JDP421 Posted November 30, 2013 Report Share Posted November 30, 2013 I'm running a 7mm cub , shearers , 30m bored and tappers to 32mm I believe . carbs running 155 mains and I'm not sure on the pilot , the bike will run good until I get to the flats and drag it will launch 2 gear override to 3 and them won't shift and if I get it blows the plugs out of the head ? And closes the gap of the plug Jetting or timing ? What do you guys think Sent from my iPhone using Tapatalk Quote Link to comment Share on other sites More sharing options...
Jereme6655 Posted November 30, 2013 Report Share Posted November 30, 2013 backing the plugs out of the heads is a symptom of detonation..... You either need to figure out why you are detonating (too much timing, not enough octane, low quality fuel, etc.) or switch to alky (requires some serious different changes to setup) Can you also elaborate and break down what your saying about shifting? I THINK your saying that you can launch in second gear, and sometimes get it to shift into 3rd but after that is when you run into detonation issues. It also could be caused by your squish tolerances (your plug gaps closing) being too tight. Either ways....id find your problem before you ride that thing again so you don't destroy the crank the cylinders and the pistons.... Quote Link to comment Share on other sites More sharing options...
JDP421 Posted November 30, 2013 Author Report Share Posted November 30, 2013 backing the plugs out of the heads is a symptom of detonation..... You either need to figure out why you are detonating (too much timing, not enough octane, low quality fuel, etc.) or switch to alky (requires some serious different changes to setup) Can you also elaborate and break down what your saying about shifting? I THINK your saying that you can launch in second gear, and sometimes get it to shift into 3rd but after that is when you run into detonation issues. It also could be caused by your squish tolerances (your plug gaps closing) being too tight. Either ways....id find your problem before you ride that thing again so you don't destroy the crank the cylinders and the pistons.... The bike will ride perfectly I'm the dune through all gears just crusing but as soon as I give it a good amount of throttle to like race it won't shift and it backs the plugs out . I'm thinking timings too high , it's at 5 and It's setup for race gas but I'm running 91 and 110 but I have a fuel mix of u4.4 110 and 91 I can drop in and I'm thinking jets could be to small so it's emptying the bowls? Sent from my iPhone using Tapatalk Quote Link to comment Share on other sites More sharing options...
n2otoofast4u Posted November 30, 2013 Report Share Posted November 30, 2013 The shifting and the plugs backing out might be related but are separate issues. You MUST get the detonation under control before it pukes the motor. If its setup for race then run race. If you don't want spendy fuel then have a set of domes cut for pump fuel. AFTER you can make passes without backing the plugs out then you can address your shifting issues. 1 Quote Link to comment Share on other sites More sharing options...
n2otoofast4u Posted November 30, 2013 Report Share Posted November 30, 2013 Also, 32mm carbs on a 7 cub is less than ideal! Quote Link to comment Share on other sites More sharing options...
JDP421 Posted November 30, 2013 Author Report Share Posted November 30, 2013 The shifting and the plugs backing out might be related but are separate issues. You MUST get the detonation under control before it pukes the motor. If its setup for race then run race. If you don't want spendy fuel then have a set of domes cut for pump fuel. AFTER you can make passes without backing the plugs out then you can address your shifting issues. What would be causing detonation issues ? If it was fuel I wouldn't be able to ride at all right ?? Sent from my iPhone using Tapatalk Quote Link to comment Share on other sites More sharing options...
n2otoofast4u Posted November 30, 2013 Report Share Posted November 30, 2013 Its possible it can live when in and out of the throttle, but its obviously not happy at wot. Quote Link to comment Share on other sites More sharing options...
JDP421 Posted November 30, 2013 Author Report Share Posted November 30, 2013 Its possible it can live when in and out of the throttle, but its obviously not happy at wot. Would u4.4 91 and 110 be a high enough octane mix? Sent from my iPhone using Tapatalk Quote Link to comment Share on other sites More sharing options...
uman1030 Posted December 1, 2013 Report Share Posted December 1, 2013 My bike wouldnt shift under hard throttle when my eccentric clutch adjustment bolt was maladjusted. Soon as the rpm came down it shifted fine but not at very high rpm. mostly 4th 5th and 6th is where it wouldn't shift. Quote Link to comment Share on other sites More sharing options...
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