Ok so iv just put a new engine in.
the engine idles fine then the revs to decide to just randomly pick up to about 5/6k, had a backfire and theres a few cracked welds in the exhaust (which i will be fixing) and seems like fuel is spitting out. i did the tutorial on this page so i was wondering what it could be!!HELP!!

No one else has replied......

So I'd thought I'd throw in my thoughts, although there are people on here who know far more about this than me.

My initial thought is that the carbs aren't seated properly and there's air being drawn in?

My next thought would be float bowls in the carbs being set to correct height.

But please wait and see what others say, I've just started mine today after it being sat for a couple of years and many of the things I did know about these bikes, I've forgotten. Bonus is that it started first time...

cheers dude ill have a look. How i go about setting float heights??

Any other suggestions??

When i say its spitting fuel i mean out of the cracks in the welds :/

I think you should also check the spark plugs, they fail very easily. But i would also suggest 80sman is on the button too. i.e. air leak or possible float height.
I measure the float height by removing the carbs take the bowls off and meaure from the flat of the carb to the top of the float. i think the haynes has a pic? then to adjust the height gently bent the floats to the correct height.

wassy123 wrote:Ok so iv just put a new engine in.
the engine idles fine then the revs to decide to just randomly pick up to about 5/6k, had a backfire and theres a few cracked welds in the exhaust (which i will be fixing) and seems like fuel is spitting out. i did the tutorial on this page so i was wondering what it could be!!HELP!!

Have you swapped the carbs over from your old engine? If so did the bike run ok?
If it did then it shows the carbs are fine so it must either be the carbs not seated right (as already mentioned) or even perished rubbers sucking are in?
If it is a plug problem dont be tempted to try and clean them up. It wont work as once a plug is wet the spark will never tract correctly again. Always buy new.
James

Hey!! Much thanks!! Took the carbs off and put my old ones back on as new engine came with carbs whichh were shocking when i opened them up! So that and air seal all done!! Now to fix my exhaust :)

Cheers