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spitting back through carb

Submitted by barry_carson1 on Fri, 12/08/2022
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 es2 engine.  when i rev my bike in neutral at a standstill to about 3 thousand revs .it keeps spitting back as the revs pickup. in the past ive had the cylinder head done all new parts and a new cylinder liner fitted with a standard piston to the engine. the timing marks on the gears are spot on there marks. the valve lifter is ok. pushrods twistable. thorspark ign. it has always done it  but i have never got round to having a close look at it.

just wondering are the 19s 600cc single timing gears the same as the 500cc, what with the longer stroke. if they are timed differently .could they get mixed up, i dont know myself. just thought i would ask.

 

 

rejoined barry

Submitted by jonathan_newton on Fri, 12/08/2022

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One notch and repeat your experiment.  It my be a touch weak. If that proves to eliminate the spitting then it may be the right solution or you need a lower cutaway on your slide.  A little experimenting with the choke may prove it air or fuel rate.

 

Jon

Submitted by barry_carson1 on Fri, 12/08/2022

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thanks for the info Jonathan. i had a new carb on the bike but havent messed with it up to now. when i say spitting back its more like compression coming out through the carb as you rev it, as though the tappets are to tight, loosing compression. not so much a weak mixture spit then die type of thing . but i will give the needle height a go ,anything is worth a try.

 

thanks, barry

Submitted by don_anson on Sat, 13/08/2022

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I'll go out on a limb and say there could be a voltage drop somewhere in the Thorspark.

I had one for a while and it was very sensitive to less than the full 6 volts. It would even stall if it was idling with the lights on and the rear brake was activated. It also had such bad spitting back while starting that I wouldn't start it in the garage for fear of it catching fire!

Maybe connect a fully charged battery to the bike and give it a try.

Submitted by barry_carson1 on Sat, 13/08/2022

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hello Don

yes i keep the battery on charge as best as i can. i must admit i dont ride the bike that often but like to keep things charged and working as best i can.

on the voltage drop side of things. concerning the thorspark i decided to solder all the joints to ignition switch, coil, fuse box ect, basically if it had a connector i would solder it rather than a connector, then put some heat shrink on over the joint.

when i fitted the thorspark it wouldnt setup on the mark they had put on the unit. all it tried to do on starting the engine was backfire and try and break my ankle. i sorted the starting side of things and it ticks over very nice and slow without cutting out apart from this annoying pulse like what i call spitting back through the carb when reving the engine up.

i think i will have to put more miles on the bike and see if the problem gets any worse.

 

thanks

       barry

 

 

 

 

 

Submitted by ian_soady on Sat, 13/08/2022

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.. would e on the slide cutaway. The book value for my ES2 is a 4 - changing this for a 3.5 made all the difference. Previously it would spit and cough on opening the throttle despite playing with the needle position, idle air screw etc. Now it picks up absolutely cleanly.

My 52 engine has a 376 1.1/16" monobloc carb fitted.

Submitted by barry_carson1 on Sat, 13/08/2022

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hello Ian

these things need trying to eliminate what it is. its just that i didnt want to upset what i have no leaks ect.

but if i want to cure it, then i suppose i will have to dig deeper to sort it. will have to choose which way to go. as you say the carb adjustments seems the best one to try first.

 

thanks

  barry

 


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