1999 yz400f popping and banging under load??

hi new to the forum and from the UK,

i brought a 1999 yz400f today tested it up the road was running fine got it home and over the field started it went up the field and it started spluttering though rev range im going to change spark plug tomorrow fresh fuel as it has been standing for a few months and clean carb out is there any other problems that it could be?? i also noticed that if you lean bike side to side the revs pick up slightly and when its upright it ticks okish did die for no apparent reason on the spot earlyer too??

would be great if someone could offer some advice,

hope you can understand me im a bit of a newbie on forums and computers lol :thumbsup:

sounds like bad gas , the most common culprit. or a burnt or tight exhaust valve

i hope new plug and fresh fuel solve the problem i really do, it almost feels like it cuts out and back in loads pops and bangs does it under loads but doesnt seem to bad on the spot!

Check the valve clearances....I bet you'll find one or more that are too tight.

Probably jarred some debris in the body free and clogged the pilot circuit. Could need new jets as the pilot is difficult to clean out.

Use premium no ethonal gas!!


today i cleaned fuel tank out as fuel smelt a bit stale then changed plug was fine when it was cold pulling well then got up to tempreture and started popping and banging, so something is going rong when its warm :thumbsup:

gonna clean carb out tomorrow and replace jets but im unsure if its going to help might??? any ideas???

havnt really got much to update about, ordered a new cdi unit and coil yesterday so they will be hear soon . i cleaned carb out again new jets all standard, having the valve clearances done tomorrow and if that dont sort it im breaking the bike up for spares sick to the back teeth of it.....:thumbsup:

The cdi rarely goes bad. It doesn't sound like it'd be an electrical issue to me. Do more research here before you give up. Somebody here will have an answer. Grayracer513 is always really helpful.

well changed the the cdi unit and coil and problem solved :ride::banana::ride:

unsure what it was if it was the coil or cdi but tbh i cant be bothered to mess about with it again, as the saying goes if it aint broke dont fix it lol of out to find some muddy fields :thumbsup:

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