1992 Brumby/Brat engine bucking problem

[wolp]

I have a 1992 Brumby with the EA81 engine and it has always been serviced and runs well.

However, recently it has a developed a problem that when it is restarted from warm/hot the engine will buck continuously.

When the engine cools down or is started from cold you can drive all day without the engine bucking. As soon as the engine is stopped and re-started the engine will 

begin bucking. I have taken this vehicle to 5 different mechanics - all good - and none have been able to work out the problem.

Does anyone have any ideas as to why this may be happening? Any ideas are fully appreciated. John

Edited August 2, 2021 by wolp
typo

[moosens]

Any other issues like surging throttle ? 
 

One thing to watch for is the black plastic breaking down and sucking bits into the carby. Likely not your issue now but given it’s age I’d keep an eye on that and actually take the ASV apart and check the metal flapper too. Again , may not be related to your current issue. But my 86 gave similar issues at one time and later as described above found the plastic saucer disintegrating. 
 

 

[wolp]

Hi Moosens, Thanks for your speedy and informative reply. The throttle does not surge when the car drives from cold. But i'm not sure if it would be surging when i've restarted the engine from warm/hot. I'll check it out. You may be on the right track. Interestingly enough during cold weather the bucking does not appear and is certainly worse during the heat of summer.

Do you see any connection here? 

I will take a look at the ASV and see if anything requires repairing and if it is related to my issue. A very good tip. Thank you.  

[el_freddo]

G’day @wolp 

This post would best serve you in the 80’s section since the Brumby is an EA81. The Aust market is probably the last market to get the legendary brumby/brat/MV model! 

Your issue to me sounds like the electronic ignition module inside the dizzy. We were just talking about these in another thread recently. They look like this:

and it’s located in the dizzy. There’s a four point star piece that needs to be removed off the shaft to remove the ignition module. Take note of which way up this goes. Two flathead screw drivers do the trick to leaver it out.

Other thought was the anti dieseling solenoid playing funny buggers when hot - or a dodgy ignition switch.

Last idea is a dying fuel pump that starves the car of fuel, or a severely blocked fuel filter. I had the blocked filter issue occur along long inclines or up short sharp hills when accelerating through the gears.

Cheers 

Bennie