Author Topic: RZ 350 Godzilla Backfire issue  (Read 442 times)

Edd

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RZ 350 Godzilla Backfire issue
« on: August 15, 2018, 06:33:29 AM »
Morning Guys

Some context regarding my bike. I have a hybrid frankenstein godzilla RZ 350 with a ypvs 29L bottom end. I have banshee barrels with a Hemmi head runs avgas 100LL premix. Carbs are 28,9mm VM Mikuni with v force reed blocks. I have a zeel ignition fitted std RZ curve and advance at the moment. Pipes are from Bosson. From research I have found you only get 28mm and 30mm intake diameters not 28,9mm. So I have decided I have 28mm carbs and I am running jetting and float heights accordingly.

Bike starts farely easy 3rd kick every time. It idles well with choke open as soon as I close the choke the LH cylinder dies and starts to backfire ?:-| if I open choke it runs fine again. From my experience it means it is not getting enough fuel. The two carbs are connected with a rubber tube as only the LHS carb has a choke plunger the tube allows the RHS carb to also get more air thus sucking through more fuel. From flow diagrams of the VM carbs it looks like the air helps to suck fuel into the cases. These carbs dont have the means to set the float levels with the clear tube method so I just set the float levels at 3/4 fuel fuel hight in the bowls once removed from carb body.

Any suggestions?

Thank You

Edd
TZR 250 3MA1
TZR 250 3XV RS(Track)
TZR 250 1KT
TZ 250 3YL
RZ 350 Hybrid
YZ 250
RD 350 Hybrid

evan_calgary

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Re: RZ 350 Godzilla Backfire issue
« Reply #1 on: August 15, 2018, 07:00:54 AM »
Air leak on that side?  Was motor pressure tested and have you sprayed a flammable substance around the boots to see if idle picks up indicating air leak?

41juergen

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Re: RZ 350 Godzilla Backfire issue
« Reply #2 on: August 15, 2018, 07:47:38 AM »
Sounds a bit like an ignition timing issue (had the same on my 3FL bike), may be the pickup cables need to be switched?

Edd

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Re: RZ 350 Godzilla Backfire issue
« Reply #3 on: August 16, 2018, 10:50:43 AM »
Hi Jeurgen

You mean swapping the orange and black wire around on the ignition coil? I have a single pick up with two lobes on the flywheel same as the 3ma and 1kt. I did swap the ignition coil leads around and it did nothing to alleviate the problem.

Edd
TZR 250 3MA1
TZR 250 3XV RS(Track)
TZR 250 1KT
TZ 250 3YL
RZ 350 Hybrid
YZ 250
RD 350 Hybrid

Edd

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  • Location: Rustenburg South Africa
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Re: RZ 350 Godzilla Backfire issue
« Reply #4 on: August 18, 2018, 04:06:35 AM »
Hi Guys

Found the issue it is the carburetor. What exactly is wrong on the carburetor i atill havent figured that out.

Edd
TZR 250 3MA1
TZR 250 3XV RS(Track)
TZR 250 1KT
TZ 250 3YL
RZ 350 Hybrid
YZ 250
RD 350 Hybrid