Rough running when cold

[doyle#23]

Hi all,

Im currently after some help with my crf50 with tb88 RH kit. The problems is, the bike starts fine cold but after a while starts to occasionally backfire out the carb. This only happens when the bikes cold and runs fine when hot besides idles abit high. I've changed jets, checked plug, cleaned carb and rechecked it for manifold leaks, and about to recheck timing which I'm certain is correct. Can anyone provide some possible info on this rough running when cold before I start chasing my tail

 

[rotn50]

Check valve clearances mate? try dumping your fuel and running fresh fuel in the tank and carb.

 

[doyle#23]

I haven't checked them for about 2tanks? Jaimie from classic Honda 50s said .022? Sound right?

 

[ClassicHonda50]

With the TB Race Head I run 0.002"inlet and 0.003"exhaust clearance.

Cheers

Jaimie

 

[doyle#23]

Thanks Jaimie, maybe my clearances are to much, would I be correct in saying with heat they get closer hence why it runs better hot?

 

[doyle#23]

Ok so after a long day of fixing aircraft I thort I'd come home and fix the crf50, after getting it to tcd and checking the valve clearances which where maybe .001-.002 out its running smoooooth! Would that extra valve clearance make it pop out carb like it was? After one front yard run I couldn't fault it which as I remember use to do it atleast 2-3 times each ride. Cheers rotn50 and Jaimie!

 

[rotn50]

Glad its sorted mate, if its now running fine then you could put it down to valve clearances I guess, not to sure lad.

 

[zwebx]

Ok so after a long day of fixing aircraft I thort I'd come home and fix the crf50, after getting it to tcd and checking the valve clearances which where maybe .001-.002 out its running smoooooth! Would that extra valve clearance make it pop out carb like it was? After one front yard run I couldn't fault it which as I remember use to do it atleast 2-3 times each ride. Cheers rotn50 and Jaimie!

the reason there are valve clearances is so that when the valve gets hot and expands it does not get held open... when it gets held open then combustion can release pressure out the inlet and into your carb... a "backfire"