Technical Misfire on acceleration

[Dragon Man]

for me it was the fuel level in the carb. in the bowl on the float i had to bend the little tab that pushed on the fuel cut off needle to stop filling the bowl. for me it was slightly over filling it.however i did have it before and a simple tune up managed to fix it using an exhaust gas tester and adjusting the mixture and idle screw.

 

[wesacosa]

thanks for that. I don't think mine is overfilling as if anything the float measurement was towards the other end of the range, odd as they symptoms seem quite similar



Starting to wonder if its underfilling though and leaving it a bit lean when you crack the throttle quickly

 

[Dragon Man]

that is behaving just like the acceleration jet is not working. on the back of the carb you will see a lever that pushes the acceleration jets pump. you can manually actuate it using a flat blade screw driver. with the engine off and a flashlight looking down the carb give it full throttle and you should see the acceleration jet send a thin jet of fuel right down into the manifold.

i am guessing that if you slowly open the throttle the engine will build up speed as normal.. its just quick bursts that causes the bogging down.

 

[wesacosa]

cheers. the jet is working but it appears to be perhaps a bit less atomised than I would expect so something to check. I did change the O ring and diaphragm so maybe I made a mistake

 

[Dragon Man]

that is interesting. ok try this.. on the distributor theres a vacuum line. have you tried clamping that pipe closed then pulling it off? did you notice any difference in the engine when you do it?

if you have another bit of pipe, put it onto that vacuum actuator and try sucking on it. you should feel resistance and not be able to suck the air from it anymore.. however if you can just keep sucking air though it that means that the diaphragm has failed in it.

i have seen this cause similar symptoms.


it is also interesting how the acceleration jet looks like it gets wet with fuel when you open the throttle.. thats something mine does not do..

 

[wesacosa]

I did check the vacuum advance already its pretty new and still working but good suggestion

I watched that again, I hadn't noticed it before how the top seemed to get wet. I will check again see if its real or just a trick of the light

 

[Dragon Man]

if you are local to me, i have a spare carb you can test with.

will the engine rev at all? can you get it off idle and hold the RPMS high?

 

[wesacosa]

if you are local to me, i have a spare carb you can test with.

will the engine rev at all? can you get it off idle and hold the RPMS high?

thanks thats a kind offer but in in South London
yeah it revs ok, its purely the quick acceleration and throttle blips. If you raise the revs slowly its fine

 

[wesacosa]

someone over on Facebook forum suggested this main jet through the diffuser doesn't look like its atomising properly , although I do wonder if that was the fault it would run badly all the time

 

[Dragon Man]

yeah the main does look strange. have you taken the smaller jets out and made sure they are clean? the little brass things as you look at the throttle opening they are just in front of it. maybe they need cleaning?

 

[wesacosa]

yeah I took it all apart, I only used carb cleaner and not compressed air though so may need to have another go

 

[Dragon Man]

i used a fine bit of wire.. it worked well!