Bonneville America Forums Forums Technical Forums Custom Corner 74' T140v bonnie

Got my 1974 T140v bonnie in May rolled it off the truck and it started fine. However, the pipes were blowing black smoke...to rich right! So I went from a 30 to a 27.5 pilot jet and a 220 to a 200 main jet (minuki carbs) Then I went from a ngk7se plug to a ngk 6se plug; but now she won't start. Both plugs have spark, although, one of the carbs (left) trickles out fuel from the over-flow, as it turns out the left plug is wet with gas and the right is dry...although I can see fuel in the line going into the right carb. I'm at a total loss. The battery has been charged and the tank is full...just need some help from ya'll so let me have it! please!

thanks fellas
james

Hi James1,

The following link is the forum you need to join:

Classic Bike

It's full of Limey's, Kiwi's, Aussies, Canucks, and yanks with plenty of Meriden era expertise and are all current owners.

With that said, when my '77 T140V started blowing blackish smoke, I ended up being much worse than carb adjustment or changing to hotter plugs. It ended up having to redo the top-end. I was using the original Amals though and have no experience with Mikuni's on my old Norton or Meriden era Bonnie. I'm guessing you may have been frequently topping off the oil?

I'd compression test each cylinder (don't have my Meriden workshop manual handy as I'm out of town.) Also, look for leaks where the headers are pressed into the heads as this was quite common. Of course, looking for leaks is hard to do if the bike doesn't start.

Main jet size on the Amal MK I's on the stock Bonnie is 190. I don't know how the Mikuni's equate, but you make actually be way too big with 200 or 220's.

Immediately toss the points and switch to a Boyer electronic ignition. Also, ditch the lucas rotor and abandon the zener and rectifier and switch to a Sparx high-output unit. It comes with a regulator that replaces said old-time electronics. These modifications are all "hidden" and do not detract from the bikes asthetics.

Again, there are still some folks here who may have an old Bonnie tucked away and can give better guidance as they still own ther older bikes. My old bikes are gone as I opted to tinker because I want to with a new bike, not because I have to with the older ones (miss them though), Also register with the link I mentioned above.

Regards,

Tom

The Prince of Darkness rears his ugly head.

Charlie

wet plugs, probley fouled, replace plugs start bike, sounds like float bowls are sticking. common froblem with those carbs.

Robert in Utah

The bike leans left on the stand, so the left carb is lower than the right. If the left float is stuck, all the gas will run through the left and little or none will make it to the right.

Clean plugs will probably get it to fire, but you need to sort the carb problems or it won't be long 'til they are fouled again.

got everything sorted out. thanks for the help. but now for the hard question and answer portion. i have a dead spot around 2500-3000 rpm. is it the carb slides sticking or is the needle and needle jet to rich for the current altitude.

2500 is about where that bike would make the pilots - main transition. If you run the engine at that speed for a bit, the sparkplugs will tell you for sure, but I suspect you may need to raise (shim up) the needles just a little. If this is so, the plugs will show a lean mix. If they show rich and you already have some shims under the needles, then they probably need to be lowered a little.