misfire under hard breaking

[gpovanman]

Over prevoius weeks, my car has developed an interesting problem:
timing is correct and points set at 57º dwell.
c.o. at tickover is 2.5
valve clearances and compressions are good, spark plugs new ish as is distributor cover and leads.

under heavy breaking and sometimes during enthusiastic cornering I get a misfire(emergency stops cut the engine but not difficult to restart)
recently cleaned and blown through carb and jets etc (was occuring before as well as after clean)
float is not punctured either
is this a common or known problem with the zenith 28 lf carb (manual choke)
as it seems centrifugal force is affecting mixture.
Thanks in advance.

 

[pepper]

I don't know about Zeniths but I know Webers have a similar problem, I've done a fair bit of off roading in Suzukis in the past and we were always changing the standard 1300 carbs (which are a load of pants) for SU's, we had people try using Webers but as soon as they tried driving up steep slopes they became miss fire hell.

 

[angel]

It is probably from fuel getting pushed away from the main jet due to centrifugal forces.

It has never happened to me on cornering and certainly not on braking. You must have very strong brakes and good tyres! I have never heard of a R4 creating such G forces!

Maybe your fuel level in the carb is too low?

 

[gpovanman]

Thanks a lot for your replies. My mechanic has had a look at the carburettor, and he says that there is no way to change the float level. Ther first thing that he suspected was that the level of fuel in the chamber was too low, and to raise the float height. When he opened up the carburettor, he was surprised to find that (as it appeared to him) that there was no way to chenge the float height. I will get him to have another look, and report back with my findings!
P.S. how difficult is it to swap onto a 32 mm carb? I have heard them mentioned on here before!

Thanks again in advance.

 

[angel]

There seems to be no way to adjust the float level height, but in practice it can be done by swapping the copper or aluminium washer under the needle valve with a thicker or thinner one (I have ever put two washers together).

Upgrading to a 32 mm carb is straightforward but you will need the accompanying manifold too.

 

[gpovanman]

The car has been sorted. I have put this post on so that if anybody else has similar problems, this may help them sort it, and it is only fair to let the people who answered my post know what the problem was. On my 1990 Clan, there were two diaphragm operated thingies, one black and one white. In both their cases, the diaphragms were broken, so they were not working as they should. Secondly, the advance/retard mechanism was a bit sticky. So my mechanic has WD40'd the a/r mechanism, and has connected the two vacuum outlets on the carb together, and it now works a treat. No missing and no struggling under load as it had been doing for the last couple of days. Thanks again to the posters who answered my original post.