PDA

View Full Version : Bonny ain't firing



wstdtlnt
07-18-2012, 12:15 PM
Hey guys,

First and foremost, some details:

1969 TR120 Bonny 650 with a 750 bore kit
Dual Amal 930's with 200 main, #3 slides and 106 needle with the clip on the middle notch. No air filters just mesh velocity stacks.
Straight pipes with an agressive upsweep, no muffler or baffles
Pazon electronic ignition.

So i did a bunch of work over the winter (mostly aesthetic) but also threw two brand new carbs in, a new pazon and reset the valves gaps. I had it running pretty decent but a tad rich. So my first question is can anyone recommend a good jet and notch set up given the bike?

New problem. I ran it for about a week with it firing on pretty much first kick when it was warm and 2 or 3 when cold. Then one day it fired normally in the morning and after work about 4 hours later it took me about 20 kicks. Rode it for about 30 mins, let it sit for about 2 hours then 100 kicks later, I still had nothin but wet t-shirt and a sore foot.

Plugs were pretty sooty, so I threw new ones in which didn't do anything. Then pulled them and held to the heads with both having spark so doesn't seem to be an ignition problem. Battery is reading 12.2 with all lights working and bright. checked my connections and fuses and everything seems to be okay. Double checked and re-did my static timing to 38 BTDC with still nothin.

Then i noticed a had a pretty big air bubble in my fuel line so I started looking at my carbs. Process of elimination led me to my second carb not letting too much fuel through. When I pull my transfer line (between carbs but leaving it hooked to my right carb) and turn on the petcock, fuel flows as it should. When i hook the left carb back up, turn the petcock to on, It doesn't let much fuel get down to the carbs. I pulled my banjo and bowl on the left carb to check for clogging in them and all the jets and they're clean as whistle as its only had a week of running. then i threw a banjo from another carb on there which seemed to let more gas through so i figured that might help. When i go to kick the bike, I get heavy kick back with the throttle slightly open and gas spits out of the back of the carb. The bowls are both full and it seems like there should be enough fuel to at least fire the bike.

Anyway i'm at a total loss now so i thought i would put out the mayday call. Holy, I apologize for the novel! Any help would be great!

Cheers

RetroRob
07-18-2012, 5:27 PM
Start with the easy stuff, gas cap vent, vapor lock ? Recheck the timing, make sure your at 38 degree slot on the crank, not TDC. Check and recheck your wiring. Check your plug gap and wires. Make sure nothing is stuck in the carb.

MrsEsterhouse16
07-18-2012, 5:30 PM
When you checked the static timing did you have to move it mutch? I would almost think kick back and spitting back thru the carbs would be a timing issue. And other basics would be valve lash, but unless you got something hung up or stuck that does not sound like your problem.

dazegoneby
07-18-2012, 6:00 PM
hows the advance unit behind timing plate?check for bad/weak springs /sticking advance unit,manualy move by hand, see if its sticking any where of its movement.but sounds like carb & timeing issues

RetroRob
07-18-2012, 6:12 PM
Check out your coils,a bad one won't work when they heat up.

Torch
07-18-2012, 7:39 PM
yep, my guess is the coils are going bad, I would replace them with a single 12 volt dual lead coil.

wstdtlnt
07-18-2012, 11:04 PM
Hey guys thanks for the feedback. Latest update. Swapped out an older carb I had which was letting more fuel through and got it to start twice. That said, I had to keep the throttle open otherwise it would just die right away. This is with the air and throttle screws as per standard. Either way can I rule out bad coils, faulty wiring and anything other than carb or timing? I'll be back down at the shop tomorrow so I'll have a look at the advance unit to check for sticking. Could this also still be valve related?

Cheers

dazegoneby
07-20-2012, 11:21 AM
Hey guys thanks for the feedback. Latest update. Swapped out an older carb I had which was letting more fuel through and got it to start twice. That said, I had to keep the throttle open otherwise it would just die right away. This is with the air and throttle screws as per standard. Either way can I rule out bad coils, faulty wiring and anything other than carb or timing? I'll be back down at the shop tomorrow so I'll have a look at the advance unit to check for sticking. Could this also still be valve related?

Cheers
,, the british whores will drive you nuts,, till you get em sorted out,,,,,when you do,,, they make up for it

wstdtlnt
07-23-2012, 10:00 AM
Hey guys,

A buddy and I figured out the problem. my valve on the right side exhaust wasn't following the cam. Re-seated it, double checked the rest of them and it fired 4th kick. I also upped my main jets from 200 to 220 and the bike feels a lot faster now. With that said, it died on me twice at top speed on the highway. It sputtered for a second then just completely died. Which seems to be a carb issue. Do you think 220 is too much for the mains? I'm also just running velocity stacks and no mufflers on the pipes.

Cheers

dazegoneby
07-24-2012, 7:45 AM
i ran 200s they worked good ,,seemed rich still>sooty plugs but all else ok,,(drag pipes with 3 in baffles,short velocity stacks,mild head work,,stock cams,,,750, 020pistons)

wstdtlnt
07-24-2012, 1:46 PM
Thanks Dazegoneby. I was gonna pop the 200's back in and see how she goes!