1st start up 780cc

[mike b]

Hi guys. I just got a 780cc motor built. It has stock 38s rejetted by builder. Im running an MSD ignition, lightened FW, Kawi coill, PFP pipe with xscream waterbox and the tank that hold that battery mount. On my first start i hit primer, nothing happening right away. cranking to get fuel to carbs. then hit primer a few more times. I had idle set a bit high. I hit button and started right up (loud as CHIT). Got scared from the noise and thought it was running away. Started two more times (all about one second or two) then shut off because high idle was scaring me lol. Next time i turned idle to just about nothing and when i hit the green button BAMB. Popped a flame out the back as a chocolate mud man found its way in my shorts. Decided to call a night because getting dark and would rather wait till day time. This is the first start up on the motor and new to AM motors so wanting to take all precautions.

Question is what could have caused backfire and will this most likely happen again? No backfire on carbs so i would think reeds are fine. Also, would it be smart to have first test in lake/test pool so I can make sure motor is working fine before I try starting on the cart again (reason to test in water so its not SO loud and that I can hear the motor better and set idle in good area.

Also scared of run aways so i figured in water would be less likely of run away since it will be under back pressure and it is does there will be water to cool the motor (Ski will be tied off on dock or trailer to insure safety of people at the lake incase of run away). I think im just being a bish about the first start up so if you think so just tell me. Just want to take care of motor. Sorry for the short novel, anything helps

 

[shepster]

Hi scary stuff hey
Backfires are normally timing or ignition related. Those would be the first places I'd look knowing carbs and everything else is good

 

[mike b]

Could back fire be related to hitting the primer a few times. Cranks motor over and that the fuel lines had air being pushed to motor. That and not letting it run. Just turning it off right away from my panzie-ness ha. I'm hoping it something to do with that because I don't want to have to take motor or ski apart

 

[bobob729]

yes it could, its not going to hurt to set it in water at all thats what i would do after i have heard it run one time after that its off to the river or lake and to check everything over. i say try it again and see what happens maybe its just trying to clear everything out of cylinders. go put it in the water and test it

 

[Byeai]

On all my new motors I've choked the carbs with my hand and cranked it over until it starts for a second then u can crank it over again not choking it and feather throttle open and should start easy remember you don't want to be cranking the motor over alot

Sent from my SAMSUNG-SGH-I337 using Tapatalk

 

[mike b]

Okay. I think I'm going to put into testing tank at nearby moto shop or the lake just to turn it on and let it idle for a bit to check things over and set my idle. Then I'll stsrt it on the cart and run it on the hose after the initial test if everything is good. It's just way louder than past skis so hard to tell if running correctly or trying to rev out (main fear with my skis)

 

[Henry Stephen]

My MSD backfired also, trigger wires were bad. This is a used system though.

 

[Midlake Crisis]

Okay. I think I'm going to put into testing tank at nearby moto shop or the lake just to turn it on and let it idle for a bit to check things over and set my idle. Then I'll stsrt it on the cart and run it on the hose after the initial test if everything is good. It's just way louder than past skis so hard to tell if running correctly or trying to rev out (main fear with my skis)

Who has a test tank?

 

[mike b]

Yamaha and Fred Cummings I believe both have tanks. I havE good connection with service at yamaha so if they had a tank in the back I was going to ask them. Maybe they'd let me, maybe they wouldnt. I'm going to test in lake in an hr just to run it on trailer to check cooling and set idle appropriate

 

[chadman154]

I sheared a flywheel key and messed with my timing and it backfired

 

[mike b]

Alright fresh off the press. Took to the lake and started right up, cooling lines and motor idle fine for about 15 minutes. i rode to end of the dock and put ski back in my truck. I need a few parts (pump seal, proper size impellor, and few misc parts and then i will test ski wilth some throttle). Hopefully next week or end of this week ill get some hours on the motor!

 

[bobob729]

Ya glad to hear it is running