Carb re-jet The last owner of my zepher 750 set up a sports muffler with shortened exhaust pipe and a kn freeflow filter. Now it dosnt idle so smooth and low revs without load are rough other than that goes okay and really isnt too bad. Carbs are clean and in balance, fuels good and clean new plugs fitter the engines low km and in good condition, do i need to rejet what size and do i need to take the carbs off to do this. Thanks mate.

the mufflers act to create back pressure and the air filter acts to restrict air intake. the cheapest way forward would be to re-jet the carbs, might be worth getting matching k&n type air filters to match

Try to adjust valves sometimes small gap will cause engine to respond rough if valves are not adjusted. Good Luck.

Hi there,

The jets are for increased performance but the jets installed must be in relation to the pipe used. An open pipe would require larger jets. If the jets came with the pipe when the previous owner purchased it, then it should work. My advise would be to tune it up, sync the carbs, and time the sparks.

If all else fail, ask the previous owner to provide the stock jets and replace it. Stock jets along with the stock pipe will almost always run the first time. Sync the carbs and tune timing. If you have it all running smooth, from there you can do upgrades like stage 1 jet kit or purchase a performance exhaust.

Please do let me know if any of this was helpful,
I'll follow it up should my suggestions fail,

Seems that the crank/timing settings needs a closerr look than to feel that the carb is faulty.The engine is becoming rougher because the firing angle is changed. I also doubt that the carb /jet kit be replaced back with the original as the new jet is not matching.
Now start the engine and set up idle to more than minimum so that the vehicle does not stall but is somewhat smooth. Now try to advance/****** the timing and notice if the engine becomes smoother irrespective of the TDC settings. If so set to the best level and bring down the Idle , do not reduce off air but check the mixture at the exhaust to have this done all over.
Somewhere in the new change a point has been missed..

The most common reason for backfiring is lack of back pressure from changing the exhaust. To compensate for the flat spot you get you put in a jet kit. This leaves the possibility of more unburned gas getting into the exhaust. Honda uses Kei Hin carbs with a fuel shut off diaphragm to help limit this condition (backfiring) by turning off the fuel to the carbs during deceleration. Even stock exhaust can pop or backfire. Typically it is caused by air getting into the exhaust either past the copper o-ring gaskets in the head or leaking muffler connections from the head pipes to the mufflers. Try replacing all the exhaust gaskets and you should minimize this condition.

This is often caused by an air leak , inlet manifolds, exhaust gaskets into the head or the gaskets between the headers and muffler.
This is assuming all the rest of the bike is set correctly, valve clearances,airfilter, clean carbs

I am not a Moto Guzi mechanic but in the world of Japanese bikes the problem would be trash in the carb partially blocking the main jet and / or internal fuel circuits. Tighten all fittings, carb to manifold as air leaks could be contributing to the problem. If your bike has fuel injection, have the fuel pump checked. Be sure the gas tank venting is not plugged whether carb or injection. Check and clean the filter screens on the pickup tubes inside the gas tank. Be certain the exhaust pipes are clear of obstructions. An internal collapse inside an exhaust pipe can restrict air flow. The bike can not run properly if it can't get rid of burned gasses. Remove the exhaust pipes briefly to eliminate the exhaust system as a problem. I guess I should mention the obvious, how clean is the air filter? Bikes gotta breathe in and out too. If these ideas don't help, just re-post the problem and perhaps someone else has an idea. Best wishes.

needs rejetting to suit thos freeflow filters
Cheeers Rob

It sounds like it is running really hot. Did you check the air filter and oil level. If not these it could be the muffler.

Because the timing is off. If the timing is too advanced, or too retarded, it will make your exhaust pipe cherry red.